JP2021163699A - Catalyst layer for polymer electrolyte fuel cell, membrane electrode assembly, and polymer electrolyte fuel cell - Google Patents

Abstract

To provide a catalyst layer for a polymer electrolyte fuel cell, a membrane electrode assembly, and a polymer electrolyte fuel cell capable of improving drainage and gas diffusibility and improving output during power generation.SOLUTION: When the cross section of a catalyst layer for a polymer electrolyte fuel cell (air electrode side electrode catalyst layer 1, fuel electrode side electrode catalyst layer 2) is analyzed by TEM-EDX, as compared to the atomic ratios of platinum (Pt) and fluorine (F) in a wide-field analysis area 50a, the atomic ratio of Pt and F in a first narrow field analysis area 50b near a carbon fiber 8 is low, and as compared to the atomic ratios of Pt and F in the wide-field analysis area 50a, the atomic ratio of Pt and F is high in a second narrow field analysis area 50c away from the carbon fiber 8.SELECTED DRAWING: Figure 3

Description

The present invention relates to a catalyst layer for a polymer electrolyte fuel cell, a membrane electrode assembly, and a polymer electrolyte fuel cell.

In recent years, fuel cells have been attracting attention as an effective solution to environmental problems and energy problems. A fuel cell oxidizes a fuel such as hydrogen using an oxidizing agent such as oxygen, and converts the chemical energy associated therewith into electrical energy.
Fuel cells are classified into alkaline type, phosphoric acid type, polymer type, molten carbonate type, solid oxide type and the like according to the type of electrolyte. Among them, polymer electrolyte fuel cells (PEFC) are expected to be applied as portable power sources, household power sources, and in-vehicle power sources because they can be operated at low temperature, have high output density, and can be miniaturized and lightweight. ing.

A polymer electrolyte fuel cell (PEFC) has a structure (film electrode junction) in which a polymer electrolyte membrane, which is an electrolyte membrane, is sandwiched between a fuel electrode (anode) and an air electrode (cathode), and hydrogen is placed on the fuel electrode side. By supplying the fuel gas containing the fuel gas and supplying the oxidizing agent gas containing oxygen to the air electrode side, power is generated by the following electrochemical reaction.

_{^{Anode: H 2 → 2H + + 2e}} - ··· ( reaction 1)
^{_{Cathode: 1 / 2O 2 + 2H +}} + 2e - → H 2 O ··· ( reaction 2)
The anode and cathode each have a laminated structure of a catalyst layer and a gas diffusion layer. The fuel gas supplied to the anode-side catalyst layer generates protons and electrons by the electrode catalyst (reaction 1). Protons move to the cathode through the polyelectrolyte and the polyelectrolyte film in the anode-side catalyst layer. The electrons pass through an external circuit and move to the cathode. In the cathode-side catalyst layer, protons, electrons, and an oxidant gas supplied from the outside react to generate water (reaction 2). In this way, the polymer electrolyte fuel cell generates electricity by passing electrons through an external circuit.

The catalyst layer is generally formed of platinum-supported carbon and a polyelectrolyte. Platinum-supported carbon contributes to electron conduction during power generation, and polyelectrolytes contribute to proton conduction. The balance of these types and contents greatly contributes to power generation performance.

On the other hand, during power generation, the diffusivity of hydrogen and oxygen to the fuel cell and the drainage performance of the water generated during power generation are also important. A fuel cell having high gas diffusivity and drainage property can derive high power generation performance.

Therefore, measures have been taken to improve gas diffusivity and drainage by imparting water repellency to the gas diffusion layer and optimizing the porosity.

Although it is possible to improve gas diffusivity and drainage by adopting an appropriate gas diffusion layer, in reality, gas diffusivity and drainage in the catalyst layer of the membrane electrode assembly are even more important. This is because the above-mentioned electrochemical reactions (reaction 1 and reaction 2) proceed in the catalyst layer, so even if the outer gas diffusion layer is optimized unless the gas diffusivity and drainage property in the catalyst layer are improved. This is because there is a limit to the improvement of power generation performance.

JP-A-2019-75277 International Publication Number WO2020 / 022191 Japanese Patent No. 5994729

In Patent Document 1, a predetermined amount of fibrous carbon is arranged in the catalyst layer (anode catalyst layer) to promote the discharge of liquid water to the outside of the catalyst layer, thereby suppressing the retention of oxygen generated in the water electrolysis reaction. doing. Further, in Patent Document 2, the diffusion path of the gas is secured by adding the proton conductive resin in the catalyst layer (cathode catalyst layer) at a mass of a predetermined ratio with respect to the mass of the particulate conductive member. Further, in Patent Document 3, in the catalyst layer (cathode and anode), the thickness of the polymer electrolyte is controlled according to the humidity so as to have appropriate proton resistance and gas diffusion resistance. However, in these methods, although the gas diffusibility and drainage property in the catalyst layer are improved, the atomic ratio in the catalyst layer is not taken into consideration.

