JP2019160428A - Catalyst layer, membrane electrode assembly, and polymer electrolyte fuel cell - Google Patents

Abstract

To provide a catalyst layer, as a catalyst layer constituting a membrane electrode assembly of a polymer electrolyte fuel cell, which is good in drainage and gas diffusion properties and in which cracks are suppressed and a membrane electrode assembly is also suppressed from being bulky.SOLUTION: A catalyst layer of the present invention includes a carbon particle, a catalyst supported on the carbon particle, a polymer electrolyte, and a fibrous material. A first fibrous material is included as the fibrous material, and the fiber length distribution of the first fibrous material satisfies a relationship of σ1<σ2 where σ1 represents a first standard deviation in a region 31 where fiber lengths are longer than a most frequent value, and σ2 represents a second standard deviation in a region 32 where fiber lengths are shorter than the most frequent value, in a histogram having a fiber length as a horizontal axis and a volume as a vertical axis.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a catalyst layer for a polymer electrolyte fuel cell.

In recent years, fuel cells have attracted attention as effective solutions for environmental problems and energy problems. A fuel cell oxidizes a fuel such as hydrogen using an oxidant such as oxygen, and converts chemical energy associated therewith into electric energy.
Fuel cells are classified into alkaline, phosphoric acid, solid polymer, molten carbonate, solid oxide, etc., depending on the type of electrolyte. The polymer electrolyte fuel cell (PEFC) is operated at low temperature, has high output density, and can be reduced in size and weight, so it is expected to be applied as a portable power source, household power source, and in-vehicle power source. ing.

A polymer electrolyte fuel cell (PEFC) has a structure in which a polymer electrolyte membrane as an electrolyte membrane is sandwiched between a fuel electrode (anode) and an air electrode (cathode), and a fuel gas containing hydrogen on the fuel electrode side, air Electric power is generated by the following electrochemical reaction by supplying an oxidant gas containing oxygen to the pole side.
Anode: H ₂ → 2H ⁺ + 2e ⁻ (1)
^{_{Cathode: 1 / 2O 2 + 2H +}} + 2e - → H 2 O ··· (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 is converted into protons and electrons by the catalyst (reaction (1) above). Protons move to the cathode through the polymer electrolyte and polymer electrolyte membrane in the anode catalyst layer. The electrons travel through the external circuit 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) above). In this way, power is generated by electrons passing through an external circuit.
Such a polymer electrolyte fuel cell is required to realize a high output even when operated in a high current density region. However, in the operation in a high current density region, a large amount of generated water is generated, so that water overflows in the catalyst layer and the gas diffusion layer, and flooding that prevents gas supply occurs. Due to this, there is a problem that the output of the fuel cell is significantly reduced.

As a proposal for solving the above problem, Patent Document 1 discloses that an electrode (catalyst layer) includes carbon particles having at least two particle size distribution centers and carbon having a large particle size distribution center. It is described that a bone body of an electrode is formed by particles, and a catalyst is supported on carbon particles having a distribution center with a small particle size.
In Patent Document 2, carbon catalyst is used as a catalyst carrier of the catalyst layer in order to realize improvement in both electric conductivity and gas diffusibility in the catalyst layer while sufficiently ensuring the durability of the polymer electrolyte fuel cell. It has been proposed to use a mixture of particles and carbon fibers.

Japanese Patent No. 3617237 Japanese Patent No. 4337406

According to the proposal of Patent Document 1, pores are generated in the catalyst layer by including different carbon materials, and improvement in drainage and gas diffusibility can be expected. However, when the carbon material is only particles, cracks in the catalyst layer are likely to be induced, resulting in a decrease in durability associated therewith.
In the proposal of Patent Document 2, since fibrous carbon is added in addition to the carbon particles carrying the catalyst, it can be expected that high power generation efficiency can be realized while suppressing cracks in the catalyst layer. However, when fibrous carbon is used, the volume of the catalyst layer increases, so when many membrane electrode assemblies are stacked, the fuel cell itself becomes enormous, and in many fuel cells including in-vehicle use There is a problem that it is difficult to achieve the required reduction in size and weight.

  The problem of the present invention is that the catalyst layer constituting the membrane electrode assembly of the polymer electrolyte fuel cell has good drainage and gas diffusibility, cracks are suppressed, and the membrane electrode assembly is also prevented from being bulky. It is to provide a catalyst layer.

In order to solve the above-mentioned problems, a first aspect of the present invention comprises a membrane electrode assembly of a polymer electrolyte fuel cell, comprising carbon particles, a catalyst supported on the carbon particles, a polymer electrolyte, and a fibrous substance And a catalyst layer having the following configuration (1).
(1) The first fibrous material is included as the fibrous material. The fiber length distribution of the first fibrous material is a histogram in which the horizontal axis is the fiber length and the vertical axis is the volume. The first standard deviation σ1 in the region where the fiber length is longer than the mode value and the fiber length is the maximum. The relationship with the second standard deviation σ2 in the region shorter than the frequent value satisfies σ1 <σ2.

