JP2024078583A - Catalyst layer and electrolyte membrane-electrode assembly for fuel cells - Google Patents

Abstract

The present disclosure provides a catalyst layer for a highly efficient fuel cell, which improves the amount of proton transfer supplied to a catalyst support.
[Solution] The catalyst layer in the present disclosure comprises a catalyst, an electrically conductive catalyst support having the catalyst supported inside its pores, and a proton conductive ionomer coating the catalyst support. The catalyst support has a surface crystallinity of 58% or more, which reduces the contact area between the ionomer and the catalyst support surface and increases the coating thickness of the ionomer coating the surface of the catalyst support, making it easier for spaced catalyst supports to come into contact with each other via the ionomer and increasing the contact area via the ionomer, thereby improving the amount of proton transfer supplied to the catalyst support.
[Selected figure] Figure 8

Description

This disclosure relates to a catalyst layer and an electrolyte membrane-electrode assembly for a fuel cell.

Patent Document 1 discloses a catalyst support material that suppresses catalyst poisoning by ionomers by supporting the catalyst in the pores of the catalyst support. This catalyst support material includes a catalyst support having pores, a catalyst, and an ionomer that coats the catalyst support with the catalyst supported in the pores.

JP 2020-64852 A

The present disclosure provides a catalyst layer for a highly efficient fuel cell that can improve the amount of proton transfer supplied to the catalyst carrier by reducing the contact area between the ionomer and the catalyst carrier surface and increasing the ionomer coating thickness.

The catalyst layer of the fuel cell in this disclosure comprises a catalyst, a conductive catalyst carrier that supports the catalyst inside the pores, and a proton-conductive ionomer that coats the catalyst carrier, and the catalyst carrier is characterized in that the degree of crystallinity of the surface is 58% or more.

The catalyst layer of the fuel cell disclosed herein uses a catalyst carrier with a high degree of surface crystallinity, which reduces the contact area between the ionomer and the catalyst carrier surface.

As a result, the ionomer is arranged in a direction approximately perpendicular to the catalyst carrier surface, increasing the thickness of the ionomer coating on the catalyst carrier surface, making it easier for spaced catalyst carriers to come into contact with each other via the ionomer and increasing the contact area via the ionomer, thereby increasing the proton path and improving the amount of proton transfer supplied to the catalyst carrier.

This makes it possible to provide a highly efficient fuel cell catalyst layer that improves catalyst utilization while suppressing catalyst poisoning by ionomers.

FIG. 2 is a schematic diagram showing a cross section of a catalyst support material in which a catalyst is supported on a catalyst support in a catalyst layer of the fuel cell according to the first embodiment; FIG. 1 is a cross-sectional view showing a schematic view of a cathode portion of an electrolyte membrane-electrode assembly in which the catalyst layer of the fuel cell according to the first embodiment is used as the cathode. FIG. 2 is an enlarged view of a main part of the catalyst layer of the fuel cell according to the first embodiment, showing a state in which the catalyst carrier is covered with an ionomer; FIG. 1 is a cross-sectional view showing a schematic configuration of an electrolyte membrane-electrode assembly in which the catalyst layer of the fuel cell according to the first embodiment is used as a cathode. FIG. 1 is a schematic diagram showing the structure of an ionomer according to a first embodiment of the present invention. FIG. 1 is a characteristic diagram showing the relationship between the crystallinity and electrochemically active surface area of the catalyst support used in the catalyst layer of the fuel cell according to the first embodiment. A flowchart showing a manufacturing process of a catalyst layer of a fuel cell according to the first embodiment. FIG. 1 is an explanatory diagram for explaining the effect of the crystallinity of the catalyst support used in the catalyst layer of the fuel cell in the first embodiment on the coating of the ionomer, and the effect of the crystallinity of the catalyst support on the continuity of the ionomer of the cathode catalyst.

(Knowledge and other information that forms the basis of this disclosure)
At the time when the inventors arrived at this disclosure, it was believed that the technology of forming a three-phase interface in the catalyst layer of a fuel cell would improve performance by contacting the catalyst with an ionomer from the viewpoint of proton supply. However, in recent years, it has been found that the catalyst is poisoned by the ionomer when the ionomer comes into contact with the catalyst, and this actually reduces the performance.

Therefore, in order to prevent the poisoning of catalysts by ionomers, the industry has generally designed products in such a way that the ionomers are not in contact with the catalyst by encapsulating the catalyst in a catalyst carrier with large mesopores, such as a mesoporous material.

