JP5046383B2 - Fuel cell and fuel cell manufacturing method - Google Patents

Description

  The present invention relates to a composite catalyst for a fuel cell, a method for producing a composite catalyst for a fuel cell, a method for producing an electrode catalyst layer for a fuel cell, and a fuel cell.

  A fuel cell directly converts chemical energy into electrical energy by supplying fuel and an oxidant to two electrically connected electrodes and causing the fuel to be oxidized electrochemically. Unlike thermal power generation, fuel cells are not subject to the Carnot cycle, and thus exhibit high energy conversion efficiency. A fuel cell is usually formed by laminating a plurality of single cells having a basic structure of a membrane / electrode assembly in which an electrolyte membrane is sandwiched between a pair of electrodes. Among them, a solid polymer electrolyte fuel cell using a solid polymer electrolyte membrane as an electrolyte membrane has advantages such as easy miniaturization and operation at a low temperature. It is attracting attention as a power source for the body.

In a solid polymer electrolyte fuel cell using hydrogen as a fuel and oxygen as an oxidant, the reaction of formula (1) proceeds at the fuel electrode (anode) during normal power generation.
_{^{2H 2 → 4H + + 4e -}} ··· (1)
The electrons generated by the equation (1) reach the oxidant electrode (cathode) after working with an external load via an external circuit. Then, the proton generated in the formula (1) moves from the fuel electrode to the oxidant electrode side in the proton conductive polymer membrane (solid polymer electrolyte membrane) in a state of being hydrated with water.

On the other hand, the reaction of the formula (2) proceeds at the oxidant electrode.
4H ⁺ + O ₂ + 4e ⁻ → 2H ₂ O (2)
That is, as a whole battery,
2H ₂ + O ₂ → 2H ₂ O (3)
The reaction is progressing.

  In order to promote the reaction of the above formula (1) or (2), each electrode (fuel electrode, oxidant electrode) is provided with an electrode catalyst. As the electrode catalyst, a catalyst in which a catalytic active substance such as catalytic metal particles such as platinum or a platinum alloy is supported on a conductive material such as carbon particles is generally used. Since catalytic metals such as platinum used for electrode catalysts are very expensive materials, the development of fuel cells that improve power utilization and show excellent power generation performance even with a small amount of platinum used in the practical use of fuel cells Is desired.

  As a method for improving the utilization rate of the catalyst metal, for example, the catalyst metal particles can be made fine. By reducing the particle size of the catalyst metal particles, the exposed surface area of the catalyst metal is increased even if the amount of the catalyst metal used is the same, and the utilization rate of the catalyst metal can be increased. However, fine catalyst metal particles are difficult to disperse and very easily aggregated, so that it is difficult to effectively increase the exposed surface area even if the particles are made fine. It is known that the particle size of platinum particles supported on carbon particles is generally about 2 to 3 nm.

The reactions (1) and (2) proceed at a three-phase interface where protons (H ⁺ ) and electrons (e ⁻ ) can be exchanged in addition to the reaction gas (fuel or oxidant). That is, disposing a catalytically active substance in the vicinity of the three-phase interface is important for improving the catalyst utilization rate.
For example, Patent Document 1 discloses a solid polymer electrolyte-catalyst composite electrode including a solid polymer electrolyte, carbon particles, and a catalyst material, where the catalyst material is on the contact surface between the carbon particles and the solid polymer electrolyte. A fuel cell electrode characterized by being mainly supported is described, and a method for producing the fuel cell electrode includes a catalyst raw material compound, a solid polymer electrolyte, and carbon particles that are reduced to produce a catalyst material Is prepared, and a catalyst raw material compound in the mixture is reduced, and a method for producing a fuel cell electrode is described. In Patent Document 1, specifically, the catalyst material is manufactured by applying the mixture, heating and drying, and then performing a reduction treatment.

  Patent Document 2 discloses a method for producing an electrode capable of preventing agglomeration of a catalyst material. A mixture of a catalyst raw material compound that is reduced to produce a catalyst material and a solid polymer electrolyte is prepared, and a catalyst in the mixture is prepared. A method for chemically reducing a raw material compound is described. Similarly to Patent Document 1, Patent Document 2 also applies a solution containing a catalyst raw material compound and a solid polymer electrolyte, heats and dries, and then reduces the catalyst raw material compound in the Examples.

JP 2000-12040 A Republished WO99 / 66575 JP-A-5-258755

  When the reduction treatment is performed after drying and solidifying the mixture containing the catalyst raw material compound and the proton conductive polymer (solid polymer electrolyte) as in Patent Document 1 and Patent Document 2, the reduction reaction of the catalyst raw material compound is performed. It ’s hard to go. Therefore, in order to produce a sufficient amount of catalyst, it is necessary to add an excessive amount of the catalyst raw material compound. Further, when the proton conductive polymer is dried, the catalyst particles generated by the reduction of the catalyst raw material compound may aggregate and may not exhibit sufficient catalytic action. That is, in the methods described in Patent Document 1 and Patent Document 2, it is difficult to sufficiently increase the catalyst utilization rate.

Patent Document 3 discloses a fuel cell in which a catalyst metal salt is reduced in an organic solution of a proton conductive polymer to deposit a catalyst metal in the proton conductive polymer to form a cathode and / or an anode. A manufacturing method is described. According to this method, a composite catalyst in which a proton conductive polymer is attached around each catalyst particle can be obtained.
However, in Patent Document 3, since the catalyst metal particles have a single layer structure, the catalyst metal inside the particles does not function as a catalyst, and the specific surface area (exposed surface area per unit weight) of the catalyst metal is small. Therefore, it cannot be said that the utilization rate improvement effect of the obtained catalyst metal is sufficient.

  On the other hand, as described above, a catalyst metal such as platinum is usually used by being supported on conductive particles such as a carbonaceous carrier such as carbon particles. While it has a function of increasing the electron conductivity of the catalyst, it is said that it is easily corroded, changes the structure of the catalyst layer, and causes a decrease in power generation performance. Furthermore, the carbon particles have a catalytic activity for the hydrogen peroxide generation reaction, and there is a problem that the proton conductive polymer membrane and the like deteriorate due to the hydrogen peroxide generated at the electrode.

  Accordingly, it has been proposed to use the catalyst metal particles as they are without being supported on a carrier such as carbon particles. However, such carrier-less catalyst metal particles are very easily aggregated depending on the particle size, and it is very difficult to form a catalyst layer in which the catalyst metal particles are highly dispersed.

  The catalyst layer is usually formed using a catalyst ink obtained by mixing catalyst metal particles with a proton conductive polymer solution in which a proton conductive polymer is dissolved. Mixability with proton conducting polymer solution is low. Therefore, in order to fully disperse the catalyst metal particles in the proton conductive polymer solution, it takes time and labor, and the manufacturing process is complicated.

  The present invention has been accomplished in view of the above circumstances, and a fuel cell composite catalyst having a high utilization rate of a catalyst metal and a method for producing the same, as well as a method for producing a catalyst layer containing the composite catalyst and the catalyst layer. It aims at providing the fuel cell provided with.

The fuel cell of the present invention comprises an ion-exchange polymer (A) on the surface of core / shell type catalyst metal fine particles (A) having a catalyst metal shell made of a catalyst metal and a metal core made of a metal species different from the catalyst metal. A catalyst layer containing the fuel cell composite catalyst to which B) is attached is provided, and the fuel cell composite catalyst is not supported on a carbonaceous support.
Since the catalyst layer containing the composite catalyst for fuel cells as described above has a three-phase interface efficiently formed, the electrode performance is high and the catalyst metal utilization rate of the composite catalyst is high. The amount used can be reduced. Therefore, the fuel cell of the present invention having the catalyst layer exhibits excellent power generation performance and can reduce the cost.
  Further, since the composite catalyst for fuel cells suppresses aggregation of the catalyst metal particles, the catalyst metal particles should be present in the catalyst layer in a highly dispersed state without being supported on a carbonaceous support. Is possible. In the fuel cell of the present invention, since the composite catalyst for a fuel cell is not supported on a carbonaceous support, it suppresses a decrease in power generation performance due to the corrosion of the carbonaceous support and the generation of hydrogen peroxide due to the catalytic action of the carbonaceous support. can do.