Further, as a method for improving the gas diffusibility and drainage property of the catalyst layer, there is a means for coarsening the particle size in the dispersion step of the catalyst ink and increasing the porosity in the catalyst layer. However, there is a problem that the catalyst inside the particles does not contribute to the reaction as the particle size becomes coarser, and as a result, the power generation performance does not improve.

The present invention has been made in view of such circumstances, and is a catalyst layer for a polymer electrolyte fuel cell capable of improving drainage and gas diffusivity and improving output during power generation. , Membrane electrode assembly and polymer electrolyte fuel cell.

In order to solve the above problems, the polymer electrolyte fuel cell catalyst layer according to one aspect of the present invention is a polymer electrolyte fuel cell catalyst layer containing carbon particles carrying a catalyst, a polymer electrolyte, and carbon fibers. When the cross section of the polymer electrolyte fuel cell catalyst layer is subjected to TEM-EDX analysis, the carbon fibers are compared with the atomic ratios of platinum (Pt) and fluorine (F) in the wide-field analysis region. The atomic ratio of Pt and F in the first narrow-field analysis region in the vicinity of is low, and Pt in the second narrow-field analysis region away from the carbon fiber is compared with the atomic ratio of Pt and F in the wide-field analysis region. It is characterized by a high atomic ratio of and F.

Further, the membrane electrode assembly according to one aspect of the present invention includes a polymer electrolyte membrane and a pair of catalyst layers sandwiching the polymer electrolyte membrane, and at least one of the pair of catalyst layers is the solid polymer. It is characterized by being an electrode catalyst layer for an electrolyte fuel cell.

Further, the polymer electrolyte fuel cell according to one aspect of the present invention is characterized by including the membrane electrode assembly and a pair of separators sandwiching the membrane electrode assembly.

According to one aspect of the present invention, the catalyst layer for a solid polymer fuel cell, the membrane electrode assembly, and the solid polymer type capable of improving drainage and gas diffusivity and improving output during power generation. Fuel cells can be provided.

It is sectional drawing which shows the structural example of the membrane electrode assembly which concerns on one Embodiment of this invention. It is sectional drawing which shows the structural example of the catalyst layer for a polymer electrolyte fuel cell which concerns on one Embodiment of this invention. It is a figure which shows the analysis area which is the object of TEM-EDX analysis in the catalyst layer for a polymer electrolyte fuel cell which concerns on one Embodiment of this invention. It is an exploded perspective view which shows the structural example of the single cell of the polymer electrolyte fuel cell which mounted the membrane electrode assembly which concerns on one Embodiment of this invention.

Hereinafter, the present invention will be described in detail. 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, and such modifications are added. Such embodiments are also included in the scope of the present invention.

[Membrane electrode assembly]
FIG. 1 shows a cross-sectional view of the membrane electrode assembly 11 according to the present embodiment. As shown in FIG. 1, the membrane electrode assembly 11 for a polymer electrolyte fuel cell according to the embodiment of the present invention (hereinafter referred to as the present embodiment) includes a polyelectrolyte film 3 and a polyelectrolyte film 3. It is provided with a pair of catalyst layers to be sandwiched. Specifically, the membrane electrode assembly 11 includes a polyelectrolyte film 3, an air electrode catalyst layer 1 formed on one surface of the polyelectrolyte film 3, and the other surface of the polyelectrolyte film 3. The structure is provided with the fuel electrode side electrode catalyst layer 2 formed in the above. The air electrode side electrode catalyst layer 1 and the fuel electrode side electrode catalyst layer 2 correspond to the catalyst layer for a polymer electrolyte fuel cell according to the present embodiment. The air electrode side electrode catalyst layer 1 is also referred to as a cathode catalyst layer. Further, the fuel electrode side electrode catalyst layer 2 is also referred to as an anode catalyst layer. Further, hereinafter, the air electrode side electrode catalyst layer 1 and the fuel electrode side electrode catalyst layer 2 may be collectively referred to as a catalyst layer.

Further, as shown in FIG. 1, a gasket 4 is arranged in the membrane electrode assembly 11 so as to surround the catalyst layer (air electrode side electrode catalyst layer 1, fuel electrode side electrode catalyst layer 2).
In the membrane electrode assembly 11 according to the present embodiment, at least one of the pair of catalyst layers sandwiching the polymer electrolyte membrane 3 is one of the catalyst layers for polymer electrolyte fuel cells according to the present embodiment (air). Either one of the polar electrode catalyst layer 1 and the fuel electrode catalyst layer 2) may be used.

