JP2022168133A - Electrode catalyst layer, membrane electrode assembly, and polymer electrolyte fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode catalyst layer for a polymer fuel cell capable of improving drainage and gas diffusibility and capable of high output.

SOLUTION: Electrocatalyst layers 2 and 3 are bonded to a polymer electrolyte membrane. The electrode catalyst layers 2 and 3 have a catalyst 13, carbon particles 14, a polymer electrolyte 15, and a fibrous substance 16. The fiber diameter of the fibrous substance 16 is 10 nm or more and 300 nm or less. The fibrous substance 16 has a fiber length of 1 μm or more and 50 μm or less and a density of 900 mg/cm³ or less.

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2023,JPO&INPIT

Description

TECHNICAL FIELD The present invention relates to an electrode catalyst layer that constitutes a membrane electrode assembly for a polymer fuel cell.

In recent years, fuel cells have attracted attention as an effective solution to environmental and energy problems. A fuel cell oxidizes a fuel such as hydrogen with an oxidant such as oxygen and converts the associated chemical energy into electrical energy.
Fuel cells are classified into alkaline type, phosphoric acid type, polymer type, molten carbonate type, solid oxide type, etc., according to the type of electrolyte. Polymer fuel cells (PEFCs) operate at low temperatures, have high output density, and can be made smaller and lighter. there is

A polymer electrolyte fuel cell (PEFC) comprises a membrane electrode assembly in which a polymer electrolyte membrane is sandwiched between a pair of electrodes consisting of a fuel electrode (anode) and an air electrode (cathode). By supplying an oxidant gas containing oxygen to the air electrode side of the fuel gas containing hydrogen, power is generated by the following electrochemical reaction.
Anode: H ₂ → 2H ⁺ +2e ⁽ 1)
Cathode: 1/2O ₂ +2H ⁺ +2e ⁻ → H ₂ O (2)

The anode and cathode each consist of a laminated structure of an electrode catalyst layer and a gas diffusion layer. The fuel gas supplied to the anode-side electrode catalyst layer is converted into protons and electrons by the electrode catalyst (reaction 1). Protons pass through the polymer electrolyte and polymer electrolyte membrane in the anode-side electrode catalyst layer and move to the cathode. Electrons travel through an external circuit to the cathode. In the electrode catalyst layer on the cathode side, protons, electrons, and an externally supplied oxidant gas react to produce water (reaction 2). Thus, electricity is generated by the electrons passing through the external circuit.

Currently, fuel cells exhibiting high output characteristics are desired in order to reduce the cost of fuel cells. However, since fuel cells generate a large amount of water during high-power operation, the electrode catalyst layer and the gas diffusion layer are flooded with water, resulting in footing that hinders the supply of gas. When footing occurs, there is a problem that the output of the fuel cell is significantly reduced.
In order to solve the above problems, Patent Documents 1 and 2 propose catalyst layers containing carbon or carbon fibers with different particle sizes.

JP-A-10-241703 Japanese Patent No. 5537178

Patent Literatures 1 and 2 describe that inclusion of different carbon materials creates pores in the electrode catalyst layer, which is expected to improve drainage and gas diffusion. However, although there are descriptions of the size, shape and content of the carbon material, there is no description of the structure of the catalyst layer, and the effect thereof has not been specifically verified.
The invention has been made in view of such circumstances, and an object of the invention is to provide an electrode catalyst layer for a polymer fuel cell capable of improving drainage and gas diffusibility and capable of high output. .

In order to solve the above problems, one aspect of the present invention provides an electrode catalyst layer bonded to a polymer electrolyte membrane, comprising a catalyst, carbon particles, a polymer electrolyte and a fibrous substance, wherein the fibrous substance The fiber diameter is 10 nm or more and 300 nm or less, the fiber length of the fibrous substance is 1 μm or more and 50 μm or less, and the density is 900 mg/cm ³ or less.

ADVANTAGE OF THE INVENTION According to one aspect of the present invention, it is possible to provide a polymer fuel cell catalyst layer capable of improving drainage and gas diffusibility and capable of high output.

1 is an exploded cross-sectional view showing a configuration example of a catalyst layer according to an embodiment of the present invention; FIG. 1 is a cross-sectional view showing a configuration example of a membrane electrode assembly according to an embodiment of the present invention; FIG. 1 is an exploded cross-sectional view showing a configuration example of a single cell of a polymer electrolyte fuel cell equipped with a membrane electrode assembly; FIG.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings.
The present invention is not limited to the embodiments described below, and modifications such as design changes can be made based on the knowledge of those skilled in the art. Other embodiments are also included in the scope of the present invention.

(electrode catalyst layer)
As shown in FIG. 1, electrode catalyst layers 2 and 3 for a polymer fuel cell according to an embodiment of the present invention (hereinafter referred to as the present embodiment) include a catalyst 13, carbon particles 14 supporting the catalyst 13, high It consists of molecular electrolyte 15 and fibrous substance 16 .
Further, the density of the electrode catalyst layers 2 and 3 of this embodiment is set to 500 mg/cm ³ or more and 900 mg/cm ³ or less. By containing the fibrous substance 16, cracks do not occur during formation, and the pores in the electrode catalyst layers 2 and 3 can be increased.

The polymer electrolyte 15 may be any material as long as it has ionic conductivity, but considering the adhesion between the electrode catalyst layers 2 and 3 and the polymer electrolyte membrane, it is possible to select a material of the same quality as the polymer electrolyte membrane. preferable. A fluorine-based resin or a hydrocarbon-based resin can be used for the polymer electrolyte 15, for example. For example, fluorine-based resins include Nafion (manufactured by DuPont, registered trademark), and hydrocarbon-based resins include engineering plastics and copolymers thereof into which sulfonic acid groups are introduced.

As the catalyst 13, a platinum group element, a metal, an alloy thereof, an oxide, a multiple oxide, or the like can be used. Platinum group elements include platinum, palladium, ruthenium, iridium, rhodium, and osmium. Examples of metals include iron, lead, copper, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, and aluminum. Among them, platinum and platinum alloys are preferable as the catalyst 13 . Moreover, if the particle size of the catalyst 13 is too large, the activity of the catalyst 13 is lowered, and if it is too small, the stability of the catalyst 13 is lowered. More preferably, it is 1 nm or more and 5 nm or less.

As the carbon particles 14 , any particles may be used as long as they are fine particles, have electrical conductivity, and are not affected by the catalyst 13 . If the particle size of the carbon particles 14 is too small, it becomes difficult to form an electron conduction path. More than 1000 nm or less is preferable. More preferably, it is 10 nm or more and 100 nm or less.
The catalyst 13 is preferably carried on the carbon particles 14 . By supporting the catalyst 13 on the carbon particles 14 having a high surface area, the catalyst 13 can be supported at a high density and the catalytic activity can be improved.

Conductive fibers and electrolyte fibers can be used as the fibrous substance 16 . Examples of conductive fibers include carbon fibers, carbon nanotubes, carbon nanohorns, and conductive polymer nanofibers. Carbon nanofibers or carbon nanotubes are particularly preferred in terms of conductivity and dispersibility. The electrolyte fiber is obtained by processing a polymer electrolyte into a fibrous form. Proton conductivity can be improved by using electrolyte fibers as the fibrous substance 16 . Furthermore, these fibrous substances 16 may be used singly, or two or more of them may be used in combination, or conductive fibers and electrolyte fibers may be used together.

The fiber diameter of the fibrous substance 16 is preferably 0.5 nm or more and 500 nm or less, more preferably 10 nm or more and 300 nm or less. By setting the content within the above range, the number of pores in the electrode catalyst layers 2 and 3 can be increased, and high output can be achieved.
The fiber length of the fibrous substance 16 is preferably 1 μm or more and 200 μm or less, more preferably 1 μm or more and 50 μm or less. By setting the thickness within the above range, the strength of the electrode catalyst layers 2 and 3 can be increased, and the occurrence of cracks during formation can be suppressed. In addition, the number of pores in the electrode catalyst layers 2 and 3 can be increased, and high output can be achieved.

