JP5376217B2 - Method for producing particles for electrode material of fuel cell, electrode material for fuel cell and method for producing the same, and method for producing electrode for fuel cell - Google Patents

Description

The present invention relates to a method for producing particles for an electrode material for a fuel cell, an electrode material for a fuel cell and a method for producing the same, and a method for producing an electrode for a fuel cell.

  Fuel cells are attracting attention as power generation systems that have little negative impact on the environment. In particular, a polymer electrolyte fuel cell using an ion exchange membrane as an electrolyte is considered promising as an in-vehicle power source because it has a low operating temperature and can be miniaturized.

Such an electrode used for a fuel cell includes a conductive material, an ion exchange resin, and a catalyst metal. When a gas containing hydrogen and a gas containing oxygen are respectively supplied to the anode and cathode of a fuel cell equipped with this electrode on both sides of the polymer electrolyte membrane, the following reaction proceeds at the anode and cathode to generate power. can get.
Anode: 2H ₂ → 4H ⁺ + 4e ⁻
Cathode: O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O
Overall: 2H ₂ + O ₂ → 2H ₂ O

  This electrode reaction takes place at a reaction site formed on the contact surface between the proton conduction path called the cluster part of the ion exchange resin and the conductive material. In order to improve the cell voltage by increasing the efficiency of the reaction, it is necessary to efficiently support the catalytic metal at the site and to sufficiently supply the reaction gas to the site. As a method for manufacturing such a fuel cell, for example, a method described in Patent Document 1 is known.

JP 2005-276443 A

  The manufacturing method of the fuel cell electrode described in Patent Document 1 is as follows. First, after preparing the mixture X containing a carbon material, a cation exchange resin, and a catalyst metal, this mixture X and a pore making agent are mixed, and the slurry containing the mixture X and a pore making agent is produced. Subsequently, after applying and drying the slurry on the sheet, a laminate of the catalyst layer and the sheet is produced. Next, the catalyst layer of the laminate is joined to the cation exchange membrane, the sheet is removed, and a joined body of the cation exchange membrane and the catalyst layer is produced. Furthermore, the electrode for fuel cells is obtained by passing through the elution process which makes the conjugate | bonded_body of a cation exchange membrane and a catalyst layer contact an acid, and elutes a pore making material.

  According to the invention of Patent Document 1, pores can be formed in the catalyst layer by elution of the pore-forming agent mixed with the mixture X when the laminate is produced in the elution step. As a result, the gas diffusivity in the catalyst layer and the discharge of water generated by the cathode electrode reaction and the like are improved, so that an increase in the polarization of the fuel cell can be suppressed even under high current density conditions. A fuel cell can be provided.

  However, in the invention of Patent Document 1, the pore-forming agent cannot exist inside the particles of the mixture X containing the carbonaceous material, the ion exchange resin, and the catalyst metal, and exists only between the particles of the mixture X. Therefore, sufficient pores could not be formed in the region inside the mixture X. As a result, the gas diffusion to the catalytic metal located at the reaction site in the region inside the mixture X was insufficient, and the reaction gas was not sufficiently supplied, so that only a low output was obtained. Therefore, a fuel cell used for an in-vehicle power source or the like needs to be studied for higher output.

  The present invention has been completed based on the above situation, and an object of the present invention is to provide a fuel cell having a high cell voltage and a high output.

As a result of intensive studies to solve the above problems, the following knowledge was obtained.
(1) When the pore forming agent is removed from the particles containing the conductive material, the ion exchange resin and the pore forming agent, a sufficient amount of pores are formed in the region inside the particles.
(2) In a fuel cell comprising a fuel cell electrode material produced using the particles according to (1), the gas diffusibility into the particles is improved, so that the reaction sites in the regions inside the particles The reaction gas can be sufficiently supplied to the catalyst metal. As a result, a fuel cell with a high cell voltage and a high output can be obtained even if the porosity is about the same as that of the fuel cell produced by the method described in Patent Document 1. It is done.
The present invention is based on such knowledge.

That is, the present invention provides a pore-forming agent from particles for a fuel cell electrode material (particles containing a pore-forming agent) containing a conductive material, an ion exchange resin, and a pore-forming agent, or particles containing the pore-forming agent. Particles for electrode material of a fuel cell obtained by removing (particle A), wherein the ion exchange resin is a cation exchange resin, the conductive material is carbon, and a catalyst metal is mainly used as the catalyst material. look including those comprising the contact surface of the proton conducting path and the carbon surface of the cation exchange resin, the volume of the particles containing the pore forming agent, the content of the pore-forming agent is 12 vol% or more 54 The electrode material for a fuel cell is characterized by having a volume% or less .

  The present invention also provides a method for producing particles for electrode material of a fuel cell, wherein the solvent is removed from a mixture containing a conductive material, an ion exchange resin, a pore forming agent and a solvent.

  The present invention also provides a method for producing an electrode material for a fuel cell, wherein the particles for the electrode material for a fuel cell are used.

  Furthermore, the present invention is a method for producing a fuel cell electrode, characterized by using the above fuel cell electrode material.