A second aspect of the present invention is a catalyst layer comprising a membrane electrode assembly of a solid polymer fuel cell, comprising carbon particles, a catalyst supported on the carbon particles, a polymer electrolyte, and a fibrous material, It has the above configuration (1) and the following configurations (2) and (3).
(2) A second fibrous material is further included as the fibrous material. The fiber length distribution of the second fibrous substance is a histogram in which the horizontal axis is the fiber length and the vertical axis is the volume, and the third standard deviation σ3 in the region where the fiber length is longer than the mode value and the fiber length is the maximum. The relationship with the fourth standard deviation σ4 in the region shorter than the frequent value satisfies σ3 <σ4. The mode value of the fiber length of the second fibrous substance exists in a region shorter than the mode value of the fiber length of the first fibrous substance.
(3) The volume of the first fibrous substance occupies 60% or more of the total volume of the first fibrous substance and the second fibrous substance.

  The catalyst layer of the embodiment of the present invention has a good drainage property and gas diffusibility, is a catalyst layer in which cracks are suppressed, and the membrane electrode assembly is also suppressed from being bulky. Therefore, it can be expected that a high output is realized even in an operation in a high current density region.

It is a schematic block diagram which shows the polymer electrolyte fuel cell which is one Embodiment of this invention. It is sectional drawing which shows the unit cell which comprises the polymer electrolyte fuel cell of FIG. It is a schematic diagram which shows the structure of the catalyst layer which comprises the unit cell of FIG. It is a graph which shows fiber length distribution of the carbon fiber contained in the catalyst layer of a 1st example. It is a graph which shows fiber length distribution of the carbon fiber contained in the catalyst layer of a 2nd example. It is a graph which shows the result obtained in the Example.

  Embodiments of the present invention (hereinafter referred to as “embodiments”) will be described below. The present invention is not limited to the embodiments described below, and modifications such as design changes can be added based on the knowledge of those skilled in the art, and such modifications have been added. Embodiments are also included in the scope of the present invention.

As shown in FIG. 1, the polymer electrolyte fuel cell 11 of the embodiment includes a membrane electrode assembly 12. The membrane electrode assembly 12 includes a polymer electrolyte membrane 1, an anode catalyst layer 2, a cathode catalyst layer 3, and a frame-shaped gasket 4. An anode catalyst layer 2 and a cathode catalyst layer 3 are respectively disposed on both surfaces of the polymer electrolyte membrane 1, and a gasket 4 is disposed on the outer periphery of the anode catalyst layer 2 and the cathode catalyst layer 3.
The polymer electrolyte fuel cell 11 includes a pair of gas diffusion layers 5 and a pair of separators 10. Each gas diffusion layer 5 is disposed to face the anode catalyst layer 2 and the cathode catalyst layer 3.

The separator 10 is made of a material that is conductive and impermeable. A gas flow path 8 for gas flow is formed on one side of the separator 10, and a cooling water flow path 9 for flow of cooling water is formed on the other side (the surface opposite to the surface where the gas flow path 8 is formed). Has been. The pair of separators 10 are arranged so as to sandwich the membrane electrode assembly 12 via the gas diffusion layers 5.
Fuel gas is supplied from the gas flow path 8 of the separator 10 on the anode catalyst layer 2 side. An example of the fuel gas is hydrogen gas. Oxidant gas is supplied from the gas flow path 8 of the separator 10 on the cathode catalyst layer 3 side. As the oxidant gas, for example, a gas containing oxygen such as air is supplied.

  The polymer electrolyte fuel cell 11 is a so-called solid electrolyte fuel cell in which a polymer electrolyte membrane 1, an anode catalyst layer 2, a cathode catalyst layer 3, a gasket 4 and a gas diffusion layer 5 are sandwiched between a pair of separators 10. This is a polymer electrolyte fuel cell having a single cell structure. However, it is also possible to employ a stack structure in which a plurality of cells (unit cells 13 shown in FIG. 2) are stacked in series via the separator 10.

As shown in FIG. 2, the unit cell 13 includes a polymer electrolyte membrane 1, an anode catalyst layer 2, a cathode catalyst layer 3 and a surface of the anode catalyst layer 2 (polymer electrolyte membrane 1 and Is a pair of gas diffusion layers 5 disposed on the surface 301 of the cathode catalyst layer 3 and the surface 301 of the cathode catalyst layer 3, and a frame-like gasket 4. A gas diffusion layer 5 is also disposed in the gasket 4.
As shown in FIG. 3, the anode catalyst layer 2 and the cathode catalyst layer 3 include a catalyst 21, carbon particles 22, a polymer electrolyte 23, and carbon fibers (fibrous substances) 24. Hereinafter, the case where the carbon fiber 24 has the fiber length distribution of FIG. 4 (first example) and the case of the carbon fiber 24 having the fiber length distribution of FIG. 5 (second example) will be described.

