JP2011204605A - Electrode catalytic layer for fuel cell, membrane electrode assembly for fuel cell comprising the electrode catalytic layer, fuel cell comprising the membrane electrode assembly, and method of manufacturing the electrode catalytic layer for fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode catalytic layer for a fuel cell, in which sufficient proton conductivity and gas diffusion are secured and the number of reaction active spots is increased to improve output performance; to provide a membrane electrode assembly for a fuel cell comprising the electrode catalytic layer; to provide a fuel cell comprising the membrane electrode assembly; and to provide a method of manufacturing the electrode catalytic layer for the fuel cell.SOLUTION: The electrode catalytic layer 21 for a fuel cell is composed of: a plurality of composite catalyst particles 11 each including at least a catalyst material 1 on a surface, in which the surface of the catalyst material 1 is coated with a polymer electrolyte layer 3; and a plurality of aggregates 12 formed by aggregation of the polymer electrolyte. The plurality of composite catalyst particles 11 are coupled with the plurality of aggregates 12, and the plurality of aggregates 12 are formed by drying a solution prepared by dissolving the polymer electrolyte.

Description

  The present invention relates to a fuel cell electrode catalyst layer, a fuel cell membrane electrode assembly including the electrode catalyst layer, a polymer electrolyte fuel cell including the membrane electrode assembly, and a fuel cell electrode catalyst layer. It is about the method.

  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.

Conventionally, the electrode catalyst layer is often formed on a substrate using an ink obtained by mixing a catalyst, a polymer electrolyte having proton conductivity, and a solvent.
FIG. 3 shows a schematic diagram of an electrode catalyst layer for a fuel cell produced by a conventional forming method.
The electrode catalyst layer 121 shown in FIG. 3 is formed by agglomerating a plurality of catalyst material-carrying particles 102 that are carbon particles carrying a catalyst material 101 such as a platinum-based noble metal on the surface. The surface is further composed of a plurality of composite catalyst particles 111 coated with a polymer electrolyte layer 103. The catalyst material-carrying particles 102 have electronic conductivity, while the polymer electrolyte layer 103 has proton conductivity.

Here, in the electrode catalyst layer 121 manufactured by such a conventional forming method, it is difficult to adjust the amount of the polymer electrolyte layer 103 on the surface of the catalyst material 101. This is because the polymer electrolyte layer 103 is formed by a single coating on the catalyst material-carrying particles 102 on which the catalyst material 101 is supported, so that the amount of the polymer electrolyte layer 103 is excessive and insufficient, and the overcoated portion and the coated The shortage occurs and the electrode characteristics cannot be improved.
That is, as shown in FIG. 3, when the polymer electrolyte layer 103 in the vicinity of the catalyst substance 101 is thick, proton conductivity can be ensured, but some of the pores between the catalyst substances 101 are likely to be clogged, and gas diffusibility may be lowered. . Conversely, if the polymer electrolyte layer 103 in the vicinity of the catalyst substance 101 is thin, gas diffusibility can be secured, but there is a problem that proton conductivity becomes 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 covering a surface of a catalyst material with a porous polymer electrolyte layer. . Patent Document 2 discloses a method for preventing elution of the polymer electrolyte layer coated on the catalyst surface by subjecting the composite particles to heat treatment in order to ensure proton conductivity more reliably.
On the other hand, in Patent Document 3, the electrode catalyst layer is configured such that a catalyst group (composite catalyst particle) covered with a polymer electrolyte layer and an electrolyte group that is an aggregate of electrolytes are connected to each other and intertwined with each other. . For this reason, it is easy to adjust the amount of the polymer electrolyte layer that is coated, and it is an electrode catalyst layer that easily balances proton conductivity and gas diffusibility.

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

However, in the methods described in Patent Documents 1 and 2, the proton conduction path is only the polymer electrolyte layer coated with the catalyst material, and the gas diffusibility and the strength of the electrode catalyst layer are detailed according to the amount of the polymer electrolyte layer. It is difficult to adjust.
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, not only polymer electrolyte aggregates are deposited but also aggregates of composite catalyst particles. In other words, the surface of the catalyst cannot be fully utilized.

  Accordingly, the present invention has been made to solve the above-described problems, and its purpose is to ensure sufficient proton conductivity and gas diffusibility, increase the reaction active point, and improve the output performance. An object of the present invention is to provide a battery electrode catalyst layer, a fuel cell membrane electrode assembly including the electrode catalyst layer, a fuel cell including the membrane electrode assembly, and a method for producing the fuel cell electrode catalyst layer.

