JPH10189003A - Electrode for fuel cell and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve performance of a cell while increasing a coefficient of use of catalyzer and enhancing characteristics of an electrode, by treating in advance catalyzer particles of a fuel cell with oxidizer such as hydrogen peroxide. SOLUTION: An electrode contains catalyzer particles, electolyte and water repellent agent. Platinum black powder and the like are appropriate for the catalyzer particles. By treating in advance the catalyzer particles, coating by the electrolyte in the next process can be sufficiently performed, and as a result, characteristics of the electrode and performance of a cell are improved. The oxidizer mentioned above should be used as a solution. It is appropriate to use a resin in perfluorocarbonsulfonic acid family. A polymer in polytetrafluoroethylene family is appropriate. A mixture of the catalyzer particles, the electrolyte and the water repellent agent is kneaded for instance, so that it is rolled to a sheet and used as a catalyzer layer.

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 fuel cell and a method for producing the same, and more particularly, to a catalyst particle comprising a carrier particle carrying an active metal, a catalyst particle in an electrode comprising an electrolyte and a water repellent. The present invention relates to a fuel cell electrode obtained by pre-treating an electrode and further improving the coating property with an electrolyte, and a method for producing the same.

[0002]

2. Description of the Related Art Fuel cells, for example, polymer electrolyte fuel cells, are characterized in that the ionic conductor, that is, the electrolyte, is solid and polymer. Typically, a membrane such as an ion exchange resin membrane is used, and both the negative electrode and the positive electrode are arranged with the polymer electrolyte membrane interposed therebetween. For example, hydrogen is supplied to the negative electrode side, and oxygen or air is supplied to the positive electrode side Thus, an electrochemical reaction is caused to generate electricity.

As a negative electrode and a positive electrode in contact with the solid polymer electrolyte, a type in which catalyst particles for accelerating a reaction are added into the electrodes has been developed. Various methods have been proposed for the production of electrodes in which a catalyst is added and used, and as one system, polytetrafluoroethylene (PTFE) is further mixed with the catalyst particles. The form is known.

For example, in US Pat. No. 3,297,484, an electrode sheet is formed by mixing catalyst particles such as platinum black and palladium black, or a mixture of catalyst particles having these particles supported on carbon particles with polytetrafluoroethylene. Is thermocompression-bonded to an ion exchange resin membrane as a polymer electrolyte, and in US Pat. No. 3,432,355, the kneaded material is separately applied as a slurry on a polytetrafluoroethylene film to form an electrode sheet, A method has been proposed in which this is thermocompression-bonded to an ion exchange resin membrane as a polymer electrolyte.

Further, “Electrochemistry” 53, No. 10 (1
985), pp. 812 to 817, an attempt to make the reaction site three-dimensional and increase the area of action is introduced. On one side, a platinum electrode is joined by an electroless plating method to form a hydrogen electrode, that is, an anode electrode, while an oxygen electrode, which is a counter electrode of this electrode, that is, a cathode electrode,
In general, it is manufactured by the following steps.

First, as an electrode catalyst powder for an oxygen electrode, platinum black powder or carbon powder carrying 10% of platinum (hereinafter referred to as “platinum-supporting carbon powder”) is used.
Amberlite IR-120B (T-3) (styrene divinylbenzene sulfonic acid resin, Na type, powder having a particle size of 30 μm, trade name, manufactured by Organo Corporation) or NA
FION (perfluorocarbon sulfonic acid resin, H
Type, 5% solution in a mixed solvent of aliphatic alcohol and water, A
ldrich Chemical Company, trade name) are mixed at various mixing ratios.

Then, polytetrafluoroethylene is added to each of the above mixtures in the form of an aqueous suspension, in the case of platinum black powder, a solid content ratio of 30%, and in the case of platinum-supporting carbon powder, 60%. After the addition and kneading, the kneaded material is rolled into a sheet, dried in vacuum, and then the oxygen electrode sheet is heated at a temperature of 100 ° C. and a pressure of 210 kg / cm 2 with respect to the NAFION membrane as a solid polymer electrolyte. Hot press.

According to this, the electrode reaction site can be three-dimensionally formed, whereby the polarization characteristics can be remarkably improved. The effect of mixing the ion exchange resin is particularly when the platinum-supported carbon is used as the electrode catalyst. It is pointed out that it is large. Here, catalyst particles made of platinum black powder or platinum-supported carbon powder are coated with the polymer electrolyte mixed therein, and the above-mentioned “in the case of platinum black powder, 30% by weight of solids,
In the case of platinum-carrying carbon powder, polytetrafluoroethylene added at a ratio of “60%” also corresponds to the binder.

In the above technique, the electrode sheet is manufactured by rolling a kneaded product of the electrode material into a sheet by rolling or the like, except in the case of US Pat. No. 3,432,355. As a mode of producing, that is, forming a sheet, there is also a method in which a porous paper or sheet is separately used as the base material, and a catalyst layer forming component such as catalyst particles is supported on the porous paper or sheet.

In this case, as the paper or sheet, for example, carbon paper having a predetermined porosity and thickness is used, and after impregnating with a polytetrafluoroethylene-based dispersion, heat treatment is performed. ,
An electrode component such as catalyst particles is adhered to and supported on the water-repellent carbon paper. One example of this is Japanese Patent Publication No. 4-162365.

The technique disclosed in this publication is characterized in that a mixture of carbon black carrying a platinum catalyst and carbon black not carrying a catalyst is used as the fine powder for the catalyst layer constituting the electrode sheet. Water-repellent carbon paper is used for sheeting, and a mixture of fine powders containing catalyst particles is sprayed on the water-repellent carbon paper, and is adhered by pressing under heating. However, these catalyst particles are coated with an ion exchange resin and treated with polytetrafluoroethylene.

The present inventor has developed a method for manufacturing an electrode for a polymer electrolyte fuel cell which simplifies the manufacturing process without using polytetrafluoroethylene and has excellent cell performance. Has filed a patent application (Japanese Patent Application Nos. Hei 4-358058 and Hei 4-358059).
Also in this case, there is no difference in using such water-repellent carbon paper as the base sheet.

In the above-mentioned technique, a platinum-supported carbon black as a catalyst particle and a solid polymer electrolyte (ion exchange resin) are made into a slurry in a solvent, and the slurry is applied on a water-repellent carbon paper in a film form or filtered. Although it is deposited and adhered in a form, according to subsequent research results, it is also possible to add and use polytetrafluoroethylene in the slurry, thereby obtaining a more effective effect.

As described above, regardless of whether or not water-repellent carbon paper is used, the electrode made of the catalyst particles and the polymer electrolyte mixed therein has the catalyst particles in the fuel cell incorporating the catalyst particles. Coexist with the phase,
By securing more three-phase interfaces, the performance of the battery can be improved. When polytetrafluoroethylene is added to this, it not only serves as a binder but also has an effect of securing a gas phase, but also has a non-conductive surface.

[0015]

In the electrode described above, the constituent materials of the catalyst layer are basically three: a catalyst particle, an electrolyte and a water repellent. Among them, the electrolyte is mixed to coat the catalyst particles and increase the reaction point of the electrode. However, these prior arts have a drawback that the electrolyte cannot sufficiently coat the catalyst particles, and the utilization of the catalyst is not improved. In the present invention, it has been found that by pre-treating the catalyst particles with an oxidizing agent, the characteristics of the electrode can be improved, the utilization efficiency can be improved, and the performance of a fuel cell incorporating the same can be remarkably improved. Is reached.

That is, the present invention improves the characteristics of an electrode obtained through this step by pretreating the catalyst particles in a fuel cell electrode of the type using catalyst particles, a polymer electrolyte and a water repellent. It is an object of the present invention to provide a fuel cell electrode and a method for manufacturing the same, which significantly improve the performance of a cell incorporating the same.

[0017]

The present invention provides a fuel cell electrode having a catalyst layer containing catalyst particles, an electrolyte, and a water repellent, wherein the catalyst particles are pretreated with an oxidizing agent. The present invention also provides a fuel cell electrode comprising a catalyst layer containing catalyst particles, an electrolyte and a water repellent, wherein the catalyst particles are pretreated with an oxidizing agent. A method for producing a fuel cell electrode is provided.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS There are various types of fuel cells, such as a phosphoric acid type, an alkaline type, and a solid polymer type, and the present invention is applicable to any of those fuel cells. Although the electrode of the present invention contains catalyst particles, an electrolyte and a water repellent, the catalyst particles are not particularly limited as long as they can be used as a catalyst for a fuel cell electrode, and examples thereof include platinum black powder,
Platinum alloy powder, carbon black powder carrying platinum or palladium, palladium black powder and the like can be mentioned.

In the present invention, by pre-treating the catalyst particles with an oxidizing agent, the next step of coating with an electrolyte can be sufficiently performed, and the electrode characteristics and
This is to improve battery performance. Oxidizing agents for this pretreatment include hydrogen peroxide, sodium hypochlorite, chlorine,
At least one selected from nitrous oxide, potassium permanganate and potassium dichromate is used. These are preferably used as a solution. In the case of hydrogen peroxide, if necessary, inactive It may be mixed with a gas and applied in a gaseous state.