  In the first example, as shown in FIG. 4, the carbon fiber 24 is a histogram in which the horizontal axis is the fiber length and the vertical axis is the volume, and the first in the region 31 where the fiber length is longer than the mode value (15 μm). The relationship between the standard deviation σ1 and the second standard deviation σ2 in the region 32 where the fiber length is shorter than the mode value satisfies σ1 <σ2. The mode value (15 μm) indicated by the broken line 33 is larger than the average value indicated by the broken line 34. The carbon fiber 24 in the first example corresponds to the first fibrous material. FIG. 4 illustrates the case where the mode value is 15 μm, but it is sufficient that the relationship between the first standard deviation σ1 and the second standard deviation σ2 satisfies σ1 <σ2, and the mode value is 15 μm. It is not limited.

In this histogram, the fiber length distribution is an asymmetric distribution, but the first standard deviation and the second standard deviation are obtained by approximating the large side and the small side with different normal distributions (Gaussian distributions) with the mode value as the boundary. It can be calculated.
Thereby, the output of the polymer electrolyte fuel cell can be improved as compared with the case where the fiber length distribution of the carbon fiber 24 contained in the catalyst layer does not satisfy σ1 <σ2, and the thickness of the catalyst layer is also increased. Can be thinned.

  In the second example, the carbon fiber 24 includes a first carbon fiber and a second carbon fiber having different fiber length distributions, and the volume ratio of the first carbon fiber (the carbon fiber having the fiber length distribution of FIG. 4) is , 60% or more based on the total volume of the carbon fiber. As shown in FIG. 5, the second carbon fiber is a histogram in which the horizontal axis is the fiber length and the vertical axis is the volume, and the third standard deviation σ3 in the region 41 where the fiber length is longer than the mode value, and the fiber The relationship with the fourth standard deviation σ4 in the region 42 whose length is shorter than the mode value satisfies σ3 <σ4. Further, the mode value of the second carbon fiber is 10 μm and exists in a region shorter than the mode value (15 μm) of the first carbon fiber. In addition, although FIG. 5 illustrates the case where the mode value of the first carbon fiber is 15 μm and the mode value of the second carbon fiber is 10 μm, this is an example, and the above relationship may be satisfied.

In the second example, the thickness of the catalyst layer can be made thinner than in the first example while maintaining the high power generation performance of the polymer electrolyte fuel cell.
The volume of the carbon fiber here is calculated from the diameter and length of the carbon fiber. For example, when considering a carbon fiber having the same diameter and twice the length, the volume is twice. To do. For example, when the same number of two types of carbon fibers having the same diameter and a length of 3: 2 are mixed, the volume ratio is 60:40.
A plurality of carbon fibers having different fiber length distributions may be mixed. By mixing a plurality of carbon fibers having different fiber length distributions, a multimodal histogram having a plurality of maximum values is often obtained when a frequency distribution with respect to the fiber length is drawn.

However, depending on the fiber distribution of the carbon fibers before mixing, there may not be a multimodal histogram when mixed, and the carbon fiber may be monomodal or multimodal, even if the histogram is unimodal or multimodal. As long as the volume ratio is within the range, the usefulness can be exhibited.
The term “multimodality” as used herein refers to having a plurality of maximum values when a frequency or existence probability corresponding to each section is plotted in a certain system. Unimodality means having a single maximum value.
The carbon fiber of the second example is a mixture of a second carbon fiber having a fiber length distribution mode value of 10 μm and a first carbon fiber having a fiber length distribution mode value of 15 μm. As shown in FIG. 5, the fiber length distribution of each carbon fiber is an asymmetric distribution, but the large side and the small side can be approximated to different normal distributions (Gaussian distributions) with the mode value as a boundary.

The frequency of each carbon fiber is indicated by a solid line, and the volume of each mixed carbon fiber at each fiber length is indicated by a broken line. The volume ratio can be calculated by integrating the volume value of a certain section.
The fiber length of the carbon fiber can be measured using a laser diffraction particle size distribution measuring device. As long as the fiber length can be measured and calculated accurately, wet measurement or dry measurement may be used.
The fiber length distribution and existence probability can be changed by pulverizing carbon fibers using pulverized beads or by sieving the carbon fibers using a filter or the like. Even when sieving, the usefulness can be exhibited as long as the volume ratio of the carbon fiber is within the above range.

The fiber length of the carbon fiber contained in the catalyst layer is, for example, about 0.1 to 200 μm, preferably about 0.5 to 100 μm, and more preferably about 1 to 50 μm. By setting it as the said range, the intensity | strength of a catalyst layer can be raised and it can suppress that a crack arises at the time of formation. Further, the pores in the catalyst layer can be lengthened, and high output can be achieved.
As described above, in the polymer electrolyte fuel cell, since the fuel gas and the oxidant gas are continuously supplied, the reaction point can be increased by allowing the gas to sufficiently penetrate deep into the catalyst layer.

Compared with a catalyst layer not containing carbon fibers, a catalyst layer containing carbon fibers has a large number of pores, and in particular, has long pores penetrating through the catalyst layer. As a result, the output is improved.
Similarly, the carbon fiber contained in the catalyst layer contributes to flooding (water clogging) in which water generated in the membrane electrode assembly is not sufficiently discharged and power generation efficiency is reduced.
Compared with a catalyst layer that does not contain carbon fiber, the catalyst layer that contains carbon fiber has a large number of pores, especially long pores that penetrate through the catalyst layer, ensuring drainage in the catalyst layer. Therefore, it is possible to suppress a decrease in efficiency of the polymer fuel cell.

