JPH11339816A - Manufacture of electrode for fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a catalyst paste from infiltrating into the porous section of an electrode base material by providing a coating film between the gas- permeable porous electrode base material face and the catalyst paste applied on the faces. SOLUTION: A gas-permeable porous electrode base material 1 is coated with a hydroxy propyl methyl cellulose aqueous solution having the concentration of about 2-3% and the viscosity of about 2000-7000 CPS, and it is dried to form a coating film 3. The coating film 3 is coated with a catalyst paste 2 mixed and dispersed with catalyst powder carrying a noble metal, PTFE serving as a water-repellent binder, an auxiliary and a solvent, it is quickly frozen in a preliminary freezing tank, and the icy solvent is eliminated by sublimation in a vacuum freeze dryer. It is then pressed by a hydraulic press, it is baked at about 200-400 deg.C to extinguish the coating film 3, and the gas permeability of the porous electrode base material 1 is secured. A catalyst layer 4 and a catalyst layer infiltration section 5 are formed on the surface of the electrode base material 1 and a porous section surface layer to obtain an electrode for a fuel cell.

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 an electrode for a fuel cell.

[0002]

2. Description of the Related Art FIG. 3 shows a general schematic sectional view of an electrode of a conventional fuel cell. FIG. 3 (a) is a schematic cross-sectional view of a manufacturing process of a conventional example, in which reference numeral 1 denotes an electrode substrate, which is a paper-like material made of conductive porous carbon fibers. Reference numeral 2 denotes a catalyst paste, which is obtained by mixing and dispersing a catalyst powder carrying a noble metal, polytetrafluoroethylene (hereinafter referred to as PTFE) as a water-repellent binder, an auxiliary, and a solvent, and treating the mixture on the electrode substrate surface. It was done. 6
Is a joining boundary portion between the catalyst layer and the electrode substrate. FIG. 3 (b) is a schematic cross-sectional view of a conventional electrode, where 1 is an electrode substrate, 4 is a catalyst layer formed on the electrode substrate surface,
Reference numeral 5 denotes a catalyst layer which penetrates into the electrode base porous portion and remains.

Next, the operation will be described. Conventionally, in a method for manufacturing an electrode for a fuel cell, a catalyst paste 2 in which a catalyst powder, PTFE as a water-repellent binder and an auxiliary agent, and a solvent are mixed and dispersed is sprayed, a doctor blade method, a roll coater method, and a screen. After directly spraying or coating the electrode substrate 1 by a method such as a printing method or a gravure printing method, the solvent is removed by heating or vacuum freeze drying to form the catalyst layer 4 on the electrode substrate surface. In addition, the catalyst layer 5 is also left in the portion of the electrode base porous portion where the catalyst paste has entered.

[0004]

A conventional method for manufacturing an electrode for a fuel cell is to directly spray or apply a catalyst paste to the electrode substrate 1 using a porous paste made of carbon fibers as described above. Since the catalyst paste 2 entirely or partially penetrates into the porous portion of the electrode substrate 1 or leaches into the back surface of the electrode substrate 1, the bonding boundary between the electrode substrate 1 and the catalyst layer 4 of the electrode is formed. It was difficult to control the thickness of the portion 6 uniformly. Further, the catalyst paste 2 penetrates into the porous portion of the electrode substrate 1 and the thickness of the catalyst layer 5 that is not effectively used for the electrode reaction increases, and the catalyst layer 2 is clogged and easily wetted with phosphoric acid as an electrolyte. Further, when leached on the back surface of the electrode substrate 1, a liquid pool or a liquid film of phosphoric acid is formed, which causes problems such as blockage, reduction, and uneven distribution of gas diffusion holes in the electrode surface. This was largely related to the aging of the electrode due to inhibition.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and has an object to make the thickness of a joining boundary between an electrode base material and a catalyst layer uniform and to form an electrode of a catalyst paste. Excellent by preventing infiltration, seepage, etc., into the porous part or the back surface of the base material, eliminating clogging of the porous part, phosphoric acid wetting and accumulation of phosphoric acid liquid on the back surface, and liquid film formation. It is intended to obtain improved gas diffusion performance and to improve characteristics and quality of the electrode.

[0006]

According to a method of manufacturing an electrode for a fuel cell according to the present invention, a catalyst powder carrying a noble metal on a gas-permeable porous electrode substrate, a water-repellent binder and an auxiliary agent are provided. In a fuel cell electrode having a catalyst layer formed by applying a catalyst paste obtained by mixing and dispersing a solvent and a solvent, an electrode substrate porous portion of the catalyst paste applied on the porous electrode substrate surface In order to prevent or suppress intrusion such as infiltration or exudation into the substrate, a coating film treatment is performed on the surface of the porous electrode substrate.

Further, the method for producing an electrode for a fuel cell according to the present invention provides a cellulosic material which is dissolved in a water-soluble or organic solvent which forms a film and thermally decomposes at 150 to 400 ° C. for coating film treatment. Alternatively, any one of polymer materials is used.

Further, the method of manufacturing an electrode for a fuel cell according to the present invention is characterized in that a roll coater or a screen printing method is used as a coating film treatment.

Further, the method of manufacturing an electrode for a fuel cell according to the present invention is characterized in that the material for coating film treatment is selected from the group consisting of hydroxypropylcellulose, hydroxypropylmethylcellulose and polyvinyl alcohol.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. As shown in a schematic cross-sectional view of the manufacturing process according to the embodiment of the present invention in FIG. 1 (a), hydroxypropyl methylcellulose (for example, 520 × 520 × 0.1 mm) is provided on a gas-permeable porous electrode substrate 1. Shin-Etsu Chemical HPMC, trade name 60SH-4
000) at a concentration of 2 to 3% and a viscosity of 2000 to 7000 CP
An aqueous solution of S was applied and dried by a roll coater method to form a coating film 3. Next, a catalyst paste 2 obtained by mixing and dispersing a catalyst powder carrying a noble metal, PTFE as a water-repellent binder, an auxiliary agent, and a solvent on a surface of the electrode substrate 1 on which the coating film is formed is roll-coated. Then, the mixture was rapidly frozen in a preliminary freezing tank, the ice-like solvent was removed by sublimation disappearance in a vacuum freeze dryer, and then baked at 200 to 400 ° C. after pressurizing with a hydraulic press. In this firing step, the coating film 3 previously formed on the surface of the electrode substrate 1 was burned off, and the gas permeability of the electrode substrate 1 as porous was secured. As shown in the schematic sectional view of the electrode according to the present invention [FIG. 1 (b)], the catalyst layers 4 and 5 are formed on the surface of the electrode substrate 1 and on the porous portion surface layer by the above-described manufacturing process. The formed electrode was produced.

Next, the operation will be described. The electrode of the present invention, which is obtained by the above-mentioned manufacturing method, is characterized in that the coating film 3 formed on the surface of the electrode substrate 1 allows the catalyst paste 2 applied to the electrode substrate 1 to soak into the porous portion of the substrate 1. Intrusion such as intrusion and seepage is suppressed only to the surface layer, and the formed catalyst layer 4 has a uniform thickness and the thickness of the joint boundary 6 between the electrode substrate 1 and the catalyst layer 4. Is uniform, so that the porous portion of the electrode substrate 1 is easily clogged and wetted with phosphoric acid. It is possible to solve the problems and the like, and obtain excellent gas diffusion performance. In addition, the coating film 3 on the electrode substrate 1 can be easily processed by a roll coater method and has no problem in productivity.

Comparative Example 1 In this example, an electrode was prepared in the same manner as in Embodiment 1 except that the catalyst paste 2 was not directly subjected to a coating film treatment by a roll coater method. For example, 520 × 520
After the electrode paste was applied to the electrode substrate 1 having a size of × 0.1 mm, the electrode produced through the same manufacturing process as that of the embodiment 1. An air pocket is formed on the back surface of the electrode substrate 1, and a phenomenon in which spot-like irregularities having a diameter of 10 to 20 mm are observed on the surface of the electrode,
It could not be used as an electrode.

