JP2009140657A - Electrode catalyst for fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode catalyst for a fuel cell for sufficiently obtaining catalyst activation. <P>SOLUTION: In the electrode catalyst including a carrier material and a catalyst component thin film formed on the carrier material, when a crystal orientation ratio on a (110) plane against the film thickness direction of the catalyst component thin film is displayed by the (110) plane of the catalyst component thin film/((100) plane of the catalyst component thin film +(111) plane of the catalyst component thin film), the crystal orientation ratio of the (110) plane exceeds 1. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electrode catalyst, particularly an electrode catalyst for a fuel cell.

  The polymer electrolyte fuel cell (PEFC) can be started at room temperature compared to other fuel cells such as phosphoric acid fuel cells (PAFC) and alkaline fuel cells (AFC), and the problem of electrolyte dissipation and retention There are few and maintenance is easy. However, platinum as a catalyst component used for the electrode reaction has a problem in the amount of resource supply, and further reduction of the amount of platinum catalyst and development of a catalyst replacing platinum are required.

  The electrode reaction takes place at the so-called three-phase interface (electrolyte-catalyst electrode-reactive gas), but in PEFC, the electrolyte is a solid film, so the reaction site is limited to the contact interface between the electrode and the film, and the platinum utilization rate is It tends to decrease. For this reason, in general, the catalyst material used for the electrode catalyst of the fuel cell is such that the catalyst particles containing platinum are arranged in a highly dispersed manner on the surface of conductive carrier particles such as carbon black so that the catalyst surface area is high. It has a different shape.

  However, when platinum is supported on conductive carrier particles such as carbon black, it is necessary to perform a reduction treatment and a heat treatment. Depending on these conditions, a sufficient catalyst may be caused due to a decrease in the crystallinity of the platinum or a coarsening of the crystal particles. There was a problem that the activity could not be obtained.

Therefore, there is Patent Document 1 as a technique for solving such a problem. In Patent Document 1, the catalyst is deposited in the form of a film on the surface of the conductive powder by a physical film formation method, whereby a catalyst having good crystallinity at a low temperature is obtained, and excellent catalytic activity is obtained with a smaller amount of platinum. I'm trying.
JP 2005-2222736 A

  However, as described in Patent Document 1, sufficient catalytic activity cannot be obtained simply by attaching the catalyst in a film form.

  Therefore, the present invention is an electrode catalyst including a support material and a catalyst component thin film formed on the support material, wherein the crystal orientation ratio of the (110) plane with respect to the film thickness direction of the catalyst component thin film is

The above problem is solved by an electrode catalyst characterized in that the crystal orientation ratio of the (110) plane exceeds 1.

  In the present invention, the catalyst shape is made into a thin film instead of a particle, and further, a catalyst component thin film oriented in a specific direction according to the support material and the thin film production conditions is produced, and in particular, the catalyst component strongly crystallized in the (110) plane direction It has been found that the catalytic activity can be greatly improved by using a thin film. Thereby, the improvement of the cell performance of a polymer electrolyte fuel cell is realizable.

  The first of the present invention is an electrode catalyst comprising a support material and a catalyst component thin film formed on the support material, wherein the crystal orientation ratio of the (110) plane relative to the film thickness direction of the catalyst component thin film is

The electrode catalyst is characterized in that the crystal orientation ratio of the (110) plane exceeds 1.

  Thus, producing a catalyst thin film that is strongly crystallized in the (110) direction particularly as a low index plane contributes to a significant improvement in catalyst activity. As a result, the specific activity of the catalyst itself is greatly improved, so that the catalytic activity can be improved, and the polymer electrolyte fuel cell equipped with the electrode catalyst is a polymer electrolyte fuel cell exhibiting good cell performance. Can be provided.

  The “electrode catalyst” in the present specification includes a catalyst component and a support material, and refers to a cathode electrode catalyst and an anode electrode catalyst. Furthermore, the “electrode catalyst layer” refers to a cathode electrode catalyst (layer) / anode electrode catalyst (layer) (hereinafter, also simply referred to as “electrode catalyst (layer)”). Is included. In addition, the “membrane-electrode assembly” in the present specification includes an anode electrode catalyst layer disposed on one surface of a polymer electrolyte membrane, a cathode electrode catalyst layer disposed on the other surface, and an anode electrode catalyst layer and a cathode electrode. A gas diffusion layer is disposed on the other surface of the catalyst layer.

  The orientation of each crystal plane according to the present invention can be confirmed by using, for example, a diffraction peak intensity ratio obtained by X-ray diffraction. Further, the crystal orientation ratio of the (110) plane with respect to the film thickness direction of the catalyst component thin film is such that the peak intensity I (220) of the (220) plane measured by X-ray diffraction and the peak intensity I of the other (111) planes. The sum of the peak intensities I (200) of the (111) and (200) planes is

It is preferable that

  Note that the (200) and (220) planes measured by X-ray diffraction are equivalent to the (100) and (110) planes which are low index planes.

