JP2006012569A - Manufacturing method for gas diffusion layer for solid polymer electrolyte fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method for a gas diffusion layer for a solid polymer electrolyte fuel cell advantageous for preventing pores of the gas diffusion layer from being excessively collapsed or the flow passage cross section of a gas passage of a separator from becoming excessively small. <P>SOLUTION: A process preparing a liquid substance consisting essentially of a conductive material such as a carbon fiber having conductivity and an extinction material which can be extinguished, a sheet formation process forming a sheet consisting essentially of the conductive material and the extinction material by separating a solid content from the liquid substance, and a pore formation process forming the pores in the sheet by extinguishing the extinction material contained in the sheet are carried out in order. The liquid substance contains a solid resin (thermosetting resin etc.), and the resin contained in the liquid substance is supported by the sheet. Therefore, the gas diffusion layer 100 formed with the sheet can be made properly hard. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a gas diffusion layer of a solid polymer electrolyte fuel cell.

  As a gas diffusion layer for a fuel cell, a sheet formed from a carbon fiber such as carbon paper or carbon cloth as a base material is widely used. And in order to acquire the performance as a gas diffusion layer, the water repellent process for performing the electroconductive process for improving electroconductivity and water repellency to these base materials is made | formed. However, since these base materials are expensive, when used as a gas diffusion layer for a fuel cell, there is a problem that the fuel cell becomes expensive and hinders practical use.

As a means for solving this problem, as disclosed in Patent Document 1, a slurry that is a liquid material mainly composed of carbon fiber and pulp is formed, and solids contained in the slurry are deposited. The sheet is then molded, and then the water-repellent polymer material (PTFE or the like) is impregnated inside the sheet, and then the sheet is heated and held, so that the pulp contained in the sheet disappears and pulp is removed. In recent years, a method for forming a porous carbon sheet by using traces as pores has been proposed. Since the carbon sheet is bonded to the carbon fiber by a polymer material (PTFE or the like) having water repellency, the carbon sheet has flexibility in bonding the carbon fiber. Therefore, this carbon sheet has the advantage of having the flexibility to be wound up in a roll shape, and therefore has a roll transportability and is excellent in productivity.
JP 2000-136493 A

  According to the above-described carbon sheet, the carbon fiber is flexible and can be wound into a roll. On the other hand, when the carbon sheet is incorporated as a gas diffusion layer together with the separator as a fuel cell, the carbon sheet In some cases, the pores present in the gas diffusion layer formed by crushing are crushed.

  Further explanation will be added. FIG. 7 schematically shows a form in which this carbon sheet is used as a gas diffusion layer. As shown in FIG. 7, when assembled as a fuel cell, the gas diffusion layer 100X made of the above-described carbon sheet is sandwiched by applying pressure to the separator 200X. For this reason, gas diffusion layer 100X is pressurized by convex part 220X which forms gas channel 210X of separator 200X. Therefore, in the gas diffusion layer 100X, in the region 110X facing the convex portion 220X of the separator 200X, the frequency with which the internal pores 111X are crushed may increase.

  Here, the pores 111X formed in the gas diffusion layer 100X have a function of supplying a reaction gas such as a fuel gas or an oxidant gas and a function of discharging water generated by the power generation reaction. For this reason, when the frequency with which the pores 111X are crushed is high, there is a problem that the above-described function is lowered and it is difficult to obtain the target power generation performance of the fuel cell.

  Furthermore, since the gas diffusion layer 100X formed of the above-described carbon sheet is flexible in the thickness direction as described above, when the gas diffusion layer 100X is sandwiched between the separators 200X, as schematically shown in FIG. In addition, a part 102X of the gas diffusion layer 100X may swell into the gas flow path 210X of the separator 200X, and the flow path cross-sectional area of the gas flow path 210X of the separator 200X may be excessively smaller than the target flow path cross-sectional area. . In this case, there is a possibility that the gas supply capability through the gas flow path 210X of the separator 200X is not sufficient.

  The present invention has been made in view of the above-described circumstances, and is advantageous in suppressing the pores of the gas diffusion layer from being excessively crushed and the cross-sectional area of the gas flow path of the separator from becoming excessively small. It is an object of the present invention to provide a method for producing a gas diffusion layer of a solid polymer electrolyte fuel cell.

  A method for producing a gas diffusion layer of a solid polymer electrolyte fuel cell according to the present invention includes a step of preparing a liquid material mainly composed of a conductive material having conductivity and a disappearable material that can be lost, and a solid from the liquid material. By separating the components and depositing them, a sheet forming process for forming a sheet mainly composed of a conductive substance and a disappearing substance and a disappearing substance contained in the sheet are eliminated to form pores inside the sheet. In the method for producing a gas diffusion layer of a solid polymer electrolyte fuel cell, which sequentially performs a pore forming step for forming a gas diffusion layer having gas diffusivity, the liquid material contains a solid resin, The resin contained in the gas diffusion layer is supported.

