JPH01227360A - Manufacture of fuel cell catalyst - Google Patents

Abstract

PURPOSE:To increase the long term reliability of a cell and to decrease time dependent output drop by applying an ultrasonic wave to a mixture of water, catalyst carriers, and chloroplatinic acid to disperse them, and by supporting fine platinum particles on the carriers with a reducing agent. CONSTITUTION:Carbon black treated with acid to increase dispersion capability is used as a catalyst carrier 22. An ultrasonic wave is applied to a mixture of the carbon carrier 22, water, and chloroplatinic acid to disperse them. By adding alkaline solution such as sodium carbonate solution and a reducing agent such as formic acid to the dispersion, the chloroplatinic acid is reduced and fine platinum particles 21 are deposited on the carriers 22. An electrode catalyst layer 25 is prepared with the catalyst particles 21, and a cell is assembled. Since the fine platinum particles are sufficiently dispersed, the long term reliability of a cell is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a phosphoric acid type fuel cell electrode catalyst, and particularly to a method for uniformly supporting fine platinum particles on a catalyst.

[Conventional technology]

A fuel cell is a device that directly converts the chemical energy of fuel into electrical energy, and its structure consists of an electrode base material 24 made of carbon, as shown in Figure 2, with an electrolyte layer (not shown) in between. An electrode 26 to which an electrode catalyst layer 25 is attached
are arranged facing each other, and each t8i is supplied from an external gas supply system.
A power generation device that supplies fuel gas and oxidizing gas to the catalytic converter, causes the oxidizing gas and fuel gas to react electrochemically on the catalyst fine particles 27 of each electrode, and extracts electrical energy from the system as a result. be.

The fine catalyst particles 27 are made by supporting fine metal particles 21 such as platinum on a single catalyst 22 such as carbon black, and these fine catalyst particles 27 are fine particles 2 of a fluororesin made of polytetrafluoroethylene (PTFE).
3 to form an electrode catalyst layer 25.

Inside the electrode catalyst layer 25, phosphoric acid, which is an electrolytic solution, and the reactive gas contact each other on the surface of the catalyst fine particles 27 to form a three-phase interface, and an electrochemical reaction such as oxidation of the fuel gas or reduction of the oxidant gas occurs. It happens. In order for this electrochemical reaction to proceed efficiently, it is necessary that many three-phase interfaces exist, and for this purpose, the catalyst fine particles 27 must be well dispersed and have a large surface area. Blue gold particles 21 on catalyst carrier 22
It is necessary that the crystallite size of the crystallites is small and that the crystallites are uniformly supported.

Conventionally, as a method for supporting noble metal fine particles 21 on a catalyst carrier 22, the catalyst carrier 22 pretreated with an acid or the like is dispersed in water, chloroplatinic acid is added thereto, an alkali is added and stirred, and then chloroplatinic acid is added using a reducing agent. was reduced to support noble metal fine particles 21.

[Problem to be solved by the invention]

However, with this method, it is not possible to highly disperse the noble metal fine particles 21, and when alloying components are added to obtain platinum alloy fine particles, the crystallite diameter of the noble metal fine particles made of platinum alloy is 40. The crystallite diameter is ~70, which is larger than the crystallite diameter of 25 to 30 before alloying. In addition, maldistribution of precious metal fine particles of platinum alloy supported on the catalyst carrier 22 has been observed, and when the battery is operated for a long time under high potential, elution and sintering of the catalyst fine particles occur, resulting in a short battery life. Ta.

This invention was made in view of the above points, and its purpose is to mix and disperse the catalyst carrier and chloroplatinic acid well with each other.
An object of the present invention is to provide a method for producing a fuel cell catalyst in which highly dispersed noble metal fine particles are uniformly supported on a catalyst carrier.

[Means to solve the problem]

According to the present invention, the above object is achieved by applying ultrasonic waves to a mixture of water, catalyst carrier 22 and chloroplatinic acid to thoroughly mix and disperse the catalyst carrier and chloroplatinic acid, and then applying a reducing agent to the catalyst carrier 22. This is achieved by supporting platinum fine particles 21 on the metal.

Carbon black or the like is used as the catalyst carrier. This carbon black can be treated with an acid to improve its dispersibility. The chloroplatinic acid is reduced by the reducing agent, and fine particles of platinum are supported on the catalyst carrier.