  The XRD measurement apparatus used for X-ray diffraction in the present invention is an X-ray diffraction apparatus (MXP18VAHF type) manufactured by Mac Science Co., Ltd. Voltage / current: 40 kV, 300 mA X-ray wavelength: CuKα. In addition, when the sample is irradiated with X-rays using the above apparatus, the peak intensity is diffracted by a certain lattice plane when tilted by an angle satisfying the Bragg condition with respect to the incident X-rays. . Using this principle, the peak intensity of each crystal plane of the sample is calculated using the diffraction peak database of each crystal plane of the catalyst component such as Pt.

  In this specification, the “thin film” refers to a state in which the film is not particulate but is continuously or intermittently disposed with a thin film thickness on the surface of the carrier. When forming a catalyst in a thin film state, it can be controlled to a specific crystal orientation depending on the support structure and support method. For example, by changing the crystal structure of the support surface, the crystal orientation of the thin film catalyst formed thereon Can be controlled. It is possible to increase the crystal orientation ratio of the (110) plane, which was difficult in the form of particles.

  As a result, high catalytic activity can be obtained, and it is possible to contribute to improvement in durability, and a fuel cell exhibiting high durability and good solid polymer battery performance can be provided.

  The catalyst component used in the catalyst component thin film according to the present invention is not particularly limited as long as it has a catalytic action for oxygen reduction reaction in the cathode electrode catalyst (layer), and a known catalyst can be used in the same manner. The anode electrode catalyst (layer) is not particularly limited as long as it has a catalytic action on the hydrogen oxidation reaction in addition to the function having a catalytic action on the oxygen reduction reaction, and a known catalyst can be used in the same manner. Specifically, it is selected from platinum, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum and the like, and alloys thereof. Is done. Of these, the catalyst component used in the catalyst component thin film according to the present invention is preferably at least Pt or an alloy containing Pt.

  The composition of the alloy is preferably 30 to 90 atomic% for platinum and 10 to 70 atomic% for the metal to be alloyed, depending on the type of metal to be alloyed. In general, an alloy is a generic term for a metal element having one or more metal elements or non-metal elements added and having metallic properties.

  The alloy structure consists of a eutectic alloy, which is a mixture of the component elements as separate crystals, a component element completely melted into a solid solution, and a component element composed of an intermetallic compound or a compound of a metal and a nonmetal. There are things that are forming. However, any may be used in the present invention.

  Moreover, the catalyst component thin film may be formed of a plurality of layers, and may be, for example, a two-layer structure including a Pt layer and a Pt alloy layer or a multilayer structure including other metals.

  Furthermore, the thickness of the catalyst component thin film according to the present invention is preferably such that the thickness of the catalyst component thin film is in the range of 1 to 200 nm when the catalyst component is formed in a thin film form on the support material. It is more preferable to make it within a range of 2 to 10 nm.

  When the thickness of the catalyst component thin film is in the range of 1 to 200 nm, both the catalyst activity and the amount of catalyst used can be achieved. On the other hand, if the thickness of the thin film is out of this range and is too thick, the amount of the catalyst used is inevitably increased, which may increase the cost. Furthermore, there is a possibility that the gaps in the electrode catalyst layer may be filled, and there is a risk of inhibiting gas diffusibility and reducing the catalyst utilization rate. The thickness may be in the above-described thickness range, and more preferably, the Pt or Pt alloy metal thin film having high redox activity is in the range of 1 to 20 nm. In addition, since the catalyst component thin film itself of the present invention is formed of a thin film, the specific surface area is smaller than that of the particulate catalyst, so that the platinum elution is prominent in the operation mode of the fuel cell, for example, duty cycle operation. Can be suppressed / prevented.

  The thickness of the catalyst component thin film according to the present invention is measured by observation with a transmission electron microscope TEM.

As a result, it is possible to provide a fuel cell that can obtain a high catalytic activity and contribute to improvement in durability, and can exhibit high durability and good polymer electrolyte battery performance. The carrier material for forming the catalyst component thin film is obtained by heat-treating at 200 to 3000 ° C. at least one selected from the group consisting of a conductive carrier material and a conductive carrier material having a surface coated with a conductive polymer. It is preferable that the heat treatment be performed at 1000 to 3000 ° C, and it is preferable that the heat treatment be performed at 2000 to 3000 ° C.

  Thereby, the catalyst component thin film formed on the support material of the present invention can increase the ratio of crystal orientation of the (110) plane.

  The conductive polymer according to the present invention is not particularly limited, but polyacetylene, poly-p-phenylene, polyaniline, polythiophene, polyindole, poly-2,5-diaminoanthraquinone, poly (o-phenylenediamine) , Poly (quinolinium) salts, poly (isoquinolinium) salts, polypyridines, polyquinoxalines, polyphenylquinoxalines, and the like, and these conductive polymers have various substituents. Also good. Specific examples of the substituent in the case of having a substituent include an alkyl group, a hydroxyl group, an alkoxy group, an amino group, a carboxyl group, a sulfonic acid group, a halogen group, a nitro group, a cyano group, an alkylsulfonic acid group, and a dialkylamino group. , Etc.