Next, as the electrolyte, styrene divinylbenzene sulfonic acid resin, perfluorocarbon sulfonic acid resin and other various ion exchange resins are used, and it is preferable to use perfluorocarbon sulfonic acid resin. In particular, when a perfluorocarbon sulfonic acid-based resin film is used as the electrolyte membrane, it is preferable to use the same type of perfluorocarbon sulfonic acid-based resin.

The water repellent used in the present invention is not particularly limited, but is preferably a polytetrafluoroethylene polymer. Here, the polytetrafluoroethylene-based polymer is meant to include not only polytetrafluoroethylene but also a copolymer such as a tetrafluoroethylene-hexafluoropropylene copolymer and other derivatives thereof.

In the present invention, the mixture containing the catalyst particles, the electrolyte and the water repellent is formed into a sheet as a catalyst layer.
A mixture containing an electrolyte and a water repellent is formed into a kneaded material, which is formed into a sheet by rolling or the like. The mixture is formed into a solution using a solvent such as alcohol, and this is coated in a film on a porous substrate surface. Similar to the embodiment, but the suspension or viscous suspension containing each catalyst particle is supported by a printing method such as screen printing, and the mixture is formed into a solution using a solvent such as alcohol, and It can be carried out in various modes such as depositing and supporting it on a porous substrate surface by a filtration method. According to the present invention, excellent effects in terms of electrode characteristics and the like can be obtained in any of these embodiments.

In any one of the above aspects, the porous substrate serves as a gas diffusion layer in the electrode, and is made of a porous paper or sheet made of various materials (in this specification, Both of them are appropriately referred to as a “sheet”), or they can be appropriately water-repellent and used. Preferably, carbon paper or water-repellent carbon paper can be used. Among them, it is particularly effective to use water-repellent carbon paper because of its excellent characteristics.

As the water-repellent carbon paper, a carbon paper having a predetermined porosity and thickness is used, impregnated with a dispersion of a polytetrafluoroethylene-based polymer, and then heat-treated to obtain a water-repellent carbon paper. It is a thing. Here, the polytetrafluoroethylene-based polymer is meant to include not only polytetrafluoroethylene but also a copolymer such as a tetrafluoroethylene-hexafluoropropylene copolymer and other derivatives thereof.

Before and after the present invention, the present inventors have found that in a fuel cell comprising a polymer electrolyte membrane and a gas diffusion electrode joined together, the gas diffusion electrode is joined to the polymer electrolyte membrane. After hydrogen treatment, by press-bonding to the polymer electrolyte membrane, to improve the water repellency of the carbon support in the catalyst, no flooding phenomenon occurs, has developed a technique to obtain an excellent fuel cell, but in the present invention If this technique is also implemented, an effect combining both advantages can be obtained.

In the process of manufacturing an electrode for a polymer electrolyte fuel cell using a mixture of catalyst particles, a polymer electrolyte and a polytetrafluoroethylene-based water repellent, the entire surface layer of the electrode is solid high. By adding a step of coating with a molecular electrolyte, the characteristics of the electrode are improved,
Although a technique for greatly improving the performance of a battery using the same has been previously developed (Japanese Patent Application Laid-Open No. 7-130372), the present invention relates to, for example, the catalyst particles constituting the electrodes in such an electrode manufacturing process. Can be applied to the pretreatment.

Here, one embodiment of the battery production including the configuration for pretreating the catalyst particles in the present invention is as follows (1) to (7). (1) A catalyst carrying platinum or the like is oxidized by placing it in an oxidizing agent solution. (2) The catalyst particles are filtered and washed with high-purity water such as distilled water. (3)
After the treated catalyst particles are dried at room temperature, they are pulverized sufficiently with a pulverizer. (4) The obtained catalyst particles and the electrolyte are mixed and heated under reduced pressure to coat the electrolyte. (5) The mixed liquid of the obtained sample and the water repellent is sprayed on water-repellent carbon paper, and a catalyst layer is formed by a solvent filtration method.
(6) The obtained electrode is heat-treated in a hydrogen stream. (7)
An electrolyte membrane is sandwiched between the two electrodes thus produced, and pressed to obtain a battery.

FIG. 1 is a view showing an example of an embodiment in which the pressure filtration method is applied in the step (5) (Japanese Patent Laid-Open No. 8-148154). In FIG. 1, 1 is a hollow cylindrical body,
It is arranged vertically as shown. 2 is an upper plate, 3 is a lower plate, 4 and 5 are upper and lower packings, respectively, and 6 is a sheet (gas diffusion plate) on which a catalyst layer is deposited. Among these, the packings 4 and 5 are formed in a shape corresponding to the shape of the upper and lower edges of the hollow cylindrical body. For example, when the hollow cylindrical body is cylindrical, the packings are annularly corresponding to the upper and lower edges. It is composed of

The upper plate 2 has a pipe 7 (with a valve) for introducing a solution to be filtered and a pipe (with a valve) for releasing air when excessive pressure is applied.
, A compressor 10 for increasing the internal pressure in the container
A pipe 9 for introducing the compressed air from is connected. Reference numeral 11 denotes a solvent outlet provided at the center of the lower plate 3, and 12 denotes a leg integrally attached to the lower plate 3. The gas diffusion plate 6 is sandwiched between the lower opening edge of the hollow cylindrical body 1 and the packing 5,
Using this as a filter, solutes in the solution, that is, catalyst particles are deposited on the upper surface.

The lower plate 3 is preferably formed in a funnel shape as shown by a dotted line in the figure, so that the solvent after filtration can flow smoothly. By configuring the upper surface of the lower plate in a funnel shape in this manner, the solvent after filtration smoothly flows toward the solvent outlet, as well as with other configurations such as the hollow cylindrical body 1. Even if there is a distribution in the thickness of the film, the flow becomes poor in the thick portion, and the deposition rate is reduced, so that a uniform layer can be obtained as a whole. The inclination is appropriately set to the extent necessary for obtaining such an effect.

In general, when operating the above apparatus, after assembling, a solution containing catalyst particles is supplied to the hollow cylindrical body 1 from the container via the conduit 7, and compressed air is introduced by the compressor 10. The inside of the hollow cylindrical body 1 is operated in a pressurized state. In this case, the degree of pressurization can be appropriately selected depending on the scale of the apparatus, the fluidity of the solution containing the catalyst particles, the properties such as the strength of the gas diffusion plate 6 itself, the degree of the funnel-like inclination of the lower plate upper surface, and the like. For example, when the diameter of the hollow cylinder is 30 cm and the height is about 5 cm, 0.1 kg / cm
² G (Gauge pressure) or less is sufficient.

[0032]

Hereinafter, the present invention will be described in more detail with reference to Examples, but it goes without saying that the present invention is not limited to these Examples. First, 2 g of catalyst particles carrying 50% by weight of platinum black with respect to carbon black particles were placed in a hydrogen peroxide solution for 1 minute. Then, the catalyst particles were filtered and washed with distilled water. After the washed catalyst particles were dried at room temperature, they were sufficiently pulverized with a pulverizer. To 2 g of the catalyst thus obtained, NAFION (perfluorocarbon sulfonic acid-based electrolyte resin, manufactured by Du Pont)
(Trade name) 1.5 g of an alcohol solution was added, mixed uniformly, and heated under reduced pressure to coat the electrolyte.

A mixture of the sample obtained in the above and polytetrafluoroethylene dispersion was sprayed on water-repellent carbon paper, and a catalyst layer was formed by a solvent filtration method as shown in FIG. Were heat-treated at a temperature of 200 ° C. in a hydrogen stream. A solid polymer electrolyte membrane (NAFION) is placed between the two electrodes thus manufactured.
Film), temperature 140 ° C, pressure 100kgf / cm ²
The battery was manufactured by pressing for 60 seconds under the above pressure, and this was used as the test sample battery of the example.

Here, as the above-mentioned water-repellent carbon paper, one prepared as follows was used. After impregnating a carbon paper having a porosity of 80% and a thickness of 0.4 mm with a dispersion of NEOFLON (registered trademark, manufactured by Daikin Industries, Ltd., tetrafluoroethylene-hexafluoropropylene copolymer), a heat treatment is carried out, and NEOFLON is used. Water-repellent carbon paper was obtained. In this case, the quantitative ratio was adjusted so that neofulon accounted for 20% by weight of the total amount.

On the other hand, as a comparative example, without carrying out the steps among the above steps and the steps related thereto, that is, without treating the catalyst particles with hydrogen peroxide water, and filtering the catalyst particles related thereto, An electrode sheet was prepared in the same manner as in the above-described embodiment except for washing without any other steps. A solid polymer electrolyte membrane was sandwiched between the two electrode sheets thus obtained, and pressed similarly to obtain a comparative test battery.

Next, the test cells of Examples and Comparative Examples were set as fuel cells, and the performance change of the cells was measured. In this measurement, hydrogen was used as fuel,
This was supplied to the anode side, while oxygen was supplied to the cathode side. The supply pressure of both gases was set to 2 atm, hydrogen was humidified at a temperature of 95 ° C., oxygen was humidified at 50 ° C., and the measurement was performed by operating the battery at 80 ° C.

FIG. 2 shows the relationship between the current density and the cell voltage measured for each test battery as described above. As shown in the figure, the cell voltage obtained in the test sample battery of the example is high, and even if the current density increases, it decreases only slightly, indicating that it is considerably superior to the comparative example.
As described above, according to the present invention, the catalyst particles can be sufficiently coated with the electrolyte, and the characteristics of the electrode can be improved. Also, the performance of a battery using this can be greatly improved.

[0038]

As described above, according to the present invention, in a fuel cell electrode containing catalyst particles, a polymer electrolyte and a water repellent, the catalyst particles are pretreated with an oxidizing agent such as hydrogen peroxide. Thereby, the coverage of the electrolyte covering the catalyst can be improved, the utilization of the catalyst can be increased, and the electrode characteristics can be improved. Also, the performance of a battery using this can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of an electrode manufacturing apparatus preferably used in an electrode manufacturing step of the present invention.

FIG. 2 is a diagram showing a relationship between a current density and a cell voltage measured for each test battery manufactured in Examples and Comparative Examples.

[Explanation of symbols]

 Reference Signs List 1 hollow cylindrical body 2 upper plate 3 lower plate 4, 5 packing 6 gas diffusion plate on which catalyst layer is deposited 7 pipe for introducing solution to be filtered (with valve) 8 pipe for releasing air at excessive pressure (with valve) 9 Compressed air inlet pipe 10 Compressor 11 Solvent outlet 12 Leg

Claims (18)

[Claims] 1. An electrode for a fuel cell, comprising a catalyst layer comprising an active metal supported on carrier particles, an electrolyte and a water repellent, wherein the catalyst particles are pretreated with an oxidizing agent. An electrode for a fuel cell, comprising: 2. The oxidizing agent for pretreatment is at least one selected from hydrogen peroxide, sodium hypochlorite, chlorine, nitrous oxide, potassium permanganate, and potassium dichromate. The fuel cell electrode according to claim 1, wherein 3. The fuel cell electrode according to claim 1, wherein said carrier particles are carbon particles. 4. The fuel cell electrode according to claim 1, wherein the active metal supported on the carrier particles is platinum, an alloy containing platinum, or palladium. 5. The fuel cell according to claim 1, wherein the active metal supported on the carrier particles is a plurality of metals selected from platinum, an alloy containing platinum, and palladium. electrode. 6. The fuel cell electrode according to claim 1, wherein the electrolyte is a perfluorocarbon sulfonic acid-based resin. 7. The fuel cell electrode according to claim 1, wherein said catalyst layer is a catalyst layer formed on carbon paper or water-repellent carbon paper as a diffusion layer. 8. The fuel cell electrode according to claim 7, wherein the water-repellent agent of the water-repellent carbon paper is a polytetrafluoroethylene-based polymer. 9. The fuel cell electrode according to claim 1, wherein said fuel cell electrode is an electrode for a polymer electrolyte fuel cell. 10. A method for producing a fuel cell electrode comprising catalyst particles comprising an active metal supported on carrier particles, an electrolyte and a catalyst layer comprising a water repellent, wherein the catalyst particles are pretreated with an oxidizing agent. A method for producing an electrode for a fuel cell. 11. The oxidizing agent for pretreatment is at least one oxidizing agent selected from hydrogen peroxide, sodium hypochlorite, chlorine, nitrous oxide, potassium permanganate and potassium dichromate. The method for producing an electrode for a fuel cell according to claim 10, wherein 12. The method for producing an electrode for a fuel cell according to claim 10, wherein said carrier particles are carbon particles. 13. The method for producing an electrode for a fuel cell according to claim 10, wherein the active metal carried on the carrier particles is platinum, an alloy containing platinum, or palladium. 14. The fuel cell electrode according to claim 10, wherein the active metal supported on the carrier particles is a plurality of metals selected from platinum, an alloy containing platinum, and palladium. Manufacturing method. 15. The method for producing an electrode for a fuel cell according to claim 10, wherein the electrolyte is a perfluorocarbon sulfonic acid-based resin. 16. The method for manufacturing a fuel cell electrode according to claim 10, wherein the catalyst layer is a catalyst layer formed on carbon paper or water-repellent carbon paper as a diffusion layer. . 17. The method for producing an electrode for a fuel cell according to claim 16, wherein the water-repellent agent of the water-repellent carbon paper is a polytetrafluoroethylene-based polymer. 18. The method for producing an electrode for a fuel cell according to claim 10, wherein the method for producing an electrode for a fuel cell is a method for producing an electrode for a polymer electrolyte fuel cell.