JP2009016055A - Manufacturing method of gas diffusion layer, and paste composition for gas diffusion layer manufacturing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a gas diffusion layer in order to suppress reduction of gas permeability and increase in contact resistance. <P>SOLUTION: The manufacturing method of the gas diffusion layer is the method of manufacturing the gas diffusion layer by coating, drying, and calcining so that a paste composition may not permeate into a conductive porous base material surface, and the paste composition and the conductive porous base material satisfy the following (A) and (B) requirements: (A) the paste composition contains carbon particles, fluororesin, dispersant, and water, and its surface tension is 35 mN/m or less: (B) the surface tension of the paste composition is smaller than that of the conductive porous base material, and a contact angle of the conductive porous base material and the paste composition is 90 to 120°. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a novel method for producing a gas diffusion layer for a fuel cell and a paste composition used for the production.

  A membrane-electrode assembly (MEA) constituting a solid polymer fuel cell has a layer structure of gas diffusion layer / catalyst layer / hydrogen ion conductive solid polymer / catalyst layer / gas diffusion layer.

  Among these, the gas diffusion layer mainly plays a role of spreading the gas supplied from the separator to the catalyst layer, and therefore, a gas diffusion layer with good gas permeability is required. In addition, conductivity is required to efficiently convert electrons generated in the catalyst layer into energy. Furthermore, if water generated by the reaction of the catalyst layer penetrates into the gas diffusion layer and stays in the gas diffusion layer, the gas diffusion layer may be hindered, so that the gas diffusion layer also needs water repellency.

  Among these methods, as a method of imparting water repellency, a method of adhering the water-repellent resin by performing a water-repellent treatment in which a conductive porous substrate (gas diffusion layer) is impregnated into the water-repellent resin is performed.

  However, when an MEA is manufactured by laminating a gas diffusion layer coated with an insulating material such as a water repellent resin on the catalyst layer, the contact resistance between the gas diffusion layer and the catalyst layer increases and the conductivity decreases. There is a problem.

  In order to solve this contact resistance problem, a conductive porous substrate coated with a water-repellent resin is coated with a layer composed of a carbon material and a water-repellent resin (so-called flattening layer) on the surface of the conductive porous substrate. A method of forming the film is proposed (Patent Document 1). In this method, a planarizing layer is formed by applying and baking a paste composition containing a carbon material and a water-repellent resin on a conductive porous substrate.

  However, in this method, the paste composition penetrates into the porous substrate, and the paste composition fills the voids inside the porous substrate. Therefore, the gas diffusibility is impaired, and on the contrary, there is a problem that the cell performance of the entire fuel cell is lowered.

Therefore, it is desired to provide a gas diffusion layer that suppresses the reduction in gas permeability inherent in the conductive porous substrate and has a reduced contact resistance.
JP 2003-115302 A

  The main object of the present invention is to provide a method for producing a gas diffusion layer for suppressing a decrease in gas permeability and an increase in contact resistance.

  In view of the above problems, the present inventors have conducted extensive research and as a result, the above problems can be solved by treating with a specific method using a specific paste composition and a specific conductive porous substrate. It has been found that a desired gas diffusion layer can be produced. That is, the present invention provides the following production method and paste composition.

Item 1. A method for producing a gas diffusion layer by applying the paste composition on the surface of the conductive porous substrate so as not to penetrate, drying and firing,
The paste composition and conductive porous substrate are the following (A) and (B):
(A) The paste composition contains carbon particles, a fluororesin, a dispersant, and water, and the surface tension is 35 mN / m or less:
(B) The surface tension of the paste composition is smaller than the surface tension of the conductive porous substrate, and the contact angle between the conductive porous substrate and the paste composition is 90 to 120 °:
A method for producing a gas diffusion layer that satisfies the above requirements.

  Item 2. Item 2. The production method according to Item 1, wherein when the paste composition is applied using a blade, the blade is not brought into contact with the surface of the conductive porous substrate.

