JP2007324092A - Method for producing platinum or platinum alloy supported catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To support platinum or platinum alloy particles having a uniform particle size uniformly and highly dispersed on a carrier, suitable for a fuel cell catalyst that does not cause problems in terms of safety and environment, or To provide a method for producing a platinum alloy-supported catalyst.
A salt or complex of an organic carboxylic acid selected from the group consisting of formic acid, acetic acid, propionic acid, lactic acid, oxalic acid, malonic acid, and maleic acid, and platinum, and optionally further, the organic carboxylic acid and palladium, Containing a salt or complex with a metal selected from the group consisting of rhodium, iridium, ruthenium, gold, silver, iron, cobalt and nickel, and the amount of platinum in the solution is 20 mol% or more of the total amount of metals and A method for producing a platinum or platinum alloy-supported catalyst, comprising impregnating a catalyst carrier with a solution having a concentration of free organic carboxylic acid of 100 g / L or less, followed by reduction treatment and appropriate heat treatment.
[Selection figure] None

Description

  The present invention relates to a method for producing a platinum or platinum alloy-supported catalyst suitable as a catalyst electrode for fuel cells, and more particularly to a method for producing a platinum or platinum alloy-supported catalyst in which platinum or platinum alloy particles are uniformly and highly dispersed.

  Since the polymer electrolyte fuel cell is small and can take out a high current density, it is expected to be used as a power source for automobiles, a distributed power source for home use, and a portable power source.

  This solid polymer fuel cell uses a metal catalyst mainly composed of Pt, and it is desired to increase the activity of the electrode catalyst. The activity of the catalyst can be enhanced by making the metal catalyst particles finely dispersed uniformly on the support.

  As a method for supporting a platinum-based catalyst, many methods have been conventionally known. For example, Patent Document 1 discloses a method in which sodium sulfite is dissolved in a chloroplatinic acid aqueous solution, and a hydrogen peroxide aqueous solution is added dropwise and mixed. A method of preparing a catalyst by supporting it on a carbon carrier as a colloidal solution with sodium oxide and drying it is disclosed.

  Patent Document 2 describes that after impregnating a carbon carrier with an ethanol solution of chloroplatinic acid, the carbon support is reduced in a hydrogen gas atmosphere at a temperature of 180 ° C. A method for obtaining a composite catalyst compact by impregnation and reduction at 180 ° C. in a hydrogen gas atmosphere is disclosed.

  In Patent Document 3, as a method for supporting a platinum-chromium-iron alloy catalyst for a fuel cell on a carbon support, the resulting platinum is dispersed by dispersing the carbon support in an aqueous chloroplatinic acid solution, adding hydrazine, and reducing the platinum. Disperse the supported catalyst in pure water. Separately, add a sodium hydroxide solution to an aqueous solution of chromium acetate and ferrous nitrate to prepare a homogeneous mixture of iron and chromium. In addition, a method is disclosed in which sodium hydroxide is added dropwise to precipitate chromium and iron as hydroxides and heat-treated at a temperature of 800 to 1000 ° C. in a nitrogen atmosphere to produce a supported catalyst.

  However, the supporting solution used for supporting the fuel cell catalyst described in the above-mentioned patent document is not always satisfactory because the catalyst may agglomerate during the alloying treatment by reduction or heat treatment at high temperature.

  In addition, a method in which an inorganic compound raw material such as chloroplatinic acid is supported on a carbon carrier and heat-treated in an atmospheric gas generates chlorine, hydrogen chloride, and nitrogen oxide gas, which has an impact on human safety and environmental aspects. The impact on is a problem.

Furthermore, when using an inorganic raw material compound, it is necessary to provide the manufacturing equipment with a gas processing facility for processing the gas generated by the reduction, and there is a problem that the equipment cost increases.
Japanese Patent Laid-Open No. 11-4595 JP-A-9-153366 JP-A-6-29028

  The main object of the present invention is to provide a fuel cell catalyst that can support platinum or platinum alloy particles having a uniform particle size uniformly and highly dispersed on a carrier without causing problems in terms of safety and environment. It is to provide a method for producing a suitable platinum or platinum alloy supported catalyst.

  As a result of various studies, the present inventors have impregnated a catalyst support in the form of a solution of a salt or complex of a specific organic carboxylic acid with platinum and other metals for alloying. Thus, the inventors have found that the above object can be achieved, and have completed the present invention.

