JP7384263B2 - catalyst ink - Google Patents

Description

The present invention relates to membrane-electrode assemblies (MEA) for fuel cells.
(assembly).

Conventionally, the manufacturing method for membrane electrode assemblies has been to bond a transfer base material provided with a catalyst layer having a desired shape with a solid polymer electrolyte membrane using a hot press, a hot laminating roll, etc., and then peel the base material. A thermal transfer method has been proposed.

For example, Patent Document 1 discloses a method using a hot press and a method using a hot laminating roll. The above-mentioned method using thermal laminating rolls involves bringing a long solid polymer electrolyte membrane into contact with a transfer base material provided with a catalyst layer having a desired shape on the front and back surfaces of the long solid polymer electrolyte membrane, and using a pair of thermal laminating rolls. The solid polymer electrolyte membrane and the catalyst layer are integrally joined by thermocompression bonding, and then only the base material is peeled off from the catalyst layer using a pair of peeling rolls, and the catalyst layer is bonded to the solid polymer electrolyte membrane. It is transferred to the electrolyte membrane surface.

Japanese Patent Application Publication No. 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 an electrolyte membrane, a solvent, and water. If the proportion and amount of water contained in the catalyst ink is low, there is a risk that the solvent will be oxidized by the action of the catalyst during the preparation of the catalyst ink, or during the coating and drying process of the catalyst ink, causing heat generation and ignition. There is sex.

Catalysts used in catalyst inks for fuel cells are generally made of carbon powder, and since carbon is hydrophobic, it has poor compatibility with water. Furthermore, since conductive polymers also have low compatibility with water, when the proportion of water in the catalyst ink increases, cracks are likely to occur in the catalyst layer formed by applying and drying the catalyst ink. When an MEA in which a cracked catalyst layer is formed is used as a fuel cell, there is a risk that the solid polymer electrolyte membrane may rupture, so there is a problem in that the durability of the MEA is poor. In addition, in a catalyst ink with a high proportion of water, the polymer chains of the conductive polymer are difficult to spread, resulting in insufficient formation of conductive paths that contribute to power generation performance, resulting in a decrease in power generation performance. .

The present invention has been made in view of the above points, and an object of the present invention is to provide a method for manufacturing a membrane electrode assembly and a catalyst ink that can obtain a membrane electrode assembly with a good appearance and no cracks in the catalyst layer. shall be.

As a means for solving the above problems, a method for manufacturing a membrane electrode assembly according to one embodiment of the present invention includes a step of preparing a catalyst ink, and a step of coating the catalyst ink on a transfer substrate to catalyze the catalyst. a step of forming a layer; and a step of 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%. It is.

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

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

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

According to one aspect of the method for manufacturing a membrane electrode assembly of the present invention, an MEA with a good appearance and no cracks in the catalyst layer can be manufactured. By obtaining an MEA with a good appearance, deterioration in power generation performance and durability can be suppressed, and the risk of ignition due to the action of the catalyst can be reduced.

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

Embodiments of the present invention will be described below with reference to the drawings. However, in each of the figures described below, mutually corresponding parts are given the same reference numerals, and descriptions of overlapping parts will be omitted as appropriate. In addition, the embodiments of the present invention are examples of configurations for embodying the technical idea of the present invention, and the materials, shapes, structures, arrangements, dimensions, etc. of each part are specified as follows. Not. The technical idea of the present invention can be modified in various ways 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 of the present embodiment includes a step of preparing a catalyst ink (hereinafter sometimes referred to as ink) (catalyst ink preparation step) and a step of coating the catalyst ink (catalyst ink coating). step) and a step of transferring the catalyst layer (thermal transfer step).

<Process 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 volatile components contained in this 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%.

The above catalysts include platinum group elements such as platinum, palladium, ruthenium, iridium, rhodium, and osmium, as well as metals such as iron, lead, copper, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, and aluminum, or platinum and other metals. An alloy of these, or an oxide, a double oxide, or the like of these can be used. Among these, platinum and platinum alloys are more preferred.

The particle size of the catalyst is preferably 0.5 nm or more and 20 nm or less, because if it is too large, the activity of the catalyst will be reduced, and if it is too small, the stability of the catalyst will be reduced.

The above-mentioned catalyst-supporting carbon is not particularly limited as long as it is in the form of fine particles, has conductivity, and does not attack the catalyst. Specifically, carbon black, graphite, graphite, activated carbon, carbon fiber, carbon nanotubes, fullerene, etc. can be used. The particle size of the catalyst-supporting carbon is preferably about 10 nm or more and 100 nm or less.

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

Specifically, as the conductive polymer material, a material such as a hydrocarbon polymer electrolyte or a fluorine polymer electrolyte can be used.
As the hydrocarbon polymer electrolyte material, electrolyte materials such as sulfonated polyether ketone, sulfonated polyether sulfone, sulfonated polyether ether sulfone, sulfonated polysulfide, and sulfonated polyphenylene can be used.

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. .

Thereafter, a solvent is added to the paste-like mixture, and the mixture is further stirred and dispersed to prepare the catalyst ink 1. The solvent is preferably an alcohol having a boiling point lower than 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 to prepare the catalyst ink. As a dispersion method, for example, ultrasonic dispersion, ball mill dispersion, bead mill dispersion, homogenizer dispersion, etc. can be used.

<Process 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 as it allows for stable coating of the catalyst layer in large quantities. If the transfer film 2 is well wetted with the catalyst ink 1 and the catalyst layers 5a (anode) and 5c (cathode) formed after drying can be thermally transferred onto 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, and polyethylene. Polymer films such as naphthalate can be used. Furthermore, heat-resistant fluororesins such as ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroperfluoroalkyl vinyl ether copolymer, and polytetrafluoroethylene can also be used.

<Step of transferring the catalyst layer>
Next, the catalyst layer-coated transfer substrates 3a and 3c prepared above are placed on the opposing surfaces of the solid polymer electrolyte membrane 4, and after thermal pressure is applied by the thermal transfer device 20, only the transfer substrate 2 is placed. is peeled off to obtain a membrane electrode assembly 6 in which catalyst layers 5a and 5c are formed on the surface of the solid polymer electrolyte membrane 4. For thermal transfer by hot pressing, a method using a hot laminating roll, a method using a hot press, etc. can be used. Further, 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 steps except the catalyst ink preparation step are continuous. However, in consideration of yield, all the steps are discontinuous, but each step may be continuous roll-to-roll. Moreover, if material loss is taken into account, all steps may be discontinuous.

The manufacturing method of the present invention will be specifically explained below using Examples. However, the present invention is not limited only to these examples.

(Example 1)
<Manufacture of membrane electrode assembly>
The catalyst ink 1 is prepared by adding water to a platinum catalyst (TEC10E50E manufactured by Tanaka Kikinzoku) and kneading the catalyst. Next, after adding a fluoropolymer electrolyte membrane dispersion solution (20% Nafion dispersion DE2020CS manufactured by Chemours), stirring was performed using a stirring device. Next, 1-propanol was added and stirring was performed again, followed by dispersion using a bead mill dispersion device. At this time, the amounts of each material were adjusted so that the weight ratio of volatile components was 90% and the ratio of water in the volatile components was 15%.

Catalyst ink 1 was applied onto a transfer substrate (Aflex, manufactured by Asahi Glass Co., Ltd., thickness 50 μm) using a die coater 10 and dried to obtain transfer substrates 3a and 3c with catalyst layers for anodes and cathodes.

For the anode catalyst layer, the thickness was adjusted so that the amount of platinum contained in the nonvolatile component was 0.1 mg/cm ² , and for the cathode catalyst layer, the thickness was adjusted so that the amount of platinum contained in the catalyst layer was 0.4 mg/cm2. The thickness was adjusted so as to be /cm ² , and a transfer base material 3c with a catalyst layer was produced. The surface of the fluoroelectrolyte membrane 4 (Nafion HP manufactured by Chemours) was sandwiched between the obtained catalyst layer-coated transfer substrates 3a and 3c, and after pressurizing with a thermal laminating roll 20 at 130° C., only the transfer substrate 2 was held. The membrane electrode assembly 6 was obtained by peeling.

(Example 2)
As Example 2, a transfer substrate with a catalyst layer was prepared in the same manner as in Example 1, except that the proportion of water in the volatile components of the catalyst ink was 35%, and then a membrane electrode assembly was prepared. .