However, catalyst carriers with large mesopores, such as mesoporous materials, have a low bulk density, which results in a thick catalyst layer. Even when a specified amount of ionomer is introduced, the cross-sectional area of the proton passages through the ionomer to conduct protons perpendicular to the electrolyte membrane to distant catalyst carriers is insufficient, resulting in an insufficient supply of protons throughout the entire catalyst layer.

In the catalyst layer, if the amount of ionomer is increased to sufficiently expand the cross-sectional area of the proton passage through the ionomer to conduct protons perpendicular to the electrolyte membrane to a distant catalyst support, the catalyst will become more poisoned by the ionomer, and this poisoning will reduce the activity of the catalyst. Therefore, increasing the proton path and suppressing catalyst poisoning are contradictory phenomena, and it is difficult to achieve both with conventional thinking.

Under these circumstances, the inventors learned that when the surface of the catalyst carrier is hydrophobized, the number of functional groups on the catalyst carrier surface decreases, and the number of bonds between the functional groups on the catalyst carrier surface and the functional groups of the ionomer decreases, resulting in a decrease in the contact area between the ionomer and the catalyst carrier surface, and the non-contact ionomer that does not come into contact with the catalyst carrier is disposed around the catalyst carrier.

Then, we came up with the idea that if we could reduce the contact area between the ionomer and the catalyst carrier surface by hydrophobizing the surface of the catalyst carrier in the catalyst layer, it would be possible to suppress poisoning of the catalyst by the ionomer while making it easier for spaced catalyst carriers to come into contact with each other via the ionomer, and the contact area via the ionomer would increase, thereby increasing the proton path and expanding the area of the catalyst layer that can supply protons.

The inventors then discovered that in order to realize this idea, it was necessary to appropriately control the crystallinity of the surface of the catalyst support, and they came to form the subject of the present disclosure in order to solve this problem.

Therefore, the present disclosure provides a highly efficient catalyst layer that can improve the amount of proton transfer supplied to the catalyst carrier while suppressing catalyst poisoning by ionomers by improving the crystallinity of the surface of the catalyst carrier.

Hereinafter, the embodiments will be described in detail with reference to the drawings. However, more detailed description than necessary may be omitted. For example, detailed description of already well-known matters or duplicate description of substantially the same configuration may be omitted.

The accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter described in the claims.

(Embodiment 1)
Hereinafter, the first embodiment will be described with reference to FIGS.

[1-1. Configuration]
(Electrochemical Devices)
As shown in FIG. 4, the electrochemical device 40 has a configuration in which an electrolyte membrane-electrode assembly 30 is sandwiched between a cathode separator 24 and an anode separator 28 .

(Electrolyte Membrane-Electrode Assembly)
4, the electrolyte membrane-electrode assembly 30 is composed of an electrolyte membrane 21, a cathode 34 including a cathode catalyst layer 22 and a cathode gas diffusion layer 23, and an anode 35 including an anode catalyst layer 26 and an anode gas diffusion layer 27. The electrolyte membrane-electrode assembly 30 is configured such that the electrolyte membrane 21 is sandwiched between the cathode 34 and the anode 35.

The electrolyte membrane 21 is a membrane that conducts protons between the cathode 34 and the anode 35, and must have both proton conductivity and gas barrier properties.

In the electrolyte membrane-electrode assembly 30 of this embodiment, a perfluorosulfonic acid resin membrane is used as the electrolyte membrane 21. Perfluorosulfonic acid resin membranes have high proton conductivity and can exist stably even in the power generation environment of a fuel cell, for example. The membrane thickness of the electrolyte membrane 21 is 10 μm. If the membrane thickness of the electrolyte membrane 21 is 10 μm, high gas barrier properties and high proton conductivity can be obtained.

The gas diffusion layers (cathode gas diffusion layer 23 and anode gas diffusion layer 27) are layers that combine current collection properties with gas permeability and water repellency, and have a substrate and a coating layer.

In the electrolyte membrane-electrode assembly 30 of this embodiment, carbon paper, a material with excellent electrical conductivity and gas and liquid permeability, is used as the base material for the gas diffusion layer.

The coating layer is interposed between the substrate and the catalyst layer (cathode catalyst layer 22 and anode catalyst layer 26) to reduce the contact resistance between the substrate and the catalyst layer and improve water drainage.

In the electrolyte membrane-electrode assembly 30 of this embodiment, the coating layer of the gas diffusion layer is made of carbon black, which is a conductive material, and polytetrafluoroethylene, which is a water-repellent resin.

The cathode catalyst layer 22 is a layer that promotes the rate of electrochemical reactions in the electrode. The cathode catalyst layer 22 contains the catalyst support material 5 shown in FIG. 1.

