JPS60210514A - Electric catalyst containing platinum highly diffused in superfine titanium carbide - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Field of Application) The present invention relates to an electrocatalyst.
), especially the cathode in fuel cells
Regarding electrocatalysts used in

BACKGROUND OF THE INVENTION Carbon supports for anode catalysts are important elements in fuel cells with regard to cell efficiency and longevity. However, conductive carbon blanks do not always exhibit sufficient resistance to corrosion caused by electrochemical oxidation in fuel cells. Thermodynamically, carbon as a material has a positive anode potential (
cathodepotential) and unstable. Corrosion at the anode in a fuel cell can lead to various manners of fuel cell performance deterioration, such as undercut.
increased platinum migration (i.e., corrosion of the carbon under the platinum catalyst) and increased diffusion losses due to rupture of the carbon-Teflon™ interface (dHfusion).
1oss). This places a fundamental limit on the lifetime of fuel cell electrodes. Furthermore, the recent trend towards higher temperatures and pressures in fuel cells where higher anode potentials are reached has led to carbon corrosion.
n) increase the likelihood of Furthermore, under practical working conditions, part-1 load operation (part-1 load operation)
ration ) is the oxygen electrode being 0 during some part of the time.
．． It is necessary that the potential be above 8 volts, which promotes carbon corrosion.

Improvements in the electrolyte portend even higher potentials at the oxygen electrode.

Therefore, for fuel cells to operate under extreme conditions,
New and improved support materials and catalysts for oxygen electrodes are needed. The phosphoric acid fuel cell (PAFC) mentioned here
) is A, Fickett, “Fuel Ce1lPo
11er Plant' 5cientific Am
erican+ 2 3 9 s70-76 (1978
(December 2013).

Titanium carbide (Tic) has been identified as a satisfactory conductor and appears to be stable in warm phosphoric acid at oxygen electrode potentials in fuel cells.

However, commercially available titanium carbide has a relatively low surface area (less than 1 n?/g) and is therefore generally not useful as an electrocatalyst support.

Microcrystalline sizes in the range of about 50-500 and 25-500 are therefore useful as electrocatalyst supports in fuel cells.
It is an object of the present invention to provide a titanium carbide support with a relatively large surface area of 125 rrr/g.

It is further an object of the present invention to provide a new electrocatalyst containing platinum impregnated on a titanium carbide support.

These and other objects of the invention will become apparent from the following description.

SUMMARY AND DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel electrocatalyst support and electrocatalyst and method for producing the same. The method involves producing an ultrafine titanium carbide catalyst support, which comprises contacting titanium tetrachloride in the gas phase with a gaseous unsaturated hydrocarbon and hydrogen in a reaction zone in the range of 500-1250°C. It is something. The capacity of hydrogen introduced into the reaction zone is such that the capacity ratio of hydrogen to titanium tetrachloride is 6 or more. The volume of unsaturated hydrocarbon introduced into the reaction zone is such that the titanium to carbon IL is 4 or less.

There are many ways to convert titanium carbide catalyst supports into catalysts by impregnation with platinum. Two methods are described, one of which (method A) is to impregnate a titanium carbide support composition with a chloroplatinic acid alcohol solution, separate the impregnated particles from the solution, dry the particles, and heat the particles at about 400°.
The process consists of exposing the particles to a hydrogen atmosphere at a temperature of about 350° C. and then exposing the particles to a carbon monoxide atmosphere at about 350°C. A second method of producing an electrocatalyst (Method B) consists of contacting the titanium carbide support composition with an aqueous solution of chloroplatinic acid, an aqueous solution of sodium dithionite, and dilute hydrogen peroxide.

The titanium carbide support composition according to the invention is characterized by a particle size in the range of 50 to 500 particles with open pores and a chain structure.

The titanium carbide support composition according to the invention is produced by the following stoichiometric reaction: 2 TiC1i +
(:zllz + 3 It□→2TiC+811CI
The above reactions are carried out in the gas phase in the presence of reactant gases alone or optionally in the presence of an inert gas such as argon.

The reaction is carried out at a temperature in the range of about 500-1250°C, preferably 650°C.
It is carried out at relatively low temperatures in the range of ~1100<0>C. The titanium tetrachloride volume concentration should be relatively dilute with respect to the hydrogen gas concentration, such that the ratio of the volume of hydrogen gas introduced into the reaction zone to the volume of titanium tetrachloride should be about 6 or more. The relative concentration of hydrocarbon gas may be high and therefore the volume of hydrocarbon gas used should be such that the ratio of titanium to carbon in the hydrocarbon gas is 4 or less. Unsaturated hydrocarbons such as ethylene, acetylene, propylene and the like are used, with acetylene being preferred.

The reaction can be carried out in a conventional tube furnace and is usually completed in about 2 to 10 hours.

Under preferred conditions, the furnace is maintained at a temperature in the range of 650-100°C, where the titanium tetrachloride vapor, hydrogen and hydrocarbon gases are mixed separately or premixed before being introduced into the reactor. will be introduced. If introduced separately, the titanium tetrachloride vapor and hydrocarbon gas are optionally introduced with an inert carrier gas such as argon gas. Argon may optionally also be used as carrier gas if all three gases are premixed. A typical production is to combine the three reactant gases in the reaction zone at a preferred temperature with a total space velocity of less than 1 O-1 hour.
e velocity) for about 4 to 8 hours. For optimum completion of the reaction, this is usually carried out by treatment of titanium tetrachloride with hydrogen for about 1 hour, followed by treatment with hydrogen for about 1 hour and cooling in an inert atmosphere.

The resulting titanium carbide has an open pore and chain structure that maintains good grain-to-grain contact and thereby good electrical conductivity for the composite catalyst layer.
It consists of fine particles with a particle size in the range of 0. Typically, the titanium carbide particles have a surface area of at least 25rd/g titanium carbide. Furthermore, such a chain structure can be easily manufactured by a conventional method for gas diffusion electrodes for fuel cells. Although this is an example of such generation, other techniques such as reactive plasma torch (rea
active plasma torch) is used.

To convert the support composition into an electrocatalyst, highly dispersed platinum is deposited onto ultrafine titanium carbide by various techniques to obtain a platinum surface area in the range of 20-90 nr/g platinum. . The platinum surface area is usually at least about 2
3 rrr/g, preferably 5'0 rrr/g platinum or more. Titanium carbide is impregnated by contacting titanium carbide particles with an alcoholic solution of chloroplatinic acid. The concentration of the chloroplatinic acid solution will vary depending on the amount of platinum desired to be deposited on the support. It is well within the skill of those skilled in the art to determine the appropriate concentration of Roroplatinum M solution according to the required specifications of a particular fuel cell design.

The particles are then separated from the solution, dried to remove the alcohol solvent, and the impregnated platinum salt is exposed to a hydrogen atmosphere at about 400° C. and then carbon monoxide at about 350° C. Reduced by exposure to atmosphere. Preferably, the particles should then be rapidly cooled; cooling to about 100°C is usually sufficient, although cooling to room temperature is preferred.

Also, titanium carbide particles can be converted into a chloroplatinic acid aqueous solution! The temperature is controlled. As mentioned above, the concentration of chloroplatinic acid, solution and amount of solution used will vary depending on the specific concentration of platinum desired in the catalyst support. This can be easily determined by a person skilled in the art according to the required specifications of the fuel cell. After contacting the particles with a chloroplatinic acid solution, the platinum salt is reduced by contacting with an aqueous sodium dithionite solution and then contacting with dilute hydrogen peroxide to remove excess dithionite. As a result, an aqueous solution of chloroplatinic acid was first reacted with sodium dithionite and hydrogen peroxide to obtain a colloidal platinum suspension, and then very fine platinum particles were adsorbed onto titanium carbide particles. It can be obtained by adding titanium carbide particles. Preferably, the particles are then washed and dried to remove residual moisture.

FIG. 1 shows a platinum-titanium carbide electrocatalyst prepared according to the present invention in which platinum is deposited on a support (0.5 μg of platinum/ad, 50% phosphoric acid, 20° C.,
mV/S scan rate;
Lammogram). In FIG. 1, the horizontal axis is in units of mV, and the vertical axis is in units of mA/cJ. The platinum surface areas obtained are shown in the drawings (al, Tbl, (C)), respectively.
It is about 23.68.94nf/g, and the measurement is 2
Potential sweep rate (po
50% at ten tia 1sweep rate)
It was done using a 1c11 electrode in phosphoric acid solution.

In FIG. 2, the oxygen reduction activity of the platinum-titanium carbide electrocatalyst according to the present invention having a platinum surface area of 23 rrr/g (solid line) is shown.
Fig. 10 shows a typical platinum-carbon electrocatalyst with a surface area of 120 rrr/g (dotted line). Each catalyst was distributed at 0.5 ■ platinum/alI, and the tests were conducted at 200° C. in a phosphoric acid fuel cell utilizing 100% phosphoric acid as the electrolyte. The vertical axis in FIG. 2 indicates the potential in mV set at 41 with respect to the reversible hydrogen electrode (R11[). As can be seen from Figure 2,
Platinum-titanium carbide catalysts can be used up to high current densities (
That is, about 4500μA/co! Platinum) was not only viable, but more viable than conventional platinum-carbon catalysts within the operable range of platinum-carbon catalysts of about 18-1000 μ/Ca.

In Figure 3, the performance of the catalyst preparation of the present invention with a platinum surface area of 68 rrr/g is shown to be further improved over a conventional platinum-carbon catalyst with a platinum surface area of 12 orrr/g. It is surprising that a simple change in the catalyst support would yield such improved benefits, especially in the very harsh conditions utilized in PAFC.

From the above description of the preferred embodiments of the invention, it will be apparent to those skilled in the art that certain modifications and alterations can be made without departing from the spirit of the invention, and such modifications,
Modifications are meant to be within the scope of this invention.

[Brief explanation of the drawing]

In the accompanying drawings, FIG.
m). FIGS. 2 and 3 are diagrams comparing the oxygen reduction activities of the platinum-titanium carbide according to the present invention (solid line) and a conventional platinum-carbon electrocatalyst (dotted line).

Claims (1)

[Claims] (1) Titanium tetrachloride in the gas phase is mixed with a gaseous unsaturated hydrocarbon and hydrogen, and the volume of hydrogen introduced into the reaction zone is such that the volume ratio of hydrogen to titanium tetrachloride is about 6 or more. and the volume of hydrocarbon introduced into the reaction zone is such that the titanium to carbon ratio is less than about 4, 500 to 1.
A method for producing ultrafine titanium carbide comprising a contacting step in a reaction zone at a temperature in the range of 250°C. (21a) 50-500 having open pores and chain structure
impregnating a titanium carbide composition characterized by a human particle size and a surface area of at least 25 rrr/g with an alcoholic solution of chloroplatinic acid, b) separating the impregnated particles from said solution and drying said particles, C) said d) exposing said particles to a carbon monoxide atmosphere at about 350°C. +31a) 50-500 with open pores and chain structure
contacting a titanium carbide composition characterized by a human particle size and a surface area of at least 25 rrr/g with an aqueous solution of chloroplatinic acid; b) contacting the particles with an aqueous solution of sodium dithionite; C) contacting the particles with an aqueous solution of sodium dithionite; A method for producing an electrocatalyst comprising the step of contacting with. (4) An electrocatalyst in which a finely powdered platinum catalyst catalytically reduces oxygen supported on titanium carbide particles,
~b and a titanium carbide surface area of at least 25rd/g titanium carbide. (5) A fuel cell consisting of a finely powdered platinum catalyst supported on titanium carbide particles, the catalyst having a
a platinum surface area in the range of 5rrr/g platinum and at least 25
An improvement characterized by a titanium carbide surface area of rd/g titanium carbide.