JPH05135773A - Catalyst for phosphoric acid type fuel cell and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve the initial characteristic and stability of a phosphoric acid type fuel cell using a platinum alloy carrying catalyst. CONSTITUTION:A platinum alloy is a ternary alloy of Pt-Ti-Co. To manufacture it, cobalt nitrate and titanium trichloride are dissolved in hot water, and a homogeneous mixed solution of a hydroxide of Ti and Co is obtained. It is added to the aqueous solution of a platinum carrying catalyst manufactured separately, Pt grains are deposited, then it is filtered, washed, dried, and heat- treated at a high temperature.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phosphoric acid fuel cell catalyst and a method for producing the same.

[0002]

2. Description of the Related Art A phosphoric acid fuel cell generally comprises a porous carbon base material having a flow passage for air or hydrogen and excellent electrical conductivity, and two gas diffusion electrodes each formed of a catalyst layer formed on the base material. , Has a structure sandwiching a matrix.
The catalyst layer is a mixture of a catalyst powder carrying a noble metal such as platinum (Pt) and polytetrafluoroethylene that imparts appropriate water repellency. In a phosphoric acid fuel cell, a reaction gas supplied to this catalyst layer is used. The three-phase coexistence of the oxygen or hydrogen with the phosphoric acid as the electrolyte and the catalyst uniformly takes place, so that the electrochemical reaction can be directly taken out as electric energy.

Conventionally, platinum, which is corrosion resistant to high temperature phosphoric acid, has been used as a catalyst for phosphoric acid fuel cells. The catalyst plays an extremely important role in the electrode reaction, and it is necessary to increase the activity and stability of the catalyst with respect to the output and life of the battery. As a method for producing a platinum catalyst, a liquid phase reduction method is generally used, and in order to make it easier to disperse carbon black in a liquid phase, an acid treatment such as nitric acid or glacial acetic acid is carried out, and then supported. An aqueous solution of chloroplatinic acid corresponding to the necessary amount of platinum is added to bring the liquid temperature to 40 to 90 ° C., and then hydrazine or formic acid as a reducing agent is dropped to reduce platinum.

Further, in order to increase the activity of the catalyst, vanadium (V), chromium (C
r), cobalt (Co), nickel (Ni), iron (F)
Alloying is performed by adding a second metal component such as e). The platinum catalyst obtained as described above is dispersed again in an aqueous solution, the nitrate of the second metal is added, and the second metal is hydroxylated with an alkaline agent such as potassium hydroxide, sodium hydroxide or aqueous ammonia. It is deposited as an object on the carbon surface. This is filtered, washed with water, dried and then placed in an inert gas atmosphere for 8 hours.
An alloy catalyst is produced by performing a heat treatment at 00 to 1000 ° C.

As described above, it is a well-known technique that an alloy catalyst obtained by adding a Group IV to VIII transition metal to a platinum catalyst improves the activity of the catalyst. JP-A-59-141169 discloses Pt-
Cr-Co system, Pt in JP-A-62-163746
-Fe-Co system, P in JP-A-63-190254
A ternary alloy catalyst such as a t-Ni-Co system is also described.

[0006]

However, although these catalysts have excellent initial activity, their characteristics deteriorate in a relatively short time. An object of the present invention is to provide a phosphoric acid fuel cell catalyst capable of maintaining stability for a long time and a method for producing the same.

[0007]

In order to solve the above-mentioned problems, the catalyst of the present invention carries a Pt-Ti-Co ternary alloy, the alloy composition of which is 10 to 25% by weight of Ti and 10 to 10% of Co. 25% by weight and 50-80% by weight of Pt. The manufacturing method is PH8 by adding ammonia water to a mixed solution of cobalt nitrate and titanium trichloride, and Ti and C.
A homogeneous mixed solution of hydroxide of o was prepared, and this solution was added to an aqueous solution of a platinum-supported catalyst prepared separately, and was sufficiently contacted to deposit Pt particles, and then heat-treated to form Pt-Ti. Obtain a Co ternary alloy supported catalyst.

