JP2020145074A - Catalyst ink and catalyst layer - Google Patents

Abstract

To provide a catalyst ink which can suppress the occurrence of cracking when being dried, and a catalyst layer prepared by use thereof.SOLUTION: A catalyst ink comprises: a catalyst carrier carbon; an ionomer; a nonion-based surfactant of which the HLB value is 16 or larger and smaller than 20; water; and alcohol of which the boiling point is 120°C or under. In the catalyst ink, the content of the nonion-based surfactant (the percentage of a weight of the nonion-based surfactant to a total weight of solid components included in the catalyst ink) is 1 wt% or more and 25 wt% or less. A catalyst layer comprises: a catalyst carrier carbon; an ionomer; and a nonion-based surfactant of which the HLB value is 16 or larger and smaller than 20. In the catalyst layer, the content of the nonion-based surfactant is 2 wt% or more and 25 wt% or less.SELECTED DRAWING: Figure 2

Description

The present invention relates to a catalyst ink and a catalyst layer, and more particularly to a catalyst ink capable of suppressing cracks during drying, and a catalyst layer produced by using the catalyst ink.

The polymer electrolyte fuel cell has a membrane electrode assembly (MEA) in which electrodes including catalyst layers are bonded to both sides of a solid polymer electrolyte membrane as a basic unit. Further, in a polymer electrolyte fuel cell, the electrode generally has a two-layer structure of a diffusion layer and a catalyst layer. The diffusion layer is for supplying reaction gas and electrons to the catalyst layer, and carbon paper, carbon cloth, or the like is used. The catalyst layer is a portion that serves as a reaction field for the electrode reaction, and is generally composed of a composite of carbon carrying an electrode catalyst such as platinum and a solid polymer electrolyte (catalyst layer ionomer).

In the fabrication of electrodes for polymer electrolyte fuel cells, catalytic inks containing a conductive carrier carrying platinum and ionomers are used. Since platinum is expensive, it is desirable to reduce the amount used. However, if the amount of platinum used is reduced, there is a problem that the power generation performance of the fuel cell is lowered. Therefore, in order to suppress the deterioration of power generation performance, Patent Document 1 discloses a technique of using an ionoma (fluorine-containing ion exchange resin having an aliphatic ring structure) having high oxygen permeability.

However, when an electrode is manufactured using a catalyst ink containing ionomer having such high oxygen permeability, cracks may occur in the electrode when the catalyst ink is applied to a substrate and dried. The occurrence of cracks in the electrodes adversely affects durability. Therefore, various proposals have been made conventionally as countermeasures against this.

For example, Patent Document 2 does not aim to improve the crack resistance of the catalyst layer containing a high oxygen permeable ionomer, but
(A) 9.0 mass% ethanol solution of fluorine-containing ion exchange resin (copolymer consisting of a repeating unit based on tetrafluoroethylene and a repeating unit based on sulfonyl vinyl fluoride ether monoma): 5.55 g,
(B) Water: 4.65 g,
(C) Platinum-supported carbon: 1.0 g and
(D) 10 mass% polyoxyethylene alkyl ether (nonionic dispersant) aqueous solution: 0.45 g
A mixture for forming a catalyst layer containing the above is disclosed.
In the same document, when a viscous mixture containing a catalyst and a fluorine-containing ion exchange resin is prepared, by adding a specific nonionic dispersant, the coatability of the viscous mixture and the dispersion in the viscous mixture are described. It is described that the dispersion stability can be greatly improved.

Patent Documents 3 and 4 disclose electrodes for fuel cells including a catalyst carrier carrying a catalyst, a low oxygen permeable first electrolyte resin, and a high oxygen permeable second electrolyte resin.
In the same document,
(A) When the low oxygen permeable first electrolyte resin is used, the aggregation of the catalyst carrier caused by the structure of the high oxygen permeable second electrolyte resin can be alleviated, and the cracking of the electrode can be prevented. And what you can do
(B) It is described that the cell voltage decreases when the ratio of the first electrolyte resin becomes 20% or more.

