KR20160082868A - carbon composite for polymer electrolyte membrane fuel cell and the preparing method thereof - Google Patents

Abstract

The present invention relates to a carbon composite for a fuel cell separating plate and a producing method thereof and, more specifically, to a carbon composite for a fuel cell separating plate having excellent electrical conductivity and mechanical strength, and to a producing method thereof. According to the present invention, a fuel cell separating plate having excellent physical properties can be produced while improving electrical conductivity and mechanical strength by controlling a kind of binders and heat treatment temperature, so the efficiency of an electrolyte fuel cell comprising the same can be improved.

Description

Technical Field [0001] The present invention relates to a carbon composite material for a fuel cell separator,

The present invention relates to a carbon composite material for a fuel cell separator and a method of manufacturing the same, and more particularly, to a fuel cell separator having excellent physical properties by controlling a binder type and a heat treatment temperature, A carbon composite material for a fuel cell separator, and a manufacturing method thereof.

The fuel cell is a switching device that converts chemical energy into electric energy. Since the product after chemical reaction only discharges electricity, heat and water, many studies are being conducted as an environmentally friendly next generation energy source. The fuel cell is classified into a polymer electrolyte membrane fuel cell (PEMFC), an alkaline fuel cell, a phosphoric acid fuel cell, a molten carbonate fuel cell, and a solid oxide fuel cell according to the electrolyte, the operating temperature, Divided.

Among them, the polymer electrolyte fuel cell is more efficient than other types of fuel cells, has a short start-up time, and can be applied to portable devices and transportation vehicles as pollution-free power generation devices, .

In particular, polymer electrolyte fuel cells using hydrogen as the fuel have the greatest potential in the candidates to be used as power sources for future automobiles that can cope with environmental pollution caused by automobile exhaust gas, energy crisis due to depletion of fossil fuel, total amount of carbon dioxide, have.

 In order to commercialize a polymer electrolyte fuel cell, manufacturing cost and weight reduction are required. Analyzing the price and weight of the polymer electrolyte fuel cell stack, the separator plate accounts for 60% of the total stack price and weighs 80%. This is because it is difficult to process the graphite which is currently used as the separating plate material, so that a considerable thickness must be maintained. Therefore, in order to reduce the price and weight of the polymer electrolyte fuel cell stack, it is essential to develop and apply new materials that can replace graphite separators.

In addition to low cost, the properties required for separator materials include excellent processability, high strength and electrical conductivity, low density and gas permeability, and chemical stability. As a candidate material that can meet these various requirements, a composite separator plate prepared by mixing a metal separator mainly composed of stainless steel and graphite and a polymer is being developed. Among them, stainless steel is excellent in workability, price, strength, and specific resistance, but corrosion of the electrolyte membrane occurs due to corrosion in a polymer electrolyte fuel cell environment, and an oxide film is formed on the surface. On the other hand, the composite separator is disadvantageous in that it has low density and excellent chemical stability but low strength and electrical conductivity.

Thus, according to Korean Patent Laid-Open No. 10-2008-0037916, there is provided a method of manufacturing a stainless steel sheet, comprising the steps of: (a) (b) a surface modification step of reducing the Fe content of the surface layer of the stainless steel sheet to form a Cr-rich passivation film having a relatively increased amount of chromium (Cr) component on the surface of the stainless steel sheet; And (c) forming a coating layer selected from a metal nitride layer (MNx), a metal carbide layer (MCy), and a metal boride layer (MBz) on the surface of the surface-modified stainless steel base material. Also disclosed is a stainless steel separator for a fuel cell, wherein a coating layer is formed on the surface produced by the above method.

Also, according to Korean Patent Laid-Open No. 10-2008-0009150, a polymer electrolyte membrane interposed between a cathode and an anode; And at least one of a negative electrode and a positive electrode comprising particles of a catalyst supported on nonconductive catalyst support particles in a matrix of conductive particles, wherein the conductive matrix particles are selected from the group consisting of boron, carbon, nitrogen, or silicon Wherein the metal compound is essentially composed of a metal compound including a non-metal element selected from the group consisting of the metal compound, and the metal compound has a resistivity within a range of less than 300 mu OMEGA cm.

As described above, studies on a polymer electrolyte fuel cell having a low cost and a high density and a high chemical stability but a high strength and electrical conductivity are required. Therefore, studies on a composite membrane having various compositions are currently being carried out in various configurations It is progressing.

It is an object of the present invention to provide a carbon composite material for a fuel cell separator and a method of manufacturing the carbon composite material, and to provide a carbon composite material for a fuel cell separator having excellent electrical conductivity and mechanical strength, and a method for manufacturing the same.

The present invention relates to a method for producing a graphite powder, comprising the steps of: preparing a mixture containing 15 to 35 parts by weight of a binder with respect to 100 parts by weight of graphite powder; Stirring the mixture and pulverizing it to produce a mixed powder; A third step of producing a molded body by press-molding the mixed powder and then heat-treating the molded body to produce a carbonized molded body; And a fourth step of impregnating the carbonized formed body with a resin and heating the mixture in an oven to cure the carbon composite material.

In a preferred embodiment of the present invention, the graphite powder has an interlayer distance of 0.335 nm to 0.0336 nm, a grain size of 0.1 to 20 μm, and a crystal size of 100 to 500 nm.

In a preferred embodiment of the present invention, the graphite powder may have a density of 2.23 g / cm ³ to 2.25 g / cm ³ and a purity of 97% to 99%.

In a preferred embodiment of the present invention, the binder includes a phenol resin, and the phenol resin may be mixed with a low-alcohol at a weight ratio of 1: 1 to 3: 1.

In a preferred embodiment of the present invention, when the binder contains a phenol resin, the mixture is stirred at 20 to 30 ° C for 20 minutes to 1 hour, and then at 50 to 100 ° C for 2 to 4 hours After drying, the pulverization can be carried out.

In a preferred embodiment of the present invention, the binder includes a coal tar pitch, and in the case where the binder is a coal tar pitch, the mixture may be stirred at 140 to 160 ° C for 20 minutes to 1 hour.

In a preferred embodiment of the present invention, the mixed powder may be 70 mesh or less.

In a preferred embodiment of the present invention, the three-step press-molding may be performed at 200 to 500 MPa.

In one preferred embodiment of the present invention, the heat treatment in step 3 may be performed at 300 ° C to 800 ° C.

In one preferred embodiment of the present invention, the resin may be at least one selected from the group consisting of an epoxy resin and a polyester resin.

In a preferred embodiment of the present invention, in the step 4, the impregnation may be performed at a vacuum of 0.3 to 1 torr.

In a preferred embodiment of the present invention, the heating in the four steps may be performed at 30 ° C to 50 ° C.

Another aspect of the present invention and including a graphite powder of 100 parts by weight in respect of phenol resin and coal tar pitch (coal tar pitch) 15 ~ 25 parts by weight the binder of one kind selected from among parts of a density of 1.5 ~ 1.7 g / cm ^3, pore And the carbon composite material for a fuel cell separator is 0.1 to 5%.

In one preferred embodiment of the present invention, the carbon composite material for a fuel cell separator may be manufactured by the manufacturing method of any one of claims 1 to 10.

In a preferred embodiment of the present invention, the carbon composite material for a fuel cell separator has a specific resistance of 4000 μΩcm to 24000 μΩcm and a bending strength of 10 MPa to 30 MPa.

In a preferred embodiment of the present invention, the carbon composite material for a fuel cell separator may be manufactured by the manufacturing method described above.

Another aspect of the present invention provides a fuel cell bipolar plate including the carbon composite material for the fuel cell bipolar plate.

Another aspect of the present invention provides an electrolyte fuel cell including a fuel cell separator.

According to the present invention, it is possible to manufacture a fuel cell separator having excellent physical properties by controlling the type of binder and the heat treatment temperature, thereby improving the efficiency of the fuel cell.

1 is a schematic view of a method of manufacturing a carbon composite material for a fuel cell separator according to the present invention.
2 is a scanning electron microscope image of graphite powder.
3 is a scanning electron microscope image of Comparative Example 1. Fig.
4 is a scanning electron microscope image of Comparative Example 2. Fig.
5 is a graph showing the surface density of the samples according to the present invention.
6 is a graph showing the porosity of the samples according to the present invention.
FIG. 7 is a graph showing a weight reduction rate due to carbonization of samples according to the present invention.
FIG. 8 is a graph showing the rate of weight increase due to impregnation of the samples according to the present invention.
9 is a graph showing the resistivity of the samples according to the present invention.
10 is a graph showing the flexural strength of the samples according to the present invention.
11 is a schematic diagram of a method for observing the microstructure of samples according to the present invention.
12 is an optical microscope image showing microstructure of samples according to the present invention.
13 is an optical microscope image showing the microstructure of the samples according to the present invention.