  The solid resin contained in the liquid material is carried on the gas diffusion layer. Such a gas diffusion layer is moderately hard while having appropriate flexibility. When the gas diffusion layer is sandwiched between separators, the pores of the gas diffusion layer are not easily crushed.

  According to the method of the present invention, the solid resin contained in the liquid material is supported on the sheet, that is, the gas diffusion layer. The gas diffusion layer carrying the resin is moderately harder than when no resin is carried. For this reason, even when the gas diffusion layer is sandwiched between separators, it is possible to prevent the pores formed inside the gas diffusion layer from being crushed excessively. Furthermore, even when the gas diffusion layer is sandwiched between the separators, it is possible to prevent a part of the gas diffusion layer from bulging into the flow path of the gas flow path where the separator is formed. As a result, it can suppress that a gas flow path becomes small too much.

  By the way, a method of curing after impregnating a liquid resin into a sheet is also conceivable. However, in this method, the impregnated and cured resin closes the pores inside the sheet, which may cause a problem that the frequency of reducing the pore volume increases. Since the pores of the sheet can function as a gas flow path and a water discharge path as described above, it is not preferable to reduce the pores of the sheet. Furthermore, in the method of curing after impregnating the liquid resin, there is a possibility that the surface of the carbon fiber is cured in a state where the liquid resin is coated. In this case, the malfunction which impairs the electroconductivity of carbon fiber arises. In this respect, if the solid resin is included in the liquid material as the starting material as in the method of the present invention, the solid resin is supported on the sheet before the pores are formed, so the above-described problems are suppressed. Is done.

  According to the method of the present invention, a step of preparing a liquid material mainly composed of a conductive material having conductivity and a disappearable disappearing material, and separating the solid content from the liquid material, the conductive material and the disappearing material are separated. A sheet forming step of forming a sheet as a main component by depositing solid content and a pore forming step of forming pores inside the sheet by eliminating the disappearing substance contained in the sheet are sequentially performed.

  Furthermore, it is preferable to impregnate the sheet with a water repellent material between the sheet forming step and the pore forming step. The water repellent material has a function of suppressing the gas passage from being clogged with water. Examples of the water repellent material include fluororesins such as tetrafluoroethylene (PTFE), tetrafluoroethylene / ethylene copolymer (ETFE), and tetrafluoroethylene / perfluoroalkoxyethylene copolymer (PFA).

  The conductive material having conductivity contained in the liquid material as the starting material may be fibrous or particulate. As the conductive material, carbon-based materials can be generally used in consideration of corrosion resistance, conductivity, and the like. Examples of carbon-based materials include carbon fibers and carbon particles. Examples of the conductive fiber such as carbon fiber include those having a diameter of 2 to 50 μm, particularly 7 to 18 μm, and a length of 1 to 50 mm, particularly 3 to 24 mm, but are not limited thereto.

  As the erasable substance contained in the liquid material, an organic substance that burns down by heating to form pores can be employed. Examples of such organic substances include plant organic substances such as pulp. Pulp is advantageous for capturing conductive materials such as carbon fibers during papermaking. The pulp has the above-described capturing ability and water absorption. The liquid as the starting material contains a solid resin. The solid resin contained in the liquid material is carried on the sheet together with a conductive material such as carbon fiber. Resins contained in liquid materials include those whose main chain has a carbon-carbon bond, those whose main chain has a bond between carbon and a non-carbon element, those whose main chain has a bond between carbon and a benzene ring Etc. can be illustrated. In general, a thermosetting resin or a thermoplastic resin can be employed.

  The thermosetting resin contained in the liquid material as the starting material can be in a state before thermosetting or a state after thermosetting. When a heat treatment such as firing is applied to the sheet as a post-process, an uncured thermosetting resin that has not been cured is mixed in a liquid material, and the thermosetting resin is supported on the sheet, and then A method of curing the thermosetting resin in the sheet by a heat treatment as a post process can be employed. When a heat treatment for eliminating the disappearance substance such as pulp carried on the sheet by combustion is performed, the thermosetting resin can be thermoset simultaneously with the heat treatment. In this case, it is not necessary to provide a process for thermosetting the thermosetting resin. However, when it is desired to further control the sheet thickness, the porosity in the sheet, and the surface state of the sheet, a hot press treatment may be performed before the heat treatment. When a phenol resin is used as the thermosetting resin, a hot press treatment at a temperature of 160 to 200 ° C., a press pressure of 2 to 10 MPa, and a press time of 1 to 10 minutes can be exemplified.

  In addition, when heat processing are not performed at a post process, the thermosetting resin after thermosetting can be contained in a liquid substance. As the thermosetting resin, phenol resin, epoxy resin, diallyl phthalate resin, unsaturated polyester resin, furan resin, urea resin, alkyd resin, melamine resin, silicone resin, or the like can be used. If it is a thermoplastic resin, when heat processing, such as baking, is considered, a thing with comparatively high heat-resistant temperature is employable. As the thermoplastic material, polyphenylene sulfide (PPS), polyether sulfone (PES), polyether ether ketone (PEEK) resin material, and the like can be used. When heat treatment is not performed in a subsequent process, or when the heat temperature is low even if heat treatment is performed, a general thermoplastic resin can be employed.

  As the resin (thermosetting resin, thermoplastic resin) contained in the liquid material described above, a form in the form of powder particles can be adopted. Although it can select suitably as a particle size, it can be set to 2-20 micrometers, 10-50 micrometers, and 20-100 micrometers. If the particle size is too small, there is a limit in adjusting the hardness of the gas diffusion layer. If the particle size is excessive, surface irregularities may be formed in the gas diffusion layer.

  If the resin is in the form of powder particles, the conductive material such as carbon fiber is prevented from being covered with the resin, and thus the conductivity of the conductive material is suppressed from being lowered. When the sheet is impregnated with a liquid resin, the area covering the conductive material such as carbon fiber increases, and the conductivity of the conductive material such as carbon fiber may be reduced.

  According to the method of the present invention, the pore forming step is a step of forming the pores by disappearing the disappearing substance of the sheet by burning by holding the sheet by heating, and in addition, the thermosetting resin of the sheet is heated. A form to be cured can be employed. In this case, it is not necessary to newly provide a step of thermosetting the thermosetting resin.

  Embodiments of the present invention will be specifically described below with reference to FIGS.

(Example)
Carbon fiber (conductive material) short fiber (typically 13μm in diameter and 3mm in length), pulp (disappearing material), and solid powdery phenol resin (Kanebo Co., Ltd.) as thermosetting resin Company Bell Pearl S890) is mixed with water in the container at a predetermined ratio and beaten in water to uniformly disperse carbon fiber, pulp and powdered phenol resin (liquid material 10) ) Was produced. The phenol resin is an uncured resin that has not undergone a curing reaction, and has an average particle diameter of 20 to 30 μm and a spherical shape. The predetermined ratio was carbon fiber: pulp: phenol resin = 6: 2: 2 by weight.

  The papermaking slurry 10 was subjected to papermaking using a mesh member. That is, the solid content and the liquid content contained in the papermaking slurry were separated by a mesh member to produce a thin sheet 20 having a thickness of about 0.3 mm (see FIG. 4). Therefore, the thin sheet 20 contains carbon fiber, pulp, and a solid powder particulate phenol resin as a thermosetting resin as main components. When pulp is not contained in the papermaking slurry 10 during the papermaking process, it is difficult to capture the carbon fibers and the solid powdery phenol resin. Since pulp is contained in the papermaking slurry 10, carbon fibers and solid powdery phenol resin are supported on the thin sheet 20. Thus, the pulp can function as a capture promoter.

  FIG. 3 shows a state where the thin sheet 20 formed by papermaking is being conveyed in a roll. As described above, the thin sheet 20 is conveyed while being bent between the plurality of rolls 500 in the manufacturing process. At this time, since the phenol resin carried on the thin sheet 20 has not finished the curing reaction, the thin sheet 20 is more flexible than after the curing reaction. Therefore, the thin sheet 20 can be easily rolled and conveyed between the rolls 500.

  In this example, a paste formed by mixing and dispersing the conductive material carbon black (Vulcan XC-72) and water repellent material (PTFE dispersion Daikin Industries D-1) at a weight ratio of 2: 1 was used. . This paste was impregnated into the thin sheet 20 from the surface to the inside by roll coating (see FIG. 4). Thereafter, the thin sheet 20 impregnated with the paste was dried, heated and held at a predetermined temperature (380 ° C.), and fired. The pulp contained in the thin sheet 20 was burned (disappeared) by firing, and the traces of the pulp were made into pores 22 (see FIG. 5). Since the pulp is fibrous, it is assumed that the pores 22 which are pulp marks basically have a shape corresponding to the carrying form of the pulp and become continuous pores with good gas permeability. Further, the powdered phenol resin is thermally cured in the thin sheet 20 by firing. The thermoset phenolic resin is harder than 20 water repellent material (PTFE) carried on a thin sheet.

  Thereafter, the thin sheet 20 was pressed in the thickness direction by hot pressing. Thus, the thickness was adjusted to be uniform in the plane, and the porous gas diffusion layer 100 according to the example was formed. The gas diffusion layer 100 basically includes carbon fibers as a conductive material, carbon black as a conductive material, a water repellent material (PTFE), and a thermosetting phenol resin as main components.

  As described above, according to the present embodiment, the papermaking slurry 10 (liquid material) as a starting material contains a solid powder particulate phenol resin in addition to carbon fibers and pulp. Therefore, the thin sheet 20 to be the gas diffusion layer 100 can carry a solid powder particle-form phenolic resin. Therefore, it is not necessary to employ a method of impregnating the inside of the sheet with a liquid resin. Therefore, it is suppressed that resin covers the carbon fiber which has electroconductivity with a large area, and the electroconductivity of the carbon fiber for ensuring the electroconductivity of the gas diffusion layer 100 is maintained favorable.

  Furthermore, since the gas diffusion layer 100 is formed of the carbon sheet carrying the phenol resin, the flexibility of the gas diffusion layer 100 can be reduced more than necessary, and the gas diffusion layer 100 can be made to have an appropriate hardness.

  FIG. 1 schematically shows a state in which the gas diffusion layer 100 is incorporated in the fuel cell together with the separator 200. As shown in FIG. 1, catalyst layers 410 and 420 are disposed between the gas diffusion layer 100 made of a carbon sheet and the electrolyte membrane 400. The catalyst layers 410 and 420 include a catalyst material such as platinum, an electron conductive material such as carbon black, and an electrolyte material. As shown in FIG. 1, the gas diffusion layer 100 made of a carbon sheet is sandwiched between separators 200 from both sides in the thickness direction. In this case, the convex part 220 which forms the gas flow path 210 of the separator 200 is formed, and the gas diffusion layer 100 is pressurized by the front end surface 220a of the convex part 220 in the thickness direction. Here, the gas diffusion layer 100 made of a carbon sheet contains a thermosetting resin that has been subjected to a thermosetting reaction, and has an appropriate hardness. For this reason, in the gas diffusion layer 100, in the region 101 facing the convex portion 220 of the separator 200, the possibility that the internal pores 22 are crushed is suppressed.

  Here, the pores 22 formed in the gas diffusion layer 100 have a gas permeation function for allowing a reaction gas such as a fuel gas or an oxidant gas to pass therethrough, and a water discharge function for discharging water generated by the power generation reaction. Have In the present embodiment, since excessive crushing of the pores 22 is suppressed, both the above-described gas permeation function and water discharge function are ensured well, and the power generation performance of the fuel cell is improved.

  Furthermore, since the gas diffusion layer 100 formed of the carbon sheet is appropriately hardened in the thickness direction by the thermosetting resin, even when the gas diffusion layer 100 is sandwiched in the thickness direction by the separator 200, Unlike the conventional embodiment shown in FIG. 7, the gas diffusion layer 100 is suppressed from bulging into the gas flow path 210 of the separator 200. Therefore, it is advantageous to ensure the cross-sectional area of the gas flow path 210 of the separator 200. Accordingly, good gas supply performance through the gas flow path 210 of the separator 200 is ensured.

  Further, according to this example, the heat treatment (baking) for forming the pores 22 by eliminating the pulp contained in the thin sheet 20 is performed, and at the same time, the thermosetting resin particles before curing are thermally cured. Can be made. Therefore, there is no increase in the number of processes, which is advantageous for cost reduction. In addition, according to the present embodiment, the heat treatment (firing) for eliminating the pulp and forming the pores 22 is performed, and at the same time, the thermosetting resin particles before curing are thermally cured, so that the heat treatment (firing) is performed. The thermosetting resin has not completed the curing reaction until the process is carried out. Therefore, the thin sheet 20 before carrying out heat treatment (firing) has good flexibility. Therefore, roll transportability, which is an advantage of the conventional papermaking method, is secured, and productivity is secured.

(Comparative example)
The comparative example was basically manufactured in the same manner as the example. However, the papermaking slurry according to the comparative example does not contain phenol resin powder particles. In the comparative example, first, carbon fiber short fibers (typically 13 μm in diameter and 3 mm in length) and pulp are mixed at a predetermined ratio (6: 4) and beaten in water. Thus, a papermaking slurry in which carbon fibers and pulp were uniformly dispersed was prepared. The papermaking slurry was processed into a net-like member, and the liquid content and solid content contained in the papermaking slurry were separated to produce a thin sheet having a thickness of about 0.3 mm as in the above example. Then, a paste in which carbon black (Vulcan XC-72) and water repellent material (PTFE dispersion Daikin Industries D-1) were mixed and dispersed at a weight ratio of 2: 1 was used, and this paste was applied to the thin sheet on the surface thereof. Then, it was impregnated with a roll coat, dried and fired at 380 ° C. to burn (disappear) the pulp contained in the thin sheet. Thereafter, the sheet was hot-pressed to adjust the thickness to be uniform in the plane, and a carbon sheet according to a comparative example was obtained.

(Power generation performance)
Using the gas diffusion layer obtained by the above method as an electrode, the power generation performance of the fuel cells of Examples and Comparative Examples was evaluated under basically the same conditions. In order to evaluate the power generation performance of the fuel cell, a membrane electrode assembly having an electrode size of 12 cm × 12 cm was produced. Then, the membrane electrode assembly was assembled with two separators sandwiched in the thickness direction (see FIG. 1). A carbon fired product was used as the separator. The gas flow path of the separator is straight. The obtained IV characteristics are shown in FIG. The horizontal axis in FIG. 6 represents current density (relative display), and the vertical axis in FIG. 6 represents voltage (relative display). As shown in FIG. 6, the power generation performance of the example was better than that of the comparative example.

(Other)
If heat treatment conditions such as temperature, treatment time, and press pressure are studied, resin materials such as thermoplastic materials such as polyphenylene sulfide (PPS), polyether sulfone (PES), and polyether ether ketone (PEEK) can be used. is there.

(Other)
In the above-described embodiments, the phenol resin contained in the papermaking slurry 10 as a starting material is an uncured resin that has not undergone a curing reaction, but may be in a semi-cured state depending on the case. In addition, the present invention is not limited to the embodiments described above and shown in the drawings, and can be implemented with appropriate modifications within a range not departing from the gist.

  The present invention can be used in a method for producing a gas diffusion layer of a solid polymer electrolyte fuel cell.

It is sectional drawing which shows typically the fuel cell incorporating the gas diffusion layer which concerns on an Example. It is a block diagram which shows typically the process in which carbon fiber, pulp, and a solid powdery phenol resin are blended to form a papermaking slurry. It is a block diagram which shows the state which is carrying out the roll conveyance of the thin sheet. It is a block diagram which shows typically the form which impregnates the thin sheet | seat from the surface with the paste containing carbon black and a water repellent material. It is a block diagram which shows the gas diffusion layer formed with the carbon sheet which has a pore. It is a graph which shows the result of having performed the electric power generation test using the fuel cell incorporating the gas diffusion layer concerning an example, and the fuel cell incorporating the gas diffusion layer concerning a comparative example. It is sectional drawing which shows typically the fuel cell incorporating the gas diffusion layer which concerns on a prior art.

Explanation of symbols

  In the figure, 100 is a gas diffusion layer, 200 is a separator, 210 is a gas flow path, 220 is a convex portion, 10 is a slurry, 20 is a thin sheet, and 22 is a pore.

Claims (5)

A step of preparing a liquid material mainly composed of a conductive material having conductivity and a disappearable material that can be lost;
A sheet forming step of forming a sheet containing the conductive material and the disappearing material as main components by separating and depositing solids from the liquid material;
A solid polymer electrolyte fuel that sequentially performs a pore forming step of forming a gas diffusion layer having gas diffusibility by eliminating a disappearing substance contained in the sheet and forming pores inside the sheet In the manufacturing method of the gas diffusion layer of the battery,
The method for producing a gas diffusion layer of a solid polymer electrolyte fuel cell, wherein the liquid material contains a solid resin, and the resin contained in the liquid material is supported on the gas diffusion layer.   2. The method for producing a gas diffusion layer of a solid polymer electrolyte fuel cell according to claim 1, wherein the resin contained in the liquid material is a thermosetting resin.   3. The method for producing a gas diffusion layer of a solid polymer electrolyte fuel cell according to claim 1, wherein the resin contained in the liquid material is in the form of powder particles.   The solid polymer electrolyte fuel according to any one of claims 1 to 3, wherein the sheet is impregnated with a water repellent material between the sheet forming step and the pore forming step. A method for producing a gas diffusion layer of a battery.   5. The pore forming step according to claim 1, wherein the pore forming step is a step of forming pores by causing the disappearing substance of the sheet to disappear by combustion by heating and holding the sheet. In addition, a method for producing a gas diffusion layer of a solid polymer electrolyte fuel cell, wherein the thermosetting resin of the sheet is thermoset.

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