[Effect]

When ultrasonic waves are applied to a mixture of water, catalyst carrier, and chloroplatinic acid, the catalyst carrier and chloroplatinic acid are each dispersed. The uniformity of the mixture is also improved.

〔Example〕

Next, embodiments of the present invention will be described based on the drawings. Acetylene black 900g and 10% by weight nitric acid aqueous solution 40g
1 was added, and the temperature was raised to about 55°C while stirring,
After stirring for about 2 hours, the cake was filtered and the pH of the cake was determined.
It was thoroughly washed with water until the temperature reached 7.

This cake was thoroughly dispersed in 407 water using ultrasound. Thereafter, an aqueous solution IO1 of chloroplatinic acid containing 100 g of platinum as a metal was added, and stirring was continued for about 30 minutes so that the platinum salt and the acetylene platter were brought into sufficient contact.

Furthermore, after this, ultrasonic waves are applied for 30 minutes. After this 0
．． 19.5 ffi of a 1M aqueous sodium carbonate solution was added, and stirring was continued for an additional 30 minutes.

After the above steps were completed, the temperature of the system was raised to 55° C. for about 2 hours. After raising the temperature, 1.07N of 30% by weight hydrogen peroxide solution was added and stirred for 5 minutes. Next, 20.5 liters of 0.1M formic acid aqueous solution was added over about 5 hours with stirring. At this time, after the zero reaction in which chloroplatinic acid was reduced by formic acid and ultrafine platinum particles were precipitated on the surface of acetylene black was completed, the cake was filtered and thoroughly washed until no chlorine ions were detected. The resulting cake was crushed and dried under vacuum at a temperature of 50°C to obtain a catalyst. As a result of analyzing the obtained catalyst, the amount of supported platinum was 10.2%, the average crystallite diameter was 25 to 30 crystallites, and the specific surface area of platinum was approximately 172 m
”/g-pt. To evaluate the thermal stability of this catalyst, it was heated at 900° C. for about 2 hours in a nitrogen atmosphere.
Heat treated at ℃. The average crystallite diameter after heat treatment was approximately 40, and it was found that it has sufficient physical properties as a platinum-supported catalyst and as a starting material for an alloy-supported catalyst of platinum and a second or third component. Fund IE after alloying iron! The crystallite size of the particles is 35 particles.

An electrode catalyst layer was prepared using the catalyst fine particles thus prepared, and the life characteristics of the battery were investigated.

The battery operating conditions are a temperature of 200℃ and a current density of 200℃.
-9 operating pressure is 4 kg/-. The results are shown in FIG. In FIG. 1, curve 11 is the life characteristic of the conventional catalyst without ultrasonic dispersion, and curve 12 is the life characteristic of the catalyst according to the embodiment of the present invention. A battery using the catalyst according to the present invention has excellent long-term reliability.

The reason for this is that the catalyst carrier and chloroplatinic acid are mixed and dispersed well by the ultrasonic energy, so that the dispersibility of the platinum fine particles generated by reduction is improved.

〔Effect of the invention〕

According to this invention, ultrasonic waves are applied to a mixture of water, a catalyst carrier, and chloroplatinic acid to thoroughly mix and disperse the catalyst carrier and chloroplatinic acid, and then platinum fine particles are supported on the catalyst carrier using a reducing agent. Therefore, the crystallite size of the platinum fine particles supported on the catalyst carrier is small and their distribution is uniform, so when used as a battery electrode, there is little sintering of the precious metal fine particles (the long-term stability of the battery is reduced). In addition, due to the high dispersibility of platinum fine particles, when alloying them, the crystallite size of the alloy fine particles can be small and uniformly distributed.
Decrease in output voltage over time during battery operation is reduced.

[Brief explanation of the drawing]

FIG. 1 is a diagram comparing the life characteristics of a catalyst according to an embodiment of the present invention with that of a conventional catalyst, and FIG. 2 is a schematic cross-sectional view showing an electrode of a battery.

Claims (1)

[Claims] 1) The method is characterized by applying ultrasonic waves to a mixture of water, catalyst carrier, and chloroplatinic acid to mix and disperse the catalyst carrier and chloroplatinic acid well, and then using a reducing agent to support platinum fine particles on the catalyst carrier. A method for producing a fuel cell catalyst.