JP2024043895A - Catalyst ink, method of manufacturing the same, and method of manufacturing membrane electrode assembly - Google Patents

Abstract

To provide a technology capable of suppressing cracks and peel-off of a formed catalyst layer when applying a catalyst ink on an electrolyte film and drying it.SOLUTION: A catalyst ink includes a solvent, a catalyst, an ionomer, and a high-boiling solvent with a boiling point equal to or more than a softening point of the ionomer. This can suppress cracks and peel-off of a catalyst layer.SELECTED DRAWING: Figure 4

Description

The present invention relates to a catalyst ink, a method for producing a catalyst ink, and a method for producing a membrane electrode assembly.

A polymer electrolyte fuel cell is a battery that uses an ion exchange membrane (electrolyte membrane) as an electrolyte. When a polymer electrolyte fuel cell is used, hydrogen gas is supplied to the catalyst layer on the anode side, and oxygen gas is supplied to the catalyst layer on the cathode side. When a proton exchange membrane is used as the ion exchange membrane, electric power is generated by the following electrochemical reaction occurring between the anode side catalyst layer and the cathode side catalyst layer.
(Anode side) H ₂ → 2H ⁺ + 2e ^-
(Cathode side) 1/2O ₂ + 2H ⁺ + 2e ^- → H ₂ O

A solid polymer electrolyte fuel cell has a membrane electrode assembly in which catalyst layers are formed on both sides of an electrolyte membrane. One method for manufacturing a membrane electrode assembly is to apply a catalyst ink to the surface of the electrolyte membrane. The catalyst ink is manufactured by mixing a catalyst, an electrolyte, and a solvent. Conventional catalyst inks are described, for example, in Patent Document 1.

JP2016-066510A

The catalyst ink described in Patent Document 1 includes carbon supporting a catalyst, an ionomer, and a solvent.

However, when conventional catalyst inks were applied to the surface of an electrolyte membrane and allowed to dry, the catalyst layer formed could crack or peel off.

The present invention was made in view of the above circumstances, and provides a technology that can suppress cracking and peeling of the formed catalyst layer when a catalyst ink is applied to an electrolyte membrane and dried. The purpose is to

In order to solve the above problems, the first invention of the present application is a catalyst ink that includes a solvent, a catalyst, an ionomer, and a high boiling point solvent whose boiling point is equal to or higher than the softening point of the ionomer.

A second invention of the present application is the catalyst ink of the first invention, wherein the catalyst includes carbon particles and a catalyst metal supported on the carbon particles.

The third invention of the present application is a catalyst ink according to the first or second invention, which contains 4% by weight or more of the high boiling point solvent.

The fourth invention of the present application is a catalyst ink according to any one of the first to third inventions, in which the high-boiling point solvent is one or more selected from the group consisting of N-methyl-2-pyrrolidone, propylene carbonate, polyhydric alcohols, and glycol ethers.

A fifth invention of the present application is a catalyst ink manufacturing method, comprising: a) preparing a mixed solution by mixing a solvent, a catalyst, an ionomer, and a high boiling point solvent whose boiling point is higher than the softening point of the ionomer; This includes the step of

The sixth invention of the present application is the method for producing a catalyst ink of the fifth invention, in which the catalyst includes carbon particles and a catalytic metal supported on the carbon particles.

The seventh invention of the present application is a method for producing a catalyst ink according to the fifth or sixth invention, in which in step a), the mixed liquid is prepared so that the content of the high boiling point solvent in the mixed liquid is 4% by weight or more.

The eighth invention of the present application is a method for producing a catalyst ink according to any one of the fifth to seventh inventions, in which the high-boiling point solvent is one or more selected from the group consisting of N-methyl-2-pyrrolidone, propylene carbonate, polyhydric alcohols, and glycol ethers.

A ninth invention of the present application is a method for manufacturing a membrane electrode assembly, which includes the steps of: A) applying the catalyst ink of any one of the first to fourth inventions to an electrolyte membrane; and B) The method includes the step of heating and drying the catalyst ink applied to the electrolyte membrane at a temperature higher than the softening point of the ionomer and lower than the boiling point of the high-boiling solvent.

The first to ninth aspects of the present application make it possible to suppress cracking and peeling of the catalyst layer.