  In order to solve the above-mentioned problems, an electrode catalyst layer for a fuel cell according to claim 1 of the present invention comprises a plurality of composites comprising at least a catalyst material on the surface, and the surface of the catalyst material is covered with a polymer electrolyte layer. The catalyst particles and a plurality of aggregates formed by aggregation of the polymer electrolyte, the plurality of composite catalyst particles are connected by the plurality of aggregates, and the plurality of aggregates are polymer It is characterized by being formed by drying a solution obtained by dissolving an electrolyte.

  According to the electrode catalyst layer for a fuel cell according to claim 1, a plurality of composite catalyst particles each having a catalyst material on at least a surface, the surface of the catalyst material being further covered with a polymer electrolyte layer, and a polymer electrolyte Is composed of a plurality of aggregates formed by agglomeration, and a plurality of composite catalyst particles are connected by a plurality of aggregates, so that not only the proton conductivity in the electrode catalyst layer is increased, but also gas diffusion By ensuring the property, the reaction active point can be increased and the output performance can be improved. In the conventional electrocatalyst layer using composite catalyst particles coated with polyelectrolyte, it is difficult to adjust the amount of polyelectrolyte layer on the surface of the catalyst material, and the proton conductivity and gas diffusivity on the catalyst surface are sufficient at the same time Can not be secured.

According to the fuel cell electrode catalyst layer of the first aspect, the plurality of aggregates are formed by drying a solution in which the polymer electrolyte is dissolved. The amount of the polymer electrolyte in the aggregate eluted into the solvent can be controlled, whereby aggregation of the composite catalyst particles can be avoided and the surface of the catalyst substance can be fully utilized.
Moreover, the fuel cell electrode catalyst layer according to claim 2 of the present invention is the fuel cell electrode catalyst layer according to claim 1, wherein each of the plurality of composite catalyst particles is the catalyst material or the catalyst. A plurality of catalyst material-carrying particles carrying a substance on the surface are formed by agglomeration, and the surface of the catalyst material or the catalyst material and the catalyst material-carrying particles is covered with the polymer electrolyte layer. Yes.

According to a third aspect of the present invention, a membrane electrode assembly for a fuel cell comprises a proton conductive polymer electrolyte membrane and a pair of fuel cell electrode catalyst layers sandwiching the proton conductive polymer electrolyte membrane. The fuel cell membrane assembly is characterized in that at least one of the pair of fuel cell electrode catalyst layers comprises the fuel cell electrode catalyst layer according to claim 1.
Furthermore, a fuel cell according to claim 4 of the present invention is a fuel cell membrane electrode assembly according to claim 3, a pair of gas diffusion layers sandwiching the fuel cell membrane electrode assembly, and the pair. And a pair of separator plates sandwiching the gas diffusion layer.

Moreover, the manufacturing method of the electrode catalyst layer for fuel cells which concerns on Claim 5 among this invention is a manufacturing method of the electrode catalyst layer for fuel cells,
A catalyst material or a mixture of catalyst material-supported particles supporting the catalyst material and a polymer electrolyte dispersed in a solvent is dried, and the catalyst material or the catalyst material is supported by the polymer electrolyte. Coating the catalyst material-supporting particles and the surface of the catalyst material to form a plurality of composite catalyst particles;
Drying a solution in which the polymer electrolyte is dissolved to form a plurality of aggregates;
A step of dispersing the composite catalyst particles and the aggregates in a solvent to prepare a catalyst ink;
A step of applying the catalyst ink on a substrate selected from a gas diffusion layer, a transfer sheet, and a polymer electrolyte membrane to form an electrode catalyst layer;
It is characterized by having.

  According to the method for producing an electrode catalyst layer for a fuel cell according to claim 5, a plurality of catalyst materials or catalyst material-supporting particles supporting the catalyst material and a surface of the catalyst material are coated with a polymer electrolyte. It is possible to obtain a fuel cell electrode catalyst layer composed of composite catalyst particles and a plurality of aggregates formed by agglomeration of the polymer electrolyte, in which a plurality of composite catalyst particles are connected by a plurality of aggregates. For this reason, not only the proton conductivity in the electrode catalyst layer can be increased, but also the gas diffusibility can be ensured to increase the reaction active point and improve the output performance. In the conventional method for producing an electrocatalyst layer using composite catalyst particles coated with a polymer electrolyte, it is difficult to adjust the amount of the polymer electrolyte layer on the surface of the catalyst material, and proton conductivity and gas diffusivity on the catalyst surface are difficult to adjust. Cannot be secured at the same time.