In the present invention , since the particles for the fuel cell electrode material (particles containing a pore-forming agent) contain a pore-forming agent, the pore-forming agent contained in the particles is removed or the pores are formed in the particles. By the action of the agent, pores can be formed inside the particles. In such a battery comprising an electrode material containing particles capable of forming pores therein and a catalyst metal, it is formed on the contact surface between the proton conduction path of the ion exchange resin and the conductive material. Since sufficient reaction gas is supplied to the catalytic metal located at the reaction site, the cell voltage can be improved.
As a result, according to the present invention, a fuel cell having a high cell voltage and a high output can be provided.

In the present invention, the particles are provided such that the ion exchange resin is a cation exchange resin, the conductive material is carbon, and the catalytic metal is provided mainly on the contact surface between the proton conduction path of the cation exchange resin and the carbon surface. Therefore, the catalytic metal is efficiently supported at the reaction site, so that even a small amount of the catalytic metal has sufficient reactivity. Therefore, according to the above configuration, a fuel cell having a high cell voltage can be provided at a low cost in cooperation with the original operation of the present invention in which the reaction gas is sufficiently supplied to the reaction site .

The method for producing particles for an electrode material of a fuel cell according to the present invention includes removing a pore-forming agent from a particle containing a conductive material, an ion-exchange resin, and a pore-forming agent in a solution containing catalyst metal ions. After soaking the particles obtained in this manner, the soaked particles may be exposed to an atmosphere in which the ions of the catalyst metal are reduced .

  Such a configuration is preferable because particles or an electrode material in which the catalytic metal is efficiently supported at the reaction site can be easily produced.

According to the present invention, a fuel cell having a high cell voltage and a high output can be provided.

The figure which shows the polarization characteristic of the fuel cell produced in Example 1, and the fuel cell produced in Comparative Example 1 Diagram showing the relationship between porosity and cell voltage

In the present invention , the particles for the electrode material of the fuel cell are particles containing a conductive material, an ion exchange resin and a pore-forming agent (also referred to as “particles containing a pore-forming agent”), and particles containing the pore-forming agent. Particles obtained by removing the pore-forming agent from (also referred to as “particle A”).
First, the particles containing the pore-forming agent and the particles A will be described.

( Particles containing pore-forming agent and particles A )
In the following description, the particles containing the pore-forming agent and the particles A are collectively referred to as “particles in the present invention ”.
As the conductive material contained in the particles in the present invention , a material containing metal or carbon is preferably used because of high electron conductivity, and a material containing carbon is particularly preferable because of high corrosion resistance.
As the material containing carbon, for example, carbon black such as acetylene black and furnace black, activated carbon, and the like can be used. Preferably, Denka Black [manufactured by Denki Kagaku Kogyo Co., Ltd.], Vulcan XC-72 (manufactured by Cabot Corp.), Black Peal 2000 (manufactured by Cabot Corp.) or Ketjenblack EC [manufactured by Ketjenblack International Co., Ltd.] Use carbon black. In addition to this, carbon having a high graphitization degree can be used. As carbon having a high degree of graphitization, Tokablack # 3855 [manufactured by Tokai Carbon Co., Ltd.], Denkaback FX-35 [Electrochemical Industry Co., Ltd.] or carbon black was baked at a high temperature to increase the degree of graphitization. Things can be used.

As the ion exchange resin contained in the particles in the present invention , a cation exchange resin and an anion exchange resin can be used.
When the particles in the present invention are used as a material for a general solid polymer fuel cell using a cation exchange resin membrane as an ion exchange membrane, it is preferable to use a cation exchange resin as the ion exchange resin. As a cation exchange resin, a cation exchange resin having proton conductivity, for example, a perfluorocarbon sulfonic acid type or a styrene-divinylbenzene sulfonic acid type cation exchange resin, or a carboxylic acid form of those resins should be used. Is preferred.

As the pore-forming agent contained in the particles containing the pore-forming agent , the following types can be used.
(1) A type of pore-forming agent that acts in the particles and increases the volume of the pores by being included in the particles together with the conductive material and the ion exchange resin. (2) In the particles together with the conductive resin and the ion exchange resin. A type of pore-forming agent that increases the volume of pores in the particles by including them and removing them later

  Specifically, as the pore-forming agent of type (1), a porous substance or a fibrous substance can be used, and it is conductive from the viewpoint that the electronic conductivity of the electrode can be increased. A substance is particularly preferable, and a material containing carbon is more preferable from the viewpoint of high corrosion resistance. As a material containing carbon, for example, fibrous carbon such as carbon fiber, carbon nanofiber, carbon nanotube, and carbon nanohorn can be used.

  As the pore-forming agent of the type (2), specifically, a metal, an inorganic compound, or particles or fibers of an organic compound that can be removed by elution, evaporation, or sublimation can be used. As the metal, for example, nickel, zinc, iron, aluminum, magnesium, copper, titanium, or chromium can be used. A metal salt can be used as the inorganic compound. As the metal salt, for example, a metal salt containing potassium, sodium, calcium, nickel, zinc, iron, aluminum, magnesium, copper, or chromium can be used. As the organic compound, a substance that can be evaporated, sublimated, or eluted with an organic solvent can be used.

  Among these pore-forming agents, those that do not substantially dissolve in water but dissolve in acid are preferable in that treatment with water can be performed before the pore-removing agent is removed. . Metals, calcium carbonate, etc. are mentioned as those having the property of not dissolving in water but dissolving in acid. Of the metals and calcium carbonate, nickel is preferable from the viewpoint of easy control of the average particle size, and calcium carbonate is preferable from the viewpoint of low cost.