Even in the case of a catalyst layer consisting only of a catalyst, carbon particles, and polymer electrolyte, it is possible to increase the number of pores by means such as reducing the ratio of the polymer electrolyte, but it is difficult to form a catalyst layer because severe cracks are induced. It is not preferable.
However, when carbon fibers are used, the structural strength of the catalyst layer is increased, and cracks can be suppressed even when there are many pores in the catalyst layer.
Compared with a catalyst layer that does not contain carbon fiber, the catalyst layer that contains carbon fiber has a large volume, and the thickness of the produced membrane electrode assembly increases, which directly leads to an increase in the size of the stacked fuel cell. In order to suppress this, the thickness of the membrane electrode assembly can be increased or decreased by mixing a plurality of carbon fibers having different fiber length distributions, and the balance between the power generation performance and the film thickness can be adjusted.

Examples of the carbon fiber include carbon fiber, carbon nanotube, carbon nanohorn, and conductive polymer nanofiber. In particular, carbon nanofibers or carbon nanotubes are preferable in terms of conductivity and dispersibility.
In this embodiment, carbon fibers are used as the fibrous material, but fibrous materials other than carbon fibers may be used.
As the fibrous material, an electron conductive fiber and a proton conductive fiber can be used. Examples of fibrous materials are shown below. Of these fibers, only one kind may be used alone, but two or more kinds may be used in combination, and an electron conductive fiber and a proton conductive fiber may be used in combination.

Examples of the electron conductive fiber include carbon fiber, carbon nanotube, carbon nanohorn, and conductive polymer nanofiber. In particular, carbon nanofibers are preferable in terms of conductivity and dispersibility. Further, it is more preferable to use an electron conductive fiber having catalytic ability because the amount of the catalyst made of a noble metal can be reduced.
When used as an air electrode of a polymer electrolyte fuel cell, a carbon alloy catalyst prepared from carbon nanofibers can be exemplified. Further, the electrode active material for the oxygen reduction electrode may be processed into a fiber shape, and a material containing at least one transition metal element selected from Ta, Nb, Ti, and Zr may be used. . Examples thereof include partial oxides of carbonitrides of these transition metal elements, or conductive oxides and conductive oxynitrides of these transition metal elements.

The proton conductive fiber is not particularly limited as long as the polymer electrolyte having proton conductivity is processed into a fiber shape, and a fluorine-based polymer electrolyte and a hydrocarbon-based polymer electrolyte can be used. Examples of the fluoropolymer electrolyte include Nafion (registered trademark) manufactured by DuPont, Flemion (registered trademark) manufactured by Asahi Glass Co., Ltd., Aciplex (registered trademark) manufactured by Asahi Kasei Co., Ltd., and Gore Select (registered trademark) manufactured by Gore. Etc. can be used.
As the hydrocarbon polymer electrolyte, electrolytes such as sulfonated polyetherketone, sulfonated polyethersulfone, sulfonated polyetherethersulfone, sulfonated polysulfide, and sulfonated polyphenylene can be used. Among these, a Nafion (registered trademark) material manufactured by DuPont can be suitably used as the polymer electrolyte. As the hydrocarbon polymer electrolyte, electrolytes such as sulfonated polyetherketone, sulfonated polyethersulfone, sulfonated polyetherethersulfone, sulfonated polysulfide, and sulfonated polyphenylene can be used.

The fiber diameter of the carbon fiber is, for example, about 0.5 to 500 nm, preferably about 5 to 400 nm, and more preferably about 10 to 300 nm. By setting it within the above range, the number of pores in the catalyst layer can be increased, and high output can be achieved.
Catalysts include platinum, palladium, ruthenium, iridium, rhodium, osmium, platinum group elements, iron, lead, copper, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum and other metals or alloys thereof. Alternatively, oxides, double oxides, and the like can be used. Of these, platinum and platinum alloys are preferred. Moreover, since the activity of a catalyst will fall when the particle size of these catalysts is too large, and stability of a catalyst will fall when too small, 0.5 nm-20 nm are preferable. More preferably, 1 nm-5 nm are good.

The carbon particles are not particularly limited as long as they are in the form of fine particles and have electrical conductivity and are not affected by the catalyst. Examples thereof include carbon black (acetylene black, furnace black, ketjen black, etc.), graphite, graphite, activated carbon, fullerene and the like.
When the particle size of the carbon particles is too small, it is difficult to form an electron conduction path. When the particle size is too large, the catalyst layer becomes thick and the resistance increases, so that the output characteristics are lowered. Therefore, about 10 nm to 1000 nm is preferable. . More preferably, 10 nm-100 nm are good.
By supporting the catalyst on carbon particles having a high surface area, the catalyst can be supported at a high density, and the catalytic activity can be improved.

