JP5742747B2 - Fuel cell, gas diffusion layer, and method of manufacturing gas diffusion layer - Google Patents

Description

  The present invention relates to a fuel cell, and more particularly to a gas diffusion layer of a fuel cell.

  When manufacturing a gas diffusion layer for a fuel cell, a technique is known in which a water repellent layer forming paste is applied to the surface of a conductive porous substrate and then dried at 200 to 400 ° C. in the atmosphere. (Patent Document 1).

JP 2010-129451 A

  However, the gas diffusion layer formed by this method has a problem that water repellency and durability of the water repellant substance are insufficient.

  The present invention has been made to solve at least a part of the above-described problems, and an object thereof is to improve the water repellency of a gas diffusion layer and the durability of a water-repellent substance.

SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.
According to one aspect of the invention, a fuel cell is provided. The fuel cell of this embodiment includes an electrolyte membrane, a catalyst layer formed on both surfaces of the electrolyte membrane, and a gas diffusion layer disposed on the surface of the catalyst layer on the opposite side of the electrolyte membrane, and the gas The diffusion layer has a base material and a water-repellent substance coated on the base material, and the water-repellent substance has a multilayer structure in which the particulate water-repellent substance adheres to each other while maintaining the particle property. It is formed separately. According to this embodiment, the water-repellent substances are in the form of particles and adhered to each other while maintaining the particle properties, and thus are formed in multiple layers, so that the water-repellent substance is high and the durability of the water-repellent substance can be improved. . In addition, since it is formed in multiple layers by adhering to each other while maintaining the particle properties, when some of the particulate water-repellent substances are peeled off, fresh particulate water-repellent substances appear on the surface, resulting in water-repellent properties. It is possible to suppress the decline of

[Application Example 1]
A fuel cell comprising: an electrolyte membrane; a catalyst layer formed on both surfaces of the electrolyte membrane; and a gas diffusion layer disposed on a surface of the catalyst layer on the opposite side of the electrolyte membrane, the gas diffusion The layer includes a base material and a water-repellent material coated on the base material, and the water-repellent material is formed by dividing a particulate water-repellent material into multiple layers.
According to this application example, the water-repellent substance is particulate and formed in multiple layers, so that the water-repellent substance is high and the durability of the water-repellent substance can be improved.

[Application Example 2]
In the fuel cell according to Application Example 1, the water-repellent substance includes polytetrafluoroethylene, perfluoroethylene-propylene copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-perfluorodiode. A fuel cell comprising one or more water-repellent substances selected from the group consisting of xol copolymers.

[Application Example 3]
The fuel cell according to Application Example 1 or 2, wherein the water-repellent substance particles have a higher adhesive strength as they are closer to the substrate.
When the water repellent material is peeled off, the particles are peeled off from the surface for each particle, so that the water repellency can be maintained even if some of the water repellent material particles are peeled off.

[Application Example 4]
A gas diffusion layer for a fuel cell, comprising: a base material; and a water-repellent material coated on the base material, wherein the water-repellent material is formed by dividing a particulate water-repellent material into multiple layers A gas diffusion layer.
According to this application example, the water-repellent substance is particulate and formed in multiple layers, so that the water-repellent substance is high and the durability of the water-repellent substance can be improved.

[Application Example 5]
A method for producing a gas diffusion layer for a fuel cell, wherein (a) a step of applying a particulate water-repellent substance to the base material of the diffusion layer, and (b) a step of sintering or drying the base material, And in the step (b), the temperature when sintering or drying is a melting point of the water-repellent substance or less, the method for producing a gas diffusion layer.
According to this application example, since the water repellent substance can be formed in multiple layers while maintaining the particle state, a gas diffusion layer having high water repellency and high durability of the water repellent substance can be produced.

[Application Example 6]
In the method for producing a gas diffusion layer according to Application Example 5, the temperature at the time of sintering or drying in the step (b) is (the melting point of the water-repellent substance −50 ° C.) or more. Method.
According to this application example, the particles of the water repellent material can be bonded while the surface of the water repellent material is melted and the particle shape is maintained, so that the adhesion between the particles can be increased.

