JPH03127458A - Method for producing platinum-supported catalyst for phosphoric acid fuel cells - Google Patents

Abstract

PURPOSE:To produce platinum bearing catalysts with high repeatability, which have extremely fine platinum particles in size and excellent dispersion properties by employing ultra pure water which is produced by a specified method, to be used for solvent mediums and cleaning in manufacturing processes. CONSTITUTION:In a process where platinum is carried by carbon powder while both carbon powder and chloroplatinic acid which are processed by hydrophilic treatment, are used as raw materials, water to be used for solvent mediums and cleaning shall be ultra pure water which is refined after it has been furthermore filtrated by a membrane filter with distillation and ion exchange processed in advance. The electrical conductivity of ultra pure water shall be around 5.9X10<-3>muS/cm. Platinum crystallite particles produced by the use of ultra pare water are small in size while exhibiting excellent catalytic performance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing a platinum-supported catalyst for a phosphoric acid fuel cell using carbon powder or the like as a catalyst carrier.

[Conventional technology]

Phosphorus! ! A type fuel cell is a device that reacts hydrogen and oxygen and converts the energy generated at the time into electricity, and FIG. 2 is a schematic cross-sectional view showing the configuration of its electrode section. As shown in FIG. 2, the electrode section consists of a fuel electrode 2 and an air ML electrode 3, which sandwich a matrix 1 impregnated with a solution. In the cell reaction, reaction (1) occurs at the fuel i electrode 2, and reaction (2) occurs at the air electrode 3 as follows.

H2→2H+2e Song・・・・・・・・・・・・
...Song (],)2H+'AOz→H20...
・・・・・・・・・・・・・・・・・・・・・・・・
(2) In order to quickly carry out the reactions in (1) and (2), a catalyst is required, and the fuel electrode 2 and air electrode 3 usually use a platinum-supported catalyst in which platinum particles are supported on carbon particles. have. In order to smoothly proceed with this battery reaction and improve battery characteristics, it is important to reduce the platinum particle size and increase the reaction area.

As one method for producing a platinum-supported catalyst, a method is known in which a platinum salt is reduced in a liquid phase to support platinum on one carbon powder. This method is based on parent 71 (in which the treated carbon powder is sufficiently brought into contact with an aqueous chloroplatinic acid solution, a colloidal agglomeration inhibitor is added, and a reducing agent having an aldehyde group is added to reduce the chloroplatinic acid. It is.

Although it is necessary to use highly purified water in the above series of processes, generally ion-exchanged water or distilled water (with an electrical conductivity of 202~ 0.7μS/3) is used. In this water, the 11' organic matter of g, t, microorganisms, fine particles, etc. remain without being completely removed, and the following r1 problem occurs.

[Problem to be solved by the invention]

Platinum-supported catalysts prepared using ion-exchanged water or distilled water do not necessarily have stable dispersion of platinum, and the output characteristics of phosphoric acid fuel cells that support these platinum-supported catalysts are still unsatisfactory. Figure 3 is a diagram showing the relationship between the electrical conductivity of water used in the production of platinum-supported catalysts and the average platinum crystal particle size. It was found that the crystal particle size increased.

Therefore, it is desired to further lower the electrical conductivity of water, that is, to manufacture platinum-supported catalysts using water of higher purity, and to improve the characteristics of batteries.

The present invention was developed in view of the above points, and its purpose is to provide a method for producing a platinum-supported catalyst using ultrapure water, which has a higher purity than ordinary ion-exchanged water or distilled water. .

[Means to solve the problem]

The uninvented method involves raising a solution of hydrophilically treated carbon powder dissolved in a colloidal form in an aqueous solution of chloroplatinic acid to a temperature at which a reducing agent acts, and then adding a colloidal agglomeration inhibitor to this bath solution. In the process of manufacturing platinum-supported catalysts for phosphoric acid fuel VL ponds, in which platinum particles are supported on carbon powder by gradually adding a reducing agent having After ion exchange, ultrapure water is purified by passing through a membrane filter.

[Effect]

The ultrapure water used in the present invention does not contain foreign substances such as organic matter, microorganisms, and fine particles that could not be removed with ion exchange water or distilled water, and has extremely low electrical conductivity and high purity, so the platinum particle size obtained is very small, and each component is better dispersed in the bath liquid than when ion-exchanged water or distilled water is used in the above manufacturing process. Therefore, the dispersion of platinum particles is also good, making it possible to produce stable platinum with good reproducibility. A supported catalyst can be obtained.

〔Example〕

The present invention will be explained below based on examples.

In the series of processes for manufacturing platinum-supported catalysts in the present invention, the water used as a solvent and washing water is purified by distilling and ion-exchanging tap water, passing through a membrane filter, and purifying the water to conduct electrical conductivity. Rate 5.9X10 PS/
It is ultrapure water with CR.

First, aceterene brakuku or furnace brakuku 9
! Add nitric acid or 10 wt % nitric acid aqueous solution 400 - to I, raise the temperature to 50"C without stirring, and stir in this state for about 2 hours, and then perform hydrophilic treatment. After this,
Wash the obtained cake thoroughly with ultrapure water until the pH becomes about 7. Add ultrapure water 4 to the colloidal cake that has been washed.
00ml is added and dispersed, and an aqueous solution of chloroplatinic acid (H2P 1C-66) containing 1g of platinum is added and stirred at room temperature. Next, after raising the temperature to 50'C, 0.1M sodium carbonate (NazCO3) aqueous solution was added to adjust the pH.
be 9 or more. After that, 3
10 d 71 of 0 wt% hydrogen peroxide (H2O2) water
0 and stir for about 5 minutes. Subsequently, a 0.1 M aqueous formic acid (HCOOH) solution as a reducing agent having an aldehyde group is gradually added over about 1 hour. After completing the above operations, wash thoroughly with ultrapure water after removing the reactants.
cormorant. Silver nitrate is added to the ultrapure water after cleaning, and the reaction in which silver chloride is produced from chlorine and silver nitrate is used, and the end point of cleaning is when the silver chloride disappears.

As described above, one platinum particle is supported on one carbon particle. As a result of chemical analysis of the obtained platinum supported catalyst, it was found that the amount of supported platinum was 10.1% on average.

For comparison, platinum-supported catalysts were prepared by the above method using ion-exchanged water as the solvent and water used for washing, and other conditions were the same, and the platinum-supported catalysts were compared with the platinum-supported catalyst of the present invention by X-ray diffraction and electron analysis. The crystal grain size and dispersion state of platinum were examined using a microscope. As a result, the average crystal particle size of platinum was 50X when ion-exchanged water was used, whereas the average S/V was when the ultrapure water of the present invention was used.

Next, a fuel electrode and an air electrode were prepared using these catalysts, and a phosphoric acid fuel cell was prepared using S to compare their characteristics. Figure 1 is a current-voltage characteristic diagram showing the results.Curve A in Figure 1 is for an uninvented battery using ultrapure water.Curve 9 is for a conventional battery using ion-exchanged water. It represents that. As can be seen from FIG. 1, a phosphoric acid fuel cell having a higher output can be obtained using the method according to the invention.

〔Effect of the invention〕

Supported platinum catalysts used in phosphoric acid fuel cells are manufactured by reducing chloroplatinic acid by bathing colloidal carbon powder in an aqueous solution of chloroplatinic acid. Traditionally, ion-exchanged water or distilled water is used in this process. As a result, the platinum particle diameter was small and the dispersibility of the platinum particles was unstable. However, as described in the examples, in the uninvention, the solvent and cleaning in the process of manufacturing the platinum supported catalyst, By using ultrapure water with low electrical conductivity and no residual foreign matter, platinum-supported catalysts with extremely large platinum particle diameters and good dispersibility can be obtained with good reproducibility. We were able to improve the output characteristics of the type combustion engine.

[Brief explanation of the drawing]

Figure 1 shows a phosphoric acid fuel using a platinum-supported catalyst proposed by the present invention! Figure 2 is a schematic sectional view showing the configuration of the electrode part of a phosphoric acid fuel cell, Figure 3 is
The figure is a line drawing showing the relationship between the drowsiness conductivity of water and the platinum particle size. ]... Matori, Kusu, 2... Fuel' 4 poles, 3...
Live electricity 00 000 Current envelope (mA-cm-') Figure Figure 08 10-710' Water siege and calculation (Socm-') Figure

Claims (1)

[Claims] 1) A solution of hydrophilically treated carbon powder dissolved in a colloidal form in an aqueous solution of chloroplatinic acid is raised to a temperature at which a reducing agent acts, and a colloidal aggregation inhibitor is added to this solution,
In a method for producing a platinum-supported catalyst for a phosphoric acid fuel cell, in which the chloroplatinic acid is reduced by gradually adding a reducing agent having an aldehyde group to support platinum particles on the carbon powder, distillation is performed as a solvent and water used for washing. and a method for producing a platinum-supported catalyst for a phosphoric acid fuel cell, characterized in that ultrapure water that has been subjected to ion exchange and further filtered and purified using a membrane filter is used.