JPH10334927A - Separator for solid high polymer fuel cell and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for a solid high polymer fuel cell possessing performance such as gas nonpermeability, conductivity, sulfuric acid resistance, required strength, and lightness at a low cost by forming the separator with carbon powder and a thermosetting resin into the prescribed shape, mainly by the resin molding method. SOLUTION: Carbon powder such as natural graphite of 80-40 vol.% and a thermosetting resin such as a phenol resin of 20-60 vol.% are mixed, a solvent such as acetone is added, and they are kneaded into a flake shape and inserted into a die of the prescribed shape for press molding. A separator with the prescribed external shape and grooves on the surface and back face is formed, and mechanical machining such as boring and screw cutting is applied, as required, to obtain a final product. The separator preferably has an electrical specific resistance of 200000 μΩ.cm or below and the practical lower limit of about 5000 μΩ.cm, and the prescribed quantities of metal materials such as titanium, gold, and silver can be blended as required according to the conductivity and strength required.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a separator for a polymer electrolyte fuel cell and a method for producing the same.

[0002]

2. Description of the Related Art Fuel cells are expected as next-generation power generators having low pollution and high power generation efficiency. Depending on the type of electrolyte, the type of this fuel cell is alkaline,
There are phosphoric acid type, molten carbonate type, solid electrolyte type, solid polymer type and the like. Among these, polymer electrolyte fuel cells are expected to be used as small-scale power generation and portable power sources.

[0003] The main performance required for a separator of a polymer electrolyte fuel cell is that it is difficult to permeate gases such as hydrogen, oxygen, and air, has a low electric resistivity, and is chemically stable in a sulfuric acid atmosphere. That it has the necessary strength as a part and that it is lightweight.

[0004] A polymer electrolyte fuel cell is currently under development. A separator made of a plate made of titanium, artificial graphite, or the like is used, and the separator is formed by machining such as cutting. is there.

[0005]

However, the titanium material has a problem that it is difficult to satisfy the above-mentioned requirement for lightness because it is heavy. Artificial graphite is a material which does not have good gas impermeability and still has many problems in this aspect. In addition, both are extremely expensive because the shapes are formed by machining, and there is a problem in that they are a bottleneck in the practical use of polymer electrolyte fuel cells.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above problems and to provide a polymer electrolyte fuel cell separator having the above-mentioned required performances at a low cost.

[0007]

In order to achieve this object, the present invention comprises a carbon powder and a thermosetting resin as components and is formed by a resin molding method as a main shape forming means. It is.

[0008] With such a configuration, the carbon powder and the thermosetting resin are used as components, so that the material is inexpensive. Also, since the resin molding method is used as the main shape forming means, it is inexpensive. it can. Moreover, since it is molded using carbon powder and thermosetting resin as components, it is required to have gas impermeability, low electric resistivity, sulfuric acid resistance, required strength and light weight required for separators of polymer electrolyte fuel cells. And so on at a practical level.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a basic configuration example of a polymer electrolyte fuel cell. Here, 1 is a fuel electrode, 2 is an electrolyte plate, and 3 is an oxidizer electrode. Reference numeral 4 denotes a separator according to the present invention, in which a large number of grooves 5 are formed on both front and back surfaces.

The separator 4 of the present invention contains carbon powder and a thermosetting resin as components, and is formed with the outer shape and grooves 5 on both front and rear surfaces as a main shape forming means by a resin molding method.

The carbon powder used here reduces the specific electrical resistance of the separator, that is, contributes to its electrical conductivity. The carbon powder is composed of known carbonaceous artificial graphite powder, graphite artificial graphite powder, and natural graphite powder. Or a mixture thereof can be used. In particular, when natural graphite powder is used, the electrical resistivity of the separator can be greatly reduced.

The thermosetting resin is for imparting required moldability and gas impermeability to the separator.
Specifically, a known phenol resin, polyimide resin, epoxy resin, furan resin, or the like can be used. Among them, a phenol resin is particularly preferably used because it easily obtains required moldability and gas impermeability and has excellent sulfuric acid resistance. The phenolic resin may be either a novolak phenolic resin or a resol phenolic resin, or a mixture thereof.

