JP4650673B2 - Separator material for fuel cell and manufacturing method thereof - Google Patents

Description

  The present invention relates to a separator material for a fuel cell such as a polymer electrolyte fuel cell and a phosphoric acid fuel cell, and a method for producing the same.

  A fuel cell directly converts chemical energy contained in fuel into electrical energy and has high conversion efficiency into electrical energy. For example, a polymer electrolyte fuel cell can generate electricity at a relatively low temperature and high output. Therefore, it is expected as a small mobile power source including an automobile power source.

  The polymer electrolyte fuel cell is usually an electrolyte membrane made of a polymer ion exchange membrane such as a fluororesin ion exchange membrane having a sulfonic acid group, and a catalyst electrode carrying a catalyst such as platinum on both sides thereof, A stack in which single cells made of separators and the like provided with unevenness (grooves) for supplying a fuel gas such as hydrogen or an oxidant gas such as oxygen or air are stacked on each electrode, and 2 provided on the outside thereof It consists of two current collectors.

  As shown in FIG. 2, the unit cell has a pair of electrodes 8 and 9 (cathode 8 and anode 9) disposed with an electrolyte membrane 10 made of an ion exchange membrane formed of, for example, a fluorine resin, The separator 6 is formed of a dense carbon material sandwiched from both sides, and the end portion of the separator is formed of a sealing material 11 made of fluoro rubber, fluoro rubber, or the like installed in a direction parallel to the gas groove. The electrodes 8 and 9 are formed of a porous body made of short carbon fibers carrying a catalyst such as platinum or a carbon black carrying a catalyst bound with a resin.

  A plurality of concave and convex grooves 7 are formed in the separator 6, and a space formed between the grooves 7 and the cathode 8 serves as an oxidant gas (oxygen-containing gas such as oxygen or air) flow path, and the grooves 7 and the anode 9 is used as a fuel gas (for example, hydrogen gas or a mixed gas containing hydrogen gas as a main component) flow path, and a chemical reaction that occurs when the fuel gas and oxidant gas are in contact with the electrode is used. Thus, current is taken out between the electrodes. In general, the battery stack is assembled by laminating the single cells into tens to hundreds.

The power generation mechanism of this fuel cell has a fuel gas (for example, hydrogen gas) supplied to the anode side of the cell and an oxidant gas (for example, oxygen gas) supplied to the cathode side that comes into contact with the electrode as described below. Electrons (e ⁻ ) generated by the reaction are taken out from the electrodes as electric energy.
Anode side; H ₂ → 2H ⁺ + 2e ⁻
Cathode side; (1/2) O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O
Total reaction: H ₂ + (1/2) O ₂ → H ₂ O

  Therefore, since it is necessary for the separator to supply the electrode with the fuel gas and the oxidant gas completely separated, a high degree of gas impermeability is required. In order to increase the power generation efficiency, it is effective to reduce the internal resistance of the battery, and it is necessary to reduce the plate thickness of the separator and to have high conductivity.

  In order to improve battery performance, the single cells in the stack are assembled so that they are in close contact with each other, and a good contact state is maintained even during power generation to prevent an increase in the contact electrical resistance between the separator and the electrode. At the same time, it is important to prevent gas leakage between single cells and gas leakage outside the single cells. That is, it is important that the material strength is high so that no breakage or breakage occurs during assembly, and that the material strength is sufficient even at a temperature of about 80 to 120 ° C., which is the operating temperature of the battery.

  Carbonaceous materials are suitable for separator materials that require such material characteristics, but graphite materials are difficult to process, and further, the material is not airtight and gas impermeability is not sufficient. There are difficulties. In addition, the glassy carbon material has a dense material structure and excellent gas impermeability, but has a drawback of poor cutting workability due to its high hardness and brittleness.

  Therefore, conventionally, a carbon / resin-cured molded body obtained by binding a carbonaceous powder such as graphite with a thermosetting resin as a binder has been used suitably, and many inventions relating to this have been proposed.

