JP2003109621A - Separator for fuel cell and fuel cell using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for a fuel cell, low in increase rate of volume and weight of the separator even dipped in the hot water, and low in bending strength drop, and to provide a fuel cell using the separator. SOLUTION: In this separator for the fuel cell, the increase rate of volume after dipped in the water of 80 deg.C±5 deg.C for more than 50 hours, is within 0.1% of that of before the dipping, the increase rate of weight after dipped in the water of 80 deg.C±5 deg.C for 50 hours is within 2% of that before dipping, and the lowering rate of bending strength after being dipped in the hot water of 80 deg.C±5 deg.C for 50 hours is within 10% of that before dipping. The fuel cell is provided with the separator.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell separator having excellent cell characteristics even when immersed in warm water, and a fuel cell using the fuel cell separator.

[0002]

2. Description of the Related Art In recent years, fuel cells have received a great deal of attention from the viewpoints of measures to prevent global warming due to the expansion of fossil fuel consumption, energy saving measures, etc., and research and development are being actively conducted by national and university research institutes, major companies, etc. Some have been commercialized.

In particular, the polymer electrolyte fuel cell has an operating temperature of about 80 ° C., which is far lower than that of other fuel cells, and is currently attracting attention as a generator for automobiles and households.
A polymer electrolyte fuel cell is roughly divided into an ion exchange membrane, a platinum catalyst, and a separator.

Among them, the function of the separator is to stably supply hydrogen and oxygen for generating energy to the fuel electrode and the oxygen electrode and to quickly discharge water and cooling water generated, which is an important factor affecting the battery characteristics. It is a member.

Further, since hundreds of separators are used for one battery (for automobile), downsizing is urgently required, and at present, separator manufacturing companies are demanded to improve the separators whose volume, weight and bending strength do not change much. It

However, in the conventional separator, hot water (cooling water or the like) was in contact with the separator during the operation of the battery, so that the separator was impregnated with hot water, resulting in an increase in volume and weight and a decrease in bending strength. Volume when immersed in warm water,
When a separator having a large change in weight and bending strength was used, it was a factor that a part of the separator incorporated in the stack was damaged or leaked.

[0007]

SUMMARY OF THE INVENTION Therefore, the present invention is directed to a fuel cell separator and a fuel cell using the same, in which the increase rate of the volume and weight of the separator is small and the decrease rate of the bending strength is small even when immersed in warm water. Is provided.

[0008]

[Means for Solving the Problems] The present invention is 80 ° C ± 5 ° C.
The fuel cell separator has a volume increase rate of 0.1% or less before immersion in warm water for 50 hours or more. The present invention also relates to the fuel cell separator, wherein the rate of increase in weight after immersion in hot water at 80 ° C ± 5 ° C for 50 hours or more is within 2% before immersion in hot water. The present invention also relates to the fuel cell separator, wherein the rate of decrease in bending strength after immersion in hot water at 80 ° C ± 5 ° C for 50 hours or more is within 10% before immersion in hot water. Further, the present invention is
The present invention relates to a fuel cell separator in which the weight increase rate after immersion in hot water at 80 ° C. ± 5 ° C. for 50 hours or more is within 2% before immersion in hot water. The present invention also relates to a fuel cell separator in which the rate of decrease in bending strength after immersion in hot water at 80 ° C ± 5 ° C for 50 hours or more is within 10% before immersion in hot water.

The present invention also relates to the fuel cell separator, wherein the separator is a molded product containing graphite and resin. The present invention also relates to the fuel cell separator, wherein the separator has a rib portion and a flat portion. The present invention also relates to the fuel cell separator, wherein the graphite is expanded graphite. The present invention also relates to the fuel cell separator, wherein the expanded graphite is a crushed powder of an expanded graphite sheet and the resin is a phenol resin. Further, in the present invention, the expanded graphite sheet pulverized powder has an average particle diameter of 25 μm to 500 μm.
The present invention relates to the above fuel cell separator. Further, the present invention relates to the fuel cell separator, wherein the resin is in powder form, undergoes ring-opening polymerization, and has an average particle size of 1 μm to 100 μm.

Further, according to the present invention, the density is 1.35 g / c.
The fuel cell separator is m ³ or more.
The present invention also relates to the fuel cell separator, wherein the molded body is molded by a compression molding method. The present invention also relates to the fuel cell separator, wherein the separator has a hole in addition to the rib and the flat part. The present invention also relates to a fuel cell having the fuel cell separator. Further, the present invention relates to a polymer electrolyte fuel cell.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The molded article (fuel cell separator) obtained by the present invention is immersed in hot water at 80 ° C. ± 5 ° C. for 50 hours or more, and the increase rate of the volume after the hot water immersion is 0 before the hot water immersion. 0.1% or less, preferably 0.05% or less, more preferably 0%, and the rate of increase in volume is 0.1 before immersion in warm water.
When it exceeds%, when the separator is incorporated in the stack, a part of the separator is damaged and the battery characteristics are deteriorated.

The volume increase rate is 0.1 before immersion in warm water.
There is no particular limitation on the rate of increase in weight and the rate of decrease in bending strength after being immersed in warm water, as long as it is within%, but for example, the rate of increase in weight is preferably within 2% before immersion in warm water, more preferably within 1%. , 0% is more preferable, and the reduction rate of the bending strength is preferably 10% or less before hot water immersion, more preferably 5% or less, and further preferably 0%.

Even under the conditions other than the above, that is, when the volume is increased by immersion in warm water at 80 ° C. ± 5 ° C. for 50 hours or more and the volume increase rate after immersion in warm water exceeds 0.1% before immersion in warm water, the increase in weight is caused. The rate is 2% or less before hot water immersion, preferably 1% or less, more preferably 0%, or the bending strength decrease rate after hot water immersion is 10% or less before hot water immersion, preferably 5% or less, If it is preferably 0%, the object of the present invention can be achieved.

In the present invention, the molded product is immersed in warm water at 80 ° C. ± 5 ° C. for 50 hours or more, and the volume increase rate after the warm water immersion is within 0.1% before the warm water immersion, and the weight increase after the hot water immersion. In order to make the rate within 2% before immersion in hot water or within 10% before immersion in warm water, the rate of decrease in bending strength may be determined by, for example, forming a resin film layer on the surface of the molded body, and further This can be achieved by forming a film of a substance having releasability (easiness of peeling of the molded product from the mold) on the substrate to improve water repellency and prevent hot water from penetrating into the molded product. By doing so, not only the rate of increase in volume can be reduced, but also the rate of increase in weight and the rate of decrease in bending strength can be reduced. There is no particular limitation on the substance having a releasing property, but it is preferable to use a fluorine-based releasing agent or a silicon-based releasing agent, and in consideration of the stain resistance of the mold molding surface, the fluorine-based releasing agent is preferable. It is preferable to use molds.

The properties of the fluorine-based releasing agent are not particularly limited, but generally, they are used in liquid or aerosol type.
In the case of a die having a complicated shape used for forming the separator, the aerosol type is preferable in consideration of uniform application of the fluorine-based release agent to the die. Further, in consideration of adverse effects on the environment, an alternative CFC-melting aerosol type fluorine-based release agent that does not use CFC is preferable. Examples of alternative CFC-melting aerosol type fluorine-based release agents include GA-6010 and GA-6310 (Daikin Industries, Ltd.).
Co., Ltd., trade name) and the like. By using these release agents, the separator of the present invention can be easily manufactured.

The thickness of the resin film and the method for forming the resin film are not particularly limited, and can be arbitrarily determined by a combination of the amount of resin used, melting point, molecular weight, reaction time, molding temperature, molding pressure and the like. However, when the formed resin film is extremely thick, the electrical characteristics tend to be deteriorated, and when it is extremely thin, the gas impermeability tends to be decreased.

There is no particular limitation on the formation of a film of a substance having a releasing property. For example, a fluorine-based releasing agent sprayed from a commonly used spray can is used as a molding die and sheet material (resin and expanded graphite). It may be uniformly sprayed on the powder mixture). The thickness is not particularly limited as long as the film is uniformly attached.

In the present invention, the temperature of the hot water in which the molded body is dipped is 80 ° C. ± 5 ° C., preferably 80 ° C. ± 3 ° C., more preferably 80 ° C. ± 1 ° C. in relation to the operating temperature of the fuel cell.
It is said that

The upper limit of the immersion time of the molded body in hot water is 50 hours or more, and there is no particular upper limit. When the immersion time is less than 50 hours, the volume and the like change with the lapse of time and do not become constant, and the rate of increase in volume and the like required in the present invention cannot be obtained.

In the fuel cell separator of the present invention, the rib portion is conductive or conductive, and forms a gas flow path when the separators are stacked via the electrolyte membrane, the fuel electrode and the air electrode. Is. Further, the flat portion forms a gripping portion of the separator and is configured so that gas does not leak when the gas passes through the flow path. Also, the rib part
It is configured so that gas does not leak when the gas passes through the flow path formed when the separators are stacked. The flat portion preferably serves as a gripping portion for fixing the whole when the separators are stacked.

Further, the fuel cell separator according to the present invention may have holes other than the rib and the flat portion, and it is particularly preferable that the flat portion has the holes. The hole portion is configured to form a long hole in the stacking direction when a large number of separators are stacked, and a hole for passing hydrogen gas, oxygen gas, and cooling water is formed. Each hole is configured to be connected to the hydrogen gas flow passage, the oxygen gas flow passage, and the cooling water flow passage formed by the rib portion of the separator. In addition, in the flat part,
It may have a hole for passing a fixing bolt when the separators are stacked.

The molded body having the rib portion and the flat portion is obtained by molding a material containing graphite and a resin into a separator shape, and particularly, one having a structure in which graphite is dispersed in the resin,
It is preferable because it is excellent in electrical properties, moldability, gas impermeability, and inexpensive. There is no particular limitation on the graphite, and natural graphite, artificial graphite or the like is preferably used if cost is important. There is no limitation on the particle size of the graphite used, and it is preferable to mix and use graphite having different particle sizes in consideration of required characteristics and moldability. Further, when importance is attached to weight reduction and mechanical strength (toughness), it is preferable to use expanded graphite, and it is particularly preferable to use crushed powder of expanded graphite sheet.

It is preferable that each of the rib portion and the flat portion has a layer containing expanded graphite and a resin, and these layers are continuous layers. Thereby, the moldability at the time of molding for obtaining the separator is good, the lightweight property is given to the separator, and the preferable properties such as high toughness and low elasticity are given to the separator.

Expanded graphite preferably used in the present invention is obtained by immersing raw graphite into a solution containing an acidic substance and an oxidizing agent to form a graphite intercalation compound, and heating the graphite intercalation compound to produce graphite. It can be manufactured by a step of expanding the crystal in the C-axis direction to obtain expanded graphite.
As a result, the expanded graphite becomes a bug-like shape and has a entangled complex shape with no directivity.

The expansive graphite preferably has a higher magnification to secure the strength and sealing property of the separator, and is not particularly limited, but is preferably 150 times or more, and 150 times to 3 times.
It is more preferably 00 times. The expanded graphite can be made into expanded graphite powder by crushing this expanded graphite, but it is preferable to compress the obtained expanded graphite by pressure to obtain a expanded graphite sheet before crushing. Further, the obtained expanded graphite powder is subjected to a treatment (high temperature treatment or the like) for reducing acidic roots contained in the pulverized powder, if necessary.

The above-mentioned raw material graphite is not particularly limited, but a highly crystallized graphite such as natural graphite, quiche graphite, or pyrolytic graphite is preferable. Natural graphite is preferable in consideration of the balance between the obtained properties and economy. The natural graphite used is not particularly limited,
Commercially available products such as F48C (trade name, manufactured by Nippon Graphite Co., Ltd.) and H-50 (trade name, manufactured by Chuetsu Graphite Co., Ltd.) can be used. These are preferably used in the form of scale-like powder.

The acidic substance used to treat the expanded graphite is
Generally, a material that can penetrate between layers of graphite such as sulfuric acid to generate an acidic root (anion) having a sufficient expansion ability is used. The amount of the acidic substance used is not particularly limited and is determined by the desired expansion ratio, and for example, it is preferable to use 100 to 1000 parts by weight with respect to 100 parts by weight of graphite.

As the oxidizing agent used together with the acidic substance, peroxides such as hydrogen peroxide, potassium perchlorate, potassium permanganate and potassium dichromate, and acids having an oxidizing action such as nitric acid are used. Hydrogen peroxide is particularly preferable from the viewpoint that it is possible to obtain good expanded graphite easily. When hydrogen peroxide is used as the oxidizing agent, it is preferably used as an aqueous solution. At this time, the concentration of hydrogen peroxide is not particularly limited, but is preferably 20% by weight to 40% by weight. The amount used is also not particularly limited, but it is preferable to add 5 parts by weight to 60 parts by weight as hydrogen peroxide solution to 100 parts by weight of graphite.

The acidic substance and the oxidizing agent are preferably used in the form of an aqueous solution. Sulfuric acid as an acidic substance is used at an appropriate concentration, but a concentration of 95% by weight or more is preferable, and concentrated sulfuric acid is particularly preferable.

In the above, the method for producing the expanded graphite sheet is described.
Although there is no particular limitation, generally, the expanded black obtained above
Sheets of lead can be formed by applying pressure with a press, roll, etc.
And are preferred. Of the expanded graphite sheet
The thickness and density are not particularly limited, but the thickness is 0.
Range of 5 mm to 1.5 mm and density of 0.2 g / cm ^Three
~ 1.7 g / cm^ThreeThe range of is preferable. The thickness is
If it is less than 0.5 mm, the obtained molded article tends to be brittle.
However, if it exceeds 1.5 mm, the moldability tends to deteriorate.
is there. The density is 0.2 g / cm^ThreeIs less than electrical resistance
The resistance tends to worsen, 1.7 g / cm^ThreeExceeds
Mechanical strength tends to decrease. The size of the density is
Adjust by adjusting the amount of pressure, roll gap, etc.
You can In addition, the crushing of the expanded graphite sheet is performed by coarse crushing and
It is preferable to carry out by fine pulverization, and thereafter, if necessary,
Classify.

In the present invention, the density of expanded graphite as a raw material is not particularly limited, but it is 0.1 g / cm ³ to.
A range of 0.4 g / cm ³ is preferred. If the density of the expanded graphite is too low, the homogeneity of mixing with the resin will decrease, and the sealing properties of the resulting molded article (fuel cell separator) will tend to deteriorate, and if the density of the expanded graphite is too high, the objective will be The effect of improving the mechanical strength and conductivity of the molded body (fuel cell separator) tends to decrease.

The average particle size of the crushed powder of the expanded graphite sheet is not particularly limited, but considering the mixing property with the resin and the moldability, the number average particle size is preferably in the range of 25 μm to 500 μm, and in the range of 50 μm to 400 μm. Is more preferable. If the particle size is less than 25 μm, the effect of entanglement of the expanded graphite powder is reduced, and the strength of the separator tends to decrease easily. On the other hand, if the particle size exceeds 500 μm, the expanded graphite flows to the narrow rib. As a result, it tends to be difficult to form a separator having a thin flat plate and high rib height.

In the present invention, the properties of the resin used are not particularly limited, but safety and shortening of the manufacturing process (low cost)
In consideration of the above, it is preferable to use a thermosetting resin, a high heat resistant resin or a thermoplastic resin which is capable of dry mixing (solventless mixing) and has a stable particle size distribution. The resin is preferably used in the form of powder or particles.

There is no limitation on the chemical structure and kind of the resin used, and examples thereof include epoxy resin (with a curing agent used together), melamine resin, curable acrylic resin, resol type and novolak type powdered phenol resin. The thermosetting resin, the powdery polyamide resin, the powdery polyamideimide resin, the phenoxy resin, the acrylic resin or the like having a high heat resistance or a thermoplastic resin is used. If necessary, a curing agent, a curing accelerator, etc. may be used in combination with the thermosetting resin. The use form of the curing agent and the curing accelerator is preferably powdery or granular. Among these resins, it is preferable to use a phenol resin, which is a thermosetting resin, because it is excellent in economical efficiency, workability, and property balance after curing.