As described above, the conventional composite separator for a fuel cell is a candidate material that can satisfy not only low cost but also excellent processability, high strength and electric conductivity, low density, gas permeability and chemical stability, And a composite separator prepared by mixing graphite and a polymer are being developed. The stainless steel is excellent in processability, price, strength, and specific resistance, but has a problem in that corrosion occurs in the environment of a polymer electrolyte fuel cell, thereby contaminating the electrolyte membrane and forming an oxide film on the surface. On the other hand, the polymer composite separator has a low density and excellent chemical stability, but has a problem of low strength and low electrical conductivity.

Accordingly, the present invention uses a coal tar pitch or a phenolic resin (Phenolic Resin), which is used for producing fine artificial graphite powder, carbon composite and artificial graphite, having high purity and high purity, as a binder and heat- And a method for producing the carbon composite material.

That is, the present invention provides a method for producing a graphite powder, comprising: preparing a mixture containing 15 to 35 parts by weight of a binder with respect to 100 parts by weight of graphite powder; Stirring the mixture and pulverizing it to produce a mixed powder; A third step of producing a molded body by press-molding the mixed powder and then heat-treating the molded body to produce a carbonized molded body; And 4) a step of preparing a carbon composite material by impregnating the carbonized formed body with an epoxy resin and heating the mixture in an oven to cure the carbon composite material. The method of manufacturing a carbon composite material for a fuel cell bipolar plate according to claim 1, Respectively. Hereinafter, the present invention will be described in more detail.

In the first step of the carbon composite material for a fuel cell separator according to the present invention, a mixture containing 15 to 35 parts by weight of a binder with respect to 100 parts by weight of the graphite powder may be prepared. More preferably, it is preferable to prepare a mixture containing 15 to 25 parts by weight of a binder with respect to 100 parts by weight of the graphite powder. When the amount of the binder is less than 15 parts by weight based on 100 parts by weight of the graphite powder, there is a problem that the mixed powder is not sintered when carbonized. When the binder contains more than 35 parts by weight with respect to 100 parts by weight of the graphite powder, There is a problem that is generated.

The graphite powder may be a conventional graphite powder. Preferably, the graphite powder may have an interlayer distance of 0.335 nm to 0.0336 nm, a grain size of 0.1 to 20 μm, a crystal size of 100 to 500 nm, , The interlayer distance is from 0.3354 nm to 0.03358 nm, the particle size is from 3 탆 to 20 탆, and the crystal size is from 100 to 400 nm. The graphite powder preferably has a density of 2.23 g / cm ³ to 2.25 g / cm ³ and a purity of 97% to 99%.

Here, the binder may include a phenol resin, and the phenol resin may include at least one selected from the group consisting of a novolak-type phenol resin and a resol-type phenol resin. At this time, the phenol resin can be used in a weight ratio of 1: 1 ~ 3 with a low alcohol, and preferably a phenol resin and a low alcohol at a weight ratio of 1: 2 ~ 3. If it is out of the above range, it is difficult to mix with the graphite powder.

In the method for producing a carbon composite material for a fuel cell separator according to the present invention, in the step 2, the mixture prepared in the above step 1 may be stirred and pulverized to prepare a mixed powder.

If the binder contains a phenol resin, the mixture is stirred at 20 to 30 ° C for 20 minutes to 1 hour, dried at 50 to 100 ° C for 2 to 4 hours, And more preferably the mixture is stirred at 25 to 30 DEG C for 30 minutes to 1 hour, dried at 80 to 100 DEG C for 2 to 4 hours and then pulverized to prepare a mixed powder have. If it is outside the above range, it is not mixed with the graphite powder, and there is a problem in that it is difficult to form because the ethanol is not dried.

In the method for producing a carbon composite material for a fuel cell separator according to the present invention, the binder may include a coal tar pitch. When the binder is a coal tar pitch, the mixture is heated at 140 to 160 ° C for 20 minutes to 1 For a period of time and pulverized to prepare a mixed powder. More preferably, the mixture is stirred at 150 to 160 ° C for 30 minutes to 1 hour and pulverized to prepare a mixed powder.

At this time, the mixed powder may be 70 mesh or less, more preferably 60 mesh or less. In the second step, the mixture is pulverized by a pulverizer and sieved to a sieve having a size of 70 mesh or less to prepare a mixed powder. When the mixed powder is more than 70 mesh, there is a problem that the porosity of the carbon composite material for a fuel cell separator to be manufactured thereafter increases and the mechanical properties are deteriorated.

