JP2010033896A - Paste composition for granting water-repellent characteristics and manufacturing method for gas diffusion layer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a paste composition capable of giving excellent conductivity and excellent water-repellent characteristics to a conductive porous base material for a fuel cell. <P>SOLUTION: The paste composition used to give water-repellent characteristics to the conductive porous base material (gas diffusion layer 1) for a fuel cell is provided. The paste composition contains a non-polymer system fluorine material, fluorine resin, a dispersant, and water. The non-polymer system fluorine material exists in the water in a dispersed state. Excellent conductivity and excellent water-repellent characteristics can be given to the conductive porous base material (gas diffusion layer 1) for a fuel cell by using the paste composition. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a novel paste composition for imparting water repellency to a conductive porous substrate for fuel cells and a novel method for producing a gas diffusion layer imparted with water repellency using the same.

  The electrolyte membrane-electrode assembly (MEA) constituting the polymer electrolyte fuel cell has a structure in which a gas diffusion layer, a catalyst layer, an ion conductive solid polymer electrolyte membrane, a catalyst layer, and a gas diffusion layer are sequentially laminated. is doing.

  Among these, since the gas diffusion layer plays a role in uniformly distributing the gas supplied from the separator to the catalyst layer, it is required to have good gas diffusibility (gas permeability). In addition, it is necessary that the electrons generated in the catalyst layer have conductivity to be efficiently transported to the separator. For this reason, a conductive porous substrate such as carbon paper is generally used as the material of the gas diffusion layer.

  Furthermore, water repellency is mentioned as the performance calculated | required by the gas diffusion layer. This is because water is generated in the catalyst layer due to the cell reaction, and if this generated water fills the pores of the gas diffusion layer, the gas diffusibility is adversely affected. This is for discharging.

  However, the conductive porous substrate itself such as carbon paper generally does not have water repellency. Therefore, in order to impart water repellency, a method of forming a water repellent layer made of a fluorine-based resin such as polytetrafluoroethylene on a conductive porous substrate has been performed (Patent Document 1).

  In addition, a method of fixing the fluorinated pitch by applying a fluorinated organic solvent in which the fluorinated pitch is dissolved to a conductive porous substrate, and drying and removing the organic solvent has been proposed (Patent Document 2). ).

  However, in the technique described in Patent Document 1, since a large amount of fluororesin having a high electric resistance is used, the electric resistance of the gas diffusion layer and the entire MEA is increased, and a decrease in conductivity is inevitable. In addition, it cannot be said that the water repellency is sufficiently improved in the layer made of a fluorine resin.

On the other hand, in the technique described in Patent Document 2, since the fluorinated pitch is difficult to bind to the conductive porous substrate, the water-repellent material mainly composed of the fluorinated pitch is dropped from the substrate, and the water repellency is long-term. There is a risk that it will not be exhibited over a period of time. Further, the technique described in Patent Document 2 uses a fluorine-based organic solvent, which is not preferable from the viewpoint of the environment.
JP 2003-115302 A JP 2000-67874 A

  An object of the present invention is to provide a method for producing a gas diffusion layer capable of imparting more excellent conductivity and water repellency to a conductive porous substrate for fuel cells, and a paste composition used therefor.

  In view of the above problems, the present inventors have made extensive studies. As a result, it has been found that the above problem can be solved by using a paste composition containing a specific component and forming a dried and fired product of the paste composition inside the conductive porous substrate. The present invention has been completed based on such findings.

This invention provides the paste composition shown to the following items 1-5, the manufacturing method of a gas diffusion layer using the same, and the gas diffusion layer obtained by it.
Item 1. A paste composition used for imparting water repellency to a conductive porous substrate for a fuel cell, the paste composition comprising a non-polymer fluorine material, a fluorine resin, a dispersant and water, The non-polymeric fluorine material is present in a dispersed state in the water.
Item 2. Item 2. The paste composition according to Item 1, wherein the nonpolymeric fluorine material is contained in a proportion of 20 to 90% by weight with respect to the total amount of the nonpolymeric fluorine material and the fluorine resin.
Item 3. Item 3. The paste composition according to Item 1 or 2, wherein the non-polymeric fluorine material is fluorinated pitch.
Item 4. Item 4. Production of a gas diffusion layer comprising a step of immersing a conductive porous substrate for a fuel cell in the paste composition according to any one of items 1 to 3, and a step of drying and firing the paste composition. Method.
Item 5. Item 5. A gas diffusion layer obtained by the production method according to Item 4.
Item 6. Item 6. A polymer electrolyte fuel cell using the gas diffusion layer according to Item 5.