The fuel cell of the present invention comprises an ion-exchange polymer (A) on the surface of core / shell type catalyst metal fine particles (A) having a catalyst metal shell made of a catalyst metal and a metal core made of a metal species different from the catalyst metal. B) comprising a catalyst layer containing a fuel cell composite catalyst to which the fuel cell composite catalyst is attached, wherein the fuel cell composite catalyst is not supported on a carbonaceous carrier,
A catalyst metal precursor (a1) having water solubility and / or organic solvent solubility and forming a catalyst metal shell by reduction; and a metal species different from the catalyst metal, and having water solubility and / or organic solvent solubility. And a metal precursor (a2) that forms a metal core by reduction, an ion-exchange polymer (b), the catalyst metal precursor (a1), the metal precursor (a2), and the high ion-exchange property. A first mixed solution in which a solvent (c) capable of dissolving the molecule (b) is mixed is prepared, and the catalytic metal precursor (a1) and the metal precursor (a2) in the first mixed solution are prepared. For a fuel cell in which core-shell type catalyst metal fine particles having a catalyst metal shell and a metal core are deposited , and an ion-exchange polymer is adhered to the surface of the core-shell type catalyst metal fine particles Compound touch The method comprising the steps of: preparing a,
Forming a catalyst layer in which the composite catalyst for a fuel cell is not supported on a carbonaceous support;
It can manufacture by the manufacturing method characterized by providing .

Alternatively, the fuel cell of the present invention has a high ion exchange property on the surface of the core-shell type catalyst metal fine particles (A) having a catalyst metal shell made of a catalyst metal and a metal core made of a metal species different from the catalyst metal. A method for producing a fuel cell comprising a catalyst layer containing a fuel cell composite catalyst to which a molecule (B) is attached, wherein the fuel cell composite catalyst is not supported on a carbonaceous carrier,
Metal precursor (a2) having water solubility and / or organic solvent solubility and forming a metal core by reduction, ion-exchange polymer (b), metal precursor (a2) and high ion-exchange property A second mixed solution in which the solvent (c1) capable of dissolving the molecule (b) is mixed is prepared, and the metal precursor (a2) in the second mixed solution is reduced to precipitate metal fine particles. Thereafter, the catalyst metal precursor (a1) which has water solubility and / or organic solvent solubility and forms a catalyst metal shell by reduction is converted into the catalyst metal precursor (a1) and the ion-exchange polymer (b). Is mixed with the solvent (c2), the ion-exchange polymer (b), and the metal fine particles to prepare a third mixed solution, and the catalyst metal precursor (in the third mixed solution ( a1) is reduced to apply catalytic metal to the surface of the metal fine particles. Out so, a step of preparing a composite catalyst for a fuel cell ion exchange polymer on the surface of the core-shell type catalyst metal fine particles are adhered with the catalyst metal shell and the metal core,
Forming a catalyst layer in which the composite catalyst for a fuel cell is not supported on a carbonaceous support;
It can manufacture also by the manufacturing method of a fuel cell characterized by providing.

As described above, when the catalytic metal precursor or the metal precursor is reduced and precipitated in the solution, the solution can be stirred and the reduction reaction of these precursors can proceed uniformly throughout the solution. In addition, the ion exchange polymer functions as a protective agent, and the growth of the catalyst metal fine particles is controlled. Therefore, according to the production method of the present invention, fine and uniform catalytic metal fine particles can be obtained.
Furthermore, according to the method for producing a fuel cell of the present invention, the composite catalyst in which the ion-exchange polymer (B) is adhered to the surface of the catalyst metal fine particles (A) is obtained in the state of a dispersion dispersed in a solvent. Therefore, a fuel cell which is provided on the surface of the ion-exchange polymer membrane by performing solvent substitution or the like as required and using the dispersion liquid and which contains at least a catalyst metal and an ion-exchange polymer A catalyst layer can be formed. By using the dispersion, it is possible to omit the step of sufficiently dispersing the catalyst metal fine particles and the ion-exchange polymer in the solution when preparing the catalyst ink as in the prior art, and the catalyst layer for the fuel cell. The manufacturing process can be simplified.

  Since the composite catalyst for a fuel cell provided by the present invention is excellent in the utilization rate of the catalyst metal, the use amount of the catalyst metal is reduced by using the composite catalyst for a fuel cell of the present invention, and the equivalent or more It is possible to obtain a fuel cell catalyst layer having catalytic performance. Furthermore, according to the present invention, the manufacturing process of the fuel cell catalyst layer can be simplified. Therefore, according to the present invention, it is possible to provide a fuel cell that has excellent power generation performance, is low in cost, and can be manufactured by a simple process.

  The composite catalyst for a fuel cell of the present invention has an ion exchange property on the surface of the core-shell type catalyst metal fine particles (A) having a catalyst metal shell made of a catalyst metal and a metal core made of a metal species different from the catalyst metal. The polymer (B) is attached.

In view of the fact that platinum, which is generally used as a catalyst for fuel cells, is very expensive and is a depleted resource, in order to improve the utilization rate thereof, the fine particles of the platinum catalyst and the fuel are used. We have intensively studied to improve the dispersibility of platinum particles in the catalyst layer of the battery. As a result, in a solution containing a water-soluble polymer such as polyvinylpyrrolidone, a metal precursor such as a metal salt or a metal complex is reduced to precipitate a zero-valent metal atom, thereby having a fine and uniform particle size. The knowledge that a dispersion liquid in which metal fine particles are dispersed is obtained.
As a water-soluble polymer that suppresses aggregation of metal fine particles and maintains a stable fine particle state, an ion-exchange polymer such as a cation exchange polymer such as perfluorocarbon sulfonic acid resin or an anion exchange polymer is used. It has been found that metal fine particles coated with an ion exchange polymer can be obtained.
Furthermore, in order to improve the utilization rate of catalyst metals such as platinum, the present inventors have made a core-shell type binary structure in which the metal catalyst particles are coated with the catalyst metal on the surface of the metal fine particles as the core. The present invention has been completed. Specifically, a composite catalyst in which a perfluorocarbon sulfonic acid resin adheres to the surface of core (gold) / shell (platinum) type fine particles was successfully prepared as a monodispersed colloidal solution.

Hereinafter, the composite catalyst for a fuel cell of the present invention will be described in detail.
As shown in FIG. 1, the composite catalyst for a fuel cell of the present invention (hereinafter sometimes simply referred to as a composite catalyst) comprises catalyst metal fine particles (A) and ion exchange adhered to the surfaces of the catalyst metal fine particles (A). It consists of a functional polymer (B). In the catalyst metal fine particles (A) constituting the composite catalyst, the shell of the catalyst metal (Pt in this embodiment) is formed on the surface of the metal fine particles (Au in this embodiment) serving as nuclei (core). It has a core-shell structure.

  In the composite catalyst of the present invention, the ion-exchange polymer (B) is attached to the surface of the catalyst metal fine particles (A). Therefore, in the catalyst layer of the fuel cell, the ion conduction path or catalyst to the catalyst metal surface An ion conduction path from the metal surface is efficiently formed. Therefore, by forming the catalyst layer using the composite catalyst of the present invention, the catalytic metal contributing to the electrode reaction is increased and the utilization rate of the catalytic metal is increased, so that the power generation performance of the fuel cell can be improved.

  Further, the ion-exchange polymer (B) attached to the surface of the catalyst metal fine particles (A) acts as a so-called protective agent, so that aggregation of the catalyst metal fine particles (A) is suppressed and a stable dispersion state is maintained. The That is, the catalyst metal fine particles are aggregated, and the reduction in the utilization rate of the catalyst metal due to the reduction in the specific surface area of the catalyst metal (the exposed surface area per unit weight of the catalyst metal constituting the catalyst metal fine particles) can be suppressed. The ion-exchange polymer (B), which is a protective agent, is also considered to play an important role in controlling the particle size and structure of the composite catalyst during the production of the composite catalyst.

  In addition, the composite catalyst of the present invention has a core-shell type structure in which only the surface layer is formed of the catalyst metal along with an increase in the specific surface area of the catalyst metal due to the fine formation of the catalyst metal fine particles (A). The amount was reduced to make it possible to further improve the utilization rate of the catalyst metal.

In addition, since the composite catalyst of the present invention has a stable dispersibility, it can maintain a highly dispersed state without agglomeration without being supported on a carrier such as carbon particles. Therefore, it is possible to form a catalyst layer that ensures power generation performance without using carbonaceous carriers such as carbon particles and carbon fibers that are known as general catalyst carriers in catalyst layers of fuel cells.
Therefore, by using the composite catalyst of the present invention, there are problems that are concerned in a fuel cell having a catalyst layer containing a carbonaceous carrier, for example, acceleration of hydrogen peroxide generation reaction by the carbonaceous carrier, It is possible to suppress the change in the porous structure of the catalyst layer due to the corrosion of the carbonaceous support and the falling off of the catalyst particles. The generation of hydrogen peroxide causes deterioration of the ion-exchange polymer due to hydrogen peroxide and radical species generated from hydrogen peroxide, and the change in the porous structure of the catalyst layer and the dropping of the catalyst particles are caused by the catalyst layer. The power generation performance is reduced. In other words, according to the present invention, it is possible to provide a fuel cell having excellent durability without causing deterioration of the constituent members of the fuel cell and performance deterioration due to the use of these carbonaceous carriers.

