JPH0845512A - Manufacture of electrode for phosphoric acid type fuel cell - Google Patents

Abstract

PURPOSE:To obtain a manufacturing method of electrode for phosphoric acid type fuel cell which can increase the utilizing efficiency of a catalyst, can improve the gas diffusing property, and furthermore, can extend the service life. CONSTITUTION:While a specific density of interface activator water solution is added to a catalyst carrier carbon powder, and it is crushed by a ball mill to make into a catalyst dispersion solution, an interface activator water solution whose density is lower than the above interface activator water solution is stirred while a PTFE dispersion is dropped to the water solution. The above catalyst dispersion solution and a specific amount of water is added to the PTFE dispersion solution, and stirred, and the mixture is filtered by a porous sheet to make the filtered material in an even thickness. After the filtered material is copied on a porous electrode plate, a press formation is applied, dried, and baked, and then, it is washed and dried again, so as to disperse the catalyst carrier carbon particles and the PTFE particles evenly, and the interface activator is removed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a phosphoric acid fuel cell electrode.

[0002]

2. Description of the Related Art An electrode for a phosphoric acid fuel cell is a catalyst carrying carbon and P on a porous electrode substrate such as carbon paper.
A water-repellent material such as TFE (polytetrafluoroethylene) is applied to form an electrode reaction layer. Conventionally, for phosphoric acid fuel cell electrodes, a surfactant is added to a catalyst-supporting carbon powder and mixed, and a PTFE dispersion is added dropwise to this mixture and a mixing / dispersing device such as a three-roll or ultrasonic homogenizer is used. Then, the mixture is mixed and dispersed to form a paste-like mixture, and the paste-like mixture is applied on a porous electrode substrate, dried, washed, dried again, press-molded, and fired.

[0003]

However, in the conventional method for manufacturing an electrode for a phosphoric acid fuel cell, the catalyst-supporting carbon powder and the PTFE powder are poorly dispersed, and agglomerates are formed. There is room for improvement in sex. Further, there is a problem that the surfactant added for improving the dispersion remains in the electrode without being removed, which promotes the wetting of the electrode and shortens its life. Therefore, in the present invention, the catalyst and the PTFE are well dispersed to form many three-layer interfaces of the catalyst, the electrolyte, and the gas. As a result, the catalyst utilization rate can be increased, the gas diffusivity can be improved, and the life can be further extended. An object of the present invention is to provide a method for manufacturing a phosphoric acid fuel cell electrode.

[0004]

In order to solve the above problems, the method for producing an electrode for a phosphoric acid fuel cell according to the present invention comprises coating a catalyst-carrying carbon powder with a PTFE powder on a porous electrode substrate. When manufacturing an electrode for a phosphoric acid fuel cell, a surfactant-containing aqueous solution of the required concentration was added to the catalyst-supporting carbon powder and pulverized with a ball mill to form a catalyst dispersion, while a surfactant with a lower concentration than the above-mentioned surfactant-containing aqueous solution was used. Stir while adding PTFE dispersion to the aqueous solution of the agent,
The catalyst dispersion and the required amount of water were added to this PTFE dispersion and stirred, and the mixture was filtered with a porous sheet so that the filtrate had a uniform thickness, and the filter was transferred to a porous electrode substrate. After that, press molding, drying, baking and washing,
It is characterized by being dried again. It is desirable to use a planetary ball mill as the ball mill. The catalyst supported on the carbon powder is preferably Pt or a Pt alloy. The required concentration of the aqueous surfactant solution has a concentration of 0.
It is preferably a 10 to 20.0% by weight aqueous surfactant solution. If it is less than 0.10% by weight, it is insufficient to disperse the crushed catalyst, and if it exceeds 10.0% by weight, the viscosity of the paste in the mill is increased and the pulverization efficiency is deteriorated. The low concentration aqueous surfactant solution is preferably a surfactant aqueous solution having a concentration of 0.01 to 0.10% by weight. The dispersion is unstable outside this range. The required amount of water is preferably such that the total surfactant concentration is 0.05 to 5.0% by weight. If it is less than 0.05% by weight, the dispersion is unstable,
If it exceeds 5.0% by weight, it is difficult to remove it later. or,
The porous sheet is preferably a PTFE sheet.

[0005]

In the method for producing the phosphoric acid fuel cell electrode of the present invention, the catalyst-supporting carbon powder is wet-milled by the ball mill to be fine, and the surface of the fine particles adsorbs the surfactant. Further, the PTFE dispersion is also dropped into the aqueous surfactant solution to be diluted, whereby aggregation is prevented and a stable dispersion liquid is obtained. Then, the catalyst dispersion and P
By mixing the TFE dispersion liquid, the catalyst-supporting carbon particles and the PTFE particles are uniformly dispersed. Further, the excess surfactant is removed by filtration, and most of the remaining surfactant is adsorbed on the catalyst-supporting carbon particles.
During calcination, it is easily decomposed and removed by the action of the catalyst, and decomposed products are also removed by washing after calcination. If it is washed before press molding, the adhesion to the porous electrode substrate deteriorates, causing cracks and peeling.

[0006]

EXAMPLES Examples of the present invention will be described below together with conventional examples. First, as a catalyst, a Pt alloy (Pt: Ni: C)
o = 2: 1: 1 (mol)) catalyst-supporting carbon powder (corresponding to 1 g of carbon) to which 5 g of a 5% by weight aqueous solution of a surfactant is added, and wet-milled for 30 minutes using a planetary ball mill to prepare a catalyst dispersion liquid. Was purified. Then, 350 g of 0.05% by weight aqueous surfactant solution was placed in a beaker, and PTFE was added thereto.
The dispersion was added dropwise and stirred for 10 minutes using a stirrer. To this PTFE dispersion, the catalyst dispersion and water sufficient to make the total surfactant concentration 0.05% by weight were added and stirred for 30 minutes. Next, the above-mentioned mixed solution is added to the porous PTFE so that the filtrate has a uniform thickness (for example, 150 μm).
After filtering with a sheet and transferring the filter to a porous electrode substrate such as carbon paper, press molding was performed. Then, it was dried at a temperature of 60 ° C. for 1 hour, baked at a temperature of 350 ° C. for 30 minutes, washed, and dried again at a temperature of 60 ° C. to obtain an electrode.

[0007]

Conventional Example First, the same catalyst-supporting carbon powder (corresponding to 2 g of carbon) as in the example was used, and 17 g of 20% by weight aqueous surfactant solution
Was added and mixed, and then the PTFE dispersion was added dropwise thereto and mixed and dispersed using a three-roll mill to obtain a paste-like mixture. Next, the above paste-like mixture is applied on a porous electrode substrate such as carbon paper so as to have a uniform thickness, dried at 60 ° C for 1 hour, washed, and dried again at 60 ° C. After that, it was press-molded and baked at a temperature of 350 ° C. for 30 minutes to obtain an electrode.

Table 1 shows the power generation characteristics when the electrodes obtained in Examples and Conventional Examples were used as electrodes for phosphoric acid fuel cells.

[0009]

[Table 1]

As is clear from Table 1, the phosphoric acid fuel cell electrodes of the examples were able to achieve higher catalyst utilization and gas diffusivity than those of the conventional examples. Regarding the electrode life, it can be seen that the life is extended because the decrease in the potential is small and the rate of increase of O ₂ -gain is small.

In the above embodiment, the planetary ball mill is used as the ball mill.
Not limited to this, a ball mill such as an attritor or a vibration may be used.

[0012]

As described above, according to the method for producing a phosphoric acid fuel cell electrode of the present invention, the catalyst-carrying carbon powder becomes fine, and the surface active agent is adsorbed on the surface of the fine particles. Aggregation of the PTFE dispersion is also hindered by the presence of the surfactant, and the catalyst-supported carbon particles and P are mixed by mixing the individually prepared catalyst dispersion with the PTFE dispersion.
Since the TFE particles are uniformly dispersed, it is possible to obtain a higher catalyst utilization rate and a higher gas diffusivity than ever before. In addition, the excess surfactant is removed by filtration, and the remaining surfactant is decomposed and removed by the action of the catalyst during firing, and is removed by washing after firing. Is less likely to progress, and its life can be extended.

Claims (6)

[Claims] 1. When manufacturing a phosphoric acid fuel cell electrode in which a catalyst-carrying carbon powder is coated on a porous electrode substrate with PTFE powder, a surfactant-containing aqueous solution of a required concentration is added to the catalyst-carrying carbon powder. While crushing with a ball mill to obtain a catalyst dispersion, while stirring the PTFE dispersion while dripping the PTFE dispersion into the surfactant aqueous solution having a lower concentration than the above surfactant aqueous solution, the catalyst dispersion and the required amount of the PTFE dispersion are added. After adding water and stirring, the mixture was filtered with a porous sheet so that the filter cake had a uniform thickness, the filter cake was transferred to a porous electrode substrate, and then press-molded, dried and baked. A method for producing an electrode for a phosphoric acid fuel cell, which comprises washing and drying again. 2. The method for producing a phosphoric acid fuel cell electrode according to claim 1, wherein a planetary ball mill is used as the ball mill. 3. The catalyst supported on the carbon powder,
It is Pt or Pt alloy, The manufacturing method of the electrode for phosphoric acid fuel cells of Claim 1 or 2 characterized by the above-mentioned. 4. The concentration of the aqueous surfactant solution having the required concentration
The method for producing an electrode for a phosphoric acid fuel cell according to claim 1, 2 or 3, which is a 0.10 to 20.0% by weight aqueous surfactant solution. 5. The low-concentration aqueous surfactant solution has a concentration of 0.
The method for producing an electrode for a phosphoric acid fuel cell according to claim 1, 2, 3 or 4, which is an aqueous solution of a surfactant of 01 to 0.10% by weight. 6. The phosphoric acid type product according to claim 1, wherein the required amount of water makes the total surfactant concentration 0.05 to 5.0% by weight. Manufacturing method of fuel cell electrode.