JP7359192B2 - Ionomer-modified hydrophobic particles, catalyst layer, catalyst ink and manufacturing method thereof - Google Patents

Description

The present invention relates to ionomer-modified hydrophobic particles, a catalyst layer, a catalyst ink, and a method for producing the same, and more particularly, the present invention relates to ionomer-modified hydrophobic particles in which the surface of the hydrophobic particles is coated with an ionomer, and a catalyst layer using the same. , as well as a catalyst ink using the same and a method for producing the same.

A polymer electrolyte fuel cell includes a membrane electrode assembly (MEA) in which a catalyst layer is bonded to both sides of an electrolyte membrane. Usually, a gas diffusion layer is further arranged outside the catalyst layer. The catalyst layer is a reaction field for electrode reactions, and is generally made of a composite of carbon supporting catalyst particles such as platinum and a solid polymer electrolyte (catalyst layer ionomer). Further, the gas diffusion layer is for supplying a reaction gas and electrons to the catalyst layer, and carbon paper, carbon cloth, or the like is used.

Polymer electrolyte fuel cells (PEFCs) are power generation devices that generate electrical energy through the reaction of oxygen and hydrogen. PEFCs can be expected to have higher efficiency and higher power density than conventional internal combustion engines. Additionally, hydrogen as a fuel can be produced from a variety of primary energy sources. Therefore, PEFCs are one of the promising candidates as a future vehicle power source.

In order to popularize PEFCs as an on-vehicle power source, there are issues to reduce costs and improve durability by reducing the amount of platinum catalyst used. Since the hydrogen oxidation reaction and oxygen reduction reaction of PEFCs occur in the catalyst layer, it is important to improve the properties of the material constituting the catalyst layer and control the structure of the catalyst layer in order to overcome the problems.
Such a catalyst layer is usually prepared by applying a catalyst ink. Catalyst ink is a slurry made by dispersing platinum-supported carbon and ionomer in a mixed solvent of water and an organic solvent. Further, the catalyst layer is a porous membrane having pores on the order of submicrometers and made of platinum-supported carbon and an ionomer.

In order to reduce the cost of PEFCs, it is necessary to reduce the amount of platinum used in the catalyst, and in order to reduce the amount of platinum, it is necessary to increase the proton conductivity in the catalyst layer. As a method for increasing proton conductivity, a method has been proposed in which an ionomer with high oxygen permeability is used as an ionomer for the catalyst layer (Patent Document 1).
In addition, as a method of increasing proton conductivity with the structure of the catalyst layer,
(a) A method in which an ionomer is made into a nonwoven fabric using a spinning device, and the resulting nonwoven fabric is coated with a catalyst ink and used as a catalyst layer (Non-Patent Document 1);
(b) A method of blending a carbon filler having a short axis length of 20 nm or more and 100 μm or less into a polymer electrolyte solution when producing a nonwoven fabric using an ionomer (Patent Document 2)
etc. are known.

When a nonwoven fabric made of an ionomer is used in the catalyst layer, proton conduction paths become more easily connected, thereby improving proton conductivity within the catalyst layer. Further, when a carbon filler is added to an electrolyte solution when producing a nonwoven fabric, electronic conductivity can also be improved. However, since a nonwoven fabric made of an ionomer needs to be manufactured using a spinning device, there is a problem in that productivity is lower than in the conventional method of manufacturing a catalyst layer using a catalyst ink.
On the other hand, in order to achieve both proton conductivity and productivity, an additive for improving proton conductivity (hereinafter also referred to as a "proton conduction aid") is added to the catalyst ink, and an additive is added to the catalyst ink to improve proton conductivity. It is also conceivable to manufacture the catalyst layer using a coating device suitable for mass production, such as the following. However, there has never been an example in which a proton conduction aid suitable for addition to catalyst ink has been proposed.

Japanese Patent Application Publication No. 2014-216157 JP 2019-183295 Publication

Journal of Power Sources, 476(2020)228584

The problem to be solved by the present invention is to provide novel ionomer-modified hydrophobic particles suitable as a proton conduction aid added to catalyst ink.
Another problem to be solved by the present invention is to provide a catalyst layer including such ionomer-modified hydrophobic particles.
Furthermore, another problem to be solved by the present invention is to provide a catalyst ink equipped with such ionomer-modified hydrophobic particles and a method for producing the same.

In order to solve the above problems, the ionomer-modified hydrophobic particles according to the present invention have the following configuration.
(1) The ionomer-modified hydrophobic particles are:
surface-modified hydrophobic particles whose surfaces are coated with an aromatic vinyl copolymer;
and an ionomer A that further coats the surface of the surface-modified hydrophobic particles.
(2) The aromatic vinyl copolymer is
Comprising a hydrophobic functional group and a cationic functional group,
It is adsorbed on the surface of the hydrophobic particles via the hydrophobic functional group.
(3) The ionomer A is
Equipped with anionic functional group,
It is ionically bonded to the cationic functional group via the anionic functional group.

The catalyst layer according to the present invention is
an electrode catalyst in which catalyst particles are supported on the surface of a carbon carrier;
A catalyst layer ionomer made of ionomer B;
and the ionomer-modified hydrophobic particles according to the present invention.

The catalyst ink according to the present invention includes:
an electrode catalyst in which catalyst particles are supported on the surface of a carbon carrier;
A catalyst layer ionomer made of ionomer B;
Ionomer-modified hydrophobic particles according to the present invention,
a hydrophilic solvent containing water for dispersing the electrode catalyst, the catalyst layer ionomer, and the ionomer-modified hydrophobic particles;
It is equipped with

Furthermore, the method for producing catalyst ink according to the present invention includes:
A first step of preparing a first dispersion liquid in which ionomer-modified hydrophobic particles according to the present invention are dispersed in a first dispersion medium;
a second step of preparing a second dispersion liquid in which the electrode catalyst and ionomer C are dispersed in a second dispersion medium;
and a third step of mixing the first dispersion liquid and the second dispersion liquid to obtain a catalyst ink.

When the surface of a hydrophobic particle is modified with an aromatic vinyl copolymer, a surface-modified hydrophobic particle having a cationic functional group introduced onto the surface of the hydrophobic particle can be obtained. Next, when the surface-modified hydrophobic particles and ionomer A are dispersed in a solvent, the cationic functional group and the anionic functional group of ionomer A are ionically bonded, and ionomer-modified hydrophobic particles are obtained.

The ionomer-modified hydrophobic particles thus obtained function as a proton conduction aid because a continuous proton conduction path is formed on the surface of the hydrophobic particles. Furthermore, since the ionomer-modified hydrophobic particles have increased surface charge due to adsorption of ionomer A, they can be dispersed in a hydrophilic solvent containing water.
Therefore, by adding ionomer-modified hydrophobic particles to a catalyst ink, applying and drying the catalyst ink, a catalyst layer with high proton conductivity can be obtained.

