JP4676191B2 - Fuel cell separator - Google Patents

Description

The present invention relates to a separator for a fuel cell. The separator is made of rubber or other elastomer, and the fuel or the like is disposed on a frame-shaped outer peripheral portion surrounding a diffusion region of fuel, air, or cooling water disposed in the central portion of the separator. By integrally forming a seal portion for preventing leakage, manufacturing of a separator and assembly of a fuel cell are facilitated.

A fuel cell generally comprises an MEA (Membrane Electrode Assembly) with an ion exchange membrane (proton exchange membrane) sandwiched between a sheet-like fuel electrode (anode) and an air electrode (cathode). It is manufactured by stacking plate-like conductive separators alternately and in multiple layers to form a stack, which is combined with a fuel tank, a pump, a circulation system, and the like. In the above stacking, a gasket or an O-ring is sandwiched between the separators on the outer peripheral part (frame part) so as to surround the electrode, and the two separators that overlap each other are disconnected from each other, and the separator The inner part of the frame is sealed. Note that a fluid supply path for diffusing fuel gas, air, or cooling water is provided on the inner side of the frame portion of the separator, that is, the portion facing the electrode, thereby constituting a diffusion portion. In addition, the fuel electrode and the air electrode may be used in combination with a gas diffusion film such as carbon paper. In addition, a cooling water diffusion portion is appropriately disposed between the MEA and the MEA.

As described above, the fuel cell stack is composed of a plate-like hard separator, a thin sheet-like electrode, an ion exchange membrane, etc., and has a large number of parts, and a gasket or an O-ring is interposed between the separators. Requires a lot of effort. In order to reduce this effort, various proposals have been made. For example, Patent Document 1 below proposes fixing a gasket or an O-ring to the separator in advance. In FIG. 1, 1 is an ion exchange membrane, 2 is an oxygen electrode, 3 is a hydrogen electrode, 5 is a separator, and a gasket 6 is bonded to the outer peripheral portion (frame portion) of the upper surface of the separator 5 located on the lower side. An MEA composed of the oxygen electrode 2, the ion exchange membrane 1, and the hydrogen electrode 3 is disposed inside the unit. The gasket 6 can be bonded to the separator 5 at the same time by applying an adhesive to the surface of the separator 5, setting it in a mold after drying, injecting rubber and a vulcanizing agent, and performing vulcanization molding. . In FIG. 2, reference numeral 8 denotes a rubber ring, the lower half of which is fitted in a groove formed on the frame surface of the separator 5 and bonded and fixed with an adhesive.
JP 2000-156234 A

Since the fuel cell separator described in Patent Document 1 has a gasket or O-ring bonded thereto, the stack assembly work is facilitated and labor is reduced. However, the separator with a gasket described above is obtained by adhering an off-the-shelf separator or an O-ring to an off-the-shelf separator body, and this adhesion work is required, and the separator body is a conductive material such as carbon as in the prior art. In contrast, it is necessary to make a thermosetting resin separator or a metal containing a large amount of the metal, whereas currently used thermosetting resin separators are glassy and very hard, brittle, and easy to break. Molding is impossible for forming gas flow paths and cooling water flow paths on the surface, and forming manifolds for supply and discharge of fuel gas, air, cooling water, etc. on the frame. After that, it was necessary to perform cutting. Therefore, enormous labor is required for the production of the separator body, and the effect of reducing labor is insufficient to the extent that the above-mentioned gaskets are bonded, and the problem that the metal is not reliable in terms of corrosiveness. was there.

This invention eliminates the brittleness and the corrosivity that the metal separator has had by using a conventional thermosetting resin separator by using rubber or other elastomer as the base material of the separator. Simultaneous molding of the gas channel, cooling water channel, frame manifold, gasket function (or O-ring function) is possible by press molding using a die, greatly increasing the labor required for manufacturing fuel cells. It will be alleviated.

The fuel cell separator according to the present invention is formed into a rectangular plate shape by a conductive material, and has a frame-shaped outer peripheral portion along the outer periphery of one surface and the other surface thereof, and a sheet-like electrode inside the outer peripheral portion. In a fuel cell separator having a central recess that can be set, the conductive material is a conductive elastomer in which an elastic polymer having rubber-like elasticity and conductive carbon are mixed, and a frame shape made of the conductive elastomer. A gasket layer made of an insulating elastomer, which is a mixture of the above elastic polymer and conductive carbon and has a lower compounding ratio of conductive carbon than the above conductive elastomer, is integrally laminated on the outer peripheral surface. A ring-shaped streak that surrounds the central recess is formed in the gasket layer on one side, and the gasket layer on the other side corresponds to the streak groove on the one side. Serial ring-like lip surrounding the central recess of those molded integrally so as to exert a sealing function fitted with the muscle grooves.