Patent Document 5 does not aim to improve the crack resistance of the catalyst layer containing high oxygen permeable ionomer, but the catalyst particles, the ionic conductive polymer electrolyte, the nonionic surfactant, and the boiling point are different. An ink for inkjet for forming a catalyst layer for a fuel cell containing a solvent having a temperature of 120 ° C. or higher is disclosed.
In the same document,
(A) By using a nonionic surfactant, the aggregation of carbon particles can be effectively prevented, and (B) when the ink is applied onto the ion conductive electrolyte membrane by using an inkjet, it is used as a solvent. It is described that when a solvent having a high boiling point is used, sticking of the ink due to drying of the ink at the ejection port is suppressed, and stable coating is possible.

Patent Document 6 describes the coatability and dispersion stability of the water-repellent paste for gas diffusion by adding a nonionic surfactant having an HLB value of 14 to 20 to the water-repellent paste for gas diffusion instead of the catalyst ink. Is stated to improve.
Further, Non-Patent Document 1 reports that by adding Additive-A to the catalyst ink, the dispersibility of the catalyst ink can be enhanced and cracks in the catalyst layer can be suppressed.

A fluorine-containing ion exchange resin having an aliphatic ring structure in the molecule has high oxygen permeability. However, when the catalyst layer is produced using the catalyst ink containing such a fluorine-containing ion exchange resin, the catalyst layer is liable to crack in the drying process. It is considered that this is because the fluorine-containing ion exchange resin having an aliphatic ring structure has rigid molecules and poor adsorption to carbon, so that carbons tend to aggregate with each other in the ink.

In order to solve this problem, Patent Documents 3 and 4 propose a method of mixing a high oxygen permeable ionomer and a low oxygen permeable ionomer such as Nafion (registered trademark). However, when a low oxygen permeable ionomer is used, the crack resistance is improved to some extent, but there is a problem that the electrode performance is also lowered.
Further, in order to improve the coatability of the catalyst ink, various surfactants are added to the catalyst ink. However, there has been no conventional example in which a catalytic ink capable of improving crack resistance without sacrificing electrode performance has been proposed even when a high oxygen permeable ionomer is contained.

Japanese Unexamined Patent Publication No. 2003-036856 Japanese Unexamined Patent Publication No. 2003-045440 Japanese Patent No. 5851150 (Japanese Unexamined Patent Publication No. 2013-037940) Japanese Unexamined Patent Publication No. 2016-058396 Japanese Unexamined Patent Publication No. 2010-086656 Japanese Unexamined Patent Publication No. 2016-085944

International journal of hydrogen energy, 36 (2011) 12465-12473

An object to be solved by the present invention is to provide a catalyst ink capable of suppressing cracks during drying without sacrificing electrode performance, and a catalyst layer produced by using the catalyst ink.
Another problem to be solved by the present invention is a catalyst capable of suppressing cracks during drying without sacrificing electrode performance even when a high oxygen permeable ionomer is used as the ionomer. An object of the present invention is to provide an ink and a catalyst layer produced by using the ink.

In order to solve the above problems, it is a gist that the catalyst ink according to the present invention has the following constitution.
(1) The catalyst ink is
Catalyst-supported carbon and
With ionomer
Nonionic surfactants with an HLB value of 16 or more and less than 20 and
water and,
It includes an alcohol having a boiling point of 120 ° C. or lower.
(2) The content of the nonionic surfactant (the ratio of the weight of the nonionic surfactant to the weight of the total solid content contained in the catalyst ink) is 1 wt% or more and 23 wt% or less.

It is a gist that the catalyst layer according to the present invention has the following constitution.
(1) The catalyst layer is
Catalyst-supported carbon and
With ionomer
Nonionic surfactants with an HLB value of 16 or more and less than 20 and
Is equipped with.
(2) The content of the nonionic surfactant is 1 wt% or more and 23 wt% or less.

