JP2012212661A - Electrode catalyst layer for fuel cell, manufacturing method of electrode catalyst layer, membrane electrode assembly for fuel cell, and solid polymer fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode catalyst layer for fuel cell in which sufficient proton conductivity and gas diffusion properties are ensured, reaction active points are increased and the output performance is enhanced.SOLUTION: The electrode catalyst layer for fuel cell comprises a catalyst aggregate consisting of catalyst particles, a polymer electrolyte and first carbon particles not carrying the catalyst particles, and second carbon particles carrying the catalyst particles. The BET specific surface area of the first carbon particles is smaller than that of the second carbon particles. Furthermore, the BET specific surface area of the first carbon particles is 50-400 m/g, and the BET specific surface area of the second carbon particles is 500-2000 m/g.

Description

  The present invention relates to an electrode catalyst layer for a fuel cell, a method for producing the electrode catalyst layer, a membrane electrode assembly containing the electrode catalyst layer, and a polymer electrolyte fuel cell comprising the membrane electrode assembly.

  A fuel cell is a power generation system that generates electricity simultaneously with heat by causing a fuel gas containing hydrogen and an oxidant gas containing oxygen to undergo reverse reaction of water electrolysis at an electrode containing a catalyst. This power generation system has features such as high efficiency, low environmental load, and low noise as compared with conventional power generation systems, and is attracting attention as a clean energy source in the future. There are several types depending on the type of ion conductor used, and those using proton conductive polymer membranes are called solid polymer fuel cells.

  By the way, polymer electrolyte fuel cells among fuel cells can be used near room temperature, and therefore, they are considered promising for use in in-vehicle power sources and household stationary power sources. In recent years, various research and development have been conducted. It has been broken.

  The polymer electrolyte fuel cell has a membrane electrode assembly (Membrane Electrode Assembly; hereinafter referred to as MEA) having a pair of electrodes on both sides of a polymer electrolyte membrane. It is a battery that is sandwiched between a pair of separator plates in which a fuel gas containing hydrogen is supplied and an oxidant gas containing oxygen is supplied to the other electrode.

  Here, the electrode for supplying the fuel gas is called a fuel electrode, and the electrode for supplying the oxidant is called an air electrode. These electrodes generally include an electrode catalyst layer formed by laminating carbon particles carrying catalyst particles such as platinum-based noble metals and a polymer electrolyte, and a gas diffusion layer having both gas permeability and electron conductivity. Consists of.

  The reaction active point of the redox reaction of the fuel gas and oxidant gas in the electrode catalyst layer is a part called a three-phase interface where the electron conductor, the proton conductor, and the surface of the catalyst to which the introduced gas can adsorb are in contact. . When the area of the three-phase interface is large and the supply paths of electrons, protons, and gases to the three-phase interface are satisfied, the redox reaction in the electrode catalyst layer proceeds smoothly and efficiently. For this reason, it is necessary to sufficiently ensure the electron and proton transfer paths, the gas diffusion paths, and the like in the electrode catalyst layer.

  Conventionally, an electrode catalyst layer is often formed on a substrate using an ink in which a catalyst, an electron conductor, a polymer electrolyte having proton conductivity, and a solvent are mixed. However, it is difficult to adjust the amount of the polymer electrolyte on the catalyst surface by such a conventional forming method.

  That is, if the electrolyte layer in the vicinity of the catalyst is thick, proton conductivity can be ensured, but some of the pores between the catalyst particles are likely to be clogged, and gas diffusibility may be reduced. Conversely, if the electrolyte layer near the catalyst is thin, gas diffusibility can be ensured, but proton conductivity will be insufficient.

  In order to solve such a problem, for example, Patent Document 1 proposes a composite catalyst that can ensure proton conductivity and gas diffusibility by coating the catalyst surface with a porous polymer electrolyte.

  Further, for example, Patent Document 2 proposes a method for preventing elution of the polymer electrolyte coated on the catalyst surface by heat-treating the composite particles in order to ensure proton conductivity more reliably.

  In addition, for example, in Patent Document 3, since the electrode catalyst layer includes an electrolyte aggregate in addition to the catalyst coated with the polymer electrolyte, the amount of the coated polymer electrolyte can be easily adjusted, and proton conductivity and We have proposed an electrode catalyst layer that easily balances gas diffusivity.

  On the other hand, for example, in Patent Document 4, in order to improve gas diffusibility, a carbon material not supporting catalyst particles for gas diffusion is added to the electrode catalyst layer in addition to the carbon material supporting catalyst, and the carbon material supporting the catalyst is added. An electrode catalyst layer comprising an aggregate of a polymer electrolyte and an aggregate of a carbon material not supporting catalyst particles is proposed.

JP 2001-300344 A Japanese Patent Laid-Open No. 7-254419 Japanese Patent Laid-Open No. 11-126615 JP 2009-252359 A

  However, in the methods described in Patent Documents 1 and 2, the proton conduction path is only the polymer electrolyte coated on the catalyst, and the gas diffusibility and the strength of the electrode catalyst layer are adjusted in detail by the amount of the polymer electrolyte. Is difficult.

  Further, in the method described in Patent Document 3, since the catalyst ink is prepared in a poor solvent in which electrolyte aggregates are deposited, the catalyst surface is fully utilized by aggregation of the catalyst coated with the polymer electrolyte. There is a problem that you can not.

  Further, in the method described in Patent Document 4, since the catalyst particles are supported on the carbon material and then coated on the polymer electrolyte, the properties of the carbon material that maintains the catalyst performance and the polymer electrolyte are suitable. It is necessary to balance the physical properties of the carbon material.

  Accordingly, the present invention solves the above-described problems, ensures sufficient proton conductivity and gas diffusibility, increases the reaction active point, and improves the output performance, and the electrode catalyst layer for a fuel cell, the electrode It is an object of the present invention to provide a method for producing a catalyst layer, a membrane electrode assembly for a fuel cell, and a polymer electrolyte fuel cell.

  The present invention employs the following configuration in order to solve the above problems.

  The first invention is an electrode catalyst layer for a fuel cell. The electrode catalyst layer includes catalyst aggregates and second carbon particles that do not carry catalyst particles. The catalyst aggregate includes catalyst particles, a polymer electrolyte, and first carbon particles that do not carry the catalyst particles. In addition, the BET specific surface area of the first carbon particles is smaller than that of the second carbon particles.

In a second invention according to the first invention, the BET specific surface area of the first carbon particles is 50 to 400 m ² / g, and the BET specific surface area of the second carbon particles is 500 to 2000 m ² / g. It is characterized by being.

  A third invention is a membrane electrode assembly for a fuel cell. The membrane electrode assembly includes a proton conductive polymer electrolyte membrane sandwiched between a pair of electrode catalyst layers and a pair of gas diffusion layers. Further, at least one of the pair of electrode catalyst layers is the electrode catalyst layer in the first invention or the second invention.

  A fourth invention is a polymer electrolyte fuel cell. In the polymer electrolyte fuel cell, the membrane electrode assembly in the third invention is sandwiched between a pair of gas diffusion layers, and the membrane electrode assembly sandwiched between the gas diffusion layers is a pair of separators. It is characterized by being pinched.

  5th invention is the manufacturing method of the electrode catalyst layer for fuel cells. The manufacturing method includes preparing a first catalyst ink in which catalyst particles, a polymer electrolyte, and first carbon particles not supporting the catalyst particles are dispersed in a solvent, drying the first catalyst ink, A catalyst aggregate forming step for forming an aggregate and a second catalyst ink in which the catalyst aggregate and the second carbon particles not supporting the catalyst particles are dispersed in a solvent are prepared. An electrode catalyst layer forming step of applying an electrode catalyst layer to form an electrode catalyst layer.

  A sixth invention is characterized in that, in the fifth invention, the drying temperature in the catalyst aggregate formation step is in the range of 30 ° C. or more and 140 ° C. or less.

  7th invention is the manufacturing method of the electrode catalyst layer for fuel cells. The manufacturing method includes a first catalyst ink adjustment step of adjusting a first catalyst ink in which catalyst particles, a polymer electrolyte, and first carbon particles not supporting catalyst particles are dispersed in a first solvent; The second catalyst ink composed of the catalyst aggregate and the second carbon particles is mixed by mixing the first catalyst ink with the second solvent in which the second carbon particles not supporting the catalyst particles are dispersed. A second catalyst ink adjusting step for adjusting; and an electrode catalyst layer forming step for forming an electrode catalyst layer by applying the second catalyst ink on the substrate. In addition, the ratio of the relative dielectric constant between the first solvent and the second solvent is in the range of 1.05: 1 to 20: 1.

  According to the present invention, while ensuring the gas diffusibility of the electrode catalyst layer, the catalyst active surface is formed by forming a catalyst aggregate in which a sufficient amount of polymer electrolyte is coated on the surface of the catalyst particles to ensure proton conductivity. An electrode catalyst layer for a fuel cell with improved output performance, a method for producing the electrode catalyst layer, a membrane electrode assembly containing the electrode catalyst layer, and a polymer electrolyte fuel cell comprising the membrane electrode assembly Can be provided. Furthermore, since it leads to a reduction in the amount of catalyst used, there is a possibility of cost reduction, so the industrial utility value is high.

