JPH08222241A - Manufacture of graphite member for solid high polymer fuel cell - Google Patents

Abstract

PURPOSE: To manufacture a graphite member which is excellent in gas impermeability and has excellent heat and electric conductivity by performing hardening processing after thermosetting resin liquid is used to impregnate a specific porous isotropic graphite material obtained by performing CIP molding and baking on carbon fine powder. CONSTITUTION: A binding agent such as pitch is added to carbonaceous powder having a maximum particle diameter of 125μm or less, and after it is heated and kneaded, CIP molding is performed by a rubber press. This mold is baked at about 800 deg.C or higher in a nonxoidizing atmosphere, and is graphitized. Thermosetting resin liquid such as phenol resin is used to impregnate an isotropic graphite material which is obtained by this and on which an average pore diameter is not more than 10μm and porosity is not more than 20%, and hardening processing is performed. It is desirable that this impregnating and hardening processing is performed in such a way that the isotropic graphite material is soaked in the thermosetting resin solution in a vessel whose pressure is reduced to 10Torr or less, and after it is held for a prescribed time, the inside of the vessel is pressurized to 3kg/cm<2> or more by air or nitrogen or the like, and is heated to 70 deg.C or more, and after primary hardening is performed, the impregnated graphite material is taken out of the vessel, and secondary hardening is performed at about 180 deg.C or less in the atmosphere, and it is completely hardened.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a solid polymer type (SPE
Type) to a method for manufacturing a graphite member used for a separator or a current collector of a fuel cell.

[0002]

2. Description of the Related Art A polymer electrolyte fuel cell is a solid polymer electrolyte membrane composed of an ion exchange membrane such as perfluorocarbon sulfonic acid, two electrodes provided on both sides thereof, and a fuel gas such as hydrogen and the like for each electrode. It is composed of a separator provided with a gas supply groove for supplying an oxidant gas such as oxygen, and two current collectors provided outside the separator.

This separator is required to have a high gas impermeability in order to supply the fuel gas and the oxidant gas to the electrodes in a completely separated state, and to efficiently dissipate the heat generated by the cell reaction. It is required to have high thermal conductivity. Further, the current collector needs to have excellent electric conductivity in order to efficiently take out the electric energy generated by the battery reaction.

As a separator or current collector required to have such material characteristics, for example, Japanese Patent Application Laid-Open No. 4-267062 discloses an example in which the material of the separator is made of pure copper or stainless steel. However, these metallic materials are in contact with hydrogen gas used as a fuel gas for a long time, so that there is a drawback that hydrogen embrittlement occurs and material deterioration is caused to deteriorate battery performance.

In the phosphoric acid fuel cell, a carbonaceous material, particularly a glassy carbon material excellent in gas impermeability is used for the separator. A glassy carbon material has a unique vitreous property obtained by molding a thermosetting resin liquid such as a phenolic resin or a furan resin, heat-curing it, and then firing and carbonizing it at a temperature of 800 ° C or higher in a non-oxidizing atmosphere. It is a carbon material.

[0006] However, while the glassy carbon material has a dense structure and exhibits high gas impermeability, it has the drawback of poor workability due to its high hardness and brittleness. Furthermore, it has the drawback of lower thermal conductivity and higher electrical resistance than graphite materials, and as a separator or current collector for polymer electrolyte fuel cells that operate at higher current densities than phosphoric acid fuel cells. Not suitable for use.

The graphite material is generally carbonaceous powder such as coke, carbon black, artificial graphite powder, natural graphite powder, etc. as an aggregate and a binder such as pitch, tar and the like is added thereto, and the mixture is heated and kneaded, then molded into a predetermined shape and fired. Since it is manufactured by graphitization and has a higher thermal conductivity and a lower electric resistance than a glassy carbon material, it is useful in various fields as a heater or a conductor. However, the graphite material has a drawback that it lacks denseness and is inferior in gas impermeability because numerous fine pore voids are present in the structure. Therefore, the graphite material cannot be used as it is as a separator or a collector of a polymer electrolyte fuel cell.

Various methods have been proposed in the past for attempting gas impermeability by impregnating the pore voids of this graphite material with a thermosetting resin liquid and heating and curing it to close the pore voids. For example, as a method for specifying the resin to be impregnated, JP-A-52-125488 discloses a method for producing an impermeable carbon product in which a carbon material is impregnated with a Friedel-Crafts resin and cured, and JP-A-59-57975 discloses. Is a method for producing an impermeable carbon material in which a carbon base material is impregnated with a compatible material of a phenol resin and pitch, and the impregnated material is carbonized or graphitized, and Japanese Patent Publication No. 6-31184 discloses a carbon material. Has proposed a method for producing an impermeable carbon material by impregnating and curing a mixed resin solution of a cresol resin and a phenol resin containing a cresol resin in a proportion of 40 to 95% by weight.

As a method for specifying the impregnation curing conditions, Japanese Patent Publication No. 5-67595 discloses that a carbonaceous material is placed in an impregnation tank, immersed in a liquid thermosetting resin under reduced pressure, and then the system is pressurized. A method for producing an impermeable carbon material has been proposed in which the liquid resin is switched to the state and heat-treated at a temperature of 30 ° C. or higher until the liquid resin is initially cured.

[0010]

However, when the impermeable carbon material obtained by these methods is used as a separator or a current collector of a polymer electrolyte fuel cell, gas impermeability, thermal conductivity and conductivity are required. However, there is a problem in that it is not sufficient to give the above in a well-balanced manner.

The inventors of the present invention have conducted research on the porosity of the graphite base material, impregnation of the thermosetting resin liquid, and curing treatment conditions. As a result, the maximum particle size of the carbonaceous powder as the raw material aggregate and the graphite base material have been investigated. It was found that gas impermeability, thermal conductivity, and conductivity can be imparted in a well-balanced manner by specifying the porosity and the conditions for impregnation and curing of the thermosetting resin liquid.

The present invention was developed based on the above findings, and an object thereof is to provide a method for producing a graphite member useful as a separator or a current collector of a polymer electrolyte fuel cell.

[0013]

In order to achieve the above object, a method for producing a graphite member for a polymer electrolyte fuel cell according to the present invention comprises a carbonaceous powder having a maximum particle size of 125 μm or less and a binder added to the carbonaceous powder and heated. After kneading, CIP molding, firing, and graphitization, average pore diameter less than 10 μm, porosity 20%
The following isotropic graphite material is impregnated with a thermosetting resin liquid and cured (Claim 1), and impregnated and cured.
After the isotropic graphite material is immersed in a thermosetting resin liquid in a container kept under a reduced pressure of Torr or less and kept for a predetermined time, the inside of the container is pressurized to 3 kg / cm ² or more and the temperature is 70 ° C or more. It is characterized in that it is performed by heating at (Claim 2).

The graphite member of the separator or the current collector is usually less than 0.1%.
It is used after being thinly processed to 5 to 1 mm, but if the particle size of carbonaceous powder such as coke, which is an aggregate, is large, particles fall off during this processing, so the maximum particle size of carbonaceous powder is 125
It is necessary to use those with a size of μm or less. If the maximum particle size exceeds 125 μm, the resin liquid is likely to flow out during impregnation and curing of the resin liquid, and the gas impermeability is impaired by the loss of carbonaceous powder when the thin film after curing is processed.
Pitch, tar, etc. are used as the binder, and the aggregate is heated and kneaded together with the binder and then CI is applied by a rubber press.
P-molding is performed to obtain a block-shaped molded body having a predetermined shape. The molded body is heated to a temperature of 800 ° C. or higher in a high-temperature furnace maintained in a non-oxidizing atmosphere to be fired and carbonized, and further in a graphitization furnace to be 2
Graphitized at a temperature of 000 ° C or higher.

In this case, the particle size distribution of the carbonaceous powder used,
The porosity of the isotropic graphite material obtained by setting the mixing ratio of the binder and the like can be adjusted. As for the porosity of the isotropic graphite material, it is necessary to use one having an average pore diameter of 10 μm or less and a porosity of 20% or less. This is because some of them flow out and the filling of the pores becomes insufficient. When the average pore diameter is small, it becomes difficult to impregnate the thermosetting resin liquid into the pores,
The average pore diameter is preferably 0.4 μm or more. The reason why the porosity is 20% or less is that when the porosity is higher than 20%, it is difficult to sufficiently fill the inside of the pores with the thermosetting resin to close the pores.

In the impregnation treatment, the isotropic graphite material having the above-mentioned porosity is placed in a container kept under a reduced pressure of 10 Torr or less to deaerate, and then a thermosetting resin liquid is injected to immerse it in the pores. Sufficiently fill with thermosetting resin liquid. The immersion time is appropriately set depending on the size of the isotropic graphite material and the resin viscosity. The thermosetting resin liquid to be used is not particularly limited, and a resin such as a phenol resin, an epoxy resin, or an unsaturated polyester resin which can withstand a sulfonic acid or sulfuric acid aqueous solution having a pH of about 3 is used. It is preferable to use a low viscosity one.

Next, the inside of the container is switched to a pressurized state, pressurized to 3 kg / cm ² or more with a pressurized gas such as air or nitrogen, and heated to a temperature of 70 ° C. or more to obtain the impregnated thermosetting resin liquid. Curing process is performed. This heat treatment under pressure is carried out until the thermosetting resin liquid is primarily cured, but if the rate of primary curing is too fast, part of the impregnated thermosetting resin liquid will flow out and the deep part of the pore voids of the graphite base material will be discharged. It is preferable that the heating temperature does not exceed 130 ° C. because it cannot be closed. The isotropic graphite material that has been subjected to this primary curing treatment is taken out of the container and heated to a temperature of 180 ° C. or lower in the atmosphere to be completely cured (secondary curing).

