JP2008251180A - Catalyst carrying carbon particle and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst layer for a solid polymer fuel cell in which occurrence of cracks is suppressed and a problem of crossover can be solved. <P>SOLUTION: The catalyst carrying carbon particles have a metal catalyst carried by carbon particles which contain the carbon particles of the average primary particle size of 50-100 nm and the carbon particles of the average primary particle size of 10-40 nm in a ratio of 1 pts.wt. for the former and 0.2-6 pts.wt. for the latter. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a novel catalyst-supported carbon particle and a method for producing the same.

  Solid polymer fuel cells are particularly actively studied from the viewpoint of achieving weight reduction, high output density, and the like as compared with other fuel cells. The polymer electrolyte fuel cell has a structure in which an ion conductive polymer electrolyte membrane is used as an electrolyte membrane, a catalyst layer and a gas diffusion base material (electrode base material) are sequentially laminated on both sides, and further sandwiched between separators. ing.

One of the problems that occur in this polymer electrolyte fuel cell is a so-called crossover. Crossover means that fuel (for example, hydrogen gas) usually reacts to hydrogen ions (H ⁺ ) at the fuel electrode where the fuel is first fed, but this reaction does not occur and the fuel (hydrogen gas) This is a phenomenon that reaches the air electrode on the opposite side through the electrolyte membrane. Since this crossover significantly deteriorates the battery performance, it is necessary to suppress it as much as possible.

  In particular, a direct methanol fuel cell (DMFC), which is a kind of polymer electrolyte fuel cell, uses liquid methanol as a fuel. Therefore, a crossover is more likely to occur than a gas such as hydrogen gas, and it is important to suppress the crossover in the DMFC.

  One cause of this crossover is a crack present in the catalyst layer. Therefore, as one countermeasure for solving the problem of crossover, for example, a method of filling a crack by spraying a paste composition containing catalyst-carrying carbon particles having a small particle diameter onto a crack generated on the catalyst layer. Has been proposed (Patent Document 1).

However, the catalyst layer obtained in Patent Document 1 is not dense on the other side of the catalyst layer that is not sprayed (surface that contacts the electrolytic membrane), and the problem of crossover has not been sufficiently solved.
JP 2006-286477 A

  Therefore, an object of the present invention is to provide a catalyst layer for a polymer electrolyte fuel cell in which the occurrence of cracks is suppressed and the crossover problem can be solved.

  As a result of intensive studies in view of the above-described conventional techniques, the present inventors have found that the above problem can be solved by including specific catalyst-supporting carbon particles in the catalyst layer. That is, the present invention relates to the following catalyst-carrying carbon particles, a method for producing the same, a catalyst layer containing the catalyst-carrying carbon particles, and the like.

  Item 1. Carbon including carbon particles having an average primary particle diameter of 50 to 100 nm and carbon particles having an average primary particle diameter of 10 to 40 nm in a ratio of 0.2 to 6 parts by weight with respect to 1 part by weight of the former. Catalyst-supported carbon particles, in which a metal catalyst is supported on the particles.

  Item 2. Item 2. The catalyst-supported carbon particles according to Item 1, wherein the latter contains 0.3 to 3 parts by weight with respect to 1 part by weight of the former.

  Item 3. Item 3. A solid polymer fuel cell catalyst layer comprising the catalyst-supporting carbon particles according to Item 1 or 2 and a hydrogen ion conductive polymer electrolyte.

  Item 4. Item 6. A polymer electrolyte fuel cell comprising the catalyst layer according to Item 3.

  Item 5. Carbon particles having an average primary particle diameter of 50 to 100 nm and carbon particles having an average primary particle diameter of 10 to 30 nm are mixed at a ratio of 0.2 to 6 parts by weight with respect to 1 part by weight of the former. The manufacturing method of the catalyst carrying | support carbon particle provided with the 2nd process of carrying | supporting a metal catalyst on the carbon particle obtained at the 1st process and the 1st process.

Catalyst-supported carbon particles The catalyst-supported carbon particles of the present invention are composed of carbon particles having an average primary particle diameter of 50 to 100 nm and carbon particles having an average primary particle diameter of 10 to 40 nm with respect to 1 part by weight of the former. Is formed by supporting a metal catalyst on carbon particles containing 0.2 to 6 parts by weight.