FIG. 1 is a schematic diagram of a polymer electrolyte fuel cell. FIG. 2 is a schematic diagram conceptually showing the composition of a cathode catalyst layer. 1 is a diagram showing an example of an organic hydride manufacturing apparatus. It is a flowchart showing the manufacturing procedure of catalyst ink. It is a flow chart showing a manufacturing procedure of a membrane electrode assembly.

The following describes an embodiment of the present invention with reference to the drawings.

<Fuel cell structure>
Fig. 1 is a schematic diagram of one cell 1 of a polymer electrolyte fuel cell (PEFC) according to one embodiment of the present invention. The polymer electrolyte fuel cell has a structure in which a plurality of cells 1 shown in Fig. 1 are stacked in series. However, the polymer electrolyte fuel cell may be composed of a single cell 1.

As shown in FIG. 1, a cell 1 of a polymer electrolyte fuel cell includes an electrolyte membrane 10, an anode catalyst layer 21, an anode gas diffusion layer 22, an anode gasket 23, an anode separator 24, a cathode catalyst layer 31, a cathode gas diffusion layer 32, a cathode gasket 33, and a cathode separator 34. Of the cell 1, a laminate formed by the electrolyte membrane 10, the anode catalyst layer 21, and the cathode catalyst layer 31 is a membrane electrode assembly (MEA) 50 according to one embodiment of the present invention.

The electrolyte membrane 10 is a thin plate-like membrane (ion exchange membrane) having ion conductivity. As the electrolyte membrane 10, a fluorine-based or hydrocarbon-based polymer electrolyte membrane is used. Specifically, as the electrolyte membrane 10, for example, a proton exchange membrane containing perfluorocarbon sulfonic acid is used. The thickness of the electrolyte membrane 10 is, for example, 5 μm to 30 μm.

The anode catalyst layer 21 is a layer that becomes the anode side electrode (negative electrode) of the polymer electrolyte fuel cell. The anode catalyst layer 21 is formed on the surface of the electrolyte membrane 10 on the anode side. Anode catalyst layer 21 includes many catalyst particles. The catalyst particles are, for example, a platinum alloy. The platinum alloy includes, for example, at least one metal selected from the group consisting of ruthenium (Ru), palladium (Pd), nickel (Ni), molybdenum (Mo), iridium (Ir), iron (Fe), etc. It is an alloy with platinum (Pt). When the polymer electrolyte fuel cell is used, hydrogen gas (H ₂ ) is supplied to the anode catalyst layer 21. Then, by the action of the catalyst particles of the anode catalyst layer 21, hydrogen is decomposed into hydrogen ions (H ⁺ ) and electrons (e ⁻ ).

The anode gas diffusion layer 22 is a layer that uniformly supplies hydrogen gas to the anode catalyst layer 21 and allows electrons generated in the anode catalyst layer 21 to flow to the anode separator 24 . The anode gas diffusion layer 22 is laminated on the outer surface of the anode catalyst layer 21. The anode catalyst layer 21 is sandwiched between the electrolyte membrane 10 and the anode gas diffusion layer 22. The anode gas diffusion layer 22 is made of a conductive and porous material. For example, carbon paper is used for the anode gas diffusion layer 22.

The anode gasket 23 is a layer for preventing hydrogen gas from leaking to the surroundings from the anode catalyst layer 21 and the anode gas diffusion layer 22. As shown in FIG. 1, the anode gasket 23 is formed on the anode side surface of the electrolyte membrane 10, and surrounds the periphery of the anode catalyst layer 21 and the anode gas diffusion layer 22.

The anode separator 24 is a layer for supplying hydrogen gas to the anode gas diffusion layer 22 and for outputting electrons flowing from the anode catalyst layer 21 through the anode gas diffusion layer 22 to the external circuit 40 . Anode separator 24 is formed on the outer surface of anode gas diffusion layer 22 and anode gasket 23 . Anode catalyst layer 21, anode gas diffusion layer 22, and anode gasket 23 are sandwiched between electrolyte membrane 10 and anode separator 24. The anode separator 24 is made of a material that is electrically conductive and impermeable to gas. Further, a large number of grooves 241 are formed in the anode separator 24. Hydrogen gas is supplied to the anode gas diffusion layer 22 through the groove 241 of the anode separator 24 .