The polymer electrolyte is not particularly limited as long as it is a resin component having proton conductivity, and among them, a fluorine-based polymer electrolyte or a hydrocarbon-based polymer electrolyte is preferably used.
For example, Nafion (registered trademark) manufactured by DuPont can be used as the fluorine-based polymer electrolyte.
As the hydrocarbon polymer electrolyte, for example, electrolytes such as sulfonated polyether ketone, sulfonated polyethersulfone, sulfonated polyetherethersulfone, sulfonated polysulfide, and sulfonated polyphenylene can be used.
As the polymer electrolyte, it is preferable to select the same material as the polymer electrolyte membrane from the viewpoint of adhesion between the catalyst layer and the electrolyte membrane.
The average thickness of the polymer electrolyte membrane is, for example, about 1 μm to 500 μm, preferably about 3 μm to 200 μm, and more preferably about 5 μm to 100 μm.

If the fiber length of the carbon fiber contained in the catalyst layer is in the above range, the catalyst layer may be a single layer or a multilayer structure.
When the catalyst layer has a multilayer structure, at most four layers or less are preferable in order to suppress an extreme decrease in power generation performance due to interface resistance. Moreover, all the thickness of each layer may be the same, and the thickness of each layer may differ.
When the catalyst layer has a multilayer structure, the composition of the catalyst, carbon particles, polymer electrolyte, carbon fiber, solvent, etc. in each layer may be the same or different.
When the catalyst layer has a multilayer structure, the boundary surface of each layer may be flat or may include a curved surface.

(Method for producing catalyst layer)
The catalyst layer can be produced by preparing a slurry for the catalyst layer, and coating and drying the transfer substrate or gas diffusion layer.
The slurry for the catalyst layer includes a catalyst, carbon particles, a polymer electrolyte, carbon fiber, and a solvent. The solvent for the catalyst layer slurry is not particularly limited as long as it can dissolve or disperse the polymer electrolyte and the catalyst.

  For example, water, alcohols (methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 3-butanol, pentanol, ethylene glycol, diacetone alcohol, 1-methoxy-2-propanol, etc.) , Ketones (acetone, methyl ethyl ketone, pentanone, methyl isobutyl ketone, diisobutyl ketone, etc.), ethers (dioxane, tetrahydrofuran, etc.), sulfoxides (dimethyl sulfoxide, etc.), amides (dimethylformamide, dimethylacetamide, etc.), etc. These can be used singly or in combination.

The solvent used in the catalyst ink is preferably one that can be easily removed by heating, and one having a boiling point of 150 ° C. or less is particularly suitable.
The concentration of the solute (conductive particles, catalyst particles, polymer electrolyte) in the slurry for the catalyst layer is, for example, 1 to 80% by weight, preferably 5 to 60% by weight, more preferably about 10 to 40% by weight. It is done.
The polymer electrolyte used in the catalyst layer slurry is not particularly limited as long as it is a resin component having proton conductivity, and among them, a fluorine polymer electrolyte or a hydrocarbon polymer electrolyte is preferably used.

For example, Nafion (registered trademark) manufactured by DuPont can be used as the fluorine-based polymer electrolyte.
As the hydrocarbon polymer electrolyte, for example, electrolytes such as sulfonated polyether ketone, sulfonated polyethersulfone, sulfonated polyetherethersulfone, sulfonated polysulfide, and sulfonated polyphenylene can be used.
The slurry for the catalyst layer can be prepared by mixing the catalyst, carbon particles, polymer electrolyte, carbon fiber, and solvent and applying a dispersion treatment. Examples of the dispersion method include ball mill, bead mill, roll mill, shear mill, wet mill, ultrasonic dispersion, and homogenizer.

As a method of applying the catalyst layer slurry onto the substrate, a conventional coating method can be used.
Specific coating methods include, for example, roll coaters, air knife coaters, blade coaters, rod coaters, reverse coaters, bar coaters, comma coaters, die coaters, gravure coaters, screen coaters, sprayers, spinners and the like.
If the same catalyst ink can be finally applied, the coating means is not particularly limited.

A desired catalyst layer can be obtained by applying the catalyst layer slurry on a substrate and volatilizing the solvent in the catalyst ink by heating.
Examples of the method for drying the catalyst layer slurry include warm air drying and IR drying. The drying temperature is about 40 to 200 ° C, preferably about 40 to 120 ° C. The drying time is about 0.5 minute to 1 hour, preferably about 1 minute to 30 minutes.
The drying step may be a single drying mechanism or a combination of a plurality of drying mechanisms.

The average thickness of the catalyst layer obtained by drying the catalyst layer slurry is, for example, about 0.1 to 100 μm, preferably about 0.5 to 50 μm, and more preferably about 1 to 20 μm.
The transfer substrate is not particularly limited as long as the catalyst layer slurry can be applied to at least one surface, the catalyst layer can be formed by heating, and the formed catalyst layer can be transferred to the polymer electrolyte membrane 1.