The conductive carrier material according to the present invention is specifically a carbon material composed of carbon black, activated carbon, coke, natural graphite, artificial graphite, etc., more specifically, acetylene black, vulcan, ketjen black, black pearl. Mainly at least one selected from graphitized acetylene black, graphitized vulcan, graphitized ketjen black, graphitized carbon, graphitized black pearl, carbon nanotube, carbon nanofiber, carbon nanohorn, carbon fibril, and fibrous carbon Examples thereof include a carbon material contained as a component and a metal material such as nickel and gold. The carrier material according to the present invention may contain one or more of the above exemplified carrier materials. As a result, the specific activity of the catalyst itself is greatly improved, so that the catalytic activity can be improved, and a polymer electrolyte fuel cell exhibiting good battery performance can be provided. “Is a carbon” means to contain a carbon atom as a main component, and is a concept that includes both a carbon atom only and a substantially carbon atom. In some cases, elements other than carbon atoms may be included in order to improve the characteristics of the fuel cell. In addition, being substantially composed of carbon atoms means that mixing of impurities of about 2 to 3% by mass or less is allowed. By using the carbon materials listed above for the electrode according to the present invention as the conductive support, a high performance anode electrode with less loss can be obtained.

  The shape of the conductive carrier material according to the present invention is not particularly limited, and examples thereof include a particulate material, a fibrous material, a fibril shape, a mesh shape, and a flat plate shape. For this, it is more preferable that the conductive carrier material has, for example, a fibrous material, a fibril shape, or a mesh shape.

  The size of the conductive carrier in the form of particles is not particularly limited. From the viewpoint of controlling the ease of loading, the catalyst utilization, and the thickness of the electrode catalyst (layer) within an appropriate range, the primary particles. The diameter is 2 to 100 nm, preferably about 20 to 50 nm.

  If the primary particle diameter of the conductive material is 2 nm or more, it becomes easy to maintain highly dispersed support without being too small with respect to the catalyst component particle diameter. As a result, sufficient electrode performance can be obtained without aggregation of catalyst components.

  Moreover, 5-80 volume% is preferable and, as for the porosity of the electroconductive support | carrier which concerns on this invention, 10-70 volume% is more preferable.

  As a method for measuring the primary particle diameter when the conductive carrier according to the present invention is in the form of particles, all the particle diameters of the primary particles of the conductive material observed in any eight visual fields of the transmission electron microscope image are used. Measurement was performed (total N> 60), and the conditions were such that the median particle size was the primary particle size. However, the primary particle diameter can be calculated not only by this measuring method but also by a known method. In the present specification, “primary particles” are generally a plurality of conductive carriers, for example, carbon materials such as the above-mentioned carbon black, which are aggregated. An individual particle.

  The shape of the carrier material according to the present invention is not particularly limited, and examples thereof include a particulate material, a fibrous material, a fibril shape, a mesh shape, and a flat plate shape. More preferably, the carrier material has, for example, a fibrous material, a fibril shape, or a mesh shape.

  Further, depending on the selection of the carrier material, it is possible to control the crystal orientation and the like of the formed catalyst component thin film. In particular, it is possible to more easily control the crystal orientation of the catalyst component thin film by using a metal material or the like having a lattice constant close to that of Pt or Pt alloy that forms the catalyst component thin film. Since the specific activity of the catalyst itself is greatly improved, the catalytic activity can be improved, and a polymer electrolyte fuel cell exhibiting good battery performance can be provided.

  The catalyst component thin film according to the present invention is preferably produced by a method selected from the group consisting of solution reduction, electrodeposition, vacuum deposition, sputtering, and CVD.

  As a method for forming a catalyst component thin film on the above-mentioned support material, a wet method such as a solution reduction method or electrodeposition, or a dry method by vapor deposition such as sputtering can be selected, but a dry method is used for producing a catalyst metal having a thin film shape. Is more suitable. In particular, the sputtering method is more effective in the present invention because the energy of the metal particles during vapor deposition is large and a denser thin film can be formed. As the carrier substance to be used, the above-mentioned materials are used, and in particular, by using a metal material having a lattice constant close to that of the metal serving as a catalyst, it becomes possible to control the crystal orientation of the catalyst component thin film more easily. For example, by selecting a carrier whose surface structure has a strong tendency to be oriented in the (110) plane, it becomes easy to orient the crystal orientation of the catalyst component thin film formed on the surface to the (110) plane. .

  In addition, since the specific activity of the catalyst itself is greatly improved, the catalytic activity can be improved, and a polymer electrolyte fuel cell exhibiting good battery performance can be provided.

  In the method of coating the surface of the conductive carrier material according to the present invention with a conductive polymer, a monomer that forms the conductive polymer by polymerization is preferably used in a solvent of 0.01 to 5 mol / l, More preferably, after dissolving at 0.1-1 mol / l, a solution containing the monomer is prepared. Next, the solution is impregnated with a conductive carrier material, a conductive carrier material is used for the anode, a graphite rod is used for the cathode, and a conductive polymer having a thickness of 1 to 30 μm by electrolytic oxidation polymerization at room temperature for 5 to 100 minutes. Form a layer.

  The solvent is not particularly limited as long as it is a solvent that can dissolve the monomer that forms the conductive polymer by polymerization, and is appropriately selected according to polymerization conditions. ), Acetonitrile (AN), N, N-dimethylformamide (DMF), water, hexane and the like.

  Other methods of coating the surface of the conductive carrier material according to the present invention with a conductive polymer include known methods such as dipping, spin coating, impregnation, and spray pyrolysis after dissolving the conductive polymer in a solvent. The conductive polymer layer can be formed by coating and drying by the above method.