  Thus, the present invention provides a salt or complex of an organic carboxylic acid selected from the group consisting of formic acid, acetic acid, propionic acid, lactic acid, oxalic acid, malonic acid and maleic acid and platinum, and optionally further, Containing a salt or complex with a metal selected from the group consisting of palladium, rhodium, iridium, ruthenium, gold, silver, iron, cobalt and nickel, and the amount of platinum in the solution is 20 mol% or more of the total amount of metals Provided is a method for producing a platinum or platinum alloy-supported catalyst comprising impregnating a catalyst carrier with a solution having a concentration of free organic carboxylic acid of 100 g / L or less, followed by reduction treatment and appropriate heat treatment. Is.

  According to the method of the present invention, a catalyst in which platinum or platinum alloy fine particles are supported uniformly and highly dispersed on a carrier can be easily produced. The resulting catalyst for fuel cells in which platinum or platinum alloy fine particles are supported on, for example, conductive carbon powder has platinum or a platinum alloy supported in a higher dispersion than the conventional platinum supported catalyst, and has a high oxygen reduction activity, In addition, since it can be easily alloyed, it has high carbon monoxide resistance, and when used in a polymer electrolyte fuel cell, its power generation efficiency can be significantly improved.

  Furthermore, the platinum complex and alloying metal complex used in the present invention generate only carbon dioxide and water when reductively decomposing into a metal. Therefore, the production method of the present invention includes chlorine gas, hydrogen chloride gas, NOx, etc. Is not generated at all, is extremely safe and has no environmental burden, can be industrially mass-produced, and can greatly reduce catalyst manufacturing equipment costs compared to conventional manufacturing methods.

  Hereinafter, the production method of the present invention will be described in more detail.

  According to the method of the present invention, a salt of platinum with an organic carboxylic acid selected from the group consisting of formic acid, acetic acid, propionic acid, lactic acid, oxalic acid, malonic acid and maleic acid, which is used for supporting platinum on a carrier, or Complexes (hereinafter collectively referred to as “platinum complexes”) are at least partially known. For example, Inorganica Chimica Acta 357 (2004) 853-858, Chemische Berichte (1966) 99 (1) 3408-3418. It can be easily obtained by methods described in the literature. In the present invention, as the platinum complex, platinum oxalate, platinum malonate, and platinum maleate are particularly preferable, and platinum oxalate is particularly preferable.

In addition, organic carboxylic acid selected from the group consisting of formic acid, acetic acid, propionic acid, lactic acid, oxalic acid, malonic acid and maleic acid used for alloying with platinum, palladium, rhodium, iridium, ruthenium, gold, A salt or complex with a metal selected from the group consisting of silver, iron, cobalt and nickel (hereinafter collectively referred to as “metal complex for alloying”) is also at least partially known and commercially available. Furthermore, it can also be produced according to the method described in the above document. Examples of metal species that can be used particularly advantageously in alloying include ruthenium, cobalt, palladium, and iridium, with ruthenium and cobalt being preferred. These alloying metal complexes can be used alone or in combination of two or more.

  The platinum complex and the metal complex for alloying can be impregnated in the support in a solution state (hereinafter, this solution is referred to as “complex solution”). As a solvent capable of dissolving these complexes, deionized water is usually preferable. However, when the complex is difficult to dissolve in water, for example, formic acid, acetic acid, propionic acid, lactic acid An aqueous solution of oxalic acid, malonic acid or maleic acid can also be used. The concentration of the platinum complex and the metal complex for alloying in the solution is not particularly limited, but the metal amount is usually in the range of 10 to 150 g / L, preferably 50 to 100 g / L. Can do. Further, when the platinum complex and the alloying metal complex are used in combination, it is desirable that platinum occupies 20 mol% or more, particularly 40 mol% or more of the total amount of metal in the solution.

  Further, in the complex solution, excess unreacted organic carboxylic acid used in preparing the platinum complex and / or the metal complex for alloying may remain, but if the amount is too large, Since aggregation of platinum or platinum alloy particles easily occurs during the reduction treatment, the concentration of the free organic carboxylic acid in the complex solution is desirably 100 g / L or less, particularly 1 g / L or less.

  Furthermore, in the complex solution, a surfactant can be included in order to improve the smoothness of the carrier when impregnated into the carrier, if necessary. Examples of the surfactant include nonionic surfactants such as polyoxyethylene tridecyl ether, ethylene glycol and N, N-dimethylethanolamine; cationic surfactants such as alkyltrimethylammonium salts; alkylbenzene sulfonic acids Anionic surfactants such as ammonium salts: amphoteric surfactants such as alkylbenzyl sulfonic acid ammonium salts.

  On the other hand, the catalyst carrier is not particularly limited, and those conventionally used as catalyst carriers can be used as well, and in particular, carbon black, acetylene black, carbon nanotube, carbon nanohorn, fullerene, etc. The conductive carbon carrier is suitable.

  After impregnating these carriers with the above complex solution, the target platinum or platinum alloy-supported catalyst can be obtained by reduction treatment and appropriate heat treatment.

  Specifically, for example, in a rotary evaporator or a kneader, the complex solution is added to the support and mixed thoroughly, and then dried, and then the resulting support to which the platinum complex or alloying metal complex is attached is In a reducing gas (eg, hydrogen gas, carbon monoxide gas, etc.) or inert gas (eg, nitrogen gas, helium gas, argon gas, etc.) atmosphere at about 200 to about 800 ° C., preferably about 300 to about Heat treatment is performed at a temperature of 400 ° C., and the platinum complex or metal complex for alloying is reduced to metal and alloyed at the same time. This makes it possible to obtain a catalyst suitable for a fuel cell in which platinum or platinum alloy particles having a fine and uniform particle size are highly dispersed and supported on a carrier.

In addition, for example, a carrier is dispersed in a complex solution, the dispersion solution is heated to a temperature of about 40 to about 100 ° C., and a reducing agent such as alcohols, aldehydes, ketones, carboxylic acids, ethers, reducing agents A gas (for example, hydrogen), hydrazine or the like is introduced to reduce the platinum complex or the alloying metal complex to a metal and simultaneously deposit it on the support to obtain a support on which platinum or platinum and the alloying metal are adhered. In the case of a carrier on which an alloying metal is deposited, it is about 200 to about 800 ° C., preferably about 300 to about 600 ° C. in an inert gas atmosphere (eg, nitrogen gas, helium gas, argon gas, etc.). It is alloyed by heat treatment at a temperature of This also makes it possible to obtain a catalyst suitable for a fuel cell in which platinum or platinum alloy particles having a fine and uniform particle size on a carrier are highly dispersed and supported.

  The supported amount of platinum or platinum alloy in the obtained catalyst is not strictly limited, but is generally 5 to 80% by mass, particularly 20 to 60% by mass. The amount of platinum or platinum alloy supported can be adjusted, for example, by the concentration of the complex solution, the amount of impregnation of the platinum complex or metal complex for alloying, and the like.

  Further, the platinum amount in the supported platinum alloy is desirably 20 mol% or more, particularly 40 mol% or more of the total metal amount. When the amount of platinum in the alloy is less than 20 mol%, the alloying metal component is eluted from the catalyst, and the stability and catalytic performance of the catalyst may be reduced.

The catalyst manufactured by the method of the present invention described above has a very high metal surface area of at least 100 m ² / g, as will be apparent from the examples described later, and is a large oxygen reduction catalyst as a fuel cell catalyst. Indicates the current value.

  Moreover, the platinum complex and alloying metal complex used in the present invention can be easily reduced and decomposed into metals and alloyed. Therefore, according to the present invention, a platinum alloy-supported catalyst having high carbon monoxide resistance can be obtained. Easy to manufacture.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

Production Example 1
20 g of platinum oxalate in terms of platinum was dissolved in 130 mL of pure water, 0.2 g of nonionic surfactant (polyoxyethylene tridecyl ether) was added to the resulting aqueous solution, and the concentration was adjusted with pure water. A platinum supporting solution having a platinum concentration of 100 g / L was obtained.

Production Example 2
20 g of platinum maleate in terms of platinum was dissolved in 130 mL of pure water, and a platinum supporting solution having a platinum concentration in the solution of 100 g / L was obtained in the same manner as in Production Example 1.

Production Example 3
20 g of platinum oxalate in terms of platinum and 19.7 g of iridium acetate in terms of iridium are dissolved in 130 mL of pure water, and 0.2 g of nonionic surfactant (polyoxyethylene tridecyl ether) is added to the resulting aqueous solution. Further, a platinum-iridium alloy supporting solution having a platinum concentration in the solution of 100 g / L and a platinum concentration of 50 mol% with respect to all the metals in the solution was obtained.

Production Example 4
20 g of platinum oxalate in terms of platinum and 10 g of ruthenium oxalate in terms of ruthenium were dissolved in 130 mL of pure water, and the platinum concentration in the solution was 100 g / L in the same manner as in Production Example 3, and for all metals in the solution. A platinum-ruthenium alloy supporting solution having a platinum concentration of 50 mol% was obtained.

Production Example 5
20 g of platinum oxalate in terms of platinum and 10.9 g of palladium oxalate in terms of palladium were dissolved in 130 mL of pure water, and the platinum concentration in the solution was 100 g / L in the same manner as in Production Example 3. A platinum-palladium alloy supporting solution having a platinum concentration of 50 mol% with respect to the metal was obtained.

Production Example 6
20 g of platinum oxalate in terms of platinum and 10.5 g of rhodium oxalate in terms of rhodium were dissolved in 130 mL of pure water, and the platinum concentration in the solution was 100 g / L in the same manner as in Production Example 3. A platinum-rhodium alloy supporting solution having a platinum concentration of 50 mol% with respect to the metal was obtained.

Production Example 7
20 g of platinum oxalate in terms of platinum and 5.7 g of iron oxalate in terms of iron were dissolved in 130 mL of pure water, and the platinum concentration in the solution was 100 g / L in the same manner as in Production Example 3. A platinum iron alloy supporting solution having a platinum concentration of 50 mol% with respect to the metal was obtained.

Production Example 8
20 g of platinum oxalate in terms of platinum and 6 g of cobalt oxalate in terms of cobalt were dissolved in 130 mL of pure water, and the platinum concentration in the solution was 100 g / L as in Production Example 3, and for all metals in the solution. A platinum-cobalt alloy supporting solution having a platinum concentration of 50 mol% was obtained.

Production Example 9
20 g of platinum oxalate in terms of platinum and 6 g of nickel oxalate in terms of nickel were dissolved in 130 mL of pure water, and the platinum concentration in the solution was 100 g / L as in Production Example 3, and for all metals in the solution. A platinum-nickel alloy supporting solution having a platinum concentration of 50 mol% was obtained.

Production Example 10
20 g of platinum oxalate in terms of platinum, 5.5 g of palladium oxalate in terms of palladium, and 10.1 g of gold oxalate in terms of gold were dissolved in 130 mL of pure water, and platinum in solution was prepared in the same manner as in Production Example 3. A platinum-palladium-gold alloy supporting solution having a concentration of 100 g / L and a platinum concentration of 50 mol% with respect to all metals in the solution and 25 mol% with respect to all metals in the palladium and gold solution was obtained.

Production Example 11
20 g of platinum oxalate in terms of platinum, 5.5 g of palladium oxalate in terms of palladium, and 5.1 g of silver oxalate in terms of silver were dissolved in 130 mL of pure water, and platinum in solution was prepared in the same manner as in Production Example 3. A platinum-palladium-silver alloy supporting solution having a concentration of 100 g / L and a platinum concentration of 50 mol% with respect to all metals in the solution and 25 mol% with respect to all metals in the palladium and silver solutions was obtained.

Production Example 12
20 g of platinum oxalate in terms of platinum and 9.1 g of cobalt oxalate in terms of cobalt were dissolved in 130 mL of pure water, and the platinum concentration in the solution was 100 g / L in the same manner as in Production Example 3. A platinum-cobalt alloy supporting solution having a platinum concentration of 40 mol% with respect to the metal was obtained.

Production Example 13
Platinum oxalate containing 20 g of platinum in terms of platinum and 2 g of cobalt oxalate in terms of cobalt were dissolved in 130 mL of pure water, and the platinum concentration in the solution was 100 g / L in the same manner as in Production Example 3. A platinum-cobalt alloy supporting solution having a platinum concentration of 80 mol% with respect to all metals was obtained.

Comparative production example 1
20 g of chloroplatinic acid in terms of platinum was weighed and dissolved in 130 g of pure water, and the concentration was adjusted with pure water to obtain a platinum supporting solution with a platinum concentration of 100 g / L.

Comparative production example 2
Pure water was added to the dinitrodiammine platinum nitric acid aqueous solution to adjust the concentration to obtain a platinum supporting solution having a platinum concentration of 100 g / L.

Comparative production example 3
200 mL of the platinum-supported solution obtained in Comparative Production Example 1 was sampled, 10 g of ruthenium chloride in terms of ruthenium was added, and the mixture was stirred and dissolved at room temperature to obtain a platinum-ruthenium alloy-supporting solution.

Comparative production example 4
20 g of platinum oxalate in terms of platinum and 57.2 g of cobalt oxalate in terms of cobalt were dissolved in 130 mL of pure water, and the platinum concentration in the solution was 100 g / L in the same manner as in Production Example 3. A platinum-cobalt alloy supporting solution having a platinum concentration of 10 mol% with respect to the metal was obtained.

Comparative Production Example 5
20 g of platinum chloride in terms of platinum, 5.5 g of palladium chloride in terms of palladium, and 5.1 g of chloroauric acid in terms of gold are dissolved in 130 mL of pure water, the concentration is adjusted with pure water, and the platinum concentration is 100 g / A platinum-palladium-gold alloy supporting solution having a platinum concentration of 50 mol% with respect to all metals in the solution and 25 mol% with respect to all metals in the palladium and gold solution was obtained.

Comparative Production Example 6
200 mL of the platinum-carrying solution obtained in Production Example 1 was collected, and 30 g of oxalic acid was added to the solution and stirred and dissolved at room temperature to obtain a platinum-carrying solution. As a result of measuring the free oxalic acid concentration in the solution, it was 150 g / L.

Examples 1-13 and Comparative Examples 1-6
200 mL of the platinum supporting solution obtained in Production Example 1 was collected and mixed with 80 g of a carbon support (Ketjen Black EC), and then a platinum complex was attached to the surface of the carbon support using a rotary evaporator. Heat treatment was performed under an atmosphere to reduce the platinum complex to a metal to obtain a platinum-supported catalyst-1.

  Using the platinum or platinum alloy-supported solution obtained in Production Examples 2 to 13 and Comparative Production Examples 1 to 6, platinum and platinum alloy-supported catalysts -2 to -13 and platinum for comparison or Platinum alloy supported catalysts -14 to -19 were obtained.

Next, using a high-precision fully automatic gas adsorption measuring device “BELSORP28SA” (trade name, manufactured by Nippon Bell Co., Ltd.), the amount of irreversible adsorption of carbon monoxide on the platinum or platinum alloy-supported catalyst-1 to 19 is determined. From the value, the catalytic metal surface area (m ² / g-Pt) was calculated. The results are shown in Table 1.

  Electrodes are prepared using the above platinum-supported catalysts-1, -8 and -14, electrochemical measurements are performed in a sulfuric acid solution, and an oxygen reduction current value per unit weight of Pt at 0.85 V (RHE) is obtained. It was. The results are shown in Table 2.

Furthermore, an anode prepared using platinum alloy-supported catalyst-4 or platinum alloy-supported catalyst-16, a cathode prepared using a platinum catalyst in which platinum is supported on carbon by 40 wt%, and a solid polymer electrolyte membrane “Nafion112” (DuPont) was joined to produce an electrode assembly. A battery was assembled using this electrode assembly, and the fuel cell power generation characteristics were evaluated when hydrogen gas or hydrogen gas containing 100 ppm of carbon monoxide was used as the anode electrode gas. The voltage at the time of using each anode electrode gas was calculated | required, and the voltage reduction rate at the time of 0.5 A * cm ^<-2 > load on the conditions containing carbon monoxide gas was computed. Note that oxygen was used as the cathode electrode gas. The results are shown in Table 3.

Example 14 and Comparative Example 7
200 mL of each of the platinum-supported solutions obtained in Production Example 1 and Comparative Production Example 1 was collected, and 80 g of a carbon support (Ketjen Black EC) was dispersed in each solution. To this solution, 10 g of an 80% aqueous hydrazine hydrate was added as a reducing agent, the platinum complex was reduced while refluxing hydrazine at a temperature of 80 ° C., and platinum particles were deposited and supported on the support to support platinum-supported catalyst-20 and -21 was obtained. The platinum surface area of the obtained platinum-supported catalyst was measured in the same manner as described above, and the results are shown in Table 4.

Claims (1)

  A salt or complex of an organic carboxylic acid and platinum selected from the group consisting of formic acid, acetic acid, propionic acid, lactic acid, oxalic acid, malonic acid and maleic acid, and optionally further, the organic carboxylic acid and palladium, rhodium, iridium, It contains a salt or complex with a metal selected from the group consisting of ruthenium, gold, silver, iron, cobalt and nickel, and the amount of platinum in the solution is 20 mol% or more of the total amount of metal and free organic carbon A method for producing a platinum or platinum alloy-supported catalyst, comprising impregnating a catalyst carrier with an acid concentration of 100 g / L or less, followed by a reduction treatment and an appropriate heat treatment.