  In the catalyst metal fine particles (A), the catalyst metal that forms the shell is not particularly limited as long as it has catalytic activity for the electrode reaction of the fuel cell, and Pt, Pd, Ir, Rh, Au. , Ru, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Ag, W, Re, Os, and the like. Of these, noble metals such as Pt, Pd, Ir, Rh, and Au are preferably used, and Pt is particularly preferably used because of its high catalytic activity.

  In the catalyst metal fine particles (A), the metal forming the core is not particularly limited as long as it is a metal species different from the catalyst metal forming the shell. For example, Pt, Pd, Ir, Rh, Au, Ru , V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Ag, W, Re, Os, and the like can be used. The core may be composed of a plurality of types of metals.

  The specific combination of the catalyst metal constituting the shell and the metal constituting the core is not particularly limited, and can be appropriately combined depending on the method for producing the catalyst metal fine particles (A) and the ion-exchange polymer (B) used in combination. That's fine. Specific combinations will be described later together with the method for producing the catalyst metal fine particles (A).

In the catalyst metal fine particles (A), the molar ratio (metal species / catalyst metal species) of the metal species constituting the metal core and the catalyst metal species constituting the catalyst metal shell is not particularly limited. Although it depends on the particle diameter, the thickness of the catalyst metal shell, etc., generally, about 1/4 to 1 / 0.2 is preferable.
The particle diameter of the metal core and the thickness of the catalyst metal shell are not particularly limited, and may be set as appropriate in consideration of the dispersibility of the composite catalyst, the electronic effect, the steric effect, etc. in addition to the utilization rate of the catalyst metal. From the viewpoint of the stability of the core / shell structure and the utilization factor of the catalyst metal, the particle diameter of the metal core is preferably 1 to 50 nm, and particularly preferably 1 to 10 nm. The thickness of the catalyst metal shell may be one atom or more for the catalyst metal. From the viewpoint of the utilization rate of the catalyst metal, the thickness of the catalyst metal shell is preferably 0.3 to 5 nm, particularly 0. It is preferably 3 to 1 nm. Depending on the thickness of the metal catalyst shell, the catalyst metal fine particles (A) may exhibit characteristics such as an alloy of the metal species forming the core and the catalyst metal species forming the shell.

The core / shell structure of the catalyst metal fine particles (A) of the present invention is not only in a state where the surface of the metal core is completely covered with the catalyst metal, but also in a state where a part of the surface of the metal core is exposed. included. Moreover, the metal which comprises a metal core or a catalyst metal shell may be oxidized.
According to the present invention, catalyst metal fine particles (A) having a particle diameter of 1 to 10 nm can be obtained, and further, catalyst metal fine particles (A) of 2 to 10 nm can be obtained. Further, according to the present invention, primary particles having the above particle diameter can be obtained in a state where uniform secondary particles are formed or in a monodispersed state.

In the present invention, the ion exchange polymer (B) is not particularly limited as long as it has a cation exchange property or an anion exchange property, and includes, for example, a cation exchange polymer membrane or an anion exchange polymer membrane. A polymer that can be used as a cation exchange polymer or anion exchange polymer constituting an electrolyte membrane in a solid polymer fuel cell can be used. The ion exchange polymer has an ion exchange group, specifically, a cation exchange group such as an acid group which is a proton dissociable group, or an anion exchange group. It is considered that this ion exchange group is adsorbed on the surface of the catalyst metal fine particles (A) and acts as a protective agent that stably maintains the dispersibility of the catalyst metal fine particles (A). Moreover, the cation exchange property or anion exchange property (B) by an ion exchange group shows water solubility and / or organic solvent solubility.
Examples of the proton-dissociable group that is a cation exchange group include a sulfonic acid group, a carboxylic acid group, and a phosphate group, and examples of the anion exchange group include a tetraalkylammonium salt. Since it is highly effective as a protective agent and is also effective for controlling the particle size and core / shell structure in the production process of core / shell type metal fine particles, it has a sulfonic acid group as an ion exchange group. An ion exchange polymer is preferably used.

Specific examples of the ion-exchange polymer (B) include those having a proton-dissociable group as described above, for example, fluorine-based polymers such as perfluorocarbon sulfonic acid resin represented by Nafion (trade name). Other examples include those obtained by introducing an ion exchange group such as a proton-dissociable group into a hydrocarbon polymer such as polyether ketone, polyether ether ketone, and polyethylene sulfide. Among them, perfluorocarbon sulfonic acid resin is preferably used. .
The ion exchange polymer (B) may be attached to the surface of the catalyst metal fine particles (A) as long as the ion exchange polymer (B) is attached to at least a part of the surface of the catalyst metal fine particles (A). In the manufacturing method as described later, in principle, the surface of the catalytic metal fine particles (A) is covered with the ion-exchange polymer (B).

  Whether or not the ion-exchangeable polymer (B) is attached to the surface of the catalytic metal fine particles (A) can be confirmed by TEM, elemental analysis, TG, IR, or the like.

  The ratio of the ion-exchangeable polymer (B) in the composite catalyst of the present invention is such that all metals constituting the catalytic metal fine particles (A) are composed of a metal core and a catalytic metal shell from the viewpoint of the balance between protection and stabilization and steric hindrance. The molar ratio of the polymer monomer unit to the total metal) is preferably 0.0001 to 10, particularly preferably 0.001 to 1. At this time, the molar ratio of the ion-exchangeable polymer (B) is converted based on 1 mol of the monomer unit constituting the ion-exchangeable polymer (B).

The production method of the composite catalyst of the present invention is not particularly limited, and a known method for obtaining metal fine particles by reducing a metal salt or a metal complex to precipitate a zero-valent metal atom is applied, and an ion-exchange polymer ( A method of producing core-shell type metal fine particles having a catalytic metal shell using B) as a protective agent (stabilizer) is mentioned.
Hereinafter, a simultaneous reduction method of reducing each precursor in a solution in which a metal precursor that forms a metal core and a catalyst metal precursor that forms a catalytic metal shell coexist, and a metal precursor that forms a metal core in the solution An example is a sequential reduction method in which after generating metal fine particles by reduction with metal, the catalytic metal precursor is reduced in a solution containing the metal fine particles and the catalytic metal precursor, and the catalytic metal is deposited on the surface of the metal fine particles. A method for producing the composite catalyst of the present invention will be described.

In the simultaneous reduction method, metal ions and catalytic metal ions are obtained by subjecting a mixed solution in which the ion-exchangeable polymer (b), the metal precursor (a2) and the metal catalyst precursor (a1) are dissolved to a reduction treatment. In which a core-shell type catalytic metal fine particle having a catalytic metal shell formed on the surface of the metal core is deposited.
Specifically, the catalyst metal precursor (a1) having water solubility and / or organic solvent solubility and forming a catalyst metal shell by reduction, a metal species different from the catalyst metal, and water solubility and / or Alternatively, a metal precursor (a2) that is soluble in an organic solvent and forms a metal core by reduction, an ion-exchange polymer (b), the catalyst metal precursor (a1), the metal precursor (a2), and A first mixed solution is prepared by mixing a solvent (c) capable of dissolving the ion-exchange polymer (b), and the catalyst metal precursor (a1) and the metal in the first mixed solution A dispersion liquid in which the composite catalyst is dispersed in the solvent (c) can be prepared by reducing the precursor (a2) and precipitating core-shell type catalyst metal fine particles having a catalyst metal shell and a metal core. (See Figure 2).

  As the catalyst metal precursor (a1) and metal precursor (a2) having water solubility and / or organic solvent solubility, a salt and / or complex of a catalyst metal species that forms a catalyst metal shell and a metal core are formed, respectively. Examples include salts and / or complexes of metal species. Specific examples include acetates, chlorides, sulfates, nitrates, sulfonates, phosphates, and complexes thereof. The catalyst metal precursor (a1) and metal precursor (a2) used in combination may have different solubility solvents, for example, one has water solubility and the other has organic solvent solubility. May be. As will be described later, since the reduction of the catalytic metal precursor (a1) and the metal precursor (a2) is preferably performed in an aqueous solution, both the catalytic metal precursor (a1) and the metal precursor (a2) It is preferable to have water solubility.

  The ratio (charge amount) of the catalyst metal precursor (a1) and the metal precursor (a2) is not particularly limited, but the ratio of the catalyst metal shell to the metal core in the core-shell type catalyst metal fine particles (A) depends on the charge amount. Since it is controlled, it may be set as appropriate. Generally, the ratio of the metal element of the metal precursor (a2) to the catalyst metal element of the catalyst metal precursor (a1) (metal element / catalyst metal element) is 1/10 to 1 / 0.01. In particular, it is preferable to charge each precursor so as to be 1/4 to 1 / 0.2.

