JP2007213988A - Electrode catalyst layer for polymer electrolyte fuel cell, its manufacturing method, and polymer electrolyte fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode catalyst layer for polymer electrolyte fuel cell improved in utilization efficiency of expensive noble metal catalyst and capable of greatly reducing manufacturing cost, and its manufacturing method. <P>SOLUTION: The electrode catalyst layer 29 comprises a porous catalyst film 21 having pores 23 in a catalyst structure 28 in which catalyst bodies 22 are arranged continuously, and a polymer electrolyte 25. The polymer electrolyte 25 is arranged by covering the surface of catalyst bodies 22 arranged continuously of the catalyst structure. The manufacturing method comprises a process in which a precursor 24 of polymer electrolyte is impregnated in the porous catalyst film 21 having pores in the catalyst structures in which the catalyst bodies are arranged continuously, a process in which the surface of the catalyst bodies arranged continuously is covered by the polymer electrolyte 25 by polymerizing the precursor of the polymer electrolyte, and a process in which the non-reacted precursor 26 of the polymer electrolyte is removed. The catalyst bodies are catalyst particulates or carbon particulates carrying the catalyst particulates. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electrode catalyst layer for a polymer electrolyte fuel cell, a production method thereof, and a polymer electrolyte fuel cell.

  Fuel cells are attracting attention as next-generation energy devices for solving energy and environmental problems. Fuel cells generate electricity using the reverse reaction of water electrolysis as described below.

  Fuel cells are classified into phosphoric acid fuel cells (PAFC), polymer electrolyte fuel cells (PEFC), solid oxide fuel cells (SOFC), molten carbonate fuel cells (MCFC), etc., depending on the type of electrolyte. Is done. Above all, polymer electrolyte fuel cells with low operating temperature, small size, light weight, and high output are highly efficient home power generation systems, clean exhaust and high fuel consumption automotive power sources, and long operating time power supplies for mobile devices. As a result, development for practical use is rapidly progressing.

  Such an electrode catalyst layer for a polymer electrolyte fuel cell has a three-dimensional porous structure including at least a polymer electrolyte and a catalyst body. As a polymer electrolyte, a fluorine-based cation exchange resin represented by Nafion (registered trademark, Nafion) manufactured by DuPont, and as a catalyst body, platinum fine particles, platinum-based alloy fine particles, or carrying them Carbon particles are widely used. Inside the electrocatalyst layer having this three-dimensional porous structure, the three-phase interface formed by the catalyst, polymer electrolyte, and pores serves as an electrochemical reaction field, and the amount thereof greatly affects the battery performance. It depends on you. In addition, since the catalyst body serves as an electron conduction path and the polymer electrolyte serves as a proton conduction path, each of them is preferably continuous over the entire electrode catalyst layer.

  For example, Patent Document 1 discloses the following method. A solid polymer electrolyte coating and a polytetrafluoroethylene layer are formed in a support made of carbon paper fibers having a three-dimensional stitch structure. An electrode catalyst coating layer is formed on the solid polymer electrolyte coating by chemical plating to obtain a three-phase interface structure in the electrode. Furthermore, after applying a solid polymer electrolyte solution on one side of the carbon paper fiber, the solid polymer electrolyte membrane is closely integrated by hot pressing.

In general, the electrode catalyst layer described above is applied to a polymer electrolyte membrane, a porous carbon electrode, or a support by applying a paste prepared by mixing a solution in which a catalyst body and a polymer electrolyte are dispersed in an organic solvent. Or a solution prepared by mixing a catalyst body and an arbitrary organic solvent on a polymer electrolyte membrane, a porous carbon electrode, or a support, and then dispersing a polymer electrolyte in the organic solvent. It is produced by a method of impregnation. Further, a polymer electrolyte membrane is sandwiched between the pair of electrode catalyst layers thus obtained, and a membrane / electrode assembly (MEA) is produced by thermocompression bonding with a hot press or the like (Patent Document 1). ).
JP-A-8-106915

  However, in the above production method, it is difficult to form a microstructure satisfying the conditions required for the electrode catalyst layer using a nanometer-order catalyst body and a dispersion solution of a highly viscous polymer electrolyte. That is, as shown in FIG. 4, since the portion 13 where the electron conduction path of the catalyst body 11 is divided and the portion 14 where the proton conduction path of the polymer electrolyte 12 is divided are formed, the battery efficiency is lowered.

  Further, in the above production method, a highly viscous polymer electrolyte dispersion solution cannot penetrate into fine pores formed in the gaps of the catalyst body, so there is a catalyst body that does not come into contact with the polymer electrolyte. To do. For the above reasons, it has been reported that the precious metal particles that act substantially effectively as a catalyst are about 10% (EA Ticianelli, CR Derouin, and S. Srinivasan, J. Electronal. Chem. 1998, 251, 275). As a result, it is necessary to use a large amount of expensive noble metal, and there arises a problem that the manufacturing cost increases.

  The present invention has been made in view of such background art, and provides a high performance and low cost electrode catalyst layer for a polymer electrolyte fuel cell and a method for producing the same.

  The present invention also provides a polymer electrolyte fuel cell using the above electrode catalyst layer.

  An electrode catalyst layer for a polymer electrolyte fuel cell for solving the above-described problem is a high-performance catalyst having at least a porous catalyst membrane in which catalyst bodies are continuously arranged and pores in the gaps, and a polymer electrolyte. An electrode catalyst layer for a molecular electrolyte fuel cell, wherein the polymer electrolyte is disposed so as to cover a surface of a catalyst body in which a porous catalyst membrane is continuously disposed.

The catalyst body is preferably catalyst fine particles or carbon fine particles carrying catalyst fine particles.
The polymer electrolyte is preferably composed of a polymer obtained by polymerizing a precursor of the polymer electrolyte.

  A method for producing an electrode catalyst layer for a polymer electrolyte fuel cell for solving the above-described problem is that a catalyst body is continuously arranged, and a precursor of a polymer electrolyte is provided on a porous catalyst film having pores in the gaps. A step of impregnating, a step of polymerizing the precursor of the polymer electrolyte so as to coat the surface of the continuously disposed catalyst body of the porous catalyst membrane with the polymer electrolyte, and a precursor of the unreacted polymer electrolyte. It includes a step of removing the body.

The precursor of the polymer electrolyte is preferably a monomer having a proton dissociable functional group in the molecule, an oligomer, or a mixture of a monomer and an oligomer.
The polymerization of the polymer electrolyte precursor is preferably performed by heating the surface of the catalyst body.

  A polymer electrolyte fuel cell for solving the above problems is a polymer electrolyte fuel cell having a pair of electrode catalyst layers and a polymer electrolyte membrane disposed between the electrode catalyst layers, the electrode A catalyst layer consists of said electrode catalyst layer, It is characterized by the above-mentioned.

INDUSTRIAL APPLICABILITY The present invention can provide an electrode catalyst layer for a polymer electrolyte fuel cell that can improve the utilization efficiency of an expensive noble metal catalyst and can greatly reduce the production cost, and a method for producing the same.
Further, the present invention can provide a polymer electrolyte fuel cell using the above electrode catalyst layer.

BEST MODE FOR CARRYING OUT THE INVENTION The best embodiment of a polymer electrolyte fuel cell electrode catalyst layer and a production method thereof will be described in detail.
<Micro structure of electrode catalyst layer>
The electrode catalyst layer for a polymer electrolyte fuel cell (hereinafter abbreviated as an electrode catalyst layer) contains at least a catalyst body and a polymer electrolyte. FIG. 1 is a schematic view showing one embodiment of an electrode catalyst layer, FIG. 1 (a) is a schematic view of a porous catalyst membrane, and FIG. 1 (b) is a schematic view of an electrode catalyst layer. In FIG. 1A, a porous catalyst membrane 21 has a structure having a large number of pores 23 in a gap between catalyst bodies 22 arranged three-dimensionally continuously. In FIG. 1B, the electrode catalyst layer 29 has a porous catalyst membrane 21 and a polymer electrolyte 25, and the surface of the catalyst body 22 in which the polymer electrolyte 25 is continuously arranged in the porous catalyst membrane. Is uniformly coated. As the catalyst body, catalyst fine particles or carbon fine particles carrying catalyst fine particles are used.

