JPH11354138A - Ribbed fuel-cell separator, its manufacture, and fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure gas non-permeability, electrical conductivity, and a liquid non-swelling property, by dispersing expanded graphite in a resin and molding ribs in one body with a flat plate, and realize weight reduction, by enabling the thickness of a flat plate part to be thinly formed. SOLUTION: A separator is formed of a material made by dispersing expanded graphite in a resin. The material is obtained by integrally molding, preferably, integrally hot-press molding, expanded graphite with a thermosetting resin or thermoplastic resin. As the expanded graphite, expanded graphite is used having worm-like shapes and compression characteristics made by immersing graphite in a strong oxidizing solution, such as a mixture of concentrated sulfuric acid and nitric acid, thereby producing a graphite interlayer compound, rinsing the graphite, and rapidly heating it so as to cause graphite crystals to extend in the C axis direction. Preferably, the height of ribs molded in one body with a flat plate is O. 5 mm or more, and more preferably, 1.0 mm or more. Preferably, a ratio (A/B) of the rib height A to the thickness B of the flat plate is 2 or more.

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 with ribs for separating a fuel gas and an oxidizing gas (air or oxygen) of a fuel cell, a method of manufacturing the same, and a fuel cell.

[0002]

2. Description of the Related Art Fuel cells are expected to be widely used in small generators and power sources for EVs in the future because of their high energy efficiency and low environmental pollution. In a fuel cell, electrodes (positive and negative electrodes) are arranged above and below an electrolyte layer, and a fuel gas and an oxidizing gas (air or oxygen) are flowed above and below the electrodes. Oxidation and reduction reactions at the electrodes, transfer of cations and electrons at the electrolyte layer It is based on the principle that chemical energy is converted into electric energy by a reaction and a potential difference is obtained. Since the fuel cell is manufactured in a structure in which the above-mentioned electrodes and electrolyte layers are alternately stacked in multiple stages, a separator (separator) for separating the fuel gas and the oxidizing gas is provided between the stacked positive and negative electrodes. Further, in order to secure a gas supply path, a structure in which a rib (groove) is provided on a separator is generally used. Further, the potential difference obtained from the single battery is generally collected by an outer current collector plate stacked in multiple stages.

[0003] Therefore, the separator is 1) separation of fuel gas and oxidizing gas (gas impermeability), 2) electrical conductivity,
3) It is required to have properties such as not swelling in water and electrolyte generated at the negative electrode. This separator is generally manufactured by a method in which a groove is machined in a graphite block or glassy carbon and ribs are formed to secure supply paths for a fuel gas and an oxidizing gas.

Further, a method of molding expanded graphite or an expanded graphite sheet obtained by subjecting scaly natural graphite to an acid treatment and then heat-treating the same, or a method of forming a pre-expanded graphite molded body into a liquid in order to prevent swelling due to liquid. (Japanese Patent Application Laid-Open Nos. 60-65781 and 60-12672).

[0005] International Publication No. WO 97/02612.
The specification describes a method in which expanded graphite powder having a specific particle size is dispersed in a thermoplastic resin or a thermosetting resin to obtain a block-shaped molded body, and then machine the grooves. However, the above-mentioned various manufacturing methods for machining are costly.In addition, the manufacturing method using expanded graphite limits the size of ribs that can be manufactured, and further causes swelling of products due to gas generated during molding. There was a problem that products could not be supplied stably and easily.

[0006]

SUMMARY OF THE INVENTION The inventions described in claims 1 to 7 solve the above-mentioned problems. In a fuel cell separator with ribs, gas impermeability, electric conductivity, and liquid impermeability are considered. An object of the present invention is to provide a ribbed separator that can secure swelling properties and can be formed to have a small thickness of a flat plate portion even in a shape having a high rib height, and can be reduced in weight.

[0007] In addition to the above-mentioned objects, the inventions according to claims 8 and 9 provide a separator with ribs, which facilitates hot-press molding of a battery. Claim 1
The invention described in No. 0 provides a ribbed separator capable of ensuring stable battery characteristics even when the separator is used for a long period of time, in addition to the above-mentioned problems.

[0008] The invention described in claim 11 is a method of manufacturing a fuel cell separator with ribs, which ensures gas impermeability, electric conductivity, and liquid non-swelling property, and further increases the height of the ribs. It is an object of the present invention to provide a method for manufacturing a ribbed separator which can be formed to have a small thickness even in a high shape and can be reduced in weight. Further, the invention described in claim 12 ensures gas impermeability, electrical conductivity, and liquid non-swelling property, and furthermore, even in a shape in which the height of the rib is high, the thickness of the flat portion is thin, and the weight is reduced. By providing the ribbed separator, a high-performance fuel cell is provided. Further, the invention described in claim 13 provides, in addition to the above-mentioned problems, a fuel cell capable of securing stable cell characteristics even when the separator is used for a long period of time.

[0009]

SUMMARY OF THE INVENTION The present invention relates to a ribbed fuel cell separator in which expanded graphite is dispersed in a resin and a rib and a flat plate are integrally formed. Further, the present invention relates to the fuel cell separator having a rib height of 0.5 mm or more. The present invention also relates to the fuel cell separator having a rib height of 1.0 mm or more. The present invention also relates to a fuel cell separator wherein the ratio (A / B) of the height (A) of the rib to the thickness (B) of the flat plate is 2 or more. Further, the present invention relates to a fuel cell separator in which the rib is disposed on one side of a flat plate.

[0010] The present invention also relates to a fuel cell separator wherein the ribs are arranged on both sides of a flat plate. The present invention also relates to a fuel cell separator wherein the thickness of the flat plate is 0.25 mm or more and 1.0 mm or less. Also, the present invention
The present invention relates to a fuel cell separator in which the rib has a taper of 2 degrees or more and less than 90 degrees. The present invention also relates to a fuel cell separator wherein the rib has a taper of 2 to 20 degrees. The present invention also relates to a fuel cell separator wherein the fuel cell is a polymer electrolyte fuel cell.

Further, the present invention provides a fuel cell with ribs, wherein a mixture of expanded graphite granulated powder and a thermosetting resin or a thermoplastic resin is used as a raw material, and the mixture is integrally hot-pressed using a mold. The present invention relates to a method for manufacturing a separator. The present invention also relates to a fuel cell having the above-described fuel cell separator. Furthermore, the present invention relates to a fuel cell in which the above-mentioned fuel cell is a solid polymer type.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A ribbed fuel cell separator according to the present invention will be described with reference to the drawings. FIG. 1 is a sectional view of a two-rib separator in which ribs 1 are arranged on both surfaces of a flat plate 2;
FIG. 3 is a cross-sectional view of a one-rib separator in which a rib 1 is arranged on one surface of a flat plate 2. FIG. 3 is a partial cross-sectional view of a fuel cell in which the separator 3, the electrolyte layer 8, and the electrodes (4 and 6) are combined. The separator 3 is composed of a fuel gas 5 flowing through the positive electrode 4 and an oxidizing gas (air) flowing through the negative electrode 6. (Or oxygen) 7 is installed at the place where the separation is performed.

The separator according to the present invention is made of a resin in which expanded graphite is dispersed in a resin.
It is obtained by using an expanded graphite powder and a thermosetting resin or a thermoplastic resin as raw materials and integrally molding, preferably, integrally, hot pressing. The expanded graphite used for the expanded graphite powder is disclosed in
Those manufactured by a known manufacturing method shown in 3799 and the like can be used. For example, graphite with a highly developed crystal structure, such as natural graphite, quiche graphite, and pyrolytic graphite, is immersed in a strongly oxidizing solution such as a mixture of concentrated sulfuric acid and nitric acid, or a mixture of concentrated sulfuric acid and hydrogen peroxide. To form a graphite intercalation compound, rinse with water and then rapidly heat to remove C
An expanded graphite having a compressive property in a worm-like shape subjected to expansion processing in the axial direction is used.

The expanded graphite used in the separator of the present invention may be expanded graphite in an expanded state, or may be pulverized powder obtained by pulverizing the expanded graphite once and pulverizing it into a predetermined shape. When the resin is a powder, the granulated powder obtained by pulverizing the sheet preformed at a constant pressure has less gas generation in the expanded graphite when mixed and molded with the resin powder, and the entanglement of the expanded graphite remains, This is preferable because the reinforcing effect of the resin can be easily secured and the strength of the separator can be improved.

The expansion ratio of expanded graphite is determined by the strength of the separator,
In order to ensure the sealing property, a higher one is preferable.
More preferably, it is twice or more. The average particle size of the expanded graphite powder mixed with the resin is preferably 50 μm or more, more preferably 50 to 500 μm, further preferably 50 to 300 μm, and more preferably 50 to 200 μm. Is most preferred. If it is less than 50 μm, the effect of entanglement of the expanded graphite is reduced, and the strength of the separator tends to decrease.
In the present invention, the average particle size is a number average value, (shares)
It can be measured with a particle size distribution analyzer such as SALD-3000J manufactured by Shimadzu Corporation.

The resin used in the present invention is a thermosetting resin such as a powdery or liquid epoxy resin, a phenol resin, a melamine resin, or the like, or a heat-resistant resin such as a polyamide resin, a polyamideimide resin, a polycarbonate resin, or a phenoxy resin. A plastic resin is used.

The resin to be used is preferably a thermosetting resin from the viewpoint of heat resistance and corrosion resistance. In particular, in terms of workability, a powdery phenol resin which generates less gas during hot pressing is preferable. As the phenol resin, a resin polymerized by ring-opening polymerization, for example, a phenol resin containing a dihydrobenzoxazine ring is preferable because gas generation is particularly low.

In the case of a powdery resin, the particle size distribution is not particularly limited. However, in order to uniformly and dryly mix with the expanded graphite granulated powder, the flow of the resin at the time of molding is taken into consideration.
The average particle size is preferably 5 μm to 50 μm.
More preferably, the average particle size is m.

The rib shape of the separator of the present invention has been optimized in consideration of the cross-sectional area of the flow path that affects the gas supply amount, the contact area between the rib and the electrode that affects the vertical conductivity, the contact area between the electrode and the gas, and the like. Set by value. From the above examination, the height of the rib is preferably 0.5 mm or more, and 1.0 mm
More preferably, it is 1.0 mm to 3.0 mm.
Is more preferable. If it is less than 0.50 mm,
Since the dimensions of the electrode and the separator are small and the flow path resistance is large, it tends to be difficult to stabilize the gas supply amount. On the other hand, a size exceeding 3.0 mm is not preferable because the size of the battery becomes large.

The ratio (A / B) of the height (A) of the rib to the thickness (B) of the flat plate is preferably 2 or more, and preferably 2 to 5 to reduce the size and weight of the battery. More preferred above. If A / B is less than 2, the thickness of the flat plate becomes too large to secure a stable flow rate, and the conductivity in the thickness direction tends to deteriorate. On the other hand, if it exceeds 5, the ribs of the separator become too high with respect to the thickness of the flat plate, the rigidity of the separator becomes insufficient, and the separator may be damaged at the time of assembling the battery. The definition of the height (A) of the rib and the thickness (B) of the flat plate are shown in FIGS. 1 and 2.

The rib of the present invention may be a double rib having ribs arranged on both sides of the flat plate shown in FIG. 1 or a single rib having ribs arranged on one surface of a flat plate shown in FIG. Since both ribs require only one flat plate, the size and weight of the battery can be reduced as compared with single ribs.

The thickness of the flat plate is preferably 0.25 mm to 1.0 mm. If the thickness is less than 0.25 mm, the gas seal level of the separator tends to deteriorate. On the other hand, 1.
If it exceeds 0 mm, the weight of the separator cannot be reduced, and the electrical resistivity tends to increase.

Preferably, the rib has a taper (C) of 2 degrees or more and less than 90 degrees, and more preferably a taper (C) of 2 degrees to 20 degrees. FIG. 1 shows the definition of the angle C. If the angle of the taper is less than 2 degrees, it tends to be difficult to separate the integrally molded product from the mold. On the other hand, if the angle of the rib exceeds 90 degrees, the contact area of the electrodes and the cross-sectional area of the flow path will decrease. This is not preferable in terms of reducing the size and weight because of the reduction.

The separator of the present invention is filled with the mixture of the expanded graphite granulated powder and the resin using a mold capable of forming a desired shape of the separator, and is integrally molded, preferably hot pressed. There is no particular limitation on the mixing ratio of the expanded graphite granulated powder and the resin, but considering the moldability and properties, the expanded graphite granulated powder /
The resin is preferably in the range of 95/5 to 20/80 (weight ratio), and particularly preferably in the range of 10/90 to 30/70. Here, when the amount of the expanded graphite granulated powder to be mixed exceeds 95/5, the moldability tends to decrease, and the mechanical strength tends to sharply decrease due to insufficient matrix. Meanwhile, 2
If it is less than 0/80, the conductivity tends to decrease.

