JP5217256B2 - Conductive porous sheet and method for producing the same - Google Patents

Description

  The present invention relates to a novel conductive porous sheet for a fuel cell and a method for producing the same.

  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 is made of a conductive porous sheet, and mainly plays a role of spreading the gas supplied from the separator to the catalyst layer (gas diffusibility). In addition to this gas diffusivity, it is also required to have low resistance and water repellency.

  As a method for manufacturing such a gas diffusion layer, various methods are provided (Patent Documents 1 and 2).

  For example, in Patent Document 1, a dispersion containing a hydrophilic organic solvent, a carbon material, a fluorine-containing resin, or the like is applied to a substrate, and then immersed in water to extract the organic solvent contained in the dispersion. Thus, a method for solidifying the fluororesin and forming a gas diffusion layer has been proposed.

  However, this method requires the step of extracting the organic solvent, so that it needs to be impregnated with water for a long time, resulting in a problem of poor productivity.

  Patent Document 2 proposes a method in which a carbon material is dispersed in a dispersant-containing hydrocarbon solvent, a voltage is applied in this solvent using a coating material as an anode, and a gas diffusion layer is formed on the surface of the anode material. Has been.

However, this method requires a step of applying a voltage, and it takes a long time to form a gas diffusion layer having a desired thickness. For this reason, the production process becomes complicated, and a problem inferior in productivity arises.
JP 11-31515 A JP 2006-63436 A

  An object of this invention is to provide the manufacturing method of the electroconductive porous sheet which was simple and cheap and excellent in productivity.

  As a result of intensive studies in view of the above-described prior art, the present inventors have solved the above problems and solved the present invention by using a specific paste composition. That is, this invention provides the following electroconductive porous sheet and its manufacturing method.

Item 1. Applying a carbon particle, a carbon fiber having an aspect ratio of 50 or more, a fluororesin, a foaming agent, and a paste composition containing a solvent on a substrate, followed by drying ; and
A method for producing a dried coating film for a conductive porous sheet , comprising a step of peeling the dried coating film from a substrate .
Item 2. Applying a carbon particle, a carbon fiber having an aspect ratio of 50 or more, a fluororesin, a foaming agent, and a paste composition containing a solvent on a substrate, followed by drying; and
The step of peeling the film that has undergone the drying step from the substrate, and the step of firing the film that has undergone the drying step
A method for producing a conductive porous sheet.
Item 3. Applying a carbon particle, a carbon fiber having an aspect ratio of 50 or more, a fluororesin, a foaming agent, and a paste composition containing a solvent on a substrate, followed by drying; and
A step of peeling the dried coating film from the substrate, and
The process of firing the dried coating
The manufacturing method of the electroconductive porous sheet provided with these in this order.
Item 4. Item 4. The production method according to any one of Items 1 to 3, wherein a substrate having a contact angle with water of 60 ° or more is used.
Item 5. Item 5. The production method according to any one of Items 1 to 4, wherein the substrate is a polymer film.

Method for Producing Conductive Porous Sheet A method for producing a conductive porous sheet of the present invention comprises a paste composition containing carbon particles, carbon fibers having an aspect ratio of 50 or more, a fluororesin, a foaming agent and a solvent. After applying on top, it is then provided with a step of drying and firing.

  The carbon particles are not limited as long as they are conductive, and known or commercially available carbon particles can be used. For example, channel black, furnace black, ketjen black, acetylene black, carbon black such as 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 1 to 1000 nm, preferably about 5 to 50 nm.

  A well-known or commercially available fluororesin can be used. Examples thereof include polytetrafluoroethylene and polyvinylidene fluoride. By containing the fluorine resin, the gas diffusion layer can have water repellency. As a result, water generated during the battery reaction can be quickly discharged to the outside, and clogging of the voids in the gas diffusion layer due to water can be suppressed.

  The carbon fiber may have an aspect ratio (fiber length / fiber diameter) of 50 or more, and is preferably about 60 to 1000. By containing such carbon fiber, the porosity of the gas diffusion layer can be improved, and the strength of the gas diffusion layer can be improved. The average fiber diameter is preferably about 100 nm to 300 nm, and the average fiber length is preferably about 10 μm to 100 μm.

  Examples of the carbon fiber include chemical vapor grown carbon fiber (VGCF) and carbon nanotube.