Examples of the ion exchange polymer (b) include those exemplified above as the ion exchange polymer (B). As described above, since the reduction of the catalytic metal precursor (a1) and the metal precursor (a2) is preferably performed in an aqueous solution, the ion-exchangeable polymer (b) is also water-soluble. It is preferable.
The charged amount of the ion-exchangeable polymer (b) is a polymer monomer unit for all metals contained in the catalytic metal precursor (a1) and the metal precursor (a2) from the viewpoint of the balance between protection and stabilization and steric hindrance. The molar ratio is preferably 0.0001 to 10, particularly preferably 0.001 to 1. At this time, the molar ratio of the ion-exchangeable polymer (b) is converted based on 1 mol of the monomer unit constituting the ion-exchangeable polymer (b).

  The solvent (c) that can dissolve the catalytic metal precursor (a1), the metal precursor (a2), and the ion-exchangeable polymer (b) is not particularly limited. It may be a mixture of seeds or more. For example, water, alcohol, or an organic solvent miscible with water or alcohol can be used. Specifically, water; alcohols such as methanol, ethanol, propanol, butanol, ethylene glycol, propylene glycol, hexylene glycol, amyl alcohol, and allyl alcohol; esters such as methyl acetate, ethyl acetate, diethyl ether, Ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, ethers; ketones such as acetone, methyl ethyl ketone, acetylacetone; dioxane, tetrahydrofuran, N-methylpyrrolidone, etc. . The type of the solvent (c) is preferably selected according to the reduction treatment method.

By reducing the catalyst metal precursor (a1) and the metal precursor (a2) in an aqueous solution, the particle size of the catalyst metal fine particles (A) can be easily controlled, and the surface of the catalyst metal fine particles (A) can be controlled. Since the dispersion stability of the composite catalyst formed by adhering the ion exchange polymer (B) can be improved, the solvent (c) is preferably water or a mixture of water and an organic solvent. Water is preferred.
The amount of the solvent (c) used is not particularly limited, and may be appropriately determined according to the solubility of each component (a1), (a2) and (b), but the metal ion concentration [(a1) and (a2)] In general, the total metal ion concentration] affects the particle diameter of the catalyst metal fine particles (A), and the metal ion concentration is generally 1 × 10 ⁻⁵ mol / l to 1 × 10 ^{−. 2} mol / l is preferable.

  The method for dissolving the catalytic metal precursor (a1), the metal precursor (a2), and the ion-exchangeable polymer (b) in the solvent (c) is not particularly limited, and a general mixing and stirring method can be used. . The components (a1), (a2) and (b) may be simultaneously added to the solvent (c) and mixed, or the components (a1), (a2) and (b) are dissolved in the solvent in advance. Each solution may be mixed (see FIG. 2).

  The combination of the catalyst metal precursor (a1), the metal precursor (a2), and the ion-exchange polymer (b) is not particularly limited, but the catalyst metal ion and the metal precursor generated by dissolution of the catalyst metal precursor (a1) ( When metal ions generated by dissolution of a2) are reduced and precipitated in the solvent (c), which metal species forms the core depends on the combination of the metal species (relative relationship of standard electrode potential) Depends on the magnitude of interaction between each metal species and the ion-exchange polymer (b).

For example, in an aqueous solution containing palladium ions and gold ions, perfluorocarbon sulfonic acid resin, which is an ion-exchange polymer (b), is considered to have a stronger interaction with palladium than gold. And then agglomerate, and then palladium atoms are deposited around the gold clusters as nuclei.
On the other hand, when there is no significant difference in the interaction strength between the ion-exchange polymer (b) and the catalytic metal and the metal as described above, a metal species having a standard electrode potential forms a core, and the standard electrode A metal species having a noble potential forms a shell. That is, a metal species having a lower standard electrode potential than the catalyst metal is combined. Specifically, when a reduction treatment is performed on a solution in which gold ions and platinum ions coexist, gold is first reduced to form a core, and then platinum is deposited around the core.

As described above, the combination of each component is appropriately determined according to the core / shell structure of the catalytic metal fine particles (A). Specific combinations (described in the order of a1, a2, and b) include platinum salts and / or platinum complexes and gold salts and / or gold complexes and perfluorocarbon sulfonic acid resins, palladium salts and / or palladium complexes. Combination of gold salt and / or gold complex and perfluorocarbon sulfonic acid resin, platinum salt and / or platinum complex and gold salt and / or combination of gold complex and polyether ketone sulfonic acid resin, platinum salt and / or platinum complex and iridium Examples thereof include a combination of a salt and / or iridium complex and a perfluorocarbon sulfonic acid resin.
Other combinations include platinum salt and / or platinum complex and gold salt and / or gold complex and perfluorocarbon tetraalkylammonium salt resin, palladium salt and / or palladium complex and gold salt and / or gold complex and perfluorocarbon tetraalkyl. Combinations of ammonium salt resins, combinations of platinum salts and / or platinum complexes and iridium salts and / or iridium complexes and perfluorocarbon tetraalkylammonium salt resins, and the like are also included.

  The first mixed solution prepared by dissolving the catalytic metal precursor (a1), the metal precursor (a2) and the ion exchange polymer (b) in the solvent (c) is a solution of the catalytic metal precursor (a1). The catalyst metal ion generated by the above and the metal ion generated by dissolution of the metal precursor (a2) coexist. The method of reducing these ions to deposit a metal element (reduction treatment) is not particularly limited. For example, hydrogen gas, alkali metal borohydride, quaternary ammonium borohydride, diborane, hydrazine, alcohol In addition to methods using a reducing agent such as alcoholamine, photoreduction (UV light, visible light, radiant light, etc.), ultrasonic reduction, microwave reduction, and the like can be mentioned. A plurality of reduction treatments may be combined. Moreover, you may heat-reflux in presence of a reducing agent. The reduction treatment is preferably performed in an inert atmosphere such as a nitrogen gas atmosphere.

In particular, when an alcohol such as ethanol or an alkali metal borohydride such as NaBH ₄ is used as the reducing agent, the particle size of the catalyst metal fine particles can be easily controlled. On the other hand, the reduction treatment in an aqueous solution makes it easy to control the particle diameter of the catalyst metal fine particles and provides high dispersion stability of the composite catalyst. Therefore, NaBH ₄ is used as the reducing agent and water as the solvent (c). It is particularly preferable to use
When NaBH ₄ is used as the reducing agent, the reduction treatment temperature is preferably −5 ° C. to 80 ° C., particularly preferably 0 to 30 ° C., and the concentration of the NaBH ₄ solution added dropwise is 0.001 mmol / l to 0.1 mmol in terms of equivalent. / L is preferable. Further, in order to prevent a rapid increase in the concentration of BaBH _{4 in} the solution, it is preferable to drop it slowly, and specifically, it is preferable to drop it at a rate of about 5 ml / 15 minutes.

  The ion-exchange polymer (B) as a protective agent is chemically and / or physically adsorbed on the catalyst metal fine particles (A) deposited by the reduction treatment, and the composite catalyst of the present application is obtained. The obtained composite catalyst can be used as it is as a dispersion dispersed in the solvent (c), or filtered using an ultrafilter or the like, and washed or solvent-dispersed as necessary. It can also be made into powder by drying. The dispersion of the composite catalyst may be appropriately adjusted for solid content and viscosity by distillation under reduced pressure or addition of a solvent.

Next, the sequential reduction method will be described. In the successive reduction method, first, a mixed solution in which the ion-exchange polymer (b) and the metal precursor (a2) are dissolved is subjected to a reduction treatment to form metal fine particles to be a metal core, and then the metal A catalyst metal precursor (a1) is added to a solution in which fine particles are dispersed and an ion-exchange polymer (b) is dissolved, and the solution is subjected to a reduction treatment to reduce the catalyst metal ions. In this method, core-shell type catalyst metal fine particles having a catalyst metal shell formed on the surface of the metal core are deposited.
Specifically, a metal precursor (a2) that has water solubility and / or organic solvent solubility and forms a metal core by reduction, an ion-exchangeable polymer (b), the metal precursor (a2), and A second mixed solution in which the solvent (c1) capable of dissolving the ion-exchange polymer (b) is mixed is prepared, and the metal precursor (a2) in the second mixed solution is reduced. After the metal fine particles are deposited, the catalyst metal precursor (a1) which has water solubility and / or organic solvent solubility and forms a catalyst metal shell by reduction is converted into the catalyst metal precursor (a1) and the ion exchange property. A solvent (c2) capable of dissolving the polymer (b), the ion-exchange polymer (b), and the metal fine particles are mixed to prepare a third mixed solution, and in the third mixed solution, The surface of the metal fine particles by reducing the catalyst metal precursor (a1) By precipitating the catalyst metals, can be prepared a dispersion composite catalyst is dispersed in the solvent (c2) (see FIG. 3).