In a catalyst ink using water and an alcohol having a boiling point of 120 ° C. or lower as a solvent, the catalyst-supported carbon particles tend to form a three-dimensional network structure because of their low dispersibility in the solvent. When the catalyst ink is dried while the catalyst-supported carbon forms a three-dimensional network structure, pores having a non-uniform size are formed, and stress is concentrated there, so that cracks are likely to occur. This tendency becomes remarkable when a high oxygen permeation ionomer is used as the ionomer.

On the other hand, when a nonionic surfactant having an HLB value of 16 to 20 is added to the catalyst ink, the hydrophobic group of the nonionic surfactant is adsorbed on the carbon surface, and the hydrophilic group is a solvent mainly composed of water. Ensure affinity. Therefore, the carbon is easily dispersed in the dispersion medium, and the three-dimensional network structure of the catalyst-supported carbon can be broken. As a result, the crack resistance of the catalyst layer is improved.
Moreover, since the nonionic surfactant does not generate ions in the solvent, it does not impair the power generation characteristics of ionomer. Further, since a solvent having a boiling point of 120 ° C. or lower is used, it is possible to suppress an increase in production cost and a decrease in performance due to a heat load during drying.

FIG. 1 (A) shows the molecular structure of polyoxyethylene (n) stearyl ether, which is a kind of nonionic surfactant. FIG. 1B shows the molecular structure of polyoxyethylene oleyl ether (E-230), which is a kind of nonionic surfactant. FIG. 2A is an SEM image of the surface of the catalyst layer obtained in Example 4. FIG. 2B is an SEM image of the surface of the catalyst layer obtained in Comparative Example 1.

Hereinafter, an embodiment of the present invention will be described in detail.
[1. Catalyst ink]
The catalyst ink according to the present invention is
Catalyst-supported carbon and
With ionomer
Nonionic surfactants with an HLB value of 16 or more and less than 20 and
water and,
It includes an alcohol having a boiling point of 120 ° C. or lower.

[1.1. Catalyst-supported carbon]
[1.1.1. composition]
The catalyst-supported carbon is composed of catalyst particles supported on a carrier surface made of a carbon material. In the present invention, the materials of the carrier and the catalyst particles are not particularly limited, and the optimum material can be selected according to the intended purpose. ..
Examples of the carrier include carbon black, carbon nanotubes, carbon nanohorns, activated carbon, natural graphite, mesocarbon microbeads, and glassy carbon powder. Any one of these may be used as the carrier, or two or more of them may be used in combination.

Examples of catalyst particles include
(A) Precious metals (Pt, Au, Ag, Pd, Rh, Ir, Ru, Os),
(B) Alloys containing two or more precious metal elements,
(C) An alloy containing one or more noble metal elements and one or more base metal elements (for example, Fe, Co, Ni, Cr, V, Ti, etc.).
and so on.
Any one of these may be used as the catalyst particles, or two or more of them may be used in combination.

Among these, the catalyst particles are preferably Pt or Pt alloy. This is because it has high activity for the electrode reaction of the fuel cell.
Examples of the Pt alloy include Pt-Fe alloy, Pt-Co alloy, Pt-Ni alloy, Pt-Pd alloy, Pt-Cr alloy, Pt-V alloy, Pt-Ti alloy, Pt-Ru alloy, and Pt-Ir. There are alloys and so on.

[1.1.2. Content]
The content of the catalyst-supported carbon in the catalyst ink is not particularly limited, and the optimum content can be selected according to the purpose. In general, if the content of catalyst-supporting carbon in the catalyst ink is too low, the performance of the catalyst layer deteriorates. Therefore, the content of the catalyst-supported carbon is preferably 1 wt% or more. The content is preferably 3 wt% or more.
On the other hand, if the content of the catalyst-supported carbon is excessive, the viscosity of the catalyst ink becomes too high, and defects such as streaks may occur during coating. Therefore, the content of the catalyst-supported carbon is preferably 20 wt% or less. The content is preferably 10 wt% or less.

