JPH04366558A - Fuel cell and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve initial characteristic and stability by forming, on an electrode base material, an electrode catalytic layer in which a catalyst having a ternary alloy of platinum, iron and nickel supported on a carbon carrier is bonded with a binder. CONSTITUTION:A carbon black such as acetylene black is added to pure water, and a chloroplatinic acid aqueous solution is added thereto followed by heating. Then, its pH is adjusted with a NaOH solution, and a hydrazine solution is added dropwise to the resulting mixture to reduce the chloroplatinic acid. After the reduction is terminated, filtration, washing and drying are conducted to provide a platinum-supporting catalyst. The platinum-supporting catalyst is dispersed in pure water. Separately, cobalt nitrate and iron nitrate are dissolved in pure water to form a homogeneous mixture of the iron formed into a hydroxide and nickel, which is then added to the solution in which a platinum-supporting catalyst 2 is dispersed, and the resulting solution is thermally treated after filtration and drying to provide a catalyst 3 supporting a ternary alloy 2A. An electrode catalytic layer 5 in which the catalyst 3 is bonded with a binder is laminated on an electrode base material 1. Thus, characteristic and stability are improved because of a small crystal particle size and less change on standing.

Description

[Detailed description of the invention]

0001

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

0002

[Prior Art] Gas diffusion electrodes for fuel cells generally consist of a porous carbon electrode base material with excellent electrical conductivity, on which an electrode catalyst layer consisting of a catalyst powder supporting a noble metal bound with polytetrafluoroethylene is laminated. It is formed by

[0003] In this electrode catalyst layer, the three-phase coexistence of oxygen or hydrogen, which is a reactant gas supplied, a phosphoric acid electrolyte, and a catalyst occurs uniformly, so that an electrochemical reaction can be directly extracted as electrical energy.

FIG. 1 is a schematic cross-sectional view showing the electrode structure of a fuel cell. The fuel cell includes an electrode base material 1 made of porous carbon having air or hydrogen flow passages, and a PTFE material 4 that imparts appropriate water repellency to the catalyst 3 supporting the platinum catalyst 2.
The electrode catalyst layer 5 is a mixture of the following. In this electrode catalyst layer, the supplied reactive gases, air and hydrogen, and the electrolyte, phosphoric acid, create a three-phase coexistence state on the surface of the catalyst particles, causing an electrochemical reaction and allowing direct extraction of electrical energy. .

Conventionally, catalysts using platinum, which are resistant to corrosion by high-temperature phosphoric acid, have been used as catalysts for phosphoric acid fuel cells. Catalysts play an extremely important role in electrode reactions, and it is necessary to increase their activity and stability to improve battery output and lifespan.

[0006] Conventional methods for producing platinum catalysts generally employ a liquid phase reduction method. Specifically, in order to easily disperse the platinum-supporting carbon black in the liquid phase, it is treated with an acid such as nitric acid or glacial acetic acid, and then the platinum necessary to support the chloroplatinic acid aqueous solution is added. Liquid temperature 40-90
After the temperature is lowered to ℃, hydrazine or formic acid is added dropwise as a reducing agent to reduce platinum.

Furthermore, in order to increase the activity of the catalyst, alloying is performed by adding a second metal component such as vanadium, chromium, cobalt, nickel, or iron to the platinum-supported catalyst. First, the platinum-reduced catalyst mentioned above is dispersed again in an aqueous solution, a nitrate of a second metal is added, and an alkali agent such as potassium hydroxide, sodium hydroxide, or aqueous ammonia is used to convert the second metal into a hydroxide onto the carbon surface. Deposit. This is filtered, washed with water, and dried at 800 to 1000℃ in an inert atmosphere.
The alloy catalyst was produced by heat treatment. It is a well-known technology that alloy catalysts in which other group IV to VIII transition metals are added to platinum catalysts can improve catalytic activity, and in order to further improve activity and stability, platinum-chromium
Cobalt (JP 59-141169), platinum-iron-cobalt (JP 62-163746)
, platinum-nickel-cobalt (JP-A-63-190
No. 254) and other ternary catalysts have also been introduced.

[0008]

However, although these catalysts have excellent initial activity, their properties deteriorate in a relatively short period of time, so there remains a need to improve their stability. This invention has been made in view of the above points, and its purpose is to provide a fuel cell with excellent characteristics and stability by developing a new catalyst material and a method for producing the same.

[0009]

[Means for Solving the Problems] According to the present invention, the above-mentioned object has an electrode catalyst layer on an electrode base material, and the electrode catalyst layer supports a ternary alloy of platinum, iron, and nickel on a carbon carrier. The catalyst is bound with a binder, or it has a first step, a second step, and a third step, and the first step is to combine nickel hydroxide and iron hydroxide on platinum-supported carbon. The second step is to heat-treat the carbon on which the hydroxide has been deposited at a temperature of 800 to 1000°C to prepare a catalyst, and the third step is to prepare an electrode in which the catalyst is bound with a binder. This is achieved by laminating the catalyst layer on the electrode base material.

0010

[Operation] By using a platinum-iron-nickel ternary alloy catalyst, which is a combination of iron and nickel, which have relatively high initial activity and excellent stability as a binary catalyst, both catalyst activity and stability are improved. can be improved.

[0011]

EXAMPLES The present invention will be explained based on examples. Weigh out 9g of carbon black such as acetylene black and transfer it to 200m.
Add to l of pure water. Next, 1 g of a chloroplatinic acid aqueous solution was added as platinum (pt), and the temperature was raised to 60°C. After the temperature became constant, the pH was adjusted to 10 with a NaOH 2N solution, and a 3% hydrazine solution was added dropwise to reduce the chloroplatinic acid. After the reduction is completed, a platinum-supported catalyst is obtained by filtering, washing, and drying with a glass filter. The platinum crystallite diameter of this platinum-supported catalyst was 28 Å.

[0012] The alloying of the platinum-supported catalyst thus obtained will be described below. First, add platinum-supported catalyst to 200ml of pure water.
dispersed into Apart from this, cobalt (Co) is 0.
15g of cobalt nitrate and 0.15g of iron (Fe)
of iron nitrate was weighed out and dissolved in 50 ml of pure water. Furthermore, ammonia water was added to this solution to adjust the pH to 8,
A homogeneous mixture of iron and nickel in the form of hydroxide is prepared using an ultrasonic disperser. This solution was added to the solution in which the platinum-supported catalyst was dispersed, and aqueous ammonia was added dropwise to adjust the pH to 9.
Adjust the temperature and allow sufficient contact for 1 to 5 hours. After filtering with a glass filter, washing with water, and drying, heat treatment is performed at 800 to 1000°C in a nitrogen stream. In this way, a catalyst supporting the ternary alloy 2A is obtained.

The platinum crystallite diameter of the alloying catalyst produced by this method was 33 Å. The resulting platinum-iron-nickel ternary alloy catalyst had superior properties in both initial activity and stability compared to conventional alloy catalysts. Table 1
shows the initial characteristics and the change in crystallite diameter after 1000 hours.

[0014]

[Table 1]

[0015]

[Effects of the Invention] According to the present invention, an electrode catalyst layer is provided on an electrode base material, and the electrode catalyst layer includes a catalyst in which a ternary alloy of platinum, iron, and nickel is supported on a carbon carrier, and is bound by a binder. or having a first step, a second step, and a third step, where the first step is to deposit nickel hydroxide and iron hydroxide on platinum-supported carbon. The second step is to heat-treat the carbon on which the hydroxide has been deposited at a temperature of 800 to 1000°C to prepare a catalyst, and the third step is to prepare an electrode catalyst layer in which the catalyst is bound with a binder. Since this is a step of laminating on an electrode base material, a ternary alloy catalyst with a small crystallite size and little change over time can be obtained, and as a result, a fuel cell with excellent characteristics and stability can be obtained.

[Brief explanation of drawings]

[Figure 1] Schematic cross-sectional view showing the 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 (4)

[Claims] [Claim 1] An electrode catalyst layer is provided on an electrode base material, and the electrode catalyst layer is formed by binding a catalyst in which a ternary alloy of platinum, iron, and nickel is supported on a carbon carrier with a binder. A fuel cell featuring: Claim 2: The method comprises a first step, a second step, and a third step, where the first step is a step of depositing nickel hydroxide and iron hydroxide on platinum-supported carbon, and the second step is a step of depositing nickel hydroxide and iron hydroxide on platinum-supported carbon. The step is to prepare a catalyst by heat-treating the carbon on which the hydroxide is deposited at a temperature of 800 to 1000°C, and the third step is to stack an electrode catalyst layer in which the catalyst is bound with a binder on the electrode base material. A method for manufacturing a fuel cell, characterized by a step of: 3. In the production method according to claim 2, the hydroxide is deposited by adding aqueous ammonia to a mixed solution of nitrates.
1. A method for producing a fuel cell, comprising: preparing a homogeneous mixture by ultrasonic dispersion of a suspension with H of 8; and bringing the homogeneous mixture into contact with platinum-supported carbon. 4. The method of manufacturing a fuel cell according to claim 2, wherein the heat treatment is performed in a nitrogen stream.