JP2011200834A - Method for manufacturing conductive carrier, catalyst carrying carrier and electrode catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst carrying carrier and a method for manufacturing the same capable of enhancing the activity and durability of a catalytic metal, and to provide an electrode catalyst and a method for manufacturing the same.SOLUTION: There is provided a method for manufacturing a conductive carrier where a metal precursor 2 is supported on the surface of a carbon-based conductive carrier 1, the metal precursor 2 is reduced to form a metal by simultaneously performing reduction treatment and heat treatment, metal carbide particles 2A are formed by carbonizing the metal, and the metal carbide particles 2A are modified on the surface of the conductive carrier 1.

Description

  The present invention relates to a method for producing a conductive carrier for forming an electrode catalyst for a fuel cell, a method for producing a catalyst carrier formed from the conductive carrier, and a method for producing an electrode catalyst formed from the catalyst carrier. Is.

  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, as one of the important elements for improving the power generation performance of the fuel cell, there is an improvement in the efficiency or activity of the electrode catalyst. At the same time, suppression of oxidative degradation of the conductive carrier during the power generation process of the fuel cell also leads to improvement in durability of the electrode catalyst, so this countermeasure against oxidative degradation is an important factor.

  Here, Patent Document 1 discloses a fuel cell having a catalyst-supported carrier whose surface is treated with metal such as tungsten, titanium, or molybdenum in order to prevent corrosion of the carbon catalyst carrier. This metal surface treatment method is performed by first reducing a metal precursor such as molybdenum and then heat-treating it.

  However, according to the present inventors, the metal carbide layer formed on the surface of the carbon support by the above-described metal surface treatment method is difficult to form uniformly on the surface of the carbon support. It has been concluded that the effect of interaction with the catalytic metal is not expected to be large, and that it is difficult to effectively improve the activity of the electrode catalyst.

JP 2008-503869 A

  The present invention has been made in view of the above-described problems, and in addition to suppressing the oxidative deterioration of the catalyst-supporting support during the power generation process of the fuel cell, the conductivity that can improve the activity and durability of the catalyst metal. It is an object to provide a method for producing a conductive carrier, a method for producing a catalyst-carrying carrier, and a method for producing an electrode catalyst.

  In order to achieve the above object, the method for producing a conductive support according to the present invention reduces the metal precursor by supporting a metal precursor on the surface of a carbon-based conductive support and simultaneously performing a reduction treatment and a heat treatment. Forming a metal, carbonizing the metal to form metal carbide particles, and modifying the metal carbide particles on the surface of the conductive support.

  In the method for producing a conductive carrier according to the present invention, a metal precursor is supported on the surface of a conductive carrier such as carbon particles, and then heat treatment is performed in a reducing atmosphere, that is, the reduction treatment and the heat treatment are performed simultaneously. In this way, the metal carbide particles can be uniformly formed on the surface of the conductive carrier. Depending on the amount of the metal precursor used, the metal carbide particles formed on the surface of the conductive support may be modified in a form in which the metal carbide particles are uniformly dispersed on the support surface or the metal carbide particles are densely arranged on the support surface. There are modified forms that are layered.

  The metal precursor is a reducible compound such as a metal carbide salt or metal oxide, and any one of tungsten, molybdenum, and titanium is used as the metal material forming the metal precursor. Is carbonized (solid solution) to form metal carbides such as tungsten carbide (WCx), molybdenum carbide (MoCx), titanium carbide (TiCx) and the like. Among these, tungsten carbide having a high interaction with a conductive carrier made of platinum or carbon is preferable.

  Here, “modification” in “the metal carbide particles are modified on the surface of the conductive carrier” means chemical bonding or adhesion.

  A conventional catalyst support, that is, a catalyst support in which a catalyst metal such as platinum is supported on the surface of a carbon-based conductive support is expected for the catalytic activity of the catalyst metal itself. However, there is almost no electron transfer (also referred to as interaction) between the conductive support of the carbon material and the platinum catalyst, and it is not possible to expect an activity effect higher than the catalytic activity effect of the platinum catalyst itself. On the other hand, in the catalyst-supported carrier comprising the conductive carrier obtained by the production method of the present invention, in addition to the catalytic activity of the catalyst metal itself, the interaction between the catalyst metal and the metal carbide particles causes The activity can be further increased. In addition, since the metal carbide particles are supported as uniformly as possible on the surface of the conductive support, the catalytic activity effect is extremely high.

  Further, the durability of the catalyst is improved by the above-described interaction, and furthermore, the metal carbide particles are supported as uniformly as possible on the surface of the conductive support, which leads to the suppression of the oxidative deterioration of the conductive support.

  Further, according to the verification by the present inventors and empirical rules, the temperature during the heat treatment performed simultaneously with the reduction of the metal precursor is preferably 700 ° C. or higher. This is a temperature condition for realizing both the reduction reaction and the carbonization reaction. When the temperature during the heat treatment is lower than 700 ° C., the reduction reaction is performed, but the sufficient carbonization reaction is not performed.

  Further, according to the verification by the present inventors, an electrode catalyst is finally produced using the catalyst-supported carrier produced by the above production method, and the power generation performance (IV) of the fuel cell having this electrode catalyst is obtained. (Characteristics) has been verified, and it has been proved that the power generation performance is higher than the power generation performance of the fuel cell having the electrode catalyst obtained by the conventional manufacturing method.

  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 a layer shape with a coating blade, for example, on a substrate such as an electrolyte membrane or a gas diffusion layer to form a coating film, and is heat-treated and dried in a hot air drying furnace or the like. Then, catalyst layers (electrode catalysts) on the anode side and the cathode side are formed.

As described above, a fuel cell having an electrode catalyst produced by using a catalyst-supported carrier obtained by the production method of the present invention and having an electrode catalyst produced by using the catalyst-supported carrier is an electrode produced by a conventional production method. Its power generation performance is higher than that of a fuel cell having a catalyst. This indicates that the activity of the catalyst contributing to power generation is enhanced.
A fuel cell having an electrode catalyst made of a catalyst-supported carrier obtained by the production method of the present invention has excellent power generation performance and high durability, and its production has recently been expanded. It is suitable for fuel cells for electric vehicles and hybrid vehicles that require high performance and high durability.

  As can be understood from the above description, according to the conductive carrier obtained by the production method of the present invention and the catalyst-carrying carrier obtained by using this conductive carrier, metal carbide particles are formed on the surface of the conductive carrier. Since it is a catalyst-carrying support that is modified as uniformly as possible and has catalytic metal particles supported on this surface, the catalytic activity can be further enhanced by the interaction between the catalytic metal and the metal carbide particles. The fuel cell is excellent in power generation performance.

(A) is the schematic diagram explaining the manufacturing method of the electroconductive support | carrier of this invention, (b), (c) is a schematic diagram which shows the electroconductive support | carrier with which the metal precursor was carry | supported together. (A) is the schematic diagram explaining the manufacturing method of a conductive support following FIG. 1a, (b) is a schematic diagram which shows the conductive support by which the metal carbide particle was modified. (A) is the schematic diagram explaining the manufacturing method of the catalyst support | carrier of this invention using the manufactured electroconductive support | carrier, (b) is a schematic diagram which shows the catalyst support | carrier with which the catalyst metal was carry | supported. .

  Hereinafter, with reference to FIGS. 1-3, the manufacturing method of the electroconductive support | carrier of this invention and the manufacturing method of a catalyst support | carrier are outlined.

  FIG. 1a is a schematic diagram illustrating a method for producing a conductive carrier according to the present invention. FIGS. 1b and 1c are schematic diagrams each showing a conductive carrier carrying a metal precursor. FIG. 2a is a schematic diagram illustrating a method for producing a conductive carrier following FIG. 1a, and FIG. 2b is a schematic diagram illustrating the conductive carrier in which metal carbide particles are modified.

  First, a carbon material conductive carrier 1 (carbon carrier) and a water-soluble ammonium tungstate 2 'are introduced into a dispersion solvent W made of water or the like contained in a container Y, and dissolved by sufficiently stirring. . Here, examples of the conductive carrier 1 include carbon compounds such as carbon carbide, in addition to carbon materials such as carbon black, carbon nanotubes, and carbon nanofibers.

Next, the conductive support 10 in which the tungsten precursor 2 shown in FIG. 1 b is supported on the surface of the carbon support 1 is obtained by heat-treating the solution and evaporating the dispersion solvent.
Further, by increasing the input amount of ammonium tungstate 2 ′, it is possible to obtain a conductive carrier 10A as shown in FIG. 1c in which the tungsten precursor 2 is densely supported to form a layer.

  The above-mentioned solution is heated and dried to evaporate and remove the solvent, whereby the conductive carrier 10 powder is obtained.

Next, as shown in FIG. 2, the conductive carrier 10 is accommodated in a heating furnace R, and H ₂ gas or CO gas, which is a reducing gas, is supplied to the furnace through a piping system K communicating with the heating furnace R. At the same time, heat treatment is performed in the furnace R with a high temperature atmosphere. The concentration of H ₂ gas and CO gas can be set arbitrarily. However, when adjusting the concentration balance of the reducing gas, an inert gas such as nitrogen gas, argon gas or helium gas can be further provided in the furnace. Good.

  Conductivity obtained by modifying tungsten carbide particles 2A (WCx particles) formed by reduction and carbonization (or solid solution) of tungsten precursor 2 on the surface of carbon support 1 by the heat treatment as shown in FIG. 2b. A carrier 20 is obtained. In addition, the temperature at the time of the heat treatment is a temperature of 700 ° C. or higher, which is a temperature that enables both a reduction reaction and a carbonization reaction of the tungsten precursor.

  The tungsten carbide particles 2A can be uniformly modified on the surface of the carbon support 1 by the above method in which the tungsten precursor is reduced and carbonized simultaneously.

  As the metal carbide for modifying the carbon support 1, molybdenum and titanium can be used in addition to tungsten. When these are used, the molybdenum carbide particles and the titanium carbide particles modify the surface of the carbon support.

  When the conductive carrier 20 modified with tungsten carbide particles is obtained, as shown in FIG. 3a, the conductive carrier 20 and the catalytic metal salt 3 ′ are put into a dispersion solvent W such as water and mixed thoroughly. By stirring, the catalyst metal 3 from the catalyst metal salt 3 ′ is reduced and supported on the surface of the tungsten carbide particles 2A, and further on the surface of the carbon carrier 1, whereby a catalyst-supported carrier 30 as shown in FIG. 3b is obtained.

  Here, as the catalyst metal forming the catalyst metal salt 3 ′, for example, any one of platinum, platinum alloy, palladium, rhodium, gold, silver, osmium, iridium and the like can be used, preferably Platinum or 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.

  Further, as the dispersion solvent W, 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 , N-methylpyrrolidone, propylene carbonate, esters such as ethyl acetate and butyl acetate, various aromatic solvents or halogen solvents, and these may be used alone or as a mixture. Can do.

  In the catalyst carrier 30 shown in FIG. 3b, in addition to the catalytic activity of the catalytic metal 3 itself such as platinum, the interaction between the catalytic metal 3 and the tungsten carbide particles 2A can further enhance the activity of the catalytic metal. It will be.

  The produced catalyst-supporting carrier 30 is put into a dispersion solvent, and a polymer electrolyte is further added, followed by stirring using an ultrasonic homogenizer, a bead mill, a ball mill, etc., thereby producing a catalyst solution (catalyst ink). Is done.

  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. In addition, as a commercially available material, it forms from a Teflon sheet (Teflon: a registered trademark, DuPont) etc.

[Power generation performance experiment and results]
The inventors of the present invention have produced a catalyst solution using the catalyst-supported carrier obtained by the production method of the present invention, and a fuel cell comprising an electrode catalyst (catalyst layer) formed using the catalyst solution (implementation) A fuel cell (Comparative Examples 1 and 2) having an electrode catalyst manufactured by Examples 1 and 2 and a conventional manufacturing method was prototyped, and the power generation performance of both was compared.

[Production Method of Example 1]
Commercially available conductive carrier Ketjen EC (manufactured by Ketjen Black International) (5.0 g) is added to 1.2 L (liter) of pure water and dispersed. It was. After stirring at room temperature for 1 hour, the solution was heated to remove pure water by evaporation. Next, the powder obtained by drying at 100 ° C. is accommodated in a quartz reaction vessel, and the temperature is raised to 700 ° C. while supplying 4% H ₂ gas, which is a reducing gas, into the vessel. Left behind for hours. Thereafter, the gas supply into the container was switched to nitrogen gas to lower the temperature, and the heat treatment was completed.

  The carbon powder obtained by the above method and having a surface modified with tungsten carbide particles was added to 1.2 L of pure water and dispersed. To this dispersion, a solution of hexahydroxoplatinum nitrate (platinum salt, catalytic metal salt) containing 5.0 g of platinum was added dropwise and stirred sufficiently. 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. 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.

[Production Method of Example 2]
The manufacturing method of Example 2 is basically the same as that of Example 1, but differs from Example 1 (700 ° C) in that the temperature condition during the heat treatment is 800 ° C. Also in Example 2, as in Example 1, the platinum support density of the obtained catalyst support carrier powder was 50% by mass of platinum as a result of waste liquid analysis.

[Production Method of Comparative Example 1]
Ketjen EC 5.0 g was added to 1.2 L of pure water and dispersed, and a solution of hexahydroxoplatinic nitric acid containing 5.0 g of platinum was dropped into this dispersion and stirred sufficiently. 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. 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 as in Examples 1 and 2.

[Production Method of Comparative Example 2]
Ketjen EC 5.0 g was added and dispersed in 1.2 L (liter) of pure water, and ammonium tungstate was added thereto and stirred to dissolve in pure water. After stirring at room temperature for 1 hour, a sodium borohydride solution dissolved in pure water was added to perform a reduction reaction of tungsten. Next, the solution was stirred for 30 minutes at room temperature, and filtered and washed with pure water. Next, the powder obtained by drying at 100 ° C. was placed in a quartz reaction vessel, heated to 800 ° C. while providing N ₂ gas in the vessel, and left at the same temperature for 2 hours. Thereafter, the gas supply into the container was switched to nitrogen gas to lower the temperature, and the heat treatment was completed. That is, in Comparative Example 2, the reduction process and the carbonization process are not performed simultaneously in the manufacturing process.

  The carbon powder obtained by the above method, the surface of which was modified with tungsten carbide particles with insufficient carbonization, was added to 1.2 L of pure water and dispersed. To this dispersion, a solution of hexahydroxoplatinum nitrate (platinum salt, catalytic metal salt) containing 5.0 g of platinum was added dropwise and stirred sufficiently. 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. 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.

[Production method of electrode catalyst (catalyst layer)]
Using the catalyst-supported carriers of Examples 1 and 2 and Comparative Examples 1 and 2 described above, an electrode catalyst was produced in the same manner. Specifically, the catalyst carrier thus prepared was added to distilled water, ethanol, ethylene glycol, propylene glycol, or the like was further added, and Nafion, which is a polymer electrolyte, was further added. Then, the above solution was sufficiently stirred and subjected to dispersion treatment by ultrasonic irradiation, bead milling, etc. to produce catalyst solutions (catalyst inks) of Examples 1 and 2 and Comparative Examples 1 and 2, respectively.

