JP2007194004A - Method of manufacturing gas diffusion layer for solid polymer fuel cell, and membrane-electrode assembly - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a gas diffusion layer for a solid polymer fuel cell capable of maintaining high water repellency for a long period of time, and to provide a membrane-electrode assembly for the solid polymer fuel cell which enables the solid polymer fuel cell to stably operate for a long period of time. <P>SOLUTION: The method of manufacturing the gas diffusion layer 13 includes: a first step for carrying out impregnation of water dispersion solution made by dispersing polytetrafluoroethylene in water into a gas diffusion layer base; a second step for coating a coating liquid made by dispersing carbon black and polytetrafluoroethylene in dispersion medium on the gas diffusion layer base 14; and a third step for baking the gas diffusion layer base 14 on which the coating liquid has been coated in order to make the gas diffusion layer 13, in particular, the water dispersion solution and/or the coating liquid are so made that non-ion surfactant whose half-mass temperature in air is in the range of 100 to 300°C of 0.5 to 10 mass% to the sum of polytetrafluoroethylene, and the surfactant is contained in the water dispersion solution and/or the coating liquid. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a gas diffusion layer for a polymer electrolyte fuel cell and a membrane electrode assembly.

  A polymer electrolyte fuel cell is configured by stacking a plurality of membrane electrode assemblies in which electrodes (cathode (air electrode) and anode (fuel electrode)) are arranged on both sides of a solid polymer electrolyte membrane via a separator. . The electrode is composed of a catalyst layer in contact with the solid polymer electrolyte membrane and a porous gas diffusion layer disposed outside the catalyst layer.

The polymer electrolyte fuel cell tends to cause a phenomenon (flooding) in which the electrodes are easily wetted with water and the pores of the gas diffusion layer are closed with water for the following reasons.
(1) Since the polymer electrolyte fuel cell operates at a low temperature of about 80 ° C., water generated at the cathode (air electrode) due to the cell reaction tends to condense.
(2) In order to maintain the conductivity of the solid polymer electrolyte membrane, air and fuel gas are supplied in a wet state so that the solid polymer electrolyte membrane is not dried.

  When flooding occurs, air or fuel gas may not reach the catalyst layer and the voltage may drop significantly. Therefore, in order to stably operate the polymer electrolyte fuel cell for a long period of time, it is necessary to impart water repellency to the gas diffusion layer so as not to cause flooding.

As a gas diffusion layer imparted with water repellency, a gas diffusion layer imparted with water repellency with polytetrafluoroethylene is known. As a method for producing the gas diffusion layer, for example, the following method has been proposed.
After impregnating the gas diffusion layer base material with an aqueous dispersion in which polytetrafluoroethylene is dispersed in water, the gas diffusion layer base material is baked at 350 ° C., and the water and the surfactant in the aqueous dispersion are removed. The gas diffusion layer base material is subjected to water repellent treatment. Furthermore, after applying a coating liquid in which carbon black and polytetrafluoroethylene are dispersed in water on a gas diffusion layer base material that has been subjected to water repellency treatment, the gas diffusion layer base material is baked to obtain a solution in the coating liquid. Water and the surfactant are removed to form a water-repellent carbon layer (Patent Document 1).

However, the gas diffusion layer obtained by this method has a problem that the water repellency cannot be maintained for a long period of time, and the gas diffusion layer gradually gets wet and causes flooding, resulting in a significant decrease in voltage.
JP 2005-019298 A (Example)

  An object of the present invention is to provide a method for producing a gas diffusion layer for a polymer electrolyte fuel cell capable of maintaining high water repellency for a long period of time, and for a polymer electrolyte fuel cell capable of stably operating the polymer electrolyte fuel cell for a long period of time. The object is to provide a membrane electrode assembly.

  The method for producing a gas diffusion layer for a polymer electrolyte fuel cell according to the present invention comprises impregnating a gas diffusion layer base material with an aqueous dispersion in which polytetrafluoroethylene is dispersed in water, and then carbon black and polytetrafluoroethylene. A gas diffusion layer for a polymer electrolyte fuel cell is manufactured by applying a coating liquid dispersed in a dispersion medium onto a gas diffusion layer base material and firing the gas diffusion layer base material coated with the coating liquid. A nonionic surfactant having a mass half-life temperature in air of 100 to 300 ° C., wherein the aqueous dispersion and / or coating solution comprises polytetrafluoroethylene and the surfactant. It is characterized by containing 0.5 to 10% by mass with respect to the total amount.

The nonionic surfactant is preferably a compound represented by the following formula (1).
R ¹ O—A—H (1).
However, R ¹ is a primary or secondary alkyl group having 8 to 18 carbon atoms, A is a polyoxyalkylene group consisting of 5 to 20 oxyethylene groups and 0 to 2 oxypropylene groups It is.