Schematic diagram of the structure of an electrode catalyst layer for a fuel cell according to an embodiment of the present invention Schematic diagram of the structure of the electrocatalyst layer produced by the conventional formation method Schematic sectional view of a membrane electrode assembly containing an electrode catalyst layer Schematic exploded view showing a polymer electrolyte fuel cell

  The electrode catalyst layer for a fuel cell according to the embodiment of the present invention will be described below. The embodiments of the present invention are 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. Embodiments to which is added can also be included in the scope of the embodiments of the present invention.

  Hereinafter, after describing the electrode catalyst layer for a fuel cell according to the embodiment of the present invention, a method for manufacturing the electrode catalyst layer will be described.

  First, an electrode catalyst layer for a fuel cell according to an embodiment of the present invention will be described.

<Electrocatalyst layer>
FIG. 1 is a schematic diagram showing the structure of an electrode catalyst layer 21 for a fuel cell according to an embodiment of the present invention. In the following description, the electrode catalyst layer 21 for a fuel cell is simply referred to as an electrode catalyst layer 21.

  As shown in FIG. 1, an electrode catalyst layer 21 according to an embodiment of the present invention includes a catalyst aggregate composed of catalyst particles 1, first carbon particles 4 that do not carry catalyst particles 1, and polymer electrolyte 3. 10 and second carbon particles 5 that do not carry the catalyst particles 1. In the following description, the first carbon particles 4 not supporting the catalyst particles 1 are simply referred to as first carbon particles 4 and the second carbon particles 5 not supporting the catalyst particles 1. Is simply referred to as second carbon particles 5.

  Here, FIG. 2 shows the structure of the electrode catalyst layer 51 produced by the conventional forming method. FIG. 2 is a schematic view showing the structure of the electrode catalyst layer 51 produced by a conventional forming method. As shown in FIG. 2, an electrode catalyst layer 51 produced by a conventional forming method includes catalyst particles 1, an electron conductor 2, and a polymer electrolyte 3.

  Returning to the description of FIG. 1, the catalyst particles 1 may be any particles as long as they have oxygen reducing ability, but platinum is particularly preferably used. In addition to platinum group elements such as palladium, ruthenium, iridium, rhodium and osmium, metals such as iron, lead, copper, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, and aluminum, or alloys thereof, or oxidation There is no problem even if a material, a double oxide or the like is used.

  Further, as the catalyst particles 1, carbonitrides of transition metal elements such as tantalum, zirconium, niobium, titanium, carbonitride partial oxides, oxides, oxynitrides, etc. may be used, carbon, You may use the substance which consists of elements other than metals, such as nitrogen and boron.

The first carbon particle 4 may be any material as long as it has a BET specific surface area of 50 to 400 m ² / g, is in the form of fine particles, has conductivity, and is not exposed to the catalyst.

  Specifically, as the first carbon particles 4, carbon black, graphite, graphite, activated carbon, carbon fiber, carbon nanotube, fullerene, or the like can be used. Further, as the first carbon particles 4, for example, carbon black, activated carbon or the like as a raw material and heat-treated at a high temperature of 1000 ° C. or higher in an inert atmosphere and graphitized may be used.

In addition, if the BET specific surface area is less than 50 m ² / g, the contact property with the catalyst particles 1 is low, and it becomes difficult to ensure the conductivity, and if it exceeds 400 m ² / g, the high concentration contained in the catalyst aggregate 10 described later. The molecular electrolyte 3 covers the first carbon particles 4 excessively, and it becomes difficult to ensure the proton conductivity on the surfaces of the catalyst particles 1.

The second carbon particles 5 may be any one as long as it has a BET specific surface area of 500 to 2000 m ² / g, is fine, has conductivity, and is not exposed to the catalyst.

Specifically, as the second carbon particles 5, carbon black, graphite, graphite, activated carbon, carbon fiber, carbon nanotube, fullerene, or the like can be used. If the BET specific surface area is less than 500 m ² / g, it becomes difficult to ensure the gas diffusibility of the electrode catalyst layer 21, and it becomes difficult to maintain the output performance of the electrode catalyst layer 21. On the other hand, if the BET specific surface area exceeds 2000 m ² / g, the thickness of the catalyst layer becomes too thick, which inhibits gas diffusion and makes it difficult to maintain output performance.

  The above-mentioned BET specific surface area is measured by nitrogen adsorption.

  On the other hand, if the particle diameters of the first carbon particles 4 and the second carbon particles 5 are too small, it is difficult to form an electron conduction path, and if too large, the gas diffusibility of the electrode catalyst layer is reduced, or the catalyst Since the utilization factor of the slag decreases, the thickness is preferably about 10 to 1000 nm, more preferably about 10 to 100 nm.

  Even if the first carbon particles 4 carry the catalyst particles 1, they can be coated with a polymer electrolyte, but when the first carbon particles 4 do not carry the catalyst particles 1. However, the first carbon particles 4 can be selected without considering the catalyst performance of the catalyst-carrying carbon particles. The second carbon particles 5 may carry the catalyst particles 1, but the second carbon particles 5 may not be sufficiently coated with a polymer electrolyte, and the supported catalyst may be present. There is a possibility that the utilization rate of the particles 1 is reduced, leading to an increase in cost.

  The polymer electrolyte 3 contained in the electrode catalyst layer 21 may be any one having proton conductivity, and a fluorine polymer electrolyte, a hydrocarbon polymer electrolyte, or the like can be used. The polymer electrolyte membrane used for the membrane / electrode assembly may be any one having proton conductivity, and a fluorine-based polymer electrolyte or a hydrocarbon-based polymer electrolyte can be used. In consideration of the adhesion between the electrode catalyst layer 21 and the polymer electrolyte membrane, it is preferable to use the same material as the electrode catalyst layer 21.

  Next, the manufacturing method of an electrode catalyst layer is demonstrated.

<Method for producing electrode catalyst layer>
In the method for producing an electrode catalyst layer according to the embodiment of the present invention, the catalyst aggregate 10 composed of the catalyst particles 1, the polymer electrolyte 3, and the first carbon particles 4, and the second carbon particles 5 are used. In the electrode catalyst layer 21, the BET specific surface area of the first carbon particles 4 is smaller than that of the second carbon particles 5.

  That is, in the electrode catalyst layer manufacturing method according to the embodiment of the present invention, the BET ratio of the first carbon particles 4 in the electrode catalyst layer 21 composed of the catalyst aggregate 10 and the second carbon particles 5 is used. The surface area is smaller than that of the second carbon particles 5. By doing in this way, the catalyst aggregate 10 which coat | covered sufficient polymer electrolyte 3 on the surface of the catalyst particle 1 can be formed, ensuring the gas diffusibility of the electrode catalyst layer 21. FIG. As a result, proton conductivity can be ensured, the reaction active point can be increased, and the output performance of the electrode catalyst layer 21 can be improved.

  The first carbon particles 4 and the second carbon particles 5 are the same in type, shape, size, etc. if the BET specific surface area of the first carbon particles 4 is smaller than that of the second carbon particles 5. Or different.

  Specifically, the method for producing the electrode catalyst layer according to the embodiment of the present invention is as follows.

  In the method for producing an electrode catalyst layer according to the embodiment of the present invention, first, catalyst particles 1, polymer electrolyte 3, and first carbon particles 4 are dispersed in a solvent to prepare a first catalyst ink. Then, the catalyst aggregate 10 is obtained by drying the first catalyst ink.

  The first catalyst ink can be dried using a container or a substrate that can withstand a required drying temperature. For example, there are a method of applying the first catalyst ink to the substrate and drying the coating film, a method of putting the first catalyst ink in an open container and drying it as it is.

  In the step of forming the catalyst aggregate 10, the amount of elution of the polymer electrolyte 3 in the catalyst aggregate 10 into the solvent can be controlled by adjusting the drying temperature.

  Specifically, the drying temperature is preferably 30 ° C. or higher and 140 ° C. or lower. When the drying temperature is less than 30 ° C., most of the polymer electrolyte 3 in the catalyst aggregate 10 is dissolved in the solvent in the step of preparing the second catalyst ink described later, and the polymer electrolyte 3 on the surface of the catalyst particles 1 is dissolved. In some cases, the output performance of the electrode catalyst layer 21 is not improved. On the other hand, when the drying temperature exceeds 140 ° C., it becomes difficult for the polymer electrolyte 3 in the catalyst aggregate 10 to elute into the second solvent described later, the proton conductivity in the electrode catalyst layer 21 decreases, and the electrode catalyst The output performance of the layer 21 may not be improved.

  More preferably, it is preferably 50 ° C. or higher and 130 ° C. or lower. When the drying temperature exceeds 130 ° C., the variation in the content of the polymer electrolyte 3 in the obtained catalyst aggregate 10 tends to increase. On the other hand, when the drying temperature is less than 50 ° C., the productivity of the catalyst aggregate 10 may decrease.

  In addition, the catalyst aggregate 10 may be obtained by the method described below in addition to the manufacturing method described above.

  First, the catalyst particles 1, the polymer electrolyte 3, and the first carbon particles 4 are dispersed in a first solvent to prepare a first catalyst ink. Further, the second catalyst ink in which the second carbon particles 5 are dispersed in the second solvent is prepared. Then, the catalyst aggregate 10 is obtained by mixing the first catalyst ink and the second catalyst ink.

  In the step of forming the catalyst aggregate 10, the polymer electrolyte 3 in the catalyst aggregate 10 is adjusted by adjusting the relative dielectric constant ratio between the first solvent and the second solvent. The amount of elution into the second solvent can be controlled.

  Specifically, the relative dielectric constant ratio between the first solvent and the second solvent is preferably in the range of 1.05: 1 to 20: 1. When the relative dielectric constant ratio is less than 1.05: 1, most of the polymer electrolyte 3 in the catalyst aggregate 10 is dissolved in the second solvent, and the amount of the polymer electrolyte 3 on the surface of the catalyst particle 1 is inadequate. The output performance of the electrode catalyst layer 21 may not be improved. On the other hand, when the relative dielectric constant ratio exceeds 20: 1, the polymer electrolyte 3 in the catalyst aggregate 10 becomes difficult to elute into the second solvent, and the proton conductivity in the electrode catalyst layer 21 decreases, and the electrode The output performance of the catalyst layer 21 may not be improved.

The relative permittivity ε ₁ of the first solvent is preferably ε ₁ > 10, and the relative permittivity ε ₂ of the second solvent is preferably 3 <ε ₂ <10.

  Here, the first catalyst ink is obtained by dispersing the catalyst particles 1, the polymer electrolyte 3, and the first carbon particles 4 in a first solvent. In the step of adjusting the first catalyst ink, the weight ratio of the catalyst particles 1, the polymer electrolyte 3, and the first carbon particles 4 in the electrode catalyst layer 21 is controlled by the composition of the catalyst ink. Can do.

  On the other hand, the second catalyst ink disperses the catalyst aggregate 10 and the second carbon particles 5 or the first catalyst ink and the second carbon particles 5 described above in the second solvent. It is obtained by. In the step of adjusting the second catalyst ink, the weight ratio of the catalyst particles 1, the polymer electrolyte 3, and the second carbon particles 5 in the electrode catalyst layer 21 is controlled by the composition of the catalyst ink. Can do.

  If the solid content in the second catalyst ink is too large, the viscosity of the catalyst ink becomes high, so that the surface of the electrode catalyst layer 21 is likely to crack, and conversely if it is too small, the film formation rate is high. It is very slow and productivity decreases. Therefore, the solid content in the second catalyst ink is preferably 1 to 50% by mass.

  Moreover, although solid content consists of the catalyst particle 1, the polymer electrolyte 3, the 1st carbon particle 4, and the 2nd carbon particle 5, since a bulky substance is used suitably for a carbon particle, each carbon particle If the amount is increased, the viscosity increases even with the same solid content, and if it is decreased, the viscosity decreases.

  In particular, in the case of the second carbon particles 5, this tendency becomes remarkable. Further, the viscosity of each catalyst ink at this time is preferably about 0.1 to 500 cP, more preferably 5 to 100 cP. Further, the viscosity can be controlled by adding a dispersing agent when dispersing each catalyst ink.

  In the production of the first catalyst ink and the second catalyst ink, a dispersion process is performed as necessary. The viscosity and particle size of each catalyst ink can be controlled by the conditions for the dispersion treatment of each catalyst ink. Distributed processing can be performed using various devices. For example, examples of the dispersion process include a process using a ball mill and a roll mill, and an ultrasonic dispersion process.

  Here, the solvent used as a dispersion medium is not particularly limited as long as it does not erode the catalyst particles 1 and the polymer electrolyte 3 and can dissolve or disperse the polymer electrolyte 3 in a highly fluid state as a fine gel. There is no. However, it is desirable to include at least a volatile organic solvent, and is not particularly limited, but alcohols, ketone solvents, ether solvents, other dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, Polar solvents such as diethylene glycol, diacetone alcohol, and 1-methoxy-2-propanol are used. Moreover, what mixed 2 or more types of these solvents can also be used.

  In addition, when a lower alcohol is used as the dispersion medium, there is a high risk of ignition, and when using such a solvent, it is preferable to use a mixed solvent with water. Water that is compatible with the polymer electrolyte 3 may be contained. The amount of water added is not particularly limited as long as the polymer electrolyte is not separated to cause white turbidity or gelation.

  Moreover, a pore forming agent may be included in the second catalyst ink. The pore forming agent can form pores by removing after the formation of the electrode catalyst layer 21. In addition, examples of the pore-forming agent include acids, alkalis, water-soluble substances, substances that sublime such as camphor, and substances that thermally decompose. It may be removed with water.

  Next, in the step of producing the electrode catalyst layer 21 from the second catalyst ink, the second catalyst ink is applied on the substrate, and the electrode catalyst layer 21 is formed through a drying step.

  In addition, as a base material, the film | membrane of a gas diffusion layer, a transfer sheet, or the polymer electrolyte 3 can be used. As the gas diffusion layer, a material having gas diffusibility and conductivity can be used. The transfer sheet may be any material having good transferability, and for example, a fluororesin film can be used.

  Next, the membrane electrode assembly containing the electrode catalyst layer will be described.

<Membrane electrode assembly>
FIG. 3 is a schematic cross-sectional view of a membrane electrode assembly 31 containing an electrode catalyst layer according to the present embodiment. As shown in FIG. 3, the membrane electrode assembly 31 according to the present embodiment includes a solid polymer electrolyte membrane 11, an electrode catalyst layer 21 provided on one surface of the solid polymer electrolyte membrane 11, And an electrode catalyst layer 21 provided on the other surface of the polymer electrolyte membrane 11. Further, an air electrode side gas diffusion layer (not shown) is provided on the surface of the electrode catalyst layer 21, and a fuel electrode side gas diffusion layer (not shown) is provided on the surface of the electrode catalyst layer 21.

  Specifically, the membrane electrode assembly 31 cuts out the base material on which the electrode catalyst layer 21 is formed, arranges a transfer sheet so as to face both surfaces of the solid polymer electrolyte membrane 11, and performs hot pressing. Can be obtained. When a gas diffusion layer or a transfer sheet is used as the substrate, the electrode catalyst layer 21 is bonded to both surfaces of the solid polymer electrolyte membrane 11 by a bonding process. In the membrane electrode assembly 31, the solid polymer electrolyte membrane 11 is used as a base material, and the second catalyst ink is directly applied to both surfaces of the solid polymer electrolyte membrane 11, so that both surfaces of the solid polymer electrolyte membrane 11 are coated. Alternatively, the electrode catalyst layer 21 can be directly formed.

  Next, a polymer electrolyte fuel cell provided with a membrane electrode assembly will be described.

<Polymer fuel cell>
Hereinafter, the polymer electrolyte fuel cell 41 provided with the membrane electrode assembly 31 according to the embodiment of the present invention will be described. FIG. 4 is a schematic exploded schematic view showing the polymer electrolyte fuel cell 41.

  As shown in FIG. 4, the polymer electrolyte fuel cell 41 includes a membrane electrode assembly 31 having electrode catalyst layers 21 on both surfaces of the solid polymer electrolyte membrane 11, and faces the electrode catalyst layer 21 to the air electrode. A side gas diffusion layer 6 and a fuel electrode side gas diffusion layer 7 are arranged, and an air electrode 8 and a fuel electrode 9 are formed, respectively. The separator 12 is made of a material that is conductive and impermeable. In the separator 12, a gas flow path 13 for gas flow and a cooling water flow path 14 for flow of cooling water are formed on the main surface opposite to the surface on which the gas flow path 13 is formed. As shown in FIG. 4, the separator 12 is disposed so as to sandwich the air electrode side gas diffusion layer 6 and the fuel electrode side gas diffusion layer 7. An example of the fuel gas is hydrogen gas. An oxidant gas is supplied from the gas flow path 13 of the separator 12 on the air electrode 8 side. As the oxidant gas, for example, a gas containing oxygen is supplied.

  In the polymer electrolyte fuel cell 41, carbon cloth having a sealing layer formed as the gas diffusion layers 6 and 7 is disposed on both surfaces of the membrane electrode assembly 31, and is further sandwiched between a pair of separators 12. It is obtained by doing.

  In the case of using a transfer sheet as the base material for the membrane electrode assembly 31 and the polymer electrolyte fuel cell 41, the transfer sheet is peeled off after joining the electrode catalyst layer 21 to the solid polymer electrolyte membrane 11, and the solid sheet It can be set as the membrane electrode assembly 31 provided with the catalyst layer 21 on both surfaces of the polymer electrolyte membrane 11. FIG. It is not necessary to peel off the base material which is the gas diffusion layers 6 and 7 after the bonding step of the gas diffusion layers 6 and 7 as the base material.

  At this time, as a coating method, a doctor blade method, a dipping method, a screen printing method, a roll coating method, a spray method, or the like can be used.

  As the gas diffusion layers 6 and 7 and the separator 12, those used in ordinary fuel cells can be used. Specifically, porous carbon materials such as carbon cloth, carbon paper, and nonwoven fabric can be used as the gas diffusion layers 6 and 7. As the separator, a carbon type or a metal type can be used. The fuel cell is manufactured by assembling other accompanying devices such as a gas supply device and a cooling device.

  Hereinafter, although this invention is further demonstrated based on Examples 1-3 and the comparative example 1, this invention is not restrict | limited by the following Example.

Example 1
[Adjustment of first catalyst ink]
Catalyst particles 1, a solution of polymer electrolyte 3 (Nafion: registered trademark, manufactured by DuPont), and first carbon particles 4 (BET specific surface area = 120 m ² / g) obtained by heat treating carbon black. A dispersion treatment was performed on the added solvent to prepare a mixture of the catalyst particles 1, the polymer electrolyte 3, and the first carbon particles 4.
[Formation of catalyst aggregates]
The said mixture was apply | coated on the base material with the doctor blade, and it was made to dry at 120 degreeC in air | atmosphere for 5 minutes. Thereafter, the catalyst aggregate 10 was obtained by collecting the mixture on the substrate.

[Adjustment of second catalyst ink]
The catalyst aggregate 10 and the second carbon particles 5 (Ketjen Black (registered trademark), trade name: EC-300J, manufactured by Lion Corporation, BET specific surface area = 800 m ² / g) are mixed in a solvent and dispersed. Went.
[Formation of electrode catalyst layer]
The second catalyst ink was applied to the transfer sheet with a doctor blade, and dried in air at 80 ° C. for 5 minutes to obtain an electrode catalyst layer 21. The thickness of the electrode catalyst layer 21 was adjusted so that the supported amount of the catalyst particles 1 was 0.3 mg / cm ² .

(Example 2)
[Adjustment of first catalyst ink]
Catalyst particles 1, a solution of polymer electrolyte 3 (Nafion: registered trademark, manufactured by DuPont), and first carbon particles 4 (BET specific surface area = 120 m ² / g) obtained by heat treating carbon black. A dispersion treatment was performed on the added first solvent to prepare a mixture of the catalyst particles 1, the polymer electrolyte 3, and the first carbon particles 4. The first solvent was ultrapure water and 1-propanol in a volume ratio of 1: 1, and the relative dielectric constant was about 55.

[Adjustment of second catalyst ink]
The second carbon particles 5 (Ketjen Black (registered trademark), trade name: EC-300J, manufactured by Lion Corporation, BET specific surface area = 800 m ² / g) were added to the second solvent for dispersion treatment. And the 1st catalyst ink was dripped and mixed, stirring, and the 2nd catalyst ink which consists of the catalyst aggregate 10 and the 2nd carbon particle 5 was adjusted. The second solvent was butyl acetate, and the relative dielectric constant was about 5.
[Formation of electrode catalyst layer]
The second catalyst ink was applied to the transfer sheet with a doctor blade, and dried in air at 80 ° C. for 5 minutes to obtain an electrode catalyst layer 21. The thickness of the electrode catalyst layer 21 was adjusted so that the supported amount of the catalyst particles 1 was 0.3 mg / cm ² .

(Example 3)
In the preparation of the first catalyst ink, (Ketjen Black (registered trademark), trade name: EC-300J, manufactured by Lion Corporation, BET specific surface area = 800 m ² / g) is used as the first carbon particles 4, The above-described implementation was performed except that (Ketjen Black (registered trademark), trade name: EC-600JD, manufactured by Lion Corporation, BET specific surface area = 1270 m ² / g) was used as the second carbon particle 5 in the preparation of the catalyst ink. The electrode catalyst layer 21 was formed in the same manner as in Example 1.

(Comparative Example 1)
[Preparation of catalyst ink by conventional technology]
The carbon particles supporting the catalyst particles and the polymer electrolyte solution were mixed in a solvent and subjected to a dispersion treatment. The composition ratio of the catalyst ink and the solvent were the same as in the examples.

[Formation of electrode catalyst layer]
In the same manner as in the example, the catalyst ink was applied to the transfer sheet and dried. The thickness of the electrode catalyst layer was adjusted so that the amount of catalyst particles supported was 0.3 mg / cm ² to form an electrode catalyst layer.

[Production of membrane electrode assembly and polymer electrolyte fuel cell]
The base material on which the electrode catalyst layer 21 prepared in Examples 1 to 3 and Comparative Example described above was formed was punched into a 5 cm ² square so as to face both surfaces of a polymer electrolyte membrane (Nafion 212, manufactured by DuPont). A transfer sheet was placed on the substrate and hot pressed at 130 ° C. to obtain a membrane electrode assembly 31. A carbon cloth having a sealing layer formed as a gas diffusion layer is disposed on both surfaces of the obtained membrane electrode assembly 31, and is further sandwiched between a pair of separators to produce a single cell polymer electrolyte fuel cell 41. did.

[Power generation characteristics]
(Evaluation conditions)
The power generation characteristics were evaluated at a cell temperature of 80 ° C. using a fuel cell measuring device manufactured by NF Circuit Design Block. Using hydrogen gas as the fuel gas and air gas as the oxidant gas, the flow rate was controlled at a constant flow rate.