Phenolic resin has a uniform particle size as a powder property, is less blocking (aggregation of powder), generates less gas during the reaction, and is easily molded, and heat treatment is completed in a short time. Phenolic resins having the above-mentioned features are preferable, and among them, it is preferable to use a phenol resin containing a dihydrobenzoxazine ring which is polymerized by ring-opening polymerization [having a chemical structural unit represented by the general formulas (A) and (B)].

[0036]

[Chemical 1] (In the formula, hydrogen bonded to the aromatic ring is substituted with an alkyl group having 1 to 3 carbon atoms, a cyclohexyl group, a phenyl group, or an alkyl group having 1 to 3 carbon atoms or an alkoxyl group, except for one of the ortho positions of the hydroxyl group. Optionally substituted with a hydrocarbon group such as a phenyl group).

[0037]

[Chemical 2] (In the formula, R ¹ is a hydrocarbon group such as an alkyl group having 1 to 3 carbon atoms, a cyclohexyl group, a phenyl group, or a phenyl group substituted with an alkyl group having 1 to 3 carbon atoms or an alkoxyl group; Hydrogen attached to may be substituted with similar hydrocarbon groups).

When a powdery phenolic resin is used as the resin, its particle size distribution is not particularly limited, but it is possible to mix it uniformly with the crushed powder of expanded graphite sheet in a short time by a dry method, and the resin flow during molding. In consideration of the above, the number average particle size is preferably in the range of 1 μm to 100 μm, and 5 μm to 50 μm.
The range of μm is more preferable.

The mixing ratio of the expanded graphite and the resin used in the present invention is determined in consideration of the values of various characteristics of the fuel cell separator which is the final molded product, but the expansion ratio is usually the mixing ratio. / Resin = 95/5 to 50/50 (weight ratio)
The range is preferably 85/15 to 60/40 (weight ratio)
Is more preferable. Here, if the mixing ratio of the expanded black powder and the resin exceeds 95/5, the mechanical strength tends to decrease sharply, while if it is less than 50/50, the amount of expanded graphite powder that is a conductive substance added Is less and the electrical characteristics tend to deteriorate.

There is no particular limitation on the method of mixing the expanded graphite and the resin, and a dry mixing method using a shaker, a V blender or the like that does not apply a large shearing force to the expanded graphite at the time of mixing in order to prevent the expanded graphite from being pulverized. It is preferable. When the expanded graphite is pulverized during mixing, the mechanical strength of the obtained fuel cell separator tends to be sharply reduced.

Further, the mixed powder can be directly used as a molding material powder, but in the present invention, in order to further improve the mixing property and the workability at the time of molding, the mixed powder is pressure-molded to form a sheet. What was made (hereinafter, "molding sheet"
Is used). There is no particular limitation on the method for producing the forming sheet, but for example, a mixture charging tank, a gate adjusting machine for adjusting the material to a constant thickness, a slitter for finishing to a constant width, a transfer device for transferring the processing material, a rolling roll for sheeting, etc. It is possible to use a molding sheet manufacturing apparatus or the like. When the flat portion has a hole, it is preferable that the sheet is formed with the hole.

In order to improve the strength of the molding sheet, the curing reaction of the resin contained in the molding sheet is partially advanced or partially (not completely) heat-melted before the production of the separator. Can be offered. There is no limitation on the curing reaction or the method of heat-melting, for example, a method of heating the obtained forming sheet, more specifically, the above-mentioned rolling roll shall be equipped with a heating device and passed through this rolling roll. There are a method of occasionally heating and a method of passing the obtained molding sheet through a heating oven.

Obtained molded product (fuel cell separator)
There are no particular restrictions on the density of the
Density is 1.35g / cm^ThreeThe above is preferable, and 1.35 g /
cm ^Three~ 1.75 g / cm^ThreeIs more preferable.
The density of the rib is 1.35 g / cm^ThreeThe above is preferred
1,45 g / cm^Three~ 1.75 g / cm^ThreeThe range of
Preferred. Sufficient machine with the above density
Since it is possible to maintain the denseness and has a large water-repellent effect,
preferable.