[Application Example 7]
In the method for producing a gas diffusion layer according to Application Example 5 or 6, in the step (b), at least one of electromagnetic waves, microwaves, infrared rays, and far infrared rays is used, and the water-repellent substance is added to the substrate. The manufacturing method of the gas diffusion layer heated from the side.
According to this application example, since the base material is heated and the water-repellent substance is heated from the base-material side, the adhesion of the water-repellent substance particles closer to the base material can be increased.

  The present invention can be realized in various forms, for example, in the form of a fuel cell gas diffusion layer, a method for manufacturing a gas diffusion layer, and the like.

It is explanatory drawing which shows the structure of the fuel cell as one Embodiment of this invention. It is explanatory drawing which shows the structure of an electric power generation unit typically. It is explanatory drawing which shows a gas diffusion layer manufacturing apparatus. It is a flowchart of the coating process of BL paste and MPL paste to the base material of a gas diffusion layer. It is an electron micrograph of the gas diffusion layer of a present Example. It is an electron micrograph of the gas diffusion layer of a comparative example.

A. Embodiment:
FIG. 1 is an explanatory diagram showing a configuration of a fuel cell as one embodiment of the present invention. The fuel cell 10 includes a fuel cell stack 100, current collecting plates 200 and 201, insulating plates 210 and 211, a pressing plate 220, end plates 230 and 231, a tension rod 240, a nut 250, and a pressing spring 260. And comprising.

  The fuel cell stack 100 includes a plurality of power generation units 110. Each power generation unit 110 is a single cell. The power generation units 110 are stacked and connected in series, and generate a high voltage as the fuel cell stack 100. The current collector plates 200 and 201 are disposed on both sides of the fuel cell stack 100, and are used to extract the voltage and current generated by the fuel cell stack 100 to the outside. The insulating plates 210 and 211 are disposed further outside the current collecting plates 200 and 201, respectively, and between the current collecting plates 200 and 201 and other members such as the end plates 230 and 231 and the tension rod 240. Insulate so that no current flows. The end plate 230 and the pressing plate 220 are disposed further outside the insulating plates 210 and 211, respectively. A pressing spring 260 is disposed further outside the pressing plate 220, and an end plate 231 is disposed further outside the pressing spring 260. The end plate 231 is disposed at a predetermined distance from the end plate 230 by the tension rod 240 and the nut 250. In this case, the pressing plate 260 is pressed in the direction of the insulating plate 211 by the pressing spring 260 and gives a predetermined fastening force to the power generation unit 110. The fuel cell 10 may be configured not to include the pressing spring 260 and the pressing plate 220.

  FIG. 2 is an explanatory diagram schematically showing the configuration of the power generation unit 110. The power generation unit 110 includes a membrane electrode assembly 120, gas diffusion layers 132 and 133, porous body gas channels 142 and 143, separator plates 152 and 153, and a seal gasket 160. The membrane electrode assembly 120 includes an electrolyte membrane 121 and catalyst layers 122 and 123.

  In the present embodiment, as the electrolyte membrane 121, for example, a proton conductive ion exchange membrane made of a fluorine resin such as perfluorocarbon sulfonic acid polymer or a hydrocarbon resin is used. The catalyst layers 122 and 123 are formed on each surface of the electrolyte membrane 121, respectively. In the present embodiment, the catalyst layers 122 and 123 are formed of, for example, catalyst-carrying particles (for example, carbon particles) carrying a platinum catalyst or a platinum alloy catalyst made of platinum and another metal.

  The gas diffusion layers 132 and 133 are disposed on the outer surfaces of the catalyst layers 122 and 123, respectively. In this embodiment, as the gas diffusion layers 132 and 133, carbon cloth or carbon paper using a carbon nonwoven fabric can be used. The porous gas channels 142 and 143 are disposed on the outer surfaces of the gas diffusion layers 132 and 133, respectively. Separator plates 152 and 153 are disposed on the outer surfaces of porous gas flow paths 142 and 143, respectively. A cooling water channel 155 is formed between the separator plate 152 and the separator plate 153 of the adjacent power generation unit 110. The seal gasket 160 is formed so as to surround the outer edges of the membrane electrode assembly 120, the gas diffusion layers 132 and 133, and the porous body gas flow paths 142 and 143. The seal gasket 160 is formed integrally with the membrane electrode assembly 120 by, for example, injection molding. Thereafter, gas diffusion layers 132 and 133 and porous body gas flow paths 142 and 143 are sequentially disposed on both surfaces of the membrane electrode assembly 120.

  FIG. 3 is an explanatory view showing a gas diffusion layer manufacturing apparatus. The gas diffusion layer manufacturing apparatus 30 includes a feeding unit 31, a winding unit 33, and a sintering / drying unit 35. The feeding unit 31 applies a water repellent paste to the base material 132 a of the gas diffusion layer 132 and sends it to the next sintering / drying unit 35. The sintering / drying unit 35 sinters or dries the paste of the water repellent material on the base material 132a. The winding unit 33 winds up the gas diffusion layer 132 including a water repellent layer formed of a sintered or dried water repellent material.

  The feeding unit 31 includes a feeding roller 311, a protective film winding roller 313, transport rollers 315 and 317, a dust collector 319, a water repellent paste coating unit 321, and a microporous layer coating unit 323 (hereinafter referred to as “MPL coating”). A pre-drying furnace 325, and a film thickness meter 327. The feeding roller 311 winds the base material 132a of the gas diffusion layer 132 with the protective film 400 interposed therebetween in a roll shape. The protective film winding roller 313 winds up the protective film 400. The dust collector 319 removes dust and dirt from the base material 132a of the gas diffusion layer 132 from which the protective film 400 has been peeled off. The water repellent paste coating unit 321 applies a first water repellent paste (hereinafter referred to as “BL paste”) to the base material 132 a of the gas diffusion layer 132. Here, as the BL paste, a paste containing a particulate water repellent material (for example, polytetrafluoroethylene) can be used. The MPL coating unit 323 applies a second water repellent paste (hereinafter referred to as “MPL paste”) containing carbon black and cerium oxide on the BL paste. The MPL paste also contains a particulate water repellent material. Carbon black in the MPL paste imparts conductivity to the gas diffusion layer 132, and cerium oxide suppresses generation of radicals that degrade the electrolyte membrane 121 (FIG. 2). The predrying furnace 325 preliminarily dries the gas diffusion layer 132 at a temperature lower than the processing temperature of the subsequent sintering or drying process. The pre-drying furnace 325 reduces the influence of the temperature difference between the processing temperature of the BL paste coating process and the MPL coating process (room temperature) and the processing temperature of the subsequent sintering or drying process, It is performed for evaporating the solvent in the MPL paste, suppressing migration of cerium, and the like. The film thickness meter 327 measures the film thickness of the gas diffusion layer 132 and determines whether or not the film thickness is within a specified range.