  The carbon particles are not particularly limited, and examples thereof include carbon black such as channel black, furnace black, ketjen black, acetylene black, and lamp black, graphite, activated carbon, carbon nanotube, and carbon nanowire. These can be used alone or in combination of two or more. Of these, ketjen black is particularly preferable.

  In the present invention, for the carbon particles, carbon particles having an average primary particle diameter of 50 to 100 nm (particularly 60 to 85 nm) and carbon particles having an average primary particle diameter of 10 to 40 nm (particularly 20 to 40 nm) are the former 1. It is essential that the latter is contained at a ratio of 0.2 to 6 parts by weight with respect to parts by weight. Preferably, the latter contains 0.3 to 3 parts by weight with respect to 1 part by weight of the former. More preferably, the carbon particles are substantially composed of carbon particles having an average primary particle diameter of 50 to 100 nm and carbon particles having an average primary particle diameter of 10 to 30 nm, and the proportion of the carbon particles is 1 weight by weight. The latter is 0.2 to 6 parts by weight with respect to parts (particularly preferably, the latter is 0.3 to 3 parts by weight with respect to 1 part by weight of the former). When a catalyst layer is formed using such carbon particles, the catalyst layer is densely formed, so that cracks in the produced catalyst layer can be reduced, and crossover of a polymer electrolyte fuel cell, particularly a direct methanol fuel cell (DMFC) ) Methanol crossover can be effectively suppressed. The densely formed particles having the average primary particle diameter of 10 to 40 nm are formed so that the catalyst-carrying carbon particles obtained from the carbon particles having an average primary particle diameter of 50 to 100 nm serve as the core and fill the gap. It is assumed that the catalyst-supporting carbon particles obtained from the carbon particles have a structure arranged.

  In the present invention, the average primary particle diameter of carbon particles is an average when 100 arbitrarily selected carbon particles are observed with a scanning electron microscope (manufactured by JEOL Datum) and the particle diameter of each carbon particle is measured. Value.

  The metal catalyst supported on the carbon particles is not particularly limited as long as it causes a fuel cell reaction in the fuel electrode or air electrode of the fuel cell. For example, platinum, a platinum alloy, a platinum compound, etc. are mentioned. Examples of the platinum alloy include an alloy of platinum and at least one metal selected from the group consisting of ruthenium, palladium, nickel, molybdenum, iridium, iron and the like. Generally, the catalyst material when used as the cathode catalyst layer is platinum, and the metal catalyst when used as the anode catalyst layer is the above-described alloy.

  The supported amount of the metal catalyst is preferably about 10 to 80% by weight, more preferably about 40 to 70% by weight with respect to the catalyst-supported carbon particles.

Catalyst Layer The catalyst layer for a polymer electrolyte fuel cell of the present invention contains the catalyst-supporting carbon particles and a hydrogen ion conductive polymer electrolyte.

  The hydrogen ion conductive polymer electrolyte is not limited as long as it has hydrogen ion conductivity, and a known or commercially available one can be used. Examples thereof include perfluorosulfonic acid-based fluorine ion exchange resins and hydrocarbon-based ion exchange resins. Specific examples of the perfluorosulfonic acid-based fluorine ion exchange resin include, for example, a polymer unit based on tetrafluoroethylene, and a perfluorosulfonic acid-based perion group having at least one functional group selected from the group consisting of a sulfonic acid group and a carboxylic acid group. Examples thereof include copolymers containing polymer units based on fluorovinyl ether. Specific examples of the hydrogen ion conductive polymer electrolyte include, for example, “Nafion” manufactured by DuPont, “Flemion” manufactured by Asahi Glass Co., Ltd., “Aciplex” manufactured by Asahi Kasei Co., Ltd., and Gore manufactured by Gore. For example, “Gore Select”.

  The proportion of the hydrogen ion conductive polymer electrolyte in the catalyst layer is usually about 5 to 60% by weight, preferably about 10 to 50% by weight, based on the total weight of the catalyst layer, from the viewpoint of power generation performance and the like. The remainder is catalyst-supported carbon particles, but may contain various known additives as necessary.

  The average film thickness of the catalyst layer is usually about 10 to 100 μm, preferably about 15 to 50 μm.

Catalyst layer-electrolyte membrane laminate and polymer electrolyte fuel cell The catalyst layer-electrolyte membrane laminate of the present invention comprises a catalyst layer laminated on both sides of the electrolyte membrane, and at least one of the electrolyte membranes. One is the catalyst layer of the present invention.

