JP2007179858A - Paste composition for forming catalyst layer and catalyst layer transfer sheet using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a paste composition for forming catalyst layer capable of manufacturing a fuel cell which is excellent in dispersibility of catalyst and has an excellent battery performance and to provide a catalyst layer transfer sheet using it. <P>SOLUTION: Paste composition for forming the catalyst layer of this invention is the paste composition for forming catalyst layer containing (1)catalyst-carrying carbon particles, (2) ion conductive polymer electrolyte, (3) solvent and (4) dispersant and the dispersant (4) is a chemical composition having a perfluoroalkyl group. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a paste composition for forming a catalyst layer and a catalyst layer transfer sheet using the same.

  A fuel cell is a system in which a catalyst layer is disposed on both surfaces of an electrolyte membrane and generates electricity by an electrochemical reaction between hydrogen and oxygen, and only water is generated during power generation. Unlike conventional internal combustion engines, fuel cells are attracting attention as next-generation clean energy systems because they do not generate environmentally harmful gases such as carbon dioxide.

  The polymer electrolyte fuel cell has a structure in which a hydrogen ion conductive polymer electrolyte membrane is used as an electrolyte membrane, a catalyst layer is arranged on both sides thereof, an electrode base material is arranged on both sides thereof, and this is further sandwiched between separators. I am doing. A catalyst layer is arranged on both sides of the electrolyte membrane layer, and then an electrode substrate is arranged on both sides thereof (that is, electrode substrate / catalyst layer / electrolyte membrane / catalyst layer / electrode substrate layer configuration) It is called an electrode-electrolyte membrane assembly.

  Conventionally, as a method for producing an electrode-electrolyte membrane assembly, (1) two electrode base materials on which a catalyst layer is formed by applying a printing method or a spray method on one side are used, and the catalyst layer surface of the electrode base material is an electrolyte. A method of placing the film in contact with both sides of the membrane and performing hot pressing (Patent Documents 1 and 2), and (2) forming a catalyst layer on both sides of the electrolyte membrane by applying a printing method or a spray method. There has been proposed a method (Patent Document 3) in which the electrode substrate is disposed so as to be in contact with the substrate and hot pressed.

  The catalyst layer forming paste composition used in the various methods described above is obtained by dissolving or dispersing carbon particles carrying a catalyst and a hydrogen ion conductive electrolyte in alcohol. As a means for obtaining stable paste properties, it is generally performed to add a polymer dispersant and a solvent of an organic compound to improve viscosity or adjust dispersibility of catalyst particles to improve coatability ( Patent Documents 4 and 5).

  However, these dispersants and solvents are necessary in the production process, but are not necessary as a constituent material of the electrode-catalyst layer membrane assembly that is the final product, resulting in impurities in the catalyst layer, resulting in a decrease in battery performance. May cause.

  In particular, in the dispersant used in Patent Documents 4 and 5, the addition amount must be increased, and the impurities in the catalyst layer inevitably increase. In addition, such a dispersant has poor affinity with the electrolyte membrane, and the dispersibility of the paste may be reduced. Furthermore, due to the decrease in dispersibility, the film formability of the catalyst layer is deteriorated, and the catalyst layer film may be uneven and defective.

Therefore, development of a paste composition for forming a catalyst layer that can produce a fuel cell with good dispersibility of the catalyst and excellent cell performance is desired.
Japanese Examined Patent Publication No. 62-61118 Japanese Patent Publication No.62-61119 Japanese Examined Patent Publication No. 2-48632 JP 2003-45437 A JP 2003-45440 A

  The main object of the present invention is to provide a catalyst layer forming paste composition that can produce a fuel cell with good dispersibility of the catalyst and excellent battery performance, and a catalyst layer transfer sheet using the same. To do.

  In view of such a situation, the present inventors have intensively studied to achieve the above object. As a result, it has been found that the above object can be achieved by using a paste composition for forming a catalyst layer having a specific configuration, and the present invention has been completed.

  Item 1. (1) A catalyst layer forming paste composition containing catalyst-carrying carbon particles, (2) an ion conductive polymer electrolyte, (3) a solvent, and (4) a dispersant, wherein (4) the dispersant is perfluoro A paste composition for forming a catalyst layer, which is a compound having an alkyl group.

  Item 2. Item 2. The paste composition according to Item 1, wherein the dispersant is a nonionic surfactant.

