JPH08141400A - Production of electrode catalyst for fuel cell - Google Patents

Abstract

PURPOSE: To provide a method of producing an electrode catalyst for fuel cell wherein the catalyst is alloyed without increasing the particle size of the alloy in diameter and is maintained at a large specific surface area and the mass activity of the catalyst can be augmented. CONSTITUTION: A catalyst of a precious metal alloy such as a platinum alloy supported on a powdery carrier such as carbon is dispersed in hot water and made into a catalytic slurry, an electroless plating liquid containing a heavy metal such as nickel and cobalt is charged into the catalytic slurry for the electroless plating of such a metal and the catalyst of the precious metal alloy having the plated heavy metal supported on its carrier is heated to a temperature of 850-950 deg.C for 2-10 minutes under a prescribed atomosphere for the alloying thereof.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an electrode catalyst suitable for a fuel cell, particularly a phosphoric acid fuel cell.

[0002]

2. Description of the Related Art Conventionally, the following method has been considered as a method for producing a noble metal alloy catalyst of this type. As one method, a catalyst in which platinum is supported on carbon powder is wetted with water, and a solution containing one or two kinds of heavy metal as an alloy component is added to and mixed with the catalyst to make a slurry and then dried. After that, it was heated under a steam flow for reduction and alloying treatment. However, with this method, it is difficult to increase the ratio of heavy metals in the alloy composition, and the alloy composition ratio could not be set to the target Pt: heavy metal = 1: 1.
In addition, since the catalyst of platinum-supported carbon powder is mixed with the solution and then dried, the heavy metal component becomes a salt crystal and is nonuniformly deposited, resulting in uneven distribution of the heavy metal component in the catalyst. In order to solve such a problem, a method of electrolessly plating a noble metal or noble metal alloy catalyst with a heavy metal and subjecting it to heat treatment for alloying is considered. By this method, the bias of heavy metals was eliminated, and it became possible to freely control the alloy composition of the catalyst. However, conventionally, suitable heating conditions for the alloying treatment have not been clarified, and sometimes the alloy catalyst has a low mass activity.

[0003]

Therefore, the present invention is directed to the production of an electrode catalyst for a fuel cell, which can stably produce an alloy catalyst having a high mass activity without lowering the mass activity of the catalyst during alloying treatment. Provide a way.

[0004]

The method for producing a fuel cell electrode of the present invention for solving the above-mentioned problems is a catalyst slurry in which a noble metal or noble metal alloy catalyst supported on a powdery carrier is dispersed in hot water. On the other hand, an electroless plating solution containing a heavy metal is added to the catalyst slurry for electroless plating, a heavy metal is plated, and a noble metal or noble metal alloy catalyst supported on a carrier is heated in a required atmosphere to form an alloying treatment. In the method for producing a precious metal alloy catalyst, the alloying treatment is performed at 850 ° C.
It is characterized by being heated at 950 ° C. or lower for 2 to 10 minutes. Carbon or the like is used as the carrier, and platinum or a platinum alloy is used as the noble metal or noble metal alloy. Further, as the heavy metal,
One or more selected from nickel, cobalt, chromium, manganese and iron are used. The required atmosphere is preferably a hydrogen-containing air flow, and 3% H _{2 to} 50
% H ₂ Residual flow in N ₂ is more preferable. The surface area of the carrier used in the present invention is preferably 60 to 300 m ² / g in order to secure the particle size of the electrode catalyst. Also, the concentration of the noble metal in the noble metal or noble metal alloy catalyst, which is plated with heavy metal and supported on carbon black, is such that the thickness of the electrode using this catalyst is less than a certain thickness when the Pt loading amount is 1.0 to 1.5 mg / cm ^2. For the reason, it is preferably 10 to 30%.

[0005]

In the conventional method, the heavy metal component is nonuniformly deposited on the noble metal or the noble metal alloy, so that the heavy metal and the noble metal or the noble metal alloy must be mixed at a high temperature for a long time. As a result, the resulting noble metal or noble metal alloy catalyst particles become large particles, that is, the specific surface area of the catalyst is reduced, and the mass activity of the catalyst is reduced. In the method for producing an electrode catalyst for a fuel cell according to the present invention, since the heavy metal is uniformly deposited on the noble metal or the noble metal alloy by electroless plating, the long-time heat treatment conventionally required is stopped and the heating time is 2 minutes to By limiting the time to 10 minutes, the alloy catalyst particle size does not increase, the specific surface area of the catalyst can be maintained large, and the mass activity of the catalyst can be increased. The size of the alloy catalyst particles obtained at this time is preferably 4.0 nm or more and 5.0 nm or less,
If it exceeds 5.0 nm, the mass activity will decrease and
If it is less than m, the durability of the alloy catalyst particles will be reduced.

[0006]

EXAMPLE An example of a method for producing an electrode catalyst for a fuel cell of the present invention will be described together with a conventional example. A platinum-carbon catalyst in which 2.85 g of platinum was supported on carbon black having a surface area of 100 m ² / g was immersed in 180 ml of boiling water and dispersed with an ultrasonic homogenizer while stirring to form a catalyst slurry. On the other hand, nickel chloride 1.94 g, cobalt chloride 1.93 g as a heavy metal salt, sodium tartrate 29.58 g as a chelating agent, and hydrazine chloride 13.49 g as a reducing agent in an aqueous solution of 320 ml, 50%
The pH was adjusted to 12.8 with a NaOH solution to obtain a plating solution. The plating solution was added to the catalyst slurry all at once and dispersed with an ultrasonic homogenizer for 2 minutes while stirring. Then, the mixture was stirred for 1 hour and electrolessly plated at a low temperature to obtain a platinum catalyst having a concentration of 20% and a particle size of 2.0 nm, which was plated with heavy metals nickel and cobalt and supported on carbon black. The platinum catalyst was filtered, washed with water several times until the washing liquid became neutral, and dried. Finally N ₂ 97%, H ₂ 3
% Under the conditions shown in Table 1 below.
3, Conventional Examples 1 and 2 were heated and alloyed to obtain a fuel cell electrode catalyst.

[0007]

[Table 1]

Examples 1 to 3 and conventional examples 1 and 2 thus obtained
The alloy particle size and mass activity of the fuel cell electrode catalyst of
900 in a fuel cell at 100 ° C, 100% phosphoric acid, 100% oxygen
When measured in mV, the results shown in Table 2 below were obtained.

[0009]

[Table 2]

As is clear from Table 2 above, the alloy particle diameters of the fuel cell electrode catalysts of Examples 1 to 3 are stable with a small variation of 5 nm or less, and the alloy particle diameter variations of the conventional examples 1 and 2 are small. It can be seen that the mass activity is significantly improved compared to the large one.

[0011]

As can be seen from the above description, according to the method for producing an electrode catalyst for a fuel cell of the present invention, the alloying treatment can be performed without increasing the alloy particle size, and the specific surface area of the catalyst can be increased. It can be maintained and the mass activity of the catalyst can be increased.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H01M 8/02 E 9444-4K // H01M 4/88 K

Claims (5)

[Claims] 1. A noble metal or noble metal alloy catalyst supported on a powdery carrier is dispersed in hot water to form a catalyst slurry, and an electroless plating solution containing a heavy metal is added to the catalyst slurry to perform electroless plating. In the method for producing a noble metal alloy catalyst, in which a noble metal or noble metal alloy catalyst, which is plated with a heavy metal and is supported on a carrier, is heated in a required atmosphere to perform alloying treatment, the alloying treatment is performed at 850 ° C or higher and 950 ° C or lower A method for producing a fuel cell electrode catalyst, which comprises heating for 2 to 10 minutes. 2. The method for producing an electrode catalyst for a fuel cell according to claim 1, wherein the carrier is carbon. 3. The method for producing a fuel cell catalyst according to claim 1, wherein the noble metal or noble metal alloy catalyst is platinum or a platinum alloy catalyst. 4. The method for producing a fuel cell electrode catalyst according to claim 1, wherein the heavy metal is one or more selected from nickel, cobalt, chromium, manganese and iron. . 5. The method for producing an electrode catalyst for a fuel cell according to claim 1, 2, 3 or 4, wherein the required atmosphere is a hydrogen-containing air flow.