  The time for heat-treating the conductive carrier material according to the present invention is preferably 1 to 30 minutes, more preferably 5 to 20 minutes.

Carrier material according to the present invention is preferably a specific surface area in the range of 10 to 500 m ² / g, more preferably in the range of 20~250m ² / g, in the range of 25~200m ² / g Is more preferable. When the amount is less than 10 m ² / g, when obtaining a desired amount of the catalyst component, the thickness of the entire catalyst layer is increased, and it may be difficult to obtain good battery performance. On the other hand, when exceeding 500 m < ² > / g, there exists a possibility that the effective utilization factor of a thin film-like catalyst metal may fall.

  The “specific surface area” in the present invention is a BET specific surface area. Generally, the measurement method of the specific surface area is a permeation method (Kozeny Carman method), a volume method, a weight method, a flow method, a constant flow method, a constant flow method. Examples thereof include a physical adsorption method such as a volumetric method and a constant pressure method, and a chemical adsorption method.

  The “specific surface area” according to the present invention is specifically measured by first putting a sample into a sample tube and evacuating the sample while heating at 250 to 350 ° C., and then measuring the sample weight. The adsorption cell is attached to the apparatus again, the sample is cooled to the liquid nitrogen temperature, and nitrogen gas is sent into the cell. When nitrogen gas is adsorbed on the sample surface and the amount of gas blown is increased, the sample surface is covered with gas molecules. The state in which the gas molecules are adsorbed in a multiple manner is plotted as a change in the amount of adsorption with respect to a change in pressure. From this graph, the adsorption amount of gas molecules adsorbed only on the sample surface is obtained from the BET adsorption isotherm. The surface area of the sample can be measured from the amount of adsorbed gas because the adsorption occupation area of nitrogen molecules is known in advance. Actually, the present invention is obtained according to the standard measurement method of the apparatus using ChemBET 3000 of Quantachrome.

Thereby, since the specific activity of the catalyst itself is greatly improved, the catalytic activity can be improved, and a polymer electrolyte fuel cell exhibiting good battery performance can be provided.
(Electrocatalyst layer)
The present invention is preferably a fuel cell electrode catalyst layer comprising an electrode catalyst, and is an electrode catalyst layer comprising the electrode catalyst according to the present invention and a polymer electrolyte.

  By constituting the electrode catalyst layer with the catalyst component thin film of the present invention, it is possible to improve the cell performance and increase the durability of the polymer electrolyte fuel cell. In addition, this makes it possible to provide a solid polymer fuel cell that exhibits high durability and good battery performance when the electrode catalyst layer is mounted on a fuel cell.

  The polymer electrolyte in the electrode catalyst layer according to the present invention is not particularly limited and a known one can be used, but the same materials as those used for the polymer electrolyte membrane can be used, and at least high proton conductivity can be used. Any material can be used. The polymer electrolyte that can be used in this case is roughly classified into a fluorine-based electrolyte containing fluorine atoms in the whole or a part of the polymer skeleton and a hydrocarbon-based electrolyte not containing fluorine atoms in the polymer skeleton.

  Specific examples of the fluorine electrolyte include perfluorocarbon sulfonic acids such as Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.), and Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.). Polymer, polytrifluorostyrene sulfonic acid polymer, perfluorocarbon phosphonic acid polymer, trifluorostyrene sulfonic acid polymer, ethylene tetrafluoroethylene-g-styrene sulfonic acid polymer, ethylene-tetrafluoroethylene Preferred examples include polymers and polyvinylidene fluoride-perfluorocarbon sulfonic acid polymers.

  Specific examples of the hydrocarbon electrolyte include polysulfone sulfonic acid, polyaryl ether ketone sulfonic acid, polybenzimidazole alkyl sulfonic acid, polybenzimidazole alkyl phosphonic acid, polystyrene sulfonic acid, polyether ether ketone sulfonic acid, polyphenyl. A suitable example is sulfonic acid.

  The polymer electrolyte preferably contains a fluorine atom because of its excellent heat resistance and chemical stability. Among them, Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.) Fluorine electrolytes such as Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.) are preferred.

  In the case where the electrode catalyst layer according to the present invention is used as a membrane-electrode assembly (MEA), the polymer electrolyte used in the polymer electrolyte membrane and the electrode catalyst layer may be different. In consideration of contact resistance and the like, it is preferable to use the same one. In addition, when the electrode catalyst according to the present invention is used as a membrane-electrode assembly (MEA), the thickness of the electrode catalyst layer is preferably 1 to 30 μm, more preferably about 2 to 10 μm.

  The polymer electrolyte is preferably coated with an electrode catalyst as a polymer that functions as an adhesive. Thereby, while being able to maintain the structure of an electrode stably, the sufficient three-phase interface where an electrode reaction advances can be ensured, and high catalyst activity can be obtained.

  The content of the polymer electrolyte contained in the electrode catalyst layer according to the present invention is not particularly limited, but is 10 to 60% by mass, more preferably 20 to 50% by mass with respect to the total amount of the catalyst component. Good.

  The content of the conductive carrier material contained in the electrode catalyst layer according to the present invention is not particularly limited, but is 20 to 60% by mass, more preferably 30 to 50% by mass, based on the total amount of the catalyst component. Good.

  The content of the conductive polymer contained in the electrode catalyst layer according to the present invention is not particularly limited, but is 20 to 60% by mass, more preferably 30 to 50% by mass with respect to the total amount of the catalyst component. Good.

  The porosity of the electrode catalyst layer is preferably 30 to 70%, more preferably 35 to 50%. If the porosity is less than 30%, gas diffusion is not sufficient, and the cell voltage in the high current region decreases. On the other hand, when the porosity exceeds 70%, the strength of the electrode catalyst layer is not sufficient, and the porosity decreases in the transfer process.

(Membrane-electrode assembly)
A third aspect of the present invention is a membrane-electrode assembly comprising a pair of electrode catalyst layers according to the present invention sandwiched on both sides of a polymer electrolyte membrane, and a pair of gas diffusion layers sandwiched on both sides of the electrode catalyst layer. It is.

  The polymer electrolyte membrane used for the membrane-electrode assembly of the present invention is not particularly limited, and examples thereof include a membrane made of the same polymer electrolyte as that used for the electrode catalyst layer. In addition, various Nafion (registered trademark of DuPont) manufactured by DuPont and perfluorosulfonic acid membranes represented by Flemion, ion exchange resins manufactured by Dow Chemical, ethylene-tetrafluoroethylene copolymer resin membrane, trifluoro Fluorine polymer electrolytes such as styrene-based polymer membranes, hydrocarbon-based resin membranes with sulfonic acid groups, etc. A membrane impregnated with a liquid electrolyte, a membrane in which a porous body is filled with a polymer electrolyte, or the like may be used. The polymer electrolyte used for the polymer electrolyte membrane and the polymer electrolyte used for each electrode catalyst layer may be the same or different, but the adhesion between each electrode catalyst layer and the polymer electrolyte membrane From the viewpoint of improving the properties, it is preferable to use the same one.

  The thickness of the polymer electrolyte membrane may be appropriately determined in consideration of the characteristics of the obtained membrane electrode assembly, but is preferably 1 to 50 μm, more preferably 2 to 30 μm, and particularly preferably 5 to 30 μm. . From the viewpoint of strength during film formation and durability during operation of the membrane electrode assembly, it is preferably more than 1 μm, and from the viewpoint of output characteristics during operation of the membrane electrode assembly, it is preferably less than 50 μm.

  The polymer electrolyte membrane includes polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) in addition to the above-described fluorine-based polymer electrolyte and membranes made of hydrocarbon resins having sulfonic acid groups. For example, a porous thin film formed from a material impregnated with an electrolyte component such as phosphoric acid or ionic liquid may be used.

  As a material used for the gas diffusion layer (hereinafter referred to as GDL) according to the present invention, a sheet-like material made of carbon paper, non-woven fabric, carbon woven fabric, paper-like paper body, felt or the like has been proposed. When GDL has excellent electron conductivity, efficient transport of electrons generated by a power generation reaction is achieved, and the performance of the fuel cell is improved. Further, if the GDL has an excellent water repellency, the generated water is efficiently discharged.

  In order to ensure high water repellency, a technique for water repellency treatment of a material constituting the GDL has also been proposed. For example, a solution containing a fluorine-based resin such as polytetrafluoroethylene (PTFE) is impregnated with a material constituting GDL such as carbon paper, and dried in the air or an inert gas such as nitrogen. Depending on the case, the hydrophilization treatment may be performed on the material constituting the GDL.

  In addition, carbon particles and a binder may be arranged on a sheet-like GDL made of the above-mentioned carbon paper or nonwoven fabric, and both may be used as a gas diffusion layer. It may be used as a layer. As a result, since the water repellent material and the carbon particles are uniformly formed on the film itself, the water repellent efficiency is increased as compared with the above application.

  Examples of the water repellent material include fluorine resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyhexafluoropropylene, and tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polypropylene, polyethylene, and the like. Is mentioned. Of these, fluororesins are preferred because they are excellent in water repellency and corrosion resistance during electrode reaction.

The “binder” refers to a substance having a bonding role. Further, in the examples according to the present invention, a fluorine-based resin having both the role of a binder and the role of water repellency is used. However, the present invention is not necessarily limited thereto, and the binder and the water-repellent material are mixed with independent substances. May be used.
In the membrane-electrode assembly according to the present invention, the amounts of additives, alcohols (methanol, ethanol, propanol, butanol, etc.), water, water repellent, and binder used as necessary are appropriately selected according to various conditions. It is what is done.

  Next, a preferred embodiment of a method for producing a membrane-electrode assembly when the carrier material according to the present invention is in the form of a fibril will be described. In addition, the following aspects show the preferable aspect of this invention, and the manufacturing method of the membrane-electrode assembly of this invention is not limited to the following method.

  After the monomer that forms the conductive polymer by polymerization is dissolved in a solvent, a solution containing the monomer is prepared. Then, the solution is impregnated with a conductive carrier material, and a conductive polymer layer is formed on the surface of the fibrillar conductive carrier material by electrolytic oxidation polymerization using a conductive carrier material for the anode and a graphite rod for the cathode. To do. Thereafter, the support material according to the present invention can be obtained by heat treatment at 200 to 3000 ° C. for 5 to 60 minutes.