[0018]

According to the method for producing a graphite member for a polymer electrolyte fuel cell of the present invention, the maximum particle size of carbonaceous powder as an aggregate such as coke and graphite powder and the porosity of the isotropic graphite base material are specified. As a result, the thermosetting resin liquid can be efficiently filled in the pore voids. Further, since the thermosetting resin liquid is impregnated and cured, the gas present in the pore voids of the isotropic graphite base material is degassed under reduced pressure, and then heated under pressure to perform the curing treatment. The impregnated thermosetting resin liquid is cured in the pore voids while the outflow is suppressed.
Therefore, it becomes possible to effectively close the pore voids of the isotropic graphite material.

The isotropic graphite material produced in this manner exhibits high gas impermeability because the pore voids are filled and closed with a thermosetting resin, and the graphite material has excellent thermal conductivity and conductivity. Since it has both, it can be used as a separator or a collector of a polymer electrolyte fuel cell.

[0020]

Hereinafter, examples of the present invention will be described in comparison with comparative examples.

Examples 1 to 7 and Comparative Examples 1 to 3 Coke powders having different maximum particle diameters were used as carbonaceous powders, pitches were added at different mixing ratios, and the mixture was heated and kneaded, and then the kneaded product was CIP molded by a rubber press, The molded product was calcined and carbonized at a temperature of 1000 ° C. in a non-oxidizing atmosphere, and further graphitized at a temperature of 3000 ° C. in a graphitizing furnace. This isotropic graphite material was processed to a length of 200 mm and a thickness of 50 mm to obtain an isotropic graphite base material having different porosity.

This graphite substrate was placed in a container and kept under a reduced pressure of 8 Torr for 5 hours for deaeration, and then a phenol resin solution (viscosity 50 poise / 20 ° C.) or an epoxy resin solution (viscosity 1 poise / 20 ° C.) Was injected and held for 0.5 hour to impregnate the pores of the graphite base material with the resin liquid. Then, the inside of the container was heated to a predetermined temperature while being pressurized to a predetermined pressure with air to cure the impregnated resin liquid, and then sliced to a thickness of 0.7 mm to obtain a separator for a polymer electrolyte fuel cell. . The porosity, impregnation and curing treatment conditions of the isotropic graphite material thus obtained are summarized in Table 1.

Next, various characteristics of these isotropic graphite materials were measured, and the results are shown in Table 2. The measured value is a value obtained by the following method. Specific resistance (μΩ · cm): According to the voltage drop method of JIS R7202 “Test method for artificial graphite electrode”. Gas permeability (cm ² / sec ・ atm): A test piece having a thickness of 0.7 mm (gas-permeable cross-sectional area 283 cm ² ) is subjected to a predetermined pressure with nitrogen gas to measure the flow rate of the nitrogen gas that permeates. I asked from. Gas permeability = Nitrogen gas permeability (cm ³ ) × test piece thickness (cm) / time (sec) × cross-sectional area of permeation (cm ² ) × differential pressure (atm) thermal conductivity (kcal / m ・ h ・ ° C) : By laser flash method.

[0024]

[Table 1] [Table Note] * F: Phenolic resin liquid, E: Epoxy resin liquid

[0025]

[Table 2] [Table Note] * Isotropic graphite material G347 manufactured by Tokai Carbon Co., Ltd.

From the results shown in Tables 1 and 2, it can be seen that the graphite materials of the examples have a smaller gas permeability than the graphite materials of the comparative examples and have a high gas impermeability. Further, the specific resistance is small and the thermal conductivity is large, and it is recognized that these characteristics are imparted in a well-balanced manner.

[0027]

As described above, according to the method for producing the graphite member for a polymer electrolyte fuel cell of the present invention, the maximum particle size of the carbonaceous powder as the aggregate and the porosity of the isotropic graphite base material are obtained. Is specified and the impregnation and curing treatment of the thermosetting resin liquid is performed under specific pressurization and heating conditions, the gas impermeability is excellent, and the conductivity and the thermal conductivity can be imparted in a well-balanced manner. Therefore, it is useful as a method for producing a graphite member used for a separator or a collector of a polymer electrolyte fuel cell.

Claims (2)

[Claims] 1. A binder is added to carbonaceous powder having a maximum particle size of 125 μm or less, and the mixture is heated and kneaded, followed by CIP molding, and then firing.
Average pore size obtained by graphitization is less than 10μm, porosity is 2
A method for producing a graphite member for a polymer electrolyte fuel cell, which comprises impregnating 0% or less of an isotropic graphite material with a thermosetting resin liquid and curing the same. 2. After impregnation and curing treatment, the isotropic graphite material is immersed in a thermosetting resin solution in a container kept under a reduced pressure of 10 Torr or less and kept for a predetermined time, and then the container is 3 kg / cm. ^The method for producing a graphite member for a polymer electrolyte fuel cell according to claim 1, wherein the pressure is applied to ² or more and heating is performed at a temperature of 70 ° C. or more.