JP2002095969A - Method for producing platinum-cobalt alloy catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for easily producing a fine highly dispersible platinum-based alloy catalyst, especially a platinum-cobalt alloy supported catalyst. SOLUTION: There is provided a method for producing a platinum-cobalt alloy supported catalyst comprising adhering a mixture of a platinum compound with a cobalt compound to a carbon powder by using a solution containing a platinum compound and a cobalt compound and subjecting the product to reduction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a platinum-cobalt alloy-supported catalyst.

[0002]

2. Description of the Related Art Platinum-supported catalysts using carbon powder as a carrier are mainly used as cathode catalysts for fuel cells.
However, in the case of a phosphoric acid fuel cell, the catalyst aggregates during operation, which causes a decrease in cell performance. For this reason, platinum-based alloy catalysts obtained by adding cobalt, chromium, etc. to platinum have been developed and used in order to obtain stable catalyst performance for a long time.

[0003] In addition, a highly supported platinum-supported catalyst is used as a cathode catalyst in a polymer electrolyte fuel cell. However, in order to reduce the amount of platinum used and obtain a highly dispersed and fine catalyst, a platinum-based alloy-supported catalyst is used. Is being developed. For example, it has been proposed to prepare a platinum-cobalt alloy-supported catalyst by dispersing carbon powder in an aqueous solution of chloroplatinic acid and an aqueous solution containing a chlorine compound such as cobalt chloride or chromium chloride, followed by drying and reduction in a hydrogen atmosphere. However, in this method,
The catalyst particles become large, and no satisfactory catalyst can be obtained.

[0004] In order to suppress the coarsening of the catalyst particles and obtain a platinum-based alloy catalyst having stable battery characteristics, for example, Japanese Patent Application Laid-Open No. Hei 5-217586 discloses that a carbon powder is impregnated with an aqueous chloroplatinic acid solution. A reducing agent such as hydrazine is added thereto to reduce the platinum to produce a platinum-supported catalyst.Then, the catalyst powder is brought into sufficient contact with an aqueous solution containing an acidic heavy metal salt such as cobalt chloride. Is made alkaline, and a hydroxide of a heavy metal such as cobalt is precipitated on the carrier.
A method has been proposed in which a hydroxide is reduced by heat treatment in a nitrogen stream at a temperature of 0 ° C. to form an alloy with platinum.

JP-A-8-141400 discloses that a platinum-supported catalyst is added to a plating solution in which a heavy metal salt such as cobalt chloride is added to an aqueous solution containing sodium tartrate and hydrazine chloride, and the pH is adjusted with sodium hydroxide or the like. A catalyst slurry dispersed in an aqueous solution is charged, and heavy metal is electrolessly plated on platinum particles at a low temperature.
A method of performing a heat treatment at 0 ° C. to obtain an alloying catalyst is disclosed.

[0006]

In any of the methods proposed in the above publications, in order to obtain a platinum-based alloy catalyst, a metal particle or a metal salt to be alloyed is deposited on a platinum-supported catalyst, and a high-temperature atmosphere is obtained. Under such conditions, the catalyst particles are apt to aggregate, and the resulting catalyst is not always satisfactory in terms of performance.

An object of the present invention is to provide a method capable of easily producing a fine and highly dispersed platinum-based alloy catalyst, particularly a platinum-cobalt alloy-supported catalyst.

[0008]

According to the present invention, a mixture of a platinum compound and a cobalt compound is deposited on carbon powder using a solution containing the platinum compound and the cobalt compound, and then reduced. A method for producing a platinum-cobalt alloy supported catalyst is provided.

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

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The platinum compounds used in the present invention are soluble in solvents such as water and alcohols described below, for example, chloroplatinic acid, tetraamminedichloroplatinum, diamminedinitroplatinum, platinum nitrate, platinumammine Complex, and the like, and in particular, JP-A-8-1761.
The following formula [Pt (NH ₃ ) x (NO ₂ ) yL] Az which can be produced by the method described in Japanese Patent Publication No. 75-75, wherein L represents an alkoxy group, an alkanoyl group or an alkanoyloxy group, and A represents H , NO ₂ or NO ₃ ,
x is 0, 1 or 2, and y is 1, 2 or 3, provided that the sum of x and y depends on the charge of the central platinum and is 3
Platinum nitroammine complex represented by the following formula, wherein z is in the range of (y-1) to (y-3) and varies depending on the charge of the central metal, is preferred.

The cobalt compound to be used in combination with the platinum compound may be a compound dissolved in a solvent used for dissolving the platinum compound, for example, cobalt nitrate, cobalt chloride, cobalt acetate, cobalt formate, cobalt acetylacetate. Nart and the like can be mentioned, and cobalt nitrate is particularly preferable.

The platinum compound and the cobalt compound can be used in any combination. However, when chloroplatinic acid and cobalt chloride are used in combination, the particle size of the alloy formed is different from that of other platinum compounds and cobalt compounds. There is a tendency to be larger than alloy particles produced in combination.

The platinum compound and the cobalt compound described above are dissolved in a common solvent that dissolves both. As such a solvent, water, alcohol, a mixed solvent thereof and the like are suitable.

Although the concentrations of the platinum compound and the cobalt compound in the solution are not particularly limited, it is generally preferable to dissolve the compounds so that the concentration of each compound is in the range of 20 to 50% by weight. The ratio of the platinum compound to the cobalt compound in the solution is usually from 2: 8 to 8: 2, preferably from 5.5: 4.5 to 4.5: 5.5. It can be in the range of 5, especially preferably approximately equimolar.

The solution containing the platinum compound and the cobalt compound thus prepared is applied to carbon powder as a catalyst carrier, and a mixture of the platinum compound and the cobalt compound is adhered to the carbon powder.

The application of the solution to the carbon powder is performed, for example, by immersing the carbon powder in a solution containing a platinum compound and a cobalt compound and then drying the solution, and spraying the solution containing the platinum compound and the cobalt compound on the carbon powder. The post-drying method can be used.

Thus, a carbon powder to which the platinum compound and the cobalt compound are adhered is obtained. Usually, the amount of the platinum compound and the cobalt compound to be deposited is preferably such that the total amount of both compounds is within the range of 5 to 900 parts by weight per 100 parts by weight of the carbon powder.

As the above-mentioned carbon powder, those commonly used as a catalyst carrier can be similarly used.
For example, carbon black, graphite, activated carbon and the like can be mentioned. These carbon powders can be used as they are, but generally, a method known per se,
For example, it is desirable to previously perform a hydrophilic treatment using nitric acid.

The resulting carbon powder to which the mixture of the platinum compound and the cobalt compound adheres is then subjected to a reduction treatment. The reduction is usually performed using hydrogen gas. Specifically, for example, a carbon powder to which a mixture of a platinum compound and a cobalt compound has adhered is placed in a gas-replaceable electric furnace and, if necessary, replaced with an inert gas atmosphere, and then reduced while flowing hydrogen gas. The reduction temperature at that time is about 15
The temperature can be in the range of 0 to about 800 ° C, preferably about 200 to about 600 ° C, and the reduction time can be usually about 1 to 4 hours.

As a result, a platinum-cobalt alloy-supported catalyst is obtained in which the platinum-cobalt alloy is preferably dispersed and adhered to the carbon powder in the form of fine particles having an average particle diameter of preferably 7 nm or less.

According to the method of the present invention described above, a platinum-cobalt alloy catalyst is supported on carbon powder in extremely fine particles by a very simple method of simultaneous reduction of a mixture of a platinum compound and a cobalt compound at a low temperature. The resulting platinum-cobalt alloy-supported catalyst can be advantageously used, for example, as an electrode catalyst layer of a fuel cell.

Hereinafter, the present invention will be described more specifically with reference to examples. However, the scope of the present invention is not limited to these examples.

