JPH0629028A - Fuel cell and its manufacture - Google Patents

Abstract

PURPOSE:To provide a fuel cell excellent in the initial characteristics and secular stability by structuring a catalyst so that a ternary alloy of platinum, iron, and chromium is borne by a carrier consisting of carbon, and fastening the catalyst onto an electrode base material using a binder. CONSTITUTION:A catalyst 3 is structured so that a ternary alloy 2A consisting of 8-24% iron, 8-24% chromium, and platinum for remainder is borne by a carrier of carbon. An electrode catalyst layer 5 is formed by laying this catalyst 3 on an electrode base material 1 using a binder. This ternary alloy catalyst has a small dia. of crystallite and presents lesser secular change. This achieves a fuel cell excellent in the initial characteristics and secular stability.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode catalyst layer of a fuel cell, and more particularly to a catalyst material and a method for producing the same.

[0002]

2. Description of the Related Art In general, a gas diffusion electrode for a fuel cell has a porous carbon electrode substrate having excellent electric conductivity, and an electrode catalyst layer obtained by binding a catalyst powder carrying a noble metal with polytetrafluoroethylene. Formed.

The three-phase coexistence of oxygen or hydrogen, which is the reaction gas supplied in the electrode catalyst layer, with the phosphoric acid electrolyte and the catalyst uniformly occurs, so that the electrochemical reaction can be directly taken out as electric energy.

FIG. 1 is a schematic sectional view showing an electrode structure of a fuel cell. The fuel cell has an electrode catalyst layer 5 in which an electrode base material 1 made of porous carbon having a flow passage for air or hydrogen and a catalyst 3 carrying a platinum catalyst 2 and PTFE 4 for imparting appropriate water repellency are mixed. Has become. In this electrode catalyst layer, the supplied reaction gases, air and hydrogen, and the electrolyte, phosphoric acid, cause a three-phase coexistence state on the surface of the catalyst particles, whereby an electrochemical reaction occurs and electrical energy can be directly extracted. .

Conventionally, as a phosphoric acid fuel cell catalyst, a catalyst using platinum, which has corrosion resistance to high-temperature phosphoric acid, has been used. The catalyst plays an extremely important role in the electrode reaction, and it is necessary to enhance the activity and stability of the catalyst in order to improve the output and life of the battery.

As a conventional method for producing a platinum catalyst, a liquid phase reduction method is generally used. Specifically, in order to facilitate dispersion of carbon black supporting platinum in the liquid phase, acid treatment such as nitric acid or glacial acetic acid is performed, and then platinum necessary for supporting an aqueous chloroplatinic acid solution is added, After adjusting the liquid temperature to 40-90 ℃, hydrazine and formic acid are added dropwise as a reducing agent to reduce platinum.

Further, in order to increase the activity of the catalyst, alloying is carried out by adding a second metal component such as vanadium, chromium, cobalt, nickel or iron to the catalyst carrying platinum. First, the platinum-reduced catalyst is dispersed again in an aqueous solution, the nitrate of the second metal is added, and the second metal is converted to hydroxide on the carbon surface with an alkaline agent such as potassium hydroxide, sodium hydroxide, or ammonia water. Deposit. This was filtered, washed with water, dried, and then heat-treated at 800 to 1000 ° C in an inert atmosphere to prepare an alloy catalyst. It is a well-known technique that an alloy catalyst obtained by adding another IV-VIII group transition metal to a platinum catalyst can improve the catalytic activity, and platinum-chromium-cobalt is further sought in order to improve the activity and stability. (JP-A-59-141169), platinum-iron-cobalt (JP-A-62-141169)
─163746), platinum-nickel-cobalt (JP
63-190254) and other three-way catalysts are also introduced.

[0008]

However, although these catalysts are excellent in initial activity, they show deterioration in characteristics in a relatively short time, so that it is necessary to improve stability. The present invention has been made in view of the above points, and an object thereof is to provide a fuel cell having excellent characteristics and stability by developing a novel catalyst substance and a method for producing the same.

[0009]

According to the first aspect of the present invention, there is provided an electrode catalyst layer on an electrode substrate, and the electrode catalyst layer is a ternary alloy of platinum, iron and chromium on a carbon support. According to the second aspect of the present invention, the catalyst supporting the catalyst is bound with a binder, and has a first step, a second step, and a third step. The first step is platinum loading. The step of depositing chromium hydroxide and iron hydroxide on the formed carbon, the second step is the step of heat-treating the deposited carbon of the hydroxide at a temperature of 800 to 1000 ° C. to prepare a catalyst, The step is achieved by binding the catalyst with a binder to prepare an electrode catalyst layer and then laminating the electrode catalyst layer on an electrode substrate.