In the method for manufacturing a carbon composite material for a fuel cell separator according to the present invention, in the step 3, the mixture powder is press-formed to produce a molded body and then heat-treated to produce a carbonized molded body. At this time, it is preferable that the uniaxial pressing is performed by the pressure molding. In this case, the three-step pressing molding may be performed at 200 to 500 MPa, more preferably 300 to 500 MPa. When the pressure molding is performed at less than 200 MPa, there is a problem that the properties of the separator plate are poor due to the low density, and there is a problem in the process that it is difficult to take out the molded separator plate when the performance exceeds 500 MPa.

In the method for producing a carbon composite material for a fuel cell separator according to the present invention, the heat treatment in the step 3 may be performed at 300 ° C to 800 ° C, preferably 500 to 700 ° C. If the heat treatment is performed at a temperature lower than 300 ° C., the resistivity may be higher than about 20000 μΩcm and the electrical conductivity may be lowered. If the heat treatment is performed at a temperature higher than 800 ° C., have.

In the method for manufacturing a carbon composite material for a fuel cell separator according to the present invention, in the step 4, the carbonized formed body may be impregnated with a resin and heated in an oven to be cured to produce a carbon composite material.

At this time, the resin may be at least one kind selected from the group consisting of epoxy resin and polyester resin, and preferably epoxy resin. The epoxy resin may be at least one selected from the group consisting of epichlorohydrin, Bisphpnol A epoxy resin and cycloalipatic epoxy resin. The polyester resin may be at least one selected from the group consisting of A polyester resin, an ortho type polyester resin, an iso type polyester resin, and a vinyl ester type polyester resin.

In the step 4, the impregnation may be performed at a vacuum of 0.3 to 1 torr.

In this case, the heating in the four steps may be performed at 30 ° C to 50 ° C, more preferably at 40 ° C to 50 ° C. If the heating is carried out at a temperature outside the above range, There is a problem that the impregnation yield can be lowered.

In addition, the present invention, contain one kinds of binders 15 and 25 having a weight is selected from phenol resin and coal tar pitch (coal tar pitch) with respect to 100 parts by weight of graphite powder portion, and a density of 1.5 ~ 1.7 g / cm ^3, the porosity Of the carbon composite material is 0.1 to 5%. At this time, the carbon composite material for a fuel cell separator may be manufactured by the above-described manufacturing method.

In the carbon composite material for a fuel cell separator according to the present invention, the carbon composite material for a fuel cell separator may have a specific resistance of 4000 μΩcm to 24000 μΩcm, a bending strength of 10 MPa to 30 MPa, 15000 mu OMEGA cm.

The present invention also provides a fuel cell bipolar plate including the carbon composite material for the fuel cell bipolar plate. The fuel cell separator according to the present invention is characterized in that the carbon composite material for a fuel cell separator has a specific resistance of 4000 μΩcm to 24000 μΩcm and a bending strength of 10 MPa to 30 MPa, The conductivity and strength are excellent and the efficiency of the fuel cell including the fuel cell can be improved.

Furthermore, the present invention provides an electrolyte fuel cell including a fuel cell separator. Since the carbon composite material for a fuel cell separator according to the present invention has a low specific resistance and exhibits excellent mechanical strength, the electrolyte fuel cell manufactured therefrom has excellent electrical conductivity and strength, and the efficiency of the fuel cell including the carbon fuel composite material is improved It is possible to manufacture an electrolyte fuel cell with reduced manufacturing cost and reduced weight.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the following examples should not be construed as limiting the scope of the present invention, and should be construed to facilitate understanding of the present invention.

[ Example ]

Example  1. Fuel cell For split plate  Manufacture of Carbon Composites 1

20 parts by weight of coal tar pitch (CTP) powders were added to 100 parts by weight of graphite powder (SFG15, TIMREX grade, see Table 1 below), mixed uniformly and heated to 150 DEG C in a stirring hot plate (GLHPS-D) Stirred and cooled to 25 < 0 > C. The mixed powder was pulverized for 1 minute in a high-speed pulverizer (RF-5900W), and powder having a size of 70 mesh or less was sieved. The sieved powder was uniaxially compacted at a pressure of 300 MPa to prepare a shaped body having a diameter of 20 mm. The resultant molded body was subjected to heat treatment at 300 ° C for 1 hour to carbonize it. After the carbonization, the carbonized molded body was impregnated with a liquid epichlorohydrin by vacuum decompression to 0.35 torr with an epoxy resin to fill the pores generated by the volatilization of the binder, and the impregnated molded body was placed in a drying oven (P-OV150 ) And cured at 40 DEG C for 1 hour to prepare a carbon composite material sample for a fuel cell separator.

