KR100553827B1 - Membrane electrode assembly for fuel cell and preparation method thereof - Google Patents

Abstract

The present invention provides an electrode-membrane assembly comprising an anode, a cathode, and an electrolyte membrane, wherein the catalyst powder is transferred to an electrolyte membrane or an electrode support by electrostatic attraction. In addition, the present invention comprises a first step of providing a catalyst powder; A second step of causing an electrostatic charge on the catalyst powder; A third step of transferring the catalyst powder to an electrolyte membrane or an electrode support by using electrostatic attraction to form a catalyst layer; And it provides a method for producing an electrode-membrane assembly comprising a fourth step of fixing the transferred catalyst layer with heat and pressure.

The present invention can improve the uniformity and processability of the catalyst layer in the production of MEA.

Description

Electrode-membrane assembly for fuel cell and method of manufacturing the same {MEMBRANE ELECTRODE ASSEMBLY FOR FUEL CELL AND PREPARATION METHOD THEREOF}

1 is a schematic diagram of a process for producing an electrode-membrane assembly by a catalyst layer transfer method using electrostatic attraction according to the present invention.

1. Catalyst powder sample supply unit

2. Doctor blade

3. Drumming roller

4. Organic Photo-conducting drum (OPD)

5. Coating layer fixing part

6. Proton Conductive Membrane Transfer

7. Proton Conductive Membrane Transfer

8. Proton Conductive Membrane Support

9. Proton conductive membrane

10. corona charging unit

11. Waste sample cleaning unit

12. Laser generator

2 is a process flow diagram illustrating a method of manufacturing a conventional electrode-membrane assembly (MEA).

Figure 3 (a) is a photograph showing the appearance of the powder coated with a proton conductive binder on the catalyst powder (particle) surface (b) is a fluorine (F) element mapping (b) contained in the binder structure to determine the distribution of the binder ( The photo shows the result of the mapping).

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode-membrane assembly (MEA), which is a part of a polymer electrolyte fuel cell (PEMFC) and a direct methanol fuel cell (DMFC), and a method of manufacturing the same. .

A fuel cell is a power generation device that obtains electricity by using an electrochemical reaction between hydrogen and oxygen. In terms of the principle of operation, hydrogen and oxygen basically react in half at different locations of the cathode and anode of the fuel cell to generate a current, and the reactive species finally go through water. The structure of a fuel cell is composed of a cathode (fuel electrode), an anode (oxygen electrode), and an electrolyte, and hydrogen is supplied to the cathode, oxidized, and releases electrons, and these electrons move to the anode through an external circuit to reduce oxygen at the anode. Used for the reaction, water is produced by combining protons moved to the anode through the electrolyte layer and oxygen ions supplied to the anode. In addition to water, heat is also generated incidentally. If heat is recovered during power generation, high efficiency power generation of 80% or more is possible, and there is no emission of pollutants because there is no combustion process.

Among these fuel cell components, the electrode-membrane assembly (MEA) is a place where an electrochemical reaction between hydrogen and oxygen occurs, and is composed of an anode, a cathode, and an electrolyte membrane such as a cationic conductive membrane (eg, a proton conductive membrane) or an oxide ion conductive membrane. It is. Electrons are generated by the oxidation reaction of hydrogen at the cathode and oxygen is reduced at the anode. MEA is formed by coating an electrode catalyst layer of the cathode and the anode on a conductive film, and the material of the electrode catalyst layer is Pt ( A catalyst substance such as platinum) or Pt-Ru (platinum-ruthenium) is supported on a carbon carrier.

Conventional methods of manufacturing MEAs include a catalyst material, a proton conductive binder material, and a water or alcohol-based solvent to prepare a paste, which is a carbon cloth or an electrode support. There is a method of coating on carbon paper, then drying and thermally fusion to proton conductive electrolyte membrane. This method corresponds to a kind of indirect coating method, the detailed process is shown in FIG.