  Any electrolyte membrane may be used as long as it has hydrogen ion conductivity, and a known or commercially available membrane can be used. For example, “Nafion” membrane manufactured by DuPont, “Flemion” membrane manufactured by Asahi Glass Co., Ltd., “Aciplex” membrane manufactured by Asahi Kasei Co., Ltd. and the like can be mentioned. The thickness of the electrolyte membrane is usually about 20 to 250 μm, preferably about 20 to 80 μm.

  The polymer electrolyte fuel cell of the present invention is formed by sequentially laminating a known or commercially available gas diffusion base material and a separator on both surfaces of the catalyst layer-electrolyte membrane laminate.

  Examples of the gas diffusion base material include carbon paper and carbon cloth.

Transfer sheet for forming a catalyst layer The transfer sheet for forming a catalyst layer of the present invention is formed by laminating the catalyst layer of the present invention on one or both surfaces of a transfer substrate.

  A known or commercially available transfer substrate can be used, for example, polyimide, polyethylene terephthalate, polypalvanic acid aramid, polyamide (nylon), polysulfone, polyethersulfone, polyphenylene sulfide, polyether ether ketone, polyetherimide, Examples thereof include polymer films such as polyarylate and polyethylene naphthalate.

  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.

  Among these, the present invention is preferably a polymer film that is inexpensive and easily available, and specifically, polyethylene terephthalate or the like is more preferable.

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

Method for Producing Catalyst-Supported Carbon Particles The method for producing catalyst-supported carbon particles of the present invention comprises carbon particles having an average primary particle size of 50 to 100 nm (preferably 60 to 85 nm) and an average primary particle size of 10 to 40 nm ( The carbon particles which are preferably 20 to 40 nm) are mixed in advance in a ratio of 0.2 to 6 parts by weight with respect to 1 part by weight of the former, and to the mixed carbon particles obtained in the first step. A second step of supporting the metal catalyst. A preferable mixing ratio is 0.3 to 3 parts by weight of the latter with respect to 1 part by weight of the former. Thereby, the catalyst carrying | support carbon particle which can form the catalyst layer which exhibits the outstanding battery characteristic can be manufactured easily.

  The method for supporting the metal catalyst on the carbon particles may be carried out according to a conventional method. For example, (1) carbon particles obtained in the first step are mixed and dispersed with an aqueous solution in which a desired metal catalyst is dissolved. Examples thereof include a method in which a particle-dispersed aqueous solution is obtained, and (2) a metal catalyst is reduced and deposited on the surface of the carbon particles by mixing a reducing agent with the obtained carbon particle-dispersed aqueous solution.

  Examples of the metal catalyst include the same ones as described above, and the concentration of the metal catalyst in the aqueous solution may be appropriately determined according to the type of the metal catalyst. For example, when the aqueous solution is a hexahydroxo platinum nitric acid aqueous solution, it is usually about 3 to 20% by weight, preferably about 5 to 10% by weight.

  The reducing agent is not particularly limited as long as it is a substance that can reduce and deposit a desired metal catalyst. For example, an aqueous sodium borohydride solution, alcohol having about 1 to 5 carbon atoms, formic acid, hydrazine, hydrogen gas, etc. Can be mentioned. In the present invention, an aqueous sodium borohydride solution and the like are particularly preferred.

  You may add various additives, such as ammonia, as needed.

  Further, if necessary, the obtained catalyst-supporting carbon particles may be washed and filtered during and after the second step.

Method for Producing Catalyst Layer The catalyst layer of the present invention is prepared by, for example, using a catalyst layer forming paste composition containing the catalyst-supporting carbon particles of the present invention, a hydrogen ion conductive polymer electrolyte, and a solvent as a gas diffusion substrate, a transfer substrate. It is obtained by applying to a substrate such as, and drying.

  The catalyst-supporting carbon particles and the hydrogen ion conductive polymer electrolyte are the same as those described above.

  The solvent is not limited, and known or commercially available solvents can be widely used. In the present invention, in particular, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, t-butanol, ethylene glycol are used. Monovalent or polyhydric alcohols having about 1 to 4 carbon atoms such as propylene glycol are preferred. These solvents can be used alone or in combination of two or more.

  The blending ratio of the paste composition is not limited, and may be appropriately determined so as to be the composition ratio of the catalyst layer. For example, the hydrogen ion conductive polymer electrolyte 25 with respect to 100 parts by weight of the catalyst-supporting carbon particles. About 60 parts by weight (preferably about 40-50 parts by weight) and about 500-1000 parts by weight of solvent (preferably about 700-900 parts by weight) may be used.