FIG. 2 shows a catalyst layer for a polymer electrolyte fuel cell (air electrode side electrode catalyst layer 1, fuel electrode side electrode catalyst layer 2) according to the present embodiment. As shown in FIG. 2, the solid polymer fuel catalyst layer according to the present embodiment has a form including carbon particles 5 carrying catalyst particles (an example of a catalyst) 6, a polymer electrolyte 7, and carbon fibers 8. ing. By containing the carbon fiber, the strength of the catalyst layer can be increased, and the generation of cracks at the time of formation can be suppressed. Further, by containing carbon fibers, the number of pores in the catalyst layer can be increased, and the drainage property and the gas diffusibility can be improved to increase the output.

As shown in FIG. 2, the catalyst particles 6 are supported on the carbon particles 5, and the periphery thereof is covered with the polymer electrolyte 7.

In the present embodiment, the carbon particles 5 may be any carbon particles 5 as long as they are fine particles, have conductivity, and are not attacked by the catalyst particles 6, and may be, for example, carbon black, graphite, graphite, activated carbon, or carbon nanotubes. , Carbon nanofiber, fullerene and the like can be used. If the particle size of the carbon particles 5 is too small, it becomes difficult to form an electron conduction path, and if it is too large, the electrode catalyst layer becomes thick and the resistance increases, which may reduce the output characteristics. Therefore, the particle size of the carbon particles 5 is preferably in the range of 10 nm or more and 1000 nm or less, and more preferably in the range of 10 nm or more and 100 nm or less.

In the present embodiment, the catalyst particles 6 include platinum, palladium, ruthenium, iridium, rhodium, osmium, and other platinum group elements, as well as iron, lead, copper, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, and the like. Metals or alloys thereof, oxides, compound oxides, etc. can be used. The compound oxide referred to here refers to an oxide composed of two types of metals. Among these, it is preferable to use platinum or a platinum alloy as the catalyst particles 6. Further, if the particle size of these catalyst particles 6 is too large, the activity of the catalyst is lowered, and if it is too small, the stability of the catalyst is lowered. Therefore, the particle size of the catalyst particles 6 is preferably in the range of 0.5 nm or more and 20 nm or less, and more preferably in the range of 1 nm or more and 5 nm or less.

Further, in the present embodiment, the polyelectrolyte 7 may be any as long as it has ionic conductivity, but considering the adhesion between the catalyst layer and the polyelectrolyte film 3, the material is the same as that of the polyelectrolyte film 3. (For example, a fluorine-based polyelectrolyte, a hydrocarbon-based polyelectrolyte, etc.) is preferably selected. For example, as the fluororesin, "Nafion (registered trademark)" manufactured by DuPont can be used. Examples of the hydrocarbon resin include engineering plastics and those in which a sulfonic acid group is introduced into a copolymer thereof.

The polymer electrolyte 7 in FIG. 2 is responsible for conducting protons during power generation and covers the carbon particles 5 carrying the catalyst particles 6. The polymer electrolyte 7 affects drainage and gas diffusivity in addition to proton conduction.

As the carbon fiber 8 in the present embodiment, carbon fiber, carbon nanofiber, carbon nanotube or the like can be used, but it is preferable to use carbon nanofiber or carbon nanotube. By containing carbon fiber 8 in the catalyst layer (air electrode side electrode catalyst layer 1, fuel electrode side electrode catalyst layer 2), drainage and gas diffusivity are improved without reducing the electromotive force, especially on the high current side. The output can be improved. Further, the carbon fiber 8 preferably has a hydrophobic fiber surface.

Further, in the present embodiment, in addition to the carbon fiber 8, a polymer electrolyte fiber having proton conductivity may be used for the catalyst layer. By adding the polymer electrolyte fiber to the catalyst layer, it is possible to improve the drainage property and the gas diffusivity without reducing the electromotive force, and to improve the output particularly on the high current side, as in the case of the carbon fiber 8. Further, both the carbon fiber 8 and the polymer electrolyte fiber may be mixed in the catalyst layer.

In the present embodiment, the fiber diameter of the carbon fiber 8 is preferably 200 nm or less. As a result, the strength of the catalyst layer can be increased, and cracks can be suppressed during formation. Similarly, the fiber diameter of the polymer electrolyte fiber is preferably 200 nm or less.

Further, in the present embodiment, the fiber length of the carbon fiber 8 is preferably in the range of 1 μm or more and 200 μm or less. Within the above range, agglomeration of carbon fibers 8 in the catalyst layer can be avoided and pores can be formed. Similarly, the polymer electrolyte fiber preferably has a fiber length in the range of 1 μm or more and 200 μm or less. As a result, it is possible to avoid agglomeration of the polymer electrolyte fibers and form pores.