  As the pore-forming agent, those having a particulate shape and having an average particle size of 0.1 μm or more and 5 μm or less are preferable, and those having an average particle size of 0.5 μm or more and 2 μm or less are particularly preferable. Details of the reason why the above range is preferable will be described later.

The particles A are obtained by removing the pore-forming agent from the particles containing the conductive material, the ion exchange resin, and the pore-forming agent described above. As a method for removing the pore-forming agent, a method for eluting, evaporating, or sublimating the pore-forming agent can be used. As the solvent used for the elution, for example, a liquid containing water, alcohol, acid, or organic solvent can be used.

The average particle diameter of the particles in the present invention is preferably in the range of 0.3 μm to 10 μm from the viewpoint of producing a catalyst layer having a uniform thickness (details will be described later). When particles having a particle size distribution peak in both the range of 0.3 μm to 2.5 μm and the range of 2.5 μm to 10 μm are used as the particles in the present invention , gas diffusibility and electronic conductivity are more suitable. This is particularly preferable.

The pore volume of the particle A is preferably such that the pore volume having a diameter of 0.01 μm to 2.5 μm is 1 cm ³ g ⁻¹ or more and 4 cm ³ g ⁻¹ or less from the viewpoint of obtaining high gas diffusibility.

The particles in the present invention are mainly provided with a catalytic metal on the contact surface between the proton conduction path of the cation exchange resin and the surface of the conductive material. When the particles in the present invention have a structure in which the catalyst metal is mainly provided on the contact surface between the proton conduction path of the cation exchange resin and the surface of the conductive material, the catalyst metal is efficiently supported at the reaction site, and at that site. This is because the reaction gas can be sufficiently supplied, so that the cell voltage of the fuel cell can be greatly increased.

Next, a method for producing particles will be described.
Particles containing a pore-forming agent can be produced by removing the solvent from a mixture containing a conductive material, an ion exchange resin, a pore-forming agent and a solvent.
In the method for producing particles , an ion exchange resin solution in which an ion exchange resin is dissolved in a solvent can be used as the ion exchange resin. In the method for producing particles, it is preferable to use a liquid containing water and alcohol in an arbitrary ratio as a solvent, but only a solvent contained in the ion exchange resin solution may be used.

  The mixture containing a conductive material, an ion exchange resin, a pore forming agent and a solvent can be produced by mixing a conductive material, an ion exchange resin, a solvent and a pore forming agent by a known method. As each component contained in the said mixture, the compound mentioned above is used.

  As a method for removing the solvent from the mixture, for example, there is a method of drying the solvent. As a method for drying the solvent, for example, standing drying, blow drying, warm air drying, infrared heating drying, far infrared heating drying, reduced pressure drying, spray drying, and the like can be used. Among these methods, it is preferable to perform spray drying from the viewpoint that particles can be obtained immediately from the state of the mixture, the particle diameter can be easily adjusted, and the treatment can be performed in a large amount.

The particles A can be produced by removing the pore-forming agent from the particles containing the pore-forming agent produced by the method described above. That is, the particle A is produced from a particle containing a pore-forming agent produced by using a pore-forming agent that can be removed by elution, evaporation, sublimation or the like [the pore-forming agent of the above type (2)]. Is obtained. Details of the method for removing the pore-forming agent will be described later.

After the particles in the present invention thus produced are immersed in a solution containing catalyst metal ions, the particles after immersion are exposed to an atmosphere in which the ions are reduced. The particles provided on the contact surface between the proton conduction path and the surface of the conductive material can be obtained .

A method for incorporating the catalytic metal into the particles will be specifically described. Here, an example in which a catalyst metal is included in particles containing a pore-forming agent will be described, but the catalyst metal can also be included in the particle A or an electrode material not including the catalyst metal by the same method.

  First, a compound containing a metal that becomes a catalyst metal is dissolved in a liquid containing water to prepare a solution containing the catalyst metal. Subsequently, the cation of the catalytic metal is adsorbed on the cation exchange resin contained in the particle by immersing the particle in the solution. The adsorption of the cation of the catalytic metal is due to an ion exchange reaction between the counter ion of the cation exchange resin and the cation of the catalytic metal. When two or more types of cations for ion exchange are used, two or more types of catalytic metal cations can be adsorbed on the particles.

The cation of the catalyst metal is difficult to adsorb on the surface of the conductive material exposed without being coated with the cation exchange resin, and the proton of the cation exchange resin is obtained by an ion exchange reaction with the cation of the cation exchange resin. Those that preferentially adsorb to the conduction path are preferred. As the cation of the catalyst metal having such adsorption characteristics, a cation containing a platinum group metal or a complex ion of a platinum group metal can be used. Specifically, platinum complex metal ions such as [Pt (NH ₃ ) ₄ ] ²⁺ , [Pt (NH ₃ ) ₆ ] ⁴⁺ , or [Ru (NH ₃ ) ₄ ] ²⁺ and [Ru (NH ₃ ) ₆ ] ⁴⁺ can be suitably used. In the present invention, in addition to the ammine complex ion, a platinum group metal complex ion coordinated with a nitrate group or a nitroso group can also be used.