  Item 3. (4) The content of the dispersant is 0.01 to 1% by weight with respect to the total amount of (1) catalyst-carrying carbon particles and (2) ion conductive polymer electrolyte in the paste composition. The paste composition according to 1 or 2.

  Item 4. Item 4. A catalyst layer transfer sheet obtained by applying the paste composition according to any one of Items 1 to 3 onto a transfer substrate and drying the paste composition.

  Item 5. Item 4. A catalyst layer-electrolyte membrane laminate formed using the paste composition according to any one of Items 1 to 3.

  Item 6. Item 6. An electrode-electrolyte membrane assembly comprising the catalyst layer-electrolyte membrane laminate according to Item 5.

  The paste composition for forming a catalyst layer of the present invention comprises (1) catalyst-supporting carbon particles, (2) an ion conductive polymer electrolyte, (3) a solvent, and (4) a paste composition for forming a catalyst layer. (4) The dispersant is a compound having a perfluoroalkyl group.

  The catalyst-supporting carbon particles (1) are known.

  Examples of the catalyst include platinum and a platinum compound. Examples of the platinum compound include an alloy of platinum and at least one metal selected from the group consisting of ruthenium, palladium, nickel, molybdenum, iridium, iron, cobalt, and the like.

  As the carbon particles as the support, for example, acetylene black, ketjen black, furnace black, activated carbon, carbon nanotube, fullerene, or the like can be used.

  The hydrogen ion conductive polymer electrolyte (2) is known.

  Examples of the hydrogen ion conductive polymer electrolyte include perfluorosulfonic acid-based fluorine ion exchange resins. By introducing a fluorine atom having a high electronegativity, it is chemically very stable, the degree of sulfonic acid group detachment is high, and high ionic conductivity can be realized. Specific examples of such a hydrogen ion conductive polymer electrolyte include “Nafion” manufactured by DuPont, “Flemion” manufactured by Asahi Glass Co., Ltd., “Aciplex” manufactured by Asahi Kasei Co., Ltd., and Gore manufactured by Gore. Examples include “Gore Select”. Usually, it is known that the hydrogen ion conductive electrolyte of (2) is used as an alcohol aqueous solution containing about 5 to 30% by weight of the electrolyte. As the alcohol, for example, methanol, ethanol diethyl ether or the like is used.

  As the solvent (3), an alcohol solvent having 4 or less carbon atoms can be used. As alcohol solvents, known alcohols can be widely used. As such an alcohol, for example, a monohydric alcohol or a polyhydric alcohol having a boiling point of about 80 to 200 ° C. can be used. More specifically, 1-propanol, 2-propanol, 1-butanol, 2-butanol, t-butanol and the like can be mentioned. The alcohol solvent is used alone or in combination of two or more. Among these monovalent alcohol solvents, 2-propanol, 1-butanol and t-butanol are preferable. Specifically, the polyhydric alcohol is preferably propylene glycol, ethylene glycol or the like, among which propylene glycol is particularly preferable, from the viewpoint of compatibility with the ion conductive electrolyte and drying efficiency when used as a paste.

  The dispersant (4) is a compound having a perfluoroalkyl group. By using this dispersant, the catalyst-supporting carbon particles and the ion conductive polymer electrolyte can be further dispersed. Because of this improvement in dispersibility, the amount of dispersant used can be reduced. Further, after the formation of the catalyst layer, the dispersant does not inhibit the catalyst performance of the catalyst layer as an impurity. Furthermore, since the affinity with an electrolyte membrane such as a fluorine ion exchange resin is good, the electrolyte membrane can be formed evenly. By these, if the paste composition of this invention is used, the catalyst layer which has the outstanding battery performance can be formed.

  Examples of the dispersant include perfluorobutyl sulfonate, perfluoroalkyl group-containing carboxylate, perfluoroalkyl group-containing trimethylammonium salt, perfluoroalkyl group-containing phosphate ester, perfluoroalkyl ethylene oxide adduct, perfluoro Examples thereof include alkyl group-containing oligomers.

  Any of anionic, cationic and nonionic surfactants can be used. Here, the anionic and cationic surfactants are dispersants that are ion-dissociated in an aqueous solution and the anionic part or cationic part exhibits surface activity. The nonionic surfactant refers to a dispersant having no ion dissociating group in an aqueous solution.