  Item 3. Item 3. The method according to Item 1 or 2, wherein the paste composition does not contain alcohol.

  Item 4. Item 4. The production method according to any one of Items 1 to 3, wherein the difference between the surface tension of the conductive porous substrate and the surface tension of the paste composition is 2.5 mN / m or more.

  Item 5. Item 5. The manufacturing method according to any one of Items 1 to 4, wherein the conductive porous substrate is subjected to a water repellent treatment in advance.

  Item 6. The manufacturing method in any one of claim | item 1 -5 whose thermal decomposition temperature of the said dispersing agent is 350 degrees C or less.

  Item 7. The gas diffusion layer obtained by the manufacturing method in any one of claim | item 1 -6.

  Item 8. A paste composition used for producing a gas diffusion layer by coating, drying and firing on the surface of a conductive porous substrate, wherein the paste composition contains carbon particles, a fluororesin, a dispersant and water. A paste composition comprising a surface tension (25 ° C.) of 35 mN / m or less.

  Item 9. The dispersant is at least one selected from the group consisting of polyoxyethylene alkylene alkyl ether, polyethylene glycol alkyl ether, polyoxyethylene fatty acid ester, and acidic group-containing structurally modified polyacrylate. Item 9. The paste composition according to Item 8.

The method for producing a gas diffusion layer of the present invention is a method for producing a gas diffusion layer by applying the paste composition to the surface of the conductive porous substrate so as not to penetrate, drying and firing,
The paste composition and the conductive porous substrate satisfy the following requirements (A) and (B).
(A) The paste composition contains carbon particles, a fluororesin, a dispersant, and water, and the surface tension is 35 mN / m or less.
(B) The surface tension of the paste composition is smaller than the surface tension of the conductive porous substrate, and the contact angle between the paste composition and the conductive porous substrate is 90 to 120 °.

  This makes it possible to provide a layer (planarization layer) that can reduce the contact resistance with the catalyst layer without blocking the voids inside the base material on the surface of the conductive porous base material. As a result, a gas diffusion layer that can exhibit excellent battery performance can be produced. This will be described in detail below.

Paste composition The paste composition of the present invention comprises carbon particles, a fluororesin, a dispersant and water, and has a surface tension (25 ° C.) of 35 mN / m or less.

  The carbon particles are not limited as long as they are conductive, and known or commercially available carbon particles can be used. For example, carbon black such as channel black, furnace black, ketjen black, acetylene black, and lamp black; graphite; activated carbon and the like can be used alone or in combination of two or more. The arithmetic average particle diameter of the carbon particles is usually about 5 nm to 200 nm, preferably about 20 nm to 80 nm.

  A well-known or commercially available fluorine resin can be used for the present invention. For example, polytetrafluoroethylene, fluorinated ethylene propylene resin, perfluoroalkoxy resin and the like can be mentioned. By containing such a fluorine resin, the gas diffusion layer can be provided with water repellency. As a result, water generated during the battery reaction can be quickly discharged to the outside, and blockage of voids in the gas diffusion layer due to the generated water can be suppressed.

  As the dispersant, known or commercially available ones can be used. In the present invention, those having a thermal decomposition temperature of 350 ° C. or less are particularly preferable. Examples of such a dispersant include polyoxyethylene alkylene alkyl ether (thermal decomposition temperature 330 ° C.), polyoxyethylene fatty acid ester (thermal decomposition temperature 330 ° C.), polyethylene glycol alkyl ether (thermal decomposition temperature 350 ° C.), acidic Examples thereof include group-containing structure-modified polyacrylate (thermal decomposition temperature: 350 ° C.). Thereby, since a dispersing agent can be decomposed | disassembled at low temperature, a large sized high temperature furnace etc. are not required but cost reduction can be achieved.