Graphite (SFG15) Ash 0.1% max. Humidity 0.5% max. Crystal height 100 nm max. Interlayer spacing 0.3354 to 0.3358 nm Particle size d10 3.7 탆 Particle size d50 8.8 탆 Particle size d90 17.9 탆

Example  2. Fuel cell For split plate  Manufacture of Carbon Composite 2

A carbon composite material sample for a fuel cell separator was prepared in the same manner as in Example 1 except that the molded body was heat-treated at 500 ° C.

Example  3. Fuel cell For split plate  Manufacture of Carbon Composites 3

A carbon composite material sample for a fuel cell separator was prepared in the same manner as in Example 1 except that the molded body was heat-treated at 700 ° C. ,

Example  4. Fuel cell For split plate  Manufacture of Carbon Composites 4

After mixing 100 parts by weight of graphite powder (SFG15, TIMREX yarn, and components shown in the following Table 1) with phenol resin (PR, Penolic Resin, CB-8081) in a weight ratio of 1: Carbon composite material sample for a fuel cell separator was prepared in the same manner as in Example 1, except that the diluted solution was added and mixed so that the resin was 20 parts by weight, the mixture was stirred at 25 DEG C for 30 minutes, and dried at 80 DEG C for 3 hours. .

Example  5. Fuel cell For split plate  Manufacture of Carbon Composites 5

A carbon composite material sample for a fuel cell separator was prepared in the same manner as in Example 4, except that the molded body was heat-treated at 500 ° C.

Example  6. Fuel cell For split plate  Manufacture of Carbon Composites 6

A carbon composite material sample for a fuel cell separator was prepared in the same manner as in Example 4, except that the molded body was heat-treated at 700 ° C.

Comparative Example  One. Fuel cell For split plate  Manufacture of Carbon Composites

20 parts by weight of coal tar pitch (CTP) powders were added to 100 parts by weight of graphite powder (SFG15, TIMREX grade, see Table 1 below), mixed uniformly and heated to 150 DEG C in a stirring hot plate (GLHPS-D) Stirred and cooled to 25 < 0 > C. The mixed powder was pulverized for 1 minute in a high-speed pulverizer (RF-5900W), and powder having a size of 70 mesh or less was sieved. The sieved powder was uniaxially compacted at a pressure of 300 MPa to prepare a carbon composite material sample for a fuel cell separator having a diameter of 20 mm.

Comparative Example  2. Fuel cell For split plate  Manufacture of Carbon Composites

The phenol resin was mixed with 100 parts by weight of graphite powder (SFG15, TIMREX yarn, components shown in the following Table 1) and mixed with 20 parts by weight of phenol resin The diluted solution was added thereto, and the mixture was stirred at 25 DEG C for 30 minutes and dried at 80 DEG C for 3 hours to prepare a mixed powder. The mixed powder was pulverized for 1 minute in a high-speed pulverizer (RF-5900W), and powder having a size of 70 mesh or less was sieved. The sieved powder was uniaxially compacted at a pressure of 300 MPa to prepare a carbon composite material sample for a fuel cell separator having a diameter of 20 mm.

Comparative Example  3. Fuel cell For split plate  Manufacture of Carbon Composites

20 parts by weight of coal tar pitch (CTP) powder was added to 100 parts by weight of graphite powder (SFG15, TIMREX, see Table 1 below), and the mixture was homogeneously mixed and heated at 150 DEG C in a stirring hot plate (GLHPS-D) Stirred and cooled to 25 < 0 > C. The mixed powder was pulverized for 1 minute in a high-speed pulverizer (RF-5900W), and powder having a size of 70 mesh or less was sieved. The sieved powder was uniaxially compacted at a pressure of 300 MPa to prepare a shaped body having a diameter of 20 mm. The formed body was carbonized by heat treatment at 300 ° C for 1 hour to prepare a carbon composite material sample for a fuel cell separator.

Comparative Example  4. Fuel cell For split plate  Manufacture of Carbon Composites

A carbon composite material sample for a fuel cell separator was prepared in the same manner as in Comparative Example 3 except that the molded body was heat-treated at 500 ° C in the same manner as in Comparative Example 3.

Comparative Example  5. Fuel cell For split plate  Manufacture of Carbon Composites

A carbon composite material sample for a fuel cell separator was prepared in the same manner as in Comparative Example 3 except that the molded body was heat-treated at 700 ° C in the same manner as in Comparative Example 3.