[1.2. Ionomer]
[1.2.1. composition]
Ionomer is for exchanging protons with catalyst particles. In the present invention, the type of ionomer is not particularly limited.

As an ionomer, for example
(A) Fluorine-containing ion exchange resin having an aliphatic ring structure and an acid group in the molecule (hereinafter, this is also referred to as "high oxygen permeation ionoma"),
(B) Fluorine-containing ion exchange resins containing repeating units based on fluoride sulfonyl vinyl ether monomas, such as Nafion (registered trademark), Flemion (registered trademark), Aquivion (registered trademark), and Aciplex (registered trademark). Collectively, it is also called "low oxygen permeation ionoma")
and so on.
Any one of these may be used for the ionomer, or two or more of them may be used in combination.

As the ionomer, a highly oxygen-permeable ionomer is particularly preferable. A catalyst layer made using a catalyst ink containing a highly oxygen permeable ionomer exhibits high oxygen permeability. Therefore, when this is used as a catalyst layer on the air electrode side, high power generation performance can be obtained.

[1.2.2. Content]
In general, the ratio of the weight of the ionomer to the weight of the carbon carrier contained in the catalyst layer (I / C) affects the performance of the catalyst layer. Therefore, the content of ionomer in the catalyst ink is preferably set so that the I / C becomes a predetermined value. In general, if the I / C ratio becomes too small, the proton conductivity decreases and the performance of the catalyst layer deteriorates. Therefore, the I / C ratio is preferably 0.2 or more. The I / C ratio is preferably 0.4 or more.
On the other hand, when the I / C ratio becomes excessive, the decrease in the pore volume in the electrode becomes large, and the performance of the catalyst layer deteriorates. Therefore, the I / C ratio is preferably 1.5 or less. The I / C ratio is preferably 1.4 or less.

[1.3. Nonionic Surfactant]
[13.1. HLB value]
The nonionic surfactant has a hydrophilic group and a hydrophobic group, and the hydrophobic group is easily adsorbed on the carbon surface. Further, unlike ionic surfactants, nonionic surfactants do not generate ions in a solvent. Therefore, when a nonionic surfactant is added to the catalyst ink, the three-dimensional network structure formed by the catalyst-supported carbon particles can be destroyed without impairing the power generation characteristics of the ionoma. Further, this makes it possible to suppress the occurrence of cracks in the drying process of the catalyst ink.

In the present invention, the nonionic surfactant needs to have an HLB value within a predetermined range.
Here, the "HLB (Hydrophilic-Lipophilic Balance) value" is a value representing the balance between the hydrophilic group and the hydrophobic group in the molecule of the surfactant, and means a value represented by the following formula (1). .. The HLB value takes a value from 0 to 20, and the closer it is to 0, the higher the lipophilicity, and the closer it is to 20, the higher the hydrophilicity.
HLB value = 20 × (molecular weight of hydrophilic part / molecular weight of surfactant)… (1)

If the HLB value becomes too small, the nonionic surfactant is hydrophobic and does not dissolve sufficiently in water, and the catalyst-supported carbon particles cannot be sufficiently dispersed. Therefore, the HLB value needs to be 16 or more. The HLB value is preferably 17 or more, more preferably 18 or more.
On the other hand, if the HLB value becomes too large, the nonionic surfactant is hydrophilic and sufficiently soluble in water, but it becomes difficult to adsorb to the catalyst-supported carbon particles, and it becomes difficult to disperse the catalyst-supported carbon particles. Therefore, the HLB value needs to be less than 20. The HLB value is preferably 19.5 or less, more preferably 19 or less.
In particular, when the ionomer is composed of a highly oxygen-permeable ionomer, the HLB value of the nonionic surfactant is preferably 17 or more and less than 20.