The nonionic _{surfactant, C 13 H 27 O- (C} 2 H 4 O) 8 (C 3 H 6 O) -H, C 13 H 27 O- (C 2 H 4 O) 9 -H, _{C 13 H 27 O- (C 2} H 4 O) 10 -H, C 10 H 21 CH (CH 3) CH 2 O- (C 2 H 4 O) 10 -H, C 6 H 13 CH (C 6 H _{13) O- (C 2 H 4} O) 9 -H, C 10 H 21 CH (CH 3) CH 2 O- (C 2 H 4 O) 8 (C 3 H 6 O) -H, C 12 H 25 It is preferably at least one selected from the group consisting of O— (C ₂ H ₄ O) ₉ —H and C ₈ H ₁₇ O— (C ₂ H ₄ O) ₆ —H.

The temperature at which the gas diffusion layer base material coated with the coating liquid is fired is preferably 300 to 390 ° C.
A membrane electrode assembly for a polymer electrolyte fuel cell of the present invention comprises a solid polymer electrolyte membrane, a catalyst layer disposed on both sides of the solid polymer electrolyte membrane, a gas diffusion layer disposed on the outside of the catalyst layer, And at least one of the two gas diffusion layers is a gas diffusion layer for a polymer electrolyte fuel cell obtained by the production method of the present invention.

According to the method for producing a gas diffusion layer for a polymer electrolyte fuel cell of the present invention, a gas diffusion layer for a polymer electrolyte fuel cell that can maintain high water repellency for a long period of time can be obtained.
According to the membrane electrode assembly for a polymer electrolyte fuel cell of the present invention, the polymer electrolyte fuel cell can be stably operated for a long period of time.

  In the present specification, a compound represented by the formula (1) is referred to as a compound (1). The same applies to compounds represented by other formulas.

(Gas diffusion layer)
The gas diffusion layer for a polymer electrolyte fuel cell (hereinafter referred to as a gas diffusion layer) can be produced by sequentially performing the following steps (a) to (d).
(A) A gas diffusion layer base material is impregnated with an aqueous dispersion in which polytetrafluoroethylene (hereinafter referred to as PTFE) is dispersed in water.
(B) If necessary, part or all of the water of the aqueous dispersion impregnated in the gas diffusion layer base material is evaporated, or the gas diffusion layer base material impregnated with the aqueous dispersion liquid is fired.
(C) A coating liquid in which carbon black and PTFE are dispersed in a dispersion medium is applied onto the gas diffusion layer substrate obtained in the step (a) or (b).
(D) The gas diffusion layer base material coated with the coating liquid is fired.

(A) Process:
Examples of the method for impregnating the gas dispersion layer base material with the aqueous dispersion include the following methods, and the method (a-1) is preferable because the operation is simple.
(A-1) A method in which the gas diffusion layer substrate is immersed in the aqueous dispersion and then pulled up from the aqueous dispersion.
(A-2) A method of removing an excess aqueous dispersion after applying and impregnating an excess aqueous dispersion onto a gas diffusion layer substrate.

The gas diffusion layer substrate is a porous substrate having conductivity. Examples of the gas diffusion layer substrate include carbon cloth, carbon paper, and carbon felt.
The aqueous dispersion is a liquid in which PTFE is dispersed in water, and includes a surfactant for dispersing PTFE in water.

  PTFE is PTFE fine particles obtained by an emulsion polymerization method. PTFE may be a homopolymer of tetrafluoroethylene, a unit derived from halogenated olefins such as chlorotrifluoroethylene and hexafluoropropylene, and other fluorine-based monomers such as perfluoro (alkyl vinyl ether). It may be modified PTFE containing. However, it is necessary to suppress the amount of the other fluorine-based monomer to an amount that the obtained modified PTFE cannot be substantially melt processed.

The average particle diameter of PTFE is preferably 0.1 to 0.5 μm, more preferably 0.15 to 0.4 μm, and particularly preferably 0.2 to 0.35 μm. By making the average particle diameter of PTFE 0.1 μm or more, the yield of PTFE is increased. By setting the average particle diameter of PTFE to 0.5 μm or less, PTFE is less likely to settle and storage stability is improved.
PTFE can be produced, for example, by a known emulsion polymerization method as described on page 28 of a fluorine resin handbook (Satokawa edition, Nikkan Kogyo Shimbun, 1990).

  As the surfactant, a nonionic surfactant having a mass half temperature of 100 to 300 ° C. (hereinafter referred to as a low-temperature pyrolytic nonionic surfactant) is preferable. When the coating liquid described below contains a low-temperature pyrolysis-type nonionic surfactant, the aqueous dispersion may not contain a low-temperature pyrolysis-type nonionic surfactant, but the water repellency of the gas diffusion layer Therefore, it is preferable that both the aqueous dispersion and the coating liquid contain a low-temperature pyrolyzable nonionic surfactant.