However, when this method is coated with a porous carbon cloth or carbon paper, the catalyst material does not have a uniform thickness on the surface and penetrates into the pores, which actually decreases the utilization rate of the catalyst during MEA operation. It is the biggest disadvantage. In addition, the process may be complicated because the electrode layer that has already been formed needs to be secondarily coated on the proton conductive film, and the interface formation between the electrolyte material and the catalyst layer may form a discontinuous interface.

In addition to the above-described manufacturing method, a conventional method is performed by mixing a catalyst material, a proton conductive binder material, and water or an alcohol solvent to make an electrode paste, and directly using a screen printing method on the surface of the proton conductive electrolyte membrane. There is a transfer coating method. However, this method has a disadvantage in that it is difficult to obtain a uniform surface coating layer due to the swelling phenomenon in which the volume expands in all directions when water or an alcohol solvent is brought into contact with the electrolyte membrane. Since it is difficult to control the viscosity of the solution, it has a disadvantage that is not suitable for large-area mass production process.

The object of the present invention is to compensate for the disadvantages of the existing method and to improve the uniformity of the catalyst layer coated during the production of the electrode-membrane assembly (MEA) of solid polymer fuel cell (PEMFC) and direct methanol fuel cell (DMFC) and to improve the production efficiency of MEA. And to improve performance.

In addition, the present inventors adopted a laser transfer method, which is a kind of dry coating process in the MEA manufacturing to achieve the above object. This method simulates a method commonly used in laser printers. It transfers and fixes a catalyst material coated with a proton conductive binder to an electrolyte membrane in a dry state using an electrostatic force without using a solvent to form a uniform catalyst coating layer of a thin film. The present invention was completed based on the above experimental results.

The present invention provides an electrode-membrane assembly comprising an anode, a cathode, and an electrolyte membrane, wherein the catalyst powder is transferred to an electrolyte membrane or an electrode support by electrostatic attraction.

In addition, the present invention

Providing a catalyst powder;

A second step of causing an electrostatic charge on the catalyst powder;

A third step of transferring the catalyst powder to an electrolyte membrane or an electrode support by using electrostatic attraction to form a catalyst layer; And

4th step of fixing the transferred catalyst layer by heat and pressure

It provides a method for producing an electrode-film assembly comprising a.

Hereinafter, the present invention will be described in detail.

1. First step: providing catalyst powder

Materials that can be used as catalysts include platinum black (Pt black), platinum-ruthenium black (Pt-Ru Black), or platinum-supported carbon catalysts (Pt / C), platinum-ruthenium-supported carbon catalysts, platinum-molybdenum black ( Pt-Mo), platinum-molybdenum (Pt-Mo) supported carbon catalyst, platinum-rhodium (Pt-Rh) black, platinum-rhodium-supported carbon catalyst, and other alloy catalysts based on platinum, in particular In the case of the supported catalyst, the content of the catalyst in the total weight of the supported catalyst is preferably 1 to 80% by weight.

The types of carriers that can be used include all common carbon black-based carriers including Vucan XC-72R, Vulcan XC-72, acetylene black, Kejon black, black pearl, etc. And conductive composite oxides including ruthenium oxide and the like.

The catalytic material is preferably used as a powder for use in dry coating processes.

The catalyst powder is preferably a mixture of catalyst particles and a proton conductive polymer binder, or coated with a proton conductive polymer binder on part or all of the surface of the catalyst particles.

In order for the catalytic material to be used as an electrode material of the fuel cell, a passage through which the proton formed by the catalytic reaction can be smoothly moved is required. Therefore, by using a polymer binder with proton conductivity, such as Nafion (Dafont), the catalyst powder surface can be simultaneously bonded to the catalyst material powder and to serve as a path through which the proton can move. It is preferable to coat.

The catalyst material and the proton conductive polymer binder form an electrode catalyst layer in the electrode-membrane assembly (MEA).

In addition, since the present invention relates to a dry coating method using an electrostatic attraction, the binder coated on the catalyst particles may also play a role of causing an electrostatic charge on the surface.

Materials that can be used as binders include all proton conductive polymer materials, including Nafion [perfluorosulfonic acid (PFSA) / PTFE copolymer], in addition to PTFE (Polytetrafluorethylene), PVDF (poly vinylidenefluoride), PEEK (Poly etheretherketone), polymers such as poly methylmethacrylate) and derivatives having proton conductivity added thereto. The binders can all carry an electrostatic charge.

The content of the binder in the powder in which the catalyst material powder and the proton conductive polymer binder are combined is preferably 1 to 80% by weight based on the weight of the catalyst. More preferably, the ratio of the catalyst powder and the binder to the maximum reaction surface area is 15 to 30% by weight.

The particle size of the catalyst powder to which the catalyst powder or binder is bound is preferably 1 to 20 µm. The smaller the particle size of the powder is, the larger the reaction surface area is, so that the catalytic reaction takes place actively.

FIG. 3 shows the results of coating Nafion binder on 40 wt% Pt / C (platinum supported carbon) catalyst powder and analyzing it using FE-SEM. The catalyst support used here is Vulcan XC-72, which is carbon black having a surface area of about 200 m ² / g. Figure 3 (a) is a photograph showing the appearance of the binder coated powder, Figure 3 (b) is a photograph of the fluorine (F) element mapping included in the structure of Nafion to determine the distribution of the binder white This indicates that fluorine is present in the visible part. As the white color darkens along the surface of the catalyst powder, it can be seen that the Nafion binder is evenly coated on the surface.

As a medium for securing sufficient fluidity of the catalyst powder during the process, silica powder or the like may be coated on the surface of the catalyst powder.

If there is no binder, it is preferable to use a binder because the reaction efficiency of the catalyst and the bonding strength of the MEA are decreased. However, in the case of manufacturing the MEA according to the method of the present invention using only the catalyst material not coated with the binder, the scope of the present invention is Belongs to.

2. Second step: electrostatic charge on the catalyst powder

In order to apply electrostatic attraction to the powder provided in the first step, a corona discharge method, an arc discharge method or a triboelectric generation method may be used.

In order for the catalyst powder to be transferred by electrostatic attraction, the amount of charge that can be added must be greater than or equal to a certain level and the charge value must be maintained during the transfer by the process cycle. For this purpose, special materials can be used that can generate and maintain charged charges.

3. The third step: transferring the catalyst powder to the electrolyte membrane or the electrode support by using electrostatic attraction to form a catalyst layer

The material of the electrolyte membrane, in particular the proton conductive membrane, may be the same material as the proton conductive binder.

By using the corona discharge method, the arc discharge method, the triboelectric generation method, or the like, charges having opposite signs than those of the catalyst powder can be formed on the electrolyte membrane or the electrode support (eg, carbon cloth, carbon paper).

Since the back surface of the catalyst powder and the electrolyte membrane or the electrode support each have a charge of opposite sign, the catalyst powder can be transferred to the electrolyte membrane or the electrode support by electrostatic attraction. MEA manufacturing method according to the present invention can also be used when applying the catalyst powder to the electrode support, this case also belongs to the scope of the present invention.

In addition, a pattern may be formed on the catalyst layer to be transferred using a method of applying laser light to a drum coated with a photosensitive agent. The catalyst layer can be activated in various ways, such as by gradually moving the materials required for the fuel cell reaction by giving a gradient to Pt / C concentration or binder amount.

4. Fourth step: fixing the transferred catalyst layer by heat and pressure

It is preferable to fix the transferred coating layer. This is to reduce the interfacial resistance with the electrolyte membrane and / or to prevent the catalyst particles from falling off.

Fixing process uses a fusion method using heat and pressure, the temperature is 50 ~ 200 degrees Celsius, the pressure is preferably 10 ~ 100kg / cm ² per unit area of the coating layer. The heat fusion temperature should be near the Tg of the electrolyte membrane and the Tg of the electrolyte membrane polymers is in the above temperature range. On the other hand, the above pressure is appropriate for the adhesion while making use of the fine pore of the electrode support.

Hereinafter, with reference to Figure 1 will be described a preferred embodiment of the present invention.