  The catalyst body is three-dimensionally continuous, and a continuous electron conduction path is ensured in the entire electrode catalyst layer. In addition, since the polymer electrolyte uniformly covers the surface of the three-dimensional continuous catalyst body, a continuous proton conduction path is formed in the entire electrode catalyst layer. Furthermore, the polymer electrolyte is also in contact with a nanometer-size deep pore catalyst formed in the catalyst body gap to form a three-phase interface.

<Method for producing electrode catalyst layer>
The method for producing an electrode catalyst layer according to the present invention comprises a first step of impregnating a porous catalyst membrane having catalyst bodies arranged continuously and having pores in the gaps with a precursor of a polymer electrolyte; A second step of coating the surface of the continuously disposed catalyst body of the porous catalyst membrane with a polymer electrolyte comprising a polymer obtained by polymerizing a precursor of molecular electrolyte; and an unreacted polymer electrolyte And a third step of removing the precursor.

Hereinafter, the first to third steps will be described in detail with reference to FIG. FIG. 2 is a process diagram showing an example of a method for producing an electrode catalyst layer.
(First step of impregnating porous catalyst membrane of catalyst body with precursor of polymer electrolyte)
2A and 2B, the porous catalyst membrane 21 of the catalyst body 22 is impregnated with a precursor 24 of a polymer electrolyte.

As the catalyst body 22 forming the porous catalyst film, catalyst fine particles or carbon fine particles supporting catalyst fine particles can be used. The porous catalyst membrane of the catalyst body is preferably produced directly on the polymer electrolyte membrane or the porous carbon electrode, but may be produced on a support such as a Teflon (registered trademark) sheet. As the catalyst fine particles, platinum fine particles having a diameter of 2 nm or more and 5 nm or less, or alloy fine particles of platinum and one or more kinds of noble metal elements are preferably used. As the noble metal element to be alloyed with platinum, it is preferable to select at least one kind from the group consisting of Au, Ag, Ru, Rh, Pd, Os, and Ir. However, if high activity can be obtained by alloying The composition is not particularly limited. Further, as the carrier, it is preferable to use carbon fine particles having a high conductivity with a BET specific surface area of 100 m ² / g or more and 1000 m ² / g or less.

  The polymer electrolyte precursor 24 is preferably a monomer, an oligomer, or a mixture of a monomer and an oligomer. A solution in which the polymer electrolyte precursor is dispersed in an organic solvent is used as a porous catalyst membrane of the catalyst body. Impregnate. In order to bring the polymer electrolyte into contact with the catalyst body existing in the deep pores of the nanometer size in the porous catalyst membrane, it is desirable to use a precursor solution of a low-viscosity polymer electrolyte. For the preparation of the precursor solution of the polymer electrolyte, a monomer or an oligomer having a low polymerization degree is preferably used. The concentration of the precursor solution of the polymer electrolyte is not particularly limited as long as it is viscous enough to penetrate into the nanometer-sized pores in the porous catalyst membrane.

The precursor of the polymer electrolyte preferably has a proton dissociable functional group in the molecule. The proton dissociative functional group is preferably at least one selected from the group consisting of —OH, —OSO ₃ H, —SO ₃ H, —COOH, —OPO (OH) _2, but is high after polymerization. There is no particular limitation as long as it exhibits proton conductivity.

(Second step of thermally polymerizing the precursor of the polymer electrolyte)
Next, in FIG. 2 (c), the polymer electrolyte precursor 24 is polymerized, and the surface of the catalyst body 22 in which the porous catalyst membrane is continuously arranged is covered with the polymer electrolyte 25.