Further, according to the method for producing an electrode catalyst layer for a fuel cell according to claim 5, the plurality of aggregates are formed by drying a solution in which the polymer electrolyte is dissolved. Thus, it is possible to control the amount of the polymer electrolyte in the aggregate eluted into the solvent, thereby avoiding the aggregation of the composite catalyst particles and fully utilizing the surface of the catalyst substance.
Moreover, the manufacturing method of the electrode catalyst layer for fuel cells which concerns on Claim 6 among this invention is drying in the process of forming these composite catalyst particles in the manufacturing method of the electrode catalyst layer for fuel cells of Claim 5. The temperature is equal to or higher than the drying temperature for forming the plurality of aggregates.
According to the method for producing a fuel cell electrode catalyst layer according to claim 6, the drying temperature in the step of forming the plurality of composite catalyst particles is equal to or higher than the drying temperature of forming the plurality of aggregates. The polymer electrolyte in the aggregate can be more easily dissolved in the solvent than the polymer electrolyte in the catalyst particles.

Moreover, the manufacturing method of the electrode catalyst layer for fuel cells which concerns on Claim 7 among this invention is a manufacturing method of the electrode catalyst layer for fuel cells of Claim 5 or 6, The process of forming these composite catalyst particles. The drying temperature is in the range of 50 ° C. or higher and 180 ° C. or lower.
According to the method for producing an electrode catalyst layer for a fuel cell according to claim 7, the drying temperature in the step of forming a plurality of composite catalyst particles is set in the range of 50 ° C. or higher and 180 ° C. or lower, whereby composite catalyst particles are obtained. Inhibition of proton conductivity of the polymer electrolyte in can be avoided, and output performance can be improved. When the drying temperature is less than 50 ° C., in the process of preparing the catalyst ink, many of the polymer electrolytes in the composite catalyst particles are dissolved in the solvent, and the output may not be improved due to the reduction of the formed reaction active sites. is there. On the other hand, when the drying 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 manufacturing method of the electrode catalyst layer for fuel cells which concerns on Claim 8 among this invention is a manufacturing method of the electrode catalyst layer for fuel cells as described in any one of Claim 5 thru | or 7. The drying temperature in the step of forming the aggregate is in the range of 30 ° C. or higher and 140 ° C. or lower.
According to the method for producing an electrode catalyst layer for a fuel cell according to claim 8, the drying temperature in the step of forming a plurality of aggregates is within the range of 30 ° C. or more and 140 ° C. or less, thereby Thus, the amount of aggregates becomes sufficient, suppressing a decrease in proton conductivity and improving the output performance. If this drying temperature is less than 30 ° C, when the catalyst ink is produced, most of the aggregates are dissolved in the solvent, and the amount of aggregates is insufficient in the electrode catalyst layer, so that the output performance is not improved. There is. On the other hand, when the drying temperature exceeds 140 ° C., it is difficult for the aggregate to elute into the solvent of the catalyst ink, the proton conductivity in the electrode catalyst layer is lowered, and the output performance may not be improved. is there.

  According to the present invention, the electrode catalyst layer is composed of a plurality of composite catalyst particles and a plurality of aggregates formed by aggregation of the polymer electrolyte, and the plurality of composite catalyst particles are connected by the plurality of aggregates. Therefore, not only the proton conductivity in the electrode catalyst layer is increased but also the gas diffusibility is ensured, thereby increasing the reaction active point and improving the output performance, and this electrode catalyst layer. A fuel cell membrane electrode assembly provided with a fuel cell, a fuel cell provided with this membrane electrode assembly, and a method for producing a fuel cell electrode catalyst layer.

  Further, according to the present invention, the degree of freedom of the composition of the catalyst ink in which the composite catalyst particles and aggregates coated with the polymer electrolyte are dispersed is high, and the surface of the catalyst can be fully utilized by preventing the aggregation of the composite catalyst particles. , Fuel cell electrode catalyst layer with increased reaction active points and improved output performance, fuel cell membrane electrode assembly including the electrode catalyst layer, fuel cell and fuel cell electrode including the membrane electrode assembly A method for producing a catalyst layer can be provided.