  Suitable foaming agents include those that foam by heating. As such a heating foaming agent, those having a decomposition temperature of 80 ° C. or more, particularly about 120 to 250 ° C. are preferable.

  The amount of gas generated by the blowing agent is not limited, and is usually about 50 to 500 ml / g, preferably about 200 to 300 ml / g. The average particle size is not limited, and is usually about 1 to 50 μm, preferably about 2 to 5 μm.

  Specific examples of the foaming agent include “CELLMIC-C2 (manufactured by Sankyo Kasei Co., Ltd.)”, “CELLMIC C-22 (manufactured by Sankyo Kasei Co., Ltd.)” and the like. By including such a foaming agent, the gas diffusion layer can be made porous.

  It does not specifically limit as a solvent, A well-known or commercially available thing can be used widely. For example, water; monohydric or polyhydric alcohol having about 1 to 4 carbon atoms such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, t-butanol, ethylene glycol, propylene glycol, etc. Are preferable. These solvents can be used singly or in combination of two or more.

  In addition, these paste compositions may contain various additives such as a dispersant.

  A known or commercially available dispersant may be used, and examples thereof include polyoxyethylene alkylene alkyl ether, polyethylene glycol alkyl ether, polyoxyethylene fatty acid ester, and acid group-containing structure-modified polyacrylate.

  The blending ratio of the paste composition is not limited. For example, the fluororesin is 10 to 5000 parts by weight (preferably 30 to 500 parts by weight) and the carbon fiber is 10 to 5000 parts by weight (preferably with respect to 100 parts by weight of the carbon particles. 50 to 500 parts by weight), 1 to 1000 parts by weight (preferably 5 to 100 parts by weight) of the foaming agent, and 50 to 50000 parts by weight (preferably 500 to 5000 parts by weight) of the solvent.

  These pastes are applied to the desired substrate and then dried and sintered to foam the blowing agent.

  The substrate is not particularly limited as long as it can apply the paste composition, and for example, a transfer substrate may be used. The transfer substrate is not particularly limited. For example, polyimide, polyethylene terephthalate, polyparvanic acid aramid, polyamide (nylon), polysulfone, polyethersulfone, polyphenylene sulfide, polyether ether ketone, polyether imide, polyarylate, polyethylene naphthalate. Examples thereof include polymer films such as phthalate and polypropylene. Further, ethylene tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroperfluoroalkyl vinyl ether copolymer (PFA), polytetrafluoroethylene (PTFE), or the like is used. You can also. In addition to the polymer film, the substrate may be paper such as coated paper such as art paper, coated paper, and lightweight coated paper, and non-coated paper such as notebook paper and copy paper. Among these, an inexpensive and easily available polymer film is preferable, and polyethylene terephthalate or the like is more preferable.

  The substrate used in the present invention preferably has a contact angle with water of 60 ° or more, particularly 70 to 90 °. Examples of the base material include ethylene tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and tetrafluoroperfluoroalkyl vinyl ether copolymer (PFA). ), Polytetrafluoroethylene (PTFE), polyethylene terephthalate and the like. By using this base material, the dry film obtained after drying the paste composition can be easily peeled from the base material. In the present invention, the contact angle between the substrate and water is determined by using an automatic contact angle measuring device OCA20 (manufactured by dataphysics) to drop a water droplet of about 1 μl (microliter) on the surface of the substrate, and contact after 30 seconds Measured by observing the corners.

  A release layer may be laminated on the transfer substrate as necessary. Examples of the release layer include those composed of known waxes and plastic films coated with known fluororesins.

  The thickness of the substrate is usually about 6 μm to 100 μm, preferably about 10 μm to 60 μm, from the viewpoints of handleability and economy.

  The method for applying the paste composition is not particularly limited. For example, knife coating, bar coating, blade coating, spraying, dip coating, spin coating, roll coating, die coating, curtain coating, screen printing, etc. Applicable.

  After the application, a drying process is performed. What is necessary is just to perform a drying process at about 60-180 degreeC (preferably 90-140 degreeC) in an atmospheric condition, for example.

  The drying time may be appropriately set according to the drying temperature or the like, but may be usually about 10 to 100 minutes.

  After drying, if necessary, the dried coating film (from which the paste composition has been dried) may be peeled off from the substrate before firing.

  After drying, firing is performed. Thereby, the water repellency of the conductive porous sheet obtained improves. The firing temperature is usually 200 ° C. or higher, preferably about 300 to 380 ° C.

  The firing atmosphere is not limited, and may be performed in the air, for example.

  The firing time may be appropriately set according to the heating temperature or the like, but is usually 30 minutes or longer, preferably about 1 to 2 hours.

  During these drying or firing steps, the foaming agent foams, and the resulting porous sheet can have a desired porosity.

Conductive porous sheet The conductive porous sheet of the present invention contains carbon particles, carbon fibers having an aspect ratio of 50 or more, and a fluororesin, and has a plurality of irregularities or through holes. Such a conductive porous sheet can be manufactured, for example, by the above-described manufacturing method of the present invention.

  Examples of the carbon particles, carbon fiber, and fluororesin are the same as those described above.

  The blending ratio is not limited. For example, 10 to 5000 parts by weight (preferably 30 to 500 parts by weight) of fluororesin and 10 to 5000 parts by weight of carbon fiber (preferably 50 to 500 parts by weight) with respect to 100 parts by weight of carbon particles. Part).

  The conductive porous sheet of the present invention has a plurality of irregularities or through holes.

  The average thickness of the conductive porous sheet is usually about 50 to 500 μm, preferably about 100 to 300 μm.

  In addition, it is assumed that the conductive porous sheet of the present invention includes both the one before peeling the substrate and the one peeled.

  The conductive porous sheet of the present invention can be used as a gas diffusion layer (gas diffusion sheet) for a fuel cell such as a polymer electrolyte fuel cell. That is, by laminating a known or commercially available catalyst layer and a hydrogen ion conductive solid polymer electrolyte membrane or the like, a membrane-electrode assembly for a fuel cell such as a polymer electrolyte fuel cell (gas diffusion layer / catalyst layer / It can be used as a hydrogen ion conductive solid polymer electrolyte membrane / catalyst layer / gas diffusion layer layer structure).

  According to the production method of the present invention, it is possible to produce a conductive porous sheet that is simple and inexpensive and excellent in productivity.

  If the conductive porous sheet of the present invention is used as a gas diffusion layer, it has low contact resistance (electrical resistance) with an adjacent catalyst layer, and has porosity and water repellency. It can be demonstrated.

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

Example 1
<Preparation of paste composition>
20 parts by weight of “Vulcan xc72R (manufactured by Cabot)” as carbon particles, 20 parts by weight of “Emulgen MS110 (manufactured by Kao)” as dispersant, and 60 parts by weight of ion-exchanged water are mixed into a planetary mixer. And stirred for 20 minutes. Next, 100 parts by weight of polytetrafluoroethylene dispersion (manufactured by Daikin Industries, “Lublon LDW40E”: solid content 40% by weight) was added as a fluororesin, and further stirred with a planetary mixer.

  Thereafter, 35 parts by weight of carbon fiber (Showa Denko, “VGCF”, aspect ratio 60), 120 parts by weight of ion conductive polymer electrolyte solution (5 wt% Nafion solution: “DE-520” manufactured by DuPont), distillation 425 parts by weight of water and 4 parts by weight of “Cermic-C2 (manufactured by Sankyo Kasei Co., Ltd.)” (decomposition temperature: 204 ° C., amount of generated gas: 270 ml / g, average particle diameter of 3 to 5 μm) as a heating foaming agent are mixed and stirred. By doing so, the paste composition of the present Example 1 was prepared.

<Production of gas diffusion layer>
The prepared paste composition was applied on a polyethylene terephthalate film substrate (“Luminer X44” manufactured by Toray Industries, Inc.) using an applicator and dried in an oven set at 130 ° C. At this time, the gap of the applicator was adjusted so that the film thickness after drying was about 230 μm. The contact angle with water of the base material before application of the paste composition was measured and found to be 70 °. This contact angle is determined by using an automatic contact angle measuring device “OCA20 (manufactured by dataphysics)” and dropping a water droplet of about 1 μl (microliter) on the substrate surface and observing the contact angle after 30 seconds. went.

  Next, the dried coating film was peeled off from the substrate, and baked in an oven at 350 ° C. for 2 hours to produce the gas diffusion layer (conductive porous sheet) of Example 1.

  At this time, in the gas diffusion sheet of Example 1, the foaming agent was decomposed during the production process, and voids having a diameter of about 100 to 500 μm were randomly formed.

Comparative Example 1
A paste composition was prepared in the same manner as in Example 1 except that the foaming agent was not blended and the blending amount of distilled water was 350 parts by weight.

  A gas diffusion layer (conductive porous sheet) of Comparative Example 1 was produced in the same manner as in Example 1 except that this paste composition was used.

  In the gas diffusion sheet of Comparative Example 1, no voids and recesses having a diameter of 100 μm or more were observed.

Comparative Example 2
The same as in Example 1, except that the blowing agent was not blended, the blending amount of carbon fiber was 80 parts by weight, the blending amount of the ion conductive polymer electrolyte solution was 200 parts by weight, and the blending amount of distilled water was 1200 parts by weight. Thus, a paste composition was prepared.

  A gas diffusion layer (conductive porous sheet) of Comparative Example 2 was produced in the same manner as in Example 1 except that this paste composition was used.

  In the gas diffusion sheet of Comparative Example 2, voids and recesses having a diameter of 100 μm or more were not observed.

<Fabrication and evaluation test of fuel cell>
Platinum catalyst supported carbon particles (Tanaka Kikinzoku Kogyo Co., Ltd., “TEC62E58”) 10 g, ion conductive polymer electrolyte solution (Nafion 5 wt% solution: “DE-520” manufactured by DuPont) 100 g, distilled water 30 g and isopropyl alcohol (IPA) By blending 100 g and stirring and mixing with a disperser, an anode catalyst layer paste composition was obtained.

  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 anode catalyst layer paste composition and the cathode catalyst layer paste composition were each applied onto a transfer substrate made of a polyethylene terephthalate film (“Luminer X44”, manufactured by Toray Industries, Inc.) using an applicator, and then at 80 ° C. for 30 minutes. The catalyst layer was formed by drying to produce 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).

  By laminating the gas diffusion layer of Example 1 on both surfaces of this electrolyte membrane-catalyst layer laminate, a membrane-electrode assembly (MEA: gas diffusion layer / catalyst catalyst layer / electrolyte membrane / anode catalyst layer) / Gas diffusion layer) was obtained, 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 Comparative Examples 1 and 2, a fuel cell was produced in the same manner as in Example 1 to obtain fuel cells of Comparative Examples 1 and 2, respectively.

  The cell performance of the fuel cells of Example 1 and Comparative Examples 1 and 2 was evaluated. Cell evaluation conditions were as follows. The obtained voltage-current characteristics are shown in FIG.

Cell temperature: 80 ° C.
Humidification temperature: cathode 80 ° C, anode 70 ° C
Gas utilization rate: cathode 40%, anode 70%
Evaluation The fuel cell using the gas diffusion layer of the present invention 1 is superior to the fuel cell using the gas diffusion layer of Comparative Example 1 in particular in the high load current density region, and the cell performance is superior. Thereby, it turns out that gas diffusibility improved by raising the contact resistance with a catalyst layer by addition of a foaming agent.

  Since the fuel cell using the gas diffusion layer of Comparative Example 2 contains a lot of carbon fibers, the gas diffusion sheet has excellent porosity (gas diffusibility), but conversely, the contact resistance with the catalyst layer is too large. It can be seen that the battery performance is low.

FIG. 1 is a diagram showing the relationship between the current and voltage of a fuel cell manufactured using the gas diffusion layers of Example 1 and Comparative Examples 1 and 2.

Claims (5)

Applying a carbon particle, a carbon fiber having an aspect ratio of 50 or more, a fluororesin, a foaming agent, and a paste composition containing a solvent on a substrate, followed by drying ; and
A method for producing a dried coating film for a conductive porous sheet , comprising a step of peeling the dried coating film from a substrate . Applying a carbon particle, a carbon fiber having an aspect ratio of 50 or more, a fluororesin, a foaming agent, and a paste composition containing a solvent on a substrate, followed by drying; and
The step of peeling the film that has undergone the drying step from the substrate, and the step of firing the film that has undergone the drying step
A method for producing a conductive porous sheet. Applying a carbon particle, a carbon fiber having an aspect ratio of 50 or more, a fluororesin, a foaming agent, and a paste composition containing a solvent on a substrate, followed by drying; and
A step of peeling the dried coating film from the substrate, and
The process of firing the dried coating
The manufacturing method of the electroconductive porous sheet provided with these in this order. The manufacturing method in any one of Claims 1-3 using the base material whose contact angle with water is 60 degrees or more. The manufacturing method in any one of Claims 1-4 whose said base material is a polymer film .

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