The above-mentioned conductive elastomer is obtained by blending conductive carbon as a reinforcing agent with an elastic polymer having rubber-like elasticity to give the separator the necessary conductivity and hardness, and is present on both sides of the separator. A gasket layer made of an insulating elastomer containing a small amount of conductive carbon is integrally laminated on the outer periphery of each of the layers, and a streak groove is formed on the gasket layer on one side, and a protrusion is formed on the gasket layer on the other side. It is a separator with a gasket in which the streak grooves and the protrusions are closely fitted so that a sealing function can be exhibited. Therefore, in the separator with gasket of the present invention, the above-mentioned conductive elastomer and insulating elastomer are each formed into a sheet or film having a desired thickness, the former is punched into a rectangle of a predetermined size, and the latter is It can be manufactured by punching into a frame shape of a size, setting them on a metal mold, performing press molding, and crosslinking, and does not require conventional cutting.

When assembling the fuel cell stack, the above-described gasket-attached separator and the MEA are alternately stacked, and the streak groove on the gasket on one side of the separator and the protrusion on the gasket on the other side of the adjacent separator are formed. Assembling is possible simply by fitting, and there is no need to set flexible and unwieldy gaskets and O-rings on the outer periphery of the frame as in the past, and it is not necessary to fix them in advance by adhesive bonding. Is greatly reduced. When the MEA proton exchange membrane having a size that covers the muscle groove is used, the fitting between the muscle groove and the protrusion is performed with the proton exchange membrane sandwiched therebetween. The function is improved and the fixation of the proton exchange membrane is ensured.

Moreover, since said gasket layer is made with the insulating elastomer, it can prevent the electrical contact between separators and can prevent the spark and electric leakage in use as a fuel cell. In addition, a gasket layer is laminated as a surface layer on the surface of the frame-shaped outer periphery, and the separator body excluding this gasket layer (surface layer) is made of a conductive elastomer having high conductivity and hardness. Compared to the case where the entire length is formed in a rectangular frame shape with an insulating elastomer, the inside of the conductive elastomer is filled, and this is set in a mold and press molded to produce a separator. It is easy and has excellent rigidity as a separator, and is easy to handle.

Examples of the elastic polymer used as a raw material for the conductive elastomer and the insulating elastomer include nitrile rubber (NBR), ethylene propylene rubber (EPDM), styrene butadiene rubber (SBR), acrylic rubber (ACR), and chlorosulfonated rubber (CSM). ), Styrene resins such as SIS, SBS, SEBS, and SEPS, EVA resins, and fluorine resins such as THV. Usually, a Ziegler-Natta catalyst is used for the production of the polymer, but the elastic polymer of the present invention is preferably one using a metallocene catalyst as a polymerization catalyst, particularly ethylene propylene rubber (EPDM), SEBS, SEPS, etc. Styrenic resins and EVA resins are preferred, and the use of this metallocene catalyst polymer eliminates elution of metal ions, chlorine ions, sulfur ions, etc., and prevents contamination of the separator by these ions.

Conductive carbon that imparts conductivity and strength to the above-mentioned elastic polymer is a powder of graphite and carbon black, which is preferable in terms of excellent workability and corrosion resistance compared to metal powder. The graphite is preferably expandable graphite from the viewpoint of conductivity, and in particular, graphite obtained by treating impurities at a high temperature of 300 to 1500 ° C. to incinerate impurities. In addition, the carbon black is preferably a conductive carbon black such as ketjen black in terms of conductivity, and in particular, carbon black that is treated at a high temperature of 500 to 900 ° C. to incinerate impurities.

In addition, conductive carbon such as graphite and carbon black is blended in the elastic polymer without mixing other compounding agents to give desired conductivity and strength. The conductivity of the conductive elastomer obtained by blending this conductive carbon is preferably 40 mΩ · cm or less in volume specific resistance. If it is higher than this range, the conductivity is insufficient, and power generation is poor when mounted on a fuel cell. It becomes. Further, the bending strength is preferably 50 to 100 MPa. If the bending strength is smaller than this range, the handling property when assembling the fuel cell is deteriorated, and if it is larger, the rubbery elasticity is lost. On the other hand, the conductivity of the insulating elastomer is preferably at least 10 ⁴ Ω · cm in volume resistivity, lower than this range, a spark or electrical leakage is likely to occur.

The conductive carbon is preferably mixed and mixed with conductive graphite and conductive carbon black, whereby the gap between relatively large and flat graphites is connected with a small powder of conductive carbon black, and the graphite Or electroconductivity improves compared with the case where carbon black is used independently. In the case of a conductive elastomer, the preferable blending amount is 100 to 150 parts by weight of graphite per 100 parts by weight of the elastic polymer. When the blending amount of graphite is insufficient, the conductivity is lowered, and on the contrary, the processability is excessive. Adversely affect. Moreover, the preferable compounding quantity of carbon black is 20-70 weight part, and when it is insufficient, electroconductivity will fall, and conversely when it is excessive, it will have a bad influence on workability.

On the other hand, in the case of an insulating elastomer, the preferable blending amount of the conductive graphite is 100 parts by weight or less of the elastic polymer and is 30 parts by weight or less. Moreover, the preferable compounding quantity of carbon black is 10 weight part or less, and when it is excessive, a sealing function will fall.

In a normal rubber composition, in addition to carbon black as a reinforcing agent, a crosslinking agent, a crosslinking aid, an anti-aging agent, a plasticizer (softener) and the like are appropriately blended with rubber. It is preferable not to use any additive other than the conductive graphite and the conductive carbon black. This prevents contamination by unnecessary ions other than protons and enables efficient power generation as a fuel cell. However, the softening agent for facilitating the kneading of the elastic polymer and the conductive carbon can be added only to those that can be removed by evaporation before commercialization, such as toluene.

In the fuel cell separator according to the present invention, as described above, the conductive elastomer and the insulating elastomer are each formed into a sheet or film having a desired thickness, the former is punched into a rectangle of a predetermined size, and the latter is predetermined. It can be manufactured by punching into a frame shape of size, stacking them in a mold, performing press molding, and crosslinking, but this crosslinking uses a crosslinking agent such as sulfur or peroxide It is preferable to carry out by electron beam irradiation, which eliminates the need for pressurization and heating during crosslinking, shortens the crosslinking time and prevents loss of shape, and prevents elution of unnecessary ions during power generation. Can do. Moreover, since an electron beam bridge | irradiation irradiates an electron beam in the state which coat | covered with inert gas presence, such as nitrogen gas, or a synthetic resin film according to a conventional method, it can also prevent oxidation.

The fuel cell separator according to the present invention can be used with a slight change in design even for a fuel cell that uses either hydrogen or methanol. For example, a manifold supply hole for fuel, air, etc., is provided in the outer periphery of the frame shape in addition to the streak grooves and protrusions, and a fluid supply path for diffusing fuel, air, etc. in the central recess inside the outer periphery However, when hydrogen is used as fuel, three types of manifold holes for hydrogen (including hydrogen dissolved in water), air and cooling water are provided on the outer periphery, and methanol is used as fuel. When doing so, two types of manifold holes for methanol and air are provided. Moreover, the groove | channel width and depth of the fluid supply path of a center recessed part are suitably changed by the object for hydrogen and for methanol. Then, a streak groove or a ridge is formed in a ring shape surrounding the manifold hole on the gasket layer surface of the outer peripheral portion. The streak and the ridge surrounding the manifold hole may be either continuous or separated from the ring-shaped streak and the ridge surrounding the central recess, respectively.

Since the separator for a fuel cell according to the present invention is obtained by blending conductive carbon as a reinforcing agent with an elastic polymer, it is superior in corrosion resistance compared to a conventional metal, and compared to a conventional thermosetting resin. Hard to break. Then, a gasket layer made of an insulating elastomer with a small amount of conductive carbon is integrally laminated on the outer periphery of the frame shape, and a streak groove is formed on one side and a ridge is formed on the other side. Since it is a separator with a gasket that exhibits a sealing function in combination, it can be easily manufactured by kneading, sheet molding, press molding and crosslinking, and when assembling the stack, the above separator and MEA are combined. Assembling, sealing between the separators, and insulation can be performed by fitting the streak grooves and the protrusions of the adjacent separators while alternately stacking them, and the assembling labor is greatly reduced.

In particular, the invention according to claim 2 uses a metallocene catalyst instead of a conventional Ziegler-Natta catalyst as a polymerization catalyst for an elastic polymer, and a mixture of graphite and carbon black in which impurities are incinerated by high heat treatment as conductive carbon. Therefore, there is no elution of metal ions and other unnecessary ions, and contamination of the separator by these ions is prevented. In the invention according to claim 3, since the crosslinking is performed by electron beam irradiation, it is possible to prevent deformation of the shape during crosslinking, oxidation and elution of unnecessary ions during power generation.

EPDM, SEBS, SEPS, or EVA-based elastic polymer using a metallocene catalyst as a polymerization catalyst, expandable graphite treated at a high temperature of 300 to 1500 ° C., conductive carbon black and toluene treated at a high temperature of 500 to 900 ° C. 100 parts of the above-mentioned elastic polymer, 100 to 150 parts of expandable graphite, 20 to 70 parts of conductive carbon black and 50 to 400 parts of toluene are blended and kneaded with a high-load kneader. Producing an elastomer. On the other hand, with respect to 100 parts of the above-mentioned elastic polymer, 30 parts by weight or less of expansive graphite and 10 parts by weight or less of conductive carbon black are blended and kneaded in the same manner as above except that the blending of toluene is omitted. To manufacture.

The conductive elastomer is supplied to an extrusion molding machine to form a sheet having a thickness of 1 to 6 mm and dried to remove toluene. Similarly, the insulating elastomer is supplied to an extrusion molding machine to form a film having a thickness of 20 to 500 μm. The conductive sheet made of the above conductive elastomer is punched into the desired separator shape, and the insulating film made of the above insulating elastomer is punched into the shape of the frame-like outer periphery of the separator, and the outer peripheral shape insulating film Is placed on both sides of the separator-shaped conductive sheet, set in a mold preheated to 130 to 230 ° C., introduced into a press machine at 170 to 230 ° C., and 2 at a surface pressure of 50 to 400 kg / m ² . Press for ~ 20 minutes, then cool the mold to 60 ~ 80 ° C, take out the molded product, introduce this molded product into the electron beam cross-linking machine, electron beam in nitrogen gas atmosphere (acceleration voltage 700KV, irradiation dose 60Mrad) To obtain a fuel cell separator with a gasket.

3 and 4, reference numeral 10 denotes a separator made of the above conductive elastomer, and gasket layers 11 and 12 are laminated on the upper and lower surfaces of the frame-shaped outer peripheral portion 10a, respectively. A groove-shaped fluid supply passage 10c is provided in a meandering manner in the central recess 10b on the upper and lower surfaces of the separator 10, that is, the portion surrounded by the gasket layers 11 and 12, and the frame-shaped outer peripheral portion 10a has a serpentine recess. A total of six manifold holes 13 are provided across the gasket layer 11 on the upper surface and the gasket layer 12 on the lower surface, and the three manifold holes 13 on the left side in FIG. 4 supply hydrogen gas, cooling water and air in order from the top. In addition, the right three manifold holes 13 are used for discharging hydrogen gas, cooling water and air in order from the bottom. One of these manifold holes 13 is connected to the fluid supply path 10c and the communication path 13a. Also, bolt holes 14 are provided across the gasket layers 11 and 12 at the four corners.

On the surface of the upper gasket layer 11 made of an insulating elastomer, a protrusion 11a is formed along the inner edge thereof, and on the surface of the lower gasket layer 12, a streak groove 12a is formed along the inner edge thereof. Further, a protrusion 11b is formed on the surface of the upper gasket layer 11 and a streak groove 12b is formed on the surface of the lower gasket layer 12 so as to individually surround the six manifold holes 13. Then, two separators 10 having the gasket layers 11 and 12 are stacked with an “MEA” 4 composed of an oxygen electrode 2, an ion exchange membrane 1 and a hydrogen electrode 3 interposed therebetween as shown in FIG. The groove 12a along the inner edge of the lower gasket layer 12 of the upper separator 10 and the protrusion 11a along the inner edge of the upper gasket layer 11 of the lower separator 10 are fitted with the ion exchange membrane 1 interposed therebetween, Seal. At the same time, the streak groove 12b around the manifold hole 13 of the lower gasket layer 12 of the upper separator 10 and the protrusion 11b around the manifold hole 13 of the upper gasket layer 11 of the lower separator 10 are fitted together and sealed. The cross-sectional shapes of the protrusions 11a and the streak grooves 12a are preferably chamfered as shown in FIGS. 5A and 5B, and the streak grooves 12b and the protrusions 11b around the manifold hole 13 are also included. It is the same.

EPDM (“Nodel IP 4725” manufactured by Goodrich) manufactured using a metallocene catalyst as a polymerization catalyst as an elastic polymer, and expandable graphite (“Cull” manufactured by Maruyo Casting Co., Ltd.) treated at a high temperature of 1000 ° C. as conductive graphite. Phyto CS-1 "), conductive carbon black (" Printex XE-2B "manufactured by Degussa) treated as a conductive carbon black at 500 to 900 ° C, and toluene as a softener were prepared. For each 100 parts of EPDM, 135 parts of conductive graphite, 30 parts of conductive carbon black, and 265 parts of toluene are blended and kneaded with a high-load kneader to produce a conductive elastomer, which is 5 mm thick with an extruder. A conductive sheet was molded and dried at a temperature of 80 ° C. On the other hand, for 100 parts of the above elastic polymer, 10 parts of conductive graphite and 3 parts of conductive carbon black are blended, and an insulating elastomer is produced by kneading in the same manner as above except that toluene is omitted. An insulating film having a thickness of 100 μm was formed.

The conductive sheet is punched into a rectangular separator having a target width of 90 mm and a length of 120 mm, while the insulating film is punched into the shape of the outer periphery of the frame of the separator, and the frame is formed on both sides of the conductive sheet. Insulating film in the form of a layer, set in a mold preheated to 180 ° C., introduced into a press machine at 180 ° C., pressed at a surface pressure of 300 kg / cm ² for 2 minutes, then cooled to a temperature of 40 ° C., A molded product having a frame-like outer peripheral portion thickness of 3.8 mm and an inner peripheral portion inner thickness of 3.3 mm was taken out. The resulting molded product is irradiated with an electron beam (acceleration voltage 700 KV, irradiation dose 60 Mrad) in a nitrogen gas atmosphere to crosslink, adjust the heat resistance, creep property and spring constant, and further remove burrs and finish the gas flow path. To obtain a pair of fuel cell separators (Examples). An MEA was incorporated into this separator and a power generation test was conducted.

In addition, as a separator of a comparative example, a commercial product of a glassy separator made of a phenolic thermosetting resin is prepared, and a rubber ring-shaped O-ring (diameter 10 mm) is sandwiched between the two frame-shaped outer peripheries, The same test as described above was performed. The results are shown in Table 1 below.

As shown in Table 1 above, the embodiment of the present invention has lower hardness and bending strength than the comparative example made of phenolic resin, is rich in elasticity, has excellent insulation at the outer periphery, and has excellent power generation performance. Was not inferior.

It is sectional drawing of a prior art example. It is sectional drawing of another prior art example. It is sectional drawing of embodiment. It is a top view of a separator. It is sectional drawing of the seal part of a separator.

Explanation of symbols

1: Ion exchange membrane 2: Oxygen electrode 3: Hydrogen electrode 4: MEA
5: Separator 6: Gasket 10: Separator 10a: Frame-shaped outer periphery, 10b: Central recess, 10c: Fluid supply path 11, 12: Gasket layer 11a, 11b: Projection 12a, 12b: Streak 13: Manifold hole 14: Bolt hole

Claims (3)

A fuel having a rectangular plate shape made of a conductive material, having a frame-shaped outer periphery along the outer periphery of one surface and the other surface, and a central recess capable of setting a sheet-like electrode inside the outer periphery. In the battery separator, the conductive material is a conductive elastomer in which an elastic polymer having rubber-like elasticity and conductive carbon are mixed, and the elastic polymer is formed on a surface of a frame-shaped outer periphery made of the conductive elastomer. And a conductive carbon, and a gasket layer made of an insulating elastomer having a low compounding ratio of conductive carbon compared to the conductive elastomer is integrally laminated. A ring-shaped streak that surrounds the central recess is formed, and a ring-shaped ridge that surrounds the central recess corresponds to the one-side streak on the gasket layer on the other side. Fuel cell separator, characterized by being integrally molded to mate with the streak groove exhibits a sealing function. The fuel cell separator according to claim 1, wherein the elastic polymer is produced using a metallocene catalyst, and the conductive carbon comprises a mixture of graphite and carbon black in which impurities are incinerated by high heat treatment. The fuel cell separator according to claim 1 or 2, wherein the conductive elastomer is crosslinked by electron beam irradiation without blending a crosslinking agent.

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