WO2005057696A2

WO2005057696A2 - Method of manufacturing fuel cell separator and fuel cell separator

Info

Publication number: WO2005057696A2
Application number: PCT/JP2004/016900
Authority: WO
Inventors: Takeharu Kuramochi; Masahiko Katsu; Nobuaki Akutsu; Kaoru Eguchi; Masahiro Omata; Hideto Kanafusa; Yoshiki Muto; Hiroshi Saitou
Original assignee: Nissan Motor Co., Ltd.
Priority date: 2003-12-12
Filing date: 2004-11-08
Publication date: 2005-06-23
Also published as: JP2005174821A; WO2005057696A3

Abstract

A method of manufacturing a fuel cell separator (1) includes: a step of providing resin (19, 21) on surfaces of first carbon particles (17); a step of mixing the first carbon particles (17) provided with the resin (19, 21) and second carbon particles (15) having larger particle diameter than that of the first carbon particles (17) so as to cause the first carbon particles (17) to penetrate gaps between the second carbon particles (15); and a step of performing compression-molding of a mixture of the first carbon particles (17) provided with the resin (19, 21) and the second carbon particles (15) to melt the resin (19, 21) and adhere the first carbon particles (17) to the second carbon particles (15) together with the resin (19, 21). By this method, portions where the carbon particles (15, 17) are in contact with each other are reduced, and the electric resistance is reduced, thus increasing the conductivity.

Description

DESCRIPTION

METHOD OF MANUFACTURING FUEL CELL SEPARATOR AND FUEL CELL SEPARATOR

TECHNICAL FIELD The present invention relates to a method of manufacturing a fuel cell separator brought into contact with a pair of electrodes sandwiching an electrolyte membrane, and relates to the fuel cell separator.

BACKGROUND ART A fuel cell is a device which directly converts chemical energy of fuel to electric energy by electrochemically reacting fuel gas (hydrogen) with oxidant gas

(air). The fuel cell, compared to other energy engines, has excellent characteristics such as higher energy efficiency and generation of no toxic exhaust gas because of not using fossil fuel. In such a fuel cell, single cells, each including a pair of electrodes sandwiching an electrolyte membrane, are stacked with separators interposed therebetween to construct a fuel cell stack. Herein, the separators are brought into contact with the electrodes to be used for collecting current from the electrodes, and each of the separators includes a gas passage for gas supply on the electrode side and a coolant passage on the other side. As such a fuel cell separator, the Japanese Patent Application Laid-Open No. 2003-17085 discloses a separator obtained by compression-molding of a mixture material into a predetermined shape, the mixture material including carbon for ensuring conductivity and a thermosetting resin for maintaining moldability and ensuring strength. The carbon material used herein is granular carbon powder, and a plurality of minute crystals with a size of 1 to 10 μm are agglomerated to form the granular carbon powder with a particle diameter of 50 to 60 μm. DISCLOSURE OF INVENTION However, since the conventional separator is made of the plurality of minute crystals of the carbon powder agglomerated, the separator has a problem that electric resistance is increased by contact between the minute crystals and the conductivity is thereby reduced. In addition, the conventional separator is formed by mixing the carbon powder and the thermosetting resin and molding the mixture by applying pressure. Accordingly, the resin could not be interposed between particles of the carbon powder sufficiently, thus reducing the strength of the separator. The present invention was accomplished in the light of the aforementioned circumstances, and an object of the present invention is to prevent reduction in conductivity and strength of the fuel cell separator. According to one aspect of the present invention, there is provided a method of manufacturing a fuel cell separator comprising: providing resin on surfaces of first carbon particles; mixing the first carbon particles provided with the resin and second carbon particles having larger particle diameter than that of the first carbon particles so as to cause the first carbon particles to penetrate gaps between the second carbon particles; and performing compression-molding of a mixture of the first carbon particles provided with the resin and the second carbon particles to melt the resin and adhere the first carbon particles to the second carbon particles together with the resin.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a cross-sectional view of a fuel cell including a separator manufactured with a method of the present invention; FIG. 2 is a cross-sectional view showing a state of compression molding of the separator; FIG. 3A is a schematic view showing a state before the compression molding of a material constituting the separator; FIG. 3B is a schematic view showing a state after the compression molding of the material constituting the separator; FIG. 4 is a schematic view of a carbon particle having resin on a surface thereof; FIGS. 5 A and 5B are schematic views for explaining a process of attaching the resin to the surface of a carbon particle in a second embodiment of the present invention; and FIG. 6 is a schematic view for explaining a process of attaching the resin to the surface of a carbon particle in a third embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, description will be made of embodiments of the present invention with reference to the drawings. FIG. 1 shows a fuel cell including separators 1 manufactured by a method of the present invention. This fuel cell is a polymer electrolyte fuel cell. The fuel cell has a structure in which the separators 1 are arranged on the both sides of a single cell 7. The single cell 7 includes a solid polymer electrolyte membrane

3 sandwiched by a pair of electrodes 5 on both sides. A plurality of the single cells 7 and separators 1 are stacked on each other to obtain a fuel cell stack. Each of the separators 1 includes gas passages la for gas supply on the side of the electrode 5 and includes coolant passages lb on the other side. The gas passages la of one separator 1 are supplied with hydrogen as fuel, and the gas passages la of the other separator 1 are supplied with air as an oxidant. Each of such separators 1 is obtained by molding a mixture material 9, which includes carbon powder and thermosetting resin mixed at a predetermined ratio, by use of a lower mold 11 and an upper mold 13 shown in FIG. 2. The lower mold 11 is provided with convex portions 11a corresponding to the foregoing gas passages la or coolant passages lb and provided with a sidewall portion l ib protruding toward the upper mold 13 in the entire periphery. On the other hand, the upper mold 13 is provided with convex portions 13a corresponding to the coolant passages lb or gas passages la. The mixture material 9 supplied between the aforementioned lower and upper molds 11 and 13 is compressed and heated to be hardened into a molded piece. After being hardened, this molded piece is taken out and cooled to obtain the separator 1. For heating, not-shown heaters embedded in the lower and upper molds 11 and 13 or the like are used. FIG. 3 A shows a state before compression molding of the aforementioned mixture material 9. This mixture material 9 has carbon particles 15 with a predetermined particle diameter and carbon particles 17 with a particle diameter smaller than that of the carbon particles 15. As shown in FIG. 4, the surface of each carbon particle 17 is entirely covered with a resin coating 19 of thermosetting resin by a chemical surface treatment. The chemical surface treatment may be a covering method (dipping method) of immersing the carbon particles 17 in a solution containing the thermosetting resin and drying the same. The chemical surface treatment may also be a covering method of spraying a solution containing the resin onto the carbon particles 17 and then drying the same or a covering method of compressing and kneading powder of the resin and the carbon particles 17. Preferably, the carbon particles 15 with larger particle diameter has a mean particle diameter of 50 μm to 150 μm, and the carbon particles 17 with smaller particle diameter has a mean particle diameter of 10 μm to 50 μm. The mean particle diameter of the carbon powder influences the performance of the separator, so the mean particle diameters of the carbon are preferred to be within the aforementioned ranges. When the mean particle diameter of the carbon particles 15 is larger than 150 μm, the gas tightness of the separator in the direction of the thickness of the separator is lowered, and the gas and coolant easily penetrates the separator. When the mean particle diameter of the carbon particles 15 is smaller than 50 μm, the number of contact points between the carbon particles is increased, thus increasing the electric resistance of the entire separator. The carbon particles 17 with a mean particle diameter of 10 to 50 μm can properly enter spatial intervals of the arrayed carbon particles 15 with larger particle diameter. The carbon particle diameter can be measured by means of a laser diffraction method or an X-ray line broadening analysis. In the method of manufacturing a separator of the present invention, each particle diameter of the carbon particles 17 and an amount of each resin coating

19 are determined so that the volume of the carbon particles 17 including the resin coatings 19 is at least 30% of the total volume of gaps between the carbon particles 15. Herein, the total volume of gaps between the carbon particles 15 designates the total volume of gaps between the carbon particles 15 in the case where the separator is fabricated by compression-molding of only the carbon particles 15. When the volume of the carbon particles 17 having the resin coating 19 is smaller than 30% of the total volume of gaps between the carbon particles 15, there may be more gaps not including the resin in the carbon particles, and the strength of the separator 1 cannot be ensured. As the thermosetting resin, for example, phenol resin or epoxy resin can be used. When the mixture material 9 shown in FIG. 3A is supplied between the upper and lowςr molds 13 and 11 as shown in FIG. 2 and subjected to hot compression molding, the resin coatings 19 are melted to spread so as to fill the gaps between the carbon particles 15 and serves to connect the carbon particles as shown in FIG. 3B. In this case, in the molded separator 1, the carbon particles 15 with larger particle diameter are in contact with each other. Compared to the conventional case where minute crystals of carbon powder are agglomerated and brought into contact with each other, the contact resistance between the carbon particles is reduced, thus increasing the conductivity. The gaps between the carbon particles 15 with larger particle diameter are filled with the carbon particles 17 with smaller particle diameter. In addition, the resin coatings 19 provided on the surfaces of the carbon particles 17 connect the carbon particles 15 with larger particle diameter and the carbon particles 17 and also connect the carbon particles 15 with each other, thus contributing increased strength of the separator. Moreover, since the carbon particles 17 with smaller particle diameter exist between the carbon particles 15 with larger particle diameter, the conductivity between the carbon particles 15 is increased, thus enhancing the electric properties of the entire separator. FIG. 5 shows a second embodiment of the present invention. In this embodiment, a plurality of resin particles 21 made of a thermosetting resin are attached to the surfaces of the carbon particles 17 with smaller particle diameter. For attachment of the resin particles 21, the carbon particles 17 shown in FIG. 5 A are subjected to an electrostatic treatment. Thereafter, the carbon particles 17 are brought into contact with the powder resin particles 21, and the resin particles 21 are attached to the surfaces of the carbon particles 17. At this time, it is preferred that the resin particles 21 are heated for enhancing adhesion with the carbon particles 17. The electrostatic treatment is that high- voltage current is applied to the carbon particles 17 to positively or negatively charge the particle surfaces. In this embodiment, the resin particles 21 are used instead of the resin coatings 19, and the other part thereof is the same as that of the first embodiment. It is thus possible to obtain an effect similar to the first embodiment. Moreover, although the resin material to be attached to the carbon particles 17 is the powder resin particles 21, the carbon particles 17 are subjected to the electrostatic treatment in advance. Therefore, when the carbon particles 17 with the resin particles 21 are mixed with the carbon particles 15, the attachment of the resin particles 21 to the carbon particles 17 can be surely maintained, and the gaps between the carbon particles 15 can be surely filled with the melted resin. In addition, such a method facilitates control of the amount of resin to be attached to the carbon particles 17 subjected to the electrostatic treatment. FIG. 6 shows a third embodiment of the present invention. This embodiment is another example in which the resin particles 21 made of thermosetting resin are attached to the surfaces of the carbon particles 17 with smaller particle diameter. The resin particles 21 are sprayed onto the carbon particles 17 with an application gun 25 provided with a preheater 23 as a heating device. The resin particles 21 within the application gun 25 are heated to around the melting point by the preheater 23, and the heated resin particles 21 are sprayed from a supply opening of the application gun 25 to the surfaces of the carbon particles 17. In the case of phenol resin, the heating temperature is controlled within 90 ± 10 °C. The aforementioned third embodiment has an effect similar to that of the second embodiment and can facilitate the operation of attaching the resin particles 21 to the carbon particles 17. According to the present invention, the volume of the carbon particles with smaller particle diameter, which are attached with the resin particles, is at least 30% of the volume of the gaps between the carbon particles with larger particle diameter. The gaps between the carbon particles with larger particle diameter can be thereby filled with the melted resin, thus ensuring the strength of the separator. In the first embodiment, since the resin is formed into a coating covering the entire surface of each carbon particle, the melted resin efficiently fills the gaps between the carbon particles with larger particle diameter. In the second embodiment, the resin is formed into powder, and the surfaces of the carbon particles are subjected to the electrostatic treatment for enhancing the adhesion between the carbon particles and the powder resin.