  The produced catalyst ink is coated on a substrate such as Teflon and dried to obtain a catalyst layer, which is hot-pressed by hot pressing on both the anode and cathode of the electrolyte membrane (Nafion), and the Teflon is peeled off to form a membrane. An electrode assembly was obtained, and fuel cell cells of both the examples and the comparative examples were produced using this.

[Experimental result]
In order to compare the catalyst performance at the initial stage, the initial voltage measurement was performed as follows. First, the cell temperature of the fuel cell is set to 80 ° C., humidified air that has been passed through the heating bubbler to the cathode side electrode is provided at RH 40%, stoichiometric ratio 7.5, and a heating bubbler is provided to the anode side electrode. Passed humidified hydrogen was provided at RH 40% and stoichiometric ratio 7.5, and current-voltage characteristics (IV characteristics) were measured using an electronic load. The platinum amount of each electrode is set to 0.3 mg / cm ² .

As a result of the experiment, the power generation performances of the fuel cells of Comparative Examples 1 and 2 were 0.780 (V / (0.2 A / cm ² )) and 0.788 (V / (0.2 A / cm ² )), respectively. In contrast, the power generation performances of Examples 1 and 2 were 0.793 (V / (0.2 A / cm ² )) and 0.802 (V / (0.2 A / cm ² )), respectively. An improvement in power generation performance of about 3% was confirmed. In addition, when both Comparative Examples 1 and 2 are compared, in Comparative Example 2, the carbonization of the metal precursor is insufficient, but the activity higher than that of Comparative Example 1 is obtained because the metal carbide particles are formed. Yes.
From this experimental result, in the production of the conductive support, the metal carbide particles are uniformly modified on the surface of the carbon support, etc., by modifying the metal carbide particles by simultaneously performing the reduction reaction and the carbonization reaction of the metal precursor, It was demonstrated that a catalyst-supporting carrier having high catalytic activity was obtained by supporting a catalyst metal on the surface of the metal carbide particles, which led to an improvement in power generation performance of the fuel cell.

  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 ... Conductive support | carrier (carbon support | carrier), 2 ... Tungsten precursor, 2 '... Ammonium tungstate, 2A ... Tungsten carbide particle, 3 ... Catalyst metal, 3' ... Catalyst metal salt, 10 ... Tungsten precursor was carry | supported Conductive carrier, 20 ... conductive carrier modified with tungsten carbide particles, 30 ... catalyst-supported carrier

Claims (6)

  By carrying a metal precursor on the surface of a carbon-based conductive support and simultaneously performing a reduction treatment and a heat treatment, the metal precursor is reduced to form a metal, and the metal is carbonized to form metal carbide particles. A method for producing a conductive carrier, wherein the metal carbide particles are modified on the surface of the conductive carrier.   The method for producing a conductive carrier according to claim 1, wherein the metal is made of any one of tungsten, molybdenum, and titanium, and the metal carbide is made of any one of tungsten carbide, molybdenum carbide, and titanium carbide.   The manufacturing method of the electroconductive support | carrier of Claim 1 or 2 with which the said heat processing is performed in 700 degreeC or more high temperature atmosphere. The reduction treatment is is to provide any kind of H ₂ gas or CO gas to the conductive support, method for producing a conductive carrier according to any one of claims 1 to 3.   The manufacturing method of the catalyst support | carrier which makes a metal carbide particle carry | support a catalyst metal among the electroconductive support | carriers obtained with the manufacturing method in any one of Claims 1-4. A catalyst solution is produced from the catalyst-supported carrier obtained by the production method according to claim 5, a polymer electrolyte, and a dispersion solvent,
A method for producing an electrode catalyst, wherein a layer composed of the catalyst solution is formed on a surface of a substrate and heat-treated to obtain an electrode catalyst.

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