It is a schematic diagram which shows the structure 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. It is a schematic diagram which shows the structure of the electrode catalyst layer for fuel cells produced with the conventional formation method.

  Below, the electrode catalyst layer for fuel cells which concerns on embodiment of this invention is demonstrated. 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.

A fuel cell electrode catalyst layer (hereinafter simply referred to as an electrode catalyst layer) 21 shown in FIG. 1 is used for a solid polymer fuel cell, and a plurality of composite catalyst particles 11 and a polymer electrolyte are aggregated. And a plurality of aggregates 12 formed by the above, and a plurality of composite catalyst particles 11 are connected by a plurality of aggregates 12.
Here, each composite catalyst particle 11 is formed by agglomerating a plurality of catalyst material-carrying particles 2 which are carbon particles carrying a catalyst material 1 such as a platinum-based noble metal on the surface, and the catalyst material 1 and the catalyst material-carrying particles 2 are formed. Is further covered with a polymer electrolyte layer 3. The catalyst material-carrying particles 2 have electronic conductivity, while the polymer electrolyte layer 3 has proton conductivity.

  Each composite catalyst particle 11 may be coated with only the catalyst material 1 with the polymer electrolyte layer 3 and may not include the catalyst material-carrying particles 2 having electron conductivity. In this case, it is necessary to mix an electron conductive substance in preparation of the catalyst ink described later. That is, each composite catalyst particle 11 only needs to have the catalyst material 1 on at least the surface, and the surface of the catalyst material 1 may be further covered with the polymer electrolyte layer 3.

  As the catalyst material 1 in each composite catalyst particle 11, platinum is preferably used. In addition to the platinum group elements of palladium, ruthenium, iridium, rhodium and osmium, iron, lead, copper, chromium, cobalt, nickel, manganese There is no problem even if a metal such as vanadium, molybdenum, gallium or aluminum or an alloy thereof, or an oxide or a double oxide is used.

Further, the catalyst-carrying particles 2 in the composite catalyst particles are a substance having electron conductivity, 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 that forms the polymer electrolyte layer 3 and each aggregate 12 contained in each composite catalyst particle 11 may be any one having proton conductivity, such as a fluorine-based polymer electrolyte and a hydrocarbon-based polymer. An electrolyte can be used. In consideration of the adhesiveness in the electrode catalyst layer 21, it is preferable to use the same material for the polymer electrolyte that forms aggregates with the polymer electrolyte crude 3 contained in each composite catalyst particle 11.

Next, a membrane electrode assembly for a fuel cell according to an embodiment of the present invention and a fuel cell including the membrane electrode assembly will be described. FIG. 2 is an exploded schematic view of the fuel cell according to the present invention.
A fuel cell 40 shown in FIG. 2 is a solid polymer fuel cell, and a joined body in which a pair of electrodes 26 and 27 are arranged on both surfaces of a polymer electrolyte membrane 23 is sandwiched between a pair of separator plates 30a and 30b. Configured. Here, of the pair of electrodes 26 and 27, the electrode 26 that supplies an oxidant gas containing oxygen is called an air electrode (cathode), and the electrode 27 that supplies a hydrogen-containing fuel gas is called a fuel electrode (anode). .

Here, the electrode 26, which is an air electrode, is composed of an electrode catalyst layer 21 disposed on the upper surface of the polymer electrolyte membrane 23 and a gas diffusion layer 24 disposed on the upper surface of the electrode catalyst layer 21. The electrode catalyst layer 21 has the same configuration as the electrode catalyst layer 21 shown in FIG.
The electrode 27 that is the fuel electrode includes an electrode catalyst layer 22 disposed on the lower surface of the polymer electrolyte membrane 23 and a gas diffusion layer 25 disposed on the lower surface of the electrode catalyst layer 22. The electrode catalyst layer 22 has the same configuration as the electrode catalyst layer 21 shown in FIG.
The pair of electrode catalyst layers 21 and 22 sandwich the polymer electrolyte membrane 23.

  A fuel cell membrane electrode assembly (hereinafter simply referred to as a membrane electrode assembly) 31 according to an embodiment of the present invention includes a polymer electrolyte membrane 23 and a pair of electrode catalyst layers 21 sandwiching the polymer electrolyte membrane 23. , 22. Here, it is sufficient that at least one of the pair of electrode catalyst layers 21 and 22 has the structure shown in FIG. 1, and the other may have the same configuration as the electrode catalyst layer 120 shown in FIG.

The fuel cell 40 including the membrane electrode assembly 31 includes the membrane electrode assembly 31, the pair of gas diffusion layers 24 and 25 that sandwich the membrane electrode assembly 31, and the pair of gas diffusion layers 24 and 25. And a pair of separator plates 30a and 30b.
On the lower surface of the separator plate 30a disposed on the gas diffusion layer 24 on the electrode 26 side, which is an air electrode, a gas flow path 28 for gas circulation is formed. On the other hand, on the upper surface of the separator plate 30a, a cooling water flow A common cooling water channel 29 is formed. Separator plate 30a is made of a conductive and impermeable material.
On the other hand, on the upper surface of the separator plate 30b disposed under the gas diffusion layer 25 on the electrode 27 side which is the fuel electrode, a gas flow path 28 for gas circulation is formed, while on the other hand, on the lower surface of the separator plate 30b, A cooling water channel 29 for circulating the cooling water is formed. Separator plate 30b is made of a conductive and impermeable material.

  In the fuel cell 40, for example, hydrogen gas is supplied as a fuel gas from the gas flow path 28 of the separator plate 30 on the electrode 27 side that is the fuel electrode. On the other hand, a gas containing oxygen, for example, is supplied as an oxidant gas from the gas flow path 28 of the separator plate 30 on the electrode 26 side which is an air electrode. An electromotive force can be generated between the electrode 27 which is a fuel electrode and the electrode 26 which is an air electrode by causing an electrode reaction between hydrogen and oxygen gas of the fuel gas in the presence of a catalyst.

The fuel cell 40 shown in FIG. 2 has a so-called single-cell solid state in which a polymer electrolyte membrane 23, electrode catalyst layers 21 and 22, and gas diffusion layers 24 and 25 are sandwiched by a pair of separator plates 30a and 30b. This is a molecular fuel cell. However, in the present invention, a plurality of cells can be stacked via the separator plates 30a and 30b to form a fuel cell.
The polymer electrolyte membrane 23 used in the membrane electrode assembly 31 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 21 and 22 and the polymer electrolyte membrane 23, the polymer electrolyte membrane 23 is preferably made of the same material as the electrode catalyst layers 21 and 22.

Next, the manufacturing method of the electrode catalyst layer 21 shown in FIG. 1 is demonstrated.
The electrode catalyst layer 21 is manufactured by a composite catalyst particle 11 formation process, an aggregate 12 formation process, a catalyst ink production process, and an electrode catalyst layer formation process described below.
In the production of the electrode catalyst layer 21, first, a mixture in which the catalyst material-carrying particles 2 that carry the catalyst material 1 and the polymer electrolyte that constitutes the polymer electrolyte membrane 3 are dispersed in a solvent is dried to obtain the catalyst material 1. The surfaces of the supported catalyst material-supporting particles 2 and the catalyst material 1 are coated with a polymer electrolyte to form a plurality of composite catalyst particles 11 (composite catalyst particle forming step).

Here, a mixture of only the catalyst substance 1 and the polymer electrolyte dispersed in a solvent may be dried, and the surface of the catalyst substance 1 may be covered with the polymer electrolyte to form a plurality of composite catalyst particles 11.
In the step of forming the composite catalyst particles 11, the catalyst material 1 in the composite catalyst particles 11 or the mixture of the catalyst material-supported particles 2 supporting the catalyst material 1 and the polymer electrolyte is dispersed in a solvent. It can be controlled by the composition. Further, in the step of forming the composite catalyst particles 11, the elution amount of the polymer electrolyte in the composite catalyst particles 11 into the solvent can be controlled by the drying temperature.

  In the step of forming the composite catalyst particles 11, the drying temperature is preferably 50 ° C. or higher and 180 ° C. or lower. When the drying 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. May not. Even when the drying temperature exceeds 180 ° C., the proton conductivity of the polymer electrolyte in the composite catalyst particles 11 is hindered, and the output performance may not be improved.