Embodiment 2 FIG. As in the first embodiment, for example, a gas-permeable porous electrode substrate 1 of 520 × 520 × 0.2 mm has a concentration of hydroxypropylcellulose (HPC manufactured by Shin-Etsu Chemical, trade name MG) of 2-3% and a viscosity of 7000-7000.
Embodiment 1 After coating and drying an aqueous solution of 20,000 CPS by a roll coater method to form a coating film 3,
An electrode was manufactured through the same manufacturing steps as in. The electrode obtained by this manufacturing method penetrates into the porous portion of the electrode substrate 1 when the catalyst paste 2 is applied, similarly to the case where the coating film 3 is formed on the surface of the electrode substrate 1 with hydroxypropylmethylcellulose of Embodiment 1. Was extremely suppressed only on the surface layer, and excellent gas diffusion performance was obtained. Further, by using hydroxypropyl cellulose for the coating film, the film forming property is good, and even if the electrode substrate 1 having a thickness of 0.2 mm is used, the catalyst paste does not enter the porous portion of the electrode substrate 1. Only the surface layer was suppressed, and good results were obtained as electrode characteristics.

Embodiment 3 As in the first embodiment, for example, a polyvinyl alcohol (a product of Shin-Etsu Chemical Co., Ltd.,
Concentration 4%, viscosity 20-100 CPS
The solution was applied and dried by screen printing to form a coating film 3, and then an electrode was manufactured through the same manufacturing process as in the first embodiment. As in the first and second embodiments, the electrode obtained by this manufacturing method was able to suppress intrusion into the porous portion of the electrode substrate 1 when the catalyst paste 2 was applied, and excellent gas diffusion performance was obtained. Further, by using polyvinyl alcohol for the coating film 3, a film is easily formed and the pot life of the aqueous solution is long and economical.

Comparative Example 2 In this example, an electrode was prepared in the same manner as in Embodiment 1 except that the catalyst paste 3 was not directly subjected to a coating film treatment by a screen printing method. For example, 200 × 20
After the electrode paste was applied to the electrode substrate 1 of 0 × 0.2 mm, the electrode produced through the same manufacturing process as in the first embodiment caused the catalyst paste 2 to penetrate into the porous portion of the electrode substrate 1 at the time of application and leached out. A large amount of the leached catalyst layer adhered to the back surface of the electrode substrate 1.

Embodiment 4 As in the first embodiment, for example, hydroxypropylcellulose (HPC manufactured by Shin-Etsu Chemical Co., Ltd., trade name: MG) has a concentration of 2 to 3% and a viscosity of 5000 to 10000 CP on a porous substrate 1 of 200 × 200 × 0.2 mm, for example.
A liquid dissolved in the ethyl alcohol solvent of S was applied and dried by a screen printing method to form a coating film 3, and then an electrode was manufactured through the same manufacturing process as in the first embodiment. Since the electrode obtained by this manufacturing method uses the solvent-based coating film material 3, the application of the water-soluble catalyst paste 2 is equal to or more than that of the first to third embodiments using the water-soluble coating film material 3. At times, the coating film material was not wetted, and the penetration of the catalyst paste 3 into the porous portion of the electrode substrate 1 could be completely suppressed, and excellent gas diffusion performance was obtained with almost no clogging. Also, by using a solvent-based coating film material 3, there is an effect that a film having stable strength can be obtained.

As shown in a schematic cross-sectional view of the manufacturing process according to the embodiment of the present invention [FIG.
0 × 520 × 0.2 mm gas-permeable porous electrode substrate 1
A high-viscosity aqueous solution of hydroxypropyl methylcellulose (HPMC manufactured by Shin-Etsu Chemical Co., Ltd., product name: 60SH-4000) having a concentration of 5% or more and a viscosity of about 50,000 CPS or more, which is close to grease, is applied by a roll coater method, dried and coated. After the film 3 was formed, an electrode was manufactured through the same manufacturing steps as in the first embodiment. As shown in FIG. 2 (b), a schematic cross-sectional view of the electrode manufactured by the above-described manufacturing process can almost prevent the catalyst layer from penetrating into the porous portion of the electrode substrate 1. The catalyst layer 4 can be formed only on the surface.

The electrode manufactured in this manner is an electrode substrate 1
Since there is no catalyst layer penetration part in the porous part, there is no clogging,
Since the gas diffusion property is further improved and the catalyst layer 4 effective for the electrode reaction can be formed at a minimum on the surface of the electrode substrate 1 with a uniform film thickness, expensive materials can be reduced, and the electrode is excellent in economical efficiency. Can be obtained. Also, by forming the thick coating film 3 on the electrode substrate 1, there is an advantage that the viscosity of the applied catalyst paste 2 can be used in a high range.

[0019]

According to the first aspect of the present invention, after the coating film treatment 3 is performed on the gas-permeable porous electrode substrate 1, the catalyst powder supporting the noble metal and the water-repellent binder are used. When applying the catalyst paste 2 in which PTFE, an auxiliary agent, and a solvent are mixed and dispersed, in order to prevent or suppress the intrusion of the catalyst paste 2 into the porous portion of the electrode substrate 1, clogging which has been a problem in the conventional example, This has the effect of eliminating gas diffusion inhibition due to phosphoric acid wetting and accumulation of phosphoric acid on the back surface of the electrode substrate 1 and generation of a liquid film.

According to the second aspect of the present invention, for the treatment of a coating film, a cellulose-based material or a polymer material which forms a film and is also dissolved in a water-soluble or organic solvent which is thermally decomposed at 150 to 400 ° C. Since either of them is used, the catalyst paste 2 does not seep into or permeate the porous portion of the electrode substrate 1, so that the thickness of the catalyst layer 4 can be made uniform and the catalyst layer 4 effective for the electrode reaction can be minimized. It is possible to obtain an electrode with excellent economy by reducing expensive materials.

According to the third aspect of the present invention, since the roll coater or the screen printing method is used as the coating film treatment, the thickness, the porosity of the electrode substrate 1 and the presence or absence of the water repellent treatment of the electrode substrate 1 are determined. Regardless of the electrode substrate 1 and the catalyst layer 4
This has an effect that it is easy to uniformly control the thickness of the bonding boundary portion.

According to the fourth aspect of the present invention, since hydroxypropylcellulose, hydroxypropylmethylcellulose or polyvinyl alcohol roll is used for the coating film treatment, the film is easily formed, and the aqueous solution has a long pot life and is economical. It has the effect of.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing Embodiments 1 to 4 of the present invention.

FIG. 2 is a schematic sectional view showing a fifth embodiment of the present invention.

FIG. 3 is a general schematic sectional view of a conventional fuel cell electrode.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electrode base material 2 Catalyst paste 3 Coating film 4 Catalyst layer 5 Catalyst layer penetration part 6 Catalyst layer joining boundary

Claims (4)

[Claims] 1. A method for applying a catalyst paste obtained by mixing and dispersing a catalyst powder carrying a noble metal, a water-repellent binder and an auxiliary agent, and a solvent onto a gas-permeable porous electrode substrate surface. Thereby, in the fuel cell electrode on which the catalyst layer is formed, the penetration of the catalyst paste applied on the porous electrode substrate surface into the electrode substrate porous portion, the seepage, and the like are prevented or suppressed. A method of producing an electrode for a fuel cell, wherein a coating film treatment is performed on the surface of a porous electrode substrate. 2. The method of claim 1, wherein the coating film is formed by using a cellulose-based material or a polymer material which forms a film and is also dissolved in a water-soluble or organic solvent which is thermally decomposed at 150 to 400 ° C. A method for producing the electrode for a fuel cell according to the above. 3. The method for producing an electrode for a fuel cell according to claim 1, wherein a roll coater or a screen printing method is used as the coating film treatment. 4. The method according to claim 2, wherein said material is selected from the group consisting of hydroxypropylcellulose, hydroxypropylmethylcellulose, and polyvinyl alcohol.