The cathode catalyst layer 31 is a layer that becomes the cathode side electrode (positive electrode) of the polymer electrolyte fuel cell. The cathode catalyst layer 31 is formed on the surface of the electrolyte membrane 10 on the cathode side (the surface opposite to the anode catalyst layer 21). The cathode catalyst layer 31 includes a large number of carbon particles supporting catalyst particles. The catalyst particles are, for example, platinum particles. However, the catalyst particles may be a mixture of platinum particles and a trace amount of ruthenium or cobalt particles. When the polymer electrolyte fuel cell is used, oxygen gas (O ₂ ), hydrogen ions (H ⁺ ), and electrons (e ⁻ ) are supplied to the cathode catalyst layer 31. Water (H ₂ O) is generated from oxygen gas, hydrogen ions, and electrons by the action of the catalyst particles of the cathode catalyst layer 31 .

Note that a more detailed composition of the cathode catalyst layer 31 will be described later.

The cathode gas diffusion layer 32 is a layer that uniformly supplies oxygen gas to the cathode catalyst layer 31 and allows electrons to flow from the cathode separator 34 to the cathode catalyst layer 31. The cathode gas diffusion layer 32 is laminated on the outer surface of the cathode catalyst layer 31. The cathode catalyst layer 31 is sandwiched between the electrolyte membrane 10 and the cathode gas diffusion layer 32. The cathode gas diffusion layer 32 is made of a conductive and porous material. For example, carbon paper is used for the cathode gas diffusion layer 32.

The cathode gasket 33 is a layer for preventing oxygen gas and water from leaking from the cathode catalyst layer 31 and the cathode gas diffusion layer 32 to the surroundings. As shown in FIG. 1, the cathode gasket 33 is formed on the cathode side surface of the electrolyte membrane 10 and surrounds the cathode catalyst layer 31 and the cathode gas diffusion layer 32.

The cathode separator 34 is a layer for supplying oxygen gas to the cathode gas diffusion layer 32 and for allowing electrons supplied from the external circuit 40 to flow to the cathode gas diffusion layer 32. The cathode separator 34 is formed on the outer surface of the cathode gas diffusion layer 32 and the cathode gasket 33. Cathode catalyst layer 31, cathode gas diffusion layer 32, and cathode gasket 33 are sandwiched between electrolyte membrane 10 and cathode separator 34. The cathode separator 34 is made of a material that is electrically conductive and impermeable to gas. Further, a large number of grooves 341 are formed in the cathode separator 34 . Oxygen gas is supplied to the cathode gas diffusion layer 32 through the groove 341 of the cathode separator 34 .

The external circuit 40 is connected between the anode separator 24 and the cathode separator 34. Specifically, the negative terminal of the external circuit 40 is electrically connected to the anode separator 24. The positive terminal of the external circuit 40 is electrically connected to the cathode separator 34.

When the solid polymer electrolyte fuel cell is in use, hydrogen gas as fuel is supplied from the anode separator 24 to the anode catalyst layer 21 through the anode gas diffusion layer 22. Then, hydrogen atoms are decomposed into hydrogen ions and electrons by the action of the catalyst particles of the anode catalyst layer 21. The hydrogen ions propagate through the electrolyte membrane 10 to the cathode catalyst layer 31. The electrons flow through the anode gas diffusion layer 22, the anode separator 24, the external circuit 40, the cathode separator 34, and the cathode gas diffusion layer 32 to the cathode catalyst layer 31. In addition, on the cathode side of the cell 1, oxygen gas is supplied from the cathode separator 34 to the cathode catalyst layer 31 through the cathode gas diffusion layer 32. Then, water is generated from the oxygen gas, hydrogen ions, and electrons by the action of the catalyst particles of the cathode catalyst layer 31. The water produced passes through the cathode gas diffusion layer 32 and the cathode separator 34 and is discharged to the outside.

<Composition of cathode catalyst layer>
Next, a more detailed composition of the cathode catalyst layer 31 will be described.

Figure 2 is a schematic diagram conceptually illustrating the composition of the cathode catalyst layer 31. As shown in Figure 2, the cathode catalyst layer 31 includes catalyst-supported carbon 51 and ionomer 52.