[1.3.2. composition]
The type of nonionic surfactant is not particularly limited as long as the above conditions for the HLB value are satisfied.
Examples of nonionic surfactants that satisfy the above conditions include, for example.
(A) Nonionic surfactant having polyoxyethylene (n) stearyl ether as a basic skeleton (for example, Brij (registered trademark) S20, Brij (registered trademark) S100, both manufactured by Sigma-Aldrich),
(B) Nonionic surfactant having polyoxyetheneoleyl ether as a basic skeleton (for example, E-230 (manufactured by NOF CORPORATION)),
and so on.
Any one of these may be used as the nonionic surfactant, or two or more of them may be used in combination.

[1.3.3. Content]
In the catalyst ink, the "content of the nonionic surfactant" means the ratio of the weight of the nonionic surfactant to the weight of the total solid content contained in the catalyst ink. The content of the nonionic surfactant in the catalyst ink affects the properties of the catalyst ink and the catalyst layer produced by using the catalyst ink.

In general, if the content of the nonionic surfactant in the catalyst ink is too small, the three-dimensional network structure formed by the catalyst-supported carbon cannot be sufficiently destroyed. As a result, the crack resistance of the catalyst layer is lowered. In order to obtain high crack resistance, the content of the nonionic surfactant needs to be 1 wt% or more. The content is preferably 2 wt% or more, more preferably 3 wt% or more.
On the other hand, if the content of the nonionic surfactant is too large, the dispersibility of the catalyst-supported carbon particles becomes too high, the voids are closed, gas diffusion becomes difficult, and the performance deteriorates. Therefore, the content of the nonionic surfactant needs to be 23 wt% or less. The content is preferably 17 wt% or less, more preferably 15 wt% or less, still more preferably 10 wt% or less.

In particular, when the ionomer is composed of a highly oxygen-permeable ionomer and the HLB value of the nonionic surfactant is 17 or more and less than 20, the content of the noonion-based surfactant in the catalyst ink is preferably 1 wt% or more and 17 wt% or less. ..

[1.4. water]
Water is added to prevent the carbon carrier from igniting when the organic solvent comes into contact with the catalyst-supported carbon. The content of water in the catalyst ink is not particularly limited as long as the ignition of the carbon carrier can be suppressed. However, increasing the water content more than necessary has no difference in effect and has no actual benefit. The water content is usually about 10 wt% to 70 wt%.

[1.5. alcohol]
[1.5.1. boiling point]
Alcohol is a necessary ingredient to disperse ionomers. However, if the boiling point of the alcohol becomes too high, the heat load during drying of the catalyst ink increases, which leads to an increase in production cost. Therefore, the alcohol preferably has a boiling point of 120 ° C. or lower. The boiling point of the alcohol is preferably 100 ° C. or lower, more preferably 83 ° C. or lower.
On the other hand, if the boiling point is too low, the drying becomes too fast, the surface of the coating film dries first, and cracks and unevenness may occur when the solvent inside evaporates. Therefore, the boiling point of alcohol is preferably 40 ° C. or higher. The boiling point is preferably 50 ° C. or higher, more preferably 60 ° C. or higher.

[1.5.2. composition]
Examples of alcohols satisfying the above conditions include methanol, ethanol, 1-propanol, 2-propanol and the like.
Any one of these may be used as the alcohol, or two or more of them may be used in combination.

[1.5.3. Content]
The content of alcohol in the catalyst ink is not particularly limited as long as the uniform dispersion of ionomer is possible. However, increasing the alcohol content more than necessary has no difference in effect and has no actual benefit. The alcohol content is usually 20 wt% to 80 wt%.

[2. Catalyst layer]
The catalyst layer according to the present invention is
Catalyst-supported carbon and
With ionomer
Nonionic surfactants with an HLB value of 16 or more and less than 20 and
Is equipped with.