  The mixing order of the above composition is not particularly limited. For example, the paste composition can be prepared by mixing and dispersing the catalyst-supporting carbon particles, the hydrogen ion conductive polymer electrolyte, and the solvent sequentially or simultaneously. Alternatively, the catalyst-carrying carbon particles can be mixed with water and then mixed with a hydrogen ion conductive polymer electrolyte and a solvent. For mixing, known mixing means can be widely applied. When water is mixed, the amount of water mixed may be about 100 to 500 parts by weight, preferably about 200 to 300 parts by weight per 100 parts by weight of the catalyst-supporting carbon particles.

  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.

  After applying the paste composition, the catalyst layer of the present invention is formed by drying. The drying temperature is not limited, but is usually about 40 to 120 ° C, preferably about 75 to 95 ° C. What is necessary is just to determine a drying time suitably according to drying temperature etc., Usually, it is about 5 minutes-2 hours, Preferably it is about 30 minutes-1 hour.

  The catalyst layer-forming transfer sheet of the present invention is obtained by applying and drying the transfer substrate. Moreover, the catalyst layer-electrolyte membrane laminate and the solid fuel type fuel cell of the present invention can be obtained by transferring the transfer sheet to at least one of the electrolyte membranes according to a conventional method.

  According to the catalyst-carrying carbon particles of the present invention, a catalyst layer with greatly reduced cracks can be produced. Therefore, the problem of crossover due to methanol can be substantially solved in a polymer electrolyte fuel cell, particularly DMFC, and excellent battery performance can be exhibited.

  Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples. In addition, this invention is not limited to a following example.

1. Example 1
(Platinum catalyst supported carbon particles)
1. 0.5 g of carbon particles (manufactured by Tokai Carbon Co., “Seast FY”, average primary particle size: 70 nm) and carbon particles (manufactured by Mitsubishi Chemical Corporation, “Ketjen Black EC”, average primary particle size: 30 nm) 5 g was added to 0.2 L of pure water to prepare a slurry containing carbon particles. While stirring this slurry, 150 g of 5 wt% hexahydroxoplatinum nitric acid aqueous solution and 1 L of pure water were successively added dropwise, and then the powder in the aqueous solution was separated by filtration.

  After the obtained powder was dispersed in 1 L of pure water, 0.01N ammonia solution was added dropwise to adjust the pH of the dispersion to 9. Next, 170 ml of a 3 wt% sodium borohydride aqueous solution was dropped and stirred sufficiently, and then the powder in the dispersion was filtered off.

  The obtained powder was heated at 80 ° C. for 48 hours and dried to produce platinum catalyst-supporting carbon particles of Example 1.

  The amount of platinum supported in the platinum catalyst-supported carbon particles was 60 wt%. The amount of platinum supported was confirmed by ICP emission analysis (manufactured by Shimadzu Corporation, product name “ICPE-9000”).

(Anode catalyst layer transfer sheet)
To 2 g of the platinum catalyst-supported carbon particles produced above, 5 g of 1-butanol, 5 g of t-butanol, 5 g of a hydrogen ion conductive polymer electrolyte-containing solution (20 wt% Nafion solution, manufactured by DuPont) and 5 g of water are added. A paste composition for forming an anode catalyst layer was prepared by stirring and mixing in a disperser.

Next, the prepared paste composition was applied to an OPP film (manufactured by Panac, Trefan, thickness 30 μm) and dried so that the weight of platinum after drying was 3.0 mg / cm ² , thereby transferring the anode catalyst layer. A sheet was produced.

  When the film thickness of the catalyst layer on the obtained transfer sheet layer was measured using a micrometer (WPSM-30 manufactured by SONY), it was 40 μm on average.

2. Comparative Example 1
(Platinum catalyst supported carbon particles)
1. 0.5 g of carbon particles (manufactured by Tokai Carbon Co., “Seast FY”, average primary particle size: 70 nm) and carbon particles (manufactured by Mitsubishi Chemical Corporation, “Ketjen Black EC”, average primary particle size: 30 nm) Platinum of Comparative Example 1 was used in the same manner as in Example 1 except that 2.0 g of carbon particles (Mitsubishi Chemical Corporation, “Ketjen Black EC”, average primary particle size: 30 nm) was used instead of 5 g. Catalyst-supported carbon particles were produced. The amount of platinum supported in the platinum catalyst-supported carbon particles was 60 wt%.