  Even when the conductive polymer layer according to the present invention is not formed on the conductive carrier material, the carrier material according to the present invention is obtained by heat-treating the conductive carrier material at 200 to 3000 ° C. for 5 to 60 minutes. Can do.

  Next, a catalyst component thin film is formed on the conductive polymer layer formed on the surface of the fibril-like conductive support material by at least one method selected from the group consisting of solution reduction, vacuum deposition, sputtering, and CVD. Form. Thereafter, an electrode catalyst having a catalyst component thin film formed on a support material and an ion conductive material such as Nafion are added to a solvent such as water or alcohol as necessary to prepare a catalyst slurry.

  The catalyst slurry of the present invention is applied to a transfer mount and dried to form an electrode catalyst layer. In this case, as the transfer mount, a known sheet such as a PTFE (polytetrafluoroethylene) sheet, a PET (polyethylene terephthalate) sheet, or a polyester sheet can be used. The transfer mount is appropriately selected according to the type of catalyst slurry used (particularly, a conductive carrier material such as carbon in the ink). In the above process, the thickness of the electrode catalyst layer is not particularly limited as long as it can sufficiently exhibit the catalytic action of the hydrogen oxidation reaction (anode side) and the oxygen reduction reaction (cathode side). Thickness can be used. Specifically, the thickness of the electrode catalyst layer is 1 to 30 μm, more preferably 2 to 10 μm.

  The catalyst slurry on the transfer mount is not particularly limited, and a known method such as a screen printing method, a deposition method, or a spray method can be similarly applied. The applied electrode catalyst layer drying conditions are not particularly limited as long as the polar solvent can be completely removed from the electrode catalyst layer. Specifically, the coating layer (electrode catalyst layer) of the catalyst slurry is dried at room temperature to 100 ° C., more preferably 50 to 80 ° C. for 30 to 60 minutes in a vacuum dryer. At this time, if the thickness of the catalyst layer is not sufficient, the coating and drying process is repeated until a desired thickness is obtained. Next, the process proceeds to the following steps.

  That is, after the solid polymer electrolyte membrane is sandwiched between the electrode catalyst layers thus produced, hot pressing is performed on the laminate. At this time, the hot press conditions are not particularly limited as long as the electrode catalyst layer and the solid polymer electrolyte membrane can be joined sufficiently closely, but are 110 to 150 ° C., more preferably 120 to 140 ° C., with respect to the electrode surface. The press pressure is preferably 1 to 5 MPa. Thereby, bondability with a solid polymer electrolyte membrane and an electrode catalyst layer can be improved.

  After performing the hot press, the composite of the electrode catalyst layer and the solid polymer electrolyte membrane (so-called CCM) can be obtained by peeling off the transfer mount.

  Moreover, about the manufacturing method of the fuel cell using the membrane-electrode assembly which concerns on this invention, it is necessary to provide a pair of gas diffusion layer on both sides of a membrane-electrode assembly. The gas diffusion layer was produced by impregnating carbon paper or the like in a solution containing a fluorine-based resin such as polytetrafluoroethylene (PTFE) as necessary, and drying in the air or an inert gas such as nitrogen. Thereafter, a gas diffusion layer is prepared.

  Then, the membrane-electrode assembly is produced by sandwiching the electrode including the electrode catalyst layer and the solid polymer electrolyte membrane using the two gas diffusion layers produced above.

  In the catalyst slurry of the present invention, the electrode catalyst may be used in any amount as long as it can sufficiently exhibit the desired action, that is, the action of catalyzing the hydrogen oxidation reaction (anode side) and the oxygen reduction reaction (cathode side). , May be used. It is preferable that the electrode catalyst is present in the catalyst slurry in an amount of 5 to 75% by mass, more preferably 10 to 60% by mass.

  The catalyst slurry of the present invention includes a water-repellent polymer such as polytetrafluoroethylene, polyhexafluoropropylene, and tetrafluoroethylene-hexafluoropropylene copolymer, if necessary, in addition to the electrode catalyst, polymer electrolyte, and solvent. , Thickeners and the like may be included. Thereby, the water repellency of the obtained electrode catalyst layer can be increased, and water generated at the time of power generation can be quickly discharged.

  The use of a thickener is effective when the catalyst slurry or the like cannot be successfully applied onto the transfer mount. The thickener that can be used in this case is not particularly limited, and a known thickener can be used. Examples thereof include glycerin, (EG (ethylene glycol), PVA (polyvinyl alcohol)), and the like. The amount of the thickener added when using the thickener is not particularly limited as long as it does not interfere with the above effect of the present invention, but is preferably 0 to 10 with respect to the total mass of the catalyst slurry. % By mass. Furthermore, the solvent constituting the catalyst slurry used in the present invention is not particularly limited, and ordinary solvents used for forming the catalyst layer can be used in the same manner. Specifically, water, lower alcohols such as cyclohexanol, ethanol and 2-propanol can be used.