Although there is no particular limitation on the production of the above-mentioned molded body, the cost of the molding machine, the dimensional accuracy of the molded body to be obtained, the rib portion and the flat portion of the expanded graphite powder in the resin that can determine the electrical characteristics and mechanical characteristics. Also, the compression molding method is preferable in consideration of the optimum orientation and the like around the hole.

The fuel cell has a structure in which the separator according to the present invention is formed by laminating a necessary number of electrolyte layers made of a solid polymer electrolyte membrane or the like and cells formed so as to sandwich the electrolyte layers. The separator in the present invention can be used as a separator for fuel cells of alkaline type, solid polymer type, phosphoric acid type, molten carbon salt type, solid acid type, etc., which are classified according to the type of electrolyte, and particularly solid polymer type fuel cells It is preferable to use

With the structure as shown above,
Even if the separator is immersed in warm water, the rate of increase in weight and volume of the separator is small, and the bending strength is not significantly reduced. In addition, the moldability is good, and there is no problem with gas impermeability, electrical properties, and mechanical properties. A separator and a fuel cell are obtained.

[0047]

EXAMPLES The present invention will be described below with reference to examples. Example 1 (1) Production of powder mixture for molding Expanded graphite sheet having a plate thickness of 1.0 mm and a density of 1.0 kg / cm ³ (manufactured by Hitachi Chemical Co., Ltd., product name Carbofit HGP-105) was roughed. Crush with a crusher and a fine crusher,
Expanded graphite sheet pulverized powder with a number average particle size of 100 μm 0.7
I got kg. Next, there is little volatile gas at the time of molding, and a powdery phenolic resin having a number average particle diameter of 20 μm, which has the chemical structural units shown in the general formulas (A) and (B) (manufactured by Hitachi Chemical Co., Ltd., trade name HR1060). 0.3 kg was added and dry mixed with a small V blender to obtain 1.0 kg of mixed powder.

(2) Production of Fuel Cell Separator 0.07 kg of the mixed powder (1 kg per 1 m ² ) was molded into a sheet with a roll to obtain a molding sheet. Next, a separator composed of a rib portion 1, a flat portion 2 and a hole (manifold) portion 3 having a shape shown in FIGS. 1 and 2 [length, width 160 mm, thickness 1.5 mm (the height of the rib portion 1 is 0.5 mm) and 6 holes 3] can be produced by heating each mold (lower mold and upper mold) to 180 ° C., and substitute CFC-melting aerosol type fluorine-based mold release agent (Daikin Industrial Co., Ltd., trade name DAIFREE GA-60
10) was sprayed uniformly.

Then, the same releasing agent as described above is uniformly sprayed on the surface of the molding sheet obtained above, the molding sheet is placed on the lower mold, and the upper mold is set on the upper part thereof. Then, it was molded by hot pressing at 180 ° C. for 10 minutes under the condition of a surface pressure of 19.6 MPa (once degassing: 5 seconds).

The molded body obtained above was heat-treated at 190 ° C. for 30 minutes, and then the flat portion was punched with a simple punching machine to form a rib portion 1, a flat portion 2 and a hole portion 3. A fuel cell separator having the shape shown in FIGS. 1 and 2 was obtained. The density of the rib portion of the obtained separator is 1.6 g /
The density of the cm ³ and the flat portion was 1.5 g / cm ³ .
The rib portion 1 in FIGS. 1 and 2 is composed of a protrusion portion 4 and a groove portion (corresponding to the protrusion portion of the mold) 5.

Example 2 The mixed powder obtained in Example 1 (1) (1 kg per 1 m ² ).
A sheet for molding was obtained by forming 0.064 kg into a sheet with a roll. Then, the same steps as in Example 1 (2) were performed to obtain a fuel cell separator having the same thickness as in Example 1.
The density of the rib portion of the obtained separator is 1.46 g / cm.
³ and the flat part had a density of 1.37 g / cm ³ .

Comparative Example 1 As a releasing agent, 100 parts by weight of wax and 100 parts of water were used.
Water-soluble wax (castrol
Product name No. A fuel cell separator having the same thickness and the same density as in Example 1 was obtained through the same steps as in Example 1 except that 170) was used.

Comparative Example 2 Mixed powder obtained in Example 1 (1) (1 kg per 1 m ² ).
0.055 kg was formed into a sheet with a roll to obtain a forming sheet. Hereinafter, a fuel cell separator having the same thickness as in Example 1 was obtained through the same steps as in Example 1 (2) except that the water-soluble wax used in Comparative Example 1 was used as the release agent. The density of the rib portion of the obtained separator is 1.3.
The density of g / cm ³ and the flat portion was 1.2 g / cm ³ .

Next, test pieces were cut out from the separators obtained in each of the above Examples and Comparative Examples, and then thoroughly washed 1
Prepare a 00 ml beaker (1 test piece / 1 piece), put 80 ml of ion-exchanged water in each beaker, further put the above-mentioned test piece, and then seal the beaker with heat-resistant wrap, Furthermore, a rubber band is used to prevent the wrap from spreading, and the wrap is placed in a constant temperature bath heated to 80 ° C and a relative humidity of 80% and left for 50 hours, after which the rate of increase in weight, the rate of increase in volume and bending. A comparative test was conducted on the rate of decrease in strength. The results are shown in Table 1.

In the above-mentioned test pieces, the weight increase rate and the volume increase rate were obtained by using three pieces each cut into a size of 3 cm × 3 cm from the rib portion and reducing the bending strength. For, 10 sheets were used which were cut from the flat portion to a size of 5 cm × 1 cm.

The rate of increase in the above weight was determined by using a scientific balance to measure the weight of the test piece before being immersed in the ion-exchanged water and the test piece after the 50-hour immersion was taken out from the beaker with tweezers and immediately The water droplets on the surface were wiped off, the weight at that time was measured, and the difference between the two was determined, and the average value was shown.

The rate of increase in volume was determined by measuring the volume of the test piece before immersing in ion-exchanged water using a caliper, a micrometer, etc., and removing the test piece after 50 hours of immersion from the beaker using tweezers. The water droplets on the surface were quickly wiped off, the volume at that time was measured, the difference between the two was determined, and the average value was shown.

Further, the decrease rate of the bending strength was determined by autograph (manufactured by Shimadzu Corporation, trade name 1M-100) with the bending strength of 5 test pieces before being immersed in ion-exchanged water for 50 hours. The bending strength of each of the finished test pieces was measured, and the difference between the two was measured, and the average value was shown.

On the other hand, fuel cells were assembled using the separators obtained in each of the above Examples and Comparative Examples, and the cell characteristics were confirmed. First, a carbon powder carrying a platinum catalyst and a perfluorosulfonic acid powder were dispersed in ethanol to prepare a paste, which was uniformly applied to carbon paper to form an electrode catalyst layer. Two pieces of carbon paper coated with this paste are cut into 100 mm square pieces, a perfluorosulfonic acid film (DuPont, Nafion, manufactured by DuPont) with a thickness of 50 μm is sandwiched so that the paste surface faces inside, and pressure bonding is applied while heating. Then, a membrane electrode assembly (MEA) was manufactured.

Next, 50 MEA separators each having the shape shown in FIGS. 1 and 2 obtained in each of the examples and the comparative examples were used, and the MEA described above was used as shown in FIG. The separator A was sandwiched between the surfaces (surfaces) A, and the periphery of the rib portion 1 and the hole portion 2 of the separator was sealed with a liquid packing (silicone rubber) to produce 50 single cells.

Then, the obtained 50 sets of single cells were
The ribs 1 and holes 2 around the separator B surface (rear surface) shown in FIG. 2 which is adjacent to the outer surface of the separator B surface (rear surface) shown in FIG. 1 are laminated while being sealed with a liquid packing (silicone rubber), The top and bottom of the laminate were sandwiched by rigid plates and fixed by applying a surface pressure of 500 KPa to obtain a stack for confirming battery characteristics.

Hydrogen gas was passed through the hole (manifold) portion 2 in the stack for confirming the battery characteristics thus obtained,
Supply air and cooling water, keep at 80 ℃, 0.4mA
The operation was performed at a current density of / cm ² for 200 hours, and the output voltage of each single cell was measured. Table 1 shows the maximum voltage and the minimum voltage in 50 cells after 200 hours have passed. The voltage immediately before the stop was described for the stack that was stopped due to a problem that occurred before the operation time of 200 hours.

[0063]

[Table 1]

As shown in Table 1, the separators of Example 1 and Example 2 according to the present invention were higher in weight increase rate, volume increase rate and bending strength than the separators of Comparative Example 1 and Comparative Example 2. It is clear that the decrease rate of the battery is small, a high output can be supplied even after 200 hours of operation, and there is no problem with the soundness of the battery stack.

[0065]

EFFECTS OF THE INVENTION The fuel cell separator of the present invention is a fuel cell separator in which the rate of increase in volume and weight of the separator and the rate of decrease in bending strength are small even when immersed in warm water. Further, the fuel cell of the present invention is a high-performance fuel cell having a fuel cell separator that has a small increase rate of the volume and weight of the separator and a small decrease rate of bending strength even when immersed in warm water.

[Brief description of drawings]

FIG. 1 is a plan view showing an example of the shape of a fuel cell separator.

FIG. 2 is a plan view showing another example of the shape of the fuel cell separator.

[Explanation of symbols]

1 rib part 2 Flat part 3 holes 4 protrusion 5 groove

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Masaaki Yokota             Hitachi, Ichiba, Ibaraki Prefecture             Seikou Co., Ltd. Yamazaki Office F-term (reference) 5H026 AA06 BB02 BB06 CC03 CC08                       EE06 EE18 HH00 HH01 HH02                       HH05 HH08 HH10

Claims (16)

[Claims] 1. A fuel cell separator in which the rate of increase in volume after immersion in hot water at 80 ° C. ± 5 ° C. for 50 hours or more is within 0.1% before immersion in hot water. 2. The fuel cell separator according to claim 1, wherein the rate of increase in weight after immersion in hot water at 80 ° C. ± 5 ° C. for 50 hours or more is within 2% before immersion in hot water. 3. The fuel cell separator according to claim 1, wherein the rate of decrease in bending strength after immersion in hot water at 80 ° C. ± 5 ° C. for 50 hours or more is within 10% before immersion in hot water. 4. A fuel cell separator in which the rate of increase in weight after immersion in hot water at 80 ° C. ± 5 ° C. for 50 hours or more is within 2% before immersion in hot water. 5. A fuel cell separator in which the rate of decrease in flexural strength after immersion in hot water at 80 ° C. ± 5 ° C. for 50 hours or more is within 10% before immersion in hot water. 6. The fuel cell separator according to claim 1, wherein the separator is a molded body containing graphite and a resin. 7. The fuel cell separator according to claim 1, wherein the separator has a rib portion and a flat portion. 8. The fuel cell separator according to claim 1, wherein the graphite is expanded graphite. 9. The fuel cell separator according to claim 1, wherein the expanded graphite is an expanded graphite sheet pulverized powder and the resin is a phenol resin. 10. The crushed powder of expanded graphite sheet has an average particle size of 2
It is 5 micrometers-500 micrometers, The separator for fuel cells in any one of Claims 1-9. 11. The resin as a powder, which undergoes ring-opening polymerization and has an average particle size of 1 μm to 100 μm.
0. The fuel cell separator according to 0. 12. The fuel cell separator according to claim 1, which has a density of 1.35 g / cm ³ or more. 13. The fuel cell separator according to claim 1, wherein the molded body is molded by a compression molding method. 14. The fuel cell separator according to claim 1, wherein the separator has a hole portion other than the rib portion and the flat portion. 15. A fuel cell comprising the fuel cell separator according to claim 1. 16. The fuel cell according to claim 15, which is a solid polymer type.