FIG. 2 is a schematic cross-sectional view of a catalyst layer according to the present invention. This is a synthesis scheme of ionomer-modified hydrophobic particles. FIG. 3(A) is a photograph of a dispersion in which surface-modified hydrophobic particles are dispersed in water. FIG. 3(B) is a photograph of a dispersion in which ionomer-modified hydrophobic particles are dispersed in water. 1 is an IV curve (after IR correction) of the fuel cells obtained in Examples 1 and 2 and Comparative Examples 1 and 2 under overhumidified conditions.

Hereinafter, one embodiment of the present invention will be described in detail.
[1. Surface-modified hydrophobic particles]
The ionomer-modified hydrophobic particles according to the present invention include surface-modified hydrophobic particles.
In addition, surface-modified hydrophobic particles
hydrophobic particles whose surfaces are hydrophobic;
and an aromatic vinyl copolymer that coats the surface of the hydrophobic particles.

[1.1. Hydrophobic particles]
[1.1.1. material]
"Hydrophobic particle" refers to a particle whose surface is hydrophobic.
"The surface is hydrophobic" means that the contact angle θ of water is 90° or more.
The hydrophobic particles are core particles of the surface-modified hydrophobic particles. The material constituting the hydrophobic particles may be a conductor or an insulator.

Examples of materials for the hydrophobic particles include:
(a) graphite;
(b) boron nitride,
(c) There are mica, talc, sericite, aluminum, alumina, titanium oxide, silica, etc. whose surfaces have been subjected to hydrophobic surface treatment.
Among these, graphite is preferable as the material for the hydrophobic particles. Graphite is suitable as a material for the hydrophobic particles because it can be easily cleaved by exfoliation treatment to obtain exfoliated graphite particles.
Here, the term "exfoliated graphite particles" refers to sheet-like particles obtained by peeling off a graphite layer to a predetermined thickness. A method for producing exfoliated graphite particles will be described later.

[1.1.2. shape]
The hydrophobic particles may be granular particles or sheet-like particles. Here, the term "sheet-like particles" refers to a shape (a two-dimensional shape or a shape close to a two-dimensional shape) in which the dimension in the plane direction is larger than the dimension in the thickness direction.
When the surface of sheet-like hydrophobic particles is coated with an aromatic vinyl copolymer, sheet-like surface-modified hydrophobic particles are obtained. Moreover, when the surface of the sheet-like surface-modified hydrophobic particles is further coated with ionomer A, sheet-like ionomer-modified hydrophobic particles are obtained.
When such ionomer-modified hydrophobic particles are added to the catalyst layer, some of the particles are oriented in a direction parallel to the surface of the catalyst layer (hereinafter also referred to as "in-plane direction"), but others are A part of the catalyst layer is oriented in a direction non-parallel to the surface of the catalyst layer (hereinafter also referred to as an "out-of-plane direction"). As a result, the proton conductivity in the thickness direction of the catalyst layer is improved.

[1.1.3. size]
The size of the hydrophobic particles is not particularly limited, and an optimal value can be selected depending on the purpose.
For example, when the hydrophobic particles are sheet-like particles such as exfoliated graphite particles, sheet-like surface-modified hydrophobic particles and sheet-like ionomer-modified hydrophobic particles are obtained. In this case, it is preferable that the average length and average thickness of the hydrophobic particles satisfy the following conditions.

[A. Average length]
"Long axis" is the line connecting the two furthest points of a sheet-like particle when viewed from the normal direction (z-axis direction) of the sheet surface (the plane with the widest area, xy plane) of the sheet-like particle ( The length of the longest straight line.
The "average major axis" refers to the average value of the major diameters of 20 or more randomly selected sheet-like particles.

When adding ionomer-modified hydrophobic particles to the catalyst layer, the average length of the hydrophobic particles affects the proton conductivity of the catalyst layer. Generally, the longer the average major axis of the hydrophobic particles, the higher the proton conductivity of the catalyst layer. This is considered to be because the longer the average major axis, the longer the proton path of ionomer A adsorbed on the surface of the surface-modified hydrophobic particles. In order to obtain such an effect, the average major axis is preferably 1 μm or more. The average major axis is more preferably 2 μm or more.

On the other hand, if the average major axis becomes too long, the performance of the catalyst layer will deteriorate on the contrary. This is considered to be because the ionomer-modified hydrophobic particles are oriented in the in-plane direction of the catalyst layer, thereby inhibiting drainage. Therefore, the average major axis is preferably 10 μm or less. The average major axis is more preferably 8 μm or less, still more preferably 6 μm or less.

[B. Average thickness]
"Thickness" refers to the maximum length of a sheet-like particle in the normal direction (z-axis direction) when viewed from a direction parallel to the sheet surface (xy plane) of the sheet-like particle.
"Average thickness" refers to the average value of the thicknesses of 20 or more randomly selected sheet-like particles.

When adding ionomer-modified hydrophobic particles to the catalyst layer, the average thickness of the hydrophobic particles affects the proton conductivity of the catalyst layer. Generally, the thicker the average thickness of the hydrophobic particles, the higher the proton conductivity of the catalyst layer. This is thought to be because the thicker the average thickness, the easier the ionomer-modified hydrophobic particles maintain their sheet structure, and the more difficult it is for the particles to bend within the catalyst layer. It is also considered that this causes the proton path of ionomer A adsorbed on the surface of the surface-modified hydrophobic particles to become longer. In order to obtain such an effect, the average thickness is preferably 10 nm or more. The average thickness is more preferably 15 nm or more.

On the other hand, if the average thickness becomes too thick, the durability of the catalyst layer decreases. This is because the ionomer-modified hydrophobic particles oriented perpendicularly to the surface of the catalyst layer may create holes in the electrolyte membrane, causing cross-leakage and accelerating the deterioration of the fuel cell. Therefore, the average thickness is preferably 300 nm or less. The average thickness is more preferably 250 nm or less, even more preferably 200 nm or less.

[1.2. Aromatic vinyl copolymer]
[1.2.1. material]
The surface of the hydrophobic particles is coated with an aromatic vinyl copolymer. In the present invention, the aromatic vinyl copolymer used includes a hydrophobic functional group and a cationic functional group. In this case, the aromatic vinyl copolymer is adsorbed on the surface of the hydrophobic particles via the hydrophobic functional group.
Moreover, the surface of the surface-modified hydrophobic particles is further coated with ionomer A, as will be described later. In the present invention, the ionomer A used is one having an anionic functional group. Ionomer A is ionically bonded to a cationic functional group via an anionic functional group.

That is, in the present invention, "aromatic vinyl copolymer" refers to
(a) a vinyl aromatic monomer containing a hydrophobic functional group that is easily adsorbed to hydrophobic particles;
(b) Refers to a copolymer obtained by copolymerizing the anionic functional group of ionomer A and a second vinyl monomer having a cationic functional group capable of ionically bonding.

Examples of the hydrophobic functional group include a phenyl group, a naphthyl group, an anthracenyl group, and a pyrenyl group. The aromatic vinyl copolymer may have any one of these hydrophobic functional groups, or may have two or more of these.

Examples of the cationic functional group include a pyridyl group, an amino group, a quaternary ammonium group, an imino group, an imidazole group, a guanidine group, and a biguanide group. The aromatic vinyl copolymer may have any one of these cationic functional groups, or may have two or more of these.

Aromatic vinyl copolymers are particularly
A vinyl aromatic monomer unit represented by the following formula (1),
A copolymer comprising a second monomer unit made of a vinyl monomer having the cationic functional group is preferred.

-(CH ₂ -CHX)-...(1)
however,
X represents any one or more hydrophobic functional groups selected from the group consisting of phenyl group, naphthyl group, anthracenyl group, and pyrenyl group, and these groups may have a substituent,
The cationic functional group is any one or more functional groups selected from the group consisting of a pyridyl group, an amino group, a quaternary ammonium group, an imino group, an imidazole group, a guanidine group, and a biguanide group.

Examples of substituents that may be included in the hydrophobic functional group group, imide group, phosphate ester group, etc. The hydrophobic functional group X may contain any one of these substituents, or may contain two or more of these substituents.

In the aromatic vinyl copolymer represented by formula (1), the vinyl aromatic monomer unit exhibits adsorption to hydrophobic particles. When the hydrophobic functional group X is adsorbed on the surface of the hydrophobic particles, the cohesive force between the hydrophobic particles decreases, making them easier to disperse in the solvent.
However, surface-modified hydrophobic particles alone do not disperse well in a hydrophilic solvent mainly composed of water. On the other hand, when ionomer A is adsorbed to the cationic functional group of the aromatic vinyl copolymer to form ionomer-modified hydrophobic particles, the ionomer-modified hydrophobic particles are well dispersed in a hydrophilic solvent mainly composed of water. .

The aromatic vinyl copolymer may be a random copolymer or a block copolymer. However, in order to sufficiently suppress aggregation of the ionomer-modified hydrophobic particles when ionomer A is adsorbed, the aromatic vinyl copolymer is preferably a block copolymer.

[1.2.2. Content of vinyl aromatic monomer units]
"Content of vinyl aromatic monomer units" refers to the ratio of the mass of vinyl aromatic monomer units to the total mass of the aromatic vinyl copolymer.
The higher the content of vinyl aromatic monomer units, the more easily the aromatic vinyl copolymer is adsorbed onto the hydrophobic particles. In order to obtain such effects, the content of vinyl aromatic monomer units is preferably 10 mass% or more. The content is more preferably 30 mass% or more, still more preferably 50 mass% or more.

On the other hand, when the content of vinyl aromatic monomer units becomes excessive, the surface-modified hydrophobic particles become excessively hydrophobic, and the adsorption amount of ionomer A decreases. As a result, the ionomer-modified hydrophobic particles become difficult to disperse in a hydrophilic solvent mainly composed of water. Furthermore, when the adsorption amount of ionomer A decreases excessively, the proton conductivity of the ionomer-modified hydrophobic particles decreases. Therefore, the content of vinyl aromatic monomer units is preferably 98 mass% or less. The content is more preferably 95 mass% or less.

[1.3. Characteristics of surface-modified hydrophobic particles]
[1.3.1. size]
The size of the surface-modified hydrophobic particles is not particularly limited, and an optimal value can be selected depending on the purpose.
In the present invention, the amount of aromatic vinyl copolymer coating the surface of the hydrophobic particles is relatively small. Therefore, the size of the hydrophobic particles coated with the aromatic vinyl copolymer (ie, the surface-modified hydrophobic particles) is approximately the same as the size of the hydrophobic particles. The details of the size of the hydrophobic particles are as described above, so the explanation will be omitted.

[1.3.2. Content of aromatic vinyl copolymer]
"Aromatic vinyl copolymer content" refers to the ratio of the aromatic vinyl copolymer mass to the total mass of the surface-modified hydrophobic particles.
However, in the present invention, when referring to "aromatic vinyl copolymer content", for convenience, it is assumed that the surface of the hydrophobic particles is uniformly coated with a film made of aromatic vinyl copolymer. , expressed as the ratio (=t/t ₀ ) of the thickness (t) of the coating to the thickness (t ₀ ) of the monomolecular film made of the aromatic vinyl copolymer.
Below, if the content of the aromatic vinyl copolymer corresponds to the amount assuming that the surface of the hydrophobic particle is covered with an n-layer monomolecular film, the aromatic vinyl copolymer at this time will be The content is also referred to as "n molecular film equivalent amount".

If the content of the aromatic vinyl copolymer becomes too low, the amount of adsorption of ionomer A will decrease, making it impossible to sufficiently suppress particle aggregation. Therefore, the content of the aromatic vinyl copolymer is preferably at least an amount equivalent to one molecule film. The content is more preferably at least an amount equivalent to a bilayer membrane, and even more preferably at least an amount equivalent to a trilayer membrane.
On the other hand, when the content of the aromatic vinyl copolymer becomes excessive, the proportion of the aromatic vinyl copolymer not adsorbed to the hydrophobic particles increases. Excess aromatic vinyl copolymer forms a polyion complex with ionomer A at a location other than the particle surface, so it may become an impurity that adversely affects the electrochemical reaction. Therefore, the content of the aromatic vinyl copolymer is preferably equal to or less than 10 molecular membranes. The content is more preferably less than or equal to 9 molecular membranes, and even more preferably less than or equal to 8 molecular membranes.

[2. Ionomer-modified hydrophobic particles]
The ionomer-modified hydrophobic particles according to the present invention have the following configuration.
(1) The ionomer-modified hydrophobic particles are:
surface-modified hydrophobic particles whose surfaces are coated with an aromatic vinyl copolymer;
and an ionomer A that further coats the surface of the surface-modified hydrophobic particles.
(2) The aromatic vinyl copolymer is
Comprising a hydrophobic functional group and a cationic functional group,
It is adsorbed on the surface of the hydrophobic particles via the hydrophobic functional group.
(3) The ionomer A is
Equipped with anionic functional group,
It is ionically bonded to the cationic functional group via the anionic functional group.

[2.1. Surface-modified hydrophobic particles]
"Surface-modified hydrophobic particles" refer to particles whose surfaces are coated with an aromatic vinyl copolymer. The details of the surface-modified hydrophobic particles, the hydrophobic particles, and the aromatic vinyl copolymer are as described above, so a description thereof will be omitted.

[2.2. Ionoma A]
[2.2.1. material]
The ionomer A may be any one having an anionic functional group capable of ionically bonding with the cationic functional group of the aromatic vinyl copolymer.
Examples of anionic functional groups include sulfonic acid groups (-SO ₃ H), carboxyl groups, and phosphoric acid groups. Ionomer A may have any one of these anionic functional groups, or may have two or more of these.

As ionomer A, for example,
(a) perfluorocarbon sulfonic acid polymers such as Nafion (registered trademark), Flemion (registered trademark), Aciplex (registered trademark), Aquiviion (registered trademark),
(b) High oxygen permeability polymer having an aliphatic cyclic structure (see Reference 1),
and so on.
Among these, ionomer A is preferably a perfluorocarbon sulfonic acid polymer. This is because it has excellent proton conductivity, robustness, and durability.
[Reference document 1] Japanese Patent Application Publication No. 2014-216157

[2.2.2. Adsorption amount of ionomer A]
"Adsorption amount of ionomer A" refers to the ratio of the mass of ionomer A to the total mass of the ionomer-modified hydrophobic particles.
If the amount of ionomer A adsorbed is too small, the proton conductivity of the ionomer-modified hydrophobic particles will decrease. Therefore, the adsorption amount of ionomer A is preferably 0.03 mass% or more. The adsorption amount is more preferably 0.1 mass% or more, still more preferably 1.0 mass% or more.
On the other hand, if the amount of ionomer A adsorbed becomes excessive, the performance may deteriorate because drainage of water generated during power generation is inhibited. Therefore, the adsorption amount of ionomer A is preferably 35.0 mass% or less. The adsorption amount is more preferably 30.0 mass% or less, still more preferably 25.0 mass% or less.