After the formation step of the composite catalyst particles 11, the solution in which the polymer electrolyte is dissolved is dried to form a plurality of aggregates 12 (aggregate formation step).
In the formation process of the aggregate 12, the elution amount of the polymer electrolyte in the aggregate into the solvent can be controlled by the drying temperature.
In the formation process of this aggregate 12, it is preferable that drying temperature is 30 degreeC or more and 140 degrees C or less. When the drying temperature is less than 30 ° C., in the process of preparing the catalyst ink, most of the aggregates 12 are dissolved in the solvent, and the amount of the aggregates 12 is insufficient in the electrode catalyst layer 21, so that the output performance. May not improve. Further, when the drying temperature exceeds 140 ° C., it is difficult for the catalyst ink to elute into the solvent, the proton conductivity in the electrode catalyst layer 21 is lowered, and the output performance may not be improved.

Whether the drying temperature in the formation process of the composite catalyst particles 11 and the drying temperature in the formation process of the aggregates 12 are higher than the drying temperature in the formation process of the aggregates 12. However, the drying temperature is preferably such that the aggregate 12 is more easily dissolved in the solvent than the polymer electrolyte in the composite catalyst particles 11.
After the formation process of the aggregate 12, the composite catalyst particles 11 and the aggregate 12 are dispersed in a solvent to prepare a catalyst ink (catalyst ink preparation process). In this catalyst ink preparation process, the weight ratio of the composite catalyst particles 11 and the aggregates 12 in the electrode catalyst layer 21 can be controlled by the composition of the catalyst ink.

  Here, the solvent used as the dispersion medium is not particularly limited as long as it does not erode the catalyst material 1 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 the dispersion medium of the catalyst substance 1, there is a high risk of ignition. When using such a solvent, 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 particles 11 and the formation process of the aggregates 12, a dispersion process is performed as necessary. The particle size of the composite catalyst particle 11 and the aggregate 12 can be controlled by the conditions of the dispersion treatment in each step. Even in the production of the 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 content of the solid content in the 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 too small, the film formation rate is very slow and the productivity is low. Since it will fall, it is preferable that it is 1-50 mass%.
The solid content consists of a catalyst material, an electron conductive material, and a polymer electrolyte. However, if the amount of the electron conductive material is increased, a bulky material is preferably used as the electron conductive material, so that the viscosity increases even with the same solid content. If it is decreased, the viscosity is lowered. Further, the viscosity of the 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 the catalyst ink is dispersed.

The catalyst ink may contain a pore forming agent.
By removing the pore former after the formation of the electrode catalyst layer 21, 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.
Then, after the catalyst ink preparation step, the catalyst ink is applied onto a substrate selected from among a gas diffusion layer, a transfer sheet, and a polymer electrolyte membrane, and an electrode catalyst layer 21 is formed through a drying step ( Step of forming an electrode catalyst layer). Thereby, the electrode catalyst layer 21 is completed.

Here, 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 polymer electrolyte membrane by a bonding process. In the membrane electrode assembly 31 of the present invention, a polymer electrolyte membrane is used as a base material, a catalyst ink is directly applied to both sides of the polymer electrolyte membrane, and an electrode catalyst layer is directly applied to both sides of the polymer electrolyte membrane. It can also be formed.
At this time, as a method for applying the catalyst ink, 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 the electrode catalyst layers 21 and 22 are bonded to the polymer electrolyte membrane 23, and the electrode catalyst layers 21 and 22 are provided on both sides of the polymer electrolyte membrane 23. The electrode assembly 31 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 21 described above, a plurality of catalyst material-supporting particles 2 supporting the catalyst material 1 on the surface are formed by agglomeration, and the surfaces of the catalyst material 1 and the catalyst material-supporting particles 2 are formed on the polymer electrolyte layer 3. Electrode composed of a plurality of composite catalyst particles 11 coated with a plurality of aggregates 12 formed by aggregation of polymer electrolytes, and a plurality of composite catalyst particles 11 connected by a plurality of aggregates 12. A catalyst layer 21 is obtained. According to the electrode catalyst layer 21, not only the proton conductivity in the electrode catalyst layer 21 is increased, but also the gas diffusibility is secured, thereby increasing the reaction active point and improving the output performance. In the conventional electrocatalyst layer using the composite catalyst particles coated with the polymer electrolyte and the manufacturing method thereof, it is difficult to adjust the amount of the polymer electrolyte layer on the surface of the catalyst material, and the proton conductivity and gas diffusion on the catalyst surface are difficult to adjust. It is impossible to secure sufficient sex at the same time. Further, it is difficult to adjust the gas diffusibility and the strength of the electrode catalyst layer in detail by the amount of the polymer electrolyte only by coating the catalyst substance 1 with the polymer electrolyte layer 3.