  The amount of the solvent used in the present invention is not particularly limited as long as the electrolyte can be completely dissolved, but the electrolyte is preferably 0.1 to 20% by mass, more preferably 0.5 to 10% in the solvent. The amount is such that the concentration becomes mass%. At this time, if the concentration of the electrolyte is 20% by mass or less, it is unlikely that the electrolyte is completely dissolved and colloid is formed. Moreover, since the electric field mass contained in it being 0.1 mass% or more is an appropriate amount, the molecular chains of the electrolyte polymer are entangled well. For this reason, the mechanical strength of the electrode catalyst layer formed is excellent. Moreover, in the catalyst slurry, the concentration of the solid content including the electrode catalyst and the solid polymer electrolyte is preferably 5 to 50% by mass, more preferably about 10 to 40% by mass in the catalyst slurry.

  The catalyst slurry of the present invention may be used for only one or both of the cathode side electrode catalyst layer and the anode side electrode catalyst layer. However, the cathode side is affected by changes in the amount of water produced due to output fluctuations in particular, resulting in changes in the wet and dry conditions. The porous structure of the electrode catalyst layer in the initial state collapses, the porosity decreases, and the amount of reactant gas supplied to the electrode catalyst layer decreases. High risk of decline. Therefore, it is preferably used at least for the anode side electrode catalyst layer.

  In the above method, the gas diffusion layer according to the present invention is further separated after bonding the electrode catalyst layer and the solid polymer electrolyte membrane by peeling off the transfer mount and further sandwiching the obtained bonded body with the gas diffusion layer. It is preferable to join the electrode catalyst layer. Alternatively, after an electrode catalyst layer is formed on the surface of the gas diffusion layer in advance to produce an electrode catalyst layer-gas diffusion layer assembly, the electrode catalyst layer-gas diffusion layer assembly is solid as described above. It is also preferable to sandwich and bond the polymer electrolyte membrane by hot pressing.

  In addition to the hot pressing method described above, a method of laminating an electrode catalyst layer, a polymer electrolyte membrane, an electrode catalyst layer, and a gas diffusion layer on the gas diffusion layer by sequential application may be used.

  A third aspect of the present invention is a fuel cell including the membrane-electrode assembly. The type of the fuel cell is not particularly limited. In the above description, the polymer electrolyte fuel cell has been described as an example, but in addition to this, a representative example is an alkaline fuel cell and a phosphoric acid fuel cell. Examples thereof include an acid electrolyte fuel cell, a direct methanol fuel cell, and a micro fuel cell. Among them, a solid polymer electrolyte fuel cell is preferable because it is small in size and can achieve high density and high output. The fuel cell is useful as a stationary power source in addition to a power source for a moving body such as a vehicle in which a mounting space is limited. In particular, the present invention can be used particularly favorably in automobile applications where system start / stop and output fluctuations frequently occur.

  The polymer electrolyte fuel cell is useful not only as a stationary power source but also as a power source for a moving body such as an automobile having a limited mounting space. In particular, moving bodies such as automobiles that are susceptible to corrosion of the carbon support due to the high output voltage required after a relatively long shutdown, and deterioration of the polymer electrolyte due to the high output voltage being taken out during operation. It is particularly preferred to be used as a power source.

  The configuration of the fuel cell is not particularly limited, and a conventionally known technique may be appropriately used. Generally, the fuel cell has a structure in which a membrane electrode assembly is sandwiched between separators.

  The separator can be used without limitation as long as it is conventionally known, such as those made of carbon such as dense carbon graphite and a carbon plate, and those made of metal such as stainless steel. The separator has a function of separating air and fuel gas, and a channel groove for securing the channel may be formed. The thickness and size of the separator, the shape of the flow channel, and the like are not particularly limited, and may be appropriately determined in consideration of the output characteristics of the obtained fuel cell.

  Further, in order to prevent the gas supplied to each electrode catalyst layer from leaking to the outside, a gas seal portion may be further provided at a portion on the gasket layer where the electrode catalyst layer is not formed. Examples of the material constituting the gas seal portion include rubber materials such as fluoro rubber, silicon rubber, ethylene propylene rubber (EPDM), polyisobutylene rubber, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyhexafluoro. Fluorine polymer materials such as propylene, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and thermoplastic resins such as polyolefin and polyester. The thickness of the gas seal portion may be 2 mm to 50 μm, preferably about 1 mm to 100 μm.

  Furthermore, a stack in which a plurality of membrane electrode assemblies are stacked via a separator and connected in series may be formed so that the fuel cell can obtain a desired voltage or the like. The shape of the fuel cell is not particularly limited, and may be determined as appropriate so that desired battery characteristics such as voltage can be obtained.

  Hereinafter, embodiments of the present invention will be described in detail with reference to Examples and Comparative Examples. The present invention is not limited to these. In addition, the analysis method and the analytical equipment employed in the present invention are as follows.

Example 1
A container containing a 0.1M aniline aqueous solution was installed, and a carbon substrate (gas diffusion substrate (GDL): plate-like material made of carbon fiber) was used as an anode and a current was applied using a graphite rod as a counter electrode. A polyaniline layer (catalyst layer thickness of 30 μm) was formed on the base material by electrolytic oxidation polymerization, and the polyaniline-formed base material was subjected to high-temperature firing at 2500 ° C. or higher for 10 minutes in a vacuum atmosphere, and then argon gas ( Inert gas was added, and the pressure was further reduced to produce a fibrillar (fibrous) electrode substrate, which was measured by the BET method, and as a result, the specific surface area of the support material was 25 m ² / g.

A catalyst that has a Pt thin film thickness of 14 nm and a Pt amount of 0.05 mg / cm ² by installing the production electrode in a sputtering apparatus, performing a sputtering operation for 150 seconds using Pt as a target metal and an output of 40 W and 5 Pa. A supported electrode was obtained. At this time, as a result of measurement with an X-ray diffractometer (MXP18VAHF type) manufactured by Mac Science, the crystal orientation ratio of the (110) plane was 1.5.
The evaluation was performed using a three-electrode glass cell in which the sample electrode supporting the catalytic metal was used as an evaluation working electrode, and a 0.5 mol / L sulfuric acid aqueous solution saturated with oxygen gas was used as an electrolyte.

  The sample electrode is immersed in an electrolytic solution, and the potential is operated from the natural potential to the low potential side at a speed of 1 mV / second. The current value at 0.85 V was measured from the potential-current curve at this time, and the value obtained by removing the Pt content was defined as the mass activity of platinum for the oxygen reduction reaction.

(Example 2)
An ink in which carbon black powder and Teflon (registered trademark) dispersion are mixed is applied on carbon paper (GDL) so that the PTFE is 10% of carbon black and PTFE, and the coating thickness is 50 μm. An electrode substrate (a porous material formed by collecting carbon black particles) was prepared by heat treatment in an air atmosphere at 300 ° C. or higher for 3 hours. As a result of measurement by BET at this time, the specific surface area of the support material was 250 m ² / g.

A catalyst that has a Pt thin film thickness of 6 nm and a Pt amount of 0.05 mg / cm ² by installing the production electrode in a sputtering apparatus, performing a sputtering operation for 150 seconds using Pt as a target metal and an output of 40 W and 5 Pa. A supported electrode was obtained. At this time, as a result of measurement with an X-ray diffractometer (MXP18VAHF type) manufactured by Mac Science, the crystal orientation ratio of the (110) plane was 1.5.

  The evaluation was performed using a three-electrode glass cell in which the sample electrode supporting the catalytic metal was used as an evaluation working electrode, and a 0.5 mol / L sulfuric acid aqueous solution saturated with oxygen gas was used as an electrolyte.

  The sample electrode is immersed in an electrolytic solution, and the potential is operated from the natural potential to the low potential side at a speed of 1 mV / second. The current value at 0.85 V was measured from the potential-current curve at this time, and the value obtained by removing the Pt content was defined as the mass activity of platinum for the oxygen reduction reaction.

(Comparative Example 1)
A sputtering method was used to deposit Pt in the form of a film on the surface of the carbon powder. Here, the amount of platinum was adjusted so as to be 50 wt% with respect to the carbon powder. The Pt-supported carbon powder thus produced was kneaded with fullerenol, a water repellent resin, and a pore former (CaCO ₃ ), and applied to a carbon substrate so that Pt was 0.05 mg / cm ² . Next, a catalyst-carrying electrode was produced by removing the pore former by acid treatment.

  The evaluation was performed using a three-electrode glass cell in which the sample electrode supporting the catalytic metal was used as an evaluation working electrode, and a 0.5 mol / L sulfuric acid aqueous solution saturated with oxygen gas was used as an electrolyte.

  The sample electrode is immersed in an electrolytic solution, and the potential is operated from the natural potential to the low potential side at a speed of 1 mV / second. The current value at 0.925 V was measured from the potential-current curve at this time, and the value obtained by dividing the Pt content was defined as the mass activity of platinum for the oxygen reduction reaction.

Claims (8)

An electrocatalyst comprising a support material and a catalyst component thin film formed on the support material,
The crystal orientation ratio of the (110) plane with respect to the film thickness direction of the catalyst component thin film,

The electrode catalyst, wherein the crystal orientation ratio of the (110) plane exceeds 1 when expressed as The crystal orientation ratio of the (110) plane with respect to the film thickness direction of the catalyst component thin film is the peak intensity I (220) of the (220) plane measured by X-ray diffraction and the peak intensity I (111) of the other (111) plane. ) And (200) plane peak intensity I (200)

The electrode catalyst according to any one of claims 1 to 3, wherein   The electrode catalyst according to any one of claims 1 to 4, wherein the catalyst component thin film is at least Pt or an alloy containing Pt.   The electrode catalyst according to any one of claims 1 to 5, wherein the carrier substance is a conductive material selected from the group consisting of a carbon material, a conductive polymer material, and a metal material. The electrode catalyst according to claim 1, wherein the support material has a specific surface area of 10 to 500 m ² / g.   The carrier material is obtained by heat-treating at least one selected from the group consisting of a conductive carrier material and a conductive carrier material whose surface is coated with a conductive polymer at 200 to 3000 ° C. 6. The method for producing an electrode catalyst according to any one of 5 above.   The electrode catalyst according to claim 1, wherein the catalyst component thin film is formed by at least one method selected from the group consisting of solution reduction, electrodeposition, vacuum deposition, sputtering, and CVD. Manufacturing method.   The electrode catalyst layer for fuel cells provided with the electrode catalyst of any one of Claims 1-5, or the electrode catalyst obtained from the manufacturing method of Claim 6 or 7.