Next, the catalyst metal cation adsorbed on the particles in the present invention is reduced by chemically reducing the particles adsorbed with the catalyst metal cation so that the surface of the conductive material and the proton conduction of the cation exchange resin Particles selectively supported on the contact surface with the path are obtained.

  In this reduction step, it is preferable to use a chemical reduction method using a reducing agent suitable for mass production, and a gas phase reduction method using hydrogen or a gas containing hydrogen, or a gas phase reduction using an inert gas containing hydrazine. The method is particularly preferred. The gas containing hydrogen is preferably a mixed gas of an inert gas such as nitrogen, helium or argon and hydrogen, and a mixed gas having a hydrogen content of 10 vol% or more is particularly preferable. When this method is used, it is preferable to use a carbonaceous material having catalytic activity for the reduction reaction of the cation of the catalytic metal as the conductive material.

When a carbonaceous material is used as the conductive material, it has an activity as a catalyst for the cation reduction reaction of the platinum group metal. Ions can be reduced. For example, the reduction temperature of platinum ammine complex ion [Pt (NH ₃ ) ₄ ] ²⁺ adsorbed in a perfluorocarbon sulfonic acid type cation exchange resin with hydrogen is about 300 ° C. (Tetsuo Sakai, Osaka Industrial Technology Laboratory quarterly report, 36, 10 (1985)), but that of [Pt (NH ₃ ) ₄ ] ²⁺ adsorbed on the surface of carbon particles modified with exchange groups (Denka Black, Vulcan XC-72, Black Peal 2000, etc.) is 180 ° C. (K. Amine, M. Mizuhata, K. Ogura, H. Takenaka, J. Chem. Soc. Faraday Trans., 91, 4451 (1995)).

  Due to the activity of the carbonaceous material as a catalyst, cations near the surface of the carbonaceous material are preferentially reduced to the catalytic metal, and thus a catalytic metal is generated on the surface of the carbonaceous material. In the reduction step, the particle size and surface properties of the catalytic metal produced on the surface of the carbonaceous material can be controlled by adjusting the type of reducing agent, reducing agent concentration, reducing pressure, and reducing time.

The particles in the present invention thus produced are preferably stored in an atmosphere having a low oxygen concentration in order to prevent the conductive material from being oxidized by oxygen, and the storage method may be nitrogen gas or argon gas. There is a method of storing the powder in a container filled with
Next, the fuel cell electrode material of the present invention will be described.

(Electrode material for fuel cell of the present invention)
The fuel cell electrode material of the present invention (hereinafter referred to as the electrode material of the present invention) is characterized by containing particles or particles A containing a pore-forming agent .
The electrode material of the present invention refers to a material used for producing a fuel cell electrode, and refers to a particle containing a pore forming agent or a particle A formed into a predetermined shape. The predetermined shape means a shape suitable for manufacturing an electrode for a fuel cell, and may be a lump shape, a flake shape, or a sheet shape in order to suppress scattering. In addition, what was made into a sheet form is preferable since it can be processed into a catalyst layer with fewer steps than in the case of other shapes.

  The electrode material of the present invention may contain a pore-forming agent or may not contain a pore-forming agent. The electrode material of the present invention may be subjected to press processing or the like for use as a fuel cell electrode. However, in the electrode material that does not contain a pore-forming agent, voids are formed in the material. There is a concern that holes may be deformed or the number of holes may be reduced due to processing performed for use as an electrode. Therefore, in the present invention, it is preferable that the electrode material contains a pore-forming agent because deformation and reduction of holes due to subsequent processing can be prevented.

Next, the manufacturing method of the electrode material of this invention is demonstrated .
And particles containing catalytic metal, the slurry containing a solvent, and dried after coating on a substrate, a catalyst layer containing the particles in the present invention (electrode material of the present invention) is formed.

  Here, when a transfer film is used as the substrate, the membrane / catalyst layer assembly can be formed by transferring the catalyst layer to the ion exchange membrane. When a gas diffusion layer is used as a substrate, a membrane / electrode assembly can be formed by bonding an ion exchange membrane and a catalyst layer. When an ion exchange membrane is used as a substrate, it can also be used as a membrane / catalyst layer assembly without performing the above-described transfer or bonding.

  As the transfer film, a resin film or a metal film can be used. As the ion exchange membrane, a cation exchange membrane or an anion exchange membrane can be used, but the same type as the ion exchange resin contained in the particles is preferable. As a cation exchange membrane, a cation exchange membrane having proton conductivity, for example, a perfluorocarbon sulfonic acid type or a styrene-divinylbenzene sulfonic acid type cation exchange membrane, or a carboxylic acid type of those resins should be used. Is preferred. Among these, a cation exchange membrane made of a perfluorocarbon sulfonic acid resin having high chemical stability and high proton conductivity is particularly preferable.

  As a solvent (solvent for producing a slurry) used in the method for producing an electrode material of the present invention, a liquid containing water, alcohol, or an organic solvent can be used, but since a suitable dispersion of particles can be obtained, For example, an organic solvent such as tetrahydrofuran, dimethylformamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone is preferably used. In addition, when the pore forming agent contained in the catalyst layer is removed after forming the catalyst layer as the electrode material, the solvent is preferably of a nature that does not remove the pore forming agent.