[2.3. Characteristics of ionomer-modified hydrophobic particles]
[2.3.1. size]
The size of the ionomer-modified hydrophobic particles is not particularly limited, and an optimal value can be selected depending on the purpose.
When the amount of ionomer A covering the surface of the surface-modified hydrophobic particles is relatively small, the size of the ionomer-modified hydrophobic particles is approximately equal to the size of the surface-modified hydrophobic particles or the hydrophobic particles. On the other hand, when the amount of coating with ionomer A is relatively large, the size of the ionomer-modified hydrophobic particles becomes larger than the size of the surface-modified hydrophobic particles or the hydrophobic particles. When the amount of coverage with ionomer A is optimized, the size of the ionomer-modified hydrophobic particles is about 1.0 to 1.5 times the size of the hydrophobic particles.

[2.3.2. Water dispersibility]
Since the outermost surface of the ionomer-modified hydrophobic particles according to the present invention is made of ionomer A, they exhibit good dispersibility in solvents containing water. Therefore, when this is added to the catalyst ink as a proton conduction aid, a catalyst layer with high proton conductivity can be obtained.

[2.3.3. Power generation performance]
Since the outermost surface of the ionomer-modified hydrophobic particles according to the present invention is made of ionomer A, they function as a good proton conduction aid. When this is added to the catalyst layer, the power generation performance is improved by 1.5 times or more compared to a catalyst layer that does not contain this.

[3. Method for producing ionomer-modified hydrophobic particles]
Ionomer-modified hydrophobic particles are
(a) preparing an aromatic vinyl copolymer;
(b) adsorbing an aromatic vinyl copolymer onto the surface of the hydrophobic particles to form surface-modified hydrophobic particles;
(c) It can be produced by further adsorbing ionomer A onto the surface of surface-modified hydrophobic particles.

[3.1. Preparation of aromatic vinyl copolymer]
First, an aromatic vinyl copolymer is prepared. Specifically, the aromatic vinyl copolymer is
(a) a vinyl aromatic monomer containing a hydrophobic functional group that is easily adsorbed to hydrophobic particles;
(b) It is obtained by copolymerizing the anionic functional group of ionomer A and a second vinyl monomer having a cationic functional group capable of ionically bonding.

Examples of vinyl aromatic monomers include styrene monomers, vinylnaphthalene monomers, vinylanthracene monomers, vinylanisole monomers, vinylbenzoic acid ester monomers, and acetylstyrene monomers.
Examples of the second vinyl monomer include 2-vinylpyridine, 4-vinylpyridine, allylamine monomer, aziridine, vinylamine, 4-vinylbenzylamine, 2-vinylbenzylamine, 3-vinylbenzylamine, 2-vinylaniline, 3 - Vinylaniline, 4-vinylaniline, etc.
The method of copolymerizing the vinyl aromatic monomer and the second vinyl monomer is not particularly limited, and any known method can be used.

[3.2. Adsorption of aromatic vinyl copolymer]
Next, an aromatic vinyl copolymer is adsorbed onto the surface of the hydrophobic particles. This results in surface-modified hydrophobic particles.
When hydrophobic particles and an aromatic vinyl copolymer are dispersed in a suitable solvent, the hydrophobic functional groups of the aromatic vinyl copolymer are adsorbed onto the surface of the hydrophobic particles. As a result, a dispersion in which surface-modified hydrophobic particles are dispersed in a solvent is obtained.

When the hydrophobic particles are graphite, hydrogen peroxide may be further added to the solution in which graphite and aromatic vinyl copolymer are dispersed. When hydrogen peroxide is added to the solution and subjected to dispersion treatment under high pressure using a wet atomization device, the hydrogen peroxide penetrates between the graphene layers and oxidizes the layer surface, causing cleavage to proceed. Moreover, at the same time, the aromatic vinyl copolymer penetrates between the cleaved graphene layers to stabilize the cleavage planes and promote delamination. As a result, surface-modified hydrophobized particles in which the aromatic vinyl copolymer is adsorbed on the surface of exfoliated graphite are obtained.

Examples of hydrogen peroxide used to cleave graphite include:
(a) Compounds having a carbonyl group (for example, urea, carboxylic acids (benzoic acid, salicylic acid, etc.), ketones (acetone, methyl ethyl ketone, etc.), carboxylic acid esters (methyl benzoate, ethyl salicylate, etc.)) and hydrogen peroxide complex,
(b) Examples include quaternary ammonium salts, compounds in which hydrogen peroxide is coordinated with compounds such as potassium fluoride, rubidium carbonate, phosphoric acid, and uric acid.

[3.3. Adsorption of ionomer A]
Next, ionomer A is adsorbed onto the surface of the surface-modified hydrophobic particles. As a result, ionomer-modified hydrophobized particles are obtained.
When the surface-modified hydrophobic particles and ionomer A are dispersed in a suitable solvent, the cationic functional group of the aromatic vinyl copolymer and the anionic functional group of ionomer A form an ionic bond. As a result, a dispersion liquid in which ionomer-modified hydrophobized particles are dispersed in a solvent is obtained.

[4. Catalyst layer]
FIG. 1 shows a schematic cross-sectional view of a catalyst layer according to the present invention.
In FIG. 1, the catalyst layer 10 is
an electrode catalyst 20 in which a catalyst is supported on the surface of a carbon carrier;
A catalyst layer ionomer 30 made of ionomer B,
The ionomer-modified hydrophobic particles 40 according to the present invention are provided.
Further, the catalyst layer 10 is formed on the surface of the electrolyte membrane 50.

[4.1. Electrode catalyst]
[4.1.1. material]
The electrode catalyst 20 consists of catalyst particles (not shown) supported on the surface of a carbon carrier (not shown). In the present invention, the material of the carbon carrier and the material of the catalyst particles are not particularly limited, and the most suitable material can be selected depending on the purpose.
Examples of carbon carriers include carbon black, activated carbon, carbon nanotubes, carbon nanohorns, fullerenes, graphitized carbon particles, and thermal black.
Examples of materials for the catalyst particles include:
(a) Precious metals such as Pt, Pd, Ru, Ir, or alloys thereof,
(b) Pt-M alloy (M is a base metal element such as Fe, Ni, Co, etc.)
and so on.

[4.1.2. Carrying rate]
“Support ratio” refers to the ratio of the mass of catalyst particles to the total mass of the electrode catalyst 20.
Generally, the higher the catalyst loading rate, the higher the activity of the catalyst layer 10. In order to obtain such an effect, the supporting rate is preferably 30 mass% or more.
On the other hand, if the supporting ratio of catalyst particles becomes excessive, the cost will increase. Therefore, the loading rate is preferably 70 mass% or less.