The mixing ratio of the carbon powder and the thermosetting resin is as follows:
(Carbon powder): (Thermosetting resin) = 80% by volume or less to 4
0% by volume or more: preferably from 20% by volume to 60% by volume. 20% by volume of thermosetting resin
If it is less than this, the compounding ratio of this resin becomes too small, and it becomes difficult to obtain required moldability, gas impermeability and strength. When the compounding ratio of the thermosetting resin exceeds 60% by volume, that is, when the compounding ratio of the carbon powder is less than 40% by volume, the electrical resistivity tends to exceed the allowable limit and become too large. Therefore, the mixing ratio is set to (carbon powder) :( thermosetting resin) = 70% by volume or less to 50% by volume.
Above: More preferably from 30% by volume to 50% by volume.

In the present invention, the electrical resistivity of the separator is preferably 200000 μΩ · cm or less. If the value exceeds this value, the electrical resistivity of the separator becomes too large, and the inconvenience of increasing the internal resistance of the fuel cell tends to occur. Although the electric resistivity is preferably as small as possible, the practical lower limit when the carbon powder and the thermosetting resin are blended in the above range is 50.
It is about 00 μΩ · cm.

[0015] The separator of the present invention may contain a sulfur-resistant metal material in addition to the carbon powder and the thermosetting resin. This metal material is useful for improving and adjusting the conductivity and strength of the separator. However, since the separator is used in a sulfuric acid atmosphere inside the fuel cell, this metal material needs to have sulfuric acid resistance as described above. Therefore, this metal material can be specifically composed of powder, fiber, or the like of titanium, gold, silver, or the like. This metal material can be contained at an appropriate mixing ratio according to the required conductivity and strength. However, if the mixing ratio is too small, it is difficult to obtain the effect. If the mixing ratio is too large, the conductivity and the strength can be improved, but the cost and the product weight increase, which is not practical.

Next, a method for producing the separator of the present invention will be described. First, a carbon powder and a thermosetting resin such as a phenolic resin are blended, for example, at a ratio in the range described above,
If necessary, a metal material is further blended to obtain a mixture. Next, a solvent such as acetone or methanol is added to the mixture and mixed, and hot kneading is performed by a hot roll facility to obtain a flake-like mixture. Then, the flaky mixture is pulverized to obtain a forming raw material. In addition, as described above, hot kneading with a hot roll facility is effective for homogenization of components, but mixing may be performed at room temperature and in a non-pressurized state.

Next, using the obtained molding material, the shape of a separator is formed by a resin molding method. As the resin molding method, a press molding method, a transfer molding method, an injection molding method, or the like can be applied. By such a resin molding method, not only the outer shape of the rectangular separator 4 shown in FIG. 1 but also a large number of grooves 5 on both the front and back surfaces are formed at a time. According to this, in principle, machining such as cutting is unnecessary, and molding can be performed at low cost. Note that, depending on the shape of the separator, a predetermined shape may not be obtained by only one resin molding using a mold. In that case, the obtained molded body is additionally subjected to machining such as drilling and thread cutting to obtain a final product.

A specific example of a typical manufacturing method is as follows. That is, first, a solid resol-type phenol resin, natural graphite powder, and a trace amount of a release agent are blended at a predetermined ratio, adjusted to an appropriate viscosity with a solvent such as methanol, and kneaded with a hot roll facility. Then, the obtained flaky mixture is pulverized with a mixer to obtain a molding material. Thereafter, the obtained molding material is typically resin-molded by a hot press machine. At this time, 130-1
It is molded at 50 ° C. and then accelerates the curing of the thermosetting resin at 150 to 180 ° C.

[0019]

Next, the present invention will be specifically described based on examples and comparative examples. In the following, the performance of the separator was evaluated according to the following items.

(1) Bulk specific gravity [g / cm ³ ] It is a measure of the lightness of the separator and is the basis for calculation of the following filling rate. The value is obtained by directly measuring a molded body, that is, a molded separator. I got

(2) Filling rate [% by volume] This is a measure of gas impermeability. Using the above bulk specific gravity, it was determined by the following equation.

That is, for example, when there are three types of raw materials, that is, carbon powder, phenol resin, and metal powder, the respective types of raw materials are A, B, and C. The expressed blended at a volume ratio [%] of V _A, V _B, respectively, in V _C, represents the specific gravity _{^{[g / cm 3] ρ A}} , ρ B, with [rho _C. Then the theoretical value of the specific gravity of the separator is a molded body ρ _ABC [g / cm ^3] _{is, ρ ABC = (V A ρ} A + V B ρ B + V C ρ C) / (V A + V B + V C) = (V _A ρ _A + V _B ρ _B + V _C ρ _C ) / 100, and the filling rate [volume%] is represented by the following equation.

(Filling rate) = ((measured bulk specific gravity of molded product)
/ Ρ _ABC ) × 100 (3) Electric resistivity [μΩ · cm] Using a constant DC current supply (manufactured by Takaba Corporation), a digital multimeter (manufactured by Takeda Riken Co., Ltd.), etc., by the voltage drop method It was measured. (4) Bending strength [kg / cm ² ] Measured by a three-point bending method using a tensile strength tester (manufactured by Tokyo Testing Machine Co., Ltd.).

Example 1 A carbon powder having a particle size of 110
A graphite artificial graphite powder having a size of not less than μm and not more than 160 μm was used. A phenol resin was used as the thermosetting resin. The mixing ratio of the carbon powder and the phenol resin was (carbon powder) :( phenol resin) = 65% by volume: 35% by volume.

The carbon powder and the phenol resin were mixed, then methanol was added, and the mixture was kneaded with a hot roll, and then pulverized to obtain a forming raw material. Next, this molding material was press-molded. The conditions were a temperature of 140 ° C., a pressure of 100 kg / cm ² , and a time of 30 minutes. After molding, the resin was cured by curing at 150 ° C. for 16 hours.

Various characteristic values of the thus obtained separator were measured, and the results as shown in Table 1 were obtained.

[0027]

[Table 1]

(Example 2) The mixing ratio of the carbon powder and the phenol resin was calculated as follows: (carbon powder) :( phenol resin) = 5
0% by volume: 50% by volume. The rest was the same as in Example 1 to obtain a separator. The various characteristic values are as shown in Table 1.

(Example 3) The mixing ratio of the carbon powder and the phenol resin was calculated as follows: (carbon powder) :( phenol resin) = 6
0% by volume: 40% by volume. The rest was the same as in Example 1 to obtain a separator. The various characteristic values are as shown in Table 1.

Example 4 In addition to carbon powder and phenolic resin, reduced silver powder was compounded as a sulfuric acid-resistant metal material. The mixing ratio is (carbon powder) :( phenol resin) :( reduced silver powder) = 59 vol%: 40 vol%: 1
% By volume. The rest was the same as in Example 1 to obtain a separator. The various characteristic values are as shown in Table 1.

(Examples 5 to 7) Compared with Example 4, the mixing ratio of the reduced silver powder and the carbon powder was changed as shown in Table 1. The rest was the same as in Example 4 to obtain a separator. The various characteristic values are as shown in Table 1.

Example 8 As a sulfuric acid-resistant metal material,
Stainless steel powder (SUS316L, particle size 10-45μ)
m). The mixing ratio was (carbon powder) :( phenol resin) :( stainless steel powder) = 57.5% by volume: 40.0% by volume: 2.5% by volume. The rest was the same as in Example 1 to obtain a separator.
The various characteristic values are as shown in Table 1.

(Example 9) As a sulfuric acid-resistant metal material,
Stainless steel fibers (SUS316, fiber diameter 8 μm, fiber length 5 mm, convergence 5000) were blended. The compounding ratio was (carbon powder) :( phenol resin) :( stainless fiber) = 57.5% by volume: 40.0 as in Example 8.
% By volume: 2.5% by volume. Other than that, a separator was obtained in the same manner as in Example 8. The various characteristic values are as shown in Table 1.

(Comparative Example 1) The mixing ratio of the carbon powder and the phenol resin was calculated as follows: (carbon powder) :( phenol resin) = 8
5% by volume: 15% by volume. The rest was the same as in Example 1 to obtain a separator. The various characteristic values are as shown in Table 1.

