JP2011240245A - Method for manufacturing of catalyst carrying carrier, and method for manufacturing of electrode catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a catalyst carrying carrier that has a comparatively large particle size of a catalytic metal after being carried and has very few variations of the particle size, and to provide a method for manufacturing an electrode catalyst using the catalyst carrying carrier obtained by the above method, concerning a method of obtaining the catalyst carrying carrier by reducing and carrying the catalytic metal on a conductive carrier surface from a precursor of the catalytic metal.SOLUTION: The method is provided for manufacturing the catalyst carrying carrier 10, which is obtained by input of the conductive carrier 1 into a dispersion solvent, by input of an acid salt 2' and basic salt 3' of the catalytic metal, and by reducing and carrying the catalytic metals 2, 3 on the conductive carrier from the acid salt 2' and basic salt 3', respectively.

Description

  The present invention relates to a method for producing a catalyst-carrying carrier that forms an electrode catalyst for a fuel cell, and a method for producing an electrode catalyst using the catalyst-carrying carrier produced by this method.

  A fuel cell of a polymer electrolyte fuel cell includes a membrane electrode assembly (MEA: an ion permeable electrolyte membrane) and electrode catalyst layers (electrode catalysts) on the anode side and the cathode side that sandwich the electrolyte membrane. Membrane Electrode Assembly), gas diffusion layers (GDL) for promoting gas flow and increasing current collection efficiency are provided outside each electrode catalyst layer, and an electrode body (MEGA: MEA and GDL joined body) is formed. And a fuel cell is formed by arranging a separator outside the gas diffusion layer. Actually, these fuel cells are stacked in the number corresponding to the power generation performance to form a fuel cell stack.

  The above-described conventional method for forming a catalyst layer includes, for example, a catalyst-supported carrier supporting a catalyst, a polymer electrolyte (ionomer), and a dispersion solvent on the surface of a substrate such as a Teflon sheet (Teflon: registered trademark, DuPont). The catalyst layer is formed by applying a catalyst solution (catalyst ink) and then drying the surface of the catalyst solution with a hot plate or the like (wet coating method). In addition, in this coating operation, there are a method of applying by spray, a method of using a doctor blade, and the like.

  By the way, in order to increase the efficiency or activity of the electrocatalyst, which is an important factor for improving the power generation performance of the fuel cell, various techniques for achieving this with an approach from the production method of the electrocatalyst have been disclosed. Examples of the catalyst production method disclosed in Patent Documents 1 and 2 can be given. Here, in the method for producing an electrode catalyst disclosed in Patent Document 1, carbon powder is dispersed in a dispersion solvent, a hexahydroxoplatinum nitrate aqueous solution (platinum acid salt) is dropped and mixed, and platinum is added to the surface of the carbon powder. A catalyst-carrying carrier is obtained by carrying it.

  On the other hand, in the method for producing an electrode catalyst disclosed in Patent Document 2, carbon powder is dispersed in a dispersion solvent, and a tetraamine platinum salt solution, a dinitrodiamine platinum solution (basic platinum salt), or a platinum nitrate solution or chloride. One of a platinic acid solution (above platinum acid salt) is dropped and mixed, and platinum is supported on the surface of the carbon powder to obtain a catalyst-supporting carrier.

  In the above Patent Documents 1 and 2, the catalytic activity is improved by these production methods. However, according to the verification by the present inventors, either an acidic salt or a basic salt is supported by reduction on the carbon powder. Even in this case, it is specified that the variation in the particle size of platinum forming the obtained catalyst-supporting carrier is large, and that the particle size of platinum itself is relatively small with respect to the desired target particle size.

  For example, when the particle size of platinum after reduction loading is small, a measure of increasing the particle size by performing a heat treatment to sinter platinum together is performed, but this causes a large variation in particle size. . Therefore, fine platinum is eluted with respect to platinum having a desired average particle diameter, for example, during an endurance test, which directly leads to a decrease in performance of the electrode catalyst.

  As described above, in the method of controlling the particle size by sintering only by heat treatment, there is a difference in the ease of movement of platinum particles depending on the support site on the surface of the carbon powder, and there are fine platinum particles that do not sinter. In particular, the fine platinum particles are easily eluted during the durability test. Further, for example, if the particle size is controlled only by heat treatment in a nitrogen atmosphere, the carbon may be deteriorated by oxidation or heat of oxygen remaining in the carbon. Development of a particle size control method that replaces the method of performing diameter control is desired.