Therefore, when the carbon particles with smaller particle diameter are mixed with the carbon particles with larger particle diameter, the attachment of the powder resin can be surely maintained, and the gaps between the carbon particles with larger particle diameter can be surely filled with the melted resin.

Moreover, the amount of resin attached to the carbon particles subjected to the electrostatic treatment can be easily controlled to the desired amount, which is effective for ensuring the strength of the separator. In the third embodiment, the resin is formed into powder, and this powder resin is heated in advance and attached to the surfaces of the carbon particles.

Accordingly, when the carbon particles with the powder resin attached thereon are mixed with the carbon particles with larger particle diameter, the attachment of the powder resin can be surely maintained, and the gaps between the carbon particles with larger particle diameter can be surely filled with the melted resin.

In addition, the amount of resin attached to the carbon particles with smaller particle diameter subjected to the electrostatic treatment can be easily controlled to the desired amount, which is effective for ensuring the strength of the separator.

Furthermore, while being heated, the powder resin is sprayed onto the carbon particles to be attached to the surfaces thereof by the application gun provided with the heating device, which can facilitate the operation of attaching the resin to the carbon particles. The entire content of a Japanese Patent Application No. P2003-415366 with a filing date of December 12, 2003 is herein incorporated by reference. Although the invention has been described above by reference to certain embodiments of the invention, the invention is not limited to the embodiments described above will occur to these skilled in the art, in light of the teachings. The scope of the invention is defined with reference to the following claims.

INDUSTRIAL APPLICABILITY The separator of the present invention includes carbon particles with larger particle diameter and carbon particles with smaller particle diameter having resin on the surfaces thereof. The separator is characterized by causing the carbon particles with smaller particle diameter to penetrate gaps between the carbon particles with larger particle diameter and performing compression-molding of the mixture material in this state to melt the resin and adhere the carbon particles to each other. Compared to the conventional separator made of minute crystals, portions where the carbon particles are in contact with each other are reduced, and the electric resistance is reduced, thus increasing the conductivity. The gaps between the carbon particles with larger particle diameter are filled with the carbon particles with smaller particle diameter, and the carbon particles are adhered to each other with the resin provided on the surfaces of the carbon particles with smaller particle diameter, thus preventing the reduction in strength of the separator.

Claims

1. A method of manufacturing a fuel cell separator, comprising: providing resin on surfaces of first carbon particles; mixing the first carbon particles provided with the resin and second carbon particles having larger particle diameter than that of the first carbon particles so as to cause the first carbon particles to penetrate gaps between the second carbon particles; and performing compression-molding of a mixture of the first carbon particles provided with the resin and the second carbon particles to melt the resin and adhere the first carbon particles to the second carbon particles together with the resin.

2. The method of claim 1, wherein the mixture of the first carbon particles provided with the resin and the second carbon particles is prepared so that an amount of the first carbon particles provided with the resin accounts for at least 30% of a total volume of gaps between the second carbon particles in the case where the separator is fabricated by compression-molding of only the second carbon particles.

3. The method of claim 1 , wherein the resin is provided on the surfaces of the first carbon particles as coatings.

4. The method of claim 1, wherein the providing includes: performing an electrostatic treatment for the first carbon particles; and bringing a powder of the resin into contact with the first carbon particles.

5. The method of claim 1 , wherein the first carbon particles are provided with the resin on the surfaces by being brought into contact with a powder of the resin previously heated.

6. The method of claim 5, wherein the resin is provided on the surfaces of the first carbon particles by being sprayed to the first carbon particles while being heated by an application gun provided with a heating device.

7. The method of claim 1, wherein a mean particle diameter of the first carbon particles is within a range from 10 μm to 50 μm, and a mean particle diameter of the second carbon particles is within a range from 50 μm to 150 μm.

8. The method of claim 1, wherein the resin is thermosetting resin.

9. A fuel cell separator formed in accordance with the process of claim 1.