For example, Patent Document 1 discloses a plate-shaped molded body composed of 60 to 85% by weight of graphite powder having a particle size distribution with an average particle size of 50 μm or less and a maximum particle size of 100 μm or less, and 15 to 45% by weight of a thermosetting resin. Thus, a graphite-resin curable molding having a material property with a specific resistance in the plane direction of 300 × 10 ⁻⁴ Ωcm or less, a ratio of specific resistance in the thickness direction / plane direction of 7 or less, and a bending strength of 300 kgf / cm ² or more. A separator member for a polymer electrolyte fuel cell and a method for manufacturing the same have been proposed.

  Patent Document 2 has a composition of 40 to 90% by weight of carbon powder and 60 to 10% by weight of a thermosetting resin, has a bending strength at room temperature of 30 MPa or more, and a bending strength reduction rate from room temperature to 100 ° C. There has been proposed a separator member for a polymer electrolyte fuel cell, which is formed from a carbon-resin cured molded body having a characteristic of 30% or less, and a method for producing the same.

  However, in a separator material made of a carbon / resin-cured molded body, when the ratio of the carbonaceous powder is increased in order to increase the conductivity, there is a drawback that the material becomes brittle and easily breaks accordingly. That is, when stacking single cells, the battery stack cannot be assembled with a sufficient tightening force, and there is a problem that it is difficult to reduce the contact resistance between the single cells.

  In order to solve these problems, it has been proposed to use an elastomer having elasticity instead of a thermosetting resin as a binder for carbonaceous powder such as graphite.

  For example, Patent Document 3 discloses a rubber composition in which 100 to 150 parts by weight of graphite powder and 80 to 150 parts by weight of carbon black are blended with 100 parts by weight of rubber components such as butyl rubber, fluororubber, and epichlorohydrin rubber. A fuel cell separator material has been proposed.

Patent Document 4 discloses a fuel cell comprising a compound compound of a resin / carbon composite material made of carbon whose surface is coated with a phenol resin and a rubber / carbon composite material made of ethylene / propylene rubber and carbon. A separator is disclosed.
JP 2000-021421 A JP 2000-243409 A JP 2001-216777 A JP 2003-308553 A

  As described above, when a thermosetting resin is used as a binder, there is a problem that the material becomes brittle and easily cracked. On the other hand, the use of an elastic elastomer such as rubber as a carbonaceous powder binder increases the breaking strain. It is possible to impart material properties that are difficult to break. However, when the mixing ratio of the graphite powder is increased in order to improve conductivity, a decrease in tear strength is observed. For example, when the mixing weight ratio is 80% by weight or more, the tear strength is remarkably decreased. Thus, a separator material for a fuel cell having sufficient characteristics in any binder is desired.

Therefore, as a result of diligent research on the solution of this problem, the inventors have covered the organic material sheet having a through hole with a mixture of carbonaceous powder and resin binder, so that the resin bond is not limited to the thermosetting resin. without such flexible elastomeric, be any resin binder, hardly and lose split to increase the break strain, tear strength impaired by high loading carbonaceous powder in order to secure high conductivity It was found to be able to improve the decrease.

That is, an object of the present invention is to provide a fuel cell separator material having an increased fracture strain and an improved reduction in tear strength, and a method for producing the same.

In order to achieve the above object, the separator material for a fuel cell according to claim 1 has an average particle diameter of 50 μm or less and a maximum particle on both surfaces of an organic sheet having an opening area ratio (R) of through holes of 25 to 85%. A mixture of graphite powder having a diameter of 100 μm or less and a resin binder mixed at a weight ratio of 90:10 to 65:35 is coated, and the mixture of the graphite powder and the resin binder is filled in the through holes of the organic sheet. It is characterized by being made. However, the opening area ratio (R) is the ratio of the opening area per unit area (opening area / total area × 100). The organic sheet is enlarged to an appropriate magnification and photographed, and this is divided into meshes. The number of openings is counted and divided by the total number of meshes.

Method for manufacturing a fuel cell separator material according to claim 2 is the method for producing a separator material for a fuel cell according to claim 1, wherein the graphite powder and a resin binder and a 90: 10-65: 35 by weight of were mixed in a ratio, the mixture ratio of the aperture area size of the through-hole (R) is deposited on both surfaces of the organic sheet is 25% to 85%, characterized by hot press molding.

A method for producing a fuel cell separator material according to claim 3 is a method for producing a fuel cell separator material according to claim 1, wherein the graphite powder and the resin binder are mixed in a weight of 90:10 to 65:35. sheeted mixed at a ratio, the opening area ratio of the through-hole of the sheet (R) abuts by adhering to both surfaces of the organic sheet is 25% to 85%, characterized by hot press molding. In the present invention, as the carbonaceous powder mixed with the resin binder, graphite powder having an average particle size of 50 μm or less and a maximum particle size of 100 μm or less is used. This graphite powder is simply referred to as carbonaceous powder.

  According to the separator material for a fuel cell of the present invention, the mixture layer of the carbonaceous powder and the resin binder is laminated on both surfaces of the organic material sheet in which the opening area ratio (R) of the through holes is in a specific range, and the organic material sheet penetrates. By having a structure filled with a mixture of carbonaceous powder and resin binder in the pores, it effectively improves the reduction in tear strength that occurs when carbonaceous powder is highly blended to ensure high conductivity. It becomes possible. In addition to the flexible elastomer, various properties such as tear strength can be remarkably improved by sandwiching the organic sheet with a resin binder having poor flexibility. And according to the manufacturing method of this invention, the separator material for fuel cells which has such an outstanding property can be manufactured easily.

  FIG. 1 is a perspective view showing the structure of a fuel cell separator material according to the present invention, wherein 1 is a fuel cell separator material, 2 is a mixture layer of carbonaceous powder and resin binder, and 3 is in a through hole of an organic material sheet. Is a packed layer filled with a mixture of carbonaceous powder and resin binder, 4 is an organic material sheet, 5 is a mixture of carbonaceous powder and resin binder filled in through holes (voids) of the organic material sheet It is. And it consists of the structure where the mixture layer 2 was laminated | stacked on both upper and lower surfaces of the filling layer 3. FIG.

  With this structure, the packed layer 3 is given a property of being hard to break due to an increased fracture strain due to the resin binder component of the mixture 5 of the carbonaceous powder and the resin binder filled in the through holes of the organic sheet 4. . The mixture layer 2 of the carbonaceous powder and the resin binder on both the upper and lower surfaces of the filling layer 3 has a conductive path formed by the mixture 5 of the carbonaceous powder and the resin binder filled in the through holes of the organic sheet 4. Therefore, it is possible to ensure the overall good conductivity.

  In this way, by having a structure in which the mixture layer 2 is laminated on the upper and lower surfaces of the filling layer 3 using the resin binder as a binder of carbonaceous powder, the breaking strain can be increased, and further high conductivity can be achieved. Therefore, it is possible to effectively improve the decrease in tear strength that occurs when the carbonaceous powder is blended in a high amount to ensure the above.

  Thermosetting materials such as olefin, vinyl, styrene, ethylene, urethane, ester, amide, polypropylene, fluororesin, etc., phenol resin, silicone resin, epoxy resin, etc. Resin or the like is used.

  And, as an organic material sheet having a through-hole, in addition to the above-mentioned resins such as plain weave, twill weave, twill tatami mat, rhombus, turtle shell, etc., card type, wet or dry paper-made chemical bond, thermal bond spunlace or Examples include nonwoven fabrics such as spun bond, melt blow type, flash spinning, and tow opening type.

  In this case, in order to achieve both the electrical resistance and the tear strength of the separator material, it is necessary to set the opening area ratio (R) of the through holes of the organic material sheet to 25 to 85%. This is because if the opening area ratio (R) is less than 25%, the electrical resistance increases, whereas if it exceeds 85%, the tear strength decreases greatly. The opening area ratio (R) is the ratio of the opening area per unit area (opening area / total area × 100). The organic material sheet is enlarged to an appropriate magnification and photographed, and this is divided into meshes to obtain the opening. Is divided by the total number of meshes and multiplied by 100.

  In order to sufficiently fill the inside of the through hole of the organic sheet with the mixture of the carbonaceous powder and the resin binder, the opening diameter of the through hole is preferably 0.1 mm or more, and the through opening diameter is It can be provided by machining, cutting or laser processing.

  In order to provide a certain degree of flexibility and strength as an organic material sheet having a through hole, for example, it is preferable that the Taber stiffness is small, and it is measured by JIS P8125-1976 “Test method for stiffness of paperboard by load bending method”. The Taber stiffness is preferably 10 mN · m or less, and the sheet thickness is preferably 500 μm or less.