[0010]

[Function] A platinum-iron-chromium ternary alloy catalyst that combines iron and chromium, which is a binary catalyst with relatively high initial activity and excellent stability, provides both catalytic activity and stability. Can be improved.

[0011]

EXAMPLES The present invention will be described based on examples. Weigh out 9g of carbon black such as acetylene black and add to 200ml of pure water. Next, 1 g of chloroplatinic acid aqueous solution was added as platinum (pt) and the temperature was raised to 60 ° C. Na after the temperature becomes constant
Adjust the pH to 10 with OH 2 N solution and add 3% hydrazine solution dropwise to reduce chloroplatinic acid. After completion of the reduction, a platinum-supported catalyst can be obtained by filtering, washing and drying with a glass filter. The platinum crystallite diameter of this platinum-supported catalyst was 28Å.

The alloying of the platinum-supported catalyst thus obtained is shown below. First, the platinum-supported catalyst is dispersed in 200 ml of pure water. Separately, 0.30 g of chromium acetate as chromium (Cr) and 0.30 g of ferrous nitrate as iron (Fe) were weighed out and purified to 50 ml of pure water.
Dissolves in. Furthermore, a sodium hydroxide solution is added to this solution to adjust the pH to 8, and an ultrasonic disperser is used to prepare a homogeneous mixed solution of iron and chromium that has become hydroxide. This solution is added to the solution in which the platinum-supported catalyst is dispersed, a sodium hydroxide solution is added dropwise to adjust the pH to 11, and the mixture is sufficiently contacted for 1 to 3 hours. Then, it is filtered with a glass filter, washed with water, dried, and then heat-treated at 800-1000 ° C in a nitrogen stream. Thus, the catalyst supporting the ternary alloy 2A is obtained.

The crystallite diameter of the alloying catalyst produced by this method was 33Å. The obtained platinum-iron-chromium ternary alloy catalyst had excellent initial activity and stability compared with the conventional alloy catalyst. Table 1 shows the initial characteristics and the change in crystallite size after 500 h.

[0014]

[Table 1]

[0015]

According to the first aspect of the present invention, the electrode catalyst layer is provided on the electrode base material, and the electrode catalyst layer is formed by binding the catalyst in which the ternary alloy of platinum, iron and chromium is supported on the carbon support with the binder. According to the second aspect of the present invention, it has a first step, a second step, and a third step, the first step is a platinum-supported carbon and chromium hydroxide. The second step is the step of depositing iron hydroxide, the second step is a step of heat-treating the hydroxide-deposited carbon at a temperature of 800 to 1000 ° C. to prepare a catalyst, and the third step is the step of binding the catalyst with a binder. It is a step of depositing an electrode catalyst layer and then laminating this electrode catalyst layer on an electrode base material, so that a ternary alloy catalyst having a small crystallite diameter and little change over time is obtained. A fuel cell having excellent characteristics and stability can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an electrode structure of a fuel cell.

[Explanation of symbols]

 1 electrode base material 2 platinum 2A ternary alloy 3 catalyst 4 PTFE 5 electrode catalyst layer

Claims (5)

[Claims] 1. An electrode catalyst layer is provided on an electrode base material, and the electrode catalyst layer is formed by binding a catalyst supporting a ternary alloy of platinum, iron and chromium on a carbon support with a binder. Is a fuel cell. 2. The fuel cell according to claim 1, wherein the composition of the ternary alloy is 8 to 24% iron and 8 to 24 chromium.
%, The balance is platinum, the fuel cell. 3. A first step, a second step, and a third step, wherein the first step is a step of depositing chromium hydroxide and iron hydroxide on carbon carrying platinum. In the process, the carbon deposited with the hydroxide is heated to a temperature of 80.
A step of preparing a catalyst by heat treatment at 0 to 1000 ° C., and a third step is a step of binding the catalyst with a binder to prepare an electrode catalyst layer, and then laminating the electrode catalyst layer on an electrode substrate. A method for manufacturing a fuel cell, characterized in that 4. The method according to claim 3, wherein the hydroxide is deposited by ultrasonically dispersing a suspension having a pH of 8 by adding a sodium hydroxide solution to a mixed solution of chromium acetate and iron nitrate. A method for producing a fuel cell, comprising preparing a homogeneous mixed solution by contacting the homogeneous mixed solution with carbon carrying platinum, and further adjusting the pH to 11. 5. The method for producing a fuel cell according to claim 3, wherein the heat treatment is performed in a nitrogen stream.