JP 2004-349113 A JP 2008-41482 A

  The present invention has been made in view of the above problems, and relates to a method for obtaining a catalyst-supported support by reducing and supporting a catalyst metal from a catalyst metal precursor on the surface of a conductive support. It is an object of the present invention to provide a method for producing a catalyst-supporting carrier having a relatively large particle size variation and a method for producing an electrode catalyst using the catalyst-supporting carrier obtained by this method.

  In order to achieve the above object, the method for producing a catalyst-supporting carrier according to the present invention comprises introducing a conductive carrier into a dispersion solvent, introducing an acidic salt and a basic salt of a catalytic metal, and forming an acidic salt and a basic salt. The catalyst metal is reduced and supported on a conductive support from each.

  The method for producing a catalyst-supporting carrier according to the present invention comprises introducing a conductive carrier and two kinds of catalyst metal precursors, ie, an acidic salt and a basic salt of a catalytic metal, into the dispersion solvent, thereby allowing the acidic salt and the basic salt to be introduced. By neutralizing the catalyst and precipitating the catalyst metal from both precursors, the catalyst metal having a relatively large particle size can be supported on the conductive support surface at the stage of neutralization and reduction precipitation. .

  In addition, the particle size of the catalyst metal can be further grown by performing a heat treatment after the reduction deposition of the catalyst metal. However, unlike the conventional manufacturing method described above, the particle size of the catalyst metal after loading is not controlled only by this heat treatment, and a catalyst metal having a certain size particle size is already loaded at the stage of heat treatment. Therefore, the problem that the conductive carrier, which has been a problem in the case of only heat treatment, can be deteriorated cannot occur.

  Further, according to the verification by the present inventors, in addition to being able to carry a catalyst metal having a desired particle size (average particle size) on the surface of the conductive support, variation in the particle size of the catalyst metal is reduced. This can lead to the elimination of catalytic metals that are too small in particle size and poor in durability.

  Here, the timing of adding the acidic salt and basic salt of the catalyst metal to the dispersion solvent may be a method in which both are added separately or a method in which both are added simultaneously.

  For example, in the case where the acidic salt and basic salt of the catalytic metal are separately added, and the initial precursor of the acidic salt is first introduced, the acidic salt of the catalytic metal is not reduced and precipitated at this stage. Therefore, it is only physically adsorbed on the surface of the conductive support in the state of this precursor.

  Next, by introducing a basic salt of the catalytic metal into the solvent, the acidic salt and the basic salt are neutralized, both catalytic metals are reduced and precipitated, and both of the catalytic metals that are reduced and precipitated are united. Thus, it is carried at a plurality of locations on the surface of the conductive carrier. That is, at this stage, the catalyst metal supported at an arbitrary location on the surface of the conductive support is already integrated into a certain size.

  In this reduction, reduction may be promoted by applying a method of introducing a reducing agent into the dispersion solvent, a method of performing heat treatment, or a combination thereof.

  According to the verification by the present inventors, an electrode catalyst was finally produced using the catalyst-supported carrier produced by the above production method, and the durability performance evaluation of the fuel cell having this electrode catalyst was performed. It has been found that the catalyst metal surface area retention rate after the durability test is improved by about 30 to 40% as compared with the conventional catalyst-supported carrier.

  Using the catalyst-carrying carrier obtained by the above method, the catalyst-carrying carrier and the polymer electrolyte are put into a dispersion solvent and stirred to produce a catalyst solution (catalyst ink).

  Then, the produced catalyst solution is stretched in layers with a coating blade, for example, on a substrate such as an electrolyte membrane or a gas diffusion layer to form a coating film, which is dried in a hot air drying furnace or the like, so that the anode side Then, a catalyst layer (catalyst electrode) on the cathode side is formed.

  As already described, a catalyst ink is produced using the catalyst-supported carrier obtained by the production method of the present invention, and a fuel cell having an electrode catalyst obtained by using the catalyst-supported carrier is an electrode produced by a conventional production method. The durability is superior to that of a fuel cell having a catalyst. This is because the catalyst that contributes to power generation has a desired particle size (average particle size), the variation in the particle size is small, and the conductive support deteriorates at the stage of particle size control. It depends on what is not.

  The fuel cell having the electrode catalyst obtained by the method for producing a conductive carrier according to the present invention and the method for producing an electrode catalyst using the conductive carrier obtained by this method has the effects as described above. Therefore, its production has been increasing recently, and it is suitable for fuel cells for electric vehicles and hybrid vehicles that require even higher performance for in-vehicle devices.

  As can be understood from the above description, according to the method for producing the catalyst-supported carrier of the present invention and the method for producing an electrode catalyst using the catalyst-supported carrier obtained by this method, the conductive solvent is dispersed in the dispersion solvent. By introducing the support and two types of catalyst metal precursors, an acidic salt and a basic salt of the catalytic metal, the acidic salt and the basic salt are neutralized to precipitate the catalytic metal from both precursors. Catalytic metal having a relatively large particle size at the stage of neutralization and reduction precipitation and with little variation in particle size can be supported on the surface of the conductive support, contributing to improvement in durability of the catalyst and the fuel cell. It will be a thing.

(A) is the figure explaining the manufacturing method of the catalyst carrying | support carrier of this invention, Comprising: It is the schematic diagram explaining the state which introduce | transduced the electroconductive support | carrier in the dispersion | distribution solvent, and has injected the acidic salt of the catalyst metal. Yes, (b) is a schematic diagram showing the intermediate produced at this stage. FIG. 1B is a schematic diagram illustrating a state in which a basic salt of a catalyst metal is introduced into a dispersion solvent following FIG. 1A, and (b) is a schematic diagram illustrating a manufactured catalyst-supporting carrier. It is the figure which showed the experimental result which measured the endurance cycle in each endurance test of each fuel cell of an example and a comparative example, and the platinum surface area maintenance rate in each endurance cycle.

Hereinafter, the method for producing the catalyst-supporting carrier of the present invention will be outlined with reference to FIGS.
FIG. 1a and FIG. 2a are schematic views illustrating the method for producing the catalyst-supporting carrier of the present invention in order, and FIG. 1b and FIG. 2b are schematic views showing intermediates produced at the stage of FIG. It is the schematic diagram which showed the catalyst carrying | support support manufactured at the stage of 2a.

  First, as shown in FIG. 1 a, the conductive carrier 1 and the acid salt 2 ′, which is a catalyst metal precursor, are introduced into the dispersion solvent accommodated in the container Y and mixed sufficiently.

  By this mixing, as shown in FIG. 1 b, an intermediate 10 ′ formed by physical adsorption of the acidic salt 2 ′ as it is on the surface of the conductive carrier 1 is generated in the dispersion solvent.

  Next, as shown in FIG. 2a, the basic salt 3 ', which is a precursor of the catalyst metal, is introduced into the dispersion solvent and sufficiently mixed.

  In the dispersion solvent, as shown in FIG. 2b, the acidic salt 2 ′ and the basic salt 3 ′ are neutralized, and both catalytic metals 2 and 3 are reduced and precipitated, and these are integrated into the overall dimensions (particle size). The large catalyst metal 4 is formed and supported on the surface of the conductive support 1 to produce the catalyst support 10. Note that reduction may be promoted by heat treatment or addition of a reducing agent for a solution obtained by adding and thoroughly mixing the basic salt 3 '.

  Further, by this heat treatment, integration of the reduced and precipitated catalyst metals 2 and 3 is promoted, final particle size control (particle size adjustment) of the formed catalyst metal 4, and a relatively small diameter. The particle size growth of the catalyst metal can also be performed.

  The produced catalyst-supporting carrier 10 is obtained by simultaneously reducing the catalyst metal constituting both salts by neutralization of the acid salt 2 ′ and the basic salt 3 ′ and supporting it on the surface of the conductive carrier. A catalyst metal having a large particle diameter (average particle diameter) can be supported. Furthermore, by supporting the catalyst metal by this method, the variation in the particle size of the catalyst metal can be reduced, and from these, it is possible to eliminate the production of the catalyst metal having a too small particle size and poor durability. .

  Here, examples of the conductive carrier 1 include carbon materials such as carbon black, carbon nanotubes, and carbon nanofibers, as well as carbon compounds typified by silicon carbide, and the like. As the catalytic metal for forming ', basic salt 3', for example, any one of platinum, platinum alloy, palladium, rhodium, gold, silver, osmium, iridium and the like can be used, preferably platinum. Alternatively, a platinum alloy is preferably used. Further, examples of the platinum alloy include platinum, aluminum, chromium, manganese, iron, cobalt, nickel, gallium, zirconium, molybdenum, ruthenium, rhodium, palladium, vanadium, tungsten, rhenium, osmium, iridium, titanium, and lead. An alloy with at least one of them can be mentioned.

  Furthermore, as a dispersion solvent, in addition to water, alcohols such as methanol, ethanol, 1-propanol, 2-propanol, ethylene glycol, diethylene glycol, acetone, methyl ethyl ketone, dimethylformamide, dimethylimidazolidinone, dimethyl sulfoxide, dimethylacetamide, Examples include N-methylpyrrolidone, propylene carbonate, esters such as ethyl acetate and butyl acetate, and various aromatic or halogen solvents, and these may be used alone or as a mixture. it can.