  The catalytic metal precursor (a1), metal precursor (a2), and ion-exchange polymer (b) having water solubility and / or organic solvent solubility are the same as those exemplified in the simultaneous reduction method, and These charge amounts may be the same as those in the simultaneous reduction method except that the catalyst metal precursor (a1) is added at different times.

Further, a solvent (c1) capable of dissolving the metal precursor (a2) and the ion exchange polymer (b), a solvent (c2) capable of dissolving the catalyst metal precursor (a1) and the ion exchange polymer (b). As in the simultaneous reduction method, it may be composed of only one kind or a mixture of two or more kinds, and can be selected and used from the solvents exemplified in the simultaneous reduction method. . The types of the solvents (c1) and (c2) are preferably selected according to the reduction treatment method for the metal precursor (a2) and the reduction treatment method for the catalyst metal precursor (a1), respectively.
The amount of the solvent (c1) and (c2) used is not particularly limited, and may be appropriately determined according to the solubility of each component (a1), (a2) and (b), but the metal ion concentration [(a1) and Considering that the total of metal ions derived from (a2) affects the particle diameter of the catalyst metal fine particles (A), the metal ion concentration is generally 1 × 10 ⁻⁵ mol / l to 1 It is preferable to set it as x10 ^<-2 > mol / l.

Method of dissolving metal precursor (a2) and ion-exchange polymer (b) in solvent (c1), catalyst metal precursor (a1), ion-exchange polymer (b), and metal precursor (a2) The method for dissolving and dispersing the metal fine particles obtained by the reduction in the solvent (c2) is not particularly limited, and a general mixing and stirring method can be used. Each component and each solvent may be mixed simultaneously, or each component may be previously dissolved and / or dispersed in a solvent and the resulting solutions may be mixed (see FIG. 3).
Furthermore, the reduction methods of the catalytic metal precursor (a1) and the metal precursor (a2) can be the same as the simultaneous reduction method.

  In the second mixed solution obtained by mixing the metal precursor (a2), the ion-exchange polymer (b), and the solvent (c1), metal ions are generated due to dissolution of the metal precursor (a2). By applying the reduction treatment, the metal elements are precipitated and aggregated, and metal fine particles are obtained. At this time, since the ion-exchange polymer (b) acts as a protective agent, the particle size of the metal fine particles is controlled, and aggregation of the metal fine particles is suppressed. The ion-exchange polymer (b) is chemically and / or physically attached to the surface of the obtained metal fine particles (see FIG. 3).

The metal fine particles to which the ion exchange polymer (b) is attached are obtained in a state of being dispersed in the solvent (c1). The catalyst metal precursor (a1) may be added and reduced to the solution in which the metal fine particles are dispersed, but the reducing agent remaining after the reduction treatment of the metal precursor (a2), unreacted raw materials and by-products are removed. Therefore, if necessary, the metal fine particles are filtered and washed using an ultra filter or the like, and solvent replacement [preferably, the ion-exchangeable polymer (b) and the catalyst metal precursor (a1) can be dissolved. Substitution in solvent (c2)] may be performed.
When solvent substitution is carried out in this way, the solvent (c1) may not be soluble in the catalyst metal precursor (a1). However, when solvent substitution is not carried out, the catalyst is used as the solvent (c1). A solvent capable of dissolving the metal precursor (a1), that is, the metal precursor (a2), the ion-exchange polymer (b), and the catalyst metal precursor (a1) can be dissolved, and the solvent (c1) and the solvent ( It is preferable to use a solvent that can be used as c2). However, the solvent (c2) may be obtained by adding a solvent capable of dissolving the catalyst metal precursor (a1) together with the catalyst metal precursor (a1).

  Next, a third mixed solution is prepared by mixing the metal fine particles to which the ion-exchange polymer (b) is adhered, the solvent (c2), and the catalytic metal precursor (a1), and in the third mixed solution The catalytic metal precursor (a1) is reduced. As a result, the catalyst metal is deposited on the surface of the metal fine particles, and the ion-exchange polymer (b) adheres to the surface of the core-shell type metal catalyst fine particles (A) having the metal fine particles as the core and the catalyst metal as the shell. Thus obtained composite catalyst can be obtained.

As described above, in the successive reduction method, after forming the metal fine particles as the core, the catalyst metal precursor that forms the catalyst metal shell is added to the solution in which the metal fine particles are dispersed, and the metal is reduced. A catalytic metal is deposited on the surface of the metal fine particles to be the core. Therefore, in the successive reduction method, it is necessary to always consider the strength of the interaction between the ion-exchange polymer (b) and each metal precursor, and the nobility of the standard electrode potential of the metal species of each metal precursor. There is no. Therefore, it can be said that the sequential reduction method has a higher degree of freedom in the combination of the catalytic metal precursor (a1), the metal precursor (a2), and the ion-exchangeable polymer (b) than the simultaneous reduction method.
For example, as a specific combination of the catalytic metal precursor (a1) and the metal precursor (a2) (described in the order of a1 and a2), a combination of a platinum salt and / or a platinum complex and a gold salt and / or a gold complex A combination of a platinum salt and / or a platinum complex and a ruthenium salt and / or a ruthenium complex, a combination of a platinum salt and / or a platinum complex and a palladium salt and / or a palladium complex, a platinum salt and / or a platinum complex and a silver salt and / or The combination of a silver complex, the combination of a platinum salt and / or a platinum complex, and a copper salt and / or a copper complex etc. are mentioned.

  As with the composite catalyst obtained by the simultaneous reduction method, the composite catalyst obtained by the sequential reduction method can be used as it is as a dispersion dispersed in the solvent (c2), or filtered using an ultrafilter or the like. Depending on the above, it can be made into a dispersion by washing and solvent substitution, or by further drying. The dispersion of the composite catalyst may be appropriately adjusted for solid content and viscosity by distillation under reduced pressure or addition of a solvent.

When the metal is reduced and deposited in a solution that can be stirred and convected, as in the simultaneous reduction method and the sequential reduction method, the reaction proceeds uniformly throughout the solution, so that fine and uniform catalytic metal particles can be obtained. . That is, catalyst metal fine particles having a uniform particle size distribution can be efficiently produced without using an excessive precursor.
In the present invention, the particle size of each fine particle can be measured by TEM, XRD, CO adsorption, small-angle X-ray, or the like.

The composite catalyst of the present invention can be suitably used for a catalyst layer of a fuel cell. Hereinafter, a fuel cell provided with a catalyst layer containing the composite catalyst of the present invention will be described. In addition, although the fuel cell provided with the proton conductive polymer membrane which is a cation exchange polymer membrane is demonstrated here as an example, the fuel cell of this invention shall be set as the structure provided with the anion exchange polymer membrane. You can also.
An example (cross-sectional view) of a single cell provided in the fuel cell is shown in FIG. In FIG. 4, a single cell 100 is provided with a fuel electrode (anode) 2 and an oxidant electrode (cathode) 3 on one side of a proton conductive polymer membrane (hereinafter sometimes referred to simply as an electrolyte membrane) 1. A membrane / electrode assembly 6 is provided. The fuel electrode 2 is formed by laminating a fuel electrode side catalyst layer 4a and a fuel electrode side gas diffusion layer 5a in this order from the side close to the electrolyte membrane 1. Similarly, the oxidant electrode 3 is formed by laminating the oxidant electrode side catalyst layer 4b and the oxidant electrode side gas diffusion layer 5b in this order from the side close to the electrolyte membrane 1.
In this embodiment, each electrode (fuel electrode, oxidant electrode) has a structure in which a catalyst layer and a gas diffusion layer are laminated, but has a single-layer structure composed of only the catalyst layer. Alternatively, a structure in which a functional layer is provided in addition to the catalyst layer and the gas diffusion layer may be used.

The membrane / electrode assembly 6 is sandwiched between two separators 7 a and 7 b to form a single cell 100. On one side of each of the separators 7a and 7b, grooves for forming a flow path of the reaction gas (fuel gas and oxidant gas) are provided. The fuel is formed by these grooves and the outer surfaces of the fuel electrode 2 and the oxidant electrode 3. A gas flow path 8a and an oxidant gas flow path 8b are defined. The fuel gas channel 8 a is a channel for supplying a fuel gas (a gas containing hydrogen or generating hydrogen) to the fuel electrode 2, and the oxidant gas channel 8 b is an oxidant gas to the oxidant electrode 3. It is a flow path for supplying (a gas containing or generating oxygen).
In the fuel cell, a plurality of single cells are mounted in series and / or connected in parallel.

  The composite catalyst of the present invention can be used in the catalyst layer as an electrode catalyst. As described above, the composite catalyst of the present invention has an electrode reaction because the ion-exchange polymer (B) is attached to the surface of the catalytic metal fine particles (A) having catalytic activity for the electrode reaction. It has a function as an electrode catalyst to be activated and can form an ion conduction path in contact with the surface of the electrode catalyst. Therefore, the three-phase interface in the catalyst layer can be efficiently formed by using the composite catalyst of the present invention.

The composite catalyst of the present invention can be obtained in a state dispersed in a solvent. Since this composite catalyst dispersion can be used in the same manner as conventional catalyst inks, it is possible to save time and effort to disperse powdered catalyst particles in an ion-exchange polymer solution as in the past. In addition, it is possible to form a catalyst layer having excellent dispersibility between the proton conductive polymer and the catalyst fine particles. That is, by using the composite catalyst dispersion obtained by the present invention, the catalyst layer production process can be simplified and the performance of the catalyst layer can be improved.
In addition to the proton conductive polymer (ion exchange polymer), a water repellent resin such as polytetrafluoroethylene (PTFE), conductive particles, and the like may be added to the composite catalyst dispersion as necessary. However, as described above, when carbonaceous particles such as carbon particles and carbon fibers are used as the conductive particles, problems such as deterioration in power generation performance due to corrosion of the carbonaceous particles and deterioration of the electrolyte membrane due to hydrogen peroxide generation may occur. Cheap. Since the composite catalyst of the present invention has high dispersibility and can maintain the dispersibility without agglomeration without being supported on a carrier, the catalyst layer is formed without being supported on a carbonaceous carrier. It is preferable. The durability of the fuel cell can be improved by including it in the catalyst layer without being supported on the carbonaceous support.

  As described above, the composite catalyst dispersion liquid can be used as a catalyst ink as it is or after adjustment of solid content and viscosity and addition of components by distillation under reduced pressure or addition of a solution as necessary. Formation of the catalyst layer with such a catalyst ink can be performed according to a general method. For example, the catalyst layer can be formed on the surface of the electrolyte membrane or the gas diffusion layer by applying the catalyst ink to the electrolyte membrane or the gas diffusion layer sheet and drying. Alternatively, a method may be used in which catalyst ink is applied to the surface of the transfer substrate and dried to prepare a catalyst transfer sheet, and the catalyst layer is transferred to the electrolyte membrane surface or the gas diffusion layer surface.

The method for applying the catalyst ink is not particularly limited, and general methods such as an inkjet method, a spray method, a doctor blade method, a gravure printing method, a die coating method, and a screen printing method can be used.
The drying method of the catalyst ink is not particularly limited, and examples thereof include vacuum drying, heat drying, combined use of vacuum drying and heat drying. The heating temperature may be adjusted according to the solvent of the catalyst ink. The catalyst ink may be applied and dried at the same time by applying the catalyst ink while heating the catalyst ink application target (electrolyte film, gas diffusion layer sheet, transfer substrate, etc.).

Moreover, a porous catalyst layer can be formed by adding a gas-foaming pore-forming agent to the catalyst ink, and foaming the pore-forming agent by heat treatment or pH treatment after applying the catalyst ink. As the gas foaming pore-forming agent, a material generally used as the pore-forming agent for the catalyst layer, such as CeCO _3, can be used.

  Furthermore, since the composite catalyst of the present invention is highly dispersible and can be obtained as a dispersion containing catalyst metal fine particles and an ion-exchange polymer in a highly dispersed state, carbon nanotubes, carbon nanohorns, conductive It is also possible to apply it to a nanoscale conductive carrier such as a polymer. Although carbon nanotubes and carbon nanohorns are carbonaceous materials and contain the above-mentioned problems due to the carbonaceous support when they are contained in the catalyst layer, they have the effect of improving the gas diffusibility of the catalyst layer, etc. It is attracting attention as a carrier. However, conventionally, since it was difficult to prepare a solution in which catalyst particles are highly dispersed, it is difficult to support catalyst fine particles in a highly dispersed state on carbon nanotubes or carbon nanohorns. On the other hand, according to the present invention, a dispersion in which catalyst fine particles are stably dispersed without agglomeration can be obtained, so that the catalyst fine particles can be supported in a highly dispersed state on carbon nanotubes or carbon nanohorns. is there.

  In the catalyst layer of the fuel cell of the present invention, the catalyst metal species forming the shell of the catalyst metal fine particles (A) or the type of metal species forming the core, the particle size of the catalyst metal fine particles (A), the ions in the composite catalyst The ratio of the exchangeable polymer (B) to the catalyst metal fine particles (A) may be changed in the thickness direction of the catalyst layer and / or the surface direction of the catalyst layer.

  In the fuel cell of the present invention, as an electrolyte membrane (proton conductive polymer membrane), those generally used as an electrolyte membrane of a fuel cell can be used without particular limitation. For example, Nafion ( Products containing fluorine-based polymer electrolytes such as perfluorocarbon sulfonic acid resin (trade name, manufactured by DuPont), and hydrocarbon polymers such as polyether ether ketone, polyether ketone, polyether sulfone, and polyphenylene sulfide And those containing a hydrocarbon polymer electrolyte into which a proton dissociable group is introduced.

  The gas diffusion layer sheet has gas diffusibility, conductivity, and a strength required as a material constituting the gas diffusion layer, for example, carbon paper, carbon cloth, which can efficiently supply gas to the catalyst layer. Carbonaceous porous bodies such as carbon felt, titanium, aluminum, copper, nickel, nickel-chromium alloy, copper and its alloys, silver, aluminum alloy, zinc alloy, lead alloy, titanium, niobium, tantalum, iron, stainless steel A conductive porous body such as a metal mesh or a metal porous body made of metal such as gold or platinum can be used. The thickness of the conductive porous body is preferably about 50 to 500 μm.

  The gas diffusion layer sheet may be composed of a single layer of the conductive porous body as described above, but a water repellent layer may be provided on the side facing the catalyst layer. The water-repellent layer usually has a porous structure containing conductive particles such as carbon particles and carbon fibers, water-repellent resin such as polytetrafluoroethylene (PTFE), and the like. The water-repellent layer is not always necessary, but it can improve the drainage of the gas diffusion layer while maintaining an appropriate amount of water in the catalyst layer and the electrolyte membrane. There is an advantage that electrical contact can be improved.

  The method for forming the water repellent layer on the conductive porous body is not particularly limited. For example, water repellent obtained by mixing conductive particles such as carbon particles, water repellent resin, and other components as necessary with an organic solvent such as ethanol, propanol, propylene glycol, water or a mixture thereof. The layer ink may be applied to at least the side of the conductive porous body facing the catalyst layer, and then dried and / or fired. Examples of the method for applying the water repellent layer ink to the conductive porous body include a screen printing method, a spray method, a doctor blade method, a gravure printing method, and a die coating method.

  In addition, the conductive porous body is formed by impregnating and applying a water-repellent resin such as polytetrafluoroethylene to the side facing the catalyst layer with a bar coater, etc. You may process so that it may be discharged well.

  The lamination of the electrolyte membrane, the catalyst layer, and the gas diffusion layer may be performed by, for example, a method in which the electrolyte membrane on which the catalyst layer is formed and the gas diffusion layer are overlapped with the catalyst layer sandwiched, and the thermocompression bonding is performed. For example, a gas diffusion layer and a polymer electrolyte membrane formed on each other may be overlapped with a catalyst layer interposed therebetween, and may be subjected to thermocompression bonding. Joining by means of thermocompression bonding between the electrolyte membrane-catalyst layer and between the catalyst layer-gas diffusion layer sheet can be performed according to a general method.

  The membrane / electrode assembly in which the electrolyte membrane is provided with a pair of electrodes (catalyst layer and gas diffusion layer) as described above can be further sandwiched by a separator to form a single cell (see FIG. 4). As the separator, for example, a carbon separator containing a high concentration of carbon fiber and made of a composite material with a resin, a metal separator using a metal material, or the like can be used. Examples of the metal separator include those made of a metal material excellent in corrosion resistance, and those coated with a coating that enhances the corrosion resistance by coating the surface with carbon or a metal material excellent in corrosion resistance. .

(Reference Example 1: Production of gold fine particles)
In a glass two-necked eggplant type flask having a capacity of 100 ml, 0.28 g of an aqueous solution of a perfluorocarbon sulfonic acid resin (trade name Nafion, perfluorocarbon sulfonic acid resin concentration 11.4 wt%) and 14 ml of ion-exchanged water were mixed. Stir for 0.5 hour. Subsequently, 1.0 ml of HAuCl ₄ .4H ₂ O aqueous solution (1.66 × 10 ⁻² M) was added, the inside of the flask was purged with nitrogen, and the mixture was stirred for 1 hour, and the perfluorocarbon sulfonic acid resin and gold ions were well conditioned. I didn't. Thereafter, 10 ml of ion-exchanged water containing 0.007 g of NaBH ₄ was slowly added dropwise with stirring to reduce gold ions and precipitate gold fine particles (Nafion-gold fine particles). The reaction solution was subjected to solvent replacement with pure water using an ultrafilter to remove impurities such as unreacted ions, NaBH ₄ , and Cl ⁻ .
The obtained gold fine particles had an average particle size of 4.0 ± 1.5 nm. Moreover, the TEM photograph and particle size distribution of the obtained gold fine particles are shown in FIG. 9 (9-A), and the results of UV-Vis spectrum measurement are shown in FIG. 6 and FIG. The particle size distribution was measured by the particle size of 200 particles in the TEM image (the same applies hereinafter).