(Comparative Example 2) The mixing ratio of the carbon powder and the phenol resin was calculated as follows: (carbon powder) :( phenol resin) = 3
5% by volume: 65% by volume. The rest was the same as in Example 1 to obtain a separator. The various characteristic values are as shown in Table 1.

In the above, all of the separators of Examples 1 to 9 can be molded by a resin molding method and can be produced at low cost. In particular, the separators of Examples 1 to 3 were prepared by mixing carbon powder and a phenol resin. However, since the mixing ratio was within a preferable range, all of the separators had a high filling rate and required gas impermeability. I was doing it. It was also inexpensive in material. In addition, the bulk specific gravity was small and the weight was configured. Also, the electrical resistivity was sufficiently small. In addition, the bending strength was sufficiently high for practical use. For this reason, it had satisfactory characteristics as a fuel cell separator.

The separators of Examples 4 to 7 are the same as those of Example 3.
These were prepared by adding reduced silver powder as a metal material and changing the added amount, that is, the blending ratio, but all had satisfactory characteristics as separators for fuel cells. In particular, as the blending ratio of the reduced silver powder increased, the electrical resistivity decreased, and the conductivity improved. The bending strength also improved as the proportion of the reduced silver powder increased.

The separators of Examples 8 and 9 were blended with stainless steel powder and stainless steel fiber as a metal material, but also had satisfactory characteristics as a fuel cell separator. The mixing ratio of these stainless steel powder and stainless steel fiber is 2.
Although it was 5% by volume, the electrical resistivity was remarkably improved in Example 9 in which the stainless steel fiber was blended, and the bending strength was superior in Example 8 in which the stainless steel powder was blended.

On the other hand, in Comparative Example 1, the carbon powder and the phenol resin were blended. However, since the blending ratio of the phenol resin was extremely low, the filling rate and the bending strength decreased correspondingly. .

In Comparative Example 2, on the contrary, since the blending ratio of the phenol resin was high, the flexural strength was correspondingly improved, but the electrical resistivity increased.

[0041]

As described above, according to the present invention, since carbon powder and thermosetting resin are the main components, they are inexpensive in terms of material, and are formed by a resin molding method as a main shape forming means. Since it can be molded at low cost and is molded with carbon powder and thermosetting resin as main components, it is required to have gas impermeability, low electrical resistivity, sulfuric acid resistance, etc. required for polymer electrolyte fuel cell separators. The required strength and lightness can be provided at a practical level.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view showing a basic configuration example of a polymer fuel cell using a separator according to an embodiment of the present invention.

[Explanation of symbols]

 4 separator 5 groove

Claims (8)

[Claims] 1. A separator for a polymer electrolyte fuel cell, comprising carbon powder and a thermosetting resin as components, and formed as a main shape forming means by a resin molding method. 2. The compounding ratio of the carbon powder and the thermosetting resin is (carbon powder) :( thermosetting resin) = 80 vol% or less to 40 vol% or more: 20 vol% to 60 vol%. The separator for a polymer electrolyte fuel cell according to claim 1, wherein: 3. The separator for a polymer electrolyte fuel cell according to claim 1, wherein the electrical resistivity is not more than 200000 μΩ · cm. 4. The method according to claim 1, further comprising a sulfuric acid-resistant metal material in addition to the carbon powder and the thermosetting resin.
9. The separator for a polymer electrolyte fuel cell according to claim 1. 5. A method for producing a separator for a polymer electrolyte fuel cell, comprising using a material comprising carbon powder and a thermosetting resin to form a shape mainly by a resin molding method. 6. The mixing ratio of the carbon powder and the thermosetting resin is (carbon powder) :( thermosetting resin) = 80% by volume or less to 40% by volume or more: 20% by volume to 60% by volume or less. 6. The method for producing a separator for a polymer electrolyte fuel cell according to claim 5, wherein: 7. The method for producing a separator for a polymer electrolyte fuel cell according to claim 5, wherein a sulfuric acid-resistant metal material is contained in addition to the carbon powder and the thermosetting resin. 8. A polymer electrolyte fuel cell comprising the separator according to any one of claims 1 to 4.