The mixture of the conductive polymer binder and the catalyst powder is charged to the powder feeder 1 and is subjected to triboelectricity by friction with the doctor blade 2 to be electrodeposited on the surface of the drum 3. Here, the gap between the doctor blades is controlled between 5 and 50 micrometers (µm), and the amount of the catalyst powder deposited on the drum 3 is kept constant by keeping the height constant. Here, the amount of charge due to friction should be maintained at the same electrical polarity. However, if the amount of charge generated is too weak or the polarity is not uniform, the quality of the catalyst layer will be adversely affected. Therefore, a voltage of 1,000 to 10,000 V is supplied to the drum 3. Therefore, the polarity and amount of the charge can be artificially controlled by corona discharge or arc discharge.

The charging unit 10 forms a constant charge layer on the surface of the organic photo-conducting drum (OPD) 4 on which the photoconductor is coated by corona discharge at a high voltage of 1,000 to 10,000 V. Here, a photoreceptor is a substance having the property of being a conductor when it receives light and remaining as an insulator when it does not receive light. When the surface of the drum in which charge is formed rotates and the laser generated by the laser generator 12 is scanned on the photosensitive member according to the scan pattern signal, the light-receiving portion becomes a conductor to form a latent image by dissipating charge. Subsequently, when the drum 3 and the drum 4 come into contact with each other in the opposite direction and are in contact with each other, the transfer of the charging catalyst powder is carried out with the opposite sign to the portion where the latent image is formed. The charge of the opposite sign is formed to attract the transferred catalyst powder layer by electrostatic attraction, which in turn migrates to the surface of the proton conductive membrane to obtain the coating layer by the defined pattern. The formed catalyst layer is fused by heat and pressure while passing through the fixing part 5 heated to 50 to 200 ° C., and the catalyst layer is fixed to the proton conductive membrane to finish the coating process. The catalyst powder remaining in the OPD without being transferred is collected by the waste sample collecting unit 11 and used again as a sample.

The uniformity of the catalyst layer coated by the electrode-membrane assembly (MEA) manufacturing method of the present invention using a laser transfer method, which is a kind of dry coating process, can be improved, and the production efficiency and performance of the MEA can be improved.

The method of the present invention using a dry coating process can omit the complicated manufacturing process and drying process of the catalyst ink, which is a disadvantage of the conventional wet coating process, and the phenomenon in which the solvent in the catalyst ink is absorbed by the cationic conductive film and the film is stretched ( Since no swelling occurs, uniform coating can be achieved.

Claims (10)

An electrode-membrane assembly comprising an anode, a cathode and an electrolyte membrane, wherein the catalyst powder is transferred to an electrolyte membrane or an electrode support by electrostatic attraction. The electrode-membrane assembly of claim 1, wherein the catalyst powder coating layer transferred to the electrolyte membrane or the electrode support is heat-sealed. The electrode-membrane assembly of claim 1, wherein the catalyst powder is a mixture of catalyst particles and a proton conductive polymer binder, or a proton conductive polymer binder is coated on a part or the entire surface of the catalyst particles. The electrode-membrane assembly of claim 3, wherein the binder content is 1 to 80% by weight of the catalyst. The electrode-membrane assembly of claim 1, wherein the catalyst powder has a particle size of 1 to 20 µm. Providing a catalyst powder; A second step of causing an electrostatic charge on the catalyst powder; A third step of transferring the catalyst powder to an electrolyte membrane or an electrode support by using electrostatic attraction to form a catalyst layer; And Fourth step of fixing the transferred catalyst layer with heat and pressure Method of producing an electrode-film assembly comprising a. The method of claim 6, wherein the catalyst powder is a mixture of catalyst particles and a proton conductive polymer binder, or a proton conductive polymer binder is coated on a part or the entire surface of the catalyst particles. The method of claim 6, wherein the method of applying electrostatic attraction during the third step is corona discharge, arc discharge, or triboelectric generation. The method of claim 6, further comprising forming a pattern of a catalyst layer by applying laser light to a drum coated with a photosensitive agent in a third step. The method of claim 6, wherein the temperature in the fourth step is 50 ~ 200 degrees Celsius, the pressure is 10 ~ 100kg / cm ² per unit area of the coating layer.

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