(Reference Example 2: Production of platinum fine particles)
In a glass two-necked eggplant type flask having a capacity of 100 ml, 0.28 g of an aqueous solution of a perfluorocarbon sulfonic acid resin (trade name Nafion, perfluorocarbon sulfonic acid resin concentration 11.4 wt%) and 14 ml of ion-exchanged water were mixed. Stir for 0.5 hour. Subsequently, 1.0 ml of H ₂ PtCl ₆ .6H ₂ O aqueous solution (1.66 × 10 ⁻² M) was added, the inside of the flask was purged with nitrogen, and the mixture was stirred for 1 hour. I got used to it. Thereafter, 10 ml of ion-exchanged water containing 0.007 g of NaBH ₄ was slowly added dropwise with stirring to reduce platinum ions and precipitate platinum fine particles (Nafion-platinum fine particles). The reaction solution was subjected to solvent replacement with pure water using an ultrafilter to remove impurities such as unreacted ions, NaBH ₄ , and Cl ⁻ .
The obtained platinum fine particles had an average particle diameter of 4.5 ± 0.8 nm. Further, a TEM photograph and particle size distribution of the obtained platinum fine particles are shown in (9-B) of FIG.

(Reference Example 3: Measurement of UV-Vis spectrum of perfluorocarbon sulfonic acid resin-Au ⁺ / Pt ⁺ )
0.28 g of an aqueous solution of a perfluorocarbon sulfonic acid resin (trade name Nafion, 11.4 wt% perfluorocarbon sulfonic acid concentration), 14 ml of ion-exchanged water, an aqueous solution of HAuCl ₄ .4H ₂ O (1.66 × 10 ⁻² M ) 1.0 ml and H ₂ PtCl ₆ .6H ₂ O aqueous solution (1.66 × 10 ⁻² M) 1.0 ml. About the obtained mixed solution, UV-Vis spectrum measurement was performed.
As shown in FIGS. 6, 8, and 10 (gold ion / platinum ion), a peak attributed to AuCl ₄ ⁻ at 320 nm and a small shoulder attributed to PtCl ₆ ²⁻ were observed at 400 nm. Also, plasmon absorption of 520 nm Au fine particles was not observed in the case of ions only (Au ⁺ and Pt ⁺ ).

(Example 1: Production of composite catalyst by sequential reduction method)
Samples 1-1 to 1-3 were produced by the following method.
First, in a 100 ml glass two-necked eggplant-shaped flask, 0.28 g of an aqueous solution of perfluorocarbon sulfonic acid resin (trade name Nafion, perfluorocarbon sulfonic acid resin concentration 11.4 wt%) and 14 ml of ion-exchanged water were added. Mix and stir for 0.5 hour. Subsequently, an HAuCl ₄ .4H ₂ O aqueous solution (1.66 × 10 ⁻² M) of the amount shown in Table 1 was added, the inside of the flask was purged with nitrogen, and the mixture was stirred for 1 hour, and the perfluorocarbon sulfonic acid resin and the gold ion I got used to it.
Thereafter, 10 ml of ion-exchanged water containing 0.007 g of NaBH ₄ was slowly added dropwise with stirring, and the mixture was further stirred for 1 hour to reduce gold ions and precipitate gold fine particles. The reaction solution was subjected to solvent replacement with pure water using an ultrafilter to remove impurities such as unreacted ions, NaBH ₄ , and Cl ⁻ .

Next, an H ₂ PtCl ₆ .6H ₂ O aqueous solution (1.66 × 10 ⁻² M) in an amount shown in Table 1 was added, and the atmosphere in the flask was replaced with nitrogen, followed by stirring for 0.5 hours. Thereafter, under stirring, 10 ml of ion-exchanged water containing the amount of NaBH ₄ shown in Table 1 was slowly added dropwise, and further stirred for 1 hour to reduce platinum ions to deposit platinum on the surface of the gold fine particles, and the core (gold ) -A composite catalyst having a perfluorocarbon sulfonic acid resin adhered to the surface of shell (platinum) type catalyst metal fine particles was produced. The reaction solution was subjected to solvent replacement with pure water using an ultrafilter to remove impurities such as unreacted ions, NaBH ₄ , and Cl ⁻ .
In each sample of Example 1, the amount of perfluorocarbon sulfonic acid resin charged was gold contained in HAuCl ₄ .4H ₂ O (gold precursor) and H ₂ PtCl ₆ .6H ₂ O (platinum precursor). It was set to 1 with respect to the total amount (mol) of platinum contained.

Table 1 shows the average particle diameters of the composite catalysts obtained in Samples 1-1 to 1-3. Moreover, the TEM photograph and particle size distribution of each sample are shown in FIG. 5, and the UV-Vis spectrum is shown in FIG.
Moreover, atomic absorption measurement of each sample was performed, and the molar ratio of gold and platinum (after preparation) was measured.
According to FIG. 6, the surface of the composite catalyst of Sample 1-2 and Sample 1-3 obtained in Example 1 is considered to be covered with platinum because the surface plasmon peculiar to the gold fine particles has disappeared. . On the other hand, in the composite catalyst of Sample 1-1, the surface plasmon peculiar to the gold fine particles was observed because of the low charge ratio of platinum, and it is considered that the gold core was exposed on a part of the surface of the composite catalyst.

(Example 2: Production of composite catalyst by simultaneous reduction method)
Samples 2-1 to 2-3 were prepared by the following method.
In a glass two-necked eggplant-shaped flask having a capacity of 100 ml, 0.28 g of an aqueous solution of perfluorocarbon sulfonic acid resin (trade name Nafion. Perfluorocarbon sulfonic acid resin concentration 11.4 wt%) and 38 ml of ion-exchanged water were mixed. Stir for 0.5 hour. Subsequently, HAUCl ₄ .4H ₂ O aqueous solution (1.66 × 10 ⁻² M) and H ₂ PtCl ₆ .6H ₂ O aqueous solution (1.66 × 10 ⁻² M) in the amounts shown in Table 2 were added. The flask was purged with nitrogen and stirred for 1 hour, so that the perfluorocarbon sulfonic acid resin, gold ions and platinum ions were well adapted.
Thereafter, 10 ml of ion-exchanged water containing 0.007 g of NaBH ₄ is slowly added dropwise with stirring, and the mixture is further stirred for 1 hour to reduce gold ions and platinum ions, and the core (gold) / shell (platinum) type catalyst metal. A composite catalyst having a perfluorocarbon sulfonic acid resin adhered to the surface of the fine particles was produced. The reaction solution was subjected to solvent replacement with pure water using an ultrafilter to remove impurities such as unreacted ions, NaBH ₄ , and Cl ⁻ .
In each sample of Example 2, the amount of perfluorocarbon sulfonic acid resin charged was gold contained in HAuCl ₄ .4H ₂ O (gold precursor) and H ₂ PtCl ₆ .6H ₂ O (platinum precursor). It was set to 1 with respect to the total amount (mol) of platinum contained.

Table 2 shows the average particle diameters of the composite catalysts obtained in Samples 2-1 to 2-3. Moreover, the TEM photograph and particle size distribution of each sample are shown in FIG. 7, and the UV-Vis spectrum is shown in FIG.
Moreover, atomic absorption measurement of each sample was performed, and the molar ratio of gold and platinum (after preparation) was measured.
According to FIG. 8, the composite catalyst of each sample obtained in Example 2 is considered to be covered with platinum because the surface plasmon peculiar to the gold fine particles has disappeared.

(Example 3: Production of composite catalyst by sequential reduction method)
In a glass two-necked eggplant-shaped flask having a capacity of 2000 ml, 11 g of an aqueous solution of perfluorocarbon sulfonic acid resin (trade name Nafion, perfluorocarbon sulfonic acid resin concentration 11.4 wt%) and 1820 ml of ion-exchanged water were mixed. Stir for minutes. Subsequently, 16 ml of HAuCl ₄ .4H ₂ O aqueous solution (1.66 × 10 ⁻² M) was added, the inside of the flask was purged with nitrogen, and the mixture was stirred for 3 hours, so that the perfluorocarbon sulfonic acid resin and the gold ion were well conditioned. . Thereafter, 10 ml of ion-exchanged water containing 0.013 mmol of NaBH ₄ was slowly added dropwise with stirring, and the mixture was further stirred for 1 hour to reduce gold ions and precipitate gold fine particles. The reaction solution was subjected to solvent replacement with pure water using an ultrafilter to remove impurities such as unreacted ions, NaBH ₄ , and Cl ⁻ .