[2.1. Catalyst-supported carbon]
The catalyst-supported carbon is composed of catalyst particles supported on a carrier surface made of a carbon material. The details of the catalyst-supported carbon are as described above, and thus the description thereof will be omitted.

[2.2. Ionomer]
The ionomer is for exchanging protons with the catalyst particles. Since the details of the ionomer are as described above, the description thereof will be omitted.

[2.3. Nonionic Surfactant]
[2.3.1. HLB value]
The catalyst layer contains a nonionic surfactant derived from the catalyst ink. The nonionic surfactant needs to have an HLB value of 16 or more and less than 20. When the ionomer is composed of a highly oxygen-permeable ionomer, the HLB value of the nonionic surfactant is preferably 17 or more and less than 20. Other points regarding the HLB value of the nonionic surfactant are as described above, and thus the description thereof will be omitted.

[2.3.3. composition]
Since the composition of the nonionic surfactant is as described above, the description thereof will be omitted.

[2.3.3. Content]
The content of the nonionic surfactant needs to be 1 wt% or more and 23 wt% or less. When the ionomer is composed of a highly oxygen-permeable ionomer and the HLB value of the nonionic surfactant is 17 or more and less than 20, the content of the noonion-based surfactant is preferably 1 wt% or more and 17 wt% or less. Other points regarding the content of the nonionic surfactant are as described above, and thus the description thereof will be omitted.

[3. Action]
In a catalyst ink using water and an alcohol having a boiling point of 120 ° C. or lower as a solvent, the catalyst-supported carbon particles tend to form a three-dimensional network structure because of their low dispersibility in the solvent. When the catalyst ink is dried while the catalyst-supported carbon forms a three-dimensional network structure, pores having a non-uniform size are formed, and stress is concentrated there, so that cracks are likely to occur. This tendency becomes remarkable when a high oxygen permeation ionomer is used as the ionomer. This is considered to be due to the following reasons.

That is, the high oxygen permeation ionomer contains a cyclic compound having a cyclic structure as a basic skeleton. A compound having such a structure generally has a rigid molecular chain, so that it has poor adsorptivity to carbon, and the carbons aggregate to form a three-dimensional network structure. When the catalyst-supported carbon particles are dried while forming a three-dimensional network structure, pores having a non-uniform size are formed. By concentrating the stress there, cracks are likely to occur, so that the crack resistance of the catalyst layer is lowered.

On the other hand, if a general-type ionomer (for example, Nafion (registered trademark)) containing few or no cyclic compounds having a cyclic structure is used, the dispersibility of the catalyst ink is improved. Therefore, the three-dimensional network structure that adversely affects the crack resistance becomes fragile, and the crack resistance is improved as compared with the catalyst ink containing the high oxygen permeable ionomer. However, the method of replacing the high oxygen permeable ionomer with a general type ionomer is a method of sacrificing electrode performance and is not an essential solution. Further, regardless of which ionomer is used, it is desired to further improve the crack resistance of the catalyst layer.

On the other hand, when a nonionic surfactant having an HLB value of 16 to 20 is added to the catalyst ink, the hydrophobic group of the nonionic surfactant is adsorbed on the carbon surface, and the hydrophilic group is a solvent mainly composed of water. Ensure affinity. Therefore, the carbon is easily dispersed in the dispersion medium, and the three-dimensional network structure of the catalyst-supported carbon can be broken. As a result, the crack resistance of the catalyst layer is improved. Further, such an effect can be obtained not only in the catalyst layer containing the general type ionomer but also in the catalyst layer containing the high oxygen permeation ionomer.
Moreover, since the nonionic surfactant does not generate ions in the solvent, it does not impair the power generation characteristics of ionomer. Further, since a solvent having a boiling point of 120 ° C. or lower is used, it is possible to suppress an increase in production cost and a decrease in performance due to a heat load during drying.