[0023]

Example 1 50 g of dinitrodiammine platinum salt in terms of platinum was concentrated in nitric acid.
500g ・ dm^-3To 100 ml of the solution of
Mix and stir at 5 ° C for 5 hours to remove dinitrodiammine platinum salt.
Dissolve and ripen the nitric acid solution of trinitrodiammine platinum
Obtained. Next, this is a rotary evaporator at 80 ° C.
Evaporation to dryness gave a yellow-brown powder. Ethanau in this powder
While maintaining the temperature below 50 ° C.
0g ・ dm^-3Preparation of Platinum Ammine Ethoxide Complex Solution
did. 80 ml of this platinum ammine ethoxide complex solution
720 ml of ethanol was added to obtain an orange-red platinum solution.
Was. The solution was added with a molar ratio of platinum to cobalt in terms of metal of 1:
50g · dm to be 1 ^-3Of aqueous cobalt nitrate solution
In addition, a supporting solution was obtained.

The carrier solution is hydrophilized with a 60% nitric acid aqueous solution, and 4.8 g of carbon powder VulcanXC-72R (Cabot) is prepared.
Was added and mixed with an ultrasonic homogenizer. Then, the supported solution was mixed at 78 ° C. with a rotary evaporator for 3 hours.
It was sucked and dried for a time. Next, the loaded dried product was placed in an electric furnace, replaced with a mixed gas of nitrogen and hydrogen containing 7% hydrogen gas, heated to 400 ° C., and kept at the same temperature for 2 hours.
Thereafter, the furnace was replaced with nitrogen gas and cooled to room temperature to obtain a platinum-cobalt alloy-supported catalyst.

Example 2 A 50 g · dm ⁻³ aqueous solution of cobalt chloride was added to a platinum ammine ethoxide solution obtained in the same manner as in Example 1 so that the molar ratio of platinum to cobalt was 1: 1 in terms of metal. A platinum-cobalt alloy-supported catalyst was obtained by treating it as a supported solution in the same manner as in Example 1.

Example 3 A 50 g · dm ^-3 aqueous solution of cobalt acetylacetonate was added to the platinum ammine ethoxide solution obtained in the same manner as in Example 1 so that the molar ratio of platinum to cobalt was 1: 1 in terms of metal. The resulting solution was treated in the same manner as in Example 1 to obtain a platinum-cobalt alloy supported catalyst.

Example 4 A chloroplatinic acid was weighed to a platinum metal amount of 4.0 g and dissolved in 800 mL of ethyl alcohol in a platinum solution so that the molar ratio of platinum to cobalt was 1: 1 in terms of metal. A platinum-cobalt alloy-supported catalyst was obtained in the same manner as in Example 1 by adding a 50 g · dm ⁻³ aqueous solution of cobalt nitrate to make a supported solution.

Comparative Example 1 To 800 mL of a platinum ammine ethoxide solution obtained in the same manner as in Example 1, 4.8 g of a carbon powder VulcanXC-72R (manufactured by Cabot) subjected to hydrophilization treatment with a 60% aqueous nitric acid solution was added, and ultrasonic waves were added. The mixture was mixed with a homogenizer to obtain a platinum-supported solution. The platinum-supported solution is heated to 79 ° C. by a rotary evaporator and then reduced by heating at the same temperature for 16 hours. Then, the platinum-supported solution is filtered and dried to obtain a platinum-supported catalyst. This platinum-supported catalyst is dispersed in 60.5 mL of an aqueous cobalt nitrate solution having a cobalt concentration of 20 g · dm ^{−3 with} an ultrasonic homogenizer, heated at 79 ° C. for 3 hours by a rotary evaporator, sucked and dried. The dried support was placed in an electric furnace, replaced with a mixed gas of nitrogen and hydrogen containing 7% hydrogen gas, heated to 400 ° C., and kept at the same temperature for 2 hours. Thereafter, the furnace was replaced with nitrogen gas and cooled to room temperature to obtain a platinum-cobalt alloy-supported catalyst.

Comparative Example 2 The supported dried product obtained in the same manner as in Comparative Example 1 was placed in an electric furnace, and replaced with a mixed gas of nitrogen and hydrogen containing 7% hydrogen gas. Hold for hours. Thereafter, the inside of the furnace was replaced with nitrogen gas, cooled to room temperature, and
A cobalt alloy supported catalyst was obtained.

The platinum obtained in the above Examples and Comparative Examples
The cobalt alloy-supported catalyst was photographed with a high-resolution scanning electron microscope (SEM). As a result, Examples 1 to
In the platinum-cobalt alloy-supported catalyst prepared in Example 4, the catalyst particles were finely dispersed on the carbon support, whereas in the platinum-cobalt alloy-supported catalysts of Comparative Examples 1 and 2, a part of the catalyst particles aggregated. I was

The average particle size of the platinum-cobalt alloy-supported catalyst dispersed on the carbon support was determined from a high-resolution SEM photograph. Table 1 shows the results.

As is clear from Table 1, the catalysts obtained in Examples 1 to 4 have a much smaller average particle diameter than the catalysts obtained in Comparative Examples 1 and 2. In addition, the lattice constants of the platinum-cobalt supported catalysts of Examples 1 to 4 obtained by the X-ray diffraction method almost coincide with the theoretical lattice constant (0.373 nm) of the platinum-cobalt alloy having the same composition. It was confirmed that the platinum-cobalt of the catalyst produced by the above method was alloyed.

[0033]

[Table 1]

Further, the cathode prepared using the platinum-cobalt supported catalysts of Example 1 and Comparative Example 2 and platinum
Anode and Proton-Conducting Polymer Electrolyte Membrane Nafion 112 Produced Using Pt-Supported Catalyst Supported at 0 wt%
(Manufactured by DuPont) to produce an electrode assembly.
A fuel cell was constructed using the assembly, and IV characteristics were measured using pure hydrogen as an anode electrode gas and oxygen as a cathode electrode gas. From the result,
The voltage at a load of 0.6 A / cm ² was determined. Table 2 shows the results. As is clear from the results in Table 2, the voltage of the platinum-cobalt supported catalyst of Example 1 was high.

[0035]

[Table 2]

Continued on the front page (72) Inventor Hideo Inoue 2-12-30 Aoyagi, Soka City, Saitama Prefecture Ishifuku Jin Kogyo Co., Ltd. Soka 1st Plant Research Department F-term (reference) 4G069 AA03 AA08 BA08A BA08B BA21A BA21B BA21C BA27A BA27B BA27C BB02A BB02B BB08A BB08B BB08C BB12A BB12B BB12C BC67A BC67B BC67C BC75A BC75B BC75C BE20A BE20B BE20C CC32 FB44 FC07 4K001 AA07 AA41 DB19 HA12

Claims (6)

[Claims] 1. A method for producing a platinum-cobalt alloy-supported catalyst, comprising depositing a mixture of a platinum compound and a cobalt compound on carbon powder using a solution containing the platinum compound and a cobalt compound, and then reducing the mixture. 2. The method according to claim 1, wherein the platinum compound is chloroplatinic acid, tetraamminedichloroplatinum, diamminedinitroplatinum, platinum nitrate or a platinumammine complex. 3. A platinum compound having the formula [Pt (NH ₃ ) _x (NO ₂ ) _y L] A _{z wherein} L represents an alkoxy group, an alkanoyl group or an alkanoyloxy group, and A represents H, NO ₂ or NO. ₃ represents, x is 0, 1 or 2, y is 1, 2 or 3, provided that the sum of x and y is in the range of 3-5 depends charge of the central platinum, z is the center (Y-1) to (y-3) depending on the charge of the metal
The method according to claim 1 or 2, which is a platinum nitroammine complex represented by the following formula: 4. The method according to claim 1, wherein the cobalt compound is cobalt nitrate, cobalt chloride, cobalt acetate, cobalt formate or cobalt acetylacetonate. 5. The method according to claim 1, wherein the ratio of the platinum compound to the cobalt compound is in the range of 2: 8 to 8: 2 in terms of the molar ratio of platinum to cobalt in terms of metal. 6. The reduction is carried out in the presence of hydrogen gas at 150-80.
The method according to any one of claims 1 to 5, which is performed at a temperature of 0 ° C.