  The paste composition of the present invention preferably contains substantially no alcohol. Examples of such alcohol include monovalent or polyhydric alcohols having about 1 to 5 carbon atoms (particularly 2 to 4 carbon atoms). Specific examples include methanol, ethanol, isopropyl alcohol (IPA), n-butanol, and t-butanol. Thus, when it does not contain alcohol, it can suppress that the paste composition apply | coated permeate | transmits an electroconductive porous base material more, and it becomes possible to maintain the porosity of an electroconductive porous base material.

  The blending ratio of the paste composition is not limited as long as it has a predetermined surface tension. For example, about 5 to 500 parts by weight (preferably 50 to 400 parts by weight) of fluororesin is dispersed with respect to 100 parts by weight of carbon particles. The agent may be about 10 to 500 parts by weight (preferably 20 to 200 parts by weight) and water about 50 to 2000 parts by weight (preferably 100 to 1000 parts by weight).

  The paste composition of the present invention must have a surface tension (25 ° C.) of about 35 mN / m or less. Preferably, it is about 34 mN / m or less. Thereby, the paste composition can be easily applied at the time of applying the paste to the porous substrate, and the repelling of the paste composition can be suppressed. The lower limit is not limited, but may be, for example, about 20 mN / m, preferably about 25 mN / m.

  The surface tension of the paste composition in the present invention is determined by using an automatic surface tension meter (CBVP-Z manufactured by Kyowa Interface Science Co., Ltd.), adjusting the temperature of the paste composition to 25 ° C., and using the plate method. It is to be measured.

Method for Producing Gas Diffusion Layer The method for producing a gas diffusion layer of the present invention is characterized in that the paste composition is applied to the surface of the conductive porous substrate so that the paste composition does not penetrate, and is dried and fired. And More specifically, the blade of the paste composition is not brought into contact with the surface of the conductive porous substrate such that the contact angle between the paste composition and the conductive porous substrate is 90 to 120 °. Apply, then dry and fire.

  In the present invention, it is essential that the contact angle between the conductive porous substrate to which the paste composition is applied and the paste composition is about 90 to 120 °. Thereby, when trying to apply the paste composition uniformly on the substrate, the paste composition is repelled on the substrate at the moment of application and the phenomenon that the paste composition cannot be applied uniformly (so-called repellency) is suppressed. The paste composition can be stably and uniformly applied thereon.

  In the present invention, the contact angle between the paste composition and the conductive porous substrate is determined by using an automatic contact angle measuring machine (“OCA20” manufactured by Eihiro Seiki Co., Ltd.) of about 1 μl (microliter) of the paste composition. It is obtained by dropping a droplet on the substrate surface and observing the contact angle after 30 seconds.

  A well-known or commercially available conductive porous substrate can be used. For example, carbon paper, carbon cloth, carbon non-woven fabric and the like can be mentioned.

  The thickness of the conductive porous substrate is not limited, but is usually about 50 μm to 1000 μm, preferably about 100 μm to 400 μm.

  The surface tension of the surface of the conductive porous substrate (the value after the water repellent treatment when subjected to the water repellent treatment) is usually 35 to 40 mN / m, preferably 36 to 39 mN / m.

  In addition, it is preferable that the surface of the conductive porous substrate of the present invention has been subjected to water repellent treatment in advance. Thereby, the electroconductive porous base material is given water repellency, and blockage inside the porous base material due to water generated by the battery reaction can be suppressed. Moreover, the phenomenon which a paste composition osmose | permeates to the inside at the time of paste composition application | coating to a base material can be suppressed, and gas diffusion performance can be improved.

  In the present invention, the surface tension of the conductive porous substrate (the surface tension of the conductive porous substrate after the water repellent treatment when the water repellent treatment is applied) is a plurality of wetting index standard solutions having different surface tensions. (Wako Pure Chemical Industries, Ltd.) (25 ° C.) is prepared, the plurality of standard solutions are dropped on the surface of the conductive porous substrate, and whether the standard solution is repelled on the substrate surface is observed. Is measured.

  In the present invention, it is essential that the surface tension of the paste composition is smaller than the surface tension of the conductive porous substrate. In particular, the difference in surface tension between the paste composition and the conductive porous substrate is preferably about 2.5 mN / m or more, more preferably about 3.0 mN / m or more. Thereby, it becomes much easier to apply without contacting the blade.

  The present invention is characterized in that the paste composition is applied so as not to penetrate the surface of the conductive porous substrate. Specifically, for example, when applying the paste composition using a blade, the applied paste composition (upper surface) is scraped by preventing the blade from coming into contact with the surface of the conductive porous substrate. Take it.

  In general, when applying a paste composition to a substrate, a blade such as a doctor blade, a wire bar, a squeegee used for screen printing, etc. are brought into contact with the surface of the coating (ie, conductive porous substrate) and pressure is applied. A method of scraping off excess paste composition is employed. On the other hand, in the present invention, the paste composition is prevented from penetrating the surface of the conductive porous substrate by, for example, performing a blade or the like so as not to contact the surface of the conductive porous substrate. Thereby, blockage | closure of the space | gap inside a conductive porous base material can be suppressed, and the gas diffusion layer which formed the planarization layer can be obtained, having favorable gas diffusion performance.

  As an apparatus used for such a coating method, for example, a known or commercially available applicator may be used.

  In the production method of the present invention, after coating, it is dried and then baked. Thereby, a planarization layer can be obtained on the surface of the conductive porous substrate. By providing this flattening layer, the unevenness of the substrate surface can be smoothed, so that the contact area between the substrate and the catalyst layer can be increased and the contact resistance can be reduced.

The coating amount of the paste composition, in terms of solid content, typically 5 to 100 g / ^{m 2,} preferably about may be set to 15 to 50 g / ^{m 2} approximately.

  The drying temperature is not limited. For example, the drying temperature may be about 50 to 150 ° C., preferably about 90 to 130 ° C. in the air.

  Although drying time is suitably determined according to drying temperature etc., what is necessary is just to normally be about 10 minutes-30 minutes.

  The firing temperature is not limited, and may be performed by heating to about 250 to 390 ° C., preferably about 300 to 350 ° C. in the atmosphere.

  The firing time is appropriately determined according to the firing temperature and the like, but it may be usually about 30 minutes to 120 minutes.

Gas diffusion layer In the gas diffusion layer obtained by the present invention, a layer (planarization layer) obtained by drying and baking the paste composition is laminated on the surface of the conductive porous substrate. For this reason, the contact resistance with the catalyst layer can be lowered without deteriorating the gas diffusion performance of the conductive porous substrate.

  The gas diffusion layer of the present invention has a structure in which the planarization layer formed on the surface of the conductive porous substrate does not substantially penetrate into the inside of the conductive porous substrate.

  The thickness of the flattening layer is determined according to the application amount of the paste composition and the like, but is usually about 10 μm to 100 μm.

  The gas diffusion layer of the present invention can be used as, for example, a gas diffusion layer for a polymer electrolyte fuel cell. That is, by laminating the gas diffusion layer of the present invention on a known or commercially available catalyst layer so that the planarizing layer contacts, and further laminating a known or commercially available hydrogen ion conductive solid polymer electrolyte membrane, It can be used as a fuel cell membrane-electrode assembly (layer structure of gas diffusion layer / catalyst layer / hydrogen ion conductive solid polymer electrolyte membrane / catalyst layer / gas diffusion layer).

  According to the production method of the present invention, in order to make the paste composition difficult to penetrate into the inside of the conductive porous substrate, the planarizing layer is formed into the conductive porous substrate without blocking the voids inside the conductive porous substrate. It can be formed near the surface of the material. For this reason, it is possible to produce a gas diffusion layer excellent in conductivity and water repellency without deteriorating the gas diffusion performance, and thus a gas diffusion layer exhibiting excellent battery performance with good current-voltage characteristics and the like.

  Hereinafter, the present invention will be described in more detail with reference to examples. In addition, this invention is not limited to the following Example.

<Preparation of paste composition>
Example 1
20 parts by weight of “Vulcan xc72R (manufactured by Cabot Corporation)” as carbon particles, 20 parts by weight of “Emulgen MS110 (manufactured by Kao Corporation)” as polyoxyethylene alkylene alkyl ether (thermal decomposition temperature 330 ° C.) and ion-exchanged water as a dispersant. 60 parts by weight was mixed, and mixed with stirring by a planetary mixer for 20 minutes. Next, 100 parts by weight of polytetrafluoroethylene dispersion (manufactured by Daikin Industries, Ltd., “Lublon LDW40E”, solid content 40% by weight) was added as a fluororesin, and the mixture was stirred with a dissolver. A paste composition was prepared.

Example 2
Instead of 20 parts by weight of polyoxyethylene alkylene alkyl ether “Emulgen MS110 (manufactured by Kao Corporation)” as a dispersant, 20 parts by weight of polyoxyethylene fatty acid ester (thermal decomposition temperature 330 ° C.) “BYK184 (manufactured by Big Chemie)” was used. Instead of 100 parts by weight of polytetrafluoroethylene dispersion (Daikin Kogyo Co., Ltd., “Lublon LDW40E”, solid content 40% by weight) as a fluororesin, polytetrafluoroethylene dispersion (Daikin Kogyo Co., Ltd., “ Example 1 except that 70 parts by weight of “Lublon LDW40E”, solid content 40% by weight) and 30 parts by weight of polytetrafluoroethylene dispersion (Mitsui / DuPont Fluorochemical Co., Ltd., “PTFE emulsion 31-J”) were used. In the same manner, the paper of Example 2 was used. A first composition was prepared.

Example 3
A paste composition of Example 3 was prepared in the same manner as in Example 1 except that 6 parts by weight of isopropyl alcohol was further added as a solvent.

Example 4
Instead of 20 parts by weight of polyoxyethylene alkylene alkyl ether “Emulgen MS110 (manufactured by Kao Corporation)” as a dispersant, 20 parts by weight of polyoxyethylene fatty acid ester (thermal decomposition temperature 330 ° C.) “BYK184 (manufactured by Big Chemie)” was used. A paste composition of Example 4 was prepared in the same manner as in Example 1 except that 30 parts by weight of isopropyl alcohol was further added as a solvent.

Comparative Example 1
Instead of 20 parts by weight of polyoxyethylene alkylene alkyl ether “Emulgen MS110 (manufactured by Kao Corporation)” as a dispersant, polycarboxylic acid-containing polyester-based dispersant (thermal decomposition start temperature 300 ° C.) “BYK190 (manufactured by BYK Chemie)” 10 weights A paste composition of Comparative Example 1 was prepared in the same manner as in Example 1 except that the amount of ion-exchanged water was 70 parts by weight instead of 60 parts by weight.

Comparative Example 2
A paste composition of Comparative Example 2 was prepared in the same manner as Comparative Example 1 except that the amount of the fluororesin added was 50 parts by weight instead of 100 parts by weight.

  The surface tensions of the paste compositions of Examples 1 to 4 and Comparative Examples 1 and 2 were evaluated. The results are shown in Table 1. The surface tension of the paste composition was measured by a plate method using an automatic surface tension meter (CBVP-Z manufactured by Kyowa Interface Science Co., Ltd.) after adjusting the temperature of the paste composition to 25 ° C.

<Water repellent treatment>
A carbon fiber woven fabric (thickness) obtained by carbonizing a polyacrylonitrile flameproof spun yarn (heating temperature: 950 ° C. in a nitrogen atmosphere) and graphitizing (heating temperature: 2000 ° C., in vacuum) as a conductive porous substrate Thickness: 0.246 mm, thickness variation coefficient: 2.3%, basis weight: 101 g / m ² , bulk density: 0.410 g / cc, volume resistivity: 0.02 Ωcm).

  The conductive porous substrate was impregnated with a fluorine-based aqueous dispersion aqueous solution (manufactured by Daikin Industries, Ltd., “Polyflon D-1E”) containing 60 wt% of polytetrafluoroethylene for 5 minutes, and then at 130 ° C. in an air atmosphere. For about 15 minutes, followed by baking at 350 ° C. for 2 hours in an air atmosphere to give a water repellent treatment.

  A plurality of wetting index standard solutions (Wako Pure Chemical Industries, Ltd.) (25 ° C) with different surface tensions are successively dropped onto the surface of the water-repellent conductive porous substrate. Then, the surface tension of the water-repellent conductive porous substrate was measured by observing whether or not it was repelled. The measured surface tension was 37.5 mN / m.

  The contact angle between this water-repellent conductive porous substrate and the paste compositions of Examples 1 to 4 or Comparative Examples 1 to 2 was measured. The measurement results are shown in Table 1. The contact angle was measured by using an automatic contact angle measuring device (“OCA20” manufactured by Eihiro Seiki Co., Ltd.) and dropping a paste composition droplet of about 1 μl (microliter) on the substrate surface, and after 30 seconds. This was done by observing the contact angle.

<Manufacture of gas diffusion layer>
Using the applicator (Shen Instruments Ltd., “Micrometer Adjustable Film Applicator, 1117/200”), the paste composition of Examples 1 to 4 was applied so that the coating amount was about 30 g / m ^{2 in} terms of solid content. It applied uniformly to the surface of a water repellent conductive porous substrate. Next, after drying at 130 ° C. in the air atmosphere, the planarization layer was formed on the surface of the conductive porous substrate by firing at 350 ° C. for 2 hours in the air atmosphere. A layer was produced.

  On the other hand, the paste compositions of Comparative Examples 1 and 2 were similarly applied to the substrate surface, but the paste composition was repelled and could not be applied uniformly.

  The results of applying the paste composition to the substrate are also shown in Table 1. The case where the coating could be performed uniformly was evaluated as “◯”, and the case where the repelling occurred and the coating could not be performed uniformly was evaluated as “x”.

Reference Example Using the bar composition (ROD, No. 30), the paste composition obtained in Example 1 was coated with the above water-repellent conductive porous material so that the coating amount was about 30 g / m ^{2 in} terms of solid content. It apply | coated to the base-material surface. At this time, it was observed that the paste composition exudes to the back surface of the substrate. Subsequently, after drying at 130 degreeC in air | atmosphere atmosphere, the planarization layer was formed in the electroconductive porous base material surface by baking at 350 degreeC in air | atmosphere atmosphere for 2 hours. It can be seen that the gas diffusion performance is inferior because the planarizing layer component has penetrated into the conductive porous substrate.

<Fuel cell and evaluation test>
(1) Manufacture of electrolyte membrane-catalyst layer laminate 10 g of platinum catalyst-supported carbon particles (Tanaka Kikinzoku Kogyo Co., Ltd., “TEC62E58”), ion conductive polymer electrolyte solution (Nafion 5 wt% solution: “DE-520” manufactured by DuPont ) 100 g, 30 g of distilled water and 100 g of isopropyl alcohol were blended and stirred and mixed in a disperser to obtain an anode catalyst layer paste composition.

  Platinum catalyst-supported carbon particles (Tanaka Kikinzoku Kogyo Co., Ltd., “TEC10E50E”) 10 g, ion conductive polymer electrolyte solution (Nafion 5 wt% solution, “DE-520”, manufactured by DuPont) 100 g, distilled water 30 g, n-butanol 50 g And 50 g of t-butanol were mixed and stirred and mixed in a disperser to obtain a catalyst layer paste composition for a cathode.

The catalyst layer paste composition for the anode and the catalyst layer paste composition for the cathode were each applied onto a transfer substrate made of a polyethylene terephthalate film (“Luminer X44” manufactured by Toray Industries, Inc.) using an applicator, and 30 at 80 ° C. A catalyst layer was formed by drying for a minute to prepare an anode catalyst layer-forming transfer sheet and a cathode catalyst layer-forming transfer sheet. The catalyst layer was applied so that the amount of platinum supported was 0.5 mg / cm ² for both the cathode catalyst layer and the anode catalyst layer.

  Using the prepared catalyst layer forming transfer sheet for cathode and catalyst layer forming transfer sheet for anode, press (press machine temperature: 130 ° C., press pressure) is applied to each surface of the electrolyte membrane (“Nafion 112”, manufactured by DuPont). 6.5 MPa), and then the transfer film was peeled off to prepare an electrolyte membrane-catalyst layer laminate (cathode catalyst layer / electrolyte membrane / anode catalyst layer).

(2) Manufacture of fuel cell By laminating the gas diffusion layer of Example 1 on both surfaces of the prepared electrolyte membrane-catalyst layer laminate, a membrane-electrode assembly (MEA: gas diffusion layer / catalyst layer for cathode) / Electrolyte membrane / catalyst layer for anode / gas diffusion layer), and then the obtained MEA was incorporated into a fuel cell to produce a polymer electrolyte fuel cell of Example 1.

  For the gas diffusion layers of Examples 2 to 4, fuel cells were manufactured in the same manner as in Example 1, and the fuel cells of Examples 2 to 4 were obtained.

(3) Battery performance evaluation The cell performance of the fuel cells of Examples 1 to 4 was evaluated. Cell evaluation conditions were as follows.
Cell temperature: 80 ° C
Humidification temperature: cathode 80 ° C, anode 70 ° C
Gas utilization rate: cathode 40%, anode 70%
The fuel cells obtained using the paste compositions of Examples 1 and 2 exhibited better cell performance than the fuel cells obtained using the paste compositions of Examples 3 and 4. This is because, since the paste compositions of Examples 1 and 2 do not contain alcohol (IPA), a planarization layer can be formed on the surface without further closing the voids inside the conductive porous substrate, and gas diffusion This is thought to be due to the ability to suppress the degradation of performance.

Claims (9)

A method for producing a gas diffusion layer by applying the paste composition on the surface of the conductive porous substrate so as not to penetrate, drying and firing,
The paste composition and the conductive porous substrate are the following (A) and (B):
(A) The paste composition contains carbon particles, a fluororesin, a dispersant, and water, and the surface tension is 35 mN / m or less:
(B) The surface tension of the paste composition is smaller than the surface tension of the conductive porous substrate, and the contact angle between the conductive porous substrate and the paste composition is 90 to 120 °:
A method for producing a gas diffusion layer that satisfies the above requirements.   The manufacturing method according to claim 1, wherein when the paste composition is applied using a blade, the blade is not brought into contact with the surface of the conductive porous substrate.   The manufacturing method of Claim 1 or 2 with which the said paste composition does not contain alcohol.   The manufacturing method in any one of Claims 1-3 whose difference of the surface tension of the said electroconductive porous base material and the surface tension of a paste composition is 2.5 mN / m or more.   The said conductive porous base material is a manufacturing method in any one of Claims 1-4 by which the water-repellent process was made | formed previously.   The manufacturing method in any one of Claims 1-5 whose thermal decomposition temperature of the said dispersing agent is 350 degrees C or less.   A gas diffusion layer obtained by the production method according to claim 1. A paste composition used for producing a gas diffusion layer by coating, drying and firing on the surface of a conductive porous substrate,
The paste composition comprising carbon particles, a fluororesin, a dispersant and water, and having a surface tension (25 ° C.) of 35 mN / m or less.   The paste composition according to claim 8, wherein the dispersant is at least one selected from the group consisting of polyoxyethylene alkylene alkyl ether, polyethylene glycol alkyl ether, polyoxyethylene fatty acid ester and acidic group-containing structurally modified polyacrylate. object.