In the present invention, graphite powder is used as the carbonaceous powder to be mixed with the resin binder , and artificial graphite, natural graphite, expanded graphite, or a mixture thereof is applied as graphite, and is pulverized by an appropriate pulverizer. Then, the particle size is adjusted by sieving. The particle size of the graphite powder is adjusted to an average particle size of 50 μm or less and a maximum particle size of 100 μm or less in order to prevent dropping of graphite powder particles and generation of cracks between particles when providing gas grooves in the separator. . In addition to graphite powder, for example, short carbon fibers having a diameter of 50 μm or less and a length of about 10 to 200 μm can be used in combination.

  The resin binder is not particularly limited as long as it has acid resistance to an electrolyte such as sulfonic acid and heat resistance that can withstand the operating temperature of the fuel cell, and either a thermosetting resin or a thermoplastic resin can be used.

  For example, as the thermosetting resin, for example, a resol type phenol resin, a phenol resin represented by a novolac type phenol resin, a furfuryl alcohol resin, a furfuryl alcohol furfural resin, a furfuryl alcohol phenol resin, or the like. , Polyimide resin, polycarbodiimide resin, polyacrylonitrile resin, pyrene-phenanthrene resin, polyvinyl chloride resin, epoxy resin, urea resin, diallyl phthalate resin, unsaturated polyester resin, melamine resin, and the like. A combination of the above can be used.

  Examples of the thermoplastic resin include acrylonitrile butadiene styrene (ABS) resin, acrylonitrile styrene copolymer (AS), high impact polystyrene (HIPS), polystyrene (PS), methyl methacrylate butadiene styrene copolymer (MBS), methacryl. Styrenic resins such as acid methyl-styrene copolymer (MS), acrylonitrile ethylene propylene rubber styrene copolymer (AES), acrylonitrile styrene acrylate (AAS), polyethylene (PE), polypropylene (PP), polybutene-1, ethylene Polyolefin resins such as vinyl acetate copolymer (EVA) and ethylene vinyl alcohol copolymer (EVOH), polyamide resins, thermoplastic polyester resins, polycarbonate (PC) resins, wholly aromatic polymers Ester resin, polyphenylene sulfide (PPS), vinyl chloride resin (PVC), polysulfone resin, polyether ether ketone resin, (modified) polyphenylene ether resin, polyoxymethylene (POM), polymethyl methacrylate (acrylic) (PMMA) , Fluororesin, polyketone (PK), norbornene, polyamideimide (PAI), polyphthalamide (PPA), and the like. These can be used alone or in admixture of two or more.

  In addition, in the case of elastomers, isoprene-based elastomers, butadiene-based elastomers, diene-based elastomers, olefin-based elastomers, ether-based elastomers, polysulfide-based elastomers, urethane-based elastomers, fluorine-based elastomers, silicone-based elastomers, and blends of two or more of these are blended. In addition to elastomers, flexible thermosetting resins such as thermoplastic elastomers and epoxy resins, blends with the above-mentioned thermosetting resins and thermoplastic resins, and thermosetting resin modified elastomers are used. You can also.

  The mixture of the carbonaceous powder and the resin binder is obtained by mixing the carbonaceous powder and the resin binder in a weight ratio of 90:10 to 65:35. When the weight ratio of the carbonaceous powder exceeds 90% by weight and the resin binder is less than 10% by weight, the fluidity of the mixture is reduced due to the small amount of the resin binder, and the structure becomes non-uniform. If it is less than 65% by weight and the resin binder exceeds 35% by weight, the amount of carbonaceous powder is reduced, so that the electrical resistance of the separator is increased and the battery performance is lowered.

  As described above, the fuel cell separator material of the present invention is obtained by applying 90:10 to 65:35 carbonaceous powder and resin binder on both surfaces of an organic material sheet having an opening area ratio (R) of through holes of 25 to 85%. It is characterized by comprising a structure in which a mixture mixed at a weight ratio of is coated, and further, a structure in which a mixture of carbonaceous powder and resin binder is filled in the through-holes of the organic material sheet, resulting in gas impermeability, Excellent material strength and electrical conductivity, etc. In addition, it is difficult to break due to large fracture strain, and also effectively reduces the tear strength that is impaired by high blending of carbonaceous powder to ensure high electrical conductivity. Can be improved.

  In the method for producing a separator for a fuel cell according to the present invention, carbonaceous powder and a resin binder are mixed at a weight ratio of 90:10 to 65:35, and the mixture has an opening area ratio (R) of 25 through holes. It is characterized by being applied to both sides of an organic material sheet of ˜85% and hot pressing.

  The carbonaceous powder and the resin binder are mixed at a weight ratio of 90:10 to 65:35 and mixed sufficiently with an appropriate kneader such as a kneader, a pressure type kneader, or a twin screw kneader. To produce a uniform mixture. The carbonaceous powder is preferably used after adjusting the particle size to an average particle size of 50 μm or less and a maximum particle size of 100 μm or less.

  After coating the mixture by a method such as coating so that the opening area ratio (R) of the through-holes has a predetermined thickness on both surfaces of the organic material sheet having a ratio of 25 to 85%, the mixture is put in a mold and an appropriate temperature, Hot pressing is performed under pressure, for example, at a temperature of 150 to 250 ° C. and a pressure of 10 to 50 MPa. During the hot pressing, the mixture is press-fitted and filled into the through holes of the organic material sheet.

  Thus, the mixture layer of the carbonaceous powder and the resin binder is formed on the upper and lower surfaces of the filling layer 3 in which the mixture of the carbonaceous powder and the resin binder is filled in the through hole of the organic sheet illustrated in FIG. The separator material for fuel cells which consists of the structure in which 2 was formed is manufactured.

  In another method for manufacturing a fuel cell separator material according to the present invention, a carbonaceous powder and a resin binder are mixed at a weight ratio of 90:10 to 65:35 to form a sheet, and the sheet is opened in a through hole. The organic material sheet having an area ratio (R) of 25 to 85% is in contact with and attached to both surfaces, and is subjected to hot pressing.

  This method is a method of coating a mixture sheet of carbonaceous powder and a resin binder on both the upper and lower surfaces of an organic sheet, and preparing a sheet of the mixture and covering the mixture sheet in contact with both sides of the organic sheet. There is an advantage that the operation becomes easy.

  Examples of the present invention will be specifically described below in comparison with comparative examples.

Examples 1-2 and Comparative Examples 1-6
Scale-like graphite powder with an average particle size of 40 μm and a maximum particle size of 80 μm or less was mixed using a two-component addition-type cured silicone rubber, which is a flexible elastomer, as a resin binder, and these were mixed at different weight ratios. Then, the mixture was sufficiently kneaded with a kneader to prepare a uniform mixture.

  As the organic sheet, non-woven fabrics having a thickness of 400 μm having different opening area ratios (R) of through-holes by using a papermaking method using olefin-based yarns were used. The mixture of the above scaly graphite powder and silicone rubber was applied to both surfaces of this olefin sheet.

  Next, a 300 mm × 480 mm × 1 mm fuel cell separator material having a three-layer structure as shown in FIG. 1 is formed by hot pressing under conditions of a temperature of 180 ° C. and a pressure of 15 MPa for 5 minutes. Manufactured.

Example 3
A flaky graphite powder whose average particle size is 40 μm and the maximum particle size is adjusted to 80 μm or less and flexible nylon as a thermoplastic resin are mixed at a weight ratio of 70:30, and the mixture is sufficiently kneaded by a kneader to obtain a uniform mixture. Created.

Example 4
A flaky graphite powder whose average particle size is 40 μm and the maximum particle size is adjusted to 80 μm or less and a flexible polyester as a thermoplastic resin are mixed at a weight ratio of 70:30, and the mixture is sufficiently kneaded by a kneader to obtain a uniform mixture. Created.

Comparative Examples 7-9
A scaly graphite powder adjusted to a particle size of an average particle size of 40 μm and a maximum particle size of 80 μm or less and a two-component addition-type cured silicone rubber are mixed at a weight ratio of 80:20 and sufficiently mixed by a kneader to obtain a uniform mixture. Produced. This mixture was put in a mold and subjected to hot pressure molding under conditions of a temperature of 180 ° C. and a pressure of 15 MPa to produce a fuel cell separator material.

  About these separator materials, tear strength, electrical resistance, etc. were measured by the following method, and the obtained results are shown in Table 1.

(1) Tear strength (N / mm);
The measurement was made in accordance with JIS K6252 with the “angle type with cut”.
The measurement was carried out at a width of 19 ± 0.05 mm and a thickness of 1 mm.
(2) Breaking strain;
It was measured according to JIS K6252.
In addition, measured at a thickness of 1 mm.
(3) Electric resistivity (mΩ · cm);
The length direction was measured according to JIS C2525.
Specimen dimensions: width 4mm x length 35mm x thickness 1mm
(4) Gas permeation amount (cm ³ / cm ² · min);
The nitrogen gas permeation amount when a pressure of 1 kg / cm ² was applied with nitrogen gas was measured.
Specimen size: 70mm diameter x 1mm thickness

  From the results shown in Table 1, in Comparative Examples 1 and 3 having a large opening area ratio (R) of the through holes as compared with Examples 1 to 4, the tear strength was significantly reduced, whereas the opening area ratio (R) of the through holes was small. In Comparative Examples 4 and 6, the electrical resistivity is high. Further, it can be seen that in Comparative Examples 1 and 2 where the weight ratio of the graphite powder is small, the electrical resistivity is high, and in Comparative Examples 5 and 6 where the weight ratio of the resin weight ratio is small, the gas permeation amount is extremely large. In Comparative Examples 7 to 9 where no organic sheet is interposed, it is recognized that the tear strength is low.

Furthermore, the fracture strains of Examples 1, 3, 4 and Comparative Examples 7, 8, 9 are shown in Table 2. Further, some of the above separator materials were examined for the presence or absence of breakage when tested by the following method, and the results are shown in Table 3.
Breakage test; dimensions of test material Separator size 300mm x 480mm x 1mm
50 test materials were stacked, heating (150 ° C.) and natural cooling (room temperature) were performed every hour while applying a pressure of 1 MPa, and the state of breakage after repeated 500 hours (times) was investigated. .

  From Tables 2 and 3, it can be seen that the separator material of the example has a large breaking strain and is less likely to cause a flexible crack or breakage.

It is a perspective view which shows the structure of the separator material for fuel cells of this invention.

1 is a partial cross-sectional view showing a schematic structure of a solid polymer fuel cell.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Separator material for fuel cells 2 Mixture layer of carbonaceous powder and resin binder 3 Packing layer in which mixture of carbonaceous powder and resin binder is filled in through hole of organic sheet 4 Organic sheet 5 Penetration of organic sheet Mixture of carbonaceous powder and resin binder filled in the holes 6 Separator 7 Gas channel groove 8 Cathode 9 Anode 10 Electrolyte membrane 11 Sealing material

Claims (3)

90:10 to 65:35 of graphite powder and resin binder having an average particle diameter of 50 μm or less and a maximum particle diameter of 100 μm or less on both surfaces of an organic material sheet having an opening area ratio (R) of 25 to 85%. A fuel cell separator material, wherein a mixture mixed at a weight ratio of 1 is coated, and the mixture of the graphite powder and the resin binder is filled in the through holes of the organic material sheet. However, the opening area ratio (R) is the ratio of the opening area per unit area (opening area / total area × 100). The organic sheet is enlarged to an appropriate magnification and photographed, and this is divided into meshes. The number of openings is counted and divided by the total number of meshes. The method for producing a fuel cell separator according to claim 1, wherein the graphite powder and the resin binder are mixed at a weight ratio of 90:10 to 65:35, and the mixture is mixed with an opening area ratio of the through holes. (R) It adheres to both surfaces of the organic substance sheet | seat which is 25 to 85%, and it hot-press-molds, The manufacturing method of the separator material for fuel cells characterized by the above-mentioned . The method for producing a fuel cell separator according to claim 1, wherein the graphite powder and the resin binder are mixed at a weight ratio of 90:10 to 65:35 to form a sheet, and the sheet is formed in a through hole. A method for producing a separator material for a fuel cell , characterized in that the organic material sheet having an opening area ratio (R) of 25 to 85% is in contact with and adhered to both surfaces and hot-pressure molded.

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