In FIG. 2, the effective catalyst layer area 7 is the area of the cathode catalyst layer 22 where protons can reach from the electrolyte membrane 21.

(Catalyst Support Material)
1 and 2, the catalyst support material 5 includes a conductive catalyst support 1 having pores 4, a catalyst 2 supported on the catalyst support 1, and an ionomer 3 having a hydrophilic functional group (side chain) and a hydrophobic main chain. The catalyst support material 5 supports the catalyst 2 at least inside the pores of the porous and conductive catalyst support 1, and a part of the outer surface of the catalyst support 1 is covered with the ionomer 3.

The catalyst 2 is divided into an extra-pore catalyst 2a supported on the outer surface of the catalyst carrier 1, and an intra-pore catalyst 2b supported in a portion deeper than the opening of the pores 4 that connect the outer surface of the catalyst carrier 1 to the inside.

In this embodiment, mesoporous carbon is used as an example of the catalyst carrier 1 used in the catalyst support material 5, but the catalyst carrier 1 is not limited to mesoporous carbon. The catalyst carrier 1 may be a material other than mesoporous carbon as long as it has the same pore diameter and pore volume as mesoporous carbon and is conductive.

Materials other than mesoporous carbon that can be used for the catalyst carrier 1 include, for example, materials composed of oxides of titanium, tin, niobium, tantalum, zirconium, aluminum, silicon, etc.

The mesoporous carbon used in the catalyst carrier 1 in this embodiment has pores 4 that communicate from the outer surface to the inside, as shown in Figures 1 and 2. The mode diameter of the pores 4 in this mesoporous carbon is 5 nm. If the mode diameter of the pores 4 is 5 nm or more, a large amount of catalyst 2 can be supported inside the catalyst carrier 1.

The mesoporous carbon used in the catalyst carrier 1 is configured to have an average particle size of 200 nm or more and 1000 nm or less. If the average particle size of the mesoporous carbon is 200 nm or more, the particle size of the mesoporous carbon that is the catalyst carrier 1 is sufficiently large relative to the length of the ionomer 3, so the area where the ionomer 3 penetrates into the pores 4 is small relative to the pore volume of the pores 4, and the proportion of the catalyst 2 that is affected by poisoning by the ionomer 3 is small.

In FIG. 3, the ionomer 3 covers the outer surface of the catalyst carrier 1. The ionomer coverage area 6 refers to the area of the catalyst carrier 1 that is covered by the ionomer 3. Protons supplied from outside the catalyst support material 5 are transported via the ionomer 3 adsorbed on the outer surface of the catalyst carrier 1 to the outer pore catalyst 2a present on the outer surface of the catalyst carrier 1 or the inner pore catalyst 2b present inside the pores 4 of the catalyst carrier 1.

The material of catalyst 2 (outside pore catalyst 2a and inside pore catalyst 2b) contains platinum and a metal different from platinum. Examples of metals different from platinum include cobalt, nickel, manganese, titanium, aluminum, chromium, iron, molybdenum, tungsten, ruthenium, palladium, rhodium, iridium, osmium, copper, and silver. Among them, an alloy of platinum and cobalt is preferable because it has high catalytic activity for the oxygen reduction reaction and good durability in the power generation environment of the fuel cell.

In this embodiment, the catalyst 2 used in the catalyst support material 5 has a molar ratio of platinum and metals other than platinum to the total metals in the catalyst 2 of 0.25 or more, and the metal other than platinum contained in the catalyst 2 is cobalt. Catalyst 2 with this composition exhibits high activity.

Cobalt, for example, is prone to elution in the power generation environment of a fuel cell, and when power is generated for a long period of time, this leads to a decrease in the power generation performance of the fuel cell. Therefore, by setting the molar ratio of cobalt to platinum (cobalt/platinum) in catalyst 2 to 1 or less, it is possible to suppress such a decrease in power generation performance. The composition of catalyst 2 is expressed as PtxCo (x is 1 or more and 4 or less).

The ionomer 3 transmits the protons that have passed through the electrolyte membrane 21 to the catalyst 2 in the cathode catalyst layer 22.

In this embodiment, the ionomer 3 is a perfluorosulfonic acid resin, which is an ion exchange resin of the same quality as the electrolyte membrane 21. This perfluorosulfonic acid resin is preferable because it has high proton conductivity among ion exchange resins and exists stably even in the power generation environment of a fuel cell.

As shown in FIG. 5, the ionomer 3 used in the cathode catalyst layer 22 of this embodiment has a polymer chain made of a random copolymer and a sulfonic acid group bonded to the polymer chain, and also has a hydrophobic portion and a hydrophilic portion. Here, the molecular structure of the polymer chain of the ionomer 3 is not particularly limited. In addition, the polymer chain is a fluorine-based polymer containing a C-F bond.