The thickness of the electrode catalyst layers 2 and 3 is preferably 30 μm or less, more preferably 10 μm or less. If the thickness is more than 30 μm, the resistance of the electrode catalyst layers 2 and 3 will increase and the output will decrease. Moreover, if the thickness is more than 30 μm, the electrode catalyst layers 2 and 3 are likely to crack, which is not preferable.
The thickness of the electrode catalyst layers 2 and 3 is preferably 5 μm or more. If the thickness is less than 5 μm, the layer thickness tends to vary, and the catalyst 13 and the polymer electrolyte 15 inside tend to be uneven. Cracks on the surfaces of the electrode catalyst layers 2 and 3 and non-uniformity in thickness are not preferable because they are highly likely to adversely affect durability when used as a fuel cell and operated for a long period of time. On the other hand, if the thickness is less than 5 μm, the concentration of water generated by power generation tends to increase in the electrode catalyst layers 2 and 3, and flooding tends to occur, resulting in a decrease in power generation performance, which is not preferable.

(Membrane electrode assembly)
A membrane electrode assembly 12 for a polymer fuel cell according to this embodiment has a structure as shown in a cross-sectional view as shown in FIG. 2, for example. This membrane electrode assembly 12 comprises a polymer electrolyte membrane 1, a cathode side electrode catalyst layer 2 formed on one side of the polymer electrolyte membrane 1, and an anode formed on the other side of the polymer electrolyte membrane 1. The side electrode catalyst layer 3 is provided. The electrode catalyst layer of the present invention corresponds to one or both of the cathode side electrode catalyst layer 2 and the anode side electrode catalyst layer 3 .

(Polymer electrolyte fuel cell)
In the polymer electrolyte fuel cell of this embodiment, as shown in FIG. and a fuel electrode side gas diffusion layer 5 are arranged respectively. As a result, the cathode-side electrode catalyst layer 2 and the air-electrode-side gas diffusion layer 4 constitute the air electrode 6 , and the anode-side electrode catalyst layer 3 and the fuel-electrode-side gas diffusion layer 5 constitute the fuel electrode 7 . be. By sandwiching the air electrode 6 and the fuel electrode 7 with a pair of separators 10, a single-cell polymer electrolyte fuel cell 11 is constructed. A set of separators 10 is made of a conductive and gas-impermeable material, and is disposed facing the air electrode side gas diffusion layer 4 or the fuel electrode side gas diffusion layer 5. 8 and a cooling water channel 9 for circulating cooling water disposed on the main surface facing the gas channel 8 .

In this polymer electrolyte fuel cell 11, an oxidant such as air or oxygen is supplied to the air electrode 6 through the gas flow path 8 of one separator 10, and hydrogen is supplied through the gas flow path 8 of the other separator 10. is supplied to the fuel electrode 7 to generate power.

(Manufacturing method of electrode catalyst layer)
The electrode catalyst layer can be produced by preparing a catalyst layer slurry, applying the prepared catalyst layer slurry to a substrate or the like, and drying the slurry.
The catalyst layer slurry comprises catalyst 13, carbon particles 14, polymer electrolyte 15, fibrous substance 16 and solvent. Although the solvent is not particularly limited, a solvent capable of dispersing or dissolving the polymer electrolyte 15 is preferred. Commonly used solvents include water, alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, tert-butyl alcohol, acetone, methyl ethyl ketone, methyl propyl ketone. , methyl butyl ketone, methyl isobutyl ketone, methyl amyl ketone, pentanone, heptanone, cyclohexanone, methyl cyclohexanone, acetonylacetone, diethyl ketone, dipropyl ketone, diisobutyl ketone, tetrahydrofuran, tetrahydropyran, dioxane, diethylene glycol Ethers such as dimethyl ether, anisole, methoxytoluene, diethyl ether, dipropyl ether, dibutyl ether, amines such as isopropylamine, butylamine, isobutylamine, cyclohexylamine, diethylamine, aniline, propyl formate, isobutyl formate, amyl formate, acetic acid Esters such as methyl, ethyl acetate, propyl acetate, butyl acetate, isobutyl acetate, pentyl acetate, isopentyl acetate, methyl propionate, ethyl propionate, butyl propionate, and other acetic acid, propionic acid, dimethylformamide, dimethylacetamide, N- Methylpyrrolidone or the like may also be used. Glycol and glycol ether solvents include ethylene glycol, diethylene glycol, propylene glycol, ethylene glycol monomethyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diacetone alcohol, 1-methoxy-2-propanol and 1-ethoxy-2. - Propanol and the like.