The method of mixing the expanded graphite granulated powder with the thermosetting resin or thermoplastic resin is not limited. When a liquid resin and a solid resin dissolved in a solvent are used, a predetermined amount of expanded graphite powder and a resin solution are mixed in a container, and the mixture is uniformly stirred using a stirrer. Here, the mixture produced using a resin containing a solvent is usually used after removing the solvent with a reduced-pressure drier or the like and pulverizing. Further, a method of dry-blending the expanded graphite powder and the powdery resin (a method of mixing without using a solvent with a shaker or a mixer) can also be used. In view of cost and workability, a dry blending method is preferable.

The molding conditions for the fuel cell separator can be selected according to the type of resin, and are not particularly limited.
Usually, the molding temperature can be a temperature from normal temperature to 400 ° C., and a preferable temperature is 150 to 200 ° C. 1
If the temperature is lower than 50 ° C., the cured product is insufficiently cured, and uncured components may be eluted during actual use. Further, when the temperature exceeds 200 ° C., the composition is rapidly cured, so that it is difficult to cure uniformly, and the product may be deformed. The preferred molding pressure is 20 to 100 kg / cm ² . If it is less than 20 kg / cm ² , the molded product will have a low density, and the battery performance tends to decrease, such as a decrease in gas permeability and an increase in electric resistivity. Also, 100kg
If it exceeds / cm ² , the molded product will have a high density, and product burrs will be likely to occur during hot pressing, which tends to deteriorate workability.

In addition, a step of degassing unnecessary substances such as condensed water generated during curing may be provided according to the type of the resin. Further, a heat treatment may be performed after the molding in order to further promote the curing of the obtained molded article.

As a use of the separator of the present invention, a fuel cell of an alkaline aqueous solution type, an acid aqueous solution type, a solid polymer type, a solid oxide type, a molten carbonate type and the like can be considered. As the electrolyte of the fuel cell, potassium hydroxide or the like is used in the case of an alkaline aqueous solution type, phosphoric acid or the like is used in the case of an acid aqueous solution type, and an ion exchange membrane or the like is used in the case of a solid polymer type. In the case of the carbonate type, lithium carbonate or the like is used,
In the case of a solid oxide type, stabilized zirconia or the like is used. Examples of the base material of the electrode include a carbon material such as carbon fiber, and, if necessary, platinum, palladium,
What provided the catalyst layer of silver, nickel, etc. on the surface is used. Hydrogen, the fuel gas, is composed of water decomposition products, natural gas,
A raw material such as petroleum, coal, methanol, or the like is reacted with water or the like as needed to extract a hydrogen-rich reformed gas, which is supplied by using the gas. The separator of the present invention is most preferably applied to a polymer electrolyte fuel cell in consideration of the operating temperature, corrosion resistance to the electrolyte, and the like.

[0029]

Next, embodiments of the present invention will be described. Example 1 An expanded graphite sheet having a thickness of 1.0 mm and a density of 1.0 g / cm ³ (Carbofit HGP-1 manufactured by Hitachi Chemical Co., Ltd.)
05) with a coarse pulverizer and a fine pulverizer to obtain an average particle size of 100 μm.
m expanded graphite granulated powder (700 g) was obtained. Next, a resol type phenol resin powder (manufactured by Dainippon Ink Co., Ltd., trade name TD
2040C), and dry-mixed with a small V-type blender to obtain 1000 g of a mixed powder.

The height of the rib is 2.5 mm and the thickness of the flat plate is 0.5 mm
The ribs are 2mm in pitch and 2mm in height with a pitch of 2mm.
In order to form a 100 mm x 100 mm separator having a rib taper of 0 degree, a mold having a shape obtained by transferring the shape of the separator is heated to 180 degrees in advance, and the above-mentioned mixed powder is weighed 2,000.
After weighing 20 g / m ² and weighing 20 g, the mixture was uniformly charged into a mold. 180
The resultant was compression-molded by a hot press under the conditions of a surface pressure of 50 kg / cm ² , a molding time of 10 minutes, and degassing three times to obtain a separator having a specified rib shape and a density of 1.4 g / cm ³ .

Example 2 (1) Production of a phenol resin (resin containing a dihydrobenzoxazine ring) that undergoes ring-opening polymerization 1.9 kg of phenol, 1.37% formalin (37% aqueous solution)
0 kg and 4 g of oxalic acid were charged into a 5-liter flask and reacted at reflux temperature for 6 hours. Continue with 6 inside
Unreacted phenol and water were removed by reducing the pressure to 666.1 Pa (50 mmHg) or less to synthesize a phenol novolak resin. The obtained resin has a softening point of 84 ° C (ring and ball method), 3
The ratio of nucleus to polynuclear / binucleate was 92/18 (peak area ratio by gel permeation chromatography).

Next, 1.7 kg of the synthesized phenol novolak resin (corresponding to 16 mol of hydroxyl groups) is mixed with 0.93 kg (corresponding to 10 mol) of aniline and stirred at 80 ° C. for 5 hours to prepare a uniform mixed solution. did. Then, 1.62 kg of formalin was charged into a 5-liter flask, and 90 ° C.
And the above-mentioned novolak / aniline mixed solution was added little by little over 30 minutes. At the end of the addition, the temperature is maintained at the reflux temperature for 30 minutes and then at 100 ° C. for 2 hours 66
Condensed water was removed by reducing the pressure to 66.1 Pa (50 mmHg) or less to obtain a resin containing a dihydrobenzoxazine ring in which 71 mol% of a reactive hydroxyl group was dihydrobenzoxazinated.

(2) Production of Separator An expanded graphite sheet having a thickness of 1.0 mm and a density of 1.0 g / cm ³ (Carbofit HGP-1 manufactured by Hitachi Chemical Co., Ltd.)
05) with a coarse pulverizer and a fine pulverizer to obtain an average particle size of 100 μm.
m of granulated powder was obtained. Next, 300 g of the phenol resin powder produced by the above method was added and dry-mixed with a small V-shaped blender to obtain 1000 g of a mixed powder.

The height of the rib is 2.5 mm and the thickness of the flat plate is 0.5 mm
The ribs are 2mm in pitch and 2mm in height with a pitch of 2mm.
In order to form a 100 mm x 100 mm separator having a rib taper of 0 degree, a mold having a shape obtained by transferring the shape of the separator is heated to 180 degrees in advance, and the above-mentioned mixed powder is weighed 2,000.
After weighing 20 g / m ² and weighing 20 g, the mixture was uniformly charged into a mold. 180
The resultant was compression-molded by a hot press under the conditions of a surface pressure of 50 kg / cm ² , a molding time of 10 minutes and a single degassing to obtain a separator having a specified rib shape and a density of 1.4 g / cm ³ .

Example 3 Using the powder mixture obtained in Example 2 (2), the height of the rib was 0.5 mm, the thickness of the flat plate was 0.25 mm, and the recess of the rib was 0.4 m.
m, in order to form a 100 mm × 100 mm separator having an 89.9-degree rib taper with an equal pitch of 0.4 mm and a convex portion of 0.4 mm, a mold in which the shape of the separator was transferred was previously heated to 180 ° and The mixed powder was weighed to 2000 g / m ² , weighed 4.43 g, and then uniformly charged into a mold. The separator was compression-molded by a 180-degree hot press under the conditions of a surface pressure of 50 kg / cm ² , a molding time of 10 minutes, and a single gas release to obtain a separator having a specified rib shape and a density of 1.4 g / cm ³ .

Comparative Example 1 Expanded graphite powder having a bulk density of 0.002 g / cm ³ (Hitachi Chemical Industries, Ltd.)
14g of Carbofit HGP-1)
It was weighed, uniformly charged into the molding die used in Example 1, and pressed under normal temperature conditions under a surface pressure of 50 kg / cm ² and degassing three times to obtain a density of 1.0 g / cm ³ . An expanded graphite separator alone was obtained.

Comparative Example 2 Melamine-modified phenolic resin (trade name: PR-406, manufactured by Hitachi Chemical Co., Ltd.) was used for the separator obtained in Comparative Example 1.
0) for 12 hours, and the resin on the surface of the molded body was washed with toluene, heated to 25 to 160 ° C., and cured by heating to form a separator having a resin impregnation rate of 30% by weight and a density of 1.3 g / cm ³ . Obtained.

Next, the electrical resistivity, gas permeability, and liquid swellability of the separators obtained in each of the above Examples and Comparative Examples were confirmed. The electrical resistivity is obtained by compression-molding a 50 mm × 50 mm 12 mm thick sample having the same density as that of the separator in addition to the actual separator, and measuring the electrical resistivity in the thickness direction by a voltage drop method. The gas permeability is determined by sealing the periphery of the separator with silicone rubber, and
An air pressure of kg / cm ² was applied, the air leakage amount Q was measured by the underwater displacement method, and calculated by the following equation.