(Examples 1 to 7, Comparative Examples 1 to 5)
[1. Preparation of sample]
[1.1. Preparation of catalyst ink]
As the catalyst-supported carbon, platinum-supported carbon (TEC10V30E manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., carbon carrier: Vulcan (registered trademark) XC72R) was used.
A Nafion (registered trademark) dispersion (manufactured by DuPont, DE2020) was used as the general type ionomer. As the high oxygen permeation ionomer, an ionomer having the chemical structure described in Patent Document 1 (hereinafter, also referred to as “ionomer A”) was used.

For nonionic surfactants,
(A) A nonionic surfactant having polyoxyethylene (n) stearyl ether as a basic skeleton (Brij (registered trademark) S20 or Brij (registered trademark) S100, both manufactured by Sigma-Aldrich), or
(B) Nonionic surfactant having polyoxyethylene oleyl ether as its basic skeleton (E-230, manufactured by NOF CORPORATION)
Was used.

FIG. 1 (A) shows the molecular structure of polyoxyethylene (n) stearyl ether. FIG. 1 (B) shows the molecular structure of E-230. Table 1 shows the physical property values of each surfactant.

Ultrapure water was added to the platinum-supported carbon, and stirring and defoaming were performed for 1 minute each using a planetary stirring / defoaming device (MAZERUSTAR KK-50S manufactured by KURABO). Ionomer and a surfactant were added thereto, and stirring and defoaming were carried out for 1 minute each.
The dispersion was dispersed with an ultrasonic homogenizer (MODEL UH-600, manufactured by SMT) for 6 minutes, and then stirred and defoamed for 1 minute each. Further, after performing dispersion treatment for 3 minutes with an ultrasonic homogenizer, stirring and defoaming were performed for 1 minute each.
1-Propanol was added to the dispersion liquid after the dispersion treatment, and stirring and defoaming were carried out for 1 minute each to obtain a catalyst ink. Table 2 shows the composition of the catalyst ink.

[1.2. Preparation of catalyst layer]
The catalyst ink was applied onto the glass substrate at 10 mm / s using an applicator and byko-drive (manufactured by BYK Gardner Company). The coating film was dried at room temperature (24 ° C., 70 to 75% RH) to obtain a catalyst layer having a film thickness of 2 μm to 18 μm.

[2. Test method]
[2.1. SEM observation]
SEM observation of the surface of the catalyst layer was performed.

[2.2. Evaluation of crack resistance]
The catalyst ink was applied on the grind gauge and dried. The prepared catalyst layer was observed with a confocal microscope (Lasertec, OPTELICS H1200) at a magnification of 20 times. The coated surface was observed in order from the thinnest film thickness, the place where cracks began to appear first was found, and the film thickness at that place was measured. The film thickness at this time was defined as the critical crack film thickness (CCT). The larger the CCT, the higher the crack resistance of the catalyst layer. The film thickness was measured by reading the step between the base material and the catalyst layer with a height resolution of about 60 nm.

[3. result]
[3.1. SEM observation]
2 (A) and 2 (B) show SEM images of the surface of the catalyst layer obtained in Example 4 and Comparative Example 1, respectively. From FIG. 2, it can be seen that a large number of cracks are observed in Comparative Example 1, whereas almost no cracks are observed in Example 4. In Comparative Example 1, the cracks were caused by insufficient coating of the catalyst-supported carbon particles of the ionoma, and when the catalyst-supported carbon particles formed a three-dimensional network structure, the catalyst-supported carbon particles and the ionoma were dried. It is considered that the agglomerated structure is formed in each of them to form a non-uniform structure, and cracks are likely to occur after drying.