[4.2. Catalyst layer ionomer]
The catalyst layer ionomer 30 is for supplying protons to the surface of the catalyst particles, and is made of ionomer B. In the present invention, the material of ionomer B is not particularly limited. Ionomer B may be the same material as ionomer A, or may be a different material.
Ionomer B is particularly preferably a perfluorocarbon sulfonic acid polymer. This is because it has excellent proton conductivity, robustness, and durability. The other points regarding ionomer B are the same as ionomer A, so the explanation will be omitted.

[4.3. Ionomer-modified hydrophobic particles]
The catalyst layer 10 according to the present invention further includes ionomer-modified hydrophobic particles 40 in addition to the electrode catalyst 20 and the catalyst layer ionomer 30. This point is different from the conventional method. The ionomer-modified hydrophobic particles 40 include surface-modified hydrophobic particles 42 and ionomer A 44 covering the surface of the surface-modified hydrophobic particles 42. The details of the ionomer-modified hydrophobic particles 40 are as described above, so the explanation will be omitted.

[4.4. Composition of catalyst layer]
The catalyst layer 10 preferably satisfies the following relationships (2) to (4).
35.0≦x≦70.0mass%…(2)
0.4<y/x<1.6...(3)
1.0≦z≦45.0mass%…(4)

however,
x (mass%) is the ratio of the mass of the electrode catalyst 20 to the total mass of the electrode catalyst 20, ionomer-modified hydrophobic particles 40, and ionomer B (catalyst layer ionomer 30) included in the catalyst layer 10;
y/x is the ratio of the total mass of ionomer B (catalyst layer ionomer 30) and ionomer A 44 covering the surface of the surface-modified hydrophobic particles 42 to the mass of the electrode catalyst 20 included in the catalyst layer 10;
z (mass%) is the ratio of the mass of the surface-modified hydrophobic particles 42 to the total mass of the electrode catalyst 20 and the surface-modified hydrophobic particles 42 included in the catalyst layer 10.

If the amount (x) of the electrode catalyst 20 contained in the catalyst layer 10 becomes too small, the activity of the catalyst layer 10 may decrease and the performance may deteriorate. Therefore, x is preferably 35.0 mass% or more. x is more preferably 45.0 mass% or more, still more preferably 50.0 mass% or more.
On the other hand, if x is excessive, the amount of catalyst used increases, resulting in high costs. Therefore, x is preferably 70.0 mass% or less. x is more preferably 65.0 mass% or less, still more preferably 60.0 mass% or less.

If the ratio (y/x) of the mass of ionomer B and ionomer A to the mass of electrode catalyst 20 becomes too small, a proton path may not be formed and proton conductivity may decrease. Therefore, y/x is preferably greater than 0.4. y/x is more preferably 0.43 or more, still more preferably 0.46 or more.
On the other hand, if y/x becomes excessive, the excess ionomer may inhibit the drainage of water generated during power generation, resulting in a decrease in performance. Therefore, y/x is preferably less than 1.6. y/x is more preferably 1.3 or less, still more preferably 1.0 or less.

As the amount (z) of surface-modified hydrophobic particles 42 (ie, ionomer-modified hydrophobic particles 40) contained in the catalyst layer 10 increases, the proton conductivity of the catalyst layer 10 improves. In order to obtain such an effect, z is preferably 1.0 mass% or more. z is more preferably 5.0 mass% or more, still more preferably 10.0 mass% or more.
On the other hand, if z becomes too large, the amount of electrode catalyst 20 per unit area decreases, and the activity decreases on the contrary. Therefore, z is preferably 45.0 mass% or less. z is more preferably 30.0 mass% or less, still more preferably 20.0 mass% or less.

[4.5. Use]
The catalyst layer 10 according to the present invention can be used as a catalyst layer of various electrochemical devices. The catalyst layer 10 according to the present invention is preferably used as a cathode, particularly in order to increase the efficiency of the oxygen reduction reaction of a polymer electrolyte fuel cell.

[5. Catalyst ink]
The catalyst ink according to the present invention includes:
an electrode catalyst in which catalyst particles are supported on the surface of a carbon carrier;
A catalyst layer ionomer made of ionomer B;
Ionomer-modified hydrophobic particles according to the present invention,
a hydrophilic solvent containing water for dispersing the electrode catalyst, the catalyst layer ionomer, and the ionomer-modified hydrophobic particles;
It is equipped with

[5.1. Electrocatalyst, catalyst layer ionomer, and ionomer-modified hydrophobic particles]
The details of the electrode catalyst, the catalyst layer ionomer, and the ionomer-modified hydrophobic particles are as described above, so a description thereof will be omitted.

[5.2. Hydrophilic solvent]
The hydrophilic solvent is used to disperse the electrode catalyst, the catalyst layer ionomer, and the ionomer-modified hydrophobic particles, and contains at least water.
The hydrophilic solvent may consist only of water, or may be a mixed solvent of water and an organic solvent. Examples of the organic solvent include ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, and tert-butanol.
When the hydrophilic solvent is a mixed solvent of water and an organic solvent, the content thereof is not particularly limited, and the optimum content can be selected depending on the purpose.

[5.3. Composition of catalyst ink]
The catalyst ink preferably satisfies the following relationships (2) to (4). Note that the details of Equations (2) to (4) are as described above, so their explanation will be omitted.
35.0≦x≦70.0mass%…(2)
0.4<y/x<1.6...(3)
1.0≦z≦45.0mass%…(4)

however,
x (mass%) is the ratio of the mass of the electrode catalyst to the total mass of the electrode catalyst, the ionomer-modified hydrophobic particles, and the ionomer B contained in the catalyst ink;
y/x is the ratio of the total mass of the ionomer B and the ionomer A covering the surface of the surface-modified hydrophobic particles to the mass of the electrode catalyst contained in the catalyst ink;
z (mass%) is the ratio of the mass of the surface-modified hydrophobic particles to the total mass of the electrode catalyst and the surface-modified hydrophobic particles contained in the catalyst ink.

[5.4. Solid content concentration]
The "solid content concentration of the catalyst ink" refers to the mass ratio of the solid content (electrode catalyst, catalyst layer ionomer, and ionomer-modified hydrophobic particles) to the total mass of the catalyst ink.
The solid content concentration of the catalyst ink is not particularly limited, and an optimal concentration can be selected depending on the purpose. The solid content concentration of the catalyst ink is usually about 1 mass% to 40 mass%.

[6. Production method of catalyst ink]
The method for producing catalyst ink according to the present invention includes:
A first step of preparing a first dispersion liquid in which ionomer-modified hydrophobic particles according to the present invention are dispersed in a first dispersion medium;
a second step of preparing a second dispersion liquid in which the electrode catalyst and ionomer C are dispersed in a second dispersion medium;
and a third step of mixing the first dispersion liquid and the second dispersion liquid to obtain a catalyst ink.