  The mass half-life temperature of the low-temperature pyrolytic nonionic surfactant is 100 to 300 ° C, preferably 150 to 290 ° C, and more preferably 200 to 280 ° C. By setting the mass half-temperature of the low-temperature pyrolysis-type nonionic surfactant to 100 ° C. or more, rapid generation of pyrolysis gas due to firing can be suppressed, and the adhesion between PTFE and the gas diffusion layer substrate can be reduced. It can be suppressed. By setting the mass half-temperature of the low-temperature pyrolysis-type nonionic surfactant to 300 ° C. or less, the low-temperature pyrolysis-type nonionic surfactant is sufficiently pyrolyzed by firing, and the PTFE surface has a nonionic surfactant activity. The gas diffusion layer can maintain high water repellency for a long time without any remaining agent.

  The content of the low-temperature pyrolytic nonionic surfactant is 0.5 to 10% by mass, preferably 1 to 8% by mass, and 2 to 6% by mass with respect to the total amount of PTFE and the surfactant. Is more preferable. By setting the content of the low-temperature pyrolysis-type nonionic surfactant to 0.5% by mass or more based on the total amount of PTFE and the surfactant, the PTFE fine particles are stably dispersed in water. Aggregation and sedimentation are suppressed. By setting the content of the low-temperature pyrolysis-type nonionic surfactant to 10% by mass or less based on the total amount of PTFE and the surfactant, the nonionic surfactant can be sufficiently removed by firing.

The content of the low temperature pyrolytic nonionic surfactant with respect to PTFE is determined as follows.
According to JIS K6893, 10 g of the aqueous dispersion was put on an aluminum dish and dried at 120 ° C. for 1 hour, and then baked at 380 ° C. for 35 minutes with a residual mass x (mass%) with respect to the aqueous dispersion (100 mass%). Later, the residual mass y (mass%) with respect to the aqueous dispersion (100 mass%) is obtained, and (xy) / xx100 is the low-temperature pyrolytic nonionic interface with respect to the total amount of PTFE and surfactant. The content of the activator (% by mass)

As the low-temperature pyrolysis-type nonionic surfactant, the compound (1) is preferable because the PTFE fine particles have a high stabilizing effect and good wettability.
R ¹ O—A—H (1).
However, R ¹ is a primary or secondary alkyl group having 8 to 18 carbon atoms, A is a polyoxyalkylene group consisting of 5 to 20 oxyethylene groups and 0 to 2 oxypropylene groups It is.

The number of carbon atoms of R ¹ is 8 to 18, preferably 10 to 16, 12 to 15 is more preferable. By setting the carbon number of R ¹ to 8 or more, the wettability of the aqueous dispersion becomes good. By setting the carbon number of R ¹ to 18 or less, the viscosity of the aqueous dispersion is stabilized. R ¹ is preferably an alkyl group having a branch because it is less likely to cause problems such as flaking, fluttering, and uneven thickness during coating.

The number of oxyethylene groups of A is 5 to 20, and 7 to 12 is preferable from the viewpoint of wettability. By setting the number of oxyethylene groups to 5 or more, the viscosity of the aqueous dispersion is stabilized. By setting the number of oxyethylene groups to 20 or less, the wettability of the aqueous dispersion is improved.
The number of oxypropylene groups in A is 0 to 2, and 1 to 2 is preferable because the antifoaming property is improved.

As the compound (1), the following compounds are preferable.
_{C 13 H 27 O- (C 2} H 4 O) 8 (C 3 H 6 O) -H,
_{C 13 H 27 O- (C 2} H 4 O) 9 -H,
_{C 13 H 27 O- (C 2} H 4 O) 10 -H,
_{C 10 H 21 CH (CH 3} ) CH 2 O- (C 2 H 4 O) 10 -H,
_{C 6 H 13 CH (C 6} H 13) O- (C 2 H 4 O) 9 -H,
_{C 10 H 21 CH (CH 3} ) CH 2 O- (C 2 H 4 O) 8 (C 3 H 6 O) -H,
_{C 12 H 25 O- (C 2} H 4 O) 9 -H,
_{C 8 H 17 O- (C 2} H 4 O) 6 -H.

Examples of commercially available low-temperature pyrolysis-type nonionic surfactants include New Coal 1308FA, New Coal 1100 manufactured by Nippon Emulsifier Co., Ltd., Taditol 15-S-9 manufactured by Dow Chemical Co., and Softanol manufactured by Nippon Shokubai Co., Ltd. Series, Lion Corporation's Lionol TD2007 and the like.
One type of low-temperature pyrolysis-type nonionic surfactant may be used alone, or two or more types may be used in combination. When using 2 or more types together, the number of carbon atoms of R ¹ , the number of oxyethylene groups of A, the number of oxypropylene groups, and the like are average values, and each numerical value is not limited to an integer.

For example, an aqueous dispersion is obtained by adding a low-temperature pyrolysis-type nonionic surfactant to an emulsion polymerization solution having a PTFE content of 10 to 40% by mass obtained by an emulsion polymerization method. After concentration by a known concentration method such as a concentration method, it is prepared by adding water and, if necessary, a low-temperature pyrolysis-type nonionic surfactant. The emulsion polymerization liquid may contain a fluorine-based surfactant used during emulsion polymerization. Examples of the fluorine-based surfactant include ammonium perfluorooctanoate.
The water contained in the aqueous dispersion may be water contained in the emulsion polymerization solution, or water added after concentration.

  In the aqueous dispersion, an anionic surfactant such as a fluorinated fatty acid salt, an alkyl sulfate salt, or a polyoxyethylene alkyl sulfate ester salt; a nonoxygen such as a polyoxyethylene polyoxypropylene copolymer, Ionic surfactants: Polyethylene oxide thickeners, polyurethane associative thickeners, silicone additives, fluorine additives, preservatives, and the like may be contained in trace amounts.

(B) Process:
The gas diffusion layer substrate obtained in the step (a) may be subjected to the step (c) while being wet with the aqueous dispersion, and (b-1) the gas diffusion layer substrate as necessary. After evaporating part or all of the water of the aqueous dispersion impregnated in step (c), it may be used in step (c), or (b-2) after calcination and step (c). .

However, if the gas diffusion layer base material obtained in step (a) is fired, the water repellency of the gas diffusion layer base material becomes too high. There is a possibility that it cannot be applied on the layer substrate.
Therefore, the gas diffusion layer base material obtained in the step (a) remains in a wet state with the aqueous dispersion liquid, or the water of the aqueous dispersion liquid impregnated in the gas diffusion layer base material in an atmosphere of room temperature to 80 ° C. It is preferable that after a part of is evaporated, it is subjected to step (c).

(C) Process:
A coating solution is applied on the gas diffusion layer substrate obtained in the step (a) or (b).
The coating liquid is a liquid in which carbon black and PTFE are dispersed in a dispersion medium, and includes a surfactant for dispersing PTFE in water.
As PTFE, the thing similar to the PTFE used for the above-mentioned aqueous dispersion liquid is mentioned.

  Carbon black imparts conductivity to the resulting coating film. Examples of commercially available carbon black include Ketjen Black EC manufactured by Lion, Vulcan XC-72 manufactured by Cabot, and acetylene black manufactured by Denki Kagaku Kogyo. The carbon black may be graphitized graphite carbon.

  As the surfactant, the above-mentioned low-temperature pyrolytic nonionic surfactant is preferable. Further, from the viewpoint of water repellency of the gas diffusion layer, it is preferable that both the aqueous dispersion and the coating liquid contain a low-temperature pyrolytic nonionic surfactant.

  The content of the low-temperature pyrolytic nonionic surfactant is 0.5 to 10% by mass, preferably 1 to 8% by mass, and 2 to 6% by mass with respect to the total amount of PTFE and the surfactant. Is more preferable. By setting the content of the low-temperature pyrolysis-type nonionic surfactant to 0.5% by mass or more based on the total amount of PTFE and the surfactant, the PTFE fine particles are stably dispersed in water. Aggregation and sedimentation are suppressed. By setting the content of the low-temperature pyrolysis-type nonionic surfactant to 10% by mass or less based on the total amount of PTFE and the surfactant, the nonionic surfactant can be sufficiently removed by firing.

Examples of the dispersion medium include water and aqueous ammonia for pH adjustment, and water is usually used.
The coating liquid can be prepared, for example, by adding carbon black to the aqueous dispersion described above and sufficiently stirring.

  Examples of the coating method include a screen printing method, a doctor blade method, and a die coating method, and a doctor blade method is preferable because a flat coating film can be obtained. When the surface of the gas diffusion layer substrate is covered with a flat coating film (water repellent carbon layer described later), it becomes difficult to mechanically damage the catalyst layer in contact with the gas diffusion layer.

(D) Process:
(C) By baking the gas diffusion layer substrate coated with the coating liquid in step (c), water and nonionic surfactant are removed from the aqueous dispersion, and PTFE is attached to the gas diffusion layer substrate. The gas diffusion layer substrate is subjected to a water repellent treatment, and at the same time, water and nonionic surfactant are removed from the coating liquid, and PTFE is attached to the surface of the gas diffusion layer substrate and carbon black, and carbon black and A coating film made of PTFE, that is, a water-repellent carbon layer is formed.

The water-repellent carbon layer is a porous layer (microporous layer) having water repellency and a gas diffusion function, and has the following advantages.
(I) When the surface of the gas diffusion layer base material has fuzz due to carbon fibers or the like, the solid polymer film or the catalyst layer may be damaged. However, the solid polymer film and the catalyst are formed by forming the water-repellent carbon layer. Can protect the layer.
(Ii) Since it is denser than the gas diffusion layer base material and can maintain sufficient contact with the catalyst layer, it is advantageous for current collection.
(iii) The water droplets produced by the battery reaction can be finely crushed and sent to the gas diffusion layer substrate side, and the water can be discharged smoothly, so that flooding is unlikely to occur even in the high current density region. Is stable.

  Since the water-repellent carbon layer has high adhesion between the water-repellent carbon layer and the gas diffusion layer base due to the anchor effect, a part of the water-repellent carbon layer penetrates into the pores of the gas diffusion layer base. It is preferable.

Examples of the firing atmosphere include an inert atmosphere such as air and nitrogen gas, and the inert atmosphere is preferable from the viewpoint of preventing adsorption of oxides to the carbon surface.
The firing temperature is preferably 300 to 390 ° C, particularly preferably 350 to 390 ° C. By setting the firing temperature to 300 ° C. or higher, the nonionic surfactant is sufficiently removed, and the gas diffusion layer can maintain high water repellency for a long period of time. By setting the firing temperature to 390 ° C. or lower, decomposition of PTFE is suppressed, and the gas diffusion layer can exhibit high water repellency.
The firing time is preferably 30 minutes to 3 hours, particularly preferably 1 to 2 hours. By setting the firing time to 30 minutes or longer, the nonionic surfactant is sufficiently removed. By setting the firing time to 3 hours or less, the decomposition of PTFE can be suppressed.

  In the method for producing a gas diffusion layer of the present invention described above, the aqueous dispersion and / or the coating liquid contains a nonionic surfactant having a mass half-temperature in air of 100 to 300 ° C. Since it is contained in an amount of 0.5 to 10% by mass with respect to the total amount of tetrafluoroethylene and surfactant, a gas diffusion layer for a polymer electrolyte fuel cell that can maintain high water repellency for a long period of time can be obtained. .

  That is, in the conventional method for producing a gas diffusion layer, it has been thought that the surfactant contained in the aqueous dispersion and / or coating solution is completely removed by firing. However, it is the present inventor that a known surfactant (for example, polyoxyethylene alkylphenol surfactant) for dispersing PTFE in water cannot be completely removed even when calcined at 350 ° C. to 390 ° C. For the first time. And since surfactant remains on the surface of the PTFE fine particles adhering to the surface of the gas diffusion layer obtained by the conventional manufacturing method, the gas diffusion layer could not maintain water repellency for a long period of time.

  In contrast, the non-ionic surfactant having a mass half-temperature in air of 100 to 300 ° C. used in the production method of the present invention is completely removed when baked at 300 to 390 ° C. The obtained gas diffusion layer can maintain high water repellency for a long period of time without the surfactant remaining on the surface of the PTFE fine particles.

(Membrane electrode assembly)
FIG. 1 is a schematic cross-sectional view showing an example of a membrane electrode assembly for a polymer electrolyte fuel cell of the present invention (hereinafter referred to as a membrane electrode assembly). The membrane electrode assembly 10 includes a solid polymer electrolyte membrane 11, a catalyst layer 12 disposed on both surfaces of the solid polymer electrolyte membrane 11, and a gas diffusion layer 13 disposed outside the catalyst layer 12, At least one of the two gas diffusion layers 13 is a gas diffusion layer obtained by the production method of the present invention.

The gas diffusion layer 13 includes a gas diffusion layer base material 14 and a water-repellent carbon layer 15 formed on the surface of the gas diffusion layer base material 14, and the water-repellent carbon layer 15 is in contact with the catalyst layer 12.
The electrodes (air electrode and fuel electrode) are composed of a catalyst layer 12 and a gas diffusion layer 13.

The gas diffusion layer obtained by the production method of the present invention is preferably used for an air electrode in which a large amount of water is generated by a cell reaction, and more preferably used for both an air electrode and a fuel electrode.
Examples of the solid polymer electrolyte membrane include solid polymer electrolyte membranes used for known membrane electrode assemblies.
As a catalyst layer, the catalyst layer used for a well-known membrane electrode assembly is mentioned.

  The membrane electrode assembly is, for example, a catalyst layer disposed on both sides of a solid polymer electrolyte membrane, and a solid polymer form obtained by the production method of the present invention outside of at least one of the two catalyst layers. The fuel cell gas diffusion layer is produced by disposing the water-repellent carbon layer on the catalyst layer side.

  In the membrane electrode assembly of the present invention described above, since the gas diffusion layer obtained by the production method of the present invention, which can maintain high water repellency for a long time, is used as the gas diffusion layer. Even when the fuel cell is operated for a long period of time, the gas diffusion layer is less likely to be flooded, and the voltage is not greatly reduced. Therefore, the polymer electrolyte fuel cell can be stably operated for a long time.

EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.
Examples 1 to 3 are examples, and example 4 is a comparative example.

  As the surfactant, compounds (1-1) to (1-3), compound (2) and compound (3) shown in Table 1 were prepared.

In the compound (1-1), C ₁₀ H ₂₁ CH (CH ₃ ) CH ₂ O (C ₂ H ₄ O) ₈ (C ₃ H ₆ O) H in which the alkyl group is branched and the alkyl group is linear 1: 1 (mass ratio) mixture with C ₁₃ H ₂₇ O (C ₂ H ₄ O) ₈ (C ₃ H ₆ O) H.
“(C ₂ H ₄ O) _9-10 ” in the compound (1-2) indicates that the average number of moles of ethylene oxide (C ₂ H ₄ O) added is 9 to 10 moles.
The compound (1-3) includes C ₁₂ H ₂₅ O (C ₂ H ₄ O) ₉ H, C ₁₃ H ₂₇ O (C ₂ H ₄ O) ₉ H, C ₁₄ H ₂₉ O (C ₂ H ₄ Although it is a mixture with O) ₉ H, “(C ₂ H ₄ O) ₉ ” has an average number of moles of ethylene oxide (C ₂ H ₄ O) added in the same manner as compound (1-2). It is shown that.
C ₆ H ₄ in the compound (3) is a phenylene group.

Various measurements in the examples were performed as follows.
(Surface active agent mass half temperature)
Using a thermal analyzer (manufactured by Perkin Elmer, TGA7), about 10 mg of the surfactant in a platinum container was heated at 10 ° C./min in an air atmosphere to obtain a thermal decomposition curve, and then the mass remained. The temperature at which the rate was 50% was read.

(PTFE and surfactant content)
According to JIS K6893, 10 g of an aqueous dispersion of PTFE was placed in an aluminum dish and dried at 120 ° C. for 1 hour, and then the residual mass x (mass%) relative to the aqueous dispersion (100 mass%) and 35 minutes at 380 ° C. The residual mass y (mass%) relative to the aqueous dispersion (100 mass%) after baking was determined. y was made into content (mass%) of PTFE. Moreover, (xy) / xx100 was made into content (mass%) of surfactant with respect to the total amount of PTFE and surfactant.

(Average particle diameter of PTFE)
An aqueous dispersion of PTFE was diluted, and the median diameter of the diluted liquid was measured using a laser scattering type particle size measuring machine (LA920, manufactured by Horiba, Ltd.), and this was defined as the average particle diameter.

[Example 1]
By the emulsion polymerization method, an emulsion polymerization liquid (A) having an average particle diameter of PTFE of 0.25 μm, a PTFE content of 25 mass%, and containing about 2000 ppm of ammonium perfluorooctanoate with respect to PTFE was obtained. .
To the emulsion polymerization liquid (A), 4% by mass of the compound (1-1) shown in Table 1 was added with respect to PTFE (100% by mass), and concentrated by an electric concentration method. Of the obtained concentrated liquid, a high-concentration liquid having a large specific gravity in the vicinity of the electrode was collected, and a supernatant liquid (containing compound (1-1)) not containing PTFE particles was removed. Thereafter, 28% by mass of ammonia water was added in an amount of 0.3% by mass with respect to the liquid just after concentration, the PTFE content was 66.0% by mass, and the compound (1-1) content was PTFE and the compound. The aqueous dispersion (1) which is 2.5 mass% with respect to the total amount with (1-1) was obtained.

The aqueous dispersion (1) is diluted with distilled water until the content of PTFE is 5% by mass, and the content of the compound (1-1) is based on the total amount of PTFE and the compound (1-1). An aqueous dispersion (2) of 2.5% by mass was obtained. Carbon paper (manufactured by Toray Industries, Inc., TGP-H-120, thickness 360 μm) was immersed in the aqueous dispersion (2) so that the adhesion amount of PTFE was 2 mg / cm ² . After pulling up the carbon paper from the aqueous dispersion (2), the aqueous dispersion (2) -impregnated carbon paper was stored in a wet state at room temperature.

  The aqueous dispersion (1) was diluted with distilled water until the PTFE content was 2.7% by mass to obtain an aqueous dispersion (3). 233.34 g of the aqueous dispersion (3) was weighed so that 6.3 g of PTFE was contained. 14.7 g of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd., Denka Black) was added to the aqueous dispersion (3). Sufficient stirring is performed to obtain a slurry-like coating liquid (4) in which the content of the compound (1-1) is 2.5% by mass with respect to the total amount of PTFE and the compound (1-1). It was.

  The coating liquid (4) was applied onto the aqueous dispersion (2) impregnated carbon paper by a die coater. The carbon paper coated with the coating liquid (4) was baked in nitrogen gas at 350 ° C. for 2 hours to form a water-repellent carbon layer to obtain a gas diffusion layer. The thickness of the water repellent carbon layer was about 40 μm.

Flemion (registered trademark) resin (produced by Asahi Glass Co., Ltd., perfluorocarbon sulfonic acid type ion exchange resin with an ion exchange capacity of 1.1 meq / g dry resin (units derived from tetrafluoroethylene and CF ₂ ═CFOCF (CF ₃ ) O) (CF ₃ ) ₂ SO ₃ H-derived copolymer)) and platinum-supported carbon (TEC10E50E, Tanaka Kikinzoku Co., Ltd.) 45.7 mass%) and 26.8: 73.2 (mass ratio), the solid content concentration is 9 mass%, and a mixed solvent of ethanol and water (ethanol: water = 1: 1 (mass). A catalyst layer forming ink was prepared using the ratio)) as a solvent.
The ink for forming the catalyst layer was applied on an ethylene-tetrafluoroethylene copolymer (hereinafter referred to as ETFE) sheet so that the Pt adhesion amount was 0.5 mg / cm ^2, and then in air at 80 ° C. for 20 minutes. And the solvent was removed to obtain an ETFE sheet with a catalyst layer.

As the solid polymer electrolyte membrane, Flemion (registered trademark) CSH25 (manufactured by Asahi Glass Co., Ltd., ion exchange capacity 1.1 meq / g dry resin, perfluorocarbon sulfonic acid type ion exchange resin membrane produced by cast molding method, thickness 25 μm) was used.
With two ETFE sheets with catalyst layers, sandwich the solid polymer electrolyte membrane so that the catalyst layer side is on the solid polymer electrolyte membrane side, and hot press at 130 ° C. and 3 MPa for 5 minutes to make the catalyst layer a solid polymer electrolyte It transferred to the electrolyte membrane and peeled only the ETFE sheet. The effective electrode area was 25 cm ² . The membrane was sufficiently heat-treated and dried to obtain a membrane / catalyst layer assembly (CCM).

  A gas diffusion layer was pressed on both surfaces of the membrane catalyst layer assembly so that the water-repellent carbon layer was on the catalyst layer side to obtain a membrane electrode assembly (hereinafter referred to as MEA). The MEA was evaluated for battery characteristics. The results are shown in Table 2.

(Evaluation of battery characteristics)
MEA is incorporated into a polymer electrolyte fuel cell and separators are placed on both outer sides of the MEA to form a measurement cell. An electronic load device (Takasago Seisakusho, FK400L) and a DC power supply (Takasago Seisakusho, EX750L) The current-voltage characteristics were measured under the following measurement conditions, and the change over time in the cell voltage was observed when driven at a constant current.
(Measurement conditions) Hydrogen outlet pressure: 0.1 MPa (normal pressure), air outlet pressure: 0.1 MPa (normal pressure), operating temperature of measurement cell: 80 ° C. in a bubbler tank through which hydrogen gas supplied to the fuel electrode is passed Temperature of hot water: 80 ° C. Temperature of hot water in bubbler tank of air supplied to the air electrode: 80 ° C., current density: maintained at 0.8 A / cm ² , fuel utilization on the fuel electrode side: 70%, air electrode Side fuel utilization: 40%.

[Example 2]
A gas diffusion layer and MEA were obtained in the same manner as in Example 1 except that the compound (1-2) shown in Table 1 was used instead of the compound (1-1) as the surfactant. About this MEA, it carried out similarly to Example 1, and evaluated the battery characteristic. The results are shown in Table 2.

[Example 3]
A gas diffusion layer and MEA were obtained in the same manner as in Example 1 except that the compound (1-3) shown in Table 1 was used instead of the compound (1-1) as the surfactant. About this MEA, it carried out similarly to Example 1, and evaluated the battery characteristic. The results are shown in Table 2.

[Example 4 (comparative example)]
A gas diffusion layer and MEA were obtained in the same manner as in Example 1 except that the compound (3) shown in Table 1 was used instead of the compound (1-1) as the surfactant. About this MEA, it carried out similarly to Example 1, and evaluated the battery characteristic. The results are shown in Table 2.

  The cell voltage drop of the MEA of Example 1 was less than that of the MEA of Example 2. That is, in the MEA of Example 1, the nonionic surfactant present in the gas diffusion layer is completely removed by firing, and the surface of PTFE is completely maintained in water repellency, whereas the MEA of Example 2 is maintained. Then, the surfactant present in the gas diffusion layer is not completely decomposed and removed by firing, and the surfactant remains on the surface of PTFE, so that the water repellency on the surface of PTFE cannot be maintained and is easily wetted. It was. Therefore, the MEA of Example 2 is easily wetted in the gas diffusion layer (the gas diffusion layer base material and the water-repellent carbon layer), the water generated by the battery reaction and the humidified water are not smoothly discharged, and the pores tend to be blocked. Became. Then, the supply of fuel gas and air was hindered, resulting in an increase in concentration overvoltage, resulting in a decrease in cell voltage.

  Since the gas diffusion layer obtained by the production method of the present invention can maintain high water repellency for a long period of time, it can be suitably used for a membrane electrode assembly that can stably operate a polymer electrolyte fuel cell for a long period of time.

It is a schematic sectional drawing which shows an example of the membrane electrode assembly for polymer electrolyte fuel cells of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Membrane electrode assembly 11 Solid polymer electrolyte membrane 12 Catalyst layer 13 Gas diffusion layer 14 Gas diffusion layer base material 15 Water-repellent carbon layer

Claims (7)

After impregnating the gas diffusion layer base material with an aqueous dispersion in which polytetrafluoroethylene is dispersed in water,
A coating liquid in which carbon black and polytetrafluoroethylene are dispersed in a dispersion medium is applied onto a gas diffusion layer substrate,
A method for producing a gas diffusion layer for a polymer electrolyte fuel cell by firing a gas diffusion layer base material coated with a coating liquid,
The aqueous dispersion contains 0.5 to 10% by mass of a nonionic surfactant having a mass half temperature in air of 100 to 300 ° C. based on the total amount of polytetrafluoroethylene and the surfactant. A method for producing a gas diffusion layer for a polymer electrolyte fuel cell, comprising: After impregnating the gas diffusion layer base material with an aqueous dispersion in which polytetrafluoroethylene is dispersed in water,
A coating liquid in which carbon black and polytetrafluoroethylene are dispersed in a dispersion medium is applied onto a gas diffusion layer substrate,
A method for producing a gas diffusion layer for a polymer electrolyte fuel cell by firing a gas diffusion layer base material coated with a coating liquid,
The coating liquid contains 0.5 to 10% by mass of a nonionic surfactant having a mass half-temperature in air of 100 to 300 ° C. based on the total amount of polytetrafluoroethylene and the surfactant. A method for producing a gas diffusion layer for a polymer electrolyte fuel cell, comprising: After impregnating the gas diffusion layer base material with an aqueous dispersion in which polytetrafluoroethylene is dispersed in water,
A coating liquid in which carbon black and polytetrafluoroethylene are dispersed in a dispersion medium is applied onto a gas diffusion layer substrate,
A method for producing a gas diffusion layer for a polymer electrolyte fuel cell by firing a gas diffusion layer base material coated with a coating liquid,
Each of the aqueous dispersion and the coating liquid contains a nonionic surfactant having a mass half-temperature in air of 100 to 300 ° C. with respect to the total amount of polytetrafluoroethylene and the surfactant. The manufacturing method of the gas diffusion layer for polymer electrolyte fuel cells characterized by containing 0.5-10 mass%. The method for producing a gas diffusion layer for a polymer electrolyte fuel cell according to any one of claims 1 to 3, wherein the nonionic surfactant is a compound represented by the following formula (1).
R ¹ OAH (1)
However, R ¹ is a primary or secondary alkyl group having 8 to 18 carbon atoms, A is a polyoxyalkylene group consisting of 5 to 20 oxyethylene groups and 0 to 2 oxypropylene groups It is. The nonionic surfactant _{is, C 13 H 27 O- (C} 2 H 4 O) 8 (C 3 H 6 O) -H, C 13 H 27 O- (C 2 H 4 O) 9 -H, _{C 13 H 27 O- (C 2} H 4 O) 10 -H, C 10 H 21 CH (CH 3) CH 2 O- (C 2 H 4 O) 10 -H, C 6 H 13 CH (C 6 H _{13) O- (C 2 H 4} O) 9 -H, C 10 H 21 CH (CH 3) CH 2 O- (C 2 H 4 O) 8 (C 3 H 6 O) -H, C 12 H 25 is _{O- (C 2 H 4 O)} 9 -H and _{C 8 H 17 O- (C 2} H 4 O) 1 or more selected from the group consisting of ₆ -H, solid polymer of claim 4 For manufacturing a gas diffusion layer for a fuel cell.   The method for producing a gas diffusion layer for a polymer electrolyte fuel cell according to any one of claims 1 to 5, wherein the temperature at which the gas diffusion layer substrate to which the coating liquid is applied is baked is 300 to 390 ° C. A solid polymer electrolyte membrane;
A catalyst layer disposed on both sides of the solid polymer electrolyte membrane;
A gas diffusion layer disposed outside the catalyst layer,
A membrane electrode for a polymer electrolyte fuel cell, wherein at least one of the two gas diffusion layers is a gas diffusion layer for a polymer electrolyte fuel cell obtained by the production method according to any one of claims 1 to 6. Joined body.

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