  For example, polyethylene terephthalate, polyamide, polyimide, polystyrene, polysulfone, polyethersulfone, polyphenylene sulfide, polyetheretherketone, polyetherimide, polybenzimidazole, polyamideimide, polyacrylate, polyethylene naphthalate, polypalvanic acid aramid, etc. Heat resistance of molecular film or polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, ethylene tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroperfluoroalkyl vinyl ether copolymer, etc. Fluorine resin film can be used.

Moreover, you may use what carried out the mold release process to these base materials, or the thing of the multilayer structure with which the release layer was integrated by coextrusion etc.
The base material may be a sheet, a film, a plate, a film, a foil, or a material obtained by sticking, adhering, adhering, or bonding at least one of these.
When the substrate has a multilayer structure, the film located on the outermost surface may have an opening. Here, the opening refers to a portion where a part of the film has been removed by means such as cutting or punching.
Further, the shape of the dried catalyst ink (that is, electrode) may be formed depending on the shape of the opening.

(Method for producing membrane electrode assembly)
As a method of manufacturing a membrane electrode assembly, a catalyst layer is formed on a transfer substrate or a gas diffusion layer, a catalyst layer is formed on a polymer electrolyte membrane by thermocompression bonding, or a catalyst layer is formed directly on a polymer electrolyte membrane. The method of doing is mentioned. Further, the method of directly forming the catalyst layer 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.
The member used for the gasket 4 is not particularly limited as long as it can apply or bond an adhesive material to at least one surface and cut the polymer electrolyte membrane 1 by bonding.

  For example, polyethylene terephthalate, polyamide, polyimide, polystyrene, polysulfone, polyethersulfone, polyphenylene sulfide, polyetheretherketone, polyetherimide, polybenzimidazole, polyamideimide, polyacrylate, polyethylene naphthalate, polypalvanic acid aramid, etc. Heat resistance of molecular film or polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, ethylene tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroperfluoroalkyl vinyl ether copolymer, etc. Fluorine resin film can be used.

Moreover, you may use what carried out the mold release process to these base materials, or the thing of the multilayer structure with which the release layer was integrated by coextrusion etc.
The member used for the gasket 4 may be a sheet, a film, a plate, a membrane, a foil, or a member obtained by sticking, adhering, adhering, or pasting at least one of them.
The average thickness of the gasket 4 is, for example, about 1 μm to 500 μm, preferably about 3 μm to 200 μm, and more preferably about 5 μm to 100 μm.
The membrane electrode assembly produced as described above has increased the proportion of pores penetrating through the catalyst layer due to the carbon fiber contained in the catalyst layer, ensuring gas permeability and drainage. While the crack is suppressed as it is, the thickness of the catalyst layer can be controlled by mixing carbon fibers having different fiber length distributions. Therefore, a single cell or a polymer electrolyte fuel cell manufactured using this membrane electrode assembly can exhibit higher power generation performance than a conventional product.

Examples of the present invention and comparative examples will be described below.
[Sample No.1]
FIG. 4 shows a platinum-supported carbon catalyst (TEC10EA50E, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.), water, 1-propanol, and a polymer electrolyte “Nafion (registered trademark) dispersion” (manufactured by Wako Pure Chemical Industries, Ltd.). The first carbon fiber having the fiber length distribution shown (that is, the carbon fiber having a mode value of 15 μm and satisfying σ1 <σ2) is mixed and dispersed for 30 minutes in a planetary ball mill, and the catalyst ink Was prepared.

The first carbon fiber is “VGCF (registered trademark) -H” (manufactured by Showa Denko KK), which is a carbon nanofiber (vapor-grown carbon fiber), having the above fiber length distribution, and having a fiber diameter. What was 10 nm-30 nm was used.
The prepared catalyst ink was applied to both surfaces of “Nafion 211 (registered trademark)” (manufactured by Dupont), which is a polymer electrolyte membrane, using a slit die coater, and placed in a warm air oven at 80 ° C. The membrane electrode assembly of Example 1 was obtained by drying until the tack disappeared.

[Sample No.2]
Platinum-supported carbon catalyst (TEC10EA50E, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.), water, 1-propanol, polymer electrolyte “Nafion (registered trademark) dispersion” (manufactured by Wako Pure Chemical Industries, Ltd.), No. 1 The first carbon fiber and the second carbon fiber having a mode value of 10 μm and satisfying σ3 <σ4 were mixed and subjected to a dispersion treatment for 30 minutes with a planetary ball mill to prepare a catalyst ink. At that time, the addition volume of the first carbon fiber was 95% of the total volume of the first carbon fiber and the second carbon fiber.
The second carbon fiber is “VGCF (registered trademark) -H” (manufactured by Showa Denko KK), which is a carbon nanofiber (vapor-grown carbon fiber), having the above fiber length distribution, and having a fiber diameter. What was 10 nm-30 nm was used.
Except for this point, a No. 2 membrane electrode assembly was obtained in the same procedure as No. 1.

