JP2003142118A - High polymer electrolyte type fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem wherein a separator plate forming a component of a high polymer electrolyte type fuel cell has been manufactured by machining a glassy carbon plate, pressing expansive graphite, pressing a metallic plate, or using a thermosetting conductive resin, but it has been difficult to reduce a cost whichever material is used, providing difficulty in bringing the fuel cell into practical use. SOLUTION: The separator is manufactured by a composite of a conductive filler and a binder resin prepared by heating and mixing them so as to make its melt viscosity stay in a range of 10-10<5> (Pa/sec) (shear rate of 6-6000 (1/sec)) at a shear rate of 6-6000 (1/sec).

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a portable power source,
The present invention relates to a fuel cell using a polymer electrolyte used in a power source for electric vehicles, a cogeneration system in a home, and the like.

[0002]

2. Description of the Related Art In a fuel cell using a polymer electrolyte, a fuel gas containing hydrogen and a fuel gas containing oxygen such as air are electrochemically reacted to simultaneously generate electric power and heat. It is what makes me. With this structure, first, a catalytic reaction layer containing carbon powder carrying a platinum-based metal catalyst as a main component is formed on both surfaces of a polymer electrolyte membrane that selectively transports hydrogen ions. Next, a diffusion layer is formed on the outer surface of the catalytic reaction layer by using, for example, carbon paper having both fuel gas permeability and electronic conductivity, and the diffusion layer and the catalytic reaction layer are combined to form an electrode.

Next, in order to prevent the supplied fuel gas from leaking to the outside and the two kinds of fuel gas from mixing with each other, a gas sealing material and a gasket are arranged around the electrodes with a polymer electrolyte membrane sandwiched therebetween. The sealing material and gasket are integrated with the electrode and the polymer electrolyte membrane in advance,
This is called MEA (electrode-electrolyte membrane assembly). MEA
An electrically conductive separator plate for mechanically fixing the MEA and electrically connecting adjacent MEAs to each other in series is arranged on the outer side of the. A gas flow path for supplying a reaction gas to the electrode surface and carrying away the generated gas and the surplus gas is formed in a portion of the separator plate that is in contact with the MEA. The gas flow channel may be provided separately from the separator plate, but it is common to provide a groove on the surface of the separator to form the gas flow channel.

In order to supply the fuel gas to this groove, a pipe jig for branching the pipe for supplying the fuel gas into the number of separators to be used and directly connecting the branch destination to the separator-shaped groove is required. . This jig is called a manifold, and the type directly connected from the fuel gas supply pipe as described above is called an external manifold. There is a type of this manifold called an internal manifold having a simpler structure. The internal manifold is one in which a through hole is provided in a separator plate having a gas flow path, the inlet and outlet of the gas flow path are passed to this hole, and the fuel gas is directly supplied from this hole.

Since the fuel cell generates heat during operation, it is necessary to cool the fuel cell with cooling water or the like in order to maintain the cell in a good temperature state. Usually, a cooling unit for flowing cooling water for every 1 to 3 cells is inserted between the separators, but a cooling water channel is often provided on the back surface of the separator to serve as the cooling unit. It is common to stack these MEAs, separators, and cooling parts alternately, stack 10 to 200 cells, sandwich the plates with a collector plate and an insulating plate, end plates, and fix them with fastening bolts from both ends. It is a structure of various laminated batteries.

The separator used in such a polymer electrolyte fuel cell has a high conductivity, a high gas-tightness with respect to the fuel gas, and a high reaction with respect to the oxidation / reduction of hydrogen / oxygen. It must have corrosion resistance, that is, acid resistance. For this reason, conventional separators have a gas flow path formed by cutting on the surface of a glassy carbon plate, or put expanded graphite powder together with a binder into a press die with a gas flow path groove, and press this. After processing
It was produced by heating and firing.

Further, in recent years, attempts have been made to use a metal plate such as stainless steel in place of the conventionally used carbon material. The separator using the metal plate is exposed to an oxidizing atmosphere at a high temperature, so that the metal plate is corroded or dissolved when used for a long period of time. When the metal plate corrodes, the electric resistance of the corroded portion increases, and the output of the battery decreases. When the metal plate is dissolved, the dissolved metal ions diffuse into the polymer electrolyte and are trapped at the ion exchange sites of the polymer electrolyte, resulting in a decrease in the ion conductivity of the polymer electrolyte itself. In order to avoid such deterioration, it has been customary to coat the surface of the metal plate with gold having a certain thickness.

Further, as proposed in Japanese Patent Laid-Open No. 6-333580, a separator made of a conductive resin made by mixing a metal powder with a thermosetting resin such as an epoxy resin, a thermoplastic resin and a conductive agent. A conductive resin prepared by mixing is being studied.

[0009]

As described above, in the method of making the separator by cutting the glassy carbon plate, the material cost itself of the glassy carbon plate is high, and
It is also difficult to reduce the cost for cutting this. Further, the gold-plated metal plate separator has a problem in the cost of gold plating. In addition, pressed graphite of expanded graphite has a problem of mechanical strength of the material, and when it is used as a power source of an electric vehicle, it may be cracked due to vibration or shock during traveling. Furthermore, a separator made of a conductive resin requires a long time to cure the thermosetting resin, so the productivity does not improve, and a large capital investment is required to reduce the cost. There were challenges.

[0010]

In order to solve the above problems, a polymer electrolyte fuel cell of the present invention is provided with a hydrogen ion conductive polymer electrolyte membrane and both surfaces of the hydrogen ion conductive polymer electrolyte membrane. In a polymer electrolyte fuel cell comprising a pair of electrodes and a pair of conductive separators having a gas flow path for supplying and discharging a fuel gas to one of the electrodes and supplying and discharging an oxidant gas to the other, The conductive separator is composed of a mixture of a conductive filler and a binder resin, and the mixture has a viscosity of 10 to 10 when melted.
⁵ (Pa · sec) and a shear rate of 6 to 6000 (1 / s
ec).

At this time, the conductive filler preferably has at least one of granular graphite having an average particle diameter of 50 μm to 200 μm and conductive carbon fiber having a fiber diameter of 10 μm or less. Furthermore, it is desirable that the binder resin is made of a thermoplastic resin.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In a polymer electrolyte fuel cell of the present invention, a conductive separator as a constituent element has a viscosity of 10 to 10 ⁵ (Pa · sec) when melted (shear rate of 6 to 6000 (1
/ sec)), which is composed of a composition of a conductive filler and a binder resin. The conductive separator is prepared, for example, by using a polyphenylene sulfide resin as a base material and mixing this with a conductive agent such as granular graphite or carbon fiber. Such a conductive separator is certainly lower in electric conductivity than glassy carbon or a metal plate. However, since it is possible to perform processing by injection molding, it is possible to improve productivity by eliminating the need for cutting gas passages and the like, which has been conventionally required for producing a separator.

Further, unlike the case of a conductive resin separator using a thermosetting resin such as an epoxy resin, there is no need for a holding time in a heated and compressed state necessary for resin curing, and there is a problem such as gas generation. Absent.

When a base material which specifically satisfies the above requirements was evaluated, the composition of the resin and the inorganic conductive material had a melt viscosity of 10 to 10 ⁵ (Pa · sec) (shear rate of 6 to 6000 (1
/ sec)) was excellent in moldability, gas-tightness, heat resistance, and dimensional stability, and was particularly suitable as a separator material for realizing the present invention.

As the binder resin, polyethylene,
Polystyrene, polypropylene, AS resin, ABS resin, methyl methacrylate resin, polyamide, polyacetal, polycarbonate, polyphenylene ether, polybutylene terephthalate, polyethylene terephthalate, polymethylpentene, syndiotactic polystyrene, polysulfone, polyether sulfone, polyphthalamide It was possible to use one kind or a mixture of two or more kinds selected from polyphenylene sulfide, polycyclohexylene dimethylene terephthalate, polyarylate, polyetherimide, polyetherketone, polyimide, liquid crystal polymer and fluororesin. Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0016]

EXAMPLES Example 1 First, a method for producing an electrode having a catalyst layer will be described with reference to FIG. An acetylene black powder carrying 25% by weight of platinum particles having an average particle size of about 30Å was used as the electrode catalyst. The catalyst powder was dispersed in isopropanol, and the dispersion solution prepared by dispersing the perfluorocarbon sulfonic acid powder shown in Chemical formula 1 in ethyl alcohol was mixed to form a catalyst paste.

[0017]

[Chemical 1]

On the other hand, the carbon paper which becomes the support of the electrode was subjected to water repellent treatment. External size 8 cm x 10 cm, thickness 360
μm carbon nonwoven fabric 11 (Toray, TGP-H-12
0) was impregnated into a fluororesin-containing aqueous dispersion (Neotron ND1 manufactured by Daikin Industries, Ltd.), which was then dried and heated at 400 ° C. for 30 minutes to impart water repellency. The catalyst layer 1 is formed by applying a catalyst paste to one surface of the carbon nonwoven fabric 11 using a screen printing method.
Formed 2. At this time, a part of the catalyst layer 12 is embedded in the carbon nonwoven fabric 11. The catalyst layer 12 thus produced and the carbon nonwoven fabric 11 were combined to form an electrode 13. Amount of platinum contained in the reaction electrode after forming the 0.5 mg / cm ^2, the amount of perfluorocarbon sulfonic acid was adjusted to be 1.2 mg / cm ^2.

Next, a pair of electrodes 13 are bonded on both sides of the proton conductive polymer electrolyte membrane 14 having an outer dimension of 10 cm × 20 cm by hot pressing so that the catalyst layer 12 is in contact with the electrolyte membrane 14 side. This is an electrode electrolyte membrane assembly (ME
A) It was set to 15. Here, as the proton-conductive polymer electrolyte, a thin film of the perfluorocarbon sulfonic acid shown in (Chemical Formula 2) was used in a thickness of 50 μm.

[0020]

[Chemical 2]

Next, the viscosity at the time of melting, which is the point of the present invention, is 10 to 10 ⁵ (Pa · sec) (shear rate 6 to 6000).
A conductive separator prepared from a composition of a conductive filler exhibiting (1 / sec)) and a binder resin will be described.

The PPS resin has an average particle size of 50 μm to 20 μm.
80 μg of 0 μm granular graphite and a melt viscosity of 32
0 to 370 ° C, shear rate 6 to 6000 (1 / sec), 10
The mixture was heated and kneaded so as to be in the range of -10 ⁵ (Pa · sec). This material was used to make pellets for producing a separator. At this time, a Capirograph manufactured by Toyo Seiki Co., Ltd. was used to measure the melt viscosity. 20 kg of PPS resin
And 80k of granular graphite having an average particle size of 50 to 200 μm
g was sufficiently kneaded with heat to prepare separator pellets. At this time, the melt viscosity of the composition was measured using Toyo Seiki Co., Ltd.
20 ~ 370 ℃, shear rate 6 ~ 6000 (1 / sec), 1
It was in the range of 0 to 10 ⁵ (Pa · sec). The pellets were put into an injection molding machine and injection-molded in a predetermined mold to prepare a conductive separator. At this time, the injection pressure was 2500 kgf / cm 2, the mold temperature was 240 ° C., and the molding time was 60 sec.

As shown in Table 1, the melt viscosity is 10
If it is less than (Pa · sec), burrs are generated and the conductivity is lowered during molding. The conductivity was evaluated by a relative value using a resistance value of an isotropic graphite plate Φ30 manufactured by Tokai Carbon Co., Ltd. and a test piece having a plate thickness of 2 mm as a reference. Also,
If the melt viscosity exceeds 10 ⁶ (Pa · sec), a short shot occurs in the mold during molding, and a separator cannot be obtained.

[0024]

[Table 1]

Further, as shown in Table 2, when the average particle diameter of the granular graphite is 50 μm or less, the conductivity is lowered,
When the average particle size was 200 μm or more, deterioration of filling property and gas permeability of the thinnest part of the separator was confirmed.

[0026]

[Table 2]

The separator produced by the above method is shown in FIG. FIG. 2 shows the shape of the gas flow grooves formed on the surface of the conductive separator. 2A shows the shape of the oxidant gas flow groove formed on the front surface, and FIG. 2B shows the shape of the fuel gas flow groove on the back surface thereof. The size of the separator is 10 cm x 20 c
m, the thickness is 4 mm, the groove portion 21 is a concave portion having a width of 2 mm and a depth of 1.5 mm, and gas flows through this portion.
The rib portion 22 between the gas flow paths is a convex portion having a width of 1 mm. In addition, a manifold hole for the oxidant gas (the injection port 23a,
Outlet 23b) and a fuel gas manifold hole (inlet 24
a, outlet 24b) and a cooling water manifold hole (inlet 2
5a, outlet 25b) was formed.

FIG. 3 shows the shape of a cooling flow path for flowing cooling water, in which the back surface of the conductive separator shown in FIG. 2 (a) is cut. In Figure 3,
The position and size of the cooling water manifold holes (injection port 31a, outlet 31b) are the same as those of the cooling water manifold hole 2 shown in FIG.
5a and 25b, and the manifold holes 34a, 34b, 35a, 35b for gas flow were also formed at the same positions and sizes as the gas manifold holes in FIG. Further, 32 is a flow portion of the water that has flowed in from the cooling water inlet 31a, and the depth of the concave shape is 1.5 mm. 33 is in the middle of the cooling water passage,
2 is a portion left as a convex portion when forming 2, and has the same height as the original conductive sheet 36. Since the cooling water flows in from the inlet 31a and is split by 33, the flow path 32
To reach the exit 31b.

Next, in the proton conductive polymer electrolyte membrane of the MEA prepared in FIG. 1, manifold holes for circulating cooling water, fuel gas and oxidant gas were formed. The structure is shown in FIG.
It was shown to. In FIG. 4, 44 is an electrode part, 45 is a proton conductive polymer electrolyte membrane, 41a, 41b, 42a and 4
2b is a manifold hole for fuel gas and oxidant gas flow, and 43a and 43b are cooling water flow manifold holes, and these holes have the same positions and sizes as the separators shown in FIGS. 2 and 3.

Using the two separators thus prepared, the surface of the MEA sheet shown in FIG.
FIG. 2 (b) was overlaid on the back side, and this was used as a unit cell. After stacking 2 cells of this unit cell, the 2-cell stack battery was sandwiched by the separators having the cooling water channel grooves shown in FIG. 3, and this pattern was repeated to form a 50 cell stack battery stack. At this time, the both ends of the battery stack were fixed with a stainless steel collector plate and an insulating plate made of an electrically insulating material, and further with an end plate and a fastening rod. The fastening pressure at this time was 10 kgf / cm ² per area of the separator.

The polymer electrolyte fuel cell of this example produced in this manner was held at 85 ° C., and 83
Hydrogen gas humidified and heated to a dew point of ° C was supplied, and air humidified and heated to a dew point of 78 ° C was supplied to the other electrode side. As a result, a battery open circuit voltage of 50 V was obtained when no load was applied and the current was not output to the outside.

This cell was subjected to a continuous power generation test under the conditions of a fuel utilization rate of 80%, an oxygen utilization rate of 40% and a current density of 0.5 A / cm ² , and the time-dependent change in output characteristics is shown in FIG. As a result, the battery of the present example has 1
It was confirmed that the battery output of 000 W (22V-45A) was maintained.

Example 2 In the above example, granular graphite was used as the inorganic conductive material for making the separator, but in this example, carbon fiber was further added to the inorganic conductive material. PPS resin, 80 kg of granular graphite having an average particle diameter of 50 μm to 200 μm and 1 kg of carbon fiber having a fiber diameter of 7 μm,
Melt viscosity is 320-370 ° C, shear rate is 6-600
The content was adjusted to 0 (1 / sec) by heating and kneading so as to be in the range of 10 to 10 ⁵ (Pa · sec). This material was used to make pellets for producing a separator. At this time, a Capirograph manufactured by Toyo Seiki Co., Ltd. was used to measure the melt viscosity. The pellets were put into an injection molding machine and injection-molded in a predetermined mold to prepare a conductive separator. At this time, the injection pressure was 2500 kgf / cm2 and the mold temperature was 240.
C., molding time was 60 sec. As shown in Table 3, improvement in conductivity was confirmed by adding carbon fiber.

[0034]

[Table 3]

As in Example 1, when the melt viscosity was less than 10 (Pa · sec) as shown in Table 4, burrs were generated and the conductivity was lowered during molding. Further, if the melt viscosity exceeds 10 ⁶ (Pa · sec), a short shot occurs in the mold during molding, and a separator cannot be obtained.

[0036]

[Table 4]

Further, as shown in Table 5, when the average particle diameter of the granular graphite is 50 μm or less, the conductivity is lowered,
When the average particle size was 200 μm or more, deterioration of filling property and gas permeability of the thinnest part of the separator was confirmed. Furthermore, as shown in FIG. 3, even if carbon fibers having a fiber diameter of 10 μm or more were mixed, no improvement in conductivity was confirmed.

[0038]

[Table 5]

Hereinafter, using this material, the same battery as the battery of Example 1 was prepared, and its characteristics were evaluated under the same conditions as in Example 1. The results are shown in Fig. 6. In FIG.
It was confirmed that the battery of this example had better characteristics than the battery prepared in Example 1.

[0040]

According to the present invention, instead of the conventional method of cutting a carbon plate, the melt viscosity is changed to a shear rate of 6 to 6000 (1 / s).
ec) 10 to 10 ⁵ (Pa · sec) (shear rate 6 to 60
It is possible to drastically reduce the cost by forming the separator plate from the composition of the conductive filler and the binder resin, which is heat-kneaded and adjusted to be in the range of 00 (1 / sec)).

[Brief description of drawings]

FIG. 1 is an ME used in a fuel cell according to a first embodiment of the present invention.
Diagram showing the configuration of A

FIG. 2 is a diagram showing a configuration of a separator used in the fuel cell according to the first embodiment of the present invention.

FIG. 3 is a diagram showing a configuration of a cooling water channel plate used in the fuel cell according to the first embodiment of the present invention.

FIG. 4 ME used in the fuel cell of Example 1 of the present invention
Diagram showing the structure of A sheet

FIG. 5 is a diagram showing a change over time in the output characteristics of the fuel cell according to the first embodiment of the present invention.

FIG. 6 is a diagram showing a change over time in the output characteristics of the fuel cell according to the second embodiment of the present invention.

[Explanation of symbols]

11 carbon nonwoven fabric 12 Catalyst layer 13 electrodes 14 Proton conductive polymer electrolyte membrane 15,45 MEA 21 groove 22 Rib section between gas channels 23,34,41 Manifold holes for oxidant gas 24, 35, 42 Fuel gas manifold holes 25,31,43 Cooling water manifold hole 32 Distribution of water 33 convex remainder 36,45 Conductive sheet

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hiroki Kusakabe             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Shin Kobayashi             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Tatsuto Yamazaki             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Nobuhiro Hase             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Shinsuke Takeguchi             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. F-term (reference) 4J002 BB031 BB121 BB171 BC031                       BC061 BD121 BG061 BN151                       CB001 CF051 CF061 CF071                       CF161 CG001 CH071 CH091                       CL001 CL061 CM041 CM051                       CN011 CN031 DA017 DA026                       FD116 FD117 GQ00                 5H026 AA06 BB01 BB02 BB08 CC01                       CC03 CC08 CX00 CX02 CX07                       EE05 EE06 EE18 HH00 HH01

Claims (3)

[Claims] 1. A hydrogen ion conductive polymer electrolyte membrane, a pair of electrodes arranged on both sides of the hydrogen ion conductive polymer electrolyte membrane, and a fuel gas is supplied to and discharged from one of the electrodes,
In a polymer electrolyte fuel cell comprising a pair of conductive separators having a gas flow path for supplying and discharging an oxidant gas to the other, the conductive separator is composed of a mixture of a conductive filler and a binder resin, The polymer electrolyte fuel cell, wherein the mixture has a viscosity when melted of 10 to 10 ⁵ (Pa · sec) and a shear rate of 6 to 6000 (1 / sec). 2. The conductive filler has an average particle diameter of 50 μm.
2. The polymer electrolyte fuel cell according to claim 1, comprising at least one of granular graphite having a diameter of ˜200 μm and conductive carbon fiber having a fiber diameter of 10 μm or less. 3. The polymer electrolyte fuel cell according to claim 1 or 2, wherein the binder resin is a thermoplastic resin.