JPS58166643A - Fuel cell - Google Patents

Abstract

PURPOSE:To reduce a use amount of noble metal used as the active ingredient of a gas diffusive electrode, by forming a carrier layer consisting of colloidal noble metal fine particles of specific size onto a mixed layer of a carbon dust and water repellent agent. CONSTITUTION:Carbon powder of acetylene black or the like, a water repellent agent of polyflon dispersion liquid or the like and water are mixed, and a plate formed by applying this mixture onto carbon paper is dried. And then a protective colloid agent is added to a solution of noble metal salt to perform wet reduction and obtain colloid dispersion liquid about 10Angstrom particle diameter of noble metal, and the regulated colloidal platinum solution is impregnated to the plate to form an electrode plate by firing. In this way, a use amount of nobel metal can be reduced to eliminate the necessity for an activating process, and the preparation process of an electrode can be simplified.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to fuel cells, and more particularly to gas diffusion electrodes.

The closest known example to the present invention, which has been carried out conventionally, is JP-A-51-86734. This known example relates to a method for adding active metals to electrodes of fuel cells comprising porous conductive particles, hydrophobically bonded and supported by a substrate. That is, in the electrotaxis 4 formed as described above, platinum ions are adsorbed only on the conductive particles by forcibly applying a potential to the front and back surfaces of the electrode after being immersed in a solution containing platinum salt. , and then dried and subjected to hydrogen gas reduction. In this known example, it is necessary to apply a potential gradient to the electrode, and as a manufacturing method for electrodes for large-scale fuel cells, it is difficult to mass produce, and it requires two steps such as depositing platinum ions and reducing hydrogen gas. It becomes a stage.

An object of the present invention is to provide a fuel cell in which the amount of noble metal used as an active component of the gas diffusion electrode used in the fuel cell is reduced.

At the gas diffusion electrode of a fuel cell, a reaction proceeds at the point where the three components, the solder, the fuel or oxidant gas, the electrolyte, and the active metal on the electrode, come into contact with each other, that is, at the three-phase interface of gas-liquid-solid.

The gas diffuses into the micropores within the electrode, but the liquid only penetrates into relatively large pores. Therefore, if the active metal is present only in a range where the electrolyte can diffuse, the effect will be great. Gas diffusion electrodes that have been commonly used in the past have been formed by the method described below.

One method is to impregnate fine carbon powder with platinum salt, and use a dry or wet reduction method to highly disperse and support platinum fine particles on the fine carbon powder. The mixture of the piezoelectrode catalyst and polytetrafluoroethylene (PTPE) thus prepared is coated on carbon paper and then fired to form an electrode plate. Another method C is
A mixture of fine carbon powder and polytetrafluoroethylene is applied to carbon paper, the fired plate is impregnated with platinum salt, and then reduced with hydrogen gas to form an electrode plate. A model of the electrode formed and broken in this manner is shown in FIGS. 1 and 2. In Fig. 1 of the conventional method, fine platinum particles are uniformly dispersed on the carbon powder.
As a result of the presence of platinum particles throughout the formed catalyst layer, the platinum in the portions where the three-phase boundary (8) is not formed is wasted. In addition, in the method shown in FIG. 2, the platinum complex ions penetrate into the micropores of the carbon powder layer to impregnate the platinum platform, giving almost the same result as the electrode plate formed by the method shown in FIG. In FIGS. 1 and 2, l is the carbon paper which is the electrode substrate, 2 is the catalyst layer,
3 is carbon powder, 4 is noble metal particle, 5 is )'TPE,
6 is a micropore of the catalyst layer, and 7 is a macropore of the catalyst layer. The present invention compensates for these drawbacks by making it possible to support fine metal particles only in the vicinity of the three-phase interface on a plate formed by applying a mixture of carbon powder and water repellent to carbon paper. be. In other words, fine particles of Sankin paulownia are produced by adding a protective colloid agent to a solution of a precious metal salt and subjecting it to wet reduction to form a colloid dispersion with a noble metal particle size of approximately 1 OA [1! It was done. By adjusting the type or concentration of the protective colloid in this colloidal dispersion and impregnating it into the plate described above, it is possible to control the relatively large pores of the carbon powder layer, that is, the site of three-phase interface formation, and the next stage of the layer. The model of the electrode (two-layer electrode) according to the present invention method is shown in Figure 3, #I.
The nine examples shown in Figure 3 are models of two-phase electrodes consisting of a mixed layer of carbon powder and water repellent and an active gold I14 supporting layer. Reference numeral 8 is a first catalyst layer, and 9 is a second catalyst layer.

Examples of the present invention will be described below, but the present invention is not limited to these examples in any way.

First, a method for producing a noble metal colloid (colloidal platinum) to be impregnated into a plate serving as an electrode of a fuel cell will be described.

(1) Colloidal platinum -Jlli: methanol 15
0 mt.

50mt of water and polyvinyl alcohol (a1 go &) L O
Dissolve g, then proceed with platinum chloride 121! Ogt-Dissolve and adjust the pH of the solution to about 2 with caustic while stirring. The bales are subjected to reflux reduction at 70 to 80C for about 10 hours.

Through the above operations, colloidal platinum having a platinum particle size of 10 to 1 SAim is obtained.

(2) Colloidal platinum-ruthenium 5ilai: Dissolve polyvinyl alcohol ls, og in 100 mt of methanol and 20 mt of water. Next, dissolve all Og of platinum chloride and 6g of ruthenium chloride, and adjust the pH of the solution with caustic alkali.
Adjust to about 2. After that, reflux reduction was carried out at 70 to 80C for 10 hours, and then 5 mA of 35% formalin was added, and 50% caustic alkali was gradually added dropwise while keeping the temperature of the solution at 600°C until the pH reached 12. The reaction was terminated, and methanol was added to make the liquid t 250 mt. Through the above operations, a colloidal platinum-ruthenium solution is prepared.

Example 1 Acetylene black and Polyflon diverge are combined. Spread this mixture on carbon paper to a thickness of about 60 μm.
Apply it so that it becomes &. The plate thus formed was thoroughly air-dried. After that, the plate was impregnated with the colloidal platinum solution mentioned above, and the amount of platinum was 0.49.
m g/cm”, air-dried, 32 (l in air)
It was fired for QIII to form an electrode plate.

Example 2 Acetylene black, Polyflon Disverge 17 liquid, and water are mixed so that the amount of PTFE is 50% by weight based on the acetylene black. This mixture is coated on carbon paper to a thickness of about 305 m. After thoroughly air-drying the plate thus formed, it was impregnated with a colloidal platinum solution to adjust the platinum content to α2Gmg/am. After air-drying, a mixture of acetylene black and PTFE was further coated to a thickness of 3
〇Apply to 100 ms degree, and after air-drying, impregnate colloidal platinum to make the total amount of platinum 0.40 mg 7 cm”.
The electrode plate was baked for 10 minutes in 0C air.
The electrode in this example has a two-layer electrode structure.

Example 3 Acetylene black, fluorinated graphite, polyflo/disverge leak, water, and a surfactant were mixed, and the amount of fluorinated graphite and PTFE was 50% each relative to acetylene black.
% by weight and 20% by weight. This mixture is coated on carbon paper to a thickness of about 60 am and thoroughly air-dried.

After that, it is impregnated with colloidal platinum, and the amount of platinum is 0.40 mg.
/cts'' and fired in air at 320C for 10 minutes to prepare an electrode plate.

Example 4 This example relates to a two-component catalyst. Mix acetylene black, Borea 0-in-day barge M/liquid and water, P
TFEJit - 50% by weight based on acetylene black. This mixture was applied to carbon paper to a thickness of 60 μm, and after sufficiently air-dried, it was impregnated with the above-mentioned colloidal platinum 4thenium, and the amount of platinum and ruthenium was adjusted to α40 m g 7
cm" and 0.20 mg/C114". The sample was fired at 10III+ in 320C air to form an electrode plate.

Comparative Example 1 An electrocatalyst carrying 12% of platinum by a wet reduction method in acetylene was mixed with Polyflon dispersion liquid and water so that the amount was 50% by weight with respect to the PTFEilt electrode catalyst. did. This mixture was coated on carbon paper to a thickness of about 60 μm, and after air drying,
It was fired in 0C air at 1101μ to form an electrode plate.

Example 5 In this example, the performance of the electrode plates formed in Examples 1 to 4 and Comparative Example 1 was detailed by adjusting the unipolar potential as an air electrode in i*oc and phosphoric acid. . The results are shown in Table 1.

Table 1 As described above, according to the present invention, even if the lid of platinum toilet 1 is reduced by 25% compared to the conventional method, the air electrode potential remains the same or higher.
1, it is possible to reduce battery costs.

According to the present invention, noble metal particles with a controlled particle size can be carried in the relatively large pores of the electrode plate structure and in the vicinity of the electrode surface, that is, the place where the three-phase interface is formed where the gas-electrolyte reaches and slows down, resulting in the same performance. The amount of precious metal used can be reduced by about 30% compared to the conventional method to obtain T-. In addition, since the colloidal precious metal impregnated into the electrode plate is already activated when IIl is manufactured, the activation process (for example, hydrogen gas reduction) of the bale impregnated with the electrode plate is not satisfactory, and the electrode manufacturing process is simplified. be done.

[Brief explanation of drawings]

Figures 1 and 2 are cross-sectional views of electrodes according to the conventional method;
The figure is a cross-sectional view of an electrode according to the invention. DESCRIPTION OF SYMBOLS 1... Carbon paper which is an electrode base material, 2... Catalyst layer, 3... Carbon powder, 4... Precious metal particles, 8...
...Continued from page 1 of Catalyst Sentinel 3PFJ ■Applicant Hitachi Chemical Co., Ltd. 2-1-1 Nishi-Shinjuku, Shinjuku-ku, Tokyo

Claims (1)

[Claims] 1. A fuel cell having a gas diffusion type 4ii consisting of a porous conductive base material, carbon powder, a water repellent agent, and catalytically active gold^, a mixed layer of carbon powder and a water repellent agent, and a noble metal. A fuel cell characterized in that support layers of fine particles are alternately formed and have a piezoelectric element. 2. The fuel cell according to claim 3111, wherein the noble metal fine particles are colloidized and have a particle size of approximately IOA. & The fuel cell according to claim 1, wherein the noble metal fine particles include at least one member of group #I8 of the periodic table. 4. The fuel cell according to claim 1, wherein the water repellent is made of polytetrafluoroethylene or a mixture of polytetrafluoroethylene and fluorinated graphite.