The catalyst-supported carbon 51 is a carbon particle that supports a catalyst, and includes carbon particles 511 that are a support, and catalyst particles 512 supported by the carbon particles 511. As the carbon particles 511, for example, carbon materials such as carbon black, carbon nanofibers, and carbon nanotubes may be used alone or in combination. The catalyst particles 512 are particles of a catalytic metal, for example, platinum (Pt) particles. However, the catalyst particles 512 may be platinum particles mixed with trace amounts of ruthenium or cobalt particles.

If the ratio of platinum to carbon particles 511 in the catalyst-supported carbon 51 is too low, it becomes difficult to obtain sufficient catalytic action. Furthermore, in order to obtain sufficient catalytic action, it becomes necessary to increase the amount of carbon particles 511, which results in a large film thickness of the cathode catalyst layer 31. On the other hand, if the ratio of platinum to carbon particles 511 is too high, the distance between the platinum particles becomes small. In that case, the platinum particles fuse together during power generation, resulting in a problem of reduced power generation performance.

Therefore, it is preferable that the ratio of platinum to carbon particles 511 is such that the thickness of the cathode catalyst layer 31 is suppressed and the distance between platinum particles is kept such that the platinum particles do not fuse together. Specifically, it is preferable that the ratio (weight ratio) of platinum to carbon particles 511 is 38% by weight or more and 65% by weight or less. It is more preferable that the ratio (weight ratio) of platinum to carbon particles 511 is 40% by weight or more and 55% by weight or less.

The ionomer 52 is an electrolyte polymer that covers the catalyst-supported carbon 51. As the ionomer 52, for example, a perfluorosulfonic acid polymer such as Nafion (registered trademark), Aquivion (registered trademark), Flemion (registered trademark), or Aciplex (registered trademark) can be used.

The ionomer 52 serves to transport the hydrogen ions supplied from the electrolyte membrane 10 within the cathode catalyst layer 31. The ionomer 52 has a polymer chain structure having an ion exchange group such as a sulfone group. The hydrogen ions supplied from the electrolyte membrane 10 combine with water in the cathode catalyst layer 31 to become oxonium ions (H ₃ O ⁺ ). The oxonium ions are then transported via the ion exchange groups of the ionomer 52.

In order to transport oxonium ions well, it is preferable to increase the number of ion exchange groups in the polymer chain of ionomer 52. Specifically, it is preferable to set the EW value, which indicates the dry mass of ionomer 52 per 1 mol of ion exchange groups (the reciprocal of the number of ion exchange groups per unit mass of ionomer 52), to 950 or less. For example, it is preferable to set the EW value to 650 or more and 950 or less.

If the ratio of ionomer 52 to catalyst-supported carbon 51 is too low, the catalyst-supported carbon 51 cannot be sufficiently coated with ionomer 52. This makes it difficult for the ionomer to effectively propagate oxonium ions. On the other hand, if the ratio of ionomer 52 to catalyst-supported carbon 51 is too high, the voids in the cathode catalyst layer 31 become smaller. This inhibits the diffusion of oxygen gas in the cathode catalyst layer 31 and the discharge of water produced in the cathode catalyst layer 31.

Therefore, the ratio of the ionomer 52 to the catalyst-supported carbon 51 is such that the catalyst-supported carbon 51 can be well covered with the ionomer 52, and oxygen gas can be diffused and water can be discharged well. It is preferable. Specifically, the ratio (weight ratio) of the ionomer 52 to the catalyst-supporting carbon 51 is preferably 30% by weight or more and 100% by weight or less. Further, it is more preferable that the ratio (weight ratio) of the ionomer 52 to the catalyst-supported carbon 51 is 60% by weight or more and 100% by weight or less. Further, it is more preferable that the ratio (weight ratio) of the ionomer 52 to the catalyst-supported carbon 51 be 75% by weight or more and 85% by weight or less.

Although the polymer electrolyte fuel cell having the membrane electrode assembly 50 has been described above, the membrane electrode assembly of the present invention can be used in a polymer electrolyte water electrolysis device that produces hydrogen by electrolyzing water. It may be something that can be done.

Further, the membrane electrode assembly of the present invention may be used in an organic hydride manufacturing apparatus used in a LOHC (Liquid Organic Hydrogen Carrier) process. An organic hydride manufacturing apparatus having the membrane electrode assembly 50 will be described below.

Figure 3 shows an example of an organic hydride production apparatus. The organic hydride production apparatus in Figure 3 includes a membrane electrode assembly 50 having an electrolyte membrane 10 and a cathode catalyst layer 31 formed on one surface of the electrolyte membrane 10. The composition of the cathode catalyst layer 31 is the same as that of the solid polymer fuel cell described above.

Sulfuric acid is stored in tank 26 on the anode side. The substance to be hydrogenated is stored in tank 36 on the cathode side. An aromatic hydrocarbon compound such as toluene is used as the substance to be hydrogenated.

When a voltage is applied between the cathode catalyst layer 31 and the anode electrode 25 by the power source 41, electrons are supplied to the cathode catalyst layer 31, causing a hydrogenation reaction of the substance to be hydrogenated. This makes it possible to obtain an organic hydride such as methylcyclohexane.

<Catalyst ink>
The cathode catalyst layer 31 of the above-mentioned polymer electrolyte fuel cell, polymer electrolyte water electrolyzer, and organic hydride manufacturing apparatus can be formed by applying catalyst ink to the surface of the electrolyte membrane 10. The catalyst ink in this embodiment is an ink (slurry) in which catalyst-supporting carbon 51 and ionomer 52 are dispersed in a solvent to which a high-boiling point solvent is added.

As the solvent, water, an organic solvent, or a mixed solvent containing water and an organic solvent is used. As the organic solvent, for example, alcohol such as methanol, ethanol, 1-propanol, or 2-propanol may be used. One type of organic solvent may be used alone, or two or more types may be used in combination.

As the solvent, it is preferable to use a mixed solvent of water and an organic solvent. In this case, the mixing ratio of water and organic solvent is preferably water:organic solvent=8:2 to 6:4 by weight.

The high boiling point solvent is an organic solvent having a boiling point equal to or higher than the softening point of the ionomer 52. By including the high boiling point solvent in the catalyst ink, the catalyst ink can be heated to the softening point of the ionomer 52 while the catalyst ink retains its liquid components. As the high boiling point solvent, various organic solvents can be used depending on the softening point of the ionomer 52. For example, one or more solvents selected from N-methyl-2-pyrrolidone, propylene carbonate, polyhydric alcohols, and glycol ethers may be used as the high-boiling solvent.

The proportion of the high boiling point solvent in the entire catalyst ink is preferably 4% by weight or more, more preferably 6% by weight or more.

<Catalyst ink manufacturing procedure>
Below, the manufacturing procedure of the catalyst ink in this embodiment will be explained. FIG. 4 is a flowchart showing the procedure for manufacturing catalyst ink in this embodiment.

In step S101, a mixed liquid is prepared by mixing a solvent, catalyst-supporting carbon 51, ionomer 52, and a high boiling point solvent. At this time, it is preferable that the ionomer 52 is mixed with other materials in the form of an ionomer solution in which a predetermined amount of the ionomer 52 is mixed in a solvent.

When using a mixture of water and an organic solvent as the solvent, it is preferable to mix the catalyst-supported carbon 51 with the water before mixing with the other materials. This makes it possible to prevent ignition due to contact between the catalyst-supported carbon 51 and the organic solvent.

In step S102, the catalyst-supported carbon 51 and ionomer 52 contained in the mixed liquid are uniformly dispersed using a predetermined dispersing machine. This results in the catalyst ink being obtained. As the dispersing machine, for example, a jet mill, a bead mill, or a ball mill can be used.

<Method for manufacturing membrane electrode assembly>
Next, a method for manufacturing the membrane electrode assembly 50 using the above catalyst ink will be described. FIG. 5 is a flowchart showing the manufacturing procedure of the membrane electrode assembly 50.

In step S201, one surface of the electrolyte membrane 10 is coated with a cathode catalyst ink manufactured by the above procedure.

In step S202, the applied catalyst ink is dried by heating to a temperature equal to or higher than the softening point of the ionomer 52. For example, the catalyst ink may be heated and dried by blowing hot air onto the catalyst ink. As a result, a coating film of the cathode catalyst layer 31 is formed on one surface of the electrolyte membrane 10.

Step S202 will be explained using an example in which a mixed solvent of water and ethanol is used as the solvent of the catalyst ink. When the catalyst ink applied to the electrolyte membrane 10 is heated, ethanol first evaporates. If the catalyst ink does not contain a high boiling point solvent, the only liquid component contained in the catalyst ink after ethanol evaporates is water. Therefore, the surface tension of the catalyst ink rapidly increases. After that, when all the liquid components of the catalyst ink evaporate and a coating film of the cathode catalyst layer 31 is formed, the force caused by the high surface tension of water remains inside the coating film, causing cracking and peeling of the coating film. cause it to occur.

On the other hand, in this embodiment, the catalyst ink contains a high boiling point solvent. Therefore, even after the ethanol evaporates, the high boiling point solvent remains in the catalyst ink in addition to water. This makes it possible to reduce the sudden increase in surface tension caused by the evaporation of ethanol. In addition, since the high boiling point solvent evaporates after the water, the coating film of the catalyst layer is formed in a state where the surface tension of the catalyst ink is low. Therefore, the residual stress remaining in the coating film of the cathode catalyst layer 31 can be reduced, and cracking and peeling of the coating film can be suppressed.

Furthermore, because the boiling point of the high-boiling point solvent is higher than the softening point of the ionomer 52, the catalyst ink is heated to the softening point of the ionomer 52 while remaining in a liquid state. This allows the coating of the cathode catalyst layer 31 to be formed with the ionomer 52 in a softened state. This further reduces the residual stress inside the cathode catalyst layer 31. In addition, the adhesion between the cathode catalyst layer 31 and the electrolyte membrane 10 can be improved.

The boiling point of the high-boiling solvent may be higher than the softening point of the polymer resin contained in the electrolyte membrane 10. Then, in step S202, the catalyst ink may be heated to a temperature equal to or higher than the softening point of the polymer resin contained in the electrolyte membrane 10. This allows the coating of the cathode catalyst layer 31 to be formed while the electrolyte membrane 10 is in a softened state. This further improves the adhesion between the electrolyte membrane 10 and the cathode catalyst layer 31.

In step S203, the anode catalyst ink is applied to the other surface of the electrolyte membrane 10.

In step S204, the catalyst ink applied to the other surface of the electrolyte membrane 10 is dried. This results in the anode catalyst layer 21 being formed on the other surface of the electrolyte membrane 10. As a result, a membrane electrode assembly 50 is obtained that includes the electrolyte membrane 10, the anode catalyst layer 21, and the cathode catalyst layer 31.

Note that steps S201 and S202 for forming the cathode catalyst layer 31 and steps S203 and S204 for forming the anode catalyst layer 21 may be reversed in order.

<Example>
Hereinafter, one embodiment of the present invention will be described with reference to examples. Note that the present embodiment is not limited to the following examples.

[Preparation of catalyst layer]
(Examples 1 to 7)
Water was added to the catalyst-supported carbon carrying platinum to obtain a first mixed liquid. Next, ethanol was added to the first mixed liquid to obtain a second mixed liquid. Next, an ionomer solution in which an ionomer was dispersed in a mixed liquid of water and ethanol was added to the second mixed liquid to obtain a third mixed liquid. Next, N-methyl-2-pyrrolidone (NMP) (Examples 1 to 3) or propylene carbonate (Examples 4 to 7), which is a high boiling point solvent, was added to the third mixed liquid to obtain a fourth mixed liquid. The softening point of the ionomer, the boiling point of the high boiling point solvent, and the weight ratio of each component contained in the fourth mixed liquid in each example are as shown in Table 1. Finally, the fourth mixed liquid was dispersed for 15 minutes using a bead mill disperser (manufactured by Imex Co., Ltd.) to obtain a catalyst ink.

Next, the above catalyst ink was applied to the surface of the electrolyte membrane using a die coating method. After that, the catalyst ink was dried by blowing hot air at 125°C for 10 minutes to produce a catalyst layer.

(Comparative Example 1)
In Comparative Example 1, a catalyst ink not containing a high boiling point solvent was prepared. In Comparative Example 1, the catalyst ink was prepared and the catalyst layer was produced in the same manner as in each of the Examples, except that the weight ratios of the components contained in the fourth mixed liquid were as shown in Table 1.

[Evaluation of catalyst layer]
The catalyst layers prepared in the examples and comparative examples were evaluated as follows.

(Crack evaluation)
Immediately after producing the catalyst layer, it was visually observed to evaluate the presence or absence of cracks in the catalyst layer. The cracking of the catalyst layer was evaluated on the following three levels.
A: No cracks B: Slight cracks C: All cracks

(Peeling Evaluation)
Using an ultrasonic tester (manufactured by NSD Corporation), ultrasonic vibration was applied to the catalyst layer for 5 minutes. After that, the catalyst layer was visually observed to evaluate whether the catalyst layer peeled off. The peeling of the catalyst layer was evaluated according to the following three levels.
A: No peeling was observed. B: Slight peeling was observed. C: The entire film was peeled off, exposing the electrolyte membrane.

[result]
The evaluation results of the examples and comparative examples are as shown in Table 1.

(Crack evaluation)
The catalyst layer of Comparative Example 1 had cracks on the entire surface. In the catalyst layer of Example 1, cracking was largely suppressed compared to Comparative Example 1, but slight cracking occurred on a part of the surface. No cracks were observed in the catalyst layers of Examples 2 to 7. From this result, it was found that cracking of the catalyst layer can be suppressed by including a high boiling point solvent in the catalyst ink.

(Peeling Evaluation)
In Comparative Example 1, the entire catalyst layer peeled off. In the catalyst layer of Example 1, peeling was significantly suppressed compared to Comparative Example 1, but slight peeling was confirmed in some parts. In Examples 2 to 7, peeling of the catalyst layer was not confirmed. From these results, it was found that peeling of the catalyst layer can be suppressed by including a high boiling point solvent in the catalyst ink.

1: Cell 10: Electrolyte membrane 21: Anode catalyst layer 22: Anode gas diffusion layer 23: Anode gasket 24: Anode separator 25: Anode electrode 31: Cathode catalyst layer 32: Cathode gas diffusion layer 33: Cathode gasket 34: Cathode separator 40: External circuit 41: Power source 50: Membrane electrode assembly 51: Catalyst-supporting carbon 52: Ionomer 241: Anode separator groove 341: Cathode separator groove 511: Carbon particle 512: Catalyst particle

Claims (9)

a solvent;
a catalyst;
Ionomer and
a high boiling point solvent whose boiling point is higher than the softening point of the ionomer;
Including catalyst ink. 2. The catalyst ink of claim 1,
The catalyst is
Carbon particles;
A catalytic metal supported on the carbon particles;
13. A catalyst ink comprising: The catalyst ink according to claim 1 or claim 2,
A catalyst ink containing 4% by weight or more of the high boiling point solvent. The catalyst ink according to claim 1 or claim 2,
In the catalyst ink, the high boiling point solvent is one or more selected from N-methyl-2-pyrrolidone, propylene carbonate, polyhydric alcohols, and glycol ethers. a) A method for producing a catalyst ink, comprising the step of preparing a mixed liquid by mixing a solvent, a catalyst, an ionomer, and a high-boiling point solvent whose boiling point is equal to or higher than the softening point of the ionomer. 6. A method for producing a catalyst ink according to claim 5, comprising the steps of:
The catalyst is
Carbon particles;
A catalytic metal supported on the carbon particles;
A method for producing a catalyst ink comprising: The catalyst ink manufacturing method according to claim 5 or 6,
In the step a), the mixed liquid is prepared such that the content of the high boiling point solvent in the mixed liquid is 4% by weight or more. 7. A method for producing a catalyst ink according to claim 5 or 6, comprising the steps of:
The method for producing a catalyst ink, wherein the high boiling point solvent is at least one selected from the group consisting of N-methyl-2-pyrrolidone, propylene carbonate, polyhydric alcohols, and glycol ethers. A) a step of applying the catalyst ink according to claim 1 or claim 2 to an electrolyte membrane;
B) heating and drying the catalyst ink applied to the electrolyte membrane at a temperature higher than the softening point of the ionomer and lower than the boiling point of the high-boiling solvent;
A method for manufacturing a membrane electrode assembly, comprising:

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