  In the method for producing an electrode material of the present invention, for example, a doctor blade method, a dip coating method, a spray method, a reverse roll method, a comma bar method, a gravure method, and an air knife method may be used as a method for applying a slurry. it can. In the production method of the present invention, as the method for drying the slurry, for example, standing drying, air drying, warm air drying, infrared heat drying, far infrared heat drying, reduced pressure drying and the like can be used.

Next, a reference example in which an electrode material is produced using particles that do not contain a catalyst metal will be described. When a slurry containing particles and a solvent is applied onto a substrate and then dried, a layered electrode material containing particles (referred to as an electrode material sheet) is formed. In addition, since this electrode material sheet does not contain a catalyst metal, before using it as an electrode for a fuel cell, for example, after the electrode material sheet is immersed in a solution containing catalyst metal ions, the electrode material sheet after immersion is used. The catalyst layer needs to be made to contain a catalyst metal by a method of exposing to an atmosphere in which the ions are reduced.

  As a method of transferring or joining the electrode material sheet to the ion exchange membrane, for example, a method of pressing or thermocompression bonding the electrode material sheet to the cation exchange membrane using a flat press machine or a roll press machine can be used. However, it can also join by making an electrode material sheet contact an ion exchange membrane.

  When heating, the temperature is preferably near the glass transition temperature of the ion exchange resin. When an electrode material sheet is formed in the gas diffusion layer, a membrane / electrode assembly can be obtained by bonding the electrode material sheet to the ion exchange membrane. Joining can be performed by thermocompression bonding. The conditions for the thermocompression bonding can be a low pressure condition as compared with the thermocompression bonding performed when a polymer film or a metal foil is used as the molding substrate. A membrane / electrode assembly can also be manufactured by incorporating a gas diffusion layer and a membrane in which a catalyst layer is formed in the cell without performing the above-described joining.

  The thicknesses of the electrode material sheet and the catalyst layer, which are the electrode materials of the present invention, are preferably 1 μm to 50 μm, respectively. When used as a catalyst layer, the thickness can be controlled by pressing. This pressing step may be performed before the bonded body is manufactured or after the bonded body is manufactured.

In the present invention, it is important that pores are formed in the particles contained in the electrode material. These pores can be removed by removing the pore-forming agent or by causing the pore-forming agent to act. It is formed. Here, a method for removing the pore forming agent from the electrode material of the present invention produced using the type (2) of the pore forming agent as a pore forming agent will be described.

In the production method of the present invention, a method of removing the pore-forming agent after forming the catalyst layer using particles containing the pore-forming agent, and a method of forming the catalyst layer using the particles A from which the pore-forming agent has been removed, There is. When the electrode material sheet or the catalyst layer is formed using the particles A, since the pores are already formed in the particles A, the deformation of the pores and the reduction of the pores are caused when the electrode material sheet is formed. Can occur. Therefore, a method of removing the pore-forming agent after forming an electrode material sheet or a catalyst layer using particles containing the pore-forming agent is preferable in order to prevent pore deformation and the like.

Specific methods for removing the pore-forming agent include a method in which particles containing the pore-forming agent or the electrode material ( catalyst layer ) of the present invention are brought into contact with a solvent to elute the pore-forming agent , and heating or depressurization is performed. Examples thereof include a method of evaporating the pore-forming agent and a method by sublimation.

When removing the pore-forming agent by contact with a solvent, for example in a solvent to elute the pore-forming agent, a method of immersing the electrode material particles or the present invention containing a pore-forming agent, forming the solvent to elute the pore-forming agent A method such as spraying onto particles containing a pore agent or the electrode material of the present invention can be used.

  In the present invention, the porosity of the electrode material sheet and the porosity of the catalyst layer are preferably in the range of 40% to 95% because gas diffusibility and electronic conductivity can be increased. From the viewpoint of maintaining the electron conductivity, it is preferable to be in the range of 93% or less.

The porosity of the electrode material sheet and the porosity of the catalyst layer can be adjusted by the amount of the pore-forming agent mixed with the particles . In the present invention, regardless of the mixing amount of the pore-forming agent, the effect of forming pores in the inner region of the particles, which was insufficient with the conventional method, can be obtained. When the pore former is used, the mixing amount of the pore former is preferably 12% by volume or more and 76% by volume or less with respect to the volume of the particles because the cell voltage is remarkably improved. It is preferable to be 70% by volume or less because proton conductivity can be improved.

Furthermore, as a result of repeated studies by the present inventors, as a pore-forming agent, nickel particles, zinc particles, iron particles, aluminum particles, magnesium particles, copper particles, chromium particles having an average particle diameter of 0.1 μm or more and 5 μm or less, and When calcium carbonate particles were used, the knowledge that an excellent effect was surely obtained by setting the mixing amount of the pore-forming agent to 12 vol% or more and 54 vol% or less with respect to the volume of the particles was obtained. . In addition, the volume% used as a unit of the mixing amount of the pore forming agent is a value calculated by the following formula.
Volume% = 100 × [volume of pore former / volume of particles]
In the above formula, the volume of the pore former was determined from the mass and specific gravity. In the above formula, the volume of the particle is the sum of the respective volumes determined from the mass and specific gravity of each particle constituent material.

In addition, when using the pore-forming agent of the above type (1), for example, pores can be formed in the particles of the present invention by the method described in the following (i) and (ii).
(I) A method using particles containing a pore- forming agent prepared using a pore- forming agent having pores . According to this method, since the pores in the pore former remain in the particles, the pores can be formed in the particles without removing the pore former.
(Ii) A method in which a fibrous pore-forming agent is included in particles containing the pore-forming agent of the present invention. According to this method, the pore-forming agent serves as a filler and suppresses aggregation of particles, and as a result, pores can be formed in the particles.
Next, the fuel cell electrode using the electrode material of the present invention will be described.

(Electrode for fuel cell of the present invention)
A fuel cell electrode is produced using a joined body of an electrode material (catalyst layer or electrode material sheet) produced using the particles according to the present invention obtained as described above and a cation exchange membrane. Here, when the electrode for a fuel cell is produced using the assembly (membrane / electrode assembly) of the electrode material sheet of the present invention and the cation exchange membrane, the above-described “method of incorporating catalytic metal into particles ”. In the same manner as described above, the catalyst material is included in the electrode material sheet of the joined body to be processed into a catalyst layer.

A fuel cell electrode (solid polymer type) has a conductive porous substrate such as carbon paper or carbon cloth outside the assembly of the cation exchange membrane and catalyst layer, and a gas flow outside. It is obtained by arranging a separator in which a groove serving as a path is formed.
Electric power can be obtained by using the fuel cell electrode for an anode and a cathode of a fuel cell provided on both surfaces of the polymer electrolyte membrane, and supplying a gas containing hydrogen and a gas containing oxygen, respectively.
Next, the effect of the present invention will be described.

(Effect of the present invention)
Since the particles in the present invention contain a pore-forming agent in the inner region of the particles, there are sufficient pores in the inner region of the particles of the electrode material for fuel cells, which was insufficient with the conventional method. Can be made. Therefore, the fuel cell including the electrode material for a fuel cell manufactured using the particles has improved gas diffusibility into the interior of the particles, so that the reaction gas is applied to the catalyst metal at the reaction site in the region inside the particles. As a result of the fact that the cell voltage can be increased due to the fact that the fuel cell is easily supplied, a high-power fuel cell can be provided.

<Examples and Comparative Examples>
Next, examples embodying the present invention will be described.
[Example 1]
In this example, after producing particles (a) containing carbon (conductive material), cation exchange resin (ion exchange resin) and nickel particles (pore-forming agent), platinum (catalyst) is added to the particles (a). The particles (A) containing the conductive material, the ion exchange resin, the pore-forming agent, and platinum were prepared by the method including the (metal).

(1) Production of Particle (A) Containing Conductive Material, Ion Exchange Resin, and Pore Forming Agent First, carbon (Cabot, Vulcan XC-72) and cation exchange resin solution (Aldrich, Nafion 5 mass) % Solution) was placed in a vacuum mixer (UH-600S, manufactured by SMT) and stirred for 30 minutes, and then an ultrasonic wave was irradiated for 2 minutes to prepare a dispersion of carbon and a cation exchange resin. The cation exchange resin solution contains a solvent. The content of the cation exchange resin was 75% by mass with respect to 100% by mass of carbon.

  Nickel particles (manufactured by Nikko Rica, average particle size 0.65 μm, specific gravity 8.9) are added to the dispersion of carbon and cation exchange resin and mixed to prepare a mixture, and then the mixture is spray dried. By processing with a machine (MDL series micro mist dryer, manufactured by Fujisaki Electric Co., Ltd.), particles (A) containing carbon, a cation exchange resin and nickel particles were produced. Spray drying was performed under the conditions of a solid content concentration of the dispersion of 5% and a temperature of 120 ° C. The solid content concentration was adjusted by diluting with isopropanol and deionized water.

(2) Production of Conductive Material, Ion Exchange Resin, Pore Forming Agent and Platinum-Containing Particles (A) Particles (A) containing carbon, cation exchange resin and nickel particles produced in (1) By immersing in (NH ₃ ) ₄ ] Cl ₂ aqueous solution, platinum ions ([Pt (NH ₃ ) ₄ ] ²⁺ ions) were adsorbed on the ion exchange groups of the cation exchange resin.

The particles (a) having adsorbed platinum ions were washed with water, dried at 60 ° C., and then left in a hydrogen atmosphere at 150 ° C. for 6 hours to reduce [Pt (NH ₃ ) ₄ ] ²⁺ ions. Then, platinum was deposited on the carbon surface to produce particles (ii) containing carbon, a cation exchange resin, nickel particles and platinum.

  In this example, the content of nickel particles in the particles (A) was 30% by mass. This content is 25% by volume in terms of volume%. In this conversion, the specific gravity of platinum was 21.5, the specific gravity of carbon was 2, the specific gravity of the cation exchange resin was 2, and the nickel particles were calculated as 8.9. In addition, content of platinum was 38 mass% with respect to the sum total of platinum and carbon.

(3) Production of catalyst layer containing particles (a) Disperse particles (a) containing platinum, carbon, cation exchange resin, and nickel particles obtained in (2) in N-methyl-2-pyrrolidone. The slurry was applied to a substrate (transfer film) and dried at 80 ° C. to obtain a sheet-like catalyst layer. Two catalyst layers were produced. The slurry was applied by a doctor blade method using a doctor blade having a gap with the substrate of 220 μm so that the platinum content in the catalyst layer was 0.5 mg / cm ² . A titanium foil was used as the substrate.

