KR20080043989A - Method of preparation for membrane/electrode assembly - Google Patents

Abstract

A method for preparing a membrane/electrode assembly is provided to produce the membrane/electrode assembly having improved electrical characteristics such as power and electroconductivity. A method for preparing a membrane/electrode assembly includes the steps of: forming a catalytic layer containing catalytic particles and a polymeric electrolyte; sintering the catalytic layer at 100-210 °C; and fusing the sintered material on a polymeric electrolyte membrane by hot pressing. The catalytic layer is formed by applying a catalytic slurry onto a gas diffusion layer or release paper, and drying the coated slurry.

Description

Method for preparing electrolyte membrane / electrode assembly {Method of preparation for Membrane / Electrode Assembly}

1 is a structural diagram of a unit cell of a polymer electrolyte fuel cell, in which 1 is a separator, 2 is a gas diffusion layer, 3 is a catalyst layer (anode and cathode), and 4 is a polymer electrolyte membrane.

2 shows a schematic diagram of reactant movement in a unit cell.

Figure 3 shows the current-voltage characteristic curves of Examples and Comparative Examples according to the present invention.

Figure 4 shows the impedance measurement of the Example and Comparative Example according to the present invention.

The present invention relates to a method for producing an electrolyte membrane / electrode assembly, and more particularly, a process of forming a catalyst layer containing catalyst particles and a polymer electrolyte, sintering the catalyst layer at high temperature, and then fusion bonding the polymer electrolyte membrane with thermocompression bonding. The present invention relates to a method for preparing an electrolyte membrane / electrode assembly suitable for a fuel cell because the polymer electrolyte penetrates deeply into the catalyst particles to have excellent electrical performance.

Due to the advantages of high power density, fast response and simple system, polymer electrolyte fuel cell (PEMFC) is currently being actively researched for use as a power source for automobiles and stationary power generation devices of 200 kW or less. Is in trial operation.

As shown in FIG. 1, which shows a unit cell structure diagram of a polymer electrolyte fuel cell, an electrolyte membrane / electrode assembly (hereinafter, referred to as a MEA), which is a main component, is located at the innermost part. An anode electrode and a cathode electrode are comprised in the form located on both surfaces of an electrolyte membrane.

In general, the anode and the cathode are manufactured so that the desired amount of catalyst is uniformly applied to the surface of the electrolyte membrane. In addition, a gas diffusion layer (GDL) is located outside the MEA, that is, the catalyst is located, and a separator having a flow field formed to supply fuel to the gas diffusion layer and discharge water generated by the reaction. (Separator) is located. The unit cell is composed of one MEA, two GDLs, and two separators, and by stacking unit cells, a stacked battery of a desired size is constructed.

Next, FIG. 2 illustrates a schematic diagram of reactant movement in a unit cell. In the anode of the fuel cell, oxidation reaction of hydrogen proceeds to generate hydrogen ions and electrons, and the generated hydrogen ions and electrons move to the cathode through the electrolyte membrane and the conductive wire, respectively. At the same time, the cathode receives hydrogen ions and electrons from the anode and generates water as the reduction reaction of oxygen proceeds. At this time, the electric energy is generated by the flow of electrons along the wire and by the flow of protons through the polymer electrolyte membrane.

On the other hand, one of the very important process in the method of manufacturing the MEA is the production process of the catalyst slurry. The main components of the catalyst slurry are catalyst particles in which a metal / nonmetallic catalyst (typically platinum, Pt) is dispersed / supported on a carbon support, a polymer electrolyte (typically Nafion) which is a proton conducting medium, and water and alcohol added to disperse it. It consists of the same solvent and various additives that can be put in to aid dispersion.

The catalyst particles used in MEAs are in the form of carbon nanoparticles of several tens of nanometers in size, with metal / nonmetallic catalysts of several nanometers in size (similar to those embedded in strawberries). In addition, the oxidation and reduction of fuel (hydrogen) and air are carried out on a metal / non-metal catalyst, in which the reaction occurs only where the polymer electrolyte Nafion is in contact with the catalyst. That is, a smooth catalytic reaction occurs only at the part where the fuel (or air), the catalyst, and the polymer electrolyte are in contact at the same time (three phase interface).

The slurry prepared for applying the catalyst particles is mixed with various solvents such as water and alcohol, various additives, and nafion which is a polymer electrolyte. In the process of mixing them, the catalyst particles and the polymer electrolyte should be evenly dispersed so that the three-phase interface is sufficiently achieved. The polymer electrolyte may be formed in various micropores ranging from a few nanometers to several hundred nanometers by the shape of the carbon carrier, which is the catalyst particle. It is very difficult to distribute all the pions evenly.

Various mechanical / chemical mixtures are carried out to disperse nanoparticle catalyst particles (tens of hundreds to hundreds of nanometers) and Nafion. The degree of dispersion of these particles has the greatest effect on increasing the efficiency of the catalyst and improving the MEA performance. This is because the polymer electrolyte, Nafion, must touch the surface of the metal / non-metal catalyst supported on the support, such as water, air, and catalyst ( This is because the supported metal / non-metal catalyst) may form a three-phase interface in contact with each other. That is, a well-dispersed slurry means that the ratio of Nafion covering (butting) of the catalyst is very high, and various attempts have been made to disperse the catalyst slurry. However, due to the limitations of the mechanical mixing method and the limitations of the chemical additives, there are many difficulties in evenly distributing the solution while improving the durability of the MEA, increasing the efficiency, and preventing side effects due to the additives.

Therefore, there is a need for a method in which the Nafion particles are brought into contact with more catalysts, not only in the process of preparing the slurry but also after the slurry is prepared, but not by mechanical / chemical mixing.

The present inventors have made efforts to evenly disperse the polymer electrolyte in the catalyst used in the electrolyte membrane / electrode assembly. As a result, in the case of the electrolyte membrane / electrode assembly (MEA) prepared by forming a catalyst layer containing the catalyst particles and the polymer electrolyte, sintering the catalyst layer at a high temperature, and fusion bonding with the polymer electrolyte membrane by thermocompression. Since the polymer electrolyte penetrates deep into the catalyst to increase the contact surface with the catalyst particles, the reactivity of the catalyst is improved, so that the performance and the electrical conductivity of the electrolyte membrane / electrode assembly (MEA) prepared therefrom are improved. It was completed.

Accordingly, an object of the present invention is to provide a method for manufacturing an electrolyte membrane / electrode assembly (MEA) with improved electrical characteristics such as output and electrical conductivity.

The present invention provides a method for producing an electrolyte membrane / electrode assembly (MEA) in which a catalyst layer containing a catalyst particle and a polymer electrolyte is formed, and the catalyst layer is sintered at 100 to 210 ° C., followed by thermal compression bonding with a polymer electrolyte membrane. There is a characteristic.

Hereinafter, the present invention will be described in detail.

The present invention is an electrolyte membrane / electrode that is sintered at high temperature by sintering the catalyst layer containing the catalyst particles and the polymer electrolyte at high temperature in order to improve the contact area between the catalyst particles and the polymer electrolyte to increase the activity of the catalyst. A method for producing a conjugate (MEA). The electrolyte membrane / electrode assembly (MEA) prepared by the above method improves electrical performance such as output and electrical conductivity.

In general, sintering refers to the joining by heating small metal powder particles in the temperature range below the melting point. The sintering force reduces the surface energy. As the sintering proceeds, adjacent particles become viscous flow in the glass. However, they are partially coalesced by diffusion processes, such as in crystalline materials, to reduce the overall surface area. As a result, the mechanical and physical properties of the material are improved.

The present invention does not change the physicochemical properties of the catalyst particles constituting the catalyst layer (the carbon carrier supporting the metal catalyst), and only the polymer (also known as Nafion particles), which is a binder and proton conducting medium, surrounding the glass temperature ( By heat treatment (sintering) in a section above Tg) and below the decomposition temperature, the polymer spreads widely and evenly between the nano-sized particles, facilitating the penetration of the nanoparticle gap of the Nafion polymer which is not sufficiently achieved in the mechanical mixing process. will be. The present invention, unlike the object of the physical strength and chemical stability due to the interface reduction and single crystallization caused by the general sintering process, the effect of maintaining the nanoparticles made of metal / carbon (binder effect) and as a proton transfer medium There is a difference in that the effect (the three-phase interface secured) is simultaneously obtained.

The electrolyte membrane / electrode assembly (MEA) is manufactured by applying a catalyst to a gas diffusion layer (GDL) and bonding it to a polymer electrolyte membrane. (Catalyst Coated on Membrane) method is representative.

The dual CCM method is difficult to apply the catalyst slurry directly to the polymer electrolyte membrane, and most of them use a decal method. The transfer method is a method in which a catalyst slurry containing catalyst particles and a polymer electrolyte is applied to a transfer (release) paper, dried, and transferred to a polymer electrolyte membrane by a high temperature / compression method. Therefore, the MEA manufacturing method that can be put into practical use is a CCG method or a CCM method. The catalyst slurry is coated / dried to form a catalyst layer and then bonded to a polymer electrolyte membrane.

Nafion, a polymer electrolyte mixed to prepare a catalyst slurry, is commercially available in the form of dispersion in water and an alcohol solvent. Glass temperature (Tg), which is one of the physical coefficients seen after drying, is 100 It is known as about -210 degreeC. When the sintering temperature is performed in the above temperature range, when the glass temperature is higher than the glass temperature, the polymer electrolyte starts to have some fluidity, but the fluidity increases with increasing temperature. Therefore, when a suitable heat is applied at a temperature of Tg or more, the polymer electrolyte (Nafion) on the surface of the catalyst particles may spread to the fine pores of the catalyst particles while having some fluidity. At this time, the catalyst particles and the polymer electrolyte are already sufficiently mixed so that even if the polymer electrolyte is only moved within a few tens of nm, it is sufficient to reach the respective micropores, and thus fluidity does not need to flow.

In addition, the sintering time is at least 5 minutes or more, it is more preferable when carried out under inert environmental conditions, the longer the sintering time is preferred, but the production cost is preferably within 1 hour. In the case of a sintering time of less than 5 minutes, the flow time of the polymer is not enough, so the effect is hard to appear.

The catalyst particles and the polymer electrolyte contained in the catalyst slurry are generally used in the art and are not particularly limited, but representative catalyst particles include a platinum catalyst loaded on a carbon carrier, and a polymer electrolyte such as Nafion. These are used 20 to 80% by weight (Pt vs Pt / Carbon) and 5 to 20% by weight (Nafion solid content), respectively, and it is easy to achieve the effect of the present invention under the above range.

Generally, the heat fusion process performed to fabricate the MEA is in the vicinity of or above Tg, but the temperature of Tg may be such that the polymer electrolyte membrane and the polymer electrolyte of the catalyst layer are fused and bonded. However, if the fusion temperature is too high, there is a possibility of damaging the structure of the polymer electrolyte membrane. Therefore, it is generally known to carry out only in the vicinity of Tg. Therefore, in the usual bonding method, Nafion, which is a polymer electrolyte in the catalyst layer, does not apply enough heat to penetrate the micropores of the catalyst.

In the present invention, after the catalyst is coated on the GDL or the release paper, the polymer electrolyte in the catalyst layer is thermally fused with the polymer electrolyte membrane after sintering to mature at a temperature higher than the heat fusion temperature for fabricating the MEA. The pores can be sufficiently penetrated. This makes it possible to create a three-phase interface of the catalyst present in the micropores without a separate mixing or dispersion process to increase the use efficiency of the catalyst, it is possible to reduce the internal electrical resistance. In addition, the catalyst layer polymer electrolyte bonds the catalyst particles in the form of a more robust mesh can be expected to increase durability.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited by the following Examples.

Example

Separately, 20 g of isopropyl alcohol (IPA, Iso-Propanol) and 20 g of water were used as a solvent, and 20 g of a 5 wt% Nafion solution and 5 g of a catalyst (commercial catalyst having 40 wt% Pt / C) were mixed and ultrasonically mixed. Mix sufficiently to prepare catalyst slurry

The slurry prepared above was coated with a laboratory bar coater on a release paper at 0.4 mgPt / cm2 based on platinum catalyst, cut into 5 cm horizontally and vertically, and the electrode was manufactured by sintering at 180 ° C. for 5 minutes. .

Electrolyte membrane / electrode assembly (MEA) was prepared by bonding the electrode prepared above to a Flemion (Flemion®, Asahi Glass, 50 um thick) membrane by a hot press method on both sides. At this time, joining was performed similarly at 150 degreeC, 5 minutes, and the pressure about 40 kgf / cm <2>.

In order to test the performance of the electrolyte membrane / electrode assembly (MEA) prepared above, the temperature of the anode inlet / cell / cathode inlet was 70/70/70 ° C., respectively, and the chemical reaction equivalent amount of hydrogen was 1.5 and air at atmospheric pressure (0 psig). It was carried out at 2.0.

Comparative example

In the same manner as in Example 1, an electrolyte membrane / electrode assembly (MEA) was prepared without the sintering process.

In order to test the performance of the electrolyte membrane / electrode assembly (MEA) prepared above, the temperature of the anode inlet / cell / cathode inlet was 70/70/70 ° C., respectively, and the chemical reaction equivalent weight of hydrogen was 1.5, It was carried out with air 2.0.

Next, as shown in the current-voltage characteristic curve of FIG. 3, when the sintering process was performed according to the present invention, the curve was moved upward and the output performance was greatly increased, and the impedance measurement value (100 mA / cm 2 constant current position, At 20 kHz to 0.1 Hz), the arc size, which represents the degree of oxidation / reduction of the catalyst, was reduced, indicating that the electrical conductivity was increased.

As described above, the electrolyte membrane / electrode assembly (MEA) manufactured according to the present invention has increased reactivity due to an increase in the contact surface between the catalyst particles and the polymer electrolyte, thereby improving the electrical properties of the electrolyte membrane / electrode assembly (MEA), thereby improving fuel efficiency. Its use is expected in the field of batteries.

Claims (3)

Forming a catalyst layer containing the catalyst particles and the polymer electrolyte, And sintering the catalyst layer at 100 to 210 ° C., followed by fusion bonding with a polymer electrolyte membrane by thermocompression bonding. The method of claim 1, wherein the catalyst layer is formed by coating and drying the gas diffusion layer or the release paper. The method of claim 1, wherein the sintering is performed for 5 minutes to 1 hour.

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