  The produced catalyst-supporting carrier 10 is put into a dispersion solvent, and further, a polymer electrolyte is put into it, and stirred using an ultrasonic homogenizer, a bead mill, a ball mill, etc., thereby a catalyst solution (catalyst ink). Is generated.

  As this polymer electrolyte, an ion exchange resin having a skeleton of an organic fluorine-containing polymer, which is a proton conductive polymer, for example, perfluorocarbon sulfonic acid resin, sulfonated polyether ketone, sulfonated polyethersulfone, sulfonated Sulfonated plastic electrolytes such as polyetherethersulfone, sulfonated polysulfone, sulfonated polysulfide, sulfonated polyphenylene, sulfoalkylated polyetheretherketone, sulfoalkylated polyethersulfone, sulfoalkylated polyetherethersulfone, sulfoalkylated Examples thereof include sulfoalkylated plastic electrolytes such as polysulfone, sulfoalkylated polysulfide, and sulfoalkylated polyphenylene. As commercially available materials, Nafion (registered trademark, manufactured by DuPont), Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.), and the like can be used.

  The produced catalyst solution is applied to any one of an electrolyte membrane, a gas diffusion layer, and a support film, which is a base material, and is dried on a hot air, hot pressed, etc., to form a catalyst layer (electrode catalyst) on the surface of the base material. ) Is formed. Here, this electrolyte membrane is, for example, a non-fluorine ion exchange membrane having a sulfonic acid group or a carbonyl group, a substituted phenylene oxide, a sulfonated polyaryletherketone, a sulfonated polyarylethersulfone, a sulfonated phenylenesulfide or the like. It is formed from a fluorine-based polymer or the like. The gas diffusion layer is formed from a fired body made of polyacrylonitrile, a fired body made of pitch, carbon materials such as graphite and expanded graphite, nanocarbon materials thereof, stainless steel, molybdenum, titanium, and the like. Furthermore, the support film is a polyethylene film, a polypropylene film, a polytetrafluoroethylene film, an ethylene / tetrafluoroethylene copolymer film, a tetrafluoroethylene / perfluoro (alkyl vinyl ether) copolymer film, a polyvinylidene fluoride film, a polyimide film. , Polyamide film, polyethylene terephthalate film, and the like. Two or more sheets made of these materials may be laminated to form a base material. A commercially available material such as a Teflon sheet (Teflon: registered trademark, DuPont) may also be used.

[Durability experiment and measurement of average particle size and variation of platinum and their results]
The present inventors produced a catalyst solution using the catalyst-supported support obtained by the production method of the present invention, and a fuel cell (Example) comprising a catalyst layer formed using the catalyst solution, A fuel cell (Comparative Examples 1 and 2) having a catalyst layer manufactured by a conventional manufacturing method was prototyped, and an experiment was conducted to measure the platinum surface area maintenance rate after the durability test. In addition, each average particle diameter and its variation were measured in Examples and Comparative Examples 1 and 2. X-ray small angle scattering was used to measure the platinum particle size and its variation.

(Method for producing catalyst-supporting carrier of Example)
The specific content of obtaining the catalyst-supported carrier by the production method of the present invention will be explained. A commercially available conductive carrier, Ketjen EC (manufactured by Ketjen Black International) (5.0 g) was added to pure 1.2 L (liter). A dispersion of hexahydroxoplatinum nitrate (platinum salt, catalytic metal salt) containing 2.5 g of platinum and tetraammineplatinum hydroxide was added dropwise to this dispersion and stirred well. Formic acid was added thereto, reduction was performed at 100 ° C., the dispersion after reduction was filtered, and the obtained powder was vacuum-dried at 100 ° C. for 10 hours. And the powder after drying was heat-processed at 300 degreeC by nitrogen atmosphere for 1 hour. The platinum carrying density of the catalyst carrying carrier powder obtained by this method was 50% by mass of platinum as a result of waste liquid analysis.