  The two catalyst layers are transferred to both surfaces of a cation exchange membrane (manufactured by DuPont, Nafion 115), and the titanium foil of the base material is removed to thereby provide a cation exchange membrane (membrane / catalyst layer) having a catalyst layer on both surfaces. A joined body) was obtained. For the transfer, a method of thermocompression bonding using a flat press machine was used.

(4) Removal of pore-forming agent The membrane / catalyst layer assembly was placed in a 0.5 mol / l sulfuric acid aqueous solution and boiled for 1 hour to elute and remove nickel particles in the catalyst layer. After measuring the volume of vacancies in the catalyst layer thus formed by mercury porosimetry, the porosity was calculated based on the following equation. In this example, the porosity of the catalyst layer after removal of the pore-forming agent was 63%.
Porosity (%) = 100 × (volume of pores contained in catalyst layer / total volume of catalyst layer)

(5) Fabrication of fuel cell electrode and polymer electrolyte fuel cell Carbon paper on both surfaces (one as an anode and the other as a cathode) of a cation exchange membrane with catalyst layers on both sides after removing the pore-forming agent A fuel cell electrode was obtained by stacking (gas diffusion layer) and thermocompression bonding.

  A polymer electrolyte fuel cell was manufactured by placing separators on the outside of the fuel cell electrode and then fixing the separator by sandwiching it between a pair of end plates. The separator is obtained by processing a graphite plate, and a groove serving as a gas flow path is provided on the surface in contact with the electrode. The end plate is obtained by processing a metal plate, and is provided with a through hole for guiding a gas in a pipe outside the battery to a gas flow path of the separator and a through hole for passing a fixing bolt. One end plate was an anode terminal and the other was a cathode terminal.

(6) Measurement of polarization characteristics Hydrogen humidified at 70 ° C. is supplied to the anode, and air humidified at 70 ° C. is supplied to the cathode, the cell temperature is set to 70 ° C., and the voltage between terminals at each current density (hereinafter referred to as cell voltage). The results of the measurement are shown in Table 1 and FIG. This result was evaluated as polarization characteristics.

[Comparative Example 1]
After carbon (Cabot, Vulcan XC-72) and a cation exchange resin (Aldrich, Nafion 5 mass% solution) are placed in a vacuum mixer (SMT, UH-600S) and stirred for 30 minutes. A dispersion of carbon and cation exchange resin was prepared by irradiating with ultrasonic waves for 2 minutes. The content of the cation exchange resin was 75% by mass with respect to 100% by mass of carbon.
A dispersion of carbon and a cation exchange resin was spray dried under the same conditions as the spray drying described in (1) of Example 1 to produce particles (c) containing carbon and a cation exchange resin.

Next, after immersing particles (c) containing carbon and a cation exchange resin in an aqueous solution [Pt (NH ₃ ) ₄ ] Cl _{2 in} the same manner as in the method described in (2) of Example 1, By reduction, particles (d) containing platinum, carbon, and a cation exchange resin were produced.

  As described in Examples 1 (3) to (5) except that the particles (d) thus obtained and nickel particles were molded using N-methyl-2-pyrrolidone dispersed. A fuel cell electrode of Comparative Example 1 was produced in the same manner as the method. The nickel particles were mixed so as to be 30% by mass with respect to the total mass of the particles (d) and the nickel particles. The porosity of the catalyst layer after elution of the nickel particles was 65%.

When a polymer electrolyte fuel cell was produced by the same method as in Example 1 using the electrode produced as described above, and then the current density was changed by the same method as in (6) of Example 1. The results of measuring the cell voltage are shown in Table 1 and FIG.
The vertical axis in FIG. 1 indicates the cell voltage (V). The horizontal axis represents current density (mAcm ⁻² ).
In FIG. 1, ◯ indicates data of Example 1. Δ indicates data of Comparative Example 1.

As apparent from Table 1 and FIG. 1, the fuel cell (Example 1) provided with the electrode for a fuel cell produced by the production method of the present invention using particles has the same porosity as that of the fuel cell of Comparative Example 1. It was obtained that the cell voltage was remarkably high even with a porosity of a certain degree. Further, according to the present invention, it was found that an increase in polarization can be suppressed even under a high current density condition, so that a high output fuel cell can be provided.

  In Comparative Example 1, a fuel cell having a catalyst layer with the same porosity as that of Example 1 was produced. However, the cell voltage was lower than that of the fuel cell produced in Example 1 for the following reason. it is conceivable that. In the method of Comparative Example 1, since the catalyst layer is prepared using a mixture of particles (D) containing a conductive material and an ion exchange resin and a pore-forming agent, the pore-forming agent is used inside the particles (D). Cannot exist in any area. As a result, even after removal of the pore-forming agent, the fuel cell produced in Comparative Example 1 does not have sufficient pores in the internal region of the particles contained in the catalyst layer, so that it is located at the reaction site. It is considered that the cell voltage was lower than that of the fuel cell produced in Example 1 because sufficient reaction gas was not supplied to the catalytic metal.

[Examples 2-4 , Reference Examples 1-2 ]
Except that the nickel particle (pore forming agent) content was changed and that the gap with the doctor blade was adjusted so that the platinum content in the catalyst layer was 0.5 mg / cm 2, the same as in Example 1. Thus, a polymer electrolyte fuel cell was obtained. In Example 2, Example 3, Example 4, Reference Example 1 and Reference Example 2 , the pore-forming agent (nickel particle) content was 15% by mass, 45% by mass and 60% by mass, respectively, with respect to the particle (A). %, 75% by mass and 80% by mass. When these contents are expressed by volume%, they are 12 volume%, 39 volume%, 54 volume%, 70 volume%, and 76 volume%, respectively. In Examples 2 to 4 and Reference Examples 1 to 2 , the porosity of the catalyst layer after the nickel particle elution treatment was 59%, 72%, 80%, 89%, and 91%, respectively.

[Comparative Examples 2 to 7]
The same as Comparative Example 1 except that the nickel particle (pore forming agent) content was changed and the gap with the doctor blade was adjusted so that the platinum content in the catalyst layer was 0.5 mg / cm ^2. Thus, a polymer electrolyte fuel cell was obtained.
In Comparative Example 2, Comparative Example 3, Comparative Example 4, Comparative Example 5, Comparative Example 6, and Comparative Example 7, the pore-forming agent content was 0% by mass, 15% by mass, and 45% by mass with respect to the particles (d), respectively. 60 mass%, 75 mass% and 80 mass%. When these contents are expressed by volume%, they are 0 volume%, 12 volume%, 39 volume%, 54 volume%, 70 volume%, and 76 volume%, respectively. In Comparative Examples 2 to 7, the porosity of the catalyst layer after the nickel particle elution treatment was 55%, 61%, 74%, 82%, 90%, and 92%, respectively.

For the fuel cells prepared in Examples 2 to 4, Reference Examples 1 to 2 and Comparative Examples 2 to 7, hydrogen humidified at 70 ° C. was supplied to the anode, and air humidified at 70 ° C. was supplied to the cathode, and the cell temperature was adjusted to 70. The cell voltage was measured when the current density was 300 mA / cm ² at a temperature of 300 ° C., and the results are shown in FIG.

In Table 2, the cell voltage at 300 mA means the cell voltage (V) when the current density is 300 mA / cm ² . Table 2 also shows data of Example 1 and Comparative Example 2. The vertical axis in FIG. 2 indicates the cell voltage (V) when the current density is 300 mA / cm ² . The horizontal axis indicates the porosity (%). In the figure, ○ indicates data of the example product (Examples 1 to 6), and Δ indicates data of the comparative example product (Comparative Examples 1 to 7).

  As is clear from Table 2 and FIG. 2, when the voltages of cells having the same porosity as in Example 2 and Comparative Example 3 are compared, it is found that the cell voltage of the fuel cell of the example is high. It was. Particularly in a fuel cell (Examples 1 to 4) having a pore former content of 15% by mass or more and 60% by mass or less (12% by volume or more and 54% by volume or less), a preferable result that the cell voltage is 0.7V or more is obtained. It was.

<Other embodiments>
The present invention is not limited to the embodiment described with reference to the above description and drawings. For example, the following embodiments are also included in the technical scope of the present invention.
(1) In the above embodiment and examples, after a catalyst metal is included in particles containing a pore-forming agent, a catalyst layer is produced using the particles , and the pore-forming agent in the particles contained in the catalyst layer is added. Although the removal method has been shown, the catalyst layer may be formed by using particles A and using particles obtained by adding catalyst metal to the particles A. Furthermore, you may produce a catalyst layer using the particle | grains containing the type | mold pore forming agent of the type of (1) which is not removed as particle | grains containing a pore forming agent .

  (2) In the above examples, nickel particles were used as the pore-forming agent. However, as the pore-forming agent, zinc particles, iron particles, aluminum particles, magnesium particles, copper particles, chromium particles, calcium carbonate particles, etc. May be used.

Claims (5)

Obtained by removing pore-forming agent from particles for fuel cell electrode material (particle containing pore-forming agent) containing conductive material, ion-exchange resin, and pore-forming agent, or particles containing said pore-forming agent Particles for fuel cell electrode material (Particle A),
The ion exchange resin is a cation exchange resin, the conductive material is carbon, and a catalyst metal is mainly provided on a contact surface between the proton conduction path of the cation exchange resin and the surface of the carbon. See
The fuel cell electrode material , wherein a content of the pore-forming agent is 12% by volume or more and 54% by volume or less with respect to a volume of the particles containing the pore-forming agent . A method for producing particles for an electrode material contained in an electrode material for a fuel cell according to claim 1,
  A method for producing particles for an electrode material for a fuel cell, wherein the solvent is removed from a mixture containing a conductive material, an ion exchange resin, a pore-forming agent and a solvent. A method for producing particles for an electrode material contained in an electrode material for a fuel cell according to claim 1,
  After immersing particles containing a conductive material, an ion exchange resin, and a pore-forming agent, or particles obtained by removing the pore-forming agent from the particles in a solution containing catalyst metal ions, The method for producing particles for an electrode material for a fuel cell, which is exposed to an atmosphere in which ions of the catalyst metal are reduced. A method for producing an electrode material for a fuel cell, comprising using particles contained in the electrode material for a fuel cell according to claim 1. A method for producing a fuel cell electrode, comprising using the fuel cell electrode material according to claim 1.

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