Comparative Example  6. Fuel cell For split plate  Manufacture of Carbon Composites

The phenol resin was mixed with 100 parts by weight of graphite powder (SFG15, TIMREX yarn, components shown in the following Table 1) and mixed with 20 parts by weight of phenol resin The diluted solution was added thereto, and the mixture was stirred at 25 DEG C for 30 minutes and then dried at 80 DEG C for 3 hours. The powder was pulverized in a high-speed pulverizer (RF-5900W) for 1 minute, and powder having a size of 70 mesh or less was sieved. The sieved powder was uniaxially compacted at a pressure of 300 MPa to prepare a shaped body having a diameter of 20 mm. The formed body was carbonized by heat treatment at 300 ° C for 1 hour to prepare a carbon composite material sample for a fuel cell separator.

Comparative Example  7. Fuel cell For split plate  Manufacture of Carbon Composites

A carbon composite material sample for a fuel cell separator was prepared in the same manner as in Comparative Example 6 except that the molded body was heat-treated at 500 ° C.

Comparative Example  8. Fuel cell For split plate  Manufacture of Carbon Composites

A carbon composite material sample for a fuel cell separator was prepared in the same manner as in Comparative Example 6 except that the molded body was heat-treated at 700 ° C.

Comparative Example  9. Fuel cell For split plate  Manufacture of Carbon Composites

A commercial product developed by uniaxially molding a mixture of a carbon-based filler and a resin was used in a sulim carbon metal (oil).

Comparative Example  10. Fuel cell For split plate  Manufacture of Carbon Composites

Commercial materials from Schunk of Germany were used.

Experimental Example  1. Fuel cell For split plate  Microstructure of Carbon Composite

The microstructures of the carbon composite material for the fuel cell separators of Examples 1 to 6 and Comparative Examples 1 to 8 were observed using a scanning electron microscope (FE-SEM, 6500F). The results are shown in Figs. 2 to 4. At this time, observations of Top-face and Side-face were observed in the same manner as in Fig. 10, and the results are shown in Figs.

Fig. 2 is an SEM image of raw graphite powder, Fig. 3 is an SEM image of Comparative Example 1, and Fig. 4 is an SEM image of Comparative Example 2. Fig.

According to FIGS. 2 to 4, SEM image observation revealed that the powder mixed with the graphite powder and CTP had the graphite pitch melted around the graphite particles. In addition, graphite powder and CTP were expected to have failed to uniformly coat CTP around the graphite powder by heating and stirring the powder. On the other hand, the powder mixed with graphite powder and PR had a granular shape due to spherical aggregation of graphite particles. As a result of stirring the solution diluted with graphite powder and phenol resin at room temperature, it was expected that the phenol resin solution was uniformly applied to the graphite powder.

11 to 12 are images showing the microstructures of the molding directions of Examples 1 and 4, in which the direction perpendicular to the molding load direction is indicated by Side-Face, and the direction parallel to the molding load direction is the Top-Face Respectively. As shown in Figs. 11 to 12, the tissues of Example 1 and Example 4 exhibited tissues in the backward direction. These results suggest that the anisotropic microstructures formed by using the fine graphite powder. The structure of Example 1 had large pores inside. These results indicate that graphite powder and coal tar pitch are not uniformly mixed. Also, as the heat treatment temperature is increased, it is judged that large pores exist inside due to thermal decomposition of coal tar pitch. It is considered that the pyrolysis gas of coal tar pitch shifted to the outside of the compact and formed open pores. For this reason, epoxy impregnation can be easily performed on mixed powder samples prepared by mixing with coal tar pitch.

On the contrary, it is expected that the phenolic resin is prepared by mixing in a liquid state at room temperature, thereby uniformly applying PR around the graphite particles. Also, it was confirmed that dense microstructure was shown as compared with Example 1 due to solidification of the binder.

Density and porosity were measured to confirm the physical properties of the finished sample. The porosity was measured by the Archimedes method. Electrical resistivity and flexural strength were measured, and the internal structure of the sample was observed using an optical microscope.

Experimental Example  2. Fuel cell For split plate  Measurement of Mechanical Properties of Carbon Composite

In order to measure the mechanical properties of the carbon composite material for the fuel cell separators of Examples 1 to 6 and Comparative Examples 1 to 8, the apparent density, the porosity, the weight change ratio, the electrical resistivity and the bending strength were measured. 5 to 10.

At this time, the porosity was measured by the Archimedes method (ISO 18754: 2003). Also, the resistivity measurement was performed using the voltage drop method. The voltage drop measured at input current of 1 A is calculated considering the cross-sectional area of the specimen. Flexural strength was measured using Excelab i-VT50 universal material tester and the internal structure of the sample was observed using an optical microscope (Nikon ECLIPSE, LV150).