(Method for Producing Catalyst-Supported Carrier of Comparative Example 1)
On the other hand, regarding the production of the catalyst-supported carrier of Comparative Example 1, 5.0 g of Ketjen EC was added to 1.2 L (liter) of pure and dispersed, and hexahydroxo platinum nitric acid (platinum salt, containing 5.0 g of platinum) was dispersed in this dispersion. Catalyst metal salt) solution was added dropwise and stirred thoroughly. Then, about 100 mL of 0.1N ammonia is added to this solution, a hydroxide is formed with a solution pH of about 10, and precipitated on the carbon surface. Further, using ethanol, platinum is removed from hexahydroxoplatinum nitrate at 90 ° C. The dispersion was filtered after reduction, and the obtained powder was vacuum-dried at 100 ° C. for 10 hours. Then, the dried powder was heat treated at 300 ° C. for 1 hour in a nitrogen atmosphere to obtain a catalyst-supporting carrier. The platinum carrying density of the catalyst carrying carrier powder obtained by this method was 50% by mass of platinum as a result of the waste liquid analysis as in the examples.

(Method for producing catalyst-supporting carrier of Comparative Example 2)
On the other hand, regarding the production of the catalyst-supporting carrier of Comparative Example 2, Ketjen EC 5.0 g was added to 1.2 L (liter) of pure and dispersed, and a solution of tetraammine platinum hydroxide containing 5.0 g of platinum was added to this dispersion. The solution was added dropwise and stirred thoroughly. Formic acid was added thereto, reduction was performed at 100 ° C., the dispersion after reduction was filtered, and the obtained powder was vacuum-dried at 100 ° C. for 10 hours. And the powder after drying was heat-processed at 300 degreeC by nitrogen atmosphere for 1 hour. The platinum carrying density of the catalyst carrying carrier powder obtained by this method was 50% by mass of platinum as a result of waste liquid analysis.
Then, the above solution was sufficiently stirred and subjected to dispersion treatment by ultrasonic irradiation, bead mill, etc., and catalyst solutions (catalyst inks) of Examples and Comparative Examples 1 and 2 were generated.

  Each produced catalyst ink was quantitatively collected with a microsyringe, applied to a glassy carbon electrode, and the electrode after application was dried to obtain a catalyst-modified electrode.

  In order to evaluate the durability of the fuel cell catalyst, 0.1 M perchloric acid was used as the electrolyte, a platinum mesh electrode was used as the counter electrode, and a reversible hydrogen electrode was used as the reference electrode. Durability evaluation was performed based on the maintenance rate of the amount of hydrogen adsorbed on platinum, and the durability condition at this time was 30000 cycles at a sweep rate of 0.3 V / s with a cycle of 0.5 to 1.1 V under nitrogen atmosphere saturation. I did it. The result of the experiment is shown in FIG. 3, and the measurement results of the average particle diameter and the variation are shown in Table 1.

As a result of the experiment, the platinum surface area retention rate at the time of 30000 cycles is 58.66% in Comparative Example 1 and 54.68% in Comparative Example 2, whereas it is 75.11% in Example. It has been demonstrated that the platinum surface area maintenance ratio is improved by about 30 to 40% as compared to the example.

  Also, from Table 1, the average particle diameter of the catalyst platinum of the example is relatively larger than that of Comparative Examples 1 and 2, and is controlled to the desired 3.3 nm. Further, the variation is reduced, for example, in the range of 3.1 to 3.5 nm with respect to 2.4 to 3.8 nm of Comparative Example 1, and 3.1 nm which is close to the desired diameter even with a particularly small particle size. Is controlled. As described above, since the average particle diameter of the catalyst platinum is relatively large and is controlled to a desired diameter, and even if it is the minimum diameter, the particle diameter is not too small. This leads to the result of the durability test described above.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and there are design changes and the like without departing from the gist of the present invention. They are also included in the present invention.

DESCRIPTION OF SYMBOLS 1 ... Electroconductive support | carrier, 2, 3, 4 ... Catalytic metal, 2 '... Acidic salt of catalytic metal, 3' ... Basic salt of catalytic metal, 10 ... Catalyst supporting carrier, 10 '... Intermediate of catalyst supporting carrier

Claims (4)

  A method for producing a catalyst-carrying carrier in which a conductive carrier is introduced into a dispersion solvent, an acidic salt and a basic salt of the catalytic metal are introduced, and the catalytic metal is reduced and supported on the conductive carrier from each of the acidic salt and the basic salt .   The method for producing a catalyst-supporting carrier according to claim 1, wherein the acidic salt and the basic salt of the catalyst metal are separately charged into the dispersion solvent.   The method for producing a catalyst-supporting carrier according to claim 1, wherein the catalyst metal acidic salt and the basic salt are simultaneously charged into the dispersion solvent.   A method for producing an electrode catalyst, wherein the catalyst-supported carrier and the polymer electrolyte produced by the production method according to any one of claims 1 to 3 are charged into a dispersion solvent and stirred to produce a catalyst solution.

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