JP5569093B2 - Method for producing electrode catalyst layer for fuel cell - Google Patents

Description

The present invention relates to a manufacturing method of the fuel cell electrode catalyst layer.

  A fuel cell is a power generation system that generates electricity simultaneously with heat by causing a hydrogen gas-containing fuel gas and an oxygen-containing oxidant gas to undergo reverse reaction of water electrolysis at an electrode including 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.

Among fuel cells, polymer electrolyte fuel cells can be used near room temperature, so 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. Yes. A solid polymer fuel cell is a battery in which a joined body in which a pair of electrodes are disposed on both sides of a polymer electrolyte membrane is sandwiched between a pair of separator plates. Here, the pair of separator plates is used to supply a separator plate having a gas flow path for supplying a fuel gas containing hydrogen to one of the electrodes, and an oxidant gas containing oxygen to the other of the electrodes. And a separator plate in which a gas flow path is formed. Of the pair of electrodes, an electrode for supplying fuel gas is called a fuel electrode, and an electrode for supplying oxidant gas is called an air electrode. These electrodes generally have electrode catalyst layers in which catalyst material-carrying particles, which are carbon particles carrying a catalyst material such as a platinum-based noble metal, and a polymer electrolyte layer, and gas permeability and electronic conductivity. It consists of a gas diffusion layer.
A polymer electrolyte membrane, an air electrode side electrode catalyst layer disposed on one surface of the polymer electrolyte membrane, and a fuel electrode side electrode catalyst layer disposed on the other surface of the polymer electrolyte membrane. A joined body called a membrane electrode assembly (hereinafter referred to as MEA) is formed.

  The reaction active point of the redox reaction with the fuel gas and oxidant gas in the electrode catalyst layer is the part called the three-phase interface where the surface of the catalyst that can adsorb the electron conductor and proton conductor and the introduced gas is in contact. is there. When the area of the three-phase interface is large and the supply paths for electrons, protons, and introduced gas 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.

  In order to increase the output of a fuel cell, for example, in Patent Document 1, the surface of a catalyst carrier that supports catalyst particles and catalyst particles is coated with a first solid polymer electrolyte layer that is insoluble in water and an organic solvent. There has been proposed a polymer electrolyte type electrochemical cell electrode having a second solid polymer electrolyte layer that is soluble or insoluble in an organic solvent on the surface of a first solid polymer electrolyte. According to this electrode, since the first solid polymer electrolyte layer is insoluble in the organic solvent, the elution of the solid polymer electrolyte layer covering the catalyst can be prevented when the electrode is produced, and the second The solid polymer electrolyte layer can strengthen the bonding of the catalyst carrier weakened by the heat treatment.

In Patent Document 1, in order to make the first solid polymer electrolyte layer insoluble in water and an organic solvent, the supported catalyst carrying the catalyst particles is immersed in the solid polymer electrolyte solution to remove the solvent. Then, after the surfaces of the catalyst particles are coated with the solid polymer electrolyte, the catalyst particles coated with the solid polymer electrolyte are heat-treated.
As another method for increasing the output of the fuel cell, a water content distribution of the electrode catalyst layer is provided.

  For example, utilizing the fact that solid polymer electrolyte resin has a moisture content dependency depending on temperature (see Patent Document 2), Patent Document 3 discloses a catalyst in which a solid polymer electrolyte resin is mixed on a gas diffusion layer. Is treated at a temperature higher than the glass transition point of this resin to form a low water content catalyst layer, and a catalyst mixed with the same solid polymer electrolyte resin is further treated at a temperature lower than the glass transition point of this resin. Then, a high water content catalyst layer is formed, a catalyst layer consisting of two layers is arranged, the solid polymer electrolyte is sandwiched between a pair of gas diffusion layers, and the membrane is formed by, for example, thermocompression bonding at 80 ° C. The production of electrode assemblies is described.

  Patent Document 4 discloses a method for producing a catalyst layer used in a membrane electrode assembly in which a catalyst layer and a diffusion layer are laminated on both surfaces of an electrolyte membrane, wherein an electrolyte resin and a catalyst-carrying conductor are provided on a base sheet. And a step of applying a catalyst solution containing a solvent and a step of heat-treating the applied catalyst solution layer, the heat treatment step being performed at a heat treatment temperature in the in-plane direction and / or in the film thickness direction of the applied catalyst solution layer. A method for producing a catalyst layer in a state where a difference is provided is described. As a result, the moisture content can be distributed in the in-plane direction and / or the film thickness direction of the catalyst layer.

Japanese Patent Laid-Open No. 7-254418 JP 2005-174827 A Japanese Patent Laid-Open No. 2002-42824 JP 2009-289623 A

However, in the method described in Patent Document 1, the proton conduction path is only the solid polymer electrolyte coated with the catalyst, and the solubility of the solid polymer electrolyte coating the catalyst in the solvent alone depends on the temperature of the heat treatment. In addition, parameters such as moisture content, proton conductivity, and gas diffusivity are affected. That is, when it is attempted to prevent the elution of the coated solid polymer electrolyte by reducing the solubility, there is a concern that the water content is excessively decreased and the output performance is decreased.
Further, in the methods described in Patent Documents 3 and 4, the electrode catalyst layer pays attention only to the difference in moisture content by heat treatment, and does not take into account ensuring proton conductivity in the electrode catalyst layer.

Accordingly, the present invention has been made to solve the above-mentioned problems, and its purpose is to provide a water content distribution to the electrode catalyst layer while ensuring sufficient proton conductivity and gas diffusibility, and output. The object is to provide a method for producing a fuel cell electrode catalyst layer with improved performance.

A method for producing a fuel cell electrode catalyst layer according to claim 1 of the present invention is a method for producing a fuel cell electrode catalyst layer, comprising a catalyst material, or catalyst material-carrying particles carrying the catalyst material, Heat-treating a mixture in which a polymer electrolyte is dispersed in a solvent, and coating the catalyst material or the catalyst material-supporting particles and the surface of the catalyst material with the polymer electrolyte to form composite catalyst particles; Dispersing the composite catalyst particles in a solvent to produce a first catalyst ink; dispersing a catalyst substance, an electron conductive substance, and a polymer electrolyte in a solvent to produce a second catalyst ink; The first catalyst ink is applied onto a substrate selected from a gas diffusion layer, a transfer sheet, and a polymer electrolyte membrane, and the second catalyst ink is applied onto the applied first catalyst ink. Apply and heat treatment After it, in that it comprises a step in which the first electrode catalyst layer and the first high water content than the electrode catalyst layer and the second electrode catalyst layer to form an electrode catalyst layer stacked in the thickness direction, the It is a feature.

According to the method for producing an electrode catalyst layer for a fuel cell according to claim 1, a first electrode catalyst comprising a catalyst material, or catalyst material-supporting particles and composite catalyst particles in which the surface of the catalyst material is coated with a polymer electrolyte. And a second electrode catalyst layer made of a catalyst material, an electron conductive material, and a polymer electrolyte, and the first electrode catalyst layer and the second electrode catalyst layer are laminated in the film thickness direction. In addition, a fuel cell electrode catalyst layer having different water content between the first electrode catalyst layer and the second electrode catalyst layer can be obtained. For this reason, while ensuring sufficient proton conductivity and gas diffusivity, the electrode catalyst layer can have a water content distribution and the output performance can be improved.

Moreover, the manufacturing method of the electrode catalyst layer for fuel cells which concerns on Claim 2 among this invention is the manufacturing method of the electrode catalyst layer for fuel cells of Claim 1, The heat processing temperature in the process of forming the said composite catalyst particle | grain is set. The temperature range is from 50 ° C. to 180 ° C.
Here, in the case where the heat treatment temperature is less than 50 ° C., in the step of producing the first catalyst ink, most of the polymer electrolyte coated with the composite catalyst particles is dissolved in the solvent and formed. The output may not be improved due to the decrease in points, and the difference in water content between the first electrode catalyst layer and the second electrode catalyst layer may be eliminated, and the output may not be improved. On the other hand, when the heat treatment temperature exceeds 180 ° C., the proton conductivity of the polymer electrolyte in the composite catalyst particles is hindered, and the output performance may not be improved.

Furthermore, the method for producing a fuel cell electrode catalyst layer according to claim 3 of the present invention is the method for producing a fuel cell electrode catalyst layer according to claim 1 or 2 , wherein the heat treatment in the step of forming the electrode catalyst layer is performed. The temperature is lower than or equal to the heat treatment temperature in the step of forming the composite catalyst particles.
When the heat treatment is performed at a temperature higher than the heat treatment temperature in the step of forming the composite catalyst particles in the step of forming the electrode catalyst layer, the water content of the first electrode catalyst layer and the second electrode catalyst layer The output performance may not be improved.

  According to the present invention, a first electrode catalyst layer composed of composite catalyst particles comprising at least a catalyst material on the surface, the surface of the catalyst material being coated with a polymer electrolyte, a catalyst material, an electron conductive material, and The second electrode catalyst layer made of the polymer electrolyte is laminated in the film thickness direction, and the first electrode catalyst layer and the second electrode catalyst layer are different in water content so that sufficient proton conduction is achieved. The fuel cell electrode catalyst layer has a water content distribution in the electrode catalyst layer while improving the performance and gas diffusibility, and the output performance is improved, and the fuel cell membrane electrode assembly having this electrode catalyst layer, A fuel cell provided with a membrane electrode assembly and a method for producing an electrode catalyst layer for a fuel cell can be provided.

It is a schematic diagram which shows the structure of 1st Embodiment of the electrode catalyst layer for fuel cells which concerns on this invention. It is a schematic diagram which shows the structure of the composite catalyst particle used for the electrode catalyst layer for fuel cells shown in FIG. It is a schematic diagram which shows the structure of 2nd Embodiment of the electrode catalyst layer for fuel cells which concerns on this invention. 1 is an exploded schematic view of a fuel cell according to the present invention.

Below, 1st Embodiment of the electrode catalyst layer for fuel cells which concerns on this invention is described with reference to drawings. FIG. 1 is a schematic diagram showing the structure of a first embodiment of an electrode catalyst layer for a fuel cell according to the present invention.
A fuel cell electrode catalyst layer (hereinafter simply referred to as an electrode catalyst layer) 2 shown in FIG. 1 is used for a solid polymer fuel cell, and is disposed on both surfaces of a polymer electrolyte membrane 1 described later (FIG. 1). 1 shows only the electrode catalyst layer disposed on the upper surface of the polymer electrolyte membrane 1).

  The electrode catalyst layer 2 includes a first electrode catalyst layer 2a composed of composite catalyst particles 10 (see FIG. 2) and a second electrode catalyst layer 2b, and the first electrode catalyst layer 2a and the second electrode catalyst. The layer 2b is laminated in the film thickness direction, and the water content of the first electrode catalyst layer 2a is different from that of the second electrode catalyst layer 2b. Here, the second electrode catalyst layer 2b is composed of a catalyst material, an electron conductive material, and a polymer electrolyte.

The electrode catalyst layer 2 can be formed, for example, by applying the first electrode catalyst layer 2a on a base material (not shown) and further applying the second electrode catalyst layer 2b thereon. It is not limited to this method.
In FIG. 1, a second electrode catalyst layer 2b is disposed on the upper surface of the polymer electrolyte membrane 1, and the first electrode catalyst layer 2a is laminated on the upper side of the second electrode catalyst layer 2b. In this case, it is preferable that the second electrode catalyst layer 2b facing the polymer electrolyte membrane 1 has a high water content and the first electrode catalyst layer 2a has a low water content.

  As shown in FIG. 2, the composite catalyst particle 10 is formed by agglomerating a plurality of catalyst material-supporting particles 12 which are carbon particles having a catalyst material 11 such as a platinum-based noble metal supported on the surface. The surface of the support particle 12 is further covered with a polymer electrolyte 13. The catalyst material-carrying particles 12 have electronic conductivity, while the polymer electrolyte layer 13 has proton conductivity.

  The composite catalyst particle 10 may be coated with only the catalyst material 11 with the polymer electrolyte 13 and may not include the catalyst material-supporting particles 12 having electron conductivity. In this case, it is necessary to mix an electron conductive substance in the preparation of the first catalyst ink described later. That is, the composite catalyst particle 10 only needs to include the catalyst material 11 on at least the surface, and the surface of the catalyst material 11 may be further covered with the polymer electrolyte layer 13.

Platinum is preferably used as the catalyst material 11 in the composite catalyst particle 10 of the first electrode catalyst layer 2a and the catalyst material in the second electrode catalyst layer 2b, but platinum of palladium, ruthenium, iridium, rhodium, osmium is used. There is no problem even if using metals such as iron, lead, copper, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, alloys thereof, oxides, double oxides, etc. in addition to group elements .
Further, the catalyst-carrying particles 12 in the composite catalyst particles 10 of the first electrode catalyst layer 2a are materials having electron conductivity, and carbon particles are preferably used. The electron conductive material in the second electrode catalyst layer 2b also serves as a carrier for supporting the catalyst material, and carbon particles are preferably used.

Any carbon particles can be used as long as they are in the form of fine particles, have conductivity and are not affected by the catalyst, but carbon black, graphite, graphite, activated carbon, carbon fiber, carbon nanotube, and fullerene are used. it can.
If the particle size of the carbon particles is too small, it becomes difficult to form an electron conduction path. If the particle size is too large, the gas diffusibility of the electrode catalyst layer 21 is lowered or the utilization factor of the catalyst is lowered. The degree is preferred. More preferably, 10-100 nm is good.

  The polymer electrolyte 13 in the composite catalyst particle 10 of the first electrode catalyst layer 2a and the polymer electrolyte in the second electrode catalyst layer 2b may have any proton conductivity, such as a fluorine-based polymer electrolyte, Hydrocarbon polymer electrolytes can be used. In consideration of the adhesion in the electrode catalyst layer 2, the same material should be used for the polymer electrolyte 3 contained in the first electrode catalyst layer 2a and the polymer electrolyte contained in the second electrode catalyst layer 2b. Is preferred.

  According to the electrode catalyst layer 2 according to the first embodiment shown in FIG. 1, a plurality of catalyst material-carrying particles 12 carrying the catalyst material 11 on the surface are formed by agglomeration, and the catalyst material 11 and the catalyst material-carrying particles 12 A first electrode catalyst layer 2a composed of composite catalyst particles 10 whose surface is coated with a polymer electrolyte 13; and a second electrode catalyst layer 2b composed of a catalyst material, an electron conductive material, and a polymer electrolyte. The first electrode catalyst layer 2a and the second electrode catalyst layer 2b are laminated in the film thickness direction, and the water content of the first electrode catalyst layer 2a and the second electrode catalyst layer 2b is different. . As a result, it is possible to provide the electrode catalyst layer 2 with improved output performance by providing the electrode catalyst 2 layer with a water content distribution while ensuring sufficient proton conductivity and gas diffusibility.

Next, 2nd Embodiment of the electrode catalyst layer for fuel cells which concerns on this invention is described with reference to FIG. FIG. 3 is a schematic view showing the structure of the second embodiment of the electrode catalyst layer for a fuel cell according to the present invention.
A fuel cell electrode catalyst layer (hereinafter simply referred to as an electrode catalyst layer) 2 shown in FIG. 3 is used for a solid polymer fuel cell, and is disposed on both surfaces of a polymer electrolyte membrane 1 described later (FIG. 3). 3 shows only the electrode catalyst layer disposed on the upper surface of the polymer electrolyte membrane 1).

  The electrode catalyst layer 2 includes a first electrode catalyst layer 2a composed of composite catalyst particles 10 (see FIG. 2) and a second electrode catalyst layer 2b, and the first electrode catalyst layer 2a and the second electrode catalyst. The layer 2b is laminated in the film thickness direction, and the water content of the first electrode catalyst layer 2a is different from that of the second electrode catalyst layer 2b. Here, the second electrode catalyst layer 2b is composed of a catalyst material, an electron conductive material, and a polymer electrolyte. In FIG. 3, the second electrode catalyst layer 2b is disposed on the upper surface of the polymer electrolyte membrane 1, and the first electrode catalyst layer 2a is laminated on the upper side of the second electrode catalyst layer 2b. In this case, it is preferable that the second electrode catalyst layer 2b facing the polymer electrolyte membrane 1 has a high water content and the first electrode catalyst layer 2a has a low water content.

The structure and composition of the composite catalyst layer 10 and the second electrode catalyst layer 2b in the first electrode catalyst layer 2a of the second embodiment are the same as those of the composite catalyst layer 10 and the second electrode catalyst layer 2a of the first embodiment. The structure and composition of the two electrode catalyst layers 2b are the same.
However, unlike the electrode catalyst layer 2 of the first embodiment, the electrode catalyst layer 2 of the second embodiment has a water-containing gradient between the first electrode catalyst layer 2a and the second electrode catalyst layer 2b. At least one intermediate layer 2c is provided (FIG. 3 shows only one intermediate layer).
This intermediate layer 2c can be formed in the same manner as the first electrode catalyst layer 2a using, for example, composite catalyst particles that have been heat-treated at a temperature different from that of the first electrode catalyst layer 2a, but is limited to this method. It is not something.

In addition, the intermediate layer 2c is the first electrode catalyst when the second electrode catalyst layer 2b facing the polymer electrolyte membrane 1 has a high water content and the first electrode catalyst layer 2a has a low water content. A slope is provided so that the water content gradually increases from the layer 2a to the second electrode catalyst layer 2b.
According to the electrode catalyst layer 2 of the second embodiment shown in FIG. 3, in the water content distribution of the electrode catalyst layer 2, the intermediate layer 2c is interposed between the first electrode catalyst layer 2a and the second electrode catalyst layer 2b. It is possible to have a hydrous distribution with a slope through the.

Next, an embodiment of a membrane electrode assembly for a fuel cell according to an embodiment of the present invention and a fuel cell provided with the membrane electrode assembly will be described. FIG. 4 is an exploded schematic view of the fuel cell according to the present invention.
A fuel cell 30 shown in FIG. 4 is a solid polymer fuel cell, and a joined body in which a pair of electrodes 21 and 22 are arranged on both surfaces of a polymer electrolyte membrane 1 is sandwiched between a pair of separator plates 8a and 8b. Configured. Here, of the pair of electrodes 21 and 22, the electrode 21 that supplies an oxidant gas containing oxygen is called an air electrode (cathode), and the electrode 22 that supplies a hydrogen-containing fuel gas is called a fuel electrode (anode). .