Paste composition The paste composition of the present invention is a paste composition for use in imparting water repellency to the surface of a conductive porous substrate for a fuel cell, and the paste composition is a non-polymer type. It contains a fluorine material, a fluorine resin, a dispersant and water, and the non-polymer fluorine material exists in a dispersed state in the water. Using this paste composition, a dried and fired product of the paste composition can be formed inside the conductive porous substrate to obtain a gas diffusion layer having both excellent conductivity and water repellency. it can.

  The non-polymeric fluorine material is not particularly limited as long as it contains fluorine and has a weight average molecular weight of about 1000 to 5000. These may be known or commercially available. In the present invention, a conductive material is particularly preferable, and examples thereof include fluorinated pitch and fluorinated graphite. By containing such a non-polymeric fluorine material, the gas diffusion layer can have high water repellency, and water generated on the catalyst layer can be efficiently discharged to the outside. It is possible to prevent clogging of the pores inside the gas diffusion layer. Further, it is possible to impart further excellent conductivity to the conductive porous substrate.

  The F / C atom of the non-polymeric fluorine material is not limited, but is usually about 1 to 2, preferably about 1.1 to 1.6. The average particle diameter is about 0.5 μm to 50 μm, preferably about 1 μm to 30 μm.

  The fluororesin of the present invention is not particularly limited as long as it contains fluorine and has a weight average molecular weight of 500,000 to 30 million. These may be known or commercially available. For example, polytetrafluoroethylene resin, fluorinated ethylene propylene resin, perfluoroalkoxy resin, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer Etc. By containing such a fluororesin, the gas diffusion layer can have water repellency, and the non-polymeric fluorine material can be more firmly bound to the inside of the conductive porous substrate. Can be maintained.

  The dispersant is not limited as long as it can disperse the fluororesin and the non-polymeric fluoromaterial in water (paste composition), and a known or commercially available dispersant can be used. Examples of such a dispersant include polyoxyethylene alkylene alkyl ether, polyethylene glycol alkyl ether, polyoxyethylene fatty acid ester, and acid group-containing structure-modified polyacrylate. These can be used alone or in combination of two or more.

  The paste composition of the present invention preferably contains no conductive carbon particles. Examples of the conductive carbon particles include carbon black such as channel black, furnace black, ketjen black, acetylene black, and lamp black; graphite; activated carbon and the like.

  The blending ratio of the paste composition is not limited as long as it contains the above components, but for example, about 5 to 300 parts by weight of a dispersant, preferably about 100 parts by weight of the total amount of the non-polymeric fluorine material and the fluorine resin. Is about 10 to 200 parts by weight, water is about 50 to 3000 parts by weight, preferably about 100 to 2500 parts by weight.

  In particular, the non-polymeric fluorine material is preferably contained in a proportion of 20 to 90% by weight, particularly 30 to 80% by weight, based on the total amount of the non-polymeric fluorine material and the fluorine-based resin. By setting it as this range, still higher conductivity and water repellency can be maintained.

Method for Producing Gas Diffusion Layer The gas diffusion layer of the present invention can be obtained by impregnating the conductive porous base material in the paste composition of the present invention, followed by drying and firing.

  As the conductive porous substrate, those generally used in fuel cells (in particular, polymer electrolyte fuel cells) may be used, and known or commercially available materials can be used. For example, carbon paper, carbon cloth, carbon non-woven fabric (carbon felt) and the like can be mentioned.

Regarding the characteristics of carbon paper, taking TGP-H-060 made by Toray as an example, thickness: 190 μm, electric resistance: thickness direction 80 mΩ · cm, surface direction 5.8 mΩ · cm, porosity: 78%, bulk density : 0.44 g / cm ³ , surface roughness: 8 μm, and the like.

  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.

Application amount of the conductive porous substrate of the paste composition is not limited, in terms of solid content, for example, 0.5 to 30 g / m ^2, preferably about may be set to 1 to 15 g / m ² approximately .

  The drying temperature is not limited, and may be, for example, about 50 to 150 ° C., preferably about 90 to 120 ° C. in the atmosphere.

  The drying time may be appropriately determined according to the drying temperature or the like, but is usually about 10 to 30 minutes.

  The temperature at the time of baking performed after drying is not limited, for example, 200 to 400 ° C., preferably about 250 to 350 ° C. in the air.

  The firing time may be appropriately determined according to the firing temperature or the like, but is usually about 10 to 180 minutes, preferably about 30 to 150 minutes.

Gas Diffusion Layer The gas diffusion layer of the present invention is obtained by the above method, and contains the dried and fired product of the paste composition of the present invention inside the conductive porous substrate. Since such a gas diffusion layer has both good conductivity and water repellency, it is possible to improve the conductivity performance of the entire MEA, and more efficiently gas the water generated in the MEA catalyst layer. It can be discharged outside the diffusion layer (and hence outside the MEA). For this reason, the fuel cell using the gas diffusion layer of the present invention exhibits excellent cell performance.

  Since the dispersant in the paste composition is decomposed when the gas diffusion layer (GDL) is fired, it is not present in the diffusion layer. The fluororesin is dissolved after firing and is in a state of adhering onto the fibers of the gas diffusion layer. The non-polymeric fluorine material is in a state of being dispersed in the form of particles on the gas diffusion layer.

The amount of the dried and fired paste composition present in the conductive porous substrate is not limited, but usually 1 to 15 g / m ² , preferably based on the conductive porous substrate. Is about ² to 12 g / m ² .

  The gas diffusion layer of the present invention can be used as a gas diffusion layer for a polymer electrolyte fuel cell. Specifically, an electrolyte membrane-catalyst layer laminate (cathode catalyst layer / electrolyte membrane / layer) in which catalyst layers (cathode catalyst layer and anode catalyst layer) are laminated on both sides of a known or commercially available ion conductive solid polymer electrolyte membrane. An anode catalyst layer) is prepared, and then the gas diffusion layer of the present invention is laminated on at least one surface of the both surfaces (cathode catalyst layer and anode catalyst layer), whereby an electrolyte membrane-electrode assembly (gas diffusion layer) / Cathode catalyst layer / electrolyte membrane / anode catalyst layer / gas diffusion layer) may be prepared and used.

  According to the present invention, since the paste composition containing a non-polymeric fluorine material, a fluorine-based resin, a dispersant and water, and the non-polymeric fluorine material is present in a dispersed state in the water is used, A gas diffusion layer having both excellent conductivity and water repellency can be produced.

  Moreover, since the paste composition of this invention uses water instead of a fluorine-type solvent as a solvent, it is favorable also in an environmental aspect.

  In the paste composition of the present invention, when a non-polymeric fluorine material and a fluorine-based resin are contained at a specific ratio, the non-polymeric fluorine material can be more firmly fixed inside the conductive porous substrate and can be used for a long time. Excellent water repellency and conductivity can be maintained.

  Therefore, when the gas diffusion layer obtained by the present invention is used, a polymer electrolyte fuel cell having excellent battery performance can be produced.

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

<Preparation of paste composition>
In preparing the paste composition, the following materials were used.
Dispersant: Polyoxyethylene alkylene alkyl ether (Emulgen MS110, manufactured by Kao Corporation)
Non-polymeric fluorine material: Fluorinated pitch, manufactured by Osaka Gas Co., Ltd., weight average molecular weight is about 3000, average particle diameter is 1.2-30 μm
Fluorine resin: polytetrafluoroethylene (PTFE), manufactured by Daikin, weight average molecular weight of 50 to 30 million Examples 1 to 4
The conductive porous substrate water repellent of the present invention is prepared by blending a dispersant, a non-polymeric fluorine material, a fluororesin and water in the proportions (parts by weight) shown in Table 1 and dispersing for about 60 minutes by media dispersion. A treatment paste composition was prepared.

Comparative Example 1
A paste composition for comparison was prepared in the same manner as in Example 1 by blending 20 parts by weight of a dispersant, 100 parts by weight of a fluororesin, and 2000 parts by weight of water.

<Manufacture of gas diffusion layer>
Carbon paper (manufactured by Toray; TGP-H-060) was used as the conductive porous substrate. The conductive porous substrate was impregnated with each paste composition prepared in Examples 1 to 4 and Comparative Example 1 for 3 minutes (each paste composition was 5.0 g / m inside the conductive porous substrate). After about ² impregnation), it was dried at 95 ° C. for about 20 minutes in an air atmosphere, and then baked for about 2 hours at 300 ° C. in the air atmosphere to produce a gas diffusion layer having water repellency.

<Production of fuel cell and its evaluation test>
(1) Production of electrolyte membrane-catalyst layer laminate 4 g of platinum catalyst-supported carbon particles (“TEC10E50E” manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.), 40 g of ion conductive polymer electrolyte membrane solution (Nafion 5 wt% solution: “DE-520” DuPont) Manufactured), 12 g of distilled water, 20 g of n-butanol and 20 g of t-butanol were mixed and stirred and mixed in a disperser to obtain a paste composition for forming an anode catalyst layer and a paste composition for forming a cathode catalyst layer. .

The paste composition for forming the anode catalyst layer and the paste composition for forming the cathode catalyst layer are each coated on a transfer substrate (material: polyethylene terephthalate film) using an applicator and dried at 95 ° C. for about 30 minutes. A catalyst layer was formed by the above, and an anode catalyst layer forming transfer sheet and a cathode catalyst layer forming transfer sheet were prepared. The coating amount of the catalyst layer was such that the platinum loading amount was about 0.45 mg / cm ^{2 for} both the anode catalyst layer and the cathode catalyst layer.

  Using the anode catalyst layer-forming transfer sheet and cathode catalyst layer-forming transfer sheet prepared above, each surface of the electrolyte membrane was hot pressed, and then only the transfer substrate was peeled off, so that the electrolyte membrane-catalyst layer A laminate was produced.

(2) Production of fuel cell By laminating the gas diffusion layers produced using the paste compositions of Examples 1 to 4 and Comparative Example 1 on both surfaces of the electrolyte membrane-catalyst layer laminate produced above, By obtaining an electrolyte membrane-electrode assembly (MEA) and then incorporating the obtained MEA into a fuel cell, the polymer electrolyte fuel cells (using the gas diffusion layers of Examples 1 to 4 and Comparative Example 1) Manufactured polymer electrolyte fuel cell).

Performance test (a) Evaluation of gas diffusion layer
(i) Conductivity Using a battery evaluation cell for a polymer electrolyte fuel cell (JARI fuel cell evaluation cell), two gas diffusion layers are sandwiched in the cell, and the cell is tightened at a pressure of 1 to 6 Nm. The cell resistance value under pressure was measured with a fuel cell AC resistance measuring instrument (manufactured by Chino Corporation). Since the cell clamping pressure applied at the time of normal battery evaluation is 4 Nm, as a result of measuring the resistance value at that pressure, the conductivity can be improved by adding a fluorinated pitch to the paste composition. It was confirmed (see Table 2).
(ii) Water repellency In Examples 1 to 4 to which fluorinated pitch was added, it was confirmed that a high contact angle of 150 to 160 ° was exhibited. For this reason, it is thought that the high discharge | emission property of the produced water in a cathode is shown by using the gas diffusion layer produced using the paste composition of Examples 1-4. The contact angle with the conductive porous substrate was determined by using an automatic contact angle measuring device (“OCA20” manufactured by Eihiro Seiki Co., Ltd.) to drop a paste composition droplet of about 1 microliter into the conductive porous material. It is calculated | required by dripping on the base-material surface and observing the contact angle 30 seconds after.

(B) Battery performance evaluation Battery performance evaluation using the above MEA was performed under the following conditions.

Cell temperature: 80 ° C
Humidification temperature: cathode 80 ° C, anode 70 ° C
Gas utilization rate: cathode 40%, anode 70%
The cell voltage value was measured when the load current was varied from 1.25 to 25A. At 1000 mA / cm ² where the influence of gas diffusion is more conspicuous, Examples 1-4 have practical levels of 570 mV to 580 mV, which is higher than 554 mV of Comparative Example 1, and this performance is a combination of fluorinated pitches. It became more noticeable as the amount increased.

  Furthermore, the internal resistance (ohmic resistance) was measured in a load current range of 1.25 to 20 A by a current interruption method (Hokuto Denko Co., Ltd., current pulse generator HC-114). The result is shown in FIG. According to FIG. 2, Comparative Example 1 showed a higher ohmic loss value than Examples 1-4. This is due to the influence of gas diffusibility due to the blockage of the pores in the GDL with the produced water and condensed water, and from this, the discharge status of the produced water and condensed water is higher in Examples 1 to 4 than in Comparative Example 1. It shows good, that is, high water repellency.

  From the above results, it was confirmed that the paste compositions of Examples 1 to 4 were effective paste compositions for producing a gas diffusion layer having both excellent conductivity and water repellency.

  The above results are summarized in Table 2.

  Moreover, from the GDL resistance values shown in Table 2, it was confirmed that Examples 1 to 4 showed better gas diffusibility than Comparative Example 1.

  From the above results, Examples 1 to 4 were confirmed to be effective paste compositions for producing a gas diffusion layer having both excellent conductivity and water repellency.

FIG. 1 shows a conceptual diagram of a gas diffusion layer of the present invention. FIG. 2 is a graph showing a measurement result of ohmic loss by the current interruption method.

Explanation of symbols

1. 1. Gas diffusion layer 2. Anode catalyst layer 3. Ion conductive solid polymer electrolyte 4. Cathode catalyst layer Electrolyte membrane-electrode assembly

Claims (6)

  A paste composition used for imparting water repellency to a conductive porous substrate for a fuel cell, the paste composition comprising a non-polymer fluorine material, a fluorine resin, a dispersant and water, A non-polymeric fluorine material is present in a dispersed state in the water.   The paste composition according to claim 1, wherein the non-polymeric fluorine material is contained in a proportion of 20 to 90% by weight with respect to the total amount of the non-polymeric fluorine material and the fluorine-based resin.   The paste composition according to claim 1 or 2, wherein the non-polymeric fluorine material is fluorinated pitch.   A gas diffusion layer comprising a step of immersing the conductive porous substrate for a fuel cell in the paste composition according to any one of claims 1 to 3, and a step of drying and firing the paste composition. Production method.   A gas diffusion layer obtained by the production method according to claim 4.   A polymer electrolyte fuel cell using the gas diffusion layer according to claim 5.

Images