  Further, since the plurality of aggregates 12 are formed by drying a solution in which the polymer electrolyte is dissolved, the amount of polymer electrolyte in the aggregates 12 in the aggregate 12 can be determined depending on the drying temperature when the catalyst ink is produced. Therefore, the aggregation of the composite catalyst particles 11 can be avoided, and the surface of the catalyst material 1 can be fully utilized. In the production method using a poor solvent that precipitates a polymer electrolyte aggregate as a dispersion solvent of the catalyst ink, not only the polymer electrolyte aggregate but also the aggregation of the composite catalyst particles may occur. The surface is not fully utilized.

  As the gas diffusion layers 24 and 25 and the separator plates 30a and 30b in the fuel cell 40, 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 24 and 25. As the separator plates 30a and 30b, carbon type or metal type can be used. The fuel cell 40 is manufactured by assembling other accompanying devices such as a gas supply device and a cooling device.

  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. 1, a dispersion treatment is performed in a solvent in which catalyst material-supporting particles 2 supporting the catalyst material 1 and a polymer electrolyte solution (Nafion: registered trademark, manufactured by DuPont) constituting the polymer electrolyte layer 3 are added. A mixture of the catalyst substance-supporting particles 2 and the polymer electrolyte layer 3 was produced. Then, the mixture was apply | coated on the base material with the doctor blade, and was dried for 5 minutes at 120 degreeC in air | atmosphere. Thereafter, the composite catalyst particles 11 were collected from the substrate.

[Method of forming aggregate]
Dispersion treatment was performed in a solvent to which a polymer electrolyte solution (Nafion: registered trademark, manufactured by DuPont) was added, and the mixture was applied onto a substrate with a doctor blade and dried at 70 ° C. for 5 minutes in an air atmosphere. Thereafter, the aggregate 12 was recovered from the substrate.
[Preparation of catalyst ink]
The composite catalyst particles 11 recovered from the substrate and the aggregates 12 recovered from the substrate were mixed in a solvent and subjected to a dispersion treatment.

[Method for forming electrode catalyst layer]
The produced catalyst ink was applied to the transfer sheet with a doctor blade and dried at 80 ° C. for 5 minutes in the air atmosphere, whereby the electrode catalyst layer 21 was formed. The thickness of the electrode catalyst layer 21 was adjusted so that the amount of the catalyst material 1 was 0.3 mg / cm ² to form the electrode catalyst layer 21.

(Comparative example)
[Method of forming composite catalyst particles]
Composite catalyst particles were formed in the same manner as in the examples.
[Method of forming aggregate]
A polymer electrolyte solution (Nafion: registered trademark, manufactured by DuPont) was added to an organic solvent little by little, and a dispersion treatment was performed to obtain a solution containing an electrolyte aggregate.

[Preparation of catalyst ink]
A solution containing the composite catalyst particles and the aggregate of the electrolyte was mixed in a solvent and subjected to a dispersion treatment.
[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, whereby the electrode catalyst layer 121 was formed. The electrode catalyst layer 121 was formed by adjusting the thickness of the electrode catalyst layer 121 so that the amount of the catalyst material 101 was 0.3 mg / cm ² .

[Production of membrane electrode assembly and fuel cell]
The base material on which the electrode catalyst layers 21 and 121 produced in (Example) and (Comparative Example) were formed was punched into a 5 cm ² square, and the polymer electrolyte membrane (Nafion 212: registered trademark, manufactured by DuPont) 23 in FIG. A transfer sheet was placed so as to face both surfaces of the film, and hot pressing was performed at 130 ° C. to obtain a membrane electrode assembly 31. On both surfaces of the obtained membrane electrode assembly 31, carbon cloth having a sealing layer formed as a gas diffusion layer 24, 25 is disposed, and is further sandwiched between a pair of separator plates 30, and a single cell solid polymer type A fuel cell 40 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 plurality of composite catalyst particles that are provided with a catalyst substance on at least a surface and the surface of the catalyst substance is covered with a polymer electrolyte layer, and the polymer electrolyte aggregates. A plurality of aggregates formed, and the plurality of composite catalyst particles are connected by the plurality of aggregates, and the plurality of aggregates are formed by drying a solution in which a polymer electrolyte is dissolved. It is characterized by that.