When the polymer electrolyte fiber is added to the catalyst layer, it is contained in a weight in the range of 0.1 times or more and 3.0 times or less with respect to the weight of the carbon particles 5 excluding the weight of the catalyst particles 6. It is preferable to have. By keeping the weight of the polymer electrolyte fiber within the above range, it is possible to promote the conduction of protons during power generation and improve the output.

As described above, the catalyst layer for a polymer electrolyte fuel cell (air electrode side electrode catalyst layer 1, fuel electrode side electrode catalyst layer 2) according to the present embodiment includes carbon particles 5 carrying catalyst particles 6 and a polymer electrolyte. 7 and carbon fiber 8 are formed. In the catalyst layer according to the present embodiment, the adsorption state of the polymer electrolyte 7 to the carbon fibers 8 contributes to the improvement of the output during power generation. As will be described in detail later, in the present embodiment, the catalyst layer selectively adsorbs the polymer electrolyte 7 to the carbon particles 5 that contribute to power generation by lowering the atomic ratio of the polymer electrolyte 7 in the vicinity of the carbon fiber 8. However, the output during power generation can be improved.

FIG. 3 shows a method of analyzing the atomic ratio by TEM-EDX (Energy Dispersive X-ray Spectroscopy). In the present embodiment, the membrane electrode assembly 11 cross-sectioned by the cryo-CP device is subjected to mapping analysis regarding the analysis area, which is the region to be analyzed by TEM-EDX, and the catalyst layer (air electrode side electrode catalyst layer 1,). The cross section of the fuel electrode side electrode catalyst layer 2) is TEM-EDX analyzed, and the atomic ratio of each element is measured. Specifically, in the cross section of the membrane electrode assembly 11, TEM-EDX analysis is performed on the catalyst layer formed on the polymer electrolyte membrane 3 to measure the atomic ratio.

In the present embodiment, an "energy dispersive X-ray spectroscopic analyzer (model number: Dual SDD)" manufactured by JEOL (JEOL Ltd.) is used for the TEM-EDX analysis. The main analysis condition by TEM-EDX is that the acceleration voltage is 200 kV.

In TEM-EDX analysis, a wide field analysis area area is 40,000 ^2, 2 types of narrow-field analysis area (first narrow viewing analysis area size is 10,000nm ^2, the second narrow viewing analysis area ), Perform mapping analysis. In FIG. 3, as an example of these analysis areas, a wide-field analysis area (an example of a wide-field analysis area) 50a, a first narrow-field analysis area (an example of a first narrow-field analysis area) 50b, and a second narrow-field analysis Area (an example of a second narrow field analysis region) 50c is shown. The first narrow-field analysis area 50b is a narrow-field analysis area in the vicinity of the carbon fibers 8 and is a narrow-field analysis area in which the occupancy rate of the carbon fibers 8 is 80% or more. The second narrow-field analysis area 50c is a narrow-field analysis area away from the carbon fibers 8 and has a carbon fiber 8 occupancy rate of 20% or less.

In the mapping analysis by TEM-EDX in the present embodiment, the wide-field analysis area 50a and the two types of narrow-field analysis areas (first narrow-field analysis area 50b and second narrow-field analysis area 50c) having different occupancy rates of carbon fibers 8 are used. ), The atomic ratio of each element (C, Pt, F) is measured.

Specifically, the catalyst layer for a polymer fuel cell (air electrode side electrode catalyst layer 1, fuel) according to the present embodiment, which includes carbon particles 5 carrying catalyst particles 6, polymer electrolyte 7, and carbon fibers 8. With respect to the electrode catalyst layer 2) on the polar side, the cross section of the catalyst layer is analyzed by TEM-EDX for the atomic ratios of each element of carbon (C), platinum (Pt), and fluorine (F). Further, the measurement result of the atomic ratio of each element in the wide-field analysis area 50a (wide-field analysis result) and each of the two types of narrow-field analysis areas (first narrow-field analysis area 50b and second narrow-field analysis area 50c). Compare with the measurement result of the atomic ratio of the element (narrow field analysis result). As a result, the atomic ratios of Pt and F in the first narrow-field analysis area 50b near the carbon fiber 8 are compared with the atomic ratios of each element in the wide-field analysis area 50a (here, the atomic ratios of Pt and F). Is low. Further, the atomic ratios of Pt and F in the second narrow-field analysis area 50c away from the carbon fiber 8 are higher than the atomic ratios of each element in the wide-field analysis area 50a. As a result, the output of the catalyst layer according to the present embodiment in power generation is improved.

Since the atomic ratio of fluorine (F) is a peak caused by the polymer electrolyte 7 in the catalyst layer, F is in the second narrow-field analysis area 50c where the occupancy rate of the carbon fiber 8 is as low as 20% or less. It can be said that a high atomic ratio is a local uneven distribution of the polymer electrolyte 7. Further, the fact that the atomic ratio of F is low in the first narrow-field analysis area 50b in the vicinity of the carbon fiber 8 where the occupancy rate of the carbon fiber 8 is as high as 80% or more means that the carbon fiber of the polymer electrolyte 7 It means that the adsorption to 8 is small.

A fuel cell generates electricity by coating a conductive material on which a catalyst is supported with a polymer electrolyte. On the other hand, since the carbon fiber does not carry a catalyst, even if it is covered with a polymer electrolyte, it does not contribute to power generation. That is, in the polymer electrolyte fuel cell having the catalyst layer according to the present embodiment, the polymer electrolyte 7 is selectively adsorbed on the carbon particles 5 on which the catalyst particles 6 are supported, thereby improving the output during power generation. be able to.

Further, the carbon fiber 8 contributes to the formation of pores and electron conduction in the catalyst layer, and can improve drainage and gas diffusibility. In the present embodiment, by selectively lowering the atomic ratio of the polymer electrolyte 7 in the vicinity of the carbon fiber 8 (first narrow-field analysis area 50b), vacancies are likely to occur, and drainage and gas diffusibility are easily generated. It is possible to improve the output at the time of power generation. The atomic ratio of not only fluorine (F) but also platinum (Pt) decreases in the vicinity of the carbon fiber 8 (first narrow-field analysis area 50b), which is due to the carbon particles 5 carrying Pt and the polyelectrolyte. This is because the adsorbent formed by selectively adsorbing 7 is difficult to adsorb to the carbon fiber 8 due to the properties of the polyelectrolyte 7. For example, when the polyelectrolyte 7 has a sulfonic acid group, the affinity with the carbon fiber 8 having a hydrophobic surface is lowered and it becomes difficult to be adsorbed on the carbon fiber 8, so that the polyelectrolyte in the vicinity of the carbon fiber 8 is difficult to be adsorbed. The atomic ratio of 7 decreases.

As described above, the catalyst layer according to the present embodiment is a catalyst layer for a polymer electrolyte fuel cell containing carbon particles 5 carrying catalyst particles 6, a polymer electrolyte 7, and carbon fibers 8, and the solid height thereof. When the cross section of the catalyst layer for a molecular fuel cell is TEM-EDX analyzed, the first narrow field of view near the carbon fiber 8 is compared with the atomic ratio of platinum (Pt) and fluorine (F) in the wide field analysis area 50a. The atomic ratio of Pt and F in the analysis area 50b is low, and the atomic ratio of Pt and F in the second narrow-field analysis area 50c away from the carbon fiber 8 is compared with the atomic ratio of Pt and F in the wide-field analysis area 50a. Is high. Thereby, the electrode catalyst layer for the polymer electrolyte fuel cell according to the present embodiment can improve the drainage property and the gas diffusivity, and can improve the output at the time of power generation.

Further, in the catalyst layer according to the present embodiment, in the TEM-EDX analysis, the atomic ratio of platinum (Pt) in the first narrow field analysis area 50b is 0.1 at% or less, and the atomic ratio of fluorine (F) is 0. It is preferable that it is 0.05 at% or less. Thereby, the output at the time of power generation can be further improved.

Further, the membrane electrode assembly 11 according to the present embodiment includes a polymer electrolyte membrane and a pair of catalyst layers sandwiching the polymer electrolyte membrane, and at least one of the pair of catalyst layers relates to the present embodiment. It may be an electrode catalyst layer for a polymer electrolyte fuel cell (air electrode side electrode catalyst layer 1, fuel electrode side electrode catalyst layer 2). Thereby, the membrane electrode assembly 11 can improve the drainage property and the gas diffusivity, and can improve the output at the time of power generation.

FIG. 4 is an exploded perspective view showing a configuration example of the polymer electrolyte fuel cell 10 equipped with the membrane electrode assembly 11. Here, the polymer electrolyte fuel cell 10 shown in FIG. 4 is an example of a fuel cell having a single cell structure. As shown in FIG. 4, the polymer electrolyte fuel cell 10 according to the present embodiment has a membrane electrode assembly 11 and a pair of separators (air electrode side separator 18C and fuel electrode side separator) sandwiching the membrane electrode assembly 11. 18A) and. Specifically, the air electrode side gas diffusion layer 17C is arranged so as to face the air electrode side electrode catalyst layer 1 of the membrane electrode assembly 11, and the fuel electrode side gas diffusion layer is opposed to the fuel electrode side electrode catalyst layer 2. 17A is arranged. Further, by sandwiching the air electrode side gas diffusion layer 17C and the fuel electrode side gas diffusion layer 17A between the air electrode side separator 18C and the fuel electrode side separator 18A, the polymer electrolyte fuel cell 10 having a single cell structure is configured. NS. A pair of separators (air electrode side separator 18C and fuel electrode side separator 18A) are made of a conductive and gas impermeable material. Further, the air electrode side separator 18C has an air electrode side gas flow path 19C for the reaction gas flow arranged so as to face the air electrode side gas diffusion layer 17C. Further, the fuel electrode side separator 18A has a fuel electrode side gas flow path 19A arranged so as to face the fuel electrode side gas diffusion layer 17A.

The polymer electrolyte fuel cell 10 shown in FIG. 4 is an example of a fuel cell having a single cell structure, but is configured by stacking a plurality of cells via a fuel electrode side separator 18A or an air electrode side separator 18C. The present invention can be applied even to a polymer electrolyte fuel cell.

In the polymer electrolyte fuel cell 10 having a single cell structure, an oxidizing agent such as air or oxygen that has passed through the air electrode side gas flow path 19C of the air electrode side separator 18C passes through the air electrode side gas diffusion layer 17C. It is supplied to the membrane electrode assembly 11. Further, fuel gas or organic fuel containing hydrogen that has passed through the fuel electrode side gas flow path 19A of the fuel electrode side separator 18A is supplied to the membrane electrode assembly 11 via the fuel electrode side gas diffusion layer 17A. As a result, the polymer electrolyte fuel cell 10 is configured to be capable of generating electricity.

The polymer electrolyte fuel cell 10 according to the present embodiment includes a membrane electrode assembly 11 including at least one of an air electrode side electrode catalyst layer 1 and a fuel electrode side electrode catalyst layer 2, and a membrane electrode assembly 11. It suffices to have a pair of separators to be sandwiched. As a result, the polymer electrolyte fuel cell 10 according to the present embodiment can improve drainage and gas diffusivity, and can improve the output at the time of power generation.

(Manufacturing method of catalyst layer)
For the catalyst layer for a polymer electrolyte fuel cell (air electrode side electrode catalyst layer 1, fuel electrode side electrode catalyst layer 2) according to the present embodiment, a catalyst layer slurry is prepared, and the substrate is coated and dried. Can be manufactured by.

The catalyst layer slurry is formed of carbon particles 5 carrying catalyst particles 6, a polyelectrolyte 7, and carbon fibers 8. The solvent in the slurry for the catalyst layer is not particularly limited, but a solvent capable of dispersing or dissolving the polymer electrolyte 7 is preferable. Commonly used solvents include water, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, tert-butyl alcohol and other alcohols, acetone, methyl ethyl ketone and methyl propyl ketone. , Methylbutyl ketone, Methylisobutylketone, Methylamylketone, Pentanone, Heptanone, Cyclohexanone, Methylcyclohexanone, Acetonylacetone, diethylketone, Dipropylketone, Diisobutylketone and other ketones, 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, acetate. Methyl, ethyl acetate, propyl acetate, butyl acetate, isobutyl acetate, pentyl acetate, isopentyl acetate, methyl propionate, ethyl propionate, butyl propionate and other esters, as well as acetic acid, propionic acid, dimethylformamide, dimethylacetamide, N- Methylpyrrolidone or the like may be used. Examples of 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. -Examples include propanol.

Examples of the method for applying the slurry for the catalyst layer include, but are not limited to, a doctor blade method, a die coating method, a dipping method, a screen printing method, a laminator roll coating method, and a spray method.

Examples of the method for drying the slurry for the catalyst layer include warm air drying and IR drying. The drying temperature may be in the range of 40 ° C. or higher and 200 ° C. or lower, preferably in the range of 40 ° C. or higher and 120 ° C. or lower. The drying time may be in the range of 0.5 minutes or more and 1 hour or less, preferably in the range of 1 minute or more and 30 minutes or less.

(Manufacturing method of membrane electrode assembly)
As a method for manufacturing the membrane electrode assembly 11, after forming the air electrode side electrode catalyst layer 1 and the fuel electrode side electrode catalyst layer 2 on the transfer base material or the gas diffusion layer, the air electrode side is thermally pressure-bonded to the polymer electrolyte membrane. Examples thereof include a method of forming the electrode catalyst layer 1 and the fuel electrode side electrode catalyst layer 2, and a method of forming the air electrode side electrode catalyst layer 1 and the fuel electrode side electrode catalyst layer 2 directly on the polymer electrolyte membrane 3. The thermocompression bonding method reduces the volume of pores during pressurization, which may lead to a decrease in drainage. Therefore, in order to form the air electrode side electrode catalyst layer 1 and the fuel electrode side electrode catalyst layer 2 according to the present embodiment, the air electrode side electrode catalyst layer 1 and the fuel electrode side electrode catalyst layer are formed directly on the polyelectrolyte film 3. The method of forming 2 is preferable.

Next, an example based on the present invention will be described.
[Example 1]
Take 20 g of platinum-supported carbon (TEC10E50E, manufactured by Tanaka Kikinzoku Co., Ltd.) in a container, add 10 g of carbon fiber (fiber diameter about 150 nm, fiber length about 10 μm) with a hydrophobic surface, and water, mix, and then add 1-propanol and electrolyte (1-propanol). Nafion (registered trademark) dispersion liquid, Wako Pure Chemical Industries, Ltd.) was added and stirred to obtain a slurry for a cathode catalyst layer and a slurry for an anode catalyst layer.
The obtained cathode catalyst layer slurry and anode catalyst layer slurry are coated on one surface and the other surface of a polymer electrolyte membrane (Nafion212 manufactured by DuPont) by a die coating method, respectively, and inside a furnace at 80 ° C. The catalyst layer for a polymer electrolyte fuel cell (air electrode side electrode catalyst layer 1, fuel electrode side electrode catalyst layer 2) was obtained by drying with.

[Example 2]
Same as Example 1 except that the solid content concentration was 1.2 times and the water ratio was 1.1 times that of the catalyst slurry (cathode catalyst layer slurry and anode catalyst layer slurry) of Example 1. A catalyst layer for a polymer electrolyte fuel cell was obtained by the procedure described in 1.
[Comparative Example 1]
A catalyst layer for a polymer electrolyte fuel cell was obtained in the same procedure as in Example 1 except that carbon fibers 8 having a hydrophilic surface were used in the preparation of the slurry for the catalyst layer.

[Measurement of atomic ratio]
With respect to the cross section of the catalyst layer for the polymer electrolyte fuel cell formed on the polymer electrolyte membrane 3 in Examples 1 and 2 and Comparative Example 1, the wide-field analysis area 50a and the first narrow-field analysis area 50b, A TEM-EDX analysis of the second narrow field analysis area 50c was performed. TEM-EDX analysis was performed to measure the atomic ratio. For the TEM-EDX analysis, an "energy dispersive X-ray spectroscopic analyzer (model number: Dual SDD)" manufactured by JEOL (JEOL Ltd.) was used. As an analysis condition, the acceleration voltage was set to 200 kV.

[Evaluation of power generation characteristics]
A gas diffusion layer (SIGRACET (registered trademark) 35BC) outside the catalyst layer for polymer electrolyte fuel cells (air electrode side electrode catalyst layer 1, fuel electrode side electrode catalyst layer 2) of Examples 1 and 2 and Comparative Example 1. (Manufactured by SGL) was placed, and the power generation characteristics were evaluated using a commercially available JARI standard cell. The cell temperature is 80 ° C., hydrogen (100% RH) is supplied to the fuel electrode side electrode catalyst layer 2 (anode catalyst layer), and air (100% RH) is supplied to the air electrode side electrode catalyst layer 1 (cathode catalyst layer). Was supplied and evaluated.

Table 1 shows the measurement results of the atomic ratio in the catalyst layer for the polymer electrolyte fuel cell of Examples 1 and 2 and Comparative Example 1.

As shown in Table 1, in the catalyst layers of Example 1 and Example 2, the number near the carbon fiber 8 was compared with the measurement result (wide field analysis result) of the atomic ratio of each element in the wide field analysis area. The results showed that the atomic ratios of platinum (Pt) and fluorine (F) in the narrow field analysis area 50b were low. Further, in the catalyst layers of Examples 1 and 2, the results show that the atomic ratios of Pt and F in the second narrow-field analysis area 50c away from the carbon fibers 8 are higher than those of the wide-field analysis results. Obtained.

In Examples 1 and 2, the atomic ratio of fluorine (F) in the first narrow-field analysis area 50b near the carbon fiber 8 is low, and the atomic ratio of F in the second narrow-field analysis area 50c away from the carbon fiber 8 is high. This means that the adsorption of the polymer electrolyte 7 to the carbon fibers 8 is small. That is, in Examples 1 and 2, it can be said that the polymer electrolyte 7 is locally unevenly distributed. Further, in Examples 1 and 2, the atomic ratio of platinum (Pt) is also low in the first narrow field analysis area 50b near the carbon fiber 8. This is because the carbon particles 5 on which Pt is carried and the polyelectrolyte 7 are selectively adsorbed, and the adsorbent due to the adsorption is difficult to adsorb to the carbon fiber 8 having a hydrophobic surface due to the properties of the polyelectrolyte 7. Because.

On the other hand, in Comparative Example 1, the atomic ratios of platinum (Pt) and fluorine (F) in the first narrow-field analysis area 50b near the carbon fiber 8 and the second narrow-field analysis area 50c away from the carbon fiber 8 The atomic ratios of Pt and F were almost the same as the atomic ratios of Pt and F in the wide-field analysis results. This means that the polymer electrolyte 7 is evenly adsorbed on each of the carbon particles 5 and the carbon fibers 8.