The hydrophilic portion in ionomer 3 refers to the smallest repeating unit in the polymer chain where a sulfonic acid group is bonded, as shown in Figure 5. The hydrophilic portion has a sulfonic acid group in one of its parts. The number of hydrophilic portions affects the poisoning of catalyst 2. Hydrophilic portions are easily bonded to catalyst 2, and catalyst 2 bonded to hydrophilic portions inhibits the oxygen reduction reaction with oxygen in the gas, so the catalytic activity of catalyst 2 decreases.

The hydrophobic portion in the ionomer 3 refers to the smallest repeating unit in the polymer chain to which no acid groups (such as sulfonic acid groups, carboxylic acid groups, or phosphonic acid groups) are bonded, as shown in FIG. 5. The structure of the hydrophobic portion is not particularly limited. The weight ratio of the ionomer 3 to the total weight of the carbon contained in the cathode catalyst layer 22 is 0.8 to 1.5. This carbon is mesoporous carbon.

The ionomer 3 covers at least a portion of the outer surface of the catalyst carrier 1. The catalyst carrier 1 has a large number of pores 4, which is useful for suppressing poisoning of the catalyst 2 by the ionomer 3 and obtaining a fuel cell catalyst in which the catalyst 2 is supported at a high loading density.

(Catalyst layer manufacturing process)
Based on the above, a description will be given of the manufacturing process of the cathode catalyst layer 22 in the electrochemical device 40. Fig. 7 is a flow chart showing the manufacturing process of the catalyst layer.

(High crystallization treatment process)
First, a method for producing the cathode catalyst layer 22 in the electrochemical device 40 will be described with reference to FIG.

Catalyst support material 5 (Tanaka Precious Metals, TECCo (PMPC-S2) 52-PN), in which the designed pore size of catalyst support 1 is 5 nm and the catalyst 2 loading rate in catalyst support 1 is 50 wt%, is sintered at a temperature of 2500°C for 5 to 20 hours in a nitrogen atmosphere. In this way, the crystallinity (%) of catalyst support 1 is improved by graphitization. Here, the crystallinity (%) is expressed by the following (Equation 1) for the [002] face of catalyst support 1.

In this way, the high crystallization treatment process (S01) was carried out.

(Ink adjustment process)
A catalyst support material 5 including a catalyst carrier 1 that has been subjected to a high crystallization treatment in the high crystallization treatment step (S01) is put into a mixed solvent containing ethanol and water in a weight ratio of ethanol:water = 1:1, and further, an ionomer 3 (IQ100B, manufactured by AGC Inc.) is added in an amount such that the weight ratio of ionomer 3 to the carbon weight of the catalyst support material 5 is 1.0, thereby preparing a slurry with a solid concentration of 7%.

The adjusted slurry was pulverized at 100 MPa using a wet atomizer (Starburst, manufactured by Sugino Machine). The pulverized slurry was then stirred for 20 minutes in a variable-rotation mixer (Mazerustar, manufactured by Kurabo Industries, Ltd.). The stirred slurry, which was the catalyst ink, was aged at room temperature for 12 hours for degassing. In this manner, the ink adjustment process (S02) was carried out.

(Coating process)
The catalyst ink for the cathode catalyst layer 22 prepared as described above was applied to approximately the center of one of the main surfaces of the electrolyte membrane 21 by extruding it using a slot die coating method (S03), and then dried, thereby preparing the cathode catalyst layer 22 on one of the main surfaces of the electrolyte membrane 21.

The following examples and comparative examples were carried out using the cathode catalyst layer 22 prepared as described above.

The cathode catalyst layer 22 of Example 1 was produced under the same conditions as the above-mentioned production method of the embodiment, except that in the high crystallization treatment step, the catalyst support material 5 was baked for 10 hours under a nitrogen atmosphere.

The cathode catalyst layer 22 of Example 2 was produced under the same conditions as the above-mentioned production method of the embodiment, except that in the high crystallization treatment process, the catalyst support material 5 was baked for 20 hours under a nitrogen atmosphere.

The comparative cathode catalyst layer 22 was produced under the same conditions as the above-mentioned production method of the embodiment, except that in the high crystallization treatment process, the catalyst support material 5 was baked for 5 hours under a nitrogen atmosphere.

Next, an anode catalyst layer 26 was formed in the approximate center of the main surface of the electrolyte membrane 21 on which the cathode catalyst layer 22 of Example 1, Example 2, and Comparative Example was provided, opposite the surface on which the cathode catalyst layer 22 was provided.