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, comprising a catalyst substance, or catalyst substance-supported particles carrying the catalyst substance, and a polymer electrolyte. And the catalyst material, the catalyst material-supporting particles supporting the catalyst material, and the surface of the catalyst material are coated with the polymer electrolyte to form a plurality of composite catalyst particles. A step of forming, drying a solution in which the polymer electrolyte is dissolved to form a plurality of aggregates, a step of dispersing the composite catalyst particles and the aggregates in a solvent to produce a catalyst ink, and a gas And a step of forming an electrode catalyst layer by applying the catalyst ink on a substrate selected from a diffusion layer, a transfer sheet, and a polymer electrolyte membrane.
Thus, by ensuring sufficient proton conductivity and gas diffusibility to the catalyst surface, it is possible to provide a fuel cell having an increased reaction active point and improved output performance. 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 Catalytic substance 2 Catalytic substance carrying particle 3 Polymer electrolyte layer 11 Composite catalyst particle 12 Aggregate 21 and 22 Electrode catalyst layer 23 Polymer electrolyte membrane 24 and 25 Gas diffusion layer 26 Electrode (air electrode)
27 Electrode (fuel electrode)
28 Gas Channel 29 Cooling Water Channel 30a Separator Plate 30b Separator Plate 31 Membrane Electrode Assembly 40 Fuel Cell 101 Catalytic Material 102 Catalytic Material Supporting Particle 103 Polymer Electrolyte Layer 111 Composite Catalyst Particle 121 Electrode Catalyst Layer

Claims (8)

Comprising at least a catalyst substance on the surface, and a plurality of composite catalyst particles, the surface of the catalyst substance being covered with a polymer electrolyte layer, and a plurality of aggregates formed by aggregation of the polymer electrolyte;
The electrode catalyst layer for a fuel cell, wherein the plurality of composite catalyst particles are connected by the plurality of aggregates, and the plurality of aggregates are formed by drying a solution obtained by dissolving a polymer electrolyte. .   Each of the plurality of composite catalyst particles is formed by agglomerating a plurality of the catalyst material or a plurality of catalyst material support particles supporting the catalyst material on the surface, and the catalyst material, or the catalyst material and the catalyst material support The electrode catalyst layer for a fuel cell according to claim 1, wherein the surface of the particles is covered with the polymer electrolyte layer. A fuel cell membrane assembly comprising a proton conductive polymer electrolyte membrane and a pair of fuel cell electrode catalyst layers sandwiching the proton conductive polymer electrolyte membrane,
3. A fuel cell membrane electrode assembly, wherein at least one of the pair of fuel cell electrode catalyst layers comprises the fuel cell electrode catalyst layer according to claim 1 or 2.   A fuel cell membrane electrode assembly according to claim 3, a pair of gas diffusion layers sandwiching the fuel cell membrane electrode assembly, and a pair of separator plates sandwiching the pair of gas diffusion layers. A fuel cell characterized by comprising: A method for producing an electrode catalyst layer for a fuel cell, comprising:
A catalyst material or a mixture of catalyst material-supported particles supporting the catalyst material and a polymer electrolyte dispersed in a solvent is dried, and the catalyst material or the catalyst material is supported by the polymer electrolyte. Coating the catalyst material-supporting particles and the surface of the catalyst material to form a plurality of composite catalyst particles;
Drying a solution in which the polymer electrolyte is dissolved to form a plurality of aggregates;
A step of dispersing the composite catalyst particles and the aggregates in a solvent to prepare a catalyst ink;
A step of applying the catalyst ink on a substrate selected from a gas diffusion layer, a transfer sheet, and a polymer electrolyte membrane to form an electrode catalyst layer;
A method for producing an electrode catalyst layer for a fuel cell, comprising:   6. The method for producing an electrode catalyst layer for a fuel cell according to claim 5, wherein a drying temperature in the step of forming the plurality of composite catalyst particles is equal to or higher than a drying temperature for forming the plurality of aggregates.   The method for producing a fuel cell electrode catalyst layer according to claim 5 or 6, wherein a drying temperature in the step of forming the plurality of composite catalyst particles is in a range of 50 ° C or higher and 180 ° C or lower.   8. The fuel cell electrode catalyst layer according to claim 5, wherein a drying temperature in the step of forming the plurality of aggregates is in a range of 30 ° C. or more and 140 ° C. or less. 9. Manufacturing method.

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