[6.1. 1st process]
First, a first dispersion liquid in which ionomer-modified hydrophobic particles according to the present invention are dispersed in a first dispersion medium is prepared (first step).
The first dispersion medium is not particularly limited as long as it is capable of uniformly dispersing the ionomer-modified hydrophobic particles. As the first dispersion medium, for example,
(a) organic solvents such as ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, tert-butanol;
(b) a mixed solvent of water and an organic solvent such as ethanol;
and so on.
The solid content concentration of the first dispersion liquid is not particularly limited as long as the catalyst ink can be manufactured. The solid content concentration is usually about 1 mass% to 80 mass%.
Moreover, the first dispersion liquid may contain free ionomer A.

[6.2. 2nd process]
Next, a second dispersion liquid in which the electrode catalyst and ionomer C are dispersed in a second dispersion medium is prepared (second step).
The second dispersion medium is not particularly limited as long as it is capable of uniformly dispersing the electrode catalyst and ionomer C. As the second dispersion medium, for example,
(a) organic solvents such as ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, tert-butanol;
(b) a mixed solvent of water and an organic solvent such as ethanol;
and so on.
Ionomer C becomes ionomer B after solvent removal. When free ionomer A is included in the first dispersion, free ionomer A also constitutes a part of ionomer B.
It is preferable that the amounts of the electrode catalyst and ionomer C added to the second dispersion medium satisfy the above-mentioned formulas (2) to (4).
The solid content concentration of the second dispersion liquid is not particularly limited as long as the catalyst ink can be manufactured. The solid content concentration is usually about 1 mass% to 40 mass%.

[6.3. Third step]
Next, the first dispersion liquid and the second dispersion liquid are mixed (third step). Thereby, a catalyst ink is obtained.
The method and conditions for mixing the first dispersion and the second dispersion are not particularly limited, and an optimal method can be selected depending on the purpose.
Furthermore, the mixing ratio of the first dispersion liquid and the second dispersion liquid is preferably a ratio that satisfies the above-mentioned formulas (2) to (4).

[7. Effect]
When the surface of a hydrophobic particle is modified with an aromatic vinyl copolymer, a surface-modified hydrophobic particle having a cationic functional group introduced onto the surface of the hydrophobic particle can be obtained. Next, when the surface-modified hydrophobic particles and ionomer A are dispersed in a solvent, the cationic functional group and the anionic functional group of ionomer A are ionically bonded, and ionomer-modified hydrophobic particles are obtained.

The ionomer-modified hydrophobic particles thus obtained function as a proton conduction aid because a continuous proton conduction path is formed on the surface of the hydrophobic particles. Furthermore, since the ionomer-modified hydrophobic particles have increased surface charge due to adsorption of ionomer A, they can be dispersed in a hydrophilic solvent containing water.
Therefore, by adding ionomer-modified hydrophobic particles to a catalyst ink, applying and drying the catalyst ink, a catalyst layer with high proton conductivity can be obtained.

By using the catalyst ink containing the ionomer-modified hydrophobic particles according to the present invention, a catalyst layer can be manufactured using a coating device suitable for mass production, such as an applicator or a die coater. Furthermore, by optimizing the average length of the ionomer-modified hydrophobic particles and the coating conditions, a catalyst layer in which the ionomer-modified hydrophobic particles are oriented in an out-of-plane direction can be obtained. As a result, the proton conductivity of the catalyst layer is improved.

(Examples 1-4, Comparative Examples 1-2)
[1. Preparation of sample]
[1.1. Preparation of ionomer-modified hydrophobic particles]
Figure 2 shows a synthesis scheme of ionomer-modified hydrophobic particles. Ionomer-modified hydrophobic particles were synthesized according to the synthesis scheme shown in FIG. 2. Poly(styrene-2-pyridine) copolymer (Poly(ST-2VP)) was used as the aromatic vinyl copolymer. Graphite was used as the hydrophobic particles.

[1.1.1. Preparation of aromatic vinyl copolymer]
Styrene (ST): 18 g, 2-vinylpyridine (2VP): 2 g, 2,2'-azodiisobutyronitrile: 50 mg, and toluene: 100 mL were mixed and polymerized at 85° C. for 6 hours under a nitrogen atmosphere. .
After cooling, it was purified by reprecipitation using chloroform as a good solvent and hexane as a poor solvent. Furthermore, the purified product was vacuum dried to obtain 3.3 g of Poly(ST-2VP).

[1.1.2. Preparation of surface-modified hydrophobic particles]
Graphite (manufactured by Nippon Graphite Industries Co., Ltd., EXP-P): 12.5 g, hydrogen peroxide-urea complex: 12.5 g, Poly (ST-2VP): 1.25 g, and N,N-dimethylformamide ( DMF) was mixed. Using a wet atomization device (manufactured by Sugino Machine Co., Ltd., Starburst, oblique collision chamber), the mixed liquid was processed for 10 passes at a pressure of 200 MPa. As a result, the graphite particles were delaminated to become exfoliated graphite, and at the same time, Poly(ST-2VP) was adsorbed to the surface of the exfoliated graphite (FIGS. 2(A) and 2(B)). The obtained dispersion was filtered, washed with DMF, and then vacuum dried to obtain surface-modified hydrophobic particles.

[1.1.3. Preparation of ionomer-modified hydrophobic particles]
The surface-modified hydrophobic particles were dispersed in a mixed solvent of 0.943 g of water and 0.432 g of ethanol. The amount of surface-modified hydrophobic particles added was 0.054 g (Example 1), 0.113 g (Example 2), 0.255 g (Example 3), or 0.85 g (Example 4).
While ultrasonically dispersing the dispersion liquid, 0.125 g of Nafion (registered trademark) (manufactured by DuPont, D2020, 21.6 mass% solution) was added dropwise. Further, ultrasonic dispersion was performed for 1 hour to obtain an aqueous dispersion of ionomer-modified hydrophobic particles (FIG. 2(C)).

[1.2. Preparation of catalyst ink]
[1.2.1. Examples 1 to 4]
[A. Preparation of catalyst ink stock solution]
Add 4.052 g of ultrapure water to 1.050 g of platinum-supported carbon (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., TEC10V30E, carrier: Vulcan (registered trademark) Defoaming and stirring were performed for 1 minute each using a vacuum cleaner (KK-50S). 2.363 g of Nafion (registered trademark) (manufactured by DuPont, D2020, 21.6 mass%) and 1.428 g of ethanol were added thereto, and defoaming and stirring were performed for 1 minute each. Furthermore, dispersion treatment was performed for 25 minutes at a rotation speed of 400 rpm using a planetary stirring ball mill (manufactured by Fritsch AG, P-7). Thereafter, defoaming and stirring were further performed for 1 minute each to obtain a catalyst ink stock solution.

[B. Addition of ionomer-modified hydrophobic particles]
The ionomer-modified hydrophobic particle aqueous dispersion (hereinafter also simply referred to as "aqueous dispersion") and the catalyst ink stock solution were mixed, and defoaming and stirring were performed for 2 min each using a planetary stirring/defoaming device. , a catalyst ink containing ionomer-modified hydrophobic particles was obtained.
In this case, the I/C ratio of the catalyst ink (the ratio of the mass of the total amount of ionomer contained in the catalyst ink (=ionomer A + ionomer B) to the mass of carbon contained in the platinum-supported carbon) is 0.75. Met.
Further, the ratio (z) of the mass of the surface-modified hydrophobic particles to the total mass of the platinum-supported carbon and the surface-modified hydrophobic particles was 4.89 mass% to 44.74%.

[1.2.2. Comparative example 1]
A catalyst ink was prepared in the same manner as in Example 1, except that surface-modified hydrophobic particles were not added during preparation of the aqueous dispersion.
[1.2.3. Comparative example 2]
A catalyst ink was prepared in the same manner as in Example 1, except that graphene nanoplatelets (GNPs) (manufactured by XG Sciences, R-7) were used in place of the surface-modified hydrophobic particles when preparing the aqueous dispersion. Note that the purchased GNPs were used as they were, and the surface was not modified with an aromatic vinyl copolymer.
Table 1 shows the blending amounts and charging compositions of the catalyst inks obtained in Examples 1 to 4 and Comparative Examples 1 to 2.

[1.3. Preparation of catalyst layer]
A catalyst ink was applied onto a polytetrafluoroethylene sheet. For coating, an applicator and Vicodrive (manufactured by BYK Gardner Company) were used. The coating speed was 10 mm/s. After drying the coating film at room temperature (24° C., 70-75% RH), heat treatment (80° C., 30 min) was performed to obtain a catalyst layer.

[2. Test method]
[2.1. Evaluation of surface-modified hydrophobic particles and ionomer-modified hydrophobic particles]
[2.1.1. Evaluation of water dispersibility]
Surface hydrophobic particles or ionomer-modified hydrophobic particles were dispersed in water, and the dispersibility in water was visually evaluated.

Separately, 0.1 g of surface-modified hydrophobic particles was added to 5 mL of water. While ultrasonically dispersing this liquid mixture, 0.043 g of ionomer was added dropwise. After performing ultrasonic dispersion for 1 hour, it was allowed to stand still and sedimentation or aggregation of the particles was visually evaluated. Hereinafter, this will also be referred to as an "ultrasonic dispersion test."

[2.1.2. Evaluation of ionomer adsorption amount]
The ionomer-modified hydrophobic particles were filtered from the ionomer-modified hydrophobic particle aqueous dispersion using a syringe filter, and the mass of the filtrate was measured. Next, the filtrate was heated at 80° C. for 1 hour to volatilize the solvent. The mass of the remaining solid content was measured, and the concentration of ionomer A (C _p ) contained in the filtrate was calculated from it. Furthermore, C _p and the initial concentration of ionomer A (C _p0 ) were substituted into equation (6) to calculate the adsorption rate Γ of the ionomer.
Γ=(C _p0 −C _p )/C _p0 …(6)

The adsorption amount W of ionomer A contained in the ionomer-modified hydrophobic particles was calculated from equation (7) based on the composition of the aqueous dispersion.
W=W ₁ ×Γ/(W ₂ +W ₁ ×Γ) …(7)
however,
W ₁ is the amount of ionomer A added to the aqueous dispersion,
W ₂ is the amount of surface-modified hydrophobic particles added to the aqueous dispersion.

[2.2. Particle size measurement]
The obtained surface-modified hydrophobic particles and ionomer-modified hydrophobic particles were observed using a scanning electron microscope (SEM). For SEM observation, the sample was coated with Pt by sputtering. For the SEM, SU3500 model manufactured by Hitachi High-Tech Corporation was used, and the accelerating voltage was 15.0 kV.

A focused ion beam device (manufactured by Hitachi High-Tech Corporation, NB500) was used to prepare the cross section of the catalyst layer. The machining was performed in two stages: rough machining and finishing machining. Rough processing was performed for 2 hours with a beam limiting aperture of 300 μm, and finishing processing was performed for 30 minutes with a beam limiting aperture of 150 μm. Liquid metal gallium was used as the ion source, and the acceleration voltage was 40 kV.
An ultra-high-resolution field emission scanning electron microscope (Regulus 8230, manufactured by Hitachi High-Tech Corporation) was used to observe the cross section of the catalyst layer.
Furthermore, using image analysis software (Image J), the major axis and thickness of the surface hydrophobic particles and ionomer-modified hydrophobic particles included in the photographed microscopic images were measured.

[2.3. Power generation performance evaluation]
The prepared catalyst layer was hot pressed on a Nafion (registered trademark) membrane (Nafion NR211) at 145° C. for 4 minutes to obtain a membrane electrode assembly (MEA). Carbon paper with a water-repellent layer was placed on both sides of the MEA as a gas diffusion layer, and this was sandwiched between separators to obtain a polymer electrolyte fuel cell.
After a break-in operation, the power generation performance was evaluated under conditions of 45° C. and 165% RH at both poles in order to evaluate performance under overhumidified conditions. The measured cell voltages were adjusted using IR correction voltages. Furthermore, performance was compared at a current density of 0.6V.

[3. result]
[3.1. Evaluation of surface-modified hydrophobic particles and ionomer-modified hydrophobic particles]
FIG. 3(A) shows a photograph of a dispersion in which surface-modified hydrophobic particles are dispersed in water. FIG. 3(B) shows a photograph of a dispersion in which ionomer-modified hydrophobic particles are dispersed in water. The surface-modified hydrophobic particles did not disperse in water. The reason for this is thought to be that highly hydrophobic Poly (ST-2VP) is adsorbed on the surface of the surface-modified hydrophobic particles.
On the other hand, the ionomer-modified hydrophobic particles were well dispersed in water. The reason for this is thought to be that the ionomer A could be bound to the surface of the surface-modified hydrophobic particles by ionic bonding using the pyridine ring of Poly(ST-2VP) as a scaffold, thereby increasing the surface charge.

[3.2. SEM observation]
Both the surface-modified hydrophobic particles and the ionomer-modified hydrophobic particles were plate-shaped. The major axis of the surface-modified hydrophobic particles (≈long axis of the ionomer-modified hydrophobic particles) was 1 to 7 μm, and the surface was smooth. Further, the thickness of the surface-modified hydrophobic particles (≈thickness of the ionomer-modified hydrophobic particles) calculated from cross-sectional observation of the catalyst layer was found to be 50 to 180 nm.

[3.3. Power generation performance evaluation]
FIG. 4 shows the IV curves (after IR correction) of the fuel cells obtained in Examples 1 and 2 and Comparative Examples 1 and 2 under overhumidified conditions. Table 2 shows the results of power generation performance evaluation. The following can be seen from FIG. 4 and Table 2.

Table 2 shows the specifications of the ionomer-modified hydrophobic particles, the mass percentage (mass%) of the surface-modified hydrophobic particles contained in the catalyst layer, and the dispersibility of the ionomer-modified hydrophobic particles in water (ultrasonic dispersion). Tests) are also shown.
In Table 2, "adsorption amount of ionomer A" is a value calculated from equation (7).
The term "mass ratio of surface-modified hydrophobic particles" refers to the mass ratio of surface-modified hydrophobic particles to the total mass of platinum-supported carbon and surface-modified hydrophobic particles.

In Table 2, regarding water dispersibility (ultrasonic dispersion test),
"○" indicates that all particles are uniformly dispersed in water even after 1 hour has passed after stopping ultrasonic dispersion.
"△" indicates that one hour after stopping ultrasonic dispersion, some particles are dispersed in water, but the remaining part settles or aggregates and floats. ,
"X" indicates that all the particles have settled or aggregated and are suspended one hour after the ultrasonic dispersion is stopped.

(1) The ionomer-modified hydrophobic particles obtained in Examples 1 to 4 all had excellent water dispersion stability. That is, exfoliated graphite particles made hydrophilic can be obtained by adsorbing an aromatic vinyl copolymer having a pyridine ring to the exfoliated graphite particles, and further adsorbing ionomer A that ionically bonds with the pyridine ring. Do you get it.
(2) In Comparative Example 2, even when the ionomer was added and subjected to ultrasonic dispersion treatment, it did not disperse in water and agglomerated. This is considered to be because the surface was not modified with the aromatic vinyl copolymer.

(3) In the high current density region, the voltages of Examples 1 to 4 were higher than those of Comparative Examples 1 and 2. Since the amount of generated water increases in proportion to the current density, the performance decline in the high current density region of Comparative Example 1 is considered to be caused by clogging (flooding) due to water.
(4) Comparative Example 2 showed higher performance than Comparative Example 1. This is considered to be an effect of the structure that is less likely to flood, which is formed by adding GNP to the catalyst layer.
(5) The performance of Examples 1 to 4 was higher than that of Comparative Example 2. The reason for this is that the ionomer is adsorbed on the surface of the surface-modified hydrophobic particles, forming a proton conduction path, and the catalyst layer is not easily drained due to the influence of the dispersant (aromatic vinyl copolymer) adsorbed on the surface. This is thought to be due to the fact that the structure has improved and is less prone to flooding.

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 ionomer-modified hydrophobic particles according to the present invention can be used as an additive for improving proton conductivity to the catalyst layer of a polymer electrolyte fuel cell, as an additive for electrodes for hydrogen production by electrolysis, and as an additive for hydrogen sensors. It can be used as an additive, an additive for hydrogen separation membranes, etc.

Claims (13)

Ionomer-modified hydrophobic particles with the following composition:
(1) The ionomer-modified hydrophobic particles are:
surface-modified hydrophobic particles whose surfaces are coated with an aromatic vinyl copolymer;
and an ionomer A that further coats the surface of the surface-modified hydrophobic particles.
(2) The aromatic vinyl copolymer is
Comprising a hydrophobic functional group and a cationic functional group,
It is adsorbed on the surface of the hydrophobic particles via the hydrophobic functional group.
(3) The ionomer A is
Equipped with anionic functional group,
It is ionically bonded to the cationic functional group via the anionic functional group. The hydrophobic particles are
Consisting of sheet-like particles,
The average major axis is 1 μm or more and 10 μm or less,
The ionomer-modified hydrophobic particles according to claim 1, having an average thickness of 10 nm or more and 300 nm or less. The ionomer-modified hydrophobic particles according to claim 1 or 2, wherein the hydrophobic particles are exfoliated graphite particles. The ionomer-modified hydrophobic particles according to any one of claims 1 to 3, wherein the adsorption amount of the ionomer A is 0.03 mass% or more and 35.0 mass% or less. From claim 1, the cationic functional group comprises any one or more functional groups selected from the group consisting of a pyridyl group, an amino group, a quaternary ammonium group, an imino group, an imidazole group, a guanidine group, and a biguanide group. 4. The ionomer-modified hydrophobic molecule according to any one of items 4 to 4. The aromatic vinyl copolymer is
A vinyl aromatic monomer unit represented by the following formula (1),
The ionomer-modified hydrophobic particles according to any one of claims 1 to 5, comprising a copolymer comprising a second monomer unit made of a vinyl monomer having a cationic functional group.
-(CH ₂ -CHX)-...(1)
however,
X represents any one or more of the above hydrophobic functional groups selected from the group consisting of phenyl group, naphthyl group, anthracenyl group, and pyrenyl group, and these groups may have a substituent,
The cationic functional group is any one or more functional groups selected from the group consisting of a pyridyl group, an amino group, a quaternary ammonium group, an imino group, an imidazole group, a guanidine group, and a biguanide group. The ionomer-modified hydrophobic particle according to any one of claims 1 to 6, wherein the ionomer A comprises a perfluorocarbon sulfonic acid polymer. an electrode catalyst in which catalyst particles are supported on the surface of a carbon carrier;
A catalyst layer ionomer made of ionomer B;
A catalyst layer comprising the ionomer-modified hydrophobic particles according to any one of claims 1 to 7. The catalyst layer according to claim 8, which satisfies the following equations (2) to (4).
35.0≦x≦70.0mass%…(2)
0.4<y/x<1.6...(3)
1.0≦z≦45.0mass%…(4)
however,
x (mass%) is the ratio of the mass of the electrode catalyst to the total mass of the electrode catalyst, the ionomer-modified hydrophobic particles, and the ionomer B contained in the catalyst layer;
y/x is the ratio of the total mass of the ionomer B and the ionomer A covering the surface of the surface-modified hydrophobic particles to the mass of the electrode catalyst included in the catalyst layer;
z (mass%) is the ratio of the mass of the surface-modified hydrophobic particles to the total mass of the electrode catalyst and the surface-modified hydrophobic particles included in the catalyst layer. The catalyst layer according to claim 8 or 9, wherein the ionomer B is made of a perfluorocarbon sulfonic acid polymer. an electrode catalyst in which catalyst particles are supported on the surface of a carbon carrier;
A catalyst layer ionomer made of ionomer B;
Ionomer-modified hydrophobic particles according to any one of claims 1 to 7;
a hydrophilic solvent containing water for dispersing the electrode catalyst, the catalyst layer ionomer, and the ionomer-modified hydrophobic particles;
catalyst ink with The catalyst ink according to claim 11, which satisfies the following equations (2) to (4).
35.0≦x≦70.0mass%…(2)
0.4<y/x<1.6...(3)
1.0≦z≦45.0mass%…(4)
however,
x (mass%) is the ratio of the mass of the electrode catalyst to the total mass of the electrode catalyst, the ionomer-modified hydrophobic particles, and the ionomer B contained in the catalyst ink;
y/x is the ratio of the total mass of the ionomer B and the ionomer A covering the surface of the surface-modified hydrophobic particles to the mass of the electrode catalyst contained in the catalyst ink;
z (mass%) is the ratio of the mass of the surface-modified hydrophobic particles to the total mass of the electrode catalyst and the surface-modified hydrophobic particles contained in the catalyst ink. A first step of preparing a first dispersion liquid in which the ionomer-modified hydrophobic particles according to any one of claims 1 to 7 are dispersed in a first dispersion medium;
a second step of preparing a second dispersion liquid in which the electrode catalyst and ionomer C are dispersed in a second dispersion medium;
A method for producing a catalyst ink, comprising a third step of mixing the first dispersion liquid and the second dispersion liquid to obtain a catalyst ink.

Images