 Display Surface density
(g / cm ³⁾ Porosity
(%) Weight reduction rate
(%) Weight increase rate
(%) Resistivity
(μΩcm) Bending strength
(MPa) Comparative Example 1 A 1.71 - - - - - Comparative Example 2 B 1.72 - - - - - Comparative Example 3 C 1.57 5.0 2.74 - - - Comparative Example 4 D 1.51 25.6 6.38 - - - Comparative Example 5 E 1.51 33.2 6.58 - - - Comparative Example 6 F 1.61 17.4 1.88 - - - Comparative Example 7 G 1.58 11.8 6.44 - - - Comparative Example 8 H 1.58 24.0 7.57 - - - Example 1 I 1.69 1.6 - 7.78 22259 10.1 Example 2 J 1.65 1.8 - 9.87 12577 14.3 Example 3 K 1.68 4.5 - 11.15 6619 17.1 Example 4 L 1.67 0.4 - 3.72 19552 20.0 Example 5 M 1.64 0.8 - 3.50 11875 13.5 Example 6 N 1.62 1.6 - 3.68 4829 16.9

As shown in Table 2 and FIG. 5 to FIG. 10, the density of Comparative Sample 1 prepared by different kinds of binders was 1.71 g / cm ³ and that of Comparative Example 2 was 1.72 g / cm ³ , According to Examples 3 ~ 8, the density decreased with increasing heat treatment temperature in both samples. More specifically, it was found that the density of each sample as the heat treatment temperature was increased was relatively higher when phenol resin was used as a binder than when using a coal tar pitch as a binder.

Further, according to Examples 1 to 6, it was confirmed that the density of the sample impregnated with the epoxy resin after the heat treatment increased compared to that before the impregnation. In this case, the increase in the density according to the heat treatment temperature was found to be larger in the case of using the coal tar pitch as the binder resin than in the case of using the phenol resin as the binder. In addition, the porosity was also increased as the heat treatment temperature increased. When the heat treatment temperature was 300 ° C, the porosity of the coal tar pitch was lower than that of the phenol resin. At 500 ℃ and 700 ℃, the porosity of the coal tar was higher than that of the phenol resin. Further, it was confirmed that the porosity was decreased when the phenol resin was used as the binder at 500 ° C.

Furthermore, after heat treatment, all the samples showed a porosity of about 5 ~ 30%, but after impregnation, it was confirmed that they decreased rapidly to about 0.4 ~ 5%. More specifically, it was confirmed that the porosity in the case of using a phenol resin binder after impregnation is lower than that in the case of using a coal tar pitch binder.

The weight reduction rate after heat treatment is higher when the coal tar pitch binder is used at 300 ° C, but it is confirmed that the weight reduction ratio is higher when the phenol resin binder is used at 500 ° C. The weight increase rate of epoxy resin after impregnation was increased by about 2% when the coal tar pitch binder was used as the heat treatment temperature increased. On the other hand, the use of the phenolic resin binder was constant regardless of the heat treatment temperature. This is expected due to the characteristics of phenol resin (PR) via coal tar pitch (CTP) and solid phase carbonization via liquid carbonization.

The weight reduction rate by carbonization and the weight increase rate by impregnation are shown in FIG. 7 and FIG. According to FIG. 7 and FIG. 8, it is known that the coal tar pitch passes through the liquid phase during the carbonization process, and thus, the open pore develops easily. On the other hand, it is known that closed pores develop in the case of phenol resin via solid phase carbonization. Therefore, when coal tar pitch is used as a binder, it is expected that the epoxy resin is impregnated into the open pores developed inside the sample, and the weight change rate after the impregnation is expected to be greatly increased. On the other hand, when a phenol resin is used as a binder, it is considered that the weight increase rate is not large due to difficulty of penetration of epoxy resin into closed pores inside the molded body.

The results of the electrical resistivity measurement according to the heat treatment temperature are shown in FIG. According to FIG. 9, the resistivity was decreased with increasing the heat treatment temperature, and the resistivity was lower when phenol resin was used than when using coal tar pitch as a binder. It can be expected that as the heat treatment temperature increases, the bond between the graphite and the binder becomes stronger, and the amount of the converted carbon structure increases due to the volatilization of the residual volatiles.

Fig. 10 shows the result of measuring the bending strength according to the heat treatment temperature. According to FIG. 10, when the heat treatment temperature was 300 ° C, the phenol resin binder was about twice as high as that in the case of using the coal tar pitch. However, as the annealing temperature increased, there was no significant difference in flexural strength between the two. In the sample preparation process for measuring the bending strength, the sample was heat treated at 300 ° C. When the coal tar pitch was used, the sample had a weak strength at the edge portion of the sample during polishing. It is considered that the coal tar pitch used as the binder is not fully carbonized and is melted by friction heat generated during polishing.