Here, the electrode 21, which is an air electrode, is composed of an electrode catalyst layer 2 disposed on the upper surface of the polymer electrolyte membrane 1 and a gas diffusion layer 4 disposed on the upper surface of the electrode catalyst layer 2. The electrode catalyst layer 2 has the same configuration as the electrode catalyst layer 2 shown in FIG.
The electrode 22 that is the fuel electrode includes an electrode catalyst layer 3 disposed on the lower surface of the polymer electrolyte membrane 1 and a gas diffusion layer 5 disposed on the lower surface of the electrode catalyst layer 3. The electrode catalyst layer 3 has the same configuration as the electrode catalyst layer 2 shown in FIG. 1 or FIG.

The pair of electrode catalyst layers 2 and 3 sandwich the polymer electrolyte membrane 1.
A fuel cell membrane electrode assembly (hereinafter simply referred to as a membrane electrode assembly) 20 according to an embodiment of the present invention includes a polymer electrolyte membrane 1 and a pair of electrode catalyst layers 2 sandwiching the polymer electrolyte membrane 1. , 3. Here, it suffices that at least one of the pair of electrode catalyst layers 2 and 3 has the structure shown in FIG. 1 or FIG. 3, and the other may have the same configuration as the conventional electrode catalyst layer.

The fuel cell 30 including the membrane electrode assembly 20 includes the membrane electrode assembly 20, the pair of gas diffusion layers 4 and 5 that sandwich the membrane electrode assembly 20, and the pair of gas diffusion layers 4 and 5. And a pair of separator plates 8a and 8b.
On the lower surface of the separator plate 8a disposed on the gas diffusion layer 4 on the electrode 21 side, which is an air electrode, a gas flow path 6 for gas circulation is formed. On the other hand, on the upper surface of the separator plate 8a, a cooling water flow is formed. A common cooling water channel 7 is formed. The separator plate 8a is made of a conductive and impermeable material.

On the other hand, on the upper surface of the separator plate 8b disposed under the gas diffusion layer 5 on the electrode 22 side which is the fuel electrode, a gas flow path 6 for gas circulation is formed. On the other hand, on the lower surface of the separator plate 8b, A cooling water channel 7 for circulating the cooling water is formed. Separator plate 8b is made of a conductive and impermeable material.
In the fuel cell 30, for example, hydrogen gas is supplied as a fuel gas from the gas flow path 6 of the separator plate 8 b on the electrode 22 side that is the fuel electrode. On the other hand, for example, a gas containing oxygen is supplied as the oxidant gas from the gas flow path 6 of the separator plate 8a on the electrode 21 side which is an air electrode. An electromotive force can be generated between the electrode 22 as the fuel electrode and the electrode 21 as the air electrode by causing an electrode reaction between hydrogen as the fuel gas and oxygen as the oxidant gas in the presence of the catalyst. .

The fuel cell 30 shown in FIG. 4 has a so-called single cell structure solid in which the polymer electrolyte membrane 1, the electrode catalyst layers 2, 3, and the gas diffusion layers 4, 5 are sandwiched by a pair of separator plates 8a, 8b. This is a polymer fuel cell. However, in the present invention, a solid molecular fuel cell can be obtained by laminating a plurality of cells via the separator plates 8a and 8b.
The polymer electrolyte membrane 1 used for the membrane electrode assembly 20 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 layers 2 and 3 and the polymer electrolyte membrane 1, the polymer electrolyte membrane 1 is preferably made of the same material as the electrode catalyst layers 2 and 3.

Next, the manufacturing method of the electrode catalyst layer 2 shown in FIG. 1 is demonstrated. The electrode catalyst layer 2 is manufactured by a composite catalyst particle 10 formation step, a first catalyst ink preparation step, a second catalyst ink preparation step, and an electrode catalyst layer formation step described below.
In the production of the electrode catalyst layer 2, first, a catalyst material-supporting particle 12 supporting the catalyst material 11 and a catalyst material-supporting particle 12 supporting the catalyst material 11 are heat-treated by mixing a catalyst material-supporting particle 12 supporting the catalyst material 11 and a polymer electrolyte 13 in a solvent. And the surface of the catalyst substance 11 is coat | covered with the polymer electrolyte 13, and the composite catalyst particle 10 is formed (formation process of a composite catalyst particle).

Here, the composite catalyst particle 10 may be formed by heat-treating a mixture in which only the catalyst substance 11 and the polymer electrolyte 13 are dispersed in a solvent and coating the surface of the catalyst substance 10 with the polymer electrolyte 13.
In the composite catalyst particle 10 forming step, the catalyst material 11 in the composite catalyst particle 10 or the mixture of the catalyst material-supported particles 12 supporting the catalyst material 11 and the polymer electrolyte 13 is dispersed in a solvent. It can be controlled by the composition. Moreover, in the process of forming the composite catalyst particle 10, the elution amount of the polymer electrolyte in the composite catalyst particle 10 into the solvent can be controlled by the heat treatment temperature.

  In the step of forming the composite catalyst particle 10, the heat treatment temperature is preferably 50 ° C. or higher and 180 ° C. or lower. When the heat treatment temperature is less than 50 ° C., in the process of preparing the catalyst ink, most of the polymer electrolyte in the composite catalyst particle 11 is dissolved in the solvent, and the output performance is improved by reducing the formed reaction active sites. In some cases, the difference in water content between the first electrode catalyst layer 2a and the second electrode catalyst layer 2b is eliminated, and the output performance may not be improved. On the other hand, even when the heat treatment temperature exceeds 180 ° C., the proton conductivity of the polymer electrolyte 13 in the composite catalyst particle 10 is hindered, and the output performance may not be improved.

After the formation step of the composite catalyst particles 10, the composite catalyst particles 10 are dispersed in a solvent to produce a first catalyst ink (first catalyst ink production step).
In the first catalyst ink production step, the elution amount of the polymer electrolyte 13 in the composite catalyst particles 10 into the solvent can be controlled by the solvent species or the solvent amount.
After the first catalyst ink production step, the catalyst material, the electron conductive material, and the polymer electrolyte are dispersed in a solvent to produce a second catalyst ink (second catalyst ink production step).
In the production process of the second catalyst ink, the weight ratio of the catalyst substance, the electron conductive substance, and the polymer electrolyte in the second electrode catalyst layer 2b is controlled by the composition of the second catalyst ink. Can do.

  Here, the solvent used as the dispersion medium is not particularly limited as long as it does not erode the catalyst material 11 or the polymer electrolyte and can dissolve or disperse the polymer electrolyte in a highly fluid state as a fine gel. . 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.

Further, when a lower alcohol is used as a dispersion medium, there is a high risk of ignition, and when such a solvent is used, it is preferable to use a mixed solvent with water. Water that is compatible with the polymer electrolyte 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.
In the formation process of the composite catalyst particle 10, a dispersion process is performed as needed. The particle size of the composite catalyst particle 10 can be controlled by the conditions of the dispersion treatment in the formation process of the composite catalyst particle 10. Even 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 the catalyst ink can be controlled by the conditions for the dispersion treatment of the 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.
If the solid content in the first catalyst ink and the second catalyst ink is too large, the viscosity of each catalyst ink becomes high, so that the surface of the electrode catalyst layer 2 tends to crack, and conversely, it is too small. Since the film forming rate is very slow and the productivity is lowered, it is preferably 1 to 50% by mass.

  The solid content is composed of a catalyst material, an electron conductive material, and a polymer electrolyte. However, when the amount of the electron conductive material is increased, a bulky material is preferably used as the electron conductive material. If it is less, the viscosity will be lower. Further, the viscosity of each of the first catalyst ink and the second catalyst ink at this time is preferably about 0.1 to 500 cP, and more preferably 5 to 100 cP. Further, the viscosity can be controlled by adding a dispersing agent when the catalyst ink is dispersed.

In addition, a pore forming agent may be included in each of the first catalyst ink and the second catalyst ink.
By removing the pore former after the formation of the electrode catalyst layer 2, pores can be formed.
Examples include substances that are soluble in acids, alkalis, and water, substances that sublime such as camphor, and substances that thermally decompose. If the substance is soluble in hot water, it may be removed with water generated during power generation.

And after the production process of the second catalyst ink, the first catalyst ink and the second catalyst ink are applied onto a substrate selected from the gas diffusion layer, the transfer sheet, and the polymer electrolyte membrane, The electrode catalyst layer 2 including the first electrode catalyst layer 2a and the second electrode catalyst layer 2b is formed through heat treatment (electrode catalyst layer forming step). Thereby, the electrode catalyst layer 2 is completed.
Here, the heat treatment temperature for the first catalyst ink and the second catalyst ink is preferably lower than or equal to the heat treatment temperature in the step of forming the composite catalyst particles 10. When heat treatment is performed at a temperature higher than the heat treatment temperature in the step of forming the composite catalyst particles 10, there is no difference in water content between the first electrode catalyst layer 2a and the second electrode catalyst layer 2b, and output performance is improved. May not improve.

When a gas diffusion layer or a transfer sheet is used as the substrate, the electrode catalyst layer 2 is bonded to both surfaces of the polymer electrolyte membrane 1 by a bonding process. Further, in the membrane electrode assembly 20 of the present invention, a polymer electrolyte membrane is used as a base material, catalyst ink is directly applied to both surfaces of the polymer electrolyte membrane, and electrode catalyst layers are directly applied to both surfaces of the polymer electrolyte membrane. It can also be formed.
At this time, as a method for applying the first and second catalyst inks, 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 a base material used in the production process of the electrode catalyst layer, a gas diffusion layer, a transfer sheet, or a polymer electrolyte membrane 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.
When a transfer sheet is used as the substrate, the transfer sheet is peeled after bonding the electrode catalyst layers 2 and 3 to the polymer electrolyte membrane 1, and the electrode catalyst layers 2 and 3 are provided on both sides of the polymer electrolyte membrane 1. The electrode assembly 20 can be obtained. It is not necessary to peel off the base material that is the gas diffusion layer after the joining step of the gas diffusion layer as the base material.