Table 2 shows the maximum output densities in the power generation evaluations of Examples 1, 2 and Comparative Example 1.

As shown in Table 2, it was confirmed that the maximum output densities of Examples 1 and 2 were higher than the maximum output densities of Comparative Example 1. That is, in Examples 1 and 2, it was confirmed that the output at the time of power generation was improved by selectively adsorbing the polymer electrolyte 7 on the carbon particles 5 on which the catalyst particles 6 were supported. On the other hand, in Comparative Example 1, by using the hydrophilic carbon fiber 8, the adsorption of the polymer electrolyte 7 to the carbon fiber 8 is increased, and as a result, the height of the catalyst particle 6 to the supported carbon particle 5 is increased. The adsorption of the molecular electrolyte 7 was reduced. Therefore, the output of power generation has decreased.
Further, in the catalyst layers of Examples 1 and 2, by selectively lowering the atomic ratio of the polymer electrolyte 7 in the vicinity of the carbon fibers 8, vacancies are likely to occur and the porosity in the catalyst layer increases. However, drainage and gas diffusivity were improved.
On the other hand, in the catalyst layer of Comparative Example 1, since the adsorption of the polymer electrolyte 7 to the carbon fibers 8 is increased, pores are less likely to be generated as compared with the catalyst layers of Examples 1 and 2, and the catalyst layer is contained. No improvement in drainage and gas diffusivity was observed without increasing the porosity.

As described above, from the evaluation results shown in Tables 1 and 2, the catalyst layer for the polymer electrolyte fuel cell of Examples 1 and 2 has improved drainage and gas diffusivity, and also improves the output during power generation. It was confirmed that it was possible.

As described above, according to the present embodiment, in the catalyst layer for a polymer fuel cell containing carbon particles carrying a catalyst, a polymer electrolyte, and carbon fibers, the cross section of the catalyst layer is C.I. As a result of analyzing the atomic ratios of Pt and F, the atomic ratios of Pt and F in the narrow field near the carbon fiber are lower than those in the wide field analysis result, and the atoms of Pt and F in the narrow field away from the carbon fiber. It is characterized by a high ratio. As a result, drainage and gas diffusivity are improved, and output in power generation is improved.

Since the present invention exerts a remarkable effect on improving the output of the fuel cell during power generation, it has high industrial utility value. For example, it is extremely suitable for application to polymer electrolyte fuel cells.

1 Air electrode side electrode catalyst layer 2 Fuel electrode side electrode catalyst layer 3 Polymer electrolyte membrane 4 Gasket 5 Carbon particles 6 Catalyst particles 7 Polymer electrolyte 8 Carbon fiber 10 Solid polymer fuel cell 11 Membrane electrode assembly 17A Fuel electrode side Gas diffusion layer 17C Air electrode side gas diffusion layer 18A Fuel electrode side separator 18C Air electrode side separator 19A Fuel electrode side gas flow path 19C Air electrode side gas flow path 50a Wide field analysis area 50b First narrow field analysis area 50c Second narrow Perspective analysis area

Claims (5)

A catalyst layer for a polymer electrolyte fuel cell containing carbon particles carrying a catalyst, a polyelectrolyte, and carbon fibers.
When the cross section of the catalyst layer for a polymer electrolyte fuel cell is TEM-EDX analyzed,
The atomic ratios of Pt and F in the first narrow-field analysis region near the carbon fibers are lower than the atomic ratios of platinum (Pt) and fluorine (F) in the wide-field analysis region.
For polymer electrolyte fuel cells characterized by a higher atomic ratio of Pt and F in the second narrow-field analysis region away from the carbon fibers as compared with the atomic ratio of Pt and F in the wide-field analysis region. Catalyst layer. In the TEM-EDX analysis of the catalyst layer for polymer electrolyte fuel cells,
The first aspect of claim 1, wherein the atomic ratio of platinum (Pt) in the first narrow-field analysis region is 0.1 at% or less, and the atomic ratio of fluorine (F) is 0.05 at% or less. Catalyst layer for polymer electrolyte fuel cells. The catalyst layer for a polymer electrolyte fuel cell according to claim 1 or 2, wherein the carbon fibers are carbon fibers or carbon nanotubes. Polyelectrolyte membrane and
A pair of catalyst layers sandwiching the polymer electrolyte membrane,
With
A membrane electrode assembly according to claim 1, wherein at least one of the pair of catalyst layers is the catalyst layer for a polymer electrolyte fuel cell according to any one of claims 1 to 3. The membrane electrode assembly according to claim 4 and
A polymer electrolyte fuel cell comprising a pair of separators sandwiching the membrane electrode assembly.

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