Examples of the method for applying the catalyst layer slurry include a doctor blade method, a die coating method, a dipping method, a screen printing method, a laminator roll coating method, and a spray method, but are not particularly limited.
The method for drying the catalyst layer slurry includes hot air drying, IR drying, and the like. The drying temperature is 40° C. or higher and 200° C. or lower, preferably 40° C. or higher and 120° C. or lower. The drying time is 0.5 minutes or more and 1 hour or less, preferably 1 or more and 30 minutes or less.

Here, in order to set the density of the electrode catalyst layer to 500 mg/cm ³ or more and 900 mg/cm ³ , the addition amount of the fibrous substance, the fiber length, the heating temperature for drying, the temperature gradient, and the This can be achieved by adjusting the conditions such as the pressure applied in the film thickness direction.

(Manufacturing method of membrane electrode assembly)
Membrane electrode assemblies can be produced by forming an electrode catalyst layer on a transfer base material or a gas diffusion layer and then forming an electrode catalyst layer on a polymer electrolyte membrane by thermocompression bonding, or by forming a catalyst layer directly on a polymer electrolyte membrane. method of forming. The method of forming the catalyst layer directly on the polymer electrolyte membrane is preferable because the adhesion between the polymer electrolyte membrane and the catalyst layer is high and the catalyst layer is not crushed.

As described above, the electrode catalyst layer of the present embodiment is composed of the catalyst 13, the carbon particles 14, the polymer electrolyte 15 and the fibrous substance 16, and has a density of 500 mg/ ^cm3 or more and 900 mg/cm3.
³ or less.
According to this configuration, it is possible to provide an electrode catalyst layer for polymer fuel cells capable of improving drainage and gas diffusibility and capable of high output.
The electrode catalyst layer of the present embodiment is extremely suitable for application to polymer electrolyte fuel cells, for example.

In this embodiment, the catalyst 13 is supported on the carbon particles 14, but the catalyst 13 may be supported on the fibrous material 16, and further supported on both the carbon particles 14 and the fibrous material 16. You may let The voids formed by the fibrous material 16 can be used as discharge paths for water produced by power generation. Here, when the catalyst 13 is supported on the fibrous substance 16, an electrode reaction also occurs in the discharge path of the produced water. On the other hand, by supporting the catalyst 13 on the carbon particles 14, the three-phase interface caused by the carbon particles 14, the catalyst 13, and the gas causes a reaction point, and the space formed by the fibrous substance 16 forms a discharge path for the generated water. and can be distinguished from each other, and the drainage property of the catalyst electrode layer can be improved.

Next, examples based on the present invention will be described.
[Calculation of density]
The density was obtained from the mass and thickness of the electrode catalyst layer. As the mass, the mass obtained from the coating amount of the slurry for the catalyst layer or the dry mass was used. The thickness was obtained by observing the cross section with a scanning electron microscope (magnification: 2000 times).

[Evaluation of power generation characteristics]
A gas diffusion layer (SIGRACET (registered trademark) 35BC, manufactured by SGL) was placed outside the electrode catalyst layer, and power generation characteristics were evaluated using a commercially available JARI standard cell. The cell temperature was set to 80° C., hydrogen (100% RH) was supplied to the anode, and air (100% RH) was supplied to the cathode.

[Example 1]
Take 20 g of platinum-supported carbon (TEC10E50E, manufactured by Tanaka Kikinzoku Co., Ltd.) in a container, add water and mix, then add 1-propanol, an electrolyte (Nafion (registered trademark) dispersion, Wako Pure Chemical Industries) and carbon nanofiber as a fibrous substance. (manufactured by Showa Denko KK, trade name "VGCF", fiber diameter: about 150 nm, fiber length: about 10 µm) was added and stirred to obtain a catalyst layer slurry.
The resulting catalyst layer slurry was applied to a polymer electrolyte membrane (Nafion 212, manufactured by DuPont) by a die coating method and dried in a furnace at 80° C. to obtain a membrane electrode having the electrode catalyst layer of Example 1. A zygote was obtained.

[Example 2]
A membrane electrode assembly having an electrode catalyst layer of Example 2 was obtained in the same manner as in Example 1, except that carbon nanotubes (fiber diameter: about 1 nm, fiber length: about 1 μm) were used as the fibrous substance.
[Example 3]
A membrane electrode assembly having the electrode catalyst layer of Example 3 was obtained in the same manner as in Example 1, except that the drying temperature was increased.
[Example 4]
A membrane electrode assembly having the electrode catalyst layer of Example 4 was obtained in the same manner as in Example 1, except that the amount of fibrous material was increased.

[Comparative Example 1]
A membrane electrode having the electrode catalyst layer of Comparative Example 1 was prepared in the same manner as in Example 1, except that the composition and coating amount of the slurry were adjusted so that the thickness of the electrode catalyst layer was less than 5 μm. A zygote was obtained.
[Comparative Example 2]
A membrane electrode having the electrode catalyst layer of Comparative Example 2 was prepared in the same manner as in Example 1, except that the composition and coating amount of the slurry were adjusted so that the thickness of the electrode catalyst layer exceeded 30 μm. A zygote was obtained.

[Comparative Example 3]
A membrane electrode assembly having an electrode catalyst layer of Comparative Example 3 was obtained in the same procedure as in Example 1, except that the coating was applied to the PET substrate and transferred to the electrolyte membrane by thermocompression bonding.
[Comparative Example 4]
A membrane electrode assembly having an electrode catalyst layer of Comparative Example 4 was obtained in the same procedure as in Example 1, except that no fibrous material was added.

[Comparative Example 5]
A membrane electrode assembly having an electrode catalyst layer of Comparative Example 5 was manufactured in the same manner as in Example 1, except that no fibrous substance was added, the PET substrate was coated, and the electrode catalyst layer was transferred to the electrolyte membrane by thermocompression bonding. Obtained.
The catalyst layers of Examples 1 to 4 and Comparative Examples 1 to 5 were observed under a microscope (magnification: 200 times) and evaluated for the presence or absence of cracks of 10 μm or more. Table 1 shows the evaluation results.

As shown in Table 1, when the fibrous substance was not added (Comparative Example 4), the PET film could be coated without cracks, but many cracks occurred in the polymer electrolyte membrane. On the other hand, when the fibrous material was added as in Examples 1-4 and Comparative Examples 1-3, the catalyst layer was free of cracks.
Further, the electrode catalyst layers of Examples 1 to 4 and Comparative Examples 1 to 5 were evaluated for the density and power generation characteristics of the electrode catalyst layers. Table 2 shows the evaluation results.
Here, each electrode catalyst layer is adjusted so that the mass of the blended catalyst is the same, but the thickness of each electrode catalyst layer is different because other configurations are different.

From Tables 1 and 2, it can be seen that cracks are likely to occur even if the density is higher than the density of the present invention when no fibrous material is added. In addition, by using an electrode catalyst layer composed of a catalyst, carbon particles, a polymer electrolyte, and a fibrous material and having a density of 500 mg/cm ³ or more and 900 mg/cm ³ or less, cracks do not occur, and drainage and gas It was found that it is possible to provide an electrode catalyst layer for a polymer fuel cell capable of improving diffusibility and high output.

1 polymer electrolyte membrane 2 cathode side electrode catalyst layer 3 anode side electrode catalyst layer 4 air electrode side gas diffusion layer 5 fuel electrode side gas diffusion layer 6 air electrode 7 fuel electrode 8 gas channel 9 cooling water channel 10 separator 11 solid height Molecular fuel cell 12 membrane electrode assembly 13 catalyst 14 carbon particles 15 polymer electrolyte 16 fibrous material

TECHNICAL FIELD The present invention relates to an electrode catalyst layer constituting a membrane electrode assembly for a polymer fuel cell, a membrane electrode assembly provided with the electrode catalyst layer, and a polymer electrolyte fuel cell provided with the membrane electrode assembly. .

Claims (3)

An electrode catalyst layer bonded to a polymer electrolyte membrane,
having a catalyst, carbon particles, a polymer electrolyte and a fibrous material,
The fibrous substance has a fiber diameter of 10 nm or more and 300 nm or less,
The fibrous substance has a fiber length of 1 μm or more and 50 μm or less,
An electrode catalyst layer having a density of 900 mg/cm ³ or less. 2. The electrode catalyst layer according to claim 1, wherein the carbon particles support the catalyst to form catalyst-supporting particles. 3. The electrode catalyst layer according to claim 1, wherein the electrode catalyst layer has a thickness of 5 [mu]m or more and 30 [mu]m or less.

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