(Anode catalyst layer transfer sheet)
An anode catalyst layer transfer sheet of Comparative Example 1 was produced in the same manner as in Example 1 except that the platinum catalyst-carrying carbon particles of Comparative Example 1 were used. The film thickness of the catalyst layer on the obtained transfer sheet layer was 75 μm on average.

3. Crack Evaluation When the catalyst layer on the catalyst layer transfer sheet of Example 1 was observed using a microscope, almost no cracks were generated, and it was confirmed that the catalyst layer was formed more densely. On the other hand, in the catalyst layer on the catalyst layer transfer sheet of Comparative Example 1, it was confirmed that many cracks occurred and the catalyst layer was not formed densely.

4). Fabrication of fuel cell (cathode catalyst layer transfer sheet)
2 g of platinum catalyst-supported carbon particles (platinum support amount: 45.7 wt%, average primary particle diameter of platinum catalyst-supported carbon particles: 30 nm, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., “TEC10E50E”), 15 g of 1-butanol, t-butanol 2 .5 g, 5 g of a hydrogen ion conductive polymer electrolyte-containing solution (20 wt% Nafion, manufactured by DuPont) and 5 g of water were added, and these were stirred and mixed in a disperser to prepare a paste composition for forming a cathode catalyst layer. .

Next, by applying and drying the prepared paste composition on a polyester film (Toray, “X44”, thickness 25 μm) so that the weight of platinum after drying is 1.0 mg / cm ² , the cathode catalyst layer A transfer sheet was prepared.

(Fuel cell)
The anode catalyst layer transfer sheet produced in Example 1 or Comparative Example 1 cut to 30 × 30 mm on one side of a hydrogen ion conductive polymer electrolyte membrane (manufactured by DuPont, “Nafion 117”, 50 mm × 50 mm) The cathode catalyst layer transfer sheets cut into 30 × 30 mm on the surface are arranged so as to face each other, and are hot-pressed under the conditions of 135 ° C., 2.3 MPa, and 150 seconds, whereby Example 1 and Comparative Example 1 A catalyst layer-electrolyte membrane laminate was produced. Next, the polymer layer fuel cells of Example 1 and Comparative Example 1 were manufactured by incorporating the prepared catalyst layer-electrolyte membrane laminates of Example 1 and Comparative Example 1 into fuel cells, respectively.

5. Current-Voltage Measurement Evaluation Regarding the polymer electrolyte fuel cells of Example 1 and Comparative Example 1, the open circuit voltage (OCV) and the maximum output density (P _max ) were measured. The measurement conditions at this time were a cell temperature of 70 ° C. and 1M methanol.

As a result, the open circuit voltage (OCV) of the fuel cell of Example 1 was 0.70 V, and the maximum output density (P _max ) was 50 mW / cm ² . On the other hand, the open circuit voltage (OCV) of the fuel cell of Comparative Example 1 was 0.63 V, and the maximum output density (P _max ) was 45 mW / cm ² . As described above, in the fuel cell of Example 1, an increase in the OCV value is seen, so that it is understood that the problem of crossover was solved by using the catalyst layer of the present invention.

Claims (5)

  Carbon including carbon particles having an average primary particle diameter of 50 to 100 nm and carbon particles having an average primary particle diameter of 10 to 40 nm in a ratio of 0.2 to 6 parts by weight with respect to 1 part by weight of the former. Catalyst-supported carbon particles, in which a metal catalyst is supported on the particles.   The catalyst-supporting carbon particles according to claim 1, wherein the latter contains 0.3 to 3 parts by weight with respect to 1 part by weight of the former.   A catalyst layer for a polymer electrolyte fuel cell, comprising the catalyst-supported carbon particles according to claim 1 or 2 and a hydrogen ion conductive polymer electrolyte.   A polymer electrolyte fuel cell comprising the catalyst layer according to claim 3. Carbon particles having an average primary particle diameter of 50 to 100 nm and carbon particles having an average primary particle diameter of 10 to 30 nm are mixed at a ratio of 0.2 to 6 parts by weight with respect to 1 part by weight of the former. A first step, and a second step of supporting a metal catalyst on the carbon particles obtained in the first step,
A method for producing catalyst-supported carbon particles comprising: