JPH0368452A - Production of platinum alloy catalyst - Google Patents

Abstract

PURPOSE:To form a Pt alloy catalyst having high output characteristics at high current density by successively supporting a specified amt. of a Pt alloy and iron on a carbon catalyst carrier and carrying out heat treatment under the conditions of specified heating rate, max. temp. and cooling rate. CONSTITUTION:A Pt alloy is supported on a carbon catalyst carrier by 20-50wt.% and iron is further supported. Heat treatment is then carried out under the conditions of 100-600 deg.C/min heating rate, 900-1,000 deg.C max. temp., 5-30sec holding time at the max. temp. and 100-600 deg.C/min cooling rate to alloy the supported Pt alloy and iron and a Pt alloy catalyst is produced. By this method, a large amt. of the Pt alloy having a small grain size is obtd. and a fuel cell having superior characteristics in a high current density region is obtd.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a method for producing a platinum alloy catalyst for fuel cells,
In particular, the present invention relates to a method for producing a platinum alloy catalyst having a small crystal grain size and excellent properties.

[Conventional technology]

A fuel cell directly converts the chemical energy of fuel into electrical energy, and its configuration is as shown in FIG. 3, in which electrodes 6 are placed across an electrolyte layer 8 made of, for example, phosphoric acid, and an external Power generation in which fuel gas and oxidant gas are supplied from the gas supply system to each of the electrodes, the fuel gas and oxidant gas are electrochemically reacted on the electrode catalyst of each electrode, and as a result, electrical energy is taken out of the system. It is a type of device.

The electrode 6 is constructed by depositing an electrode catalyst layer 5 on a porous carbon base material 4. The seed catalyst layer 5 is formed by supporting the catalyst particles 1 on the surface of the catalyst carrier 2 and then binding them with fine particles 3 of fluorine resin.

Inside this electrode catalyst layer 5, the gas from the carbon base material side and the electrolytic solution from the electrolytic solution layer come into contact, a three-phase interface is formed, and an electrochemical reaction progresses. Silicon carbide particles 9 retain electrolyte 8 .

In order to carry out this electrochemical reaction efficiently, it is necessary to increase the number of three-phase interfaces where the catalyst particles, electrolyte, and gas in the electrode catalyst layer are in contact with each other, and to increase the activity of the catalyst particles. In order to increase the number of three-phase interfaces, the particle diameter of the catalyst particles is reduced to increase the catalyst surface area. Further, in order to increase the activity of the catalyst, for example, in the case of a phosphorus #II type fuel cell, a platinum alloy is used to increase the activity.

The platinum alloy catalyst is used by being supported on a carbon blank catalyst carrier in a proportion of 5 to 20% by weight. Conventionally, chloroplatinic acid was reduced in a chloroplatinic acid solution to precipitate platinum on a carbon catalyst support, then iron nitrate was reduced in a nitric Mt&solution to deposit iron on a carbon support, and then 800% ~90
A fine platinum alloy catalyst supported on a carbon catalyst carrier was obtained by heat treatment at a temperature of 0° C. for 1 to 2 hours. This platinum alloy catalyst is used in a phosphoric acid fuel cell at 100 to 200 m
A current density of A/- was used.

[Problem IX that the invention attempts to solve]

However, in recent years there has been a demand for further improvements in battery performance, and
High output characteristics at high current densities of 00 mA/- or more are now required. To achieve this, it is necessary to increase the amount of catalyst supported than before, but in doing so, conventional heat treatment methods have the problem that the catalyst particles become bulky, reducing the effective surface area of the catalyst and making it impossible to obtain the desired high output characteristics. For example, as shown in Figure 2, the platinum alloy was 10 (curve 10), 2
0 (song &lI 11).

(Curve 12), 40 (Curve & 113) The catalyst particle diameters when supported by weight% are 40, 100, 200, and 40, respectively.
No improvement was observed in the polarization characteristics of the cell.

The present invention has been made in view of the above-mentioned points, and its object is to provide a method for producing a platinum alloy catalyst that has excellent output characteristics at high current density by reducing the particle size of a highly supported catalyst.

Means for Solving CFAB] According to the present invention, the above-mentioned object is a method for producing a platinum alloy catalyst having a first step, a second step, and a third step, in which the first step is a carbon catalyst carrier. Platinum alloy on top of 20~5
The second step is to support iron on the carbon catalyst carrier, and the third step is to alloy the supported platinum and iron by heat treatment. , The heat treatment is performed at a temperature increase rate of 100 to 600°C/min. +
The maximum temperature is 900-1000℃! lHolding time at high temperature 5-30m, cooling rate 100-600℃/old n
This is achieved by doing .

[Effect]

Since the heat treatment time for alloying is short, alloying is performed without causing crystal growth of catalyst particles.

〔Example〕

Next, embodiments of the present invention will be described based on the drawings.

(Execution g41) 800 g of acetylene black is sufficiently dispersed in the water of step 401 using ultrasonic waves. Add 201 of an aqueous solution of chloroplatinic acid containing 200 g of platinum as metal and stir thoroughly. Add 19.51 of an aqueous solution of O,I MNalCO
The temperature is raised to 55°C over about 2 hours. Add 1.071 g of 30% by weight hydrogen peroxide solution, and add 20 g of 0.2 M formic acid aqueous solution.
5. Add j over 5 hours. 6. After the reaction is complete, filter the cake and wash thoroughly until no chlorine ions are detected. This catalyst carrier 5 is dried under vacuum at 50°C to obtain a catalyst carrier on which 20% by weight of platinum is supported.
00g is dispersed in an aqueous O,OIMFe(NOs)3 solution 38j, and stirred at 50°C for 1h. This is platinum alloy &11
As a precept, it is equivalent to 42.8 atomic percent of iron. While continuing to stir, add 0.1% N)1. OR aqueous solution 247 is added dropwise over 20 hours. At this time, iron hydroxide Fe (OH) s is deposited on the catalyst carrier. Suction filter the solid matter and wash with water for 50 minutes.
Vacuum dry at °C. Grind it, put it in an electric furnace, pour a mixed gas containing 7% hydrogen gas into nitrogen gas, and heat it to 200 to 350
Heat for 1 h at a temperature of °C. At this time, the catalyst carrier supporting platinum and iron obtained in the step 0 or more in which iron is completely reduced is loaded into an infrared instantaneous heating device, and nitrogen gas is heated for 15 m1n to remove oxygen in the furnace. Flowing a small amount of nitrogen gas next, and maintaining a nitrogen atmosphere at 600℃/
(2) The temperature was raised at a rate of ln, and maintained at a temperature of 950°C for 303 hours. Temperature drop is 600℃/sin.

When the platinum alloy catalyst is measured by X-ray diffraction method, a platinum alloy catalyst is obtained by cooling to room temperature (supporting amount is about 24%), and an average crystal grain size of 40 is obtained. No platinum or iron diffraction lines were observed in the platinum alloy catalyst, and the diffraction angles 2θ were 41.1°, 33°, and 47.4°.
superlattice lines are observed. These are each (111)
These are the diffraction lines of the (110) plane, and (020) plane. This fact indicates that alloying has been completely completed.The polarization characteristics of the phosphoric acid fuel cell using the platinum alloy catalyst according to this example are shown by curve 15 in FIG.
0 is the polarization characteristic when the platinum alloy catalyst is 10% by weight.

At high current densities of 200 to 600 −^/−, the platinum alloy catalyst according to this example has better characteristics than conventional catalysts.

(Example 2) A catalyst carrier carrying 40% by weight of platinum and 10% by weight of iron was loaded into an infrared instantaneous heating device, and the temperature was raised at a rate of 100°C/min. to 1000°C under a nitrogen atmosphere. So 5
Hold for 3 hours and heat at 100°C/min. The temperature decreased at a rate of . By cooling to room temperature, a platinum alloy catalyst with a supported amount of 50% by weight is obtained. The average crystal grain size of the platinum alloy catalyst thus obtained was 70%.O alloying was complete.O polarization characteristics are shown in track &116 in FIG.

In this example, reduced precipitation of iron is obtained by reducing an iron compound solution with a reducing agent such as hydrazine.

(Example 3) A catalyst carrier carrying 16% by weight of platinum and 4% by weight of iron was loaded into an infrared instantaneous heating device and heated at 250°C under a nitrogen atmosphere.
/min. The temperature was raised at a rate of 250°C/min. The temperature decreased at a rate of . The average crystal grain size of the obtained platinum alloy catalyst was 30.

The fully alloyed zero polarization profile is shown in curve 14 of FIG.

In addition to the above experimental conditions, the temperature increase rate was 100 to 600°C/sin.
.

The objective can be achieved with any combination of maximum temperature of 900 to 1000°C, holding time of 5 to 30 seconds, and cooling rate of 100 to b.

Further, the alloy composition of platinum and iron is not limited to the composition in the examples.

〔Effect of the invention〕

According to this invention, there is provided a method for producing a platinum alloy catalyst comprising a first step, a second step, and a third step, wherein the first step is to deposit 20 to 50% of the platinum alloy on a carbon catalyst carrier.
The second step is to support iron on the carbon catalyst carrier, and the third step is to alloy the supported platinum and iron by heat treatment. , The heat treatment has a temperature increase rate of 100 to 600°C/sln, +
The maximum temperature is 900-1000°C, the holding time at the maximum temperature is 5-30s, and the cooling rate is 100-600°C/min.
Since this is carried out under high loading, a platinum alloy with a small crystal grain size can be obtained, and a fuel cell with excellent characteristics in a high current density region can be obtained.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the polarization characteristics of a battery using a platinum alloy catalyst according to an embodiment of the present invention in comparison with conventional polarization characteristics;
FIG. 2 is a diagram showing the polarization characteristics of a battery using a conventional platinum alloy catalyst, and FIG. 3 is a schematic cross-sectional view showing a phosphoric acid fuel cell. 1: catalyst particles, 2: catalyst carrier. e Temperature window (fM/cyr=□) Figure 1 Current density (fM/cw) Figure 2

Claims (1)

[Claims] 1) A method for producing a platinum alloy catalyst comprising a first step, a second step, and a third step, wherein the first step is to deposit 20 to 50% of the platinum alloy on a carbon catalyst carrier.
The second step is to support iron on the carbon catalyst carrier, and the third step is to alloy the supported platinum and iron by heat treatment. , The heat treatment is performed at a temperature increase rate of 100 to 600°C/min. ,
The maximum temperature is 900-1000°C, the holding time at the maximum temperature is 5-30s, and the cooling rate is 100-600°C/min.
A method for producing a platinum alloy catalyst, characterized in that the method is carried out by: