JPH08148153A - Solid polymeric fuel cell electrode and manufacture thereof - Google Patents

Abstract

PURPOSE: To provide the electrode improving the cell efficiency substantially by using catalyst particles obtained through the application of a coat under the specified condition, regarding the subject electrode where catalyst particles coated with a polymeric electrolyte are used. CONSTITUTION: In applying suspension as a mixture of catalyst particles (e.g. carbon black particles carrying platinum thereon) and a polymeric electrolyte (e.g. perfluorocarbon sulfonic acid resin) dissolved in a solvent therefor as a coating material after the removal of the solvent, a solvent (e.g. butyl acetate) acting to coagulate and form the electrode into a colloidal state is added to the solvent (e.g. water and ethanol) for dissolving the electrolyte, and a mixed solvent thereby prepared is used. After dissolving the particles and a polymeric electrolyte film solution in the mixed solvent, the solvent for dissolving the electrolyte is removed and the catalyst particles obtainable therefrom are used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode for a polymer electrolyte fuel cell in which catalyst particles are coated with a polymer electrolyte and a method for producing the same, and more specifically, catalyst particles are coated with a polymer electrolyte. In a solid polymer electrolyte fuel cell electrode and a method for producing the same, an electrode obtained by coating an electrolyte membrane solution in which a catalyst particle used in the electrode is dissolved in a solvent for dissolving a polymer electrolyte, and The manufacturing method is related.

[0002]

2. Description of the Related Art A polymer electrolyte fuel cell is characterized in that an ionic conductor, that is, an electrolyte, is a solid and a polymer. A resin film or the like is used, and both electrodes of the negative electrode and the positive electrode are arranged with the electrolyte sandwiched therebetween. For example, hydrogen as a fuel is supplied to the negative electrode side, and oxygen or air is supplied to the positive electrode side to cause an electrochemical reaction. And generate electricity.

For both the negative electrode and the positive electrode in contact with the solid polymer electrolyte, there is a type in which a catalyst for accelerating the reaction is added and used. As a method for producing this type of electrode, Have been proposed so far, for example, in U.S. Pat. No. 3,297,484, catalyst particles such as platinum black and palladium black, or particles obtained by supporting them on carbon particles are referred to as polytetrafluoroethylene. Another method is to mix and form an electrode sheet, and thermocompression-bond this to an ion exchange resin membrane.
No. 47471 discloses a method of depositing a catalyst metal layer on the inner surface of an ion exchange resin membrane and then growing the catalyst metal layer on the surface. As the catalyst component here, platinum or other platinum is introduced. Group metals are shown.

In "Electrochemistry" 53, No. 10, P.I.
812-817 (1985), a fuel cell using a NAFION-117 membrane (manufactured by Du Pont, trade name), which is a kind of perfluorocarbon sulfonic acid resin membrane, as a solid polymer electrolyte, Attempts have been introduced that the reaction site (reaction region) is made three-dimensional by joining electron-ion mixed conductors using a corresponding material to increase the action area. According to this, a platinum electrode is bonded to one surface of a NAFION-117 membrane as a solid polymer electrolyte by an electroless plating method (permeation method) to form a hydrogen electrode, that is, an anode, while the counter electrode of this electrode is The constituent oxygen electrode, that is, the cathode side electrode, is generally manufactured by the following steps.

First, as the electrode catalyst powder for the oxygen electrode, platinum black powder or carbon powder carrying 10% platinum (hereinafter referred to as "platinum-supporting carbon powder") was used.
Amberlite IR-120B (T-3) [styrene-divinylbenzenesulfonic acid resin, Na type, powder with a particle size of 30 μm, manufactured by Organo, trade name] or NA
FION-117 (perfluorocarbon sulfonic acid resin, H type, 5% solution in a mixed solvent of aliphatic alcohol and water, manufactured by Aldrich Chemical Company, trade name)
Are mixed in various mixing ratios.

Next, polytetrafluoroethylene was added to each of the mixtures obtained above in a solid content weight ratio of 30% in the case of platinum black powder, 60% in the case of platinum-supported carbon powder, and water suspension. After being added as a turbid liquid and kneaded, rolled to form a sheet, and dried in a vacuum, and the sheet was dried at a temperature of 10 to a NAFION membrane as a solid polymer electrolyte.
Hot pressing is performed at 0 ° C. and a pressure of 210 kg / cm ² . Then, there, by mixing an ion exchange resin film into the oxygen electrode bonded to the NAFION film as a solid polymer electrolyte, the reaction site can be made three-dimensional and the polarization characteristics can be remarkably improved. It has been pointed out that the effect of mixing the exchange resin film is particularly large when carbon carrying platinum is used as the electrode catalyst.

In addition, in Japanese Patent Laid-Open No. 4-162365, carbon black carrying a platinum catalyst and carbon black carrying no catalyst are respectively prepared from butanol of NAFION which is a kind of solid polymer electrolyte. Soak in the solution,
Then, a method characterized by treating the mixture of both particles with a dispersion of polytetrafluoroethylene, etc. has been introduced. In this method, the amount of catalyst used is reduced, and a low-cost and high-performance electrode is obtained. It is said that it will be possible to manufacture a small-sized and high-power-density fuel cell.

In this respect, the present inventor has been conducting various researches and developments on a method for producing such an electrode used in a polymer electrolyte fuel cell, but in return, without using polytetrafluoroethylene. , Has previously developed and proposed a method of simplifying the manufacturing process and manufacturing a fuel cell having excellent performance using this electrode (Japanese Patent Application No.
No. 35058, Japanese Patent Application No. 4-358059), and even in this case, there is no difference in coating the catalyst particles with the polymer electrolyte.

As described above, in the process of manufacturing an electrode for a polymer electrolyte fuel cell, first, as catalyst particles,
For example, platinum black or carbon black particles supporting platinum are produced, and the particles and the solid polymer electrolyte solution are further mixed with a solvent to prepare a suspension. Accordingly, polytetrafluoroethylene or the like as a binder will be mixed,
Prior to the mixing step (1), the step of removing the solvent therein from the suspension is essential.

This solvent removal operation may be left to the natural evaporation of the solvent, but in order to evaporate and evaporate the solvent by heating the suspension and to accelerate them, the operation is performed in vacuum. That is, it is carried out in a reduced pressure state, and for this purpose, the heating and depressurizing operations are usually carried out in a boiling state so far, and then the powder thus obtained is dispersed in water to form an electrode. Is being made.

On the other hand, the inventors of the present invention have found that the boiling state itself in the solvent removal operation causes variations in the distribution of each component in the composition, which influences the characteristics of the electrode itself and, by extension, the battery. Output, sustainability, and other factors that have a subtle effect on its performance, and when removing the solvent, this solvent removal operation is performed by heating the suspension while stirring it, and reducing the pressure until it reaches a boiling state. By doing so, a method for improving the characteristics of the electrode obtained through the above and remarkably improving the performance of the battery has been previously developed and proposed (Japanese Patent Application No. 5-297279).

According to the method according to this proposal, it is possible to impart such excellent electrode characteristics and to improve the performance of the battery remarkably. However, regarding the removal operation of the solvent, the composition of the solvent itself is changed. While further researching and studying, including by chance, by accidentally adding a unique component as the composition of the solvent and devising a process for using this solvent, its electrode characteristics and battery performance were improved. The present invention has been achieved by finding that it can be further improved.

[0013]

That is, the present invention is
In a polymer electrolyte fuel cell electrode in which catalyst particles are coated with a polymer electrolyte, a suspension of the catalyst particles and the polymer electrolyte in a solvent is carried out as a part of the coating process. In the operation of removing the solvent,
By mixing and using a solvent component having a specific function as the solvent, the characteristics of the obtained electrode are further improved,
It is an object of the present invention to provide an electrode and a method for producing the same, which can remarkably improve the performance of a battery using the same.