[0039]

(Equation 1) In the above equation, T is the pressing time (second), D is the thickness of the test piece (mm), and S is the pressure receiving area (cm ² ). The liquid swellability is obtained by immersing the separator in hot water at 90 ° C. for 24 hours and measuring the rate of change in plate thickness. Table 1 shows the appearance and physical properties of the separator.

[0040]

[Table 1]

As is clear from the above Examples and Comparative Examples, the ribbed fuel cell separator of the present invention has a rib height of 0.5 mm or more, preferably 1.0 mm With the above, the thickness of the flat plate becomes 0.25
1.0mm, the height of the rib (A) and the ratio of the thickness of the flat plate (B) in the range of 2 to 5 are ideally formed by mixing expanded graphite granulated powder with thermosetting and thermoplastic resin. It can be secured by hot pressing. The obtained separator is electrically conductive,
It has excellent gas permeability and liquid swelling characteristics, and can secure stable characteristics even when used for a separator for a long time.

[0042]

The ribbed separator according to any one of claims 1 to 7 is excellent in gas impermeability, electric conductivity, and liquid non-swelling property, and has a flat plate portion even in a shape having a high rib height. The thickness can be reduced, and the weight can be reduced. The ribbed separator according to the eighth and ninth aspects facilitates the hot-press forming of the battery in addition to the above-mentioned effects.

According to the ribbed separator of the tenth aspect, in addition to the above effects, stable battery characteristics can be ensured even when the separator is used for a long period of time. According to the method for manufacturing a ribbed separator according to claim 11, gas permeability, electrical conductivity, and liquid non-swelling property are ensured, and the plate thickness of the flat plate portion is increased even in a shape having a high rib height. Can be formed thinly,
A lightweight separator can be manufactured. The fuel cell according to claim 12, wherein the gas impermeability, electric conductivity,
Even in a shape having a high liquid non-swelling property and a high rib height, the flat plate portion has a small thickness and a lightweight separator with ribs, so that the performance is high. In the fuel cell according to the thirteenth aspect, in addition to the above effects, stable cell characteristics can be ensured even when the separator is used for a long time.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a double rib separator of the present invention.

FIG. 2 is a cross-sectional view showing one example of a single rib separator of the present invention.

FIG. 3 is a partial cross-sectional view of a fuel cell using both rib separators.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Rib 2 Flat plate 3 Separator with both ribs 4 Positive electrode 5 Fuel gas passage 6 Negative electrode 7 Oxidant gas passage 8 Electrolyte layer

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Harufumi Hasuda 3-3-1 Ayukawacho, Hitachi City, Ibaraki Pref. Hitachi Chemical Co., Ltd. Yamazaki Plant

Claims (13)

[Claims] 1. A ribbed fuel cell separator in which expanded graphite is dispersed in a resin, and a rib and a flat plate are integrally formed. 2. The fuel cell separator according to claim 1, having a rib height of 0.5 mm or more. 3. The fuel cell separator according to claim 1, having a rib height of 1.0 mm or more. 4. The fuel cell separator according to claim 1, wherein the ratio (A / B) of the height (A) of the rib to the thickness (B) of the flat plate is 2 or more. 5. The fuel cell separator according to claim 1, wherein the rib is disposed on one surface of the flat plate. 6. The fuel cell separator according to claim 1, wherein the ribs are arranged on both sides of the flat plate. 7. The fuel cell separator according to claim 1, wherein the thickness of the flat plate is 0.25 mm or more and 1.0 mm or less. 8. The fuel cell separator according to claim 1, wherein the rib has a taper of 2 degrees or more and less than 90 degrees. 9. The fuel cell separator according to claim 1, wherein the rib has a taper of 2 to 20 degrees. 10. The fuel cell separator according to claim 1, wherein the fuel cell is a solid polymer type. 11. A process for producing a ribbed fuel cell separator, comprising using a mixture of expanded graphite granulated powder and a thermosetting resin or a thermoplastic resin as a raw material and integrally molding the mixture using a mold. . 12. A fuel cell comprising a fuel cell separator according to any one of claims 1 to 10 or obtained by the production method according to claim 11. 13. The fuel cell according to claim 12, wherein the fuel cell is a polymer electrolyte fuel cell.