  Among these, nonionic surfactants are particularly preferable. By using a nonionic surfactant, it is possible to effectively prevent aggregation with conductive carbon particles. Moreover, since wettability can be improved, the effect as surfactant, such as a dispersibility, can fully be exhibited with a smaller addition amount.

  The proportion of the components (1) to (4) contained in the paste composition for forming the catalyst layer of the present invention is not limited and can be appropriately selected within a wide range.

  The method for preparing the paste composition can also be appropriately selected within a wide range. In the preparation, the components (1) to (4) may be dispersed simultaneously, or the components (4) may be added after dispersing (1) to (3). Can be optimized depending on the type of the electrolyte and the solvent type.

  For example, in the paste composition for forming a catalyst layer of the present invention, the component (2) is about 0.3 to 3 parts by weight (preferably 0.4 parts per 1 part by weight of the catalyst-carrying carbon particles of (1). ~ 2 parts by weight), (3) component is about 5-50 parts by weight (preferably about 10-25 parts by weight), and the remainder is water and (4) dispersant. The ratio of water is usually about 10 to 10 times the weight of the catalyst-supported carbon particles.

  The content of the dispersant is usually 0.01 to 1% by weight, preferably 0.8%, based on the total amount of (1) catalyst-carrying carbon particles and (2) ion conductive polymer electrolyte in the catalyst-forming paste. 01 to 0.5% by weight. By setting the content within this range, it is possible to sufficiently achieve the dispersion stability of the catalyst-carrying carbon particles, etc., and at the same time, it is possible to effectively prevent the agglomeration of the catalyst-carrying carbon particles and to prevent the precipitation on the catalyst layer surface. it can.

Catalyst Layer Transfer Sheet The catalyst layer transfer sheet of the present invention is produced by applying the catalyst layer forming paste composition onto a transfer substrate and drying it.

  The catalyst layer may be formed on one surface of the transfer substrate, or may be formed on both surfaces of the transfer substrate.

  Examples of the transfer substrate include polyimide, polyethylene terephthalate (PET), polyparvanic acid aramid, polyamide (nylon), polysulfone, polyethersulfone, polyphenylene sulfide, polyether ether ketone, polyetherimide, polyarylate, polyethylene naphthalate. Examples thereof include polymer films such as phthalate.

  Further, heat resistance of ethylene tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroperfluoroalkyl vinyl ether copolymer (PFA), polytetrafluoroethylene (PTFE), etc. Fluorine resin can also be used.

  Further, in addition to the polymer film, the transfer substrate may be paper such as art paper, coated paper, lightweight coated paper, or other non-coated paper such as notebook paper or copy paper. Further, the transfer substrate may be a sheet made of carbon fibers such as carbon cloth, carbon paper, and carbon felt.

  The thickness of the transfer substrate is usually about 6 μm to 100 μm, preferably about 10 μm to 50 μm, more preferably about 15 μm to 30 μm, from the viewpoints of handleability and economy.

  Therefore, as the transfer substrate, a polymer film that is inexpensive and easily available is preferable, and polyethylene terephthalate or the like is more preferable.

  The method for applying the paste composition is not particularly limited. For example, knife coating, bar coating, blade coating, spraying, dip coating, spin coating, roll coating, die coating, curtain coating, screen printing, etc. Applicable.

  A coating film is formed by applying and then drying the paste composition of the present invention. A drying temperature is about 40-120 degreeC normally, Preferably it is about 75-95 degreeC.

  If the temperature reached on the coating film surface is 105 ° C. or higher, the possibility of ignition in the drying process is significantly increased, which is dangerous. Therefore, the temperature reached is preferably 85 ° C. or higher and lower than 105 ° C.

  Although depending on the drying temperature, the drying time is usually about 5 minutes to 2 hours, preferably about 30 minutes to 1 hour.

  The thickness of the coating film is usually about 10 μm to 50 μm, preferably about 15 μm to 30 μm.

Catalyst layer-electrolyte membrane laminate The catalyst layer-electrolyte membrane laminate of the present invention is formed using the paste composition.

  The catalyst layer-electrolyte membrane laminate may be formed by directly applying and drying the paste composition onto the electrolyte membrane, or may be formed by transferring the catalyst layer transfer sheet to the electrolyte membrane.

  When the catalyst layer-electrolyte membrane laminate of the present invention is produced by applying and drying the paste composition on the electrolyte membrane, the application method described above can be used. In this case, the thickness of the catalyst layer is usually about 10 μm to 50 μm, preferably about 15 μm to 30 μm.

  When manufacturing by transferring the catalyst layer transfer sheet to the electrolyte membrane, for example, after placing the catalyst layer transfer sheet so that the catalyst layer surface faces the electrolyte membrane surface and pressurizing, the substrate of the transfer sheet is What is necessary is just to manufacture by peeling from a catalyst layer surface. By repeating this operation twice, a catalyst layer-electrolyte membrane laminate in which the catalyst layer surface is laminated on both surfaces of the electrolyte membrane can be produced.

  In consideration of workability, the catalyst layer surface is preferably laminated on both surfaces of the electrolyte membrane at the same time. In this case, for example, the transfer sheet may be disposed so that the catalyst layer surface of the transfer sheet faces both surfaces of the electrolyte membrane, pressurize, and then the substrate of the transfer sheet may be peeled off.

  The pressure level is usually about 0.5 Mpa to 20 Mpa, preferably about 1 Mpa to 10 Mpa in order to avoid transfer defects. Further, it is preferable to heat the pressure surface during this pressure operation in order to avoid transfer failure. The heating temperature is usually 200 ° C. or lower, preferably about 120 to 150 ° C., in order to avoid damage or modification of the electrolyte membrane.

  The electrolyte membrane is a known one. Specific examples of the electrolyte membrane include “Nafion” membrane manufactured by DuPont, “Flemion” membrane manufactured by Asahi Glass Co., Ltd., “Aciplex” membrane manufactured by Asahi Kasei Co., Ltd., and the like. The thickness of the electrolyte membrane is usually about 20 μm to 250 μm, preferably about 20 μm to 80 μm.

Electrode-electrolyte membrane assembly The electrode-electrolyte membrane assembly of the present invention is produced, for example, by placing an electrode substrate on both sides of the catalyst layer-electrolyte membrane laminate produced above and pressurizing it.

  The electrode base material is well known, and various electrode base materials constituting a fuel electrode or an air electrode can be used.

  The pressure level is usually about 0.1 Mpa to 100 Mpa, preferably about 5 Mpa to 15 Mpa. It is preferable to heat at the time of this pressurization operation, and heating temperature may be about 120-150 degreeC normally.

  ADVANTAGE OF THE INVENTION According to this invention, the paste composition for catalyst layer formation excellent in the dispersibility can be provided.

  According to the present invention, the amount of dispersant used can be reduced. Further, after the formation of the catalyst layer, the dispersant used in the present invention does not inhibit the catalyst performance of the catalyst layer as an impurity. Furthermore, since this dispersant has good affinity with an electrolyte membrane such as a fluorine ion exchange resin, the catalyst layer forming paste composition of the present invention can be formed evenly on the electrolyte membrane.

  By using the paste composition for forming a catalyst layer of the present invention, a catalyst layer transfer sheet, a catalyst layer-electrolyte laminate, which can produce a high-quality fuel cell with high power generation efficiency and excellent battery performance, battery life, etc. And an electrode-electrolyte membrane assembly can be obtained.

  The present invention will be further clarified by the following examples and comparative examples. In addition, this invention is not limited to the following Example.

Example 1
(Preparation of paste composition)
1 g of platinum catalyst-supporting carbon (Pt: 46.5% by weight, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., “TEC10E50E”) was stirred and mixed in 3 g of water with a disperser to prepare an aqueous dispersion of platinum-supporting carbon.

  To the aqueous dispersion prepared above, 10 g of a 5 wt% Nafion solution (hydrogen ion conductive polymer electrolyte, manufactured by DuPont, solvent: water and 1-propanol), and 2-propanol (manufactured by Kishida Chemical) as the solvent. 10 g, 0.0075 g ((1) catalyst-supporting carbon particles and (2) ion-conducting polymer electrolyte) perfluoroalkyl group-containing oligomer (Dainippon Ink, “F-470”) which is a nonionic dispersant as a dispersant The paste composition of the present invention was prepared by mixing 0.5 wt% with respect to the total amount of the above and stirring and mixing with a disperser.

(Preparation of catalyst layer transfer sheet)
Next, the prepared paste composition was applied onto a PET film so that the amount of platinum after drying was 0.5 mg / cm ² with a doctor blade, and dried for 15 minutes at 95 ° C. in an air atmosphere. A catalyst layer transfer sheet of the present invention was produced.

(Production of catalyst layer-electrolyte membrane laminate)
Using the obtained two catalyst layer transfer sheets, after being sandwiched under conditions of 150 ° C. and 5 Mpa so as to be in contact with a hydrogen ion conductive polymer electrolyte membrane (Nafion 112, manufactured by DuPont, 50 μm thick), By peeling the PET film, the catalyst layer-electrolyte membrane laminate (catalyst layer / electrolyte membrane / catalyst layer) of the present invention was produced.

Comparative Example 1
(Preparation of paste composition)
Instead of 0.0075 g of a perfluoroalkyl group-containing oligomer (Dainippon Ink, “F-470”) which is a nonionic dispersant as a dispersant, a 10% by weight polyoxyethylene alkyl ether aqueous solution which is a nonionic dispersant A paste composition of Comparative Example 1 was prepared in the same manner as in Example 1 except that 0.45 g (manufactured by Lion Corporation, trade name: Ribonox NC-300) was used.

(Preparation of catalyst layer transfer sheet)
Next, a catalyst layer transfer sheet of Comparative Example 1 was produced in the same manner as in Example 1 except that the paste composition of Comparative Example 1 was used as the paste composition.

(Production of catalyst layer-electrolyte membrane laminate)
Using the catalyst layer transfer sheet of Comparative Example 1 on one side of the hydrogen ion conductive polymer electrolyte membrane and the catalyst layer transfer sheet of Example 1 on the other side, the catalyst layer of Comparative Example 1 under the same conditions as in Example 1 -An electrolyte membrane laminate (catalyst layer / electrolyte membrane / catalyst layer) was prepared.

Comparative Example 2
(Preparation of paste composition)
Instead of 0.0075 g of a perfluoroalkyl group-containing oligomer (Dainippon Ink, “F-470”), which is a nonionic dispersant, as a dispersant, a 10% by weight polystyrene sodium sulfonate aqueous solution (anionic dispersant) ( A paste composition of Comparative Example 2 was prepared in the same manner as in Example 1 except that 0.45 g (Aldrich) was used.

(Preparation of catalyst layer transfer sheet)
Next, a catalyst layer transfer sheet of Comparative Example 2 was produced in the same manner as in Example 1 except that the paste composition of Comparative Example 2 was used as the paste composition.

(Production of catalyst layer-electrolyte membrane laminate)
Using the catalyst layer transfer sheet of Comparative Example 2 on one side of the hydrogen ion conductive polymer electrolyte membrane and the catalyst layer transfer sheet of Example 1 on the other side, under the same conditions as Example 1, the catalyst layer of Comparative Example 2 -An electrolyte membrane laminate (catalyst layer / electrolyte membrane / catalyst layer) was prepared.

Test Example An electrode substrate (carbon paper made of carbon fiber, TGP-H-090, manufactured by Toray Industries, Inc.) is formed on both sides of each catalyst layer-electrolyte membrane laminate produced in Example 1 and Comparative Examples 1-2. Each single cell battery was fabricated by placing and sandwiching with separators. The battery performance was evaluated by measuring the current-voltage characteristics of this single cell battery. The result is shown in FIG. From FIG. 1, it was found that the battery produced using the paste composition for forming a catalyst layer of the present invention showed a high voltage even when the current value was increased.

FIG. 1 is a graph showing the relationship between the current and voltage of a battery comprising the catalyst layer-electrolyte membrane laminate of Example 1 and Comparative Examples 1-2.

Claims (6)

  (1) A catalyst layer forming paste composition containing catalyst-carrying carbon particles, (2) an ion conductive polymer electrolyte, (3) a solvent, and (4) a dispersant, wherein (4) the dispersant is perfluoro A paste composition for forming a catalyst layer, which is a compound having an alkyl group.   The paste composition according to claim 1, wherein the dispersant is a nonionic surfactant. (4) Content of a dispersing agent is 0.01 to 1 weight% with respect to the total amount of (1) catalyst carrying | support carbon particle and (2) ion conductive polymer electrolyte in a paste composition. Item 3. The paste composition according to Item 1 or 2.   The catalyst layer transfer sheet formed by apply | coating the paste composition in any one of Claims 1-3 on a transfer base material, and drying.   The catalyst layer-electrolyte membrane laminated body formed using the paste composition in any one of Claims 1-3.   An electrode-electrolyte membrane assembly comprising the catalyst layer-electrolyte membrane laminate according to claim 5.

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