[Sample No.3]
A membrane electrode assembly of No. 3 was obtained in the same procedure as No. 2, except that the added volume of the first carbon fiber was 90% of the total volume of the first carbon fiber and the second carbon fiber. It was.
[Sample No.4]
A membrane electrode assembly of No. 4 was obtained in the same procedure as No. 2, except that the addition volume of the first carbon fiber was 80% of the total volume of the first carbon fiber and the second carbon fiber. It was.

[Sample No.5]
A membrane electrode assembly of No. 5 was obtained in the same procedure as No. 2, except that the addition volume of the first carbon fiber was 70% of the total volume of the first carbon fiber and the second carbon fiber. It was.
[Sample No.6]
A membrane electrode assembly of No. 6 was obtained in the same procedure as No. 2, except that the addition volume of the first carbon fiber was 60% of the total volume of the first carbon fiber and the second carbon fiber. It was. The graph of FIG. 5 shows the fiber length distribution of carbon fibers contained in the catalyst layer of this sample.

[Sample No.7]
A membrane electrode assembly of No. 7 was obtained in the same procedure as No. 2, except that the addition volume of the first carbon fiber was 50% of the total volume of the first carbon fiber and the second carbon fiber. It was.
[Sample No.8]
A membrane electrode assembly of No. 8 was obtained in the same procedure as No. 2, except that the addition volume of the first carbon fiber was 30% of the total volume of the first carbon fiber and the second carbon fiber. It was.

[Sample No.9]
Instead of the first carbon fiber (that is, the carbon fiber that has a mode value of 15 μm and satisfies σ1 <σ2), the third carbon fiber (that is, the mode value is 15 μm and satisfies σ1 = σ2) No. 9 membrane electrode assembly was obtained in the same procedure as No. 1, except that the catalyst ink was prepared using carbon fiber.
[Sample No. 10]
A membrane electrode assembly of No. 10 was obtained in the same procedure as No. 1, except that the catalyst ink was prepared without adding carbon fiber.

Each catalyst ink prepared in each example was measured using a laser diffraction particle size distribution measuring device, and the fiber length was calculated. Moreover, after performing the application | coating process with a die coater, catalyst ink was collect | recovered from the die coater and it confirmed that the particle size distribution of the catalyst ink was not changing.
In adjusting the content ratio of the first and second carbon fibers, two types of vapor-grown carbon fibers having different fiber length distributions are kneaded, and the center (mode) of these fiber length distributions is the second. It is about 10 μm for the carbon fiber and 15 μm for the first carbon fiber. However, when the preparation is repeated, the centers of the fiber length distributions are not exactly 10 μm and 15 μm, and there are variations of about 8.5 μm to 11.5 μm and 13.5 μm to 16.5 μm, respectively. Similarly, the volume ratio was adjusted.
The power generation performance and the thickness (μm) of the catalyst layer on the cathode side of the solid polymer fuel cell provided with the membrane electrode assembly of each sample thus obtained were measured as follows.

[Measurement of power generation performance]
Using a carbon cloth as a gas diffusion layer, disposing carbon cloth on both surfaces of each membrane electrode assembly, and sandwiching them with a pair of separators, each solid polymer fuel cell having a single cell structure was obtained. And the IV characteristic of each polymer electrolyte fuel cell was measured using the fuel cell measuring device (APMT-02 by Toyo Technica Co., Ltd.). At this time, pure hydrogen was used as the fuel gas, air was used as the oxidant gas, and a reversible hydrogen electrode (RHE) was used as the reference electrode, and the output voltage at 0.5 A / cm ² output was measured. The measurement was performed at N = 3, and the average value was calculated.

By dividing each average value by the output voltage of the polymer electrolyte fuel cell using the membrane electrode assembly of sample No. 10 (without the carbon fiber in the catalyst layer), sample No. 10 was 100 The relative value of the output voltage was calculated as 0.0. This value is shown in Table 1 together with the ratio of the first carbon fiber contained in the catalyst layer of each example.
Moreover, the relationship between the ratio (content ratio) of the first carbon fibers in the carbon fibers contained in the catalyst layer of each sample and the relative value (performance ratio) of the power generation performance is shown in the graph of FIG. In the graph of FIG. 6, the median value and the error range of the actual measurement value (relative value) are described.

[Measurement of catalyst layer thickness]
The thickness of the catalyst layer was measured by observing the cross section of the catalyst layer using a scanning electron microscope (SEM). Specifically, using a FE-SEM S-4800 manufactured by Hitachi High-Technology Co., Ltd., observing at 1000 times, measuring the thickness of the catalyst layer at five observation points, the average value is the thickness of the electrode catalyst layer It was. This value is also shown in Table 1.
At that time, when the membrane electrode assembly in which the carbon fibers contained in the catalyst layer are all third carbon fibers is used (No. 9), the thickness of the catalyst layer is smaller than the standard. Therefore, it was judged that the effect of suppressing the bulkiness of the membrane electrode assembly was observed.

[Observation of catalyst layer appearance]
After the catalyst ink of each sample was applied to the polymer electrolyte membrane and dried to form a catalyst layer, the catalyst layer was visually inspected by reflected light and transmitted light.
As a result, when a membrane electrode assembly containing no carbon fiber was used in the catalyst layer (No. 10), many cracks occurred, but the membrane electrode assemblies of Samples Nos. 1 to 9 In comparison with .10, it was confirmed that all cracks were reduced.

From the above results, by using a membrane electrode assembly including a first carbon fiber (a carbon fiber having a mode value of 15 μm and satisfying σ1 <σ2) in the catalyst layer, the carbon fiber is contained in the catalyst layer. Compared to the case of using a membrane electrode assembly that does not contain, the power generation performance of the polymer electrolyte fuel cell can be increased, cracks can be suppressed in the catalyst layer, and the third in the catalyst layer. It can be seen that the membrane electrode assembly can be suppressed from being bulky as compared to the case of using the membrane electrode assembly including carbon fibers (the carbon fiber having the mode value of 15 μm and σ1 = σ2).
Further, the first carbon fiber and the second carbon fiber (mode fibers having a mode value of 10 μm and satisfying σ3 <σ4) having different fiber length distributions are mixed in the catalyst layer, and the first carbon fiber is By using a membrane electrode assembly that is 60% by volume or more of the entire carbon fiber, cracks can be suppressed in the catalyst layer, and the power generation performance of the polymer electrolyte fuel cell can be particularly enhanced. It turns out that the effect which can suppress that a joined body is bulky is high.

According to the present invention, it has sufficient drainage and gas diffusibility necessary to avoid flooding, which is a problem in the operation of polymer electrolyte fuel cells, and can exhibit high power generation performance over the long term. An electrode catalyst layer, a membrane electrode assembly, and a polymer electrolyte fuel cell can be provided.
Therefore, since the present invention can be suitably used for a stationary cogeneration system using a solid polymer fuel cell, a fuel cell vehicle, and the like, the industrial utility value is great.

DESCRIPTION OF SYMBOLS 1 ... Polymer electrolyte membrane 2 ... Anode catalyst layer 3 ... Cathode catalyst layer 4 ... Gasket 5 ... Gas diffusion layer 8 ... Gas flow path 9 ... Cooling water flow path 10. ..Separator 11 ... Polymer fuel cell 12 ... Membrane electrode assembly 13 ... Unit cell 21 ... Catalyst 22 ... Carbon particle 23 ... Polymer electrolyte 24 ... Carbon Fiber 31... Region where the fiber length is longer than the mode value in the fiber length distribution of the first carbon fiber 32... Region 41 where the fiber length is shorter than the mode value in the fiber length distribution of the first carbon fiber 41 ... A region where the fiber length is longer than the mode value in the fiber length distribution of the second carbon fiber 42 ... A region 201 where the fiber length is shorter than the mode value in the fiber length distribution of the second carbon fiber・ Surface of the anode catalyst layer (surface opposite to the polymer electrolyte membrane)
301 ... surface of the cathode catalyst layer (surface opposite to the polymer electrolyte membrane)

Claims (7)

A catalyst layer constituting a membrane electrode assembly of a polymer electrolyte fuel cell,
Including carbon particles, a catalyst supported on the carbon particles, a polymer electrolyte, and a fibrous material,
Including a first fibrous material as the fibrous material;
The fiber length distribution of the first fibrous substance is a histogram in which the horizontal axis is the fiber length and the vertical axis is the volume, and the first standard deviation σ1 in the region where the fiber length is longer than the mode value and the fiber length is A catalyst layer in which the relationship with the second standard deviation σ2 in a region shorter than the mode value satisfies σ1 <σ2. The fibrous material further includes a second fibrous material,
The fiber length distribution of the second fibrous substance is a histogram in which the horizontal axis is the fiber length and the vertical axis is the volume, and the third standard deviation σ3 in the region where the fiber length is longer than the mode value and the fiber length is The relationship with the fourth standard deviation σ4 in the region shorter than the mode value satisfies σ3 <σ4,
The mode value of the fiber length of the second fibrous substance exists in a region shorter than the mode value of the fiber length of the first fibrous substance,
The catalyst layer according to claim 1, wherein the volume of the first fibrous material occupies 60% or more of the total volume of the first fibrous material and the second fibrous material.   The mode of the fiber length of said 1st fibrous substance is 13.5 micrometers or more and 16.5 micrometers or less, The catalyst layer of Claim 1 or 2.   The catalyst layer according to any one of claims 1 to 3, wherein the first fibrous substance is at least one of an electron conductive fiber and a proton conductive fiber.   The catalyst layer according to claim 4, wherein the first fibrous material is an electron conductive fiber and is at least one selected from carbon nanofibers, carbon nanotubes, and transition metal-containing fibers. A membrane electrode assembly comprising a polymer electrolyte membrane, and an anode side catalyst layer and a cathode side catalyst layer respectively disposed on both sides of the polymer electrolyte membrane,
The membrane electrode assembly in which at least one of the anode side catalyst layer and the cathode side catalyst layer is a catalyst layer according to any one of claims 1 to 5.   A polymer electrolyte fuel cell comprising the membrane electrode assembly according to claim 6.

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