Experimental Example  3. Fuel cell For split plate  Measurement of Mechanical Properties of Carbon Composite

The carbon composite materials of Examples 1 to 6 and Comparative Examples 9 to 10 were evaluated for their mechanical properties using the Archimedes method (ISO 18754: 2003) in order to examine the mechanical properties of the carbon composite material for a fuel cell bipolar plate manufactured according to the present invention. Respectively. The resistivity measurements were made using the voltage drop method. The voltage drop measured at input current of 1 A is calculated considering the cross-sectional area of the specimen. The results are shown in Table 3 below.

Display The surface density (g / cm ³ ) Electrical resistivity
(μΩ cm ) Bending strength ( MPa ) Example  One I 1.69 22259 10.1 Example  2 J 1.65 12577 14.3 Example  3 K 1.68 6619 17.1 Example  4 L 1.67 19552 20.0 Example  5 M 1.64 11875 13.5 Example  6 N 1.62 4829 16.9 Comparative Example  9 SLBP 9 1.91 8974 31.9 Comparative Example  10 FU 4369 1.93 6421 33.9

According to Table 3, it can be confirmed that the comparative examples 9 to 10, which are commercial products, have relatively high density and strength. This is because they are produced by adding reinforcing agents such as carbon and carbon fiber as commercial separating plates which are generally used do.

On the other hand, according to the present invention, it is confirmed that the resistivity exhibits the best specific resistance in Example 6, and therefore, it can be confirmed that it exhibits excellent electric conductivity.

Claims (17)

1) preparing a mixture comprising 15 to 35 parts by weight of a binder per 100 parts by weight of graphite powder;
Stirring the mixture and pulverizing it to produce a mixed powder;
A third step of producing a molded body by press-molding the mixed powder and then heat-treating the molded body to produce a carbonized molded body; And
And a fourth step of impregnating the carbonized formed article with a resin and then heating the same in an oven to cure the carbon composite material.
The carbon composite material for a fuel cell separator according to claim 1, wherein the graphite powder has an interlayer distance of 0.335 nm to 0.0336 nm, a particle size of 0.1 to 20 μm, and a crystal size of 100 to 500 nm .
The method of claim 1, wherein the graphite powder has a density of 2.23 g / cm ³ to 2.25 g / cm ³ and a purity of 97% to 99%.
The method of claim 1, wherein the binder comprises a phenol resin and the phenolic resin is mixed with a low-alcohol at a weight ratio of 1: 1 to 3: 1.
The method according to claim 1, wherein when the binder contains a phenol resin, the mixture is stirred at 20 to 30 ° C for 20 minutes to 1 hour, dried at 50 to 100 ° C for 2 to 4 hours, The carbon composite material for a fuel cell separator according to claim 1,
2. The fuel cell separator according to claim 1, wherein the binder comprises a coal tar pitch, and in the case where the binder is a coal tar pitch, the mixture is stirred at 140 to 160 DEG C for 20 minutes to 1 hour Carbon composite material.
The method of claim 1, wherein the mixed powder is 70 mesh or less.
The method of claim 1, wherein the three-step press molding is performed at 200 to 500 MPa.
The method of claim 1, wherein the heat treatment is performed at 300 ° C to 800 ° C in the third step.
The method of claim 1, wherein the resin is at least one selected from the group consisting of epoxy resin and polyester resin.
The method of claim 1, wherein the impregnation is performed at a vacuum of 0.3 to 1 torr.
The method of claim 1, wherein the heating in the fourth step is performed at 30 ° C to 50 ° C.
And 15 to 25 parts by weight of one kind of binder selected from phenol resin and coal tar pitch based on 100 parts by weight of graphite powder,
A density of 1.5 to 1.7 g / cm ³ , and a porosity of 0.1 to 5%.
The carbon composite material according to claim 13, wherein the carbon composite material for a fuel cell separator has a specific resistance of 4000 μΩcm to 24000 μΩcm and a flexural strength of 10 MPa to 30 MPa.
14. The carbon composite material for a fuel cell separator according to claim 13, wherein the carbon composite material for a fuel cell separator is manufactured by the method of any one of claims 1 to 12.
A fuel cell bipolar plate comprising the carbon composite material for a fuel cell bipolar plate according to any one of claims 13 to 14.
An electrolyte fuel cell comprising the fuel cell separator of claim 16.

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