(Measurement result)
The membrane electrode assemblies 31 produced in Examples 1 to 3 exhibited a power generation evaluation that was particularly superior to the membrane electrode assemblies 31 produced in the comparative examples. This is presumed that in Examples 1 to 3, the proton conductivity on the catalyst surface was increased by forming the catalyst aggregate 10 composed of the catalyst particles 1, the polymer electrolyte 3, and the carbon particles, and the reaction active points increased. Is done.

  Moreover, the membrane electrode assembly 31 produced in Examples 1 and 2 showed a power generation evaluation superior to the membrane electrode assembly 31 produced in Example 3. This is presumably because in Example 3, the BET specific surface area of the first carbon particles 4 was too large, the polymer electrolyte 3 on the catalyst surface was insufficient, and the proton conductivity was lowered.

  When a membrane electrode assembly was produced using the electrode catalyst layer for a fuel cell according to the present invention and a polymer electrolyte fuel cell having the membrane electrode assembly was produced, it was found that high power generation characteristics were exhibited.

  An electrode catalyst layer for a fuel cell according to the present invention, and a method for producing the electrode catalyst layer include a membrane electrode assembly containing the electrode catalyst layer, a polymer electrolyte fuel cell including the membrane electrode assembly, and the like Can be used usefully.

DESCRIPTION OF SYMBOLS 1 Catalyst particle 2 Electronic conductor 3 Polymer electrolyte 4 1st carbon particle 5 2nd carbon particle 6 Air electrode side gas diffusion layer 7 Fuel electrode side gas diffusion layer 8 Air electrode 9 Fuel electrode 10 Catalyst aggregate 11 Solid height Molecular electrolyte membrane 12 Separator 13 Gas flow path 14 Cooling water flow path 21, 51 Electrode catalyst layer 31 Membrane electrode assembly 41 Solid polymer fuel cell

Claims (7)

An electrode catalyst layer for a fuel cell,
A catalyst aggregate comprising catalyst particles, a polymer electrolyte, and first carbon particles not supporting the catalyst particles;
Second carbon particles not carrying the catalyst particles,
The electrode catalyst layer for a fuel cell, wherein the BET specific surface area of the first carbon particles is smaller than that of the second carbon particles. The BET specific surface area of the first carbon particles is 50 to 400 m ² / g,
2. The electrode catalyst layer for a fuel cell according to claim 1, wherein the second carbon particles have a BET specific surface area of 500 to 2000 m ² / g. A membrane electrode assembly for a fuel cell,
A proton conductive polymer electrolyte membrane sandwiched between a pair of electrode catalyst layers is sandwiched between a pair of gas diffusion layers,
The membrane electrode assembly for a fuel cell, wherein at least one of the pair of electrode catalyst layers is the electrode catalyst layer according to claim 1.   The membrane electrode assembly according to claim 3 is sandwiched between a pair of gas diffusion layers, and the membrane electrode assembly sandwiched between the gas diffusion layers is sandwiched between a pair of separators. A polymer electrolyte fuel cell. A method for producing an electrode catalyst layer for a fuel cell, comprising:
A first catalyst ink in which catalyst particles, a polymer electrolyte, and first carbon particles not supporting the catalyst particles are dispersed in a solvent is prepared, and the first catalyst ink is dried to form a catalyst aggregate. A catalyst agglomerate forming step,
A second catalyst ink in which the catalyst aggregate and the second carbon particles not supporting the catalyst particles are dispersed in a solvent is prepared, and the second catalyst ink is applied onto a substrate to form an electrode catalyst. A method for producing an electrode catalyst layer for a fuel cell, comprising: an electrode catalyst layer forming step of forming a layer.   6. The method for producing an electrode catalyst layer for a fuel cell according to claim 5, wherein the drying temperature in the catalyst aggregate formation step is within a range of 30 ° C. or more and 140 ° C. or less. A method for producing an electrode catalyst layer for a fuel cell, comprising:
A first catalyst ink adjustment step of adjusting a first catalyst ink in which catalyst particles, a polymer electrolyte, and first carbon particles not supporting the catalyst particles are dispersed in a first solvent;
A second solvent composed of a catalyst aggregate and the second carbon particles is mixed by mixing the first catalyst ink with the second solvent in which the second carbon particles not supporting the catalyst particles are dispersed. A second catalyst ink adjustment step for adjusting the catalyst ink;
An electrode catalyst layer forming step of applying the second catalyst ink on a substrate to form an electrode catalyst layer,
The method for producing an electrode catalyst layer for a fuel cell, wherein a ratio of a relative dielectric constant between the first solvent and the second solvent is in a range of 1.05: 1 to 20: 1.