[0014]

DISCLOSURE OF THE INVENTION The present invention relates to an electrode for a polymer electrolyte fuel cell using catalyst particles coated with a polymer electrolyte, in which the catalyst particles and (A) polymer electrolyte are dissolved. By removing the solvent from the suspension mixed with the polyelectrolyte dissolved in the solvent,
At the time of coating, a mixed solvent obtained by adding (B) a solvent that functions to agglomerate the polyelectrolyte into a colloidal state to a solvent that dissolves the polyelectrolyte (A) is used. An electrode for a polymer electrolyte fuel cell, characterized by comprising catalyst particles obtained by dissolving particles and a polymer electrolyte membrane solution and then removing a solvent that dissolves the polymer electrolyte by evaporation. Is provided.

The present invention also provides a method for producing an electrode for a polymer electrolyte fuel cell in which catalyst particles are coated with a polymer electrolyte, in a solvent in which the catalyst particles and (A) polymer electrolyte are dissolved in advance. When coating is performed by removing the solvent from the suspension mixed with the dissolved polyelectrolyte, (A) the polyelectrolyte is aggregated with respect to the solvent in which the (A) polyelectrolyte is dissolved. A solvent that acts as a colloidal state by adding a solvent that dissolves the catalyst particles and the polymer electrolyte membrane solution in this mixed solvent, and then removes the solvent that dissolves the polymer electrolyte by evaporation. The present invention provides a method for manufacturing an electrode for a polymer fuel cell.

As the solvent for dissolving the polymer electrolyte (A), a solvent which can dissolve the polymer electrolyte for catalyst particle coating can be used as a single solvent or a mixed solvent of two or more kinds. Examples thereof include acetone, a mixed solvent of water and ethanol, and a mixed solvent of water and propanol. Further, as the solvent (B) that functions to aggregate the polymer electrolyte into a colloidal state, a single solvent or a mixed solvent of two or more kinds of solvents serves to aggregate the polymer electrolyte into a colloidal state. Any solvent can be used, and examples thereof include butyl acetate, ethyl propionate, and methyl butyrate.

The type of the catalyst particles used in the present invention is not particularly limited, and any catalyst known so far for electrodes of polymer electrolyte fuel cells can be used, for example, platinum. In the case of a system catalyst, it can be used in the form of platinum black powder, platinum alloy powder, carbon black carrying platinum and the like. As the polymer electrolyte, various ion exchange resins and the like can be used. Particularly, as the solid polymer electrolyte membrane, a NAFION membrane-based part is used.
When using a fluorocarbon sulfonic acid resin membrane,
It is desirable to use the same type of perfluorocarbon sulfonic acid resin.

Further, the catalyst particles coated with the polymer electrolyte obtained by the method of the present invention are then sheeted, and any sheeting is effective regardless of the mode of sheeting. Can be applied. That is, as a mode of the sheet formation, a binder is added to a mixture of catalyst particles and a polymer electrolyte to obtain a kneaded product, which is then sheeted by rolling or the like, and a kneaded product is prepared by adding a binder to the mixture. The solution of this mixture is deposited and supported on the surface of the porous electrode base material as a solution, and the solution of the mixture is applied to the surface of the porous electrode base material by coating or filtration. Let
Although there are other methods, according to the catalyst treatment method of the present invention,
Even when any of the following modes is adopted, excellent effects can be obtained in terms of the electrode characteristics and the like.

In the case of adopting one of these modes, the porous electrode substrate has a water repellent card because of its excellent characteristics.
It is advantageous to use a bomber, and the water repellent agent is preferably a polytetrafluoroethylene-based polymer. Here, the polytetrafluoroethylene-based polymer is meant to include not only polytetrafluoroethylene but also a tetrafluoroethylene-hexafluoropropylene copolymer and other copolymers thereof.

The catalyst layer of the solid polymer fuel cell electrode comprises catalyst particles and a polymer electrolyte,
There are catalyst particles and solid polymer electrolytes to which a polytetrafluoroethylene-based polymer is added, and the like. According to the electrode of the present invention and the method for producing the same, in any of these cases, the electrode characteristics and battery An excellent effect can be obtained in terms of characteristics.

Next, in one embodiment, carbon particles supporting platinum are used as catalyst particles, (A) water and ethanol are used as a solvent for dissolving the polymer electrolyte, and (B) the polymer electrolyte is aggregated. The case where butyl acetate is used as a solvent that acts to make it into a colloidal state will be described. Three
Carbon particles (catalyst particles) supporting 0 to 50% platinum are placed in a container, for example, a flask, and distilled water is added. Next, 25 times or more of distilled water containing ethanol was added thereto. An appropriate amount of the polymer electrolyte membrane solution was added to the catalyst, and the amount of ethanol added was 50 to 200.
Add% by weight butyl acetate. The solution obtained in, is heated to a temperature of about 50 ° C., and the pressure is gradually reduced to bring it to a boil.

The steam (azeotrope of ethanol and water) generated by the boiling of, is liquefied in a cooling tube kept at a temperature of about 5 ° C. Here, the ethanol and water are removed in this way, and the solvent is then only butyl acetate, and the polymer electrolyte aggregates into a state in which the catalyst particles are mixed appropriately. , And the solution obtained by removing ethanol and water with polyflon dispersion (registered trademark, manufactured by Daikin Industries, Ltd.) is added to the solution in an amount of 20 to 200% by weight with respect to the catalyst and mixed.
Next, for example, the solution obtained above is applied onto a water repellent carbon paper having a porosity of 80% and a thickness of 0.4 mm to deposit only the solute. This is impregnated with a solution of the polymer electrolyte membrane to form an electrode.

[0023]

EXAMPLES An example of the present invention will be described below, but it goes without saying that the present invention is not limited to this example. First, 2 g of catalyst particles supporting 50% by weight of platinum with respect to carbon black particles and NAFION-117 (perfluorocarbon sulfonic acid resin, manufactured by Du Pont,
Take the product name) in a flask with a capacity of 1 liter (1 liter),
20 ml of distilled water was added to this. Then, 500 ml of ethanol was added thereto, and butyl acetate was further added in an amount of 300 ml of ethanol. The temperature of the solution obtained in
The mixture was heated to 0 ° C., and the pressure was gradually reduced to boil.

The steam (azeotrope of ethanol and water) generated in step (1) was liquefied in a cooling tube maintained at a temperature of 5 ° C. ,
Then, a dispersion of polyflon (polytetrafluoroethylene, manufactured by Daikin Industries, Ltd., registered trademark) was added to the solution obtained by removing ethanol and water so as to be 120% by weight with respect to the catalyst and mixed. On the other hand, the porosity is 80
%, A carbon paper having a thickness of 0.4 mm and a disperser of neofron (tetrafluoroethylene-hexafluoropropylene copolymer, manufactured by Daikin Industries, Ltd.)
After impregnation with John, heat treatment was carried out to obtain a carbon paper water repellent with NEOFLON. The quantitative ratio was adjusted so that neofuron accounted for 20% by weight in the total amount.

The water repellent carbon paper obtained in,
The solution obtained above was applied and only the solute was deposited. Nafion solution (polymer electrolyte solution, Aldrich Chemical Co., trade name)
Was impregnated into an electrode. The NAFION-117 membrane was sandwiched and integrated between two sheets of this electrode sheet, and a current collector was adhered to both surfaces of the obtained joined body by a conventional method, and a hydrogen inlet / outlet and an oxygen inlet / outlet were provided. A test solid polymer fuel cell was obtained.

FIG. 1 shows the relationship between the current density and the cell voltage measured for this test fuel cell. FIG. 1 also shows, as a comparative example, measurement data of a battery produced in the same manner as in the example, except that the butyl acetate according to the present invention was not used and the operation related thereto was not performed. Here, the operating condition is a hydrogen flow rate of 0.1 l / mi.
n, oxygen flow rate 0.5 l / min, hydrogen pressure 2.0 at
m, oxygen pressure 2.0 atm, and battery temperature 60 ° C.

There is a correlation between the current density and the cell voltage,
Although the cell voltage gradually decreases as the current density increases, as shown in the figure, in the test solid polymer fuel cell, the cell voltage gradually decreases as the current density increases. It can be seen that it is lower and lower. This result is due to the small-scale test battery for the test, but in consideration of the fact that the practical fuel cell has a larger scale and is used for a long period of time, the effect of improving the battery efficiency by the present invention is obtained. Is clear.

[0028]

As described above, according to the present invention, catalyst particles and an electrolyte membrane solution are previously prepared as a method for coating the polymer electrolyte membrane on the catalyst particles which are the electrode constituent material of the polymer electrolyte fuel cell. For example, by dissolving it in a mixed solvent of water, ethanol and butyl acetate, removing water and ethanol by evaporation and using only butyl acetate as a solvent, the characteristics of the electrode obtained through this are markedly improved. In addition, the characteristics and performance of a polymer electrolyte fuel cell using this electrode can be significantly improved.

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between a cell density and a measured current density of a polymer electrolyte fuel cell having electrode sheets manufactured in Examples and Comparative Examples (conventional example).

Claims (8)

[Claims] 1. An electrode for a polymer electrolyte fuel cell using catalyst particles coated with a polymer electrolyte, wherein the catalyst particles and the polymer electrolyte (A) are dissolved in a solvent. When the coating is carried out by removing the solvent from the suspension obtained by mixing and, the function of (B) aggregating the polymer electrolyte with the solvent for dissolving the (A) polymer electrolyte to form a colloidal state. Using a mixed solvent obtained by adding a solvent to dissolve the catalyst particles and the polymer electrolyte membrane solution into this, the catalyst particles obtained by removing the solvent to dissolve the polymer electrolyte by evaporation, An electrode for a polymer electrolyte fuel cell, which is characterized by being used. 2. The solvent for dissolving the polymer electrolyte (A) is a mixed solvent of water and ethanol, and the solvent (B) for coagulating the polymer electrolyte into a colloidal state is acetic acid. The polymer electrolyte fuel cell electrode according to claim 1, which is butyl. 3. The electrode comprises a catalyst particle coated with a polymer electrolyte.
3. The electrode for a polymer electrolyte fuel cell according to claim 1, which is an electrode obtained by depositing and carrying catalyst particles formed by coating on a water repellent carbon paper. 4. The solid polymer electrolyte for coating the catalyst particles is of a perfluorocarbon sulfonic acid resin type, and the water repellent agent of the water repellent carbon paper is polytetrafluoroethylene. The polymer electrolyte fuel cell electrode according to claim 3, which is a polymer. 5. A method for producing an electrode for a polymer electrolyte fuel cell, which comprises coating catalyst particles with a polymer electrolyte, wherein the catalyst particles and (A) the polymer electrolyte are previously dissolved in a solvent. In coating by removing the solvent from the suspension mixed with the molecular electrolyte,
For the solvent that dissolves this (A) polymer electrolyte,
(B) A solvent that functions to aggregate the polymer electrolyte into a colloidal state is added, the catalyst particles and the polymer electrolyte membrane solution are dissolved in this mixed solvent, and then the polymer electrolyte is dissolved by evaporation. A method for producing an electrode for a polymer electrolyte fuel cell, which comprises removing the solvent to be used. 6. The solvent (A) for dissolving the polymer electrolyte is a mixed solvent of water and ethanol, and the solvent (B) for aggregating the polymer electrolyte into a colloidal state is acetic acid. It is butyl, The manufacturing method of the electrode for polymer electrolyte fuel cells of Claim 5. 7. The electrode comprises a catalyst particle coated with a polymer electrolyte.
The method for producing an electrode for a polymer electrolyte fuel cell according to claim 5 or 6, which is of a type in which the coated catalyst particles are deposited and carried on a water repellent carbon paper. 8. A solid polymer electrolyte for coating catalyst particles is of a perfluorocarbon sulfonic acid resin type, and a water repellent agent of a water repellent carbon paper is polytetrafluoroethylene. The method for producing an electrode for a polymer electrolyte fuel cell according to claim 7, which is a polymer.