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

(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 proportion of water in the catalyst ink was 12% (Comparative Example 1), 40% (Comparative Example 2), and 58% (Comparative Example 3). After that, a membrane electrode assembly was produced. The results of evaluation performed in the same manner as in Example 1 are shown in Table 1 and FIG. 2.

(Comparative Examples 4 and 5)
After preparing a transfer substrate with a catalyst layer in the same manner as in Example 1 except that the weight ratio of volatile components of 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 catalyst ink temperature and appearance were evaluated based on the "ratio 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 when preparing the catalyst ink, and the evaluation result of the appearance of the catalyst layer, and the power generation performance results of the membrane electrode assembly are shown in FIG. 2.
Regarding the quality of the catalyst ink temperature in Table 1, cases where the temperature rise of the catalyst ink during bead mill dispersion was less than 10°C were evaluated as ○, and cases where it was 10°C or higher were evaluated as ×. This is because as the temperature of the catalyst ink increases, the solvent tends to evaporate, which may cause a change in the composition of the catalyst ink.
From Example 1, the reason why the catalyst ink temperature evaluation is good when the proportion of water in the volatile components is 15% or more is because the catalyst is sufficiently wetted with water at the beginning, so that the heat generated by the catalyst ink due to the catalytic reaction when the solvent is mixed is reduced. This is because it was suppressed.
In the case of Comparative Example 1 with a water ratio of 12%, the temperature of the catalyst ink increased by 10° C. or more, so it was rated as ×. In addition, because the amount of water initially added was small, catalyst lumps were observed at the bottom of the liquid preparation container.

Next, in the evaluation of appearance, Examples 1 and 2 and Comparative Example 1 were given a rating of ○ because no defects were observed in their appearance. However, when the proportion of water in Comparative Example 2 was 40% or more, many cracks were observed in the appearance of the transfer substrate with a catalyst layer, so it was rated as ×.

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

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

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

On the other hand, as shown in Comparative Example 4, when the weight ratio was less than 90%, the catalyst surface could not be sufficiently wetted with water, so the catalyst ink temperature rose. In addition, the appearance was rated as x because it was easy to form lumps during dispersion, unevenness occurred during coating, and unevenness occurred in the catalyst layer after drying.
In addition, as shown in Comparative Example 5, when the weight ratio is greater than 95%, the absolute amount of water increases too much, and the water ratio increases during the drying process, resulting in cracks, so the appearance evaluation is It was evaluated.

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

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 (4)

After sandwiching the surface of the solid polymer electrolyte membrane with a transfer substrate with a catalyst layer on which a catalyst layer is formed and applying pressure with a hot laminating roll, only the transfer substrate is peeled off, and the A catalyst ink for forming the catalyst layer provided in a membrane electrode assembly formed by transferring the catalyst layer onto the surface of a solid polymer electrolyte membrane and then performing a drying process, the catalyst ink comprising:
The catalyst ink includes volatile components and catalyst-supported carbon,
The weight ratio of the volatile components contained is 90% or more and 95% or less,
and the ratio of water in the volatile component is 15% or more and less than 40%,
The volatile components are water and alcohol,
A catalyst ink characterized in that the alcohol is 1-propanol. Coating a catalyst ink on a transfer base material to form a catalyst layer, sandwiching the surface of the solid polymer electrolyte membrane with a catalyst layer-attached transfer base material on which the catalyst layer is formed on the transfer base material, After applying pressure with a hot laminating roll, only the transfer base material is peeled off, and the catalyst layer is transferred to the surface of the solid polymer electrolyte membrane, and then a membrane electrode assembly is formed without going through a drying process. A catalyst ink for forming a catalyst layer, comprising:
The catalyst ink includes volatile components and catalyst-supported carbon,
The weight ratio of the volatile components contained is 90% or more and 95% or less,
and the ratio of water in the volatile component is 15% or more and less than 40%,
The volatile components are water and alcohol,
A catalyst ink characterized in that the alcohol is 1-propanol. The catalyst ink according to claim 1 or 2, wherein the catalyst ink further contains a conductive polymer. The catalyst ink according to claim 1 or 2, wherein the catalyst ink further contains a fluoropolymer electrolyte.

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