Next, 64 ml of a H ₂ PtCl ₆ .6H ₂ O aqueous solution (1.66 × 10 ⁻² M) was added, and the atmosphere in the flask was replaced with nitrogen, followed by stirring for 3 hours. Thereafter, 10 ml of ion-exchanged water containing 0.013 mmol of NaBH ₄ is slowly added dropwise with stirring, and the mixture is further stirred for 1 hour to reduce platinum ions and deposit platinum on the surface of the gold fine particles. A composite catalyst in which perfluorocarbon sulfonic acid resin was adhered to the surface of (platinum) type catalyst metal fine particles was produced. The reaction solution was subjected to solvent replacement with pure water using an ultrafilter to remove impurities such as unreacted ions, NaBH ₄ , and Cl ⁻ , and further concentrated to a solid content concentration of 2.4 wt%.

Table 3 shows the average particle diameter of the obtained composite catalyst and the molar ratio of gold and platinum (charge ratio and after preparation). Moreover, the UV-Vis spectrum of the obtained composite catalyst is shown in FIG. 10, and the TEM photograph and the particle size distribution are shown in FIG. 11 (11-B). 10 and 11 (11-A) show the UV-Vis spectrum and TEM photograph of the particles with the perfluorocarbon sulfonic acid resin adhered to the surface of the gold fine particles obtained in the production process of the composite catalyst of Example 3. And the particle size distribution.
From FIG. 10, it can be considered that the surface of the composite catalyst obtained in Example 3 is covered with platinum because the surface plasmon peculiar to the gold fine particles has disappeared.

(Example 4: Production of composite catalyst by simultaneous reduction method)
In a glass two-necked eggplant-shaped flask having a capacity of 2000 ml, 11 g of an aqueous solution of perfluorocarbon sulfonic acid resin (trade name Nafion, perfluorocarbon sulfonic acid resin concentration 11.4 wt%) and 1820 ml of ion-exchanged water are mixed for 30 minutes. Stir. Subsequently, 16 ml of an aqueous solution of HAuCl ₄ .4H ₂ O (1.66 × 10 ⁻² M) and 64 ml of an aqueous solution of H ₂ PtCl ₆ .6H ₂ O (1.66 × 10 ⁻² M) were added. After purging with nitrogen, the mixture was stirred for 3 hours, and the perfluorocarbon sulfonic acid resin, gold ion, and platinum ion were mixed well. Then, 5 ml of ion-exchanged water containing 0.013 mmol of NaBH ₄ is slowly added dropwise with stirring, and the mixture is further stirred for 1 hour to reduce gold ions and platinum ions, and the core (gold) / shell (platinum) type catalytic metal. A composite catalyst having a perfluorocarbon sulfonic acid resin adhered to the surface of the fine particles was produced. The reaction solution was subjected to solvent replacement with pure water using an ultrafilter to remove impurities such as unreacted ions, NaBH ₄ , and Cl ⁻ , and further concentrated to a solid content concentration of 3.0 wt%.

Table 3 shows the average particle diameter of the obtained composite catalyst and the molar ratio of gold and platinum (charge ratio and after preparation). Further, FIG. 10 shows a UV-Vis spectrum of the obtained composite catalyst, and FIG. 11 (11-C) shows a TEM photograph and a particle size distribution.
From FIG. 10, it can be considered that the surface of the composite catalyst obtained in Example 4 is covered with platinum because the surface plasmon peculiar to the gold fine particles has disappeared.
Moreover, comparing the composite catalysts obtained in Example 3 and Example 4 from FIG. 11, Example 4 produced by the simultaneous reduction method has a smaller particle size than Example 3 produced by the sequential reduction method. I understand that.

It is a conceptual diagram which shows the structure of the composite catalyst of this invention. It is a figure explaining the manufacturing method of the composite catalyst by a simultaneous reduction method. It is a figure explaining the manufacturing method of the composite catalyst by a sequential reduction method. It is sectional drawing which shows an example of the single cell with which the fuel cell of this invention is equipped. 2 is a TEM photograph and particle size distribution of the composite catalyst obtained in Example 1. FIG. It is a result of UV-Vis spectrum measurement of the composite catalyst obtained in Example 1 and the particles obtained in Reference Example 1 and Reference Example 3. 2 is a TEM photograph and particle size distribution of the composite catalyst obtained in Example 2. It is a result of the UV-Vis spectrum measurement of the composite catalyst obtained in Example 2 and the particles obtained in Reference Example 1 and Reference Example 3. 2 is a TEM photograph and particle size distribution of particles obtained in Reference Example 1 and Reference Example 2. It is the result of the UV-Vis spectrum measurement of the composite catalyst obtained in Example 3 and Example 4, and the particle | grains obtained in Reference Example 1 and Reference Example 3. 4 is a TEM photograph and particle size distribution of the composite catalyst obtained in Example 3 and Example 4.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electrolyte membrane 2 ... Fuel electrode 3 ... Oxidant electrode 4 ... Catalyst layer (4a: Fuel electrode side catalyst layer, 4b: Oxidant electrode side catalyst layer)
5. Gas diffusion layer (5a: fuel electrode side gas diffusion layer, 5b: oxidant electrode side gas diffusion layer)
6 ... Membrane / electrode assembly 7 ... Separator (7a: fuel electrode side separator, 7b: oxidant electrode side separator)
8 ... reactive gas flow path (8a: fuel gas flow path, 8b: oxidant gas flow path)
100 ... Single cell

Claims (3)

The ion-exchangeable polymer (B) is attached to the surface of the core-shell type catalyst metal fine particles (A) having a catalyst metal shell made of a catalyst metal and a metal core made of a metal species different from the catalyst metal. Comprising a catalyst layer containing a composite catalyst for a fuel cell;
Wherein the fuel cell composite catalyst is not supported on a carbonaceous carrier, a fuel cell. The ion-exchangeable polymer (B) is attached to the surface of the core-shell type catalyst metal fine particles (A) having a catalyst metal shell made of a catalyst metal and a metal core made of a metal species different from the catalyst metal. A method for producing a fuel cell comprising a catalyst layer containing a fuel cell composite catalyst, wherein the fuel cell composite catalyst is not supported on a carbonaceous carrier,
A catalyst metal precursor (a1) having water solubility and / or organic solvent solubility and forming a catalyst metal shell by reduction; and a metal species different from the catalyst metal, and having water solubility and / or organic solvent solubility. And a metal precursor (a2) that forms a metal core by reduction, an ion-exchange polymer (b), the catalyst metal precursor (a1), the metal precursor (a2), and the high ion-exchange property. A first mixed solution in which a solvent (c) capable of dissolving the molecule (b) is mixed is prepared, and the catalytic metal precursor (a1) and the metal precursor (a2) in the first mixed solution are prepared. Catalyst for fuel cell, in which core-shell type catalyst metal fine particles having a catalyst metal shell and a metal core are deposited, and an ion-exchange polymer is attached to the surface of the core-shell type catalyst metal fine particles To prepare And,
Forming a catalyst layer in which the composite catalyst for a fuel cell is not supported on a carbonaceous support;
A method for producing a fuel cell, comprising: The ion-exchangeable polymer (B) is attached to the surface of the core-shell type catalyst metal fine particles (A) having a catalyst metal shell made of a catalyst metal and a metal core made of a metal species different from the catalyst metal. A method for producing a fuel cell comprising a catalyst layer containing a fuel cell composite catalyst, wherein the fuel cell composite catalyst is not supported on a carbonaceous carrier,
Metal precursor (a2) having water solubility and / or organic solvent solubility and forming a metal core by reduction, ion-exchange polymer (b), metal precursor (a2) and high ion-exchange property A second mixed solution in which the solvent (c1) capable of dissolving the molecule (b) is mixed is prepared, and the metal precursor (a2) in the second mixed solution is reduced to precipitate metal fine particles. Thereafter, the catalyst metal precursor (a1) which has water solubility and / or organic solvent solubility and forms a catalyst metal shell by reduction is converted into the catalyst metal precursor (a1) and the ion-exchange polymer (b). Is mixed with the solvent (c2), the ion-exchange polymer (b), and the metal fine particles to prepare a third mixed solution, and the catalyst metal precursor (in the third mixed solution ( a1) is reduced to apply catalytic metal to the surface of the metal fine particles. Out so, a step of preparing a composite catalyst for a fuel cell ion exchange polymer on the surface of the core-shell type catalyst metal fine particles are adhered with the catalyst metal shell and the metal core,
Forming a catalyst layer in which the composite catalyst for a fuel cell is not supported on a carbonaceous support;
A method for producing a fuel cell, comprising: