JP2000348740A - Separator of solid high polymer type fuel cell and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably generate power over a long time by forming a separator with a resin mold body containing carbon powder and a thermoset resin as constituents and by setting the concentration of impurities contained in the resin mold body to a specific vague or less. SOLUTION: Impurities contained in a resin mold body are specifically base metal ones and the concentration of ones having ionizing tendency larger than that of Hg is set to 100 ppm or less. Those kinds of metals are K, Na, Ba, Ca, Mg, Al, Fe, Ni, Sn, Pb, Cu, Si and P, and easily ionize in the presence of hydrogen ions to adhere or attach to the inside and surface of an ion exchange film so that the film is poisoned. Therefore, the lower the concentration thereof is, the more the risk of the poisoning is reduced, so that it is preferably set to 0.01-5 ppm. Accordingly, it is preferable that carbon material used as a starting material is processed with a halogen compound, for instance, a chlorine gas at a heating temperature of around 2000-2300 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polymer electrolyte fuel cell separator and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, there has been a demand for a next-generation power generation apparatus that is clean and has high power generation efficiency. Fuel cells (Fu) that directly convert the chemical energy of oxygen and hydrogen into electric energy
The expectations for el Cell) are increasing. At present, types of fuel cells include a phosphoric acid type, an alkaline type, a molten carbonate type, a solid electrolyte type, a solid polymer type (also referred to as an ion exchange membrane type), and the like. In particular, polymer electrolyte fuel cells (PEFC: Polymer Electrolyte
Fuel Cell) is considered to be suitable for use as a small and portable power source (for example, a power source for an electric vehicle). Therefore, development is currently being vigorously pursued for practical use.

[0003] This type of fuel cell has a membrane / electrode laminate in which electrodes are arranged on both sides of an ion exchange membrane. This ion exchange membrane can selectively pass hydrogen ions (H ⁺ ). These electrodes carry a metal catalyst such as platinum. One of the pair of electrodes is called a hydrogen electrode (cathode), and the other is called an oxygen electrode (anode). A pair of separators is arranged on both sides of the membrane / electrode laminate, and the outer periphery of both electrodes and the ion exchange membrane are sandwiched by the separators. As a material for a separator, conventionally, a resin molded body mainly containing carbon powder and a thermosetting resin has been proposed.

The hydrogen gas (H ₂ ) supplied through the separator on the hydrogen electrode side becomes hydrogen ions (H ⁺ ) by a catalytic reaction at the hydrogen electrode. The hydrogen ions move toward the oxygen electrode while passing through the ion exchange membrane. Oxygen gas (O ₂ ) is supplied to the oxygen electrode side. Therefore, hydrogen ions and oxygen gas react with each other by a catalytic reaction at the oxygen electrode, and water (H ₂ O) is generated. In the course of such a reaction, electrons (e ⁻ ) move from the hydrogen electrode to the oxygen electrode, and current flows from the oxygen electrode to the hydrogen electrode. In other words, using oxygen gas and hydrogen gas as fuel,
An electromotive force is obtained by a reverse reaction of the electrolysis reaction.

When the ion exchange membrane (electrolyte membrane) is dried, the desired characteristics cannot be obtained because the electromotive force decreases due to the increase in the electric resistance. For this reason, it is necessary to keep the ion-exchange membrane in a wet state during operation, and thus the cell is always in a state where moisture is present.

[0006]

However, the conventional separator made of a resin molded body still contains a considerable amount of metal impurities such as iron, nickel and chromium (at least 300 ppm or more in total). When the impurity concentration is high, impurities in the cell are ionized by water in the cell, thereby poisoning the ion exchange membrane (that is, impurity cations adhere or adsorb to the inside and the surface of the ion exchange membrane). There was a problem. Therefore, the electromotive force tends to be unstable early. Therefore, in order to realize a fuel cell that can be used stably for a long period of time, it has been considered that some improvement regarding the separator is necessary.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a polymer electrolyte fuel cell separator capable of generating power stably for a long period of time.

Another object of the present invention is to provide a manufacturing method suitable for manufacturing the above excellent separator.

[0009]

According to a first aspect of the present invention, there is provided a resin molded product comprising a carbon powder and a thermosetting resin, and the resin molded product comprises: The gist of the present invention is a separator of a polymer electrolyte fuel cell having an impurity concentration of 100 ppm or less.

[0010] According to the second aspect of the present invention, the resin molded body is composed of a carbon powder and a thermosetting resin, and the concentration of base metal impurities contained in the resin molded body is 100 p.
The gist of the present invention is a separator of a polymer electrolyte fuel cell having a pm or less.

According to the third aspect of the present invention, the resin molded body is composed of a carbon powder and a thermosetting resin, and is a base metal impurity contained in the resin molded body and having a higher ionization tendency than mercury. The gist is a separator of a polymer electrolyte fuel cell having a concentration of 100 ppm or less.

[0012] According to the present invention, the resin molded body is composed of a carbon powder and a thermosetting resin, and is a base metal impurity contained in the resin molded body and having a higher ionization tendency than mercury. The gist is a separator of a polymer electrolyte fuel cell having a concentration of 10 ppm or less.

[0013] In the invention according to the fifth aspect, a solid polymer type fuel comprising a resin molded body containing carbon powder and a thermosetting resin as components, and wherein the concentration of impurities contained in the resin molded body is 100 ppm or less. A method for producing a separator for a battery, comprising: after treating the carbon powder with a halogen compound under heating, performing resin molding using the carbon powder. The method is the gist.

The "action" of the present invention will be described below. According to the first to fourth aspects of the present invention, since the concentration of impurities contained in the resin molded product is lower than in the conventional case, even if the impurities are ionized, the ion exchange membrane is not poisoned. Therefore, according to the fuel cell using the same, a stable electromotive force can be obtained for a long period of time.

In this case, it is particularly preferable that the concentration of the base metal impurity, and more particularly the concentration of the base metal impurity having a higher ionization tendency than mercury, is 100 ppm or less.
This is because the above-mentioned impurities are the main factors for poisoning the ion exchange membrane. In the invention according to claim 4, the concentration of base metal impurities having a higher ionization tendency than mercury is set to an extremely low value of 10 ppm or less. Therefore, according to the fuel cell using this, a stable electromotive force can be obtained more reliably over a long period of time.

According to the fifth aspect of the invention, the halogen compound reacts with the impurities contained in the carbon powder due to the heat at the time of heating to produce a metal halide compound. Since such compounds are generally gaseous at high temperatures, the gaseous compounds can easily escape to the outside of the carbon powder. Therefore, if resin molding is performed using the carbon powder that has undergone such treatment, the concentration of impurities in the resin molded body can be easily and reliably reduced.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a polymer electrolyte fuel cell 1 according to an embodiment of the present invention will be described in detail with reference to FIGS.

The fuel cell 1 shown in FIGS. 1 and 2 is a so-called single cell type. The fuel cell 1 of the present embodiment includes one unit of a membrane / electrode laminate and two separators 2.

The membrane / electrode laminate has a structure in which electrodes 4A and 4B are arranged on both sides of the ion exchange membrane 3. One is a hydrogen electrode 4A and the other is an oxygen electrode 4B. The ion exchange membrane 3 can selectively pass hydrogen ions. In the present embodiment, a membrane made of a fluororesin-based material such as Teflon is used as the ion exchange membrane 3. The hydrogen electrode 4A and the oxygen electrode 4B are air-permeable mats containing carbon fiber as a main component, and are processed in a rectangular shape here. Platinum and palladium are supported as catalysts on the mat-like material. Note that a fluorine resin or the like may be added to the mat-like material.

A pair of separators 2 are disposed on both sides of the membrane / electrode laminate. The separator 2 of the present embodiment is a rectangular and plate-like solid body, and is formed to be slightly larger than the hydrogen electrode 4A and the oxygen electrode 4B. On the inner surface side of the separator 2, a concave portion 2b having a shape and a depth capable of accommodating the hydrogen electrode 4A and the oxygen electrode 4B is provided. Similarly, a plurality of parallel grooves 2 a are formed on the inner surface side of the separator 2. The outer peripheral portion of the ion exchange membrane 3 protruding from both electrodes 4A and 4B is sandwiched by the inner peripheral portions of both separators 2 in a sealed state. As a result, the membrane / electrode laminate is fixed between the separators 2 so as not to be displaced.

A plurality of gas supply / discharge holes 5 are provided in two of four sides of the separator 2.
These gas supply / exhaust holes 5 extend in parallel along the surface direction of the separator 2, and are connected to the outer region of the separator 2 and the recess 2.
b. Therefore, the gas or the like flowing into the concave portion 2b through the gas supply / discharge hole group 5 on one side surface is in the groove 2b.
After flowing along the line a, it flows out again to the external region through the group of gas supply / discharge holes 5 on the other side surface. The separator 2 is also provided with a gas vent hole 6 communicating with the concave portion 2b. The gas vent hole 6 extends along the thickness direction of the separator 2.

In the case of the fuel cell 1, as a material for the separator 2, a resin molded body containing carbon powder and a thermosetting resin as its components is used. The role of the carbon powder in the resin molded body is to reduce the electrical resistivity and improve the conductivity of the separator 2. Usable carbon powders include natural graphite powders, as well as artificial graphite powders, glassy carbon, mesocarbon, carbon black and the like. Of course, a mixture of these can also be used. In this case, it is desirable to use a high-purity carbon powder with as small an impurity content as possible. Specifically, in the present embodiment, flaky artificial graphite powder having an impurity concentration of about 200 ppm to 300 ppm is used as the carbon powder.

The role of the thermosetting resin in the resin molding is to give the separator 2 a property that does not allow gas to permeate, and to give suitable moldability. Examples of usable thermosetting resins include an epoxy resin, a polyimide resin, and a phenol resin. Among these, it is particularly preferable to select a phenol resin. This is because the phenolic resin is excellent not only in moldability and gas impermeability but also in acid resistance, heat resistance and cost. The phenol resin includes a novolak resin and a resol resin. Of course, a mixture of a novolak phenol resin and a resol phenol resin may be used.

The mixing ratio of the carbon powder (A for convenience) and the thermosetting resin (B for convenience) is as follows: A: B = 90 w
t% to 50% by weight: preferably 10% to 50% by weight. However, A: B = 80wt% -60wt%: 20wt
% To 40 wt% is even more preferred. If the mixing ratio of the thermosetting resin is too large, the electrical resistivity may be excessively increased. On the other hand, if the mixing ratio of the thermosetting resin is too small, suitable moldability, gas impermeability, and mechanical strength may not be obtained.

The electrical resistivity of the separator 2 is 50
It is preferably about 00 μΩ · cm to 200000 μΩ · cm, and more preferably about 5000 μΩ · cm to 50,000 μΩ · cm. If this value is too large, separator 2
This is because the internal resistance of the fuel cell 1 increases due to the increase in the electric resistivity. Conversely, if this value is excessively reduced, it may be difficult to select raw materials.

In the case of the separator 2 of the present embodiment, the concentration of impurities contained in the resin molded product is extremely lower than that of the conventional product. More specifically, the concentration of a base metal impurity having a higher ionization tendency than mercury is
The total is less than 100 ppm. "Base metal impurities" refers to those excluding noble metal impurities such as gold, silver, mercury, and platinum group, and specifically, potassium, sodium, barium, calcium, magnesium, aluminum, iron, nickel, tin, and lead. , Copper, silicon, phosphorus and the like. Most of these metal species have the property of relatively easily ionizing in the presence of hydrogen ions. In other words, the impurity metal ions generated in this manner are attached or adsorbed to the inside and the surface of the ion exchange membrane 3, and are a main factor for poisoning the ion exchange membrane 3.

The concentration of the base metal impurity having a large ionization tendency is desirably 20 ppm or less in total, preferably 10 ppm or less, more preferably about 0.01 ppm to 5 ppm. Is good. This is because the lower the value of the concentration of such metal impurities, the lower the risk of poisoning the ion exchange membrane 3.

Next, a procedure for manufacturing the separator 2 of the present embodiment will be described. First, a carbon powder as a starting material is treated with a halogen compound under heating. Specifically, here, a treatment using chlorine gas as the halogen compound is performed. As a result, the concentration of impurities in the carbon powder can be reduced. The heating temperature is 2000 ° C
~ 2300 ° C.

Next, the carbon powder subjected to the heat treatment and the thermosetting resin are blended in the above-mentioned preferred range to obtain a mixture. The mixture is adjusted to an appropriate viscosity by adding a solvent such as methanol, and well kneaded using a kneader. Instead of methanol, for example, acetone, higher viscosity higher alcohols, or the like may be used as the solvent. The obtained flaky mixture is pulverized by a mixer or the like to obtain a raw material for molding.

Next, using the obtained molding raw material, a separator 2 having a predetermined shape is formed by a resin molding method (for example, a press molding method, a transfer molding method, an injection molding method, an extrusion molding method, etc.). At this time, not only the outer shape of the separator 2 but also the groove 2a, the concave portion 2b, the gas supply / discharge hole 5, and the gas discharge hole 6 are preferably formed at the same time. In other words, such a method eliminates the need for cutting or the like, which is convenient for cost reduction. At the time of such resin molding, for example, a hot press molding machine is used. At this time, the molding raw material is molded at 150 ° C. to 200 ° C. using a mold,
Further, at 200 ° C. to 250 ° C., the curing of the thermosetting resin contained in the raw material is promoted.

The separator 2 manufactured in this manner is divided into an ion exchange membrane 3, a hydrogen electrode 4A and an oxygen electrode 4B.
When assembled together, the desired fuel cell 1 shown in FIG.
Is completed.

Next, the principle of power generation in the fuel cell 1 will be described with reference to FIG. In use, a load such as a motor is electrically connected as an external circuit between the hydrogen electrode 4A and the oxygen electrode 4B. In this state, the hydrogen electrode 4A
Hydrogen gas is continuously supplied together with water into the concave portion 2b through the groove 2a of the separator 2 on the side. Similarly, oxygen electrode 4
Through the gas supply / discharge hole 5 and the groove 2a of the separator 2 on the B side, oxygen gas is continuously supplied together with water into the recess 2b.

The hydrogen gas supplied via the separator 2 on the side of the hydrogen electrode 4A becomes hydrogen ions by a catalytic reaction at the hydrogen electrode 4A. The generated hydrogen ions move toward the oxygen electrode 4B while passing through the ion exchange membrane 3. The hydrogen ions reaching the oxygen electrode 4B side are
Reacts with oxygen gas by the catalytic reaction in the above to generate water. In the process in which such a reaction occurs, electrons move from the hydrogen electrode 4A to the oxygen electrode 4B. Therefore, current flows from the oxygen electrode 4B to the hydrogen electrode 4A, and as a result, an electromotive force can be obtained. Then, a direct current is supplied to the external circuit, and a motor, which is a load, is driven.

[0034]

EXAMPLES [Preparation of sample] As carbon powder, the particle size is about 25 μm to 50 μm and the impurity concentration is 200 p.
A flake-like graphite artificial graphite powder having a pm to 300 ppm was selected. This powder is heated at about 2100 ° C.
By treating with chlorine gas for a predetermined time, the impurity concentration was reduced to 5 ppm or less. In addition, a solid resole phenol resin was used as the thermosetting resin. The mixing ratio of the carbon powder and the phenol resin is as follows: A: B = 65 wt
%: 35 wt% was set.

After mixing the heat-treated high-purity carbon powder and the phenol resin, methanol was added to the mixture as a solvent. After kneading this well using a kneader,
The obtained kneaded material was pulverized to obtain a raw material for molding. Next, the raw material for molding was press-molded by a general hot press molding machine to obtain a rectangular resin molded body to be used as the separator 2. As conditions for hot press molding, the temperature was set to 200 ° C., the pressure was set to 50 kg / cm ² , and the time was set to 30 minutes.
Minutes. In this resin molded body, the concentration of base metal impurities having a higher ionization tendency than mercury was about 100 ppm in total. The sample 1 thus obtained was used as the separator 2 of Example 1.

The base metal impurity concentration is 50
Samples 2, 3, 4, and 5 at ppm, 15 ppm, 8 ppm, and 4 ppm were produced under the respective processing conditions. These were sequentially positioned as the separators 2 of Examples 2, 3, 4, and 5. On the other hand, a sample 6 was prepared without performing any chlorine gas treatment on the carbon powder under heating, and this was used as a separator of a comparative example. In the separator of the comparative example, the base metal impurity concentration was 3 in total.
It was contained in an amount of 00 ppm or more. In addition, the measurement of the base metal impurity concentration in each sample was performed based on conventionally known emission spectroscopy.

Incidentally, the electrical resistivity of the resin moldings of Samples 1 to 6 were 20 μΩ · cm and 18 μΩ, respectively.
Ω ・ cm 、 15μΩ ・ cm 、 11μΩ ・ cm 、 18μΩ
Cm and 20 μΩcm. [Comparative Test Method and Results] Samples of the above-mentioned six types of separators 2 were used as ion-exchange membranes 3 and hydrogen electrodes 4A, respectively.
And the oxygen electrode 4B, and individually
Was manufactured. Then, these fuel cells 1 were continuously operated in a state where the external circuit was connected, and the state of the temporal variation of the voltage value (V) of the electromotive force was examined. The results are conceptually shown in the graph of FIG.

It has been found that the voltage value of the fuel cell 1 using the separator of the comparative example fluctuates after a certain period of time has elapsed since the start of operation. Therefore, it was expected that if the use was continued further, the ion exchange membrane 3 would be poisoned by the ionized impurities and the voltage value would surely drop. On the other hand, in the fuel cells 1 using the separators 2 of Examples 1 to 5, at least the voltage value did not change after the same time had elapsed. Therefore, the stability of the voltage value of the electromotive force was higher than the comparative example.

Therefore, according to each example of the present embodiment, the following effects can be obtained. (1) In the separator 2 of each example of the present embodiment, the base metal impurity concentration contained in the resin molded body is 100 pp.
m or less, and in each case, the base metal impurity concentration is considerably lower than that of the conventional product. Therefore, even if the impurities are ionized, the ion exchange membrane 3 is not poisoned. Therefore, the fuel cell 1 using this
According to this, a stable electromotive force can be obtained over a long period of time. In particular, in the separators 2 of Examples 4 and 5, the base metal impurity concentration is set to an extremely low value of 10 ppm or less. Therefore, according to the fuel cell 1 using this, a stable electromotive force can be obtained more reliably over a long period of time.

(2) Since the separator 2 of the present embodiment contains carbon powder and a thermosetting resin as main components, it is made of a relatively inexpensive material. Further, since the separator 2 is manufactured through a resin molding method, it can be obtained at relatively low cost. Moreover, with such a resin molded body, various characteristics required for the separator 2 of the polymer electrolyte fuel cell 1 can be realized relatively easily. That is, suitable gas impermeability, low electric resistivity, acid resistance, light weight, and the like can be obtained.

(3) The separator 2 of this embodiment is manufactured by treating a carbon powder with a chlorine gas under high-temperature heating, and then performing resin molding using the carbon powder. At this time, the chlorine gas and impurities contained in the carbon powder react with each other due to the heat to generate a metal chloride. Since compounds of this type are generally gaseous at high temperatures, the gaseous metal chloride can easily escape to the outside of the carbon powder. Therefore, if resin molding is performed using the carbon powder that has undergone such treatment, the concentration of impurities in the resin molded body can be easily and reliably reduced. Therefore, the above excellent separator 2 can be reliably obtained.

The embodiment of the present invention may be modified as follows. It is also possible to use a different type of carbon powder from that used in the above-described embodiment, or a different type of thermosetting resin from that used in the above-described embodiment.

As the halogen compound, a substance other than chlorine gas, for example, fluorine gas or the like may be used. However,
From the viewpoint of cost and the like, it is preferable to select chlorine gas. -The shape of the concave portion 2b in the separator 2 is not necessarily limited to a rectangular shape. If unnecessary, the concave portion 2b
May be omitted.

The separator 2 of the present invention can be embodied not only as a component for a single cell type, but also as a component for other types (so-called multi-cell type). . For example, a pair of separators 12 in another example of a fuel cell 11 shown in FIG. 5 has grooves 2a and concave portions 2b on both surfaces. The groove 2a formed on one surface and the groove 2a formed on the other surface have, for example, a relationship orthogonal to each other.
The fuel cell 11 having the above-described structure is used in a state in which several tens to several hundreds of cells are stacked to form a “fuel cell stack”. The individual fuel cells 1 which are single cells
1 may be connected in series to obtain each sufficient electromotive force.

Next, in addition to the technical ideas described in the claims, the technical ideas grasped by the above-described embodiments will be listed below together with their effects. (1) The resin molding according to claim 5, wherein a high-purity carbon powder is used as the carbon powder. Therefore, according to the invention described in the technical idea 1, since the impurity concentration in the resin molded body is further reduced, a stable electromotive force can be obtained more reliably over a long period of time.

(2) In claim 5, the halide is chlorine gas. Therefore, this technical idea 2
According to the invention described in (1), the use of a particularly inexpensive halogen compound can reduce the production cost.

(3) It is composed of a resin molded product containing carbon powder and a thermosetting resin, and is a metal impurity contained in the resin molded product, excluding gold, silver, mercury, and platinum group. The concentration is 100 ppm or less (preferably 20 ppm
ppm or less, more preferably 10 ppm or less).

(4) A solid body comprising a membrane / electrode laminate in which electrodes are arranged on both sides of an ion exchange membrane, and a pair of separators sandwiching an outer peripheral portion of the ion exchange membrane protruding from both electrodes. In the polymer fuel cell, the separator is made of a resin molded product containing carbon powder and a thermosetting resin as components, and the concentration of impurities contained in the resin molded product is 100 ppm or less (preferably 20 ppm or less, more preferably 20 ppm or less). Is 10 ppm or less). Therefore, according to the invention described in the technical idea 4, it is possible to provide a fuel cell capable of generating power stably for a long period of time.

(5) A fuel cell stack comprising a plurality of the fuel cells described in the technical concept 4 as a single cell, and connected in series in a state where the single cells are stacked. Therefore, according to the invention described in the technical idea 5,
A fuel cell stack capable of stably generating a sufficient amount of electromotive force for a long period of time can be provided.

[0050]

As described above in detail, according to the first to third aspects of the present invention, it is possible to provide a polymer electrolyte fuel cell separator capable of generating power stably for a long period of time.

According to the fourth aspect of the present invention, a stable electromotive force can be obtained more reliably over a long period of time. According to the fifth aspect of the present invention, it is possible to provide a manufacturing method suitable for manufacturing the above excellent separator having a low impurity concentration.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view of a polymer electrolyte fuel cell according to an embodiment of the present invention.

FIG. 2 is a schematic sectional view of the fuel cell according to the embodiment.

FIG. 3 is a diagram illustrating the principle of the fuel cell according to the embodiment.

FIG. 4 is a graph conceptually showing a result of a comparative test.

FIG. 5 is a schematic cross-sectional view of another example of a fuel cell.

[Explanation of symbols]

1. Solid polymer fuel cell, 2: Solid polymer fuel cell separator.

Claims (5)

[Claims] 1. A separator for a polymer electrolyte fuel cell comprising a resin molded body containing carbon powder and a thermosetting resin as components, and wherein the concentration of impurities contained in the resin molded body is 100 ppm or less. 2. A separator for a polymer electrolyte fuel cell comprising a resin molded body containing carbon powder and a thermosetting resin as components, and having a base metal impurity concentration of 100 ppm or less in the resin molded body. 3. A solid comprising a resin molded product containing carbon powder and a thermosetting resin, wherein the concentration of base metal impurities contained in the resin molded product and having a higher ionization tendency than mercury is 100 ppm or less. Polymer fuel cell separator. 4. A solid comprising a resin molded body containing carbon powder and a thermosetting resin, wherein the concentration of base metal impurities contained in the resin molded body and having a higher ionization tendency than mercury is 10 ppm or less. Polymer fuel cell separator. 5. A method for producing a separator for a polymer electrolyte fuel cell, comprising a resin molded body containing carbon powder and a thermosetting resin as components, and having an impurity concentration of 100 ppm or less in the resin molded body. A method for producing a separator for a polymer electrolyte fuel cell, wherein the carbon powder is treated with a halogen compound under heating, and then resin molding is performed using the carbon powder.