The anode catalyst layer 26 was prepared as follows. First, a commercially available platinum-supported carbon black catalyst (Tanaka Kikinzoku Kogyo Co., Ltd., TEC10E50E) was added to a mixed solvent containing equal amounts of water and ethanol and stirred to prepare a slurry.

Next, an amount of ionomer 3 was added to the prepared slurry such that the weight ratio of ionomer (IQ100B, manufactured by AGC Inc.) to the carbon of the platinum carbon black catalyst was 0.6, and the mixture was stirred for 20 minutes using a variable-rotation, planetary-axis mixer (Mazerustar, manufactured by Kurabo Industries, Ltd.).

The catalyst ink for the anode catalyst layer 26 thus prepared was applied by spraying to approximately the center of the main surface of the electrolyte membrane 21 opposite the cathode catalyst layer 22 side, on which the cathode catalyst layer 22 is provided, and then dried to prepare the anode catalyst layer 26 on the main surface of the electrolyte membrane 21 opposite the cathode catalyst layer 22 side.

A gas diffusion layer (GDL25BC, manufactured by SGL Carbon Japan Co., Ltd.) was placed on the exposed surface of each of the cathode catalyst layer 22 and anode catalyst layer 26 of Examples 1, 2, and the Comparative Example, and a pressure of 1 MPa was applied for 5 minutes in a high-temperature environment of 140°C to produce the electrolyte membrane-electrode assemblies 30 of Examples 1, 2, and the Comparative Example.

The obtained electrolyte membrane-electrode assemblies 30 of Examples 1, 2, and Comparative Example were sandwiched between a cathode separator 24 having a serpentine-shaped flow path formed in a groove on the surface facing the cathode 34 of the electrolyte membrane-electrode assembly 30, and an anode separator 28 having a serpentine-shaped flow path formed in a groove on the surface facing the anode 35 of the electrolyte membrane-electrode assembly 30, and then assembled into a specified jig to produce the electrochemical devices 40 of Examples 1, 2, and Comparative Example, which serve as fuel cell cells.

[1-2. motion]
The operation and function of the electrochemical device 40 configured as above will be described below.

The temperature of the electrochemical device 40 was kept at 65°C, and hydrogen with a dew point of 60°C was supplied to the flow path between the anode separator 28 and the anode 35, and nitrogen with a dew point of 65°C was supplied to the flow path between the cathode separator 24 and the cathode 34.

The working electrode of a potentio-galvanostat (HZ-3000, Hokuto Denko Corporation) was connected to the cathode 34, and the counter electrode and reference electrode were connected to the anode 35, and cyclic voltammetry was measured to measure the amount of electricity resulting from hydrogen adsorption by Pt.

The obtained quantity of electricity was divided by the theoretical value of the hydrogen adsorption quantity of electricity per unit surface area of Pt (0.21 mC/cm ² ) to calculate the electrochemically active surface area (m ² /g-Pt).

In this way, the results of the electrochemically active surface area when the crystallinity (%) of the catalyst carrier 1, expressed by (Equation 1), is changed in the electrochemical devices 40 produced in Example 1, Example 2, and Comparative Example are shown in Figure 6.

In the comparative example, the crystallinity of the catalyst support 1 was 38% and the electrochemically active surface area was 38.6 m ² /g-Pt, whereas in Example 1, the crystallinity of the catalyst support 1 was 65% and the electrochemically active surface area was 45.1 m ² /g-Pt, and in Example 2, the crystallinity of the catalyst support 1 was 95% and the electrochemically active surface area was 43.6 m ² /g-Pt.

The change in electrochemically active surface area versus the degree of crystallinity (%) of the catalyst support 1 in Figure 6 can be explained as shown in Figure 8. The sulfonic acid groups, which are the hydrophilic parts of the ionomer 3, strongly interact with and adsorb to the hydrophilic functional groups (OH groups, COOH groups, etc.) on the surface of the catalyst support 1 or the outside pore catalyst 2a.

At this time, the ionomer 3 is more thermodynamically stable when adsorbed on the surface of the catalyst carrier 1 than when dispersed in the ink slurry.

Therefore, when the crystallinity (%) of the catalyst carrier 1 is low, at 38%, as in the comparative example, there are many hydrophilic functional groups (OH groups, COOH groups, etc.) on the surface of the catalyst carrier 1, and the coverage area of the ionomer 3 on the catalyst carrier 1 becomes large.