  The polymer electrolyte precursor 24 is thermally polymerized only on the surface of the catalyst body 22, and the surface of the catalyst body constituting the porous catalyst film 21 is made of a polymer obtained by polymerizing the precursor of the polymer electrolyte. Cover with polymer electrolyte 25. As a method for thermally polymerizing the precursor of the polymer electrolyte only on the surface of the catalyst body, a method of generating heat from the surface of the catalyst body is preferable. For example, the current can be generated from the surface of the catalyst body by passing an electric current through the porous catalyst membrane of the catalyst body, but any method can be used that can generate heat from the surface of the catalyst body and thermally polymerize the precursor of the polymer electrolyte. This is not a limitation.

(Third step of removing unreacted polymer electrolyte precursor)
Next, in FIG. 2D, the unreacted polymer electrolyte precursor 26 is removed, and a porous electrode catalyst layer 29 composed of the catalyst body 22 and the polymer electrolyte 25 is produced.

  When the unreacted polymer electrolyte precursor is removed from the mixture film of the catalyst body after thermal polymerization, the polymer electrolyte produced by polymerization, and the precursor of the unreacted polymer electrolyte, the catalyst body and the polymer are removed. A porous electrode catalyst layer 29 having pores 23 made of an electrolyte is formed. As a method for removing the unreacted polymer electrolyte precursor, a method of immersing the mixed film in a solvent that is a poor solvent for the polymer electrolyte and a good solvent for the polymer electrolyte precursor, The method is not limited to this as long as it can remove only the unreacted polymer electrolyte precursor.

<Polymer electrolyte fuel cell>
FIG. 3 is a schematic view showing one embodiment of a polymer electrolyte fuel cell according to the present invention.
The polymer electrolyte fuel cell has a membrane / electrode assembly (Membrane Electrode Assembly) in which a pair of the electrode catalyst layers are arranged as an anode-side electrode catalyst layer 33 and a cathode-side electrode catalyst layer 34 with a polymer electrolyte membrane 32 interposed therebetween. The basic unit is a cell composed of (MEA) 31, anode side gas diffusion layer 35, cathode side gas diffusion layer 36, anode side separator 37, and cathode side separator 38.

  As the polymer electrolyte membrane, commercially available products such as Nafion (manufactured by DuPont), Flemion (manufactured by Asahi Glass), and Aciplex (manufactured by Asahi Kasei) can be used. However, fuel cells such as low gas permeability and high proton conductivity can be used. The polymer electrolyte is not particularly limited as long as it has the necessary characteristics. The fuel diffusion layer is installed to efficiently supply the fuel gas to the electrode catalyst layer and collect current of each electrode, and has conductivity, water repellency, porosity such as carbon cloth, carbon paper, foam metal, etc. preferable. The separator serves as a fuel gas flow path, a partition plate for separating the fuel gas between adjacent cells, and an electrical connector, and is made of carbon or metal having electrical conductivity, strength, and corrosion resistance. A separator is preferably used.

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples.
Example 1
In this example, an electrode catalyst layer for a polymer electrolyte fuel cell is prepared using platinum fine particles as a catalyst body for forming a porous catalyst membrane and polystyrene sulfonic acid as a polymer electrolyte.

  A polymer electrolyte precursor solution is prepared using water as a solvent, sodium styrenesulfonate as a monomer, divinylbenzene as a crosslinking agent, and ammonium persulfate as a polymerization initiator. The composition of the precursor solution is 45 ml of water, 10 g of sodium styrenesulfonate, 0.1 g of divinylbenzene, and 0.1 g of ammonium persulfate. A porous catalyst film made of platinum fine particles is sufficiently impregnated with the precursor solution, and then dried. Electrodes are connected to both ends of the thus produced porous catalyst membrane, and a current is passed so that the surface temperature of the platinum fine particles becomes 100 ° C. After maintaining at the temperature for a predetermined time, the electrode catalyst layer is obtained by immersing in 1M sulfuric acid to remove unreacted precursor and elution of sodium ions.

Example 2
In this example, an electrode catalyst layer for a polymer electrolyte fuel cell is produced using carbon particles carrying platinum / palladium alloy fine particles as a catalyst body for forming a porous catalyst membrane and polyacrylic acid as a polymer electrolyte. It is.

  A polymer electrolyte precursor solution is prepared using water as a solvent, sodium acrylate as a monomer, polyethylene glycol diacrylate as a crosslinking agent, and ammonium persulfate as a polymerization initiator. The composition of the precursor solution is 45 ml of water, 5 g of sodium acrylate, 0.05 g of polyethylene glycol diacrylate, and 0.1 g of ammonium persulfate. A polyethylene glycol diacrylate having a number average molecular weight of 258 was used as a crosslinking agent. A porous catalyst film composed of carbon particles carrying platinum / palladium alloy fine particles is sufficiently impregnated with the precursor solution and then dried. Electrodes are connected to both ends of the thus produced porous catalyst membrane, and an electric current is passed so that the surface temperature of the platinum / palladium fine particles becomes 80 ° C. After maintaining at the temperature for a predetermined time, the electrode catalyst layer is obtained by immersing in 1M sulfuric acid to remove unreacted precursor and elution of sodium ions.

  The electrode catalyst layer according to the present invention can be used for small polymer electrolyte fuel cells for mobile devices such as mobile phones.

It is the schematic which shows one embodiment of an electrode catalyst layer. It is process drawing which shows an example of the manufacturing method of an electrode catalyst layer. 1 is a schematic view showing one embodiment of a polymer electrolyte fuel cell. It is sectional drawing which shows the electrode catalyst layer of the conventional polymer electrolyte fuel cell.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Catalyst body 12 Polymer electrolyte 13 Split part of proton conduction path 14 Split part of electron conduction path 21 Porous catalyst membrane 22 Catalyst body 23 Pore 24 Precursor of polymer electrolyte 25 Polymer electrolyte 26 Unreacted polymer electrolyte 29 Electrode catalyst layer 31 Membrane / electrode composite 32 Polymer electrolyte 33 Anode side electrode catalyst layer 34 Cathode side electrode catalyst layer 35 Anode side gas diffusion layer 36 Cathode side gas diffusion layer 37 Anode side separator 38 Cathode side separator

Claims (7)

  An electrode catalyst layer for a polymer electrolyte fuel cell having at least a catalyst body arranged continuously and having a porous catalyst membrane having pores in the gap and a polymer electrolyte, wherein the polymer electrolyte is porous An electrode catalyst layer for a polymer electrolyte fuel cell, characterized in that it is disposed so as to cover the surface of a catalyst body in which a porous catalyst membrane is continuously arranged.   2. The electrode catalyst layer for a polymer electrolyte fuel cell according to claim 1, wherein the catalyst body is catalyst fine particles or carbon fine particles supporting catalyst fine particles.   3. The electrode catalyst layer for a polymer electrolyte fuel cell according to claim 1, wherein the polymer electrolyte is made of a polymer obtained by polymerizing a precursor of a polymer electrolyte.   In the method for producing an electrode catalyst layer for a polymer electrolyte fuel cell, a step of impregnating a polymer catalyst precursor into a porous catalyst membrane in which catalyst bodies are continuously arranged and pores are provided in the gaps; A step of polymerizing a precursor of the molecular electrolyte to coat the surface of the continuously arranged catalyst body of the porous catalyst membrane with the polymer electrolyte, and a step of removing the precursor of the unreacted polymer electrolyte A method for producing an electrode catalyst layer for a polymer electrolyte fuel cell.   5. The electrode catalyst layer for a polymer electrolyte fuel cell according to claim 4, wherein the precursor of the polymer electrolyte is a monomer, an oligomer or a mixture of a monomer and an oligomer having a proton dissociable functional group in the molecule. Manufacturing method.   6. The method for producing an electrode catalyst layer for a polymer electrolyte fuel cell according to claim 4, wherein the polymerization of the precursor of the polymer electrolyte is performed by heating the surface of the catalyst body.   4. A polymer electrolyte fuel cell comprising a pair of electrode catalyst layers and a polymer electrolyte membrane disposed between the electrode catalyst layers, wherein the electrode catalyst layer is an electrode according to any one of claims 1 to 3. A polymer electrolyte fuel cell comprising a catalyst layer.

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