JP7172021B2 - METHOD FOR MANUFACTURING MEMBRANE ELECTRODE ASSEMBLY - Google Patents

Description

The present invention relates to a method for manufacturing a membrane-electrode assembly (MEA) for a fuel cell.

Conventionally, as a method for manufacturing a membrane electrode assembly, a transfer substrate having a catalyst layer having a desired shape and a solid polymer electrolyte membrane are thermocompressed with a hot press or a hot laminate roll, and then the substrate is peeled off. A thermal transfer method has been proposed.

For example, Patent Literature 1 discloses a technique using a hot press and a technique using a heat laminate roll. The technique using the above heat lamination rolls is to bring a long solid polymer electrolyte membrane and a transfer substrate provided with a catalyst layer having a desired shape on the front and back surfaces thereof into contact with each other, and then use a pair of heat lamination rolls. By thermocompression bonding, the solid polymer electrolyte membrane and the catalyst layer are integrally bonded, and then only the substrate is peeled from the transfer substrate using a pair of peeling rolls from the catalyst layer, and the catalyst layer is separated from the solid polymer. It is transferred to the surface of the electrolyte membrane.

JP-A-10-64574

In the method of thermally transferring a catalyst layer to a solid polymer electrolyte membrane as in Patent Document 1, it is necessary to prepare a catalyst ink.
This catalyst ink contains a catalyst, a conductive polymer similar to the electrolyte membrane, a solvent, and water. If the ratio of water contained in the catalyst ink is low and the water content is low, the solvent will be oxidized by the action of the catalyst during the preparation of the catalyst ink and during the coating and drying process of the catalyst ink, resulting in heat generation and ignition. have a nature.

Catalysts used in catalyst inks for fuel cells are generally made of carbon powder, and since this carbon is hydrophobic, it has poor compatibility with water. Also, since the conductive polymer has low compatibility with water, cracks are likely to occur in the catalyst layer formed by coating and drying the catalyst ink when the proportion of water in the catalyst ink is high. An MEA with a cracked catalyst layer has a problem that the durability of the MEA is inferior because the solid polymer electrolyte membrane may break when used as a fuel cell. In addition, since the polymer chains of the conductive polymer are difficult to spread in the catalyst ink with a high water ratio, the formation of conductive paths that contribute to power generation performance becomes insufficient, resulting in a problem of lower power generation performance. .

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for producing a membrane electrode assembly and a catalyst ink that can obtain a membrane electrode assembly having a good appearance without cracks in the catalyst layer. and

As a means for solving the above problems, a method for manufacturing a membrane electrode assembly according to one aspect of the present invention includes a step of preparing a catalyst ink, and applying the catalyst ink onto a transfer substrate to obtain a catalyst. forming a layer; and transferring the catalyst layer to the surface of the solid polymer electrolyte membrane by a thermal transfer method,
The step of preparing the catalyst ink is a step of preparing a catalyst ink in which the weight ratio of volatile components is 90% or more and 95% or less and the ratio of water in the volatile components is 15% or more and less than 40%. is.

Further, in the method for manufacturing a membrane electrode assembly according to one aspect of the present invention, the volatile components of the catalyst ink in the method for manufacturing a membrane electrode assembly are water and alcohol, and the alcohol is more volatile than water. is preferably high.

Further, in the method for manufacturing a membrane electrode assembly according to one aspect of the present invention, all or part of the steps excluding the step of preparing the catalyst ink may be continuous.

Further, in the method for manufacturing a membrane electrode assembly according to one aspect of the present invention, all steps may be discontinuous.

Further, as a means for solving the above problems, a catalyst ink according to an aspect of the present invention contains volatile components in a weight ratio of 90% or more and 95% or less, and water in the volatile components is ratio is 15% or more and less than 40%.

According to one aspect of the method for producing a membrane electrode assembly of the present invention, it is possible to produce an MEA with good appearance without cracks in the catalyst layer. By obtaining an MEA with a good appearance, it is possible to suppress deterioration in power generation performance and durability, and to reduce the risk of ignition due to the action of the catalyst.

1 is a schematic diagram of one embodiment of a method for manufacturing a membrane electrode assembly; FIG. 4 is a graph showing power generation performance in Examples and Comparative Examples of membrane electrode assemblies.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, in each drawing described below, the same reference numerals are given to the parts that correspond to each other, and the description of overlapping parts will be omitted as appropriate. Further, the embodiment of the present invention exemplifies the configuration for embodying the technical idea of the present invention, and the material, shape, structure, arrangement, dimensions, etc. of each part are specified as follows. not. Various modifications can be made to the technical idea of the present invention within the technical scope defined by the claims.

FIG. 1 is a schematic diagram for explaining one embodiment of the method for manufacturing a membrane electrode assembly of the present invention. The method for manufacturing a membrane electrode assembly according to the present embodiment comprises a step of preparing catalyst ink (hereinafter sometimes referred to as ink) (catalyst ink preparation step), and a step of applying catalyst ink (catalyst ink coating step) and a step of transferring the catalyst layer (thermal transfer step).

<Step of preparing catalyst ink>
First, the catalyst ink 1 is prepared. The catalyst ink 1 contains catalyst-supporting carbon and a conductive polymer as non-volatile components, and water and a solvent as volatile components. The weight ratio of the volatile components contained in the catalyst ink 1 is 90% or more and 95% or less, and the ratio of water in the volatile components is 15% or more and less than 40%.

In addition to platinum group elements such as platinum, palladium, ruthenium, iridium, rhodium, and osmium, the above catalysts include metals such as iron, lead, copper, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, and aluminum, or platinum. These alloys, their oxides, multiple oxides, etc. can be used. Among these, platinum and platinum alloys are more preferable.

If the particle size of the catalyst is too large, the activity of the catalyst will decrease, and if it is too small, the stability of the catalyst will decrease.

The catalyst-carrying carbon is not particularly limited as long as it is particulate, has electrical conductivity, and does not attack the catalyst. Specifically, carbon black, graphite, graphite, activated carbon, carbon fiber, carbon nanotube, fullerene, etc. can be used. The particle size of the catalyst-carrying carbon is preferably about 10 nm or more and 100 nm or less.

First, water is added to the catalyst-carrying carbon, and kneaded so that the surface of the carbon is sufficiently wet with water. Good surface wetting in the first stage reduces the risk of ignition. Next, a conductive polymer exhibiting good proton conductivity is added and further stirred to form a paste.

Specifically, materials such as hydrocarbon-based polymer electrolytes and fluorine-based polymer electrolytes can be used as the conductive polymer material.
Electrolyte materials such as sulfonated polyetherketone, sulfonated polyethersulfone, sulfonated polyetherethersulfone, sulfonated polysulfide, and sulfonated polyphenylene can be used as the hydrocarbon-based polymer electrolyte material.

As the fluorine-based polymer electrolyte material, for example, Nafion (registered trademark) manufactured by DuPont, Flemion (registered trademark) manufactured by Asahi Glass, Aciplex (registered trademark) manufactured by Asahi Kasei, Gore Select (registered trademark) manufactured by Gore, etc. can be used. .

After that, the catalyst ink 1 is prepared by adding a solvent to the paste-like mixture and further stirring and dispersing the mixture. The solvent is preferably an alcohol having a boiling point lower than that of water, and more preferably lower alcohols such as ethanol, 1-propanol and 2-propanol. Since lower alcohols have relatively high compatibility with water, a stable catalyst ink 1 can be produced. Various dispersion methods can be used as the dispersion method for preparing the catalyst ink. As a dispersion method, for example, ultrasonic dispersion, ball mill dispersion, bead mill dispersion, homogenizer dispersion, or the like can be used.

<Step of applying catalyst ink>
Next, the catalyst ink 1 is applied onto the transfer film 2 made of a polymer film using a die coater 10 . For coating, a die coating method is preferred, which enables large-scale and stable coating of the catalyst layer. If the transfer film 2 is well wetted by the catalyst ink 1, and the catalyst layers 5a (anode) and 5c (cathode) formed after drying can be thermally transferred to the surface of the solid polymer electrolyte membrane 4 by the thermal transfer device 20, It is not particularly limited.
Examples of transfer films include polyimide, polyethylene terephthalate, polyparvanic aramid, polyamide (nylon), polysulfone, polyethersulfone, polyethersulfone, polyphenylene sulfide, polyetheretherketone, polyetherimide, polyacrylate, polyethylene. A polymer film such as naphthalate can be used. Heat-resistant fluororesins such as ethylenetetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroperfluoroalkylvinylether copolymer, and polytetrafluoroethylene can also be used.

<Step of transferring catalyst layer>
Next, the catalyst layer-attached transfer substrates 3a and 3c prepared above are placed on the facing surfaces of the solid polymer electrolyte membrane 4, and thermally pressurized by the thermal transfer device 20. After that, only the transfer substrate 2 is transferred. are peeled off to obtain a membrane electrode assembly 6 having catalyst layers 5a and 5c formed on the surface of the solid polymer electrolyte membrane 4 . For thermal transfer by hot pressing, a method using a hot laminate roll, a method using a hot press, or the like can be used. As the solid polymer electrolyte membrane material, the same material as the conductive polymer material contained in the catalyst ink 1 can be used.

Here, in consideration of productivity, it is preferable that all the steps except for the catalyst ink liquid preparation step are continuous. However, when the yield is considered, the entire process is discontinuous, but each process may be a continuous roll-to-roll process. Moreover, all steps may be discontinuous in consideration of loss of materials.

EXAMPLES The production method of the present invention will be specifically described below with reference to examples. However, the invention is not limited to only these examples.

(Example 1)
<Production of membrane electrode assembly>
Catalyst ink 1 is prepared by adding water to a platinum catalyst (TEC10E50E manufactured by Tanaka Kikinzoku Co., Ltd.) and kneading the catalyst. Next, after adding a fluorine-based polymer electrolyte membrane dispersion solution (20% Nafion dispersion DE2020CS manufactured by Chemours), the mixture was stirred with a stirring device. Next, 1-propanol was added, and after stirring again, dispersion was carried out using a bead mill dispersion device. At this time, the amount of each material was adjusted so that the weight ratio of the volatile component was 90% and the ratio of water in the volatile component was 15%.

Catalyst ink 1 was applied onto a transfer substrate (AFLEX manufactured by Asahi Glass Co., Ltd., thickness 50 μm) with a die coater 10 and dried to obtain transfer substrates 3a and 3c with a catalyst layer for anode and cathode.

For the anode catalyst layer, the thickness was adjusted so that the amount of platinum contained in the non-volatile component was 0.1 mg/cm ² . /cm ² to prepare a transfer base material 3c with a catalyst layer. The surface of the fluorine-based electrolyte membrane 4 (Nafion HP manufactured by Chemours) was sandwiched between the obtained transfer substrates 3a and 3c with the catalyst layer. By peeling off, a membrane electrode assembly 6 was obtained.

(Example 2)
As Example 2, a transfer base material with a catalyst layer was produced in the same manner as in Example 1, except that the ratio of water in the volatile components of the catalyst ink was changed to 35%, and then a membrane electrode assembly was produced. .

(Example 3)
As Example 3, a transfer base material with a catalyst layer was produced in the same manner as in Example 1, except that the weight ratio of the volatile components in the catalyst ink was changed to 95%, and then a membrane electrode assembly was produced.

(Comparative Examples 1 to 3)
A transfer substrate with a catalyst layer was prepared in the same manner as in Example 1 except that the ratio of water in the catalyst ink was changed to 12% (Comparative Example 1), 40% (Comparative Example 2), and 58% (Comparative Example 3). After producing, a membrane electrode assembly was produced. Table 1 and FIG. 2 show the results of evaluation performed in the same manner as in Example 1.

(Comparative Examples 4 and 5)
A transfer substrate with a catalyst layer was produced in the same manner as in Example 1, except that the weight ratio of the volatile components in the catalyst ink was changed to 88% (Comparative Example 4) and 96% (Comparative Example 5). An electrode assembly was produced.

(Evaluation result 1)
For Examples 1 and 2 and Comparative Examples 1 to 3, the temperature and appearance of the catalyst ink were evaluated according to the "proportion of water in the volatile components of the catalyst ink." Table 1 shows the evaluation results of the temperature, which is a measure of the heat generation of the catalyst ink during preparation of the catalyst ink, and the evaluation results of the appearance of the catalyst layer, and FIG. 2 shows the power generation performance results of the membrane electrode assembly.
In Table 1, the temperature rise of the catalyst ink during bead mill dispersion was judged to be ◯ when the temperature rise of the catalyst ink was less than 10°C, and X was judged to be 10°C or more. This is because the increase in the temperature of the catalyst ink facilitates volatilization of the solvent, possibly causing a change in the composition of the catalyst ink.
From Example 1, the catalyst ink temperature evaluation is good when the ratio of water in the volatile components is 15% or more. This is because it was suppressed.
In the case of Comparative Example 1, in which the proportion of water was 12%, the temperature of the catalyst ink increased by 10° C. or more. In addition, since the amount of water initially charged was small, it was confirmed that lumps of the catalyst remained at the bottom of the liquid preparation container.

Next, in the evaluation of the appearance, in Examples 1, 2, and Comparative Example 1, no defect was found in the appearance, so the evaluation was given as ◯. However, when the ratio of water in Comparative Example 2 was 40% or more, a large number of cracks were observed in the appearance of the catalyst layer-attached transfer base material, so the evaluation was made as x.

When the power generation performance of the membrane electrode assemblies of Examples 1 and 2 and Comparative Examples 1 to 3 were evaluated, the power generation evaluation results shown in FIG. 2 were obtained. In Comparative Examples 2 and 3, which had many cracks, the performance was remarkably deteriorated.

(Evaluation result 2)
Next, for Examples 1 and 3 and Comparative Examples 1 to 3, the temperature and appearance of the catalyst ink were evaluated according to the "weight ratio of the volatile components of the catalyst ink." Table 2 shows the evaluation results. The evaluation criteria are the same as those in Table 1.

As shown in Table 2, in Examples 1 and 3 in which the weight ratio was 90% or more and 95% or less, the temperature rise of the catalyst ink during bead mill dispersion was less than 10°C, which was favorable. Also, no defects were found in the appearance of the transfer base material with the catalyst layer.

On the other hand, as shown in Comparative Example 4, when the weight ratio was less than 90%, the surface of the catalyst could not be sufficiently wetted with water, resulting in an increase in catalyst ink temperature. In addition, the appearance was evaluated as x because lumps were likely to occur during dispersion, unevenness occurred during coating, and unevenness occurred in the catalyst layer after drying.
In addition, when the weight ratio was more than 95% as shown in Comparative Example 5, the absolute amount of water increased too much, and the water ratio increased during the drying process, causing cracks. was evaluated.

As described above, according to one embodiment of the present invention, by keeping the water ratio of the catalyst ink low, deterioration of the appearance and power generation performance of the membrane electrode assembly can be suppressed, and the ratio of volatile components can be increased. Therefore, it is possible to provide a method for manufacturing a membrane electrode assembly and a useful catalyst ink for use in the method, taking safety into consideration.

Reference Signs List 1 Catalyst ink 2 Transfer base material 3a, 3c Transfer base material with catalyst layer 4 Solid polymer electrolyte membrane 5a, 5c Catalyst layer 6 Membrane electrode assembly 10... Die coater 20... Thermal transfer device

Claims (6)

A step of preparing a catalyst ink, a step of coating the catalyst ink on a transfer substrate to form a catalyst layer, and a step of transferring the catalyst layer to the surface of a solid polymer electrolyte membrane by a thermal transfer method. including
The step of preparing the catalyst ink includes: adding water to the catalyst-carrying carbon to knead the catalyst-carrying carbon; A molecular dispersion solution is added and stirred, and an alcohol solvent, which is a volatile component, is further added to the stirred mixture containing the catalyst-carrying carbon and the conductive polymer dispersion solution, and the mixture is stirred to obtain the volatile component, the The catalyst ink is prepared so that the total weight ratio of water and the alcohol solvent is 90% or more and 95% or less, and the total weight ratio of the water in the volatile component is 15% or more and less than 40%. is a process,
The step of transferring the catalyst layer is a step of transferring the catalyst layer so that the catalyst layer is in contact with both surfaces of the solid polymer electrolyte membrane,
A method for manufacturing a membrane electrode assembly, wherein the alcohol is 1-propanol. 2. The method for manufacturing a membrane electrode assembly according to claim 1, wherein all or each step except for the step of preparing the catalyst ink is continuous. In the step of transferring the catalyst layer, the surface of the solid polymer electrolyte membrane is sandwiched between the catalyst layer-attached transfer substrate prepared in the step of forming the catalyst layer, and the surface of the solid polymer electrolyte membrane is pressed with a heat laminate roll. 3. The process according to claim 2 , wherein only the substrate is peeled off, the catalyst layer is transferred to the surface of the solid polymer electrolyte membrane, and then a membrane electrode assembly is obtained without a drying process. A method for manufacturing a membrane electrode assembly. In the step of preparing the catalyst ink, an alcohol solvent, which is a volatile component, is further added to the mixture containing the catalyst-supporting carbon and the conductive polymer dispersion solution, and the mixture is stirred. The total weight ratio of the water and the alcohol solvent is 90% or more and 95% or less, and the total weight ratio of the water in the volatile component is 15% or more and less than 40%. A step of preparing
4. The method for manufacturing a membrane electrode assembly according to any one of claims 1 to 3 , wherein the temperature rise of the catalyst ink during the dispersing process is less than 10[deg.]C. 5. The method for manufacturing a membrane electrode assembly according to claim 4 , wherein the dispersion treatment is ultrasonic dispersion, ball mill dispersion, bead mill dispersion, or homogenizer dispersion. 5. The method of manufacturing a membrane electrode assembly according to claim 4 , wherein the dispersing treatment is dispersing treatment using a bead mill dispersing device.

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