  By the method for producing the electrode catalyst layer 2 described above, a plurality of catalyst material-supporting particles 12 supporting the catalyst material 11 on the surface are formed by aggregation, and the surfaces of the catalyst material 11 and the catalyst material-supporting particles 12 are formed by the polymer electrolyte 13. A first electrode catalyst layer comprising a first electrode catalyst layer 2a made of coated composite catalyst particles 10 and a second electrode catalyst layer 2b made of a catalyst material, an electron conductive material, and a polymer electrolyte. 2a and the second electrode catalyst layer 2b are laminated in the film thickness direction, and an electrode catalyst layer 2 having a different water content between the first electrode catalyst layer 2a and the second electrode catalyst layer 2b is obtained. . As a result, while ensuring sufficient proton conductivity and gas diffusibility, the electrode catalyst layer 2 can have a water content distribution and the output performance can be improved.

Only the first electrode catalyst layer 2b (first catalyst ink) composed of the composite catalyst particles 10 coated with the polymer electrolyte 13 is subjected to a heat treatment to prevent elution of the polymer electrolyte 13 coated with the composite catalyst particles 10. The water content and proton conductivity of the entire electrode catalyst layer 2 may be reduced.
On the other hand, with only the second electrode catalyst layer 2b (second catalyst ink) made of the catalyst material, the electron conductive material, and the polymer electrolyte, the securing of proton conductivity in the electrode catalyst layer 2 is not considered. Therefore, the surface of the catalyst cannot be fully utilized to improve the output.

As the gas diffusion layers 4 and 5 and the separator plates 8a and 8b in the fuel cell 30, 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 4 and 5. As the separator plates 8a and 8b, carbon type or metal type can be used. The fuel cell 30 is manufactured by assembling other accompanying devices such as a gas supply device and a cooling device.
The embodiments of the present invention are not limited to the embodiments described above, 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.

  The fuel cell electrode catalyst layer, the fuel cell membrane electrode assembly including the electrode catalyst layer, the fuel cell including the membrane electrode assembly, and the method for producing the fuel cell electrode catalyst layer according to the present invention will be described in detail below. The present invention will be described with reference to specific examples and comparative examples, but the present invention is not limited to the following examples.

(Example)
[Method of forming composite catalyst particles]
In FIG. 2, a dispersion treatment is performed in a solvent in which catalyst material-supporting particles 12 supporting the catalyst material 11 and a polymer electrolyte solution (Nafion: registered trademark, manufactured by DuPont) constituting the polymer electrolyte 3 are added. A mixture of the catalyst substance-supporting particles 12 and the polymer electrolyte 3 was produced. Then, the mixture was apply | coated on the base material with the doctor blade, and was dried for 5 minutes at 140 degreeC in air | atmosphere. Thereafter, the composite catalyst particles 10 were recovered from the substrate.

[Production of first catalyst ink]
The composite catalyst particles 10 collected from the base material were mixed in a solvent and subjected to a dispersion treatment.
[Production of second catalyst ink]
A catalyst material, an electron conductive material, and a polymer electrolyte were mixed in a solvent and subjected to a dispersion treatment.
[Method for forming electrode catalyst layer]
The produced first catalyst ink was applied to a transfer sheet with a doctor blade and dried at 70 ° C. for 5 minutes in an air atmosphere. Similarly, the second catalyst ink was applied thereon and dried at 70 ° C. for 20 minutes in an air atmosphere to produce a two-layer electrode catalyst layer 2. The coating amount per unit area of the first catalyst ink and the second catalyst ink was 1: 1 by mass ratio. The thickness of the electrode catalyst layer 2, the amount of the catalytic material 11 is adjusted to 0.3 mg / cm ^2, to form an electrode catalyst layer 2.

(Comparative example)
[Preparation of catalyst ink]
The catalyst material-carrying particles carrying the catalyst material and the polymer electrolyte solution constituting the polymer electrolyte 3 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.
[Method for forming electrode catalyst layer]
In the same manner as in the example, the catalyst ink was applied to the transfer sheet and dried to form an electrode catalyst layer. The thickness of the electrode catalyst layer was adjusted so that the amount of the catalyst substance was 0.3 mg / cm ² to form the electrode catalyst layer.

[Production of membrane electrode assembly and fuel cell]
The base material on which the electrode catalyst layer produced in (Example) and (Comparative Example) was formed was punched into a 5 cm ² square, and the polymer electrolyte membrane (Nafion 212: registered trademark, manufactured by DuPont) 1 in FIG. A transfer sheet was placed so as to face each other, and hot pressing was performed at 130 ° C. to obtain a membrane electrode assembly 20. A carbon cloth in which a sealing layer is formed as the gas diffusion layers 4 and 5 is disposed on both surfaces of the obtained membrane electrode assembly 20, and is further sandwiched between a pair of separator plates 8a and 8b. A molecular fuel cell 30 was produced.

[Power generation characteristics]
(Evaluation conditions)
Using a GFT-SG1 fuel cell measuring device manufactured by Toyo Technica Co., Ltd., power generation characteristics were evaluated at a cell temperature of 80 ° C. 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)
As a result of power generation evaluation, the polymer electrolyte fuel cell of the example had high proton conductivity and sufficiently maintained gas diffusibility, so that flooding was suppressed at a high output compared with the comparative example, and good A good power generation characteristic was obtained.

  The electrode catalyst layer for a fuel cell according to the present invention comprises a first electrode catalyst layer comprising composite catalyst particles comprising at least a catalyst material on the surface, the surface of the catalyst material being coated with a polymer electrolyte, a catalyst material, A second electrode catalyst layer composed of an electron conductive substance and a polymer electrolyte, wherein the first electrode catalyst layer and the second electrode catalyst layer are laminated in the film thickness direction, and The first electrode catalyst layer and the second electrode catalyst layer differ in water content.

  The method for producing an electrode catalyst layer for a fuel cell according to the present invention is a method for producing an electrode catalyst layer for a fuel cell, wherein the catalyst material or catalyst material-supported particles carrying the catalyst material, a polymer electrolyte, Heat-treating a mixture in which the catalyst material is dispersed in a solvent, and coating the catalyst material or the catalyst material-supporting particles and the surface of the catalyst material with the polymer electrolyte to form composite catalyst particles; and the composite catalyst particles Are dispersed in a solvent to produce a first catalyst ink, a catalyst substance, an electron conductive substance, and a polymer electrolyte are dispersed in a solvent to produce a second catalyst ink, a gas diffusion layer, The first catalyst ink and the second catalyst ink are applied on a substrate selected from a transfer sheet and a polymer electrolyte membrane, and the first electrode catalyst layer and the second electrode catalyst are subjected to heat treatment. Electricity with layer It is characterized by comprising a step of forming a catalyst layer.

  This provides an electrode catalyst layer for a fuel cell in which the electrode catalyst layer has a water content distribution and improved output performance while ensuring sufficient proton conductivity and gas diffusivity, and a method for producing the electrode catalyst layer can do. Therefore, it is possible to provide a fuel cell with better power generation characteristics than the conventional manufacturing method, and further to reduce the amount of catalyst used.

DESCRIPTION OF SYMBOLS 1 Polymer electrolyte membrane 2,3 Electrode catalyst layer 2a 1st electrode catalyst layer 2b 2nd electrode catalyst layer 2c Intermediate | middle layer 4,5 Gas diffusion layer 6 Gas flow path 7 Cooling water flow path 8a, 8b Separator plate 10 Composite catalyst Particle 11 Catalytic substance 12 Catalytic substance carrying particle 13 Polymer electrolyte 20 Membrane electrode assembly 21 Electrode (air electrode)
22 Electrode (fuel electrode)

Claims (3)

A method for producing an electrode catalyst layer for a fuel cell, comprising:
The catalyst material or a mixture of the catalyst material-supporting particles supporting the catalyst material and a polymer electrolyte dispersed in a solvent is heat-treated, and the surfaces of the catalyst material or the catalyst material-supporting particles and the catalyst material are treated. Coating with the polymer electrolyte to form composite catalyst particles;
Dispersing the composite catalyst particles in a solvent to produce a first catalyst ink;
A step of dispersing a catalyst substance, an electron conductive substance, and a polymer electrolyte in a solvent to produce a second catalyst ink;
The first catalyst ink is applied onto a substrate selected from a gas diffusion layer, a transfer sheet, and a polymer electrolyte membrane, and the second catalyst ink is applied onto the applied first catalyst ink. It was applied, through a heat treatment step of a high water content than the first electrode catalyst layer first electrode catalyst layer and the second electrode catalyst layer to form an electrode catalyst layer stacked in the thickness direction When,
A method for producing an electrode catalyst layer for a fuel cell, comprising:   2. The method for producing an electrode catalyst layer for a fuel cell according to claim 1, wherein a heat treatment temperature in the step of forming the composite catalyst particles is in a range of 50 ° C. or higher and 180 ° C. or lower.   The method for producing an electrode catalyst layer for a fuel cell according to claim 1 or 2, wherein a heat treatment temperature in the step of forming the electrode catalyst layer is lower than or equal to a heat treatment temperature in the step of forming the composite catalyst particles. .

Images