[3.2. Evaluation of crack resistance]
Table 3 shows the results. In Table 3, "⊚" indicates that the CCT is 12 μm or more (that is, the crack resistance is extremely good). “◯” indicates that the CCT is 7 μm or more and less than 12 μm (that is, the crack resistance is good). “X” indicates that the CCT is less than 7 μm (that is, the crack resistance is inferior). From Table 3, the following can be seen.

(1) In Examples 1 to 7, the CCT was 7 μm or more, whereas in Comparative Examples 1 to 5, the CCT was less than 7 μm.
(2) When Nafion (registered trademark), which is a representative of general ionomers, is used as the ionomer, crack resistance is excellent when a nonionic surfactant having an HLB value of 16.6 or 18.9 is used. A catalyst layer was obtained (Examples 1, 3, 5). However, when the HLB value was 15.6 or less, the crack resistance decreased (Comparative Example 1). The reason for this is considered to be that when the HLB value becomes low, the dispersibility of the platinum-supported carbon in the solvent decreases. From this, it was found that a nonionic surfactant having an HLB value of 16 or more and less than 20 is preferable.

(3) When the content of the nonionic surfactant was 0.9 wt% (Comparative Example 3), the crack resistance was lowered. It is considered that this is because if the amount of the nonionic surfactant is too small, the three-dimensional network structure of the platinum-supported carbon particles, which adversely affects the crack resistance, cannot be broken. Further, when the content of the nonionic surfactant was 26.6% or 23.1% (Comparative Examples 4 and 5), the crack resistance was lowered. It is considered that this is because the strength of the catalyst layer decreases when the amount of the nonionic surfactant is too large. From this, it was found that the content of the nonionic surfactant is preferably 1 wt% or more and 23 wt% or less.

(4) When ionomer A, which is a representative of high oxygen permeation ionomer, was used, the CCT was 8 mm or more when a nonionic surfactant having an HLB value of 18.9 was used (Examples 2, 4, and 3. 6). On the other hand, when the HLB value became 16.6 or less, the CCT decreased slightly (Example 7). From this, it was found that when ionomer A is used, it is preferable to use a nonionic surfactant having an HLB value of 17 or more and less than 20.
(5) Comparative Examples 4 and 5 all have low crack resistance. It is considered that this is because the content of the nonionic surfactant is too large. On the other hand, Comparative Example 3 has low crack resistance. It is considered that this is because the content of the nonionic surfactant is too low. From these facts, it was found that the content of the nonionic surfactant is preferably 1 to 23 wt%.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist of the present invention.

The catalyst ink according to the present invention can be used for producing a catalyst layer for various electrochemical devices such as fuel cells. Further, the catalyst layer according to the present invention can be used as a catalyst layer for various electrochemical devices such as fuel cells.

Claims (4)

A catalytic ink having the following configurations.
(1) The catalyst ink is
Catalyst-supported carbon and
With ionomer
Nonionic surfactants with an HLB value of 16 or more and less than 20 and
water and,
It includes an alcohol having a boiling point of 120 ° C. or lower.
(2) The content of the nonionic surfactant (the ratio of the weight of the nonionic surfactant to the weight of the total solid content contained in the catalyst ink) is 1 wt% or more and 23 wt% or less. The ionomer is composed of a highly oxygen permeable ionomer.
The nonionic surfactant has an HLB value of 17 or more and less than 20.
The catalyst ink according to claim 1, wherein the content of the noonion-based surfactant is 1 wt% or more and 17 wt% or less. A catalyst layer having the following configuration.
(1) The catalyst layer is
Catalyst-supported carbon and
With ionomer
Nonionic surfactants with an HLB value of 16 or more and less than 20 and
Is equipped with.
(2) The content of the nonionic surfactant is 1 wt% or more and 23 wt% or less. The ionomer is composed of a highly oxygen permeable ionomer.
The nonionic surfactant has an HLB value of 17 or more and less than 20.
The catalyst layer according to claim 3, wherein the content of the noonion-based surfactant is 1 wt% or more and 17 wt% or less.

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