This reduces the thickness of the ionomer 3 coating the outer surface of the catalyst carrier 1. When considering the cathode catalyst layer 22, the small thickness of the ionomer 3 coating the outer surface of the catalyst carrier 1 reduces the area of contact between adjacent catalyst support materials 5 via the ionomer 3, reducing the effective catalyst layer area 7 and thus reducing the electrochemically active surface area.

On the other hand, when the crystallinity (%) of the catalyst carrier 1 is increased to 65% as in Example 1, the amount of hydrophilic functional groups (OH groups, COOH groups, etc.) on the surface of the catalyst carrier 1 decreases. Therefore, the amount of sulfonic acid groups, which are the hydrophilic part of the ionomer 3, adsorbed via the hydrophilic functional groups (OH groups, COOH groups, etc.) on the surface of the catalyst carrier 1 or the outside pore catalyst 2a decreases.

Therefore, the coverage area of the ionomer 3 on the catalyst carrier 1 in Example 1 is smaller than that in the comparative example, and the coverage thickness of the ionomer 3 covering the catalyst carrier 1 is greater than that in the comparative example.

In Example 1, when considering the cathode catalyst layer 22, the coating thickness of the ionomer 3 coating the catalyst support 1 is large, so the area of contact between adjacent catalyst support materials 5 via the ionomer 3 is reduced compared to the comparative example, and it is believed that by expanding the effective catalyst layer area 7, the electrochemically active surface area could be expanded to 45.1 m ² /g-Pt.

Furthermore, when the crystallinity (%) of the catalyst support 1 is increased to 95% as in Example 2, the amount of hydrophilic functional groups (OH groups, COOH groups, etc.) on the surface of the catalyst support 1 is further reduced. Therefore, the amount of sulfonic acid groups, which are the hydrophilic parts of the ionomer 3, adsorbed via the hydrophilic functional groups (OH groups, COOH groups, etc.) on the surface of the catalyst support 1 or the outside pore catalyst 2a is further reduced compared to Example 1. Therefore, the contact area between the ionomer 3 and the catalyst support 1 becomes too small, making it impossible to supply sufficient protons to the catalyst support 1, and it is believed that the electrochemically active surface area in Example 2 decreased again to 43.6 m ² /g-Pt.

Regarding the electrochemically active surface area, the value of the electrochemically active surface area in Example 2 (43.6 m ² /g-Pt) is about 4% lower than the value of the electrochemically active surface area in Example 1 (45.1 m ² /g-Pt), but is still sufficient as the effective catalyst layer region 7.

Assuming that the electrochemically active surface area increases linearly in the range of crystallinity (%) of catalyst support 1 from 38% to 65%, the crystallinity (%) value of catalyst support 1 that provides an electrochemically active surface area equivalent to the electrochemically active surface area value of 43.6 m ² /g-Pt in Example 2 can be calculated to be 58%.

Therefore, if the crystallinity (%) of the catalyst carrier 1 is 58% or more, it is believed possible to obtain an electrochemically active surface area equal to or greater than that of Example 2.

From the above, by carrying out an appropriate high crystallization treatment process as in Example 1, it is possible to provide a highly efficient cathode catalyst layer 22 by expanding the effective catalyst layer area 7 in the cathode catalyst layer 22, increasing the available surface area of the catalyst 2, and improving the utilization rate of the catalyst 2.

[1-3. Effects, etc.]
As described above, in this embodiment, the cathode catalyst layer 22 comprises the catalyst 2, the conductive catalyst support 1 supporting the catalyst 2 at least inside the pores 4, and the proton-conductive ionomer 3 coating the catalyst support 1. The catalyst support 1 is characterized in that the degree of crystallinity of its surface is 58% or more.

By controlling the degree of crystallinity (%) of the surface of the catalyst carrier 1 to 58% or more, the number of functional groups on the surface of the catalyst carrier 1 is reduced, and the number of bonds between the functional groups on the surface of the catalyst carrier 1 and the hydrophilic parts contained in the ionomer 3 is reduced.

As a result, the contact area between the ionomer 3 and the surface of the catalyst carrier 1 is reduced, so that the non-contact ionomer 3 that does not come into contact with the surface of the catalyst carrier 1 is arranged around the catalyst carrier 1, and the distance from the catalyst carrier 1 increases, allowing the coating thickness of the ionomer 3 on the catalyst carrier 1 to be increased.

The catalyst carriers 1 spaced apart from each other can easily come into contact with each other via the ionomer 3, and the contact area via the ionomer 3 can be increased, thereby increasing the proton path, reducing the resistance to proton movement, and expanding the effective catalyst layer area 7 to which protons can be supplied. This makes it possible to obtain a highly efficient cathode catalyst layer 22 with improved catalyst utilization while suppressing catalyst poisoning by the ionomer.