[0008]

The catalyst of the present invention obtained as described above is one of the conventional catalysts carrying a binary alloy or a ternary alloy.
Ti and Co are selected as alloy components having relatively high initial activity and excellent stability, and Pt-Ti is obtained by combining them.
By supporting a ternary alloy of —Co, both catalytic activity and stability can be enhanced.

[0009]

EXAMPLES The present invention will be described below based on examples. The catalyst of the present invention is a catalyst carrying a ternary alloy of Pt-Ti-Co, and the alloy composition is Ti10 to 2 by weight.
5%, Co 10 to 25%, and the balance Pt 50 to 80
%. 10 to 25% for both Ti and Co
The reason for this is that if the content is 10% or less, the properties are insufficient, and if it is 25% or more, the corrosion resistance of the catalyst is poor.

The Pt-Ti-Co alloy supported catalyst of the present invention can be manufactured as follows. First, weigh 9g of carbon black such as acetylene black,
This is added to 200 ml of pure water. Next, 1 g of chloroplatinic acid aqueous solution is added and the temperature is raised to 60 ° C. After the temperature became constant, adjust the pH to 10 with 2N NaOH solution, and adjust to 3
% Hydrazine solution is added dropwise to reduce chloroplatinic acid. After completion of the reduction, the platinum-supported catalyst can be obtained by filtering with a glass filter, washing and drying.
The platinum crystallite diameter of this platinum-supported catalyst is 28Å.

Next, the platinum-supported catalyst obtained as described above is alloyed. First, the platinum-supported catalyst was replaced with pure water 200
Disperse in ml. Separately, 0.3 g of cobalt nitrate and 0.3 g of titanium trichloride were dissolved in 50 ml of hot water and added, and ammonia water was added to adjust the pH to 8, and a hydroxide was added using an ultrasonic disperser. A homogeneous mixed solution of Ti and Co is prepared. This solution is added to the solution in which the platinum-supported catalyst is dispersed, ammonia water is added dropwise to adjust the pH to 11, and it is sufficiently contacted for 1 to 3 hours. Then, after filtering with a glass filter, washing with water and drying, 10
Heat treatment is performed at 00 to 1200 ° C. The obtained catalyst has a ternary alloy crystallite diameter of 32Å.

The initial activity and stability of the ternary alloy-supported catalyst of the present invention are shown in Table 1 in comparison with the conventional catalyst. The life characteristics are values when the battery is operated for 1000 hours.

[Table 1] As can be seen from Table 1, the catalyst of the present invention has the highest initial voltage characteristic value, the smallest difference in alloy crystallite diameter before and after the test, and excellent stability as compared with the conventionally used catalyst.

[0013]

While the conventional catalyst supporting Pt or its alloy is insufficient in the initial characteristics and stability of the fuel cell, the present invention, as described in the embodiment, is a catalyst supporting a binary alloy. As a combination of Ti, which improves the characteristics as described above, and Co, which is relatively good and is used in a catalyst supporting a ternary alloy,
Since it is a Pt-Ti-Co based ternary alloy-supported catalyst,
The initial characteristics and stability of the fuel cell could be improved as compared with the conventional catalyst.

Claims (3)

[Claims] 1. A catalyst for a phosphoric acid fuel cell in which a matrix is sandwiched between gas diffusion electrodes composed of an electrode substrate and a catalyst layer, wherein a phosphoric acid carrying a Pt-Ti-Co ternary alloy is carried. Type fuel cell catalyst. 2. The catalyst according to claim 1, wherein the composition of the ternary alloy is 10 to 25% by weight of Ti, 10 to 25% of Co,
A catalyst for a phosphoric acid fuel cell, characterized in that the balance is Pt. 3. In producing the catalyst according to claim 1 or 2, cobalt nitrate and titanium trichloride are dissolved in hot water, ammonia water is added to adjust the pH to 8, and the mixture is homogenized using an ultrasonic disperser. After the solution was prepared, this solution was added to an aqueous solution of a platinum-supported catalyst prepared separately, and sufficiently contacted, filtered, washed with water and dried, and then this was placed in an inert atmosphere for 8 hours.
A method for producing a catalyst for a phosphoric acid fuel cell, which comprises performing a heat treatment at 00 to 1000 ° C.