  The sintering / drying unit 35 has a length that is approximately four times the length of the pre-drying furnace 325, and includes a backup roll 351, a hot air generator 353, a hot air blowing nozzle 355, and far infrared radiation. A device 357 and a thermometer 359 are provided. The backup roll 351 supports the gas diffusion layer 132 to be conveyed from below. The hot air generator 353 generates hot air and sends it to the hot air blowing nozzle 355. There are a plurality of hot air blowing nozzles 355, which are alternately provided on the upper side and the lower side of the gas diffusion layer 132 along the conveying direction of the gas diffusion layer 132. The far-infrared radiation device 357 is paired with the hot air blowing nozzle 355 and is provided on the opposite side of the hot air blowing nozzle 355 with the gas diffusion layer 132 interposed therebetween. That is, the far-infrared radiation device 357 heats the gas diffusion layer 132 with far-infrared rays from the side opposite to the hot air blowing nozzle 355. Due to the far-infrared effect, the base material 132a easily absorbs far-infrared rays, so that the gas diffusion layer 132 is heated from the base material 132a. For this reason, the BL paste and the MPL paste have a higher adhesive force because the temperature increases toward the base material 132a. The thermometer 359 measures the surface temperature of the gas diffusion layer 132. The hot air generator 353, the hot air blowing nozzle 355, and the far-infrared radiation device 357 are controlled so that the temperature of the gas diffusion layer 132 falls within a predetermined temperature range. For example, the gas diffusion layer 132 is not more than the melting point (327 ° C.) of the resin (for example, polytetrafluoroethylene) in the BL paste and MPL paste and is close to the melting point (for example, the difference from the melting point is 50 ° C. or less). It is controlled so that it will fit in.

  The winding unit 33 includes a winding roller 331, a protective film feeding roller 333, a transport roller 335, a film thickness meter 337, and a streak inspection device 339. The winding roller 331 winds up the gas diffusion layer 132. The protective film feeding roller 333 rolls up and stores the protective film 400 and feeds the protective film 400 to the winding roller 331 in accordance with the winding of the gas diffusion layer of the winding roller 331. The protective film 400 is still wound on the outermost layer of the winding roller 331 that has wound the gas diffusion layer 132 so that the overlapping portion does not adhere when the winding roller 331 winds the gas diffusion layer 132. It arrange | positions so that it may be pinched | interposed between the gas diffusion layers 132 which are not. The film thickness meter 337 measures the film thickness of the gas diffusion layer 132. The streak inspection device 339 inspects whether the gas diffusion layer 132 has streaks or wrinkles.

  FIG. 4 is a flowchart of a process of applying BL paste and MPL paste to the base material of the gas diffusion layer. In step S100, a BL paste (first water repellent paste) is produced. The BL paste is produced, for example, by dissolving polytetrafluoroethylene (hereinafter referred to as “PTEF”) in a solvent (for example, ethanol and water). In step S110, an MPL paste (second water repellent paste) is produced. The MPL paste is produced by dissolving PTFE, carbon black, and cerium oxide in a solvent (for example, ethanol and water). Since carbon black and cerium oxide are not water-soluble, the MPL paste becomes a suspension.

  In step S120, the BL paste is applied to the base material 132a of the gas diffusion layer 132. This coating can be carried out by spraying or by a die coater. In step S130, the MPL paste is applied on the BL paste. Since the MPL paste contains insoluble carbon black and cerium oxide, this coating can be performed by a die coater.

  In step S140, the gas diffusion layer 132 is dried in the predrying furnace 325 (FIG. 3). In step S150, the gas diffusion layer 132 is sintered or dried. Note that the sintering or drying temperature in step S150 is in a temperature range close to the melting point (327 ° C.) of PTEF, and the pre-drying temperature in step S140 is lower than the temperature in step S150 (for example, 150 ° C.). . If the sintering or drying temperature is higher than the melting point of PTEF, the PTFE will melt and become particulate. On the other hand, if the melting point of PTEF is too low, the surfaces of the PTFE particles do not melt and do not adhere to each other, so that PTFE is easily peeled off. Therefore, the sintering or drying temperature in step S150 is preferably a temperature sufficiently close to the melting point of PTEF (for example, the difference from the melting point is 50 ° C. or less). In step S160, the film thickness and streaks of the gas diffusion layer 132 are inspected.

B. Examples and comparative examples:
CP-EXP161PC manufactured by Toray Industries, Inc. was used as the base material 132a of the gas diffusion layer 132. As PTFE used for the BL paste, AD911E manufactured by Asahi Glass Co., Ltd. was used. Asahi Glass Co., Ltd. AD911E has a fine particle shape with a particle size of about 0.3 microns. This was dissolved in a solvent (mixed solvent of ethanol and water) and applied to the substrate 132a by a spray method. The basis weight of the BL paste was (0.35 ± 0.25) mg per 1 cm ^{2 of} the gas diffusion layer.

The following materials were used as materials for the MPL paste: PTFE: AD911E from Asahi Glass Co., Ltd.
Carbon black: Denka Black (registered trademark) of Denki Kagaku Kogyo Co., Ltd.
Cerium oxide: Taiyo S of Taiyo Mining Co., Ltd.
The mass percentage ratio of PTFE, carbon black, and cerium oxide in the MPL paste was 2: 8: 1. This mixture was suspended in a solvent (a mixed solvent of ethanol and water) and then applied onto the water-repellent paste of the gas diffusion layer 132 using a die coater. The basis weight of the MPL paste was (4.2-0.7) mg to (4.2 + 0.3) mg per 1 cm ^{2 of} the gas diffusion layer.

  In the pre-drying furnace 325, heating was performed at 150 ° C. for about 2 minutes. Next, in the sintering / drying unit 35, the maximum temperature of the surface of the gas diffusion layer 132 was set to 327 ° C., and sintered or dried for about 8 minutes. Here, 327 ° C. is the melting point of PTFE. The comparative example is the same as the example except that the maximum temperature of the surface of the gas diffusion layer 132 in the sintering / drying unit 35 is set to 400 ° C.

  FIG. 5 is an electron micrograph of the gas diffusion layer of this example. FIG. 6 is an electron micrograph of a gas diffusion layer of a comparative example. As is clear from the comparison between the two, in this example, the particles of the PTFE are adhered to the fibers of the base material 132a while maintaining the particle property of PTFE. Further, the layer made of PTFE particles has a multilayer structure divided into a plurality of layers L1 and L2. On the other hand, in the comparative example, the PTFE particles are completely dissolved and adhered to the base material 132a in a state where the particles are continuous.

  In this example, since PTFE is in the form of particles, the surface area of the hydrophobic group is larger than that of the comparative example, and the water repellency is higher than that of the comparative example. In addition, when the gas diffusion layer 132 is used in a fuel cell, even when PTFE near the surface layer is peeled off due to a change with time, only a part of the particles are peeled off. The PTFE particles are adhered without being peeled off. Therefore, even after some PTFE particles are peeled off, fresh PTFE particles appear on the surface, so that the water repellency is hardly lowered. On the other hand, in the gas diffusion layer of the comparative example, when PTFE is peeled off, almost all of the PTFE peels off continuously, so that fresh PTFE hardly appears on the surface and the water repellency may be lowered. Thus, this example has higher water repellency and higher water repellency durability than the comparative example.

  Such a particulate structure of PTFE can be obtained by sintering or drying at a temperature below the melting point of PTFE so that the PTFE particles are not excessively dissolved in the step of sintering or drying PTFE. it can. The surface temperature of the gas diffusion layer 132 due to the difference in sintering or drying is preferably not higher than the melting point of PTFE and as close to the melting point as possible. If it is too low, the PTFE particles will not adhere to each other. Moreover, it is preferable to heat the base material 132a using far infrared rays in the sintering or drying process, and to heat the BL paste layer or the MPL paste layer with the heat. In addition, you may heat using electromagnetic waves, a microwave, and infrared rays other than a far infrared ray. Thereby, the temperature closer to the base material 132a side of the water-repellent layer formed from the BL paste and the MPL paste can be increased to increase the adhesive strength. In FIG. 5, PTFE is divided into a plurality of different layers, and among these layers, the PTFE particles are more firmly bonded to each other as the layer is closer to the fiber of the base material 132.

  In this example, PTFE was used as a water-repellent material when preparing BL paste and MPL paste. However, in addition to PTFE, perfluoroethylene-propylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether. Other water-repellent substances such as a copolymer (FPA) and a tetrafluoroethylene-perfluorodioxole copolymer (TFE / PDD) may be used.

  In this example, two water-repellent pastes of BL paste and MPL paste were used and applied separately, but one water-repellent paste (MPL paste is preferred) at a time without separating them. You may apply.

  In the present embodiment, the description is made using one gas diffusion layer 132, but the same applies to the other gas diffusion layer 133.

  The embodiments of the present invention have been described above based on some examples. However, the above-described embodiments of the present invention are for facilitating the understanding of the present invention and limit the present invention. It is not a thing. The present invention can be changed and improved without departing from the spirit and scope of the claims, and it is needless to say that the present invention includes equivalents thereof.

DESCRIPTION OF SYMBOLS 10 ... Fuel cell 30 ... Gas diffusion layer manufacturing apparatus 31 ... Delivery part 33 ... Winding part 35 ... Drying part 100 ... Fuel cell stack 110 ... Power generation unit 120 ... Membrane electrode assembly 121 ... Electrolyte membrane 122, 123 ... Catalyst layer 132 DESCRIPTION OF SYMBOLS 133 ... Gas diffusion layer 132a ... Base material 142, 143 ... Porous gas flow path 152, 153 ... Separator plate 155 ... Cooling water flow path 160 ... Seal gasket 200 ... Current collecting plate 210 ... Insulating plate 220 ... Pressing plate 230, 231 ... End plate 240 ... Tension rod 250 ... Nut 260 ... Pressing spring 311 ... Feeding roller 313 ... Protective film winding roller 315, 317 ... Conveying roller 319 ... Dust collector 321 ... Water-repellent paste coating part 323 ... Microporous layer coating part 325 ... Pre-drying furnace 327 ... Film thickness meter 331 ... Winding roller 333 ... protective paper feed roller 335 ... transport roller 337 ... film thickness meter 339 ... streak inspection device 351 ... backup roll 353 ... hot air generator 355 ... hot air blowing nozzle 357 ... far infrared radiation device 359 ... thermometer 400 …Protective film

Claims (7)

A fuel cell,
An electrolyte membrane;
A catalyst layer formed on both surfaces of the electrolyte membrane;
A gas diffusion layer disposed on a surface opposite to the electrolyte membrane of the catalyst layer;
With
The gas diffusion layer is
A substrate;
A water repellent material coated on the substrate;
Have
The water-repellent material is formed by dividing the particulate water-repellent material into multiple layers while maintaining the particle property ,
Fuel cell. The fuel cell according to claim 1, wherein
The water repellent material is selected from the group consisting of polytetrafluoroethylene, perfluoroethylene-propylene copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-perfluorodioxole copolymer. A fuel cell comprising one or more water-repellent substances. The fuel cell according to claim 1 or 2,
The fuel cell is such that the particles of the water-repellent substance are more adhesive as they are closer to the substrate. A gas diffusion layer for a fuel cell,
A substrate;
A water repellent material coated on the substrate;
Have
The water-repellent substance is a gas diffusion layer in which particulate water-repellent substances are bonded to each other while maintaining the particle property and are divided into multiple layers. A method for producing a gas diffusion layer for a fuel cell, comprising:
(A) applying a particulate water-repellent substance to the base material of the diffusion layer in multiple layers;
(B) sintering or drying the substrate;
With
Wherein in the step (b), by temperature and below the melting point of the water-repellent substance at which to sintering or drying, the particulate water repellent material to adhere to one another while maintaining the particulate, gas diffusion layer Manufacturing method. In the manufacturing method of the gas diffusion layer according to claim 5,
The method for producing a gas diffusion layer, wherein a temperature at the time of sintering or drying in the step (b) is (melting point of the water-repellent substance −50 ° C.) or higher. In the manufacturing method of the gas diffusion layer according to claim 5 or 6,
The method for producing a gas diffusion layer, wherein in the step (b), the water-repellent substance is further heated from the substrate side using at least one of electromagnetic waves, microwaves, infrared rays, and far infrared rays.

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