As in this embodiment, the catalyst carrier 1 used in the cathode catalyst layer 22 may have a crystallinity (%) of the surface of the catalyst carrier 1 of 95% or less.

By setting the degree of crystallinity (%) of the surface of the catalyst carrier 1 to 95% or less, the proportion of ionomer 3 that is not in contact with the surface of the catalyst carrier 1 can be suppressed to a predetermined value or less. Therefore, the gaps formed between the catalyst carriers 1 are not blocked by the ionomer 3 that is not in contact with the surface of the catalyst carrier 1, and the gap diameter can be set to a predetermined value or more.

As a result, the gaps formed between the catalyst support materials 5 are not blocked by the ionomer 3, and oxygen can diffuse through the gaps formed between the catalyst support materials 5 and be supplied to the vicinity of the catalyst 2, thereby increasing the number of available catalysts 2 and obtaining a highly efficient cathode catalyst layer 22.

As in this embodiment, the cathode catalyst layer 22 may have a thickness of 10 μm or more.

By increasing the coating thickness of the ionomer 3 on the catalyst carrier 1, proton conductivity can be improved through the ionomer 3 even if the thickness of the cathode catalyst layer 22 is 10 μm or more. Therefore, protons are sufficiently supplied from the electrolyte membrane 21 to the catalyst 2 supported on the catalyst carrier 1, so that the number of available catalysts 2 can be increased and a highly efficient cathode catalyst layer 22 can be obtained.

As in this embodiment, the electrochemical device 40 includes an electrolyte membrane 21, an anode 35 provided on one main surface of the electrolyte membrane 21, and a cathode 34 provided on the other main surface of the electrolyte membrane 21, and the cathode 34 may include the cathode catalyst layer 22 of this embodiment.

As a result, the cathode 34 in the electrolyte membrane-electrode assembly 30 has a cathode catalyst layer 22 composed of a catalyst support material 5 having a catalyst carrier 1 whose crystallinity has been improved by a high crystallization process.

As a result, by reducing the contact area between the ionomer 3 and the surface of the catalyst carrier 1, it is possible to suppress poisoning of the catalyst by the ionomer, while reducing the resistance to proton movement and expanding the effective catalyst layer area 7 to which protons can be supplied, resulting in a highly efficient cathode catalyst layer 22 and making the electrolyte membrane-electrode assembly 30 more efficient.

Other Embodiments
As described above, the first embodiment has been described as an example of the technology disclosed in the present application. However, the technology in the present disclosure is not limited to this, and can be applied to embodiments in which modifications, substitutions, additions, omissions, etc. are made. In addition, it is also possible to combine the components described in the first embodiment to create a new embodiment.

Therefore, other embodiments are given below as examples.

In the first embodiment, an example was described in which a catalyst carrier 1 with a mode diameter of pores 4 of 5 nm was used in the cathode catalyst layer 22. The mode diameter of the pores 4 of the catalyst carrier 1 used in the cathode catalyst layer 22 may be 3 nm or more and 10 nm or less. Therefore, the mode diameter of the pores 4 of the catalyst carrier 1 used in the cathode catalyst layer 22 is not limited to 6 nm.

However, if a catalyst carrier 1 with a mode diameter of pores 4 of 3 nm or more is used in the cathode catalyst layer 22, the partial pressure of oxygen in the air (oxygen-containing gas) in the pores 4 can be improved. Also, if a catalyst carrier 1 with a mode diameter of pores 4 of 10 nm or less is used in the cathode catalyst layer 22, the ionomer 3 is less likely to penetrate into the pores 4, so a highly efficient cathode catalyst layer 22 can be obtained.

In the first embodiment, an example was described in which a mesoporous material (mesoporous carbon) having pores 4 of a size called mesopores was used for the catalyst carrier 1 of the cathode catalyst layer 22. The catalyst carrier 1 used for the cathode catalyst layer 22 only needs to have excellent electrical conductivity and water repellency. Therefore, the catalyst carrier 1 used for the cathode catalyst layer 22 is not limited to a mesoporous material having pores 4 of a size called mesopores.

However, if a mesoporous material having pores 4 of a size called mesopores is used as the catalyst carrier 1 for the cathode catalyst layer 22, a highly efficient cathode catalyst layer 22 can be obtained because of its high mass activity.

Ketjen black may also be used as the catalyst carrier 1 used in the cathode catalyst layer 22. If ketjen black is used as the catalyst carrier 1 used in the cathode catalyst layer 22, it can have excellent electrical conductivity and drainage properties, and therefore a highly efficient cathode catalyst layer 22 can be obtained.

In the first embodiment, the catalyst 2 supported inside the pores 4 of the catalyst carrier 1 is a cathode catalyst layer 22 made of platinum and a metal other than platinum. The catalyst 2 of the cathode catalyst layer 22 may be made of a material that allows an oxidation-reduction reaction to proceed. Therefore, the material of the catalyst 2 supported inside the pores 4 of the catalyst carrier 1 of the cathode catalyst layer 22 is not limited to platinum.

If cobalt, nickel, manganese, titanium, aluminum, chromium, iron, molybdenum, tungsten, ruthenium, palladium, rhodium, iridium, osmium, copper, silver, etc. are used as a metal other than platinum in the catalyst 2 supported inside the pores 4 of the catalyst carrier 1 of the cathode catalyst layer 22, a highly efficient cathode catalyst layer 22 can be obtained because it has high mass activity.

Cobalt may also be used as the metal different from platinum in catalyst 2. By using cobalt as the metal different from platinum in catalyst 2, a catalyst 2 with excellent mass activity and durability can be produced.

In the first embodiment, an electrolyte membrane-electrode assembly 30 using an electrolyte membrane 21 with a thickness of 10 μm has been described. The thickness of the electrolyte membrane 21 used in the electrolyte membrane-electrode assembly 30 may be 5 μm or more and 50 μm or less. Therefore, the thickness of the electrolyte membrane 21 used in the electrolyte membrane-electrode assembly 30 is not limited to 10 μm.

If the thickness of the electrolyte membrane 21 used in the electrolyte membrane-electrode assembly 30 is 5 μm or more, high gas barrier properties can be obtained. Also, if the thickness of the electrolyte membrane 21 used in the electrolyte membrane-electrode assembly 30 is 50 μm or less, the resistance of protons moving through the electrolyte membrane 21 can be reduced, resulting in high proton conductivity.

In the first embodiment, the method of producing the cathode catalyst layer 22 was described using a slot die coating method. The method of producing the cathode catalyst layer 22 may be any method that is commonly used for the electrolyte membrane-electrode assembly 30. Therefore, the method of producing the cathode catalyst layer 22 is not limited to the slot die coating method.

However, if the slot die coating method is used as a method for producing the cathode catalyst layer 22, the catalyst ink is not exposed to air until it is applied to the electrolyte membrane, allowing for stable coating, and the catalyst ink can be applied without waste, making it possible to produce a uniform catalyst layer the size of the slot die width. In addition, the adhesion between the cathode catalyst layer 22 and the cathode gas diffusion layer 23 is good.

The above-described embodiments are intended to illustrate the technology disclosed herein, and various modifications, substitutions, additions, omissions, etc. may be made within the scope of the claims or their equivalents.

This disclosure is useful, for example, in the cathode of an electrolyte membrane-electrode assembly that constitutes a cell of a fuel cell. Specifically, this disclosure can be applied to fuel cell stacks, etc.

REFERENCE SIGNS LIST 1 Catalyst support 2 Catalyst 2a Catalyst outside pores 2b Catalyst inside pores 3 Ionomer 4 Pore 5 Catalyst support material 6 Ionomer coating area 7 Effective catalyst layer area 21 Electrolyte membrane 22 Cathode catalyst layer 23 Cathode gas diffusion layer 24 Cathode separator 26 Anode catalyst layer 27 Anode gas diffusion layer 28 Anode separator 30 Electrolyte membrane-electrode assembly 34 Cathode 35 Anode 40 Electrochemical device

Claims (5)

A catalyst, a conductive catalyst support having the catalyst supported at least inside pores, and a proton-conductive ionomer coating the catalyst support,
A catalyst layer for a fuel cell, wherein the catalyst support has a surface crystallinity of 58% or more. The catalyst layer of the fuel cell according to claim 1, wherein the catalyst support has a surface crystallinity of 95% or less. The catalyst layer of the fuel cell according to claim 1 or 2, characterized in that the catalyst layer has a thickness of 10 μm or more. an electrolyte membrane, an anode provided on one main surface of the electrolyte membrane, and a cathode provided on the other main surface of the electrolyte membrane;
3. An electrolyte membrane-electrode assembly, wherein the cathode comprises the catalyst layer of the fuel cell according to claim 1. an electrolyte membrane, an anode provided on one main surface of the electrolyte membrane, and a cathode provided on the other main surface of the electrolyte membrane;
The electrolyte membrane-electrode assembly, wherein the cathode comprises the catalyst layer of the fuel cell according to claim 3.

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