JP2000021420A - Polymer electrolyte fuel cell - Google Patents

Abstract

(57) [Problem] To provide a gas flow path by using a carbon plate as a separator plate, which is a component of a polymer electrolyte fuel cell, and cutting the surface of the separator plate. In this method, it has been difficult to reduce not only the material cost of the carbon plate but also the cost for cutting it. Instead, a method using a metal plate is conceivable.However, in the method using a metal plate, the metal plate is exposed to an oxidizing atmosphere at a high temperature. There was a problem that the power generation efficiency of the battery gradually decreased. SOLUTION: On a metal thin plate constituting a separator, a gas flow path is formed in a main portion where an electrode is located by press molding or the like, and a conductive oxide layer is formed on this surface portion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a portable power supply,
The present invention relates to a fuel cell using a solid polymer electrolyte used for an electric vehicle power supply, a home cogeneration system, and the like.

[0002]

2. Description of the Related Art A fuel cell using a solid polymer electrolyte is
Electric power and heat are simultaneously generated by electrochemically reacting a fuel gas containing hydrogen and a fuel gas containing oxygen such as air. First, its structure
On both surfaces of a polymer electrolyte membrane that selectively transports hydrogen ions, a catalyst reaction layer mainly composed of carbon powder carrying a platinum-based metal catalyst is formed. Next, a diffusion layer having both gas permeability and electronic conductivity is formed on the outer surface of the catalyst reaction layer, and the diffusion layer and the catalyst reaction layer are combined to form an electrode.

Next, a gas seal material or a gasket is arranged around the electrodes with a polymer electrolyte membrane interposed therebetween so that the supplied fuel gas does not leak outside or the two types of fuel gas do not mix with each other. This sealing material and gasket are integrated with the electrode and polymer electrolyte membrane beforehand,
This is referred to as MEA (electrode electrolyte membrane assembly). MEA
A conductive separator plate for mechanically fixing the MEA and electrically connecting adjacent MEAs in series with each other is arranged outside the. A gas flow path for supplying a reaction gas to the electrode surface and carrying away generated gas and surplus gas is formed in a portion of the separator plate that contacts the MEA. Although the gas flow path can be provided separately from the separator plate, a method of providing a gas flow path by providing a groove on the surface of the separator is general.

In order to supply the fuel gas into the groove, a pipe jig for branching the pipe for supplying the fuel gas into the number of separators to be used and connecting the branch directly 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 which has a simpler structure. In the internal manifold, a through hole is provided in a separator plate in which a gas flow path is formed, an inlet / outlet for gas flow is passed to the hole, and fuel gas is supplied directly from the hole.

[0005] 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 every 1 to 3 cells is inserted between the separators. In many cases, a cooling water flow path is provided on the back surface of the separator to serve as a cooling unit. The MEA, the separator and the cooling section are alternately stacked, and after stacking 10 to 200 cells, it is common to sandwich this with an end plate via a current collector plate and an insulating plate and fix it from both ends with fastening bolts. This is the structure of a simple stacked battery.

In such a polymer electrolyte fuel cell,
The separator is required to have high conductivity, high gas tightness with respect to the fuel gas, and high corrosion resistance to the reaction when redoxing hydrogen / oxygen. For this reason, the conventional separator is usually made of a carbon material such as glassy carbon or expanded graphite, and the gas flow path is formed by cutting the surface of the separator or, in the case of expanded graphite, by molding using a mold.

However, in recent years, attempts have been made to use a metal plate such as stainless steel in place of a conventionally used carbon material.

[0008]

In the conventional method of cutting a carbon plate, it is difficult to reduce not only the material cost of the carbon plate but also the cost of cutting the carbon plate, and the method using expanded graphite is also difficult. The cost is high, and this is considered as an obstacle for practical use.

In the above-described method using a metal plate, the metal plate is exposed to an oxidizing atmosphere at a high temperature. When the metal plate is corroded, the electric resistance of the corroded portion increases, and the output of the battery decreases. Further, when the metal plate is dissolved, the dissolved metal ions diffuse into the polymer electrolyte and are trapped at ion exchange sites of the polymer electrolyte. As a result, the ion conductivity of the polymer electrolyte itself decreases. Due to these causes, there has been a problem that when the metal plate is used as it is for the separator and the battery is operated for a long period of time, the power generation efficiency gradually decreases.

[0010]

SUMMARY OF THE INVENTION The point of the present invention is to suppress the corrosion and dissolution of a conductive separator made of a metal plate as a material, so that the conductive separator is chemically resistant even when exposed to an acidic atmosphere while maintaining conductivity. That is, a method for maintaining the activity has been found.

That is, the polymer electrolyte fuel cell of the present invention comprises:
In a polymer electrolyte fuel cell in which a pair of electrodes sandwiching a polymer electrolyte membrane and a unit cell having means for supplying and discharging fuel gas to and from the electrodes are stacked with a conductive separator interposed therebetween, The separator is made of a metal plate coated with a conductive inorganic compound, and the conductive separator forms a gas flow groove for flowing the fuel gas, and the gas flow groove is formed of a material having a gas sealing property for the fuel gas. And means for supplying and discharging the fuel gas.

At this time, it is effective that the conductive inorganic compound is a conductive inorganic oxide, a conductive inorganic nitride, or a conductive inorganic carbide.

Further, it is effective that the gas flow grooves formed in the conductive separator have a plurality of linear shapes parallel to each other.

Further, it is preferable that the convex portion of the gas flow groove formed on one surface of the conductive separator forms a recess of the gas flow groove on the back surface of the conductive separator.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

[0016]

(Example 1) A catalyst for a reaction electrode was prepared by supporting 25% by weight of platinum particles having an average particle size of about 30 on acetylene black-based carbon powder. A dispersion solution of the perfluorocarbon sulfonic acid powder shown in Chemical Formula 1 in ethyl alcohol was mixed with a solution of this catalyst powder dispersed in isopropanol to form a paste. Using this paste as a raw material, an electrode catalyst layer was formed on one surface of a carbon nonwoven fabric having a thickness of 250 μm using a screen printing method. 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.

[0017]

Embedded image

These electrodes have the same structure for both the positive electrode and the negative electrode, and the catalyst layers printed on both sides of the center portion of the proton conductive polymer electrolyte membrane having an area slightly larger than the electrodes so that the catalyst layers are in contact with the electrolyte membrane side. The electrode / electrolyte assembly (MEA) was formed by joining by hot pressing. Here, as the proton conductive polymer electrolyte, a thin film of the perfluorocarbon sulfonic acid shown in Chemical Formula 2 with a thickness of 25 μm was used.

[0019]

Embedded image

The structure of each component of the polymer electrolyte fuel cell manufactured in this embodiment is shown in FIGS.

First, a metal plate coated with a conductive oxide
A method for producing a conductive separator is described. Shown in FIG.
As described above, using a SUS316 plate having a thickness of 0.3 mm,
5.6mm pitch in 10cm x 9cm area
The corrugated part 1 (groove width about 2.8mm) is pressed
Therefore, it was formed. At this time, the depth of the groove 2 (the height of the mountain 3)
It was about 1 mm. Next, In was topped on this surface.
0.5 μm of tin oxide layer by vacuum electron beam evaporation
It was formed in thickness. The degree of vacuum during evaporation is 5 × 10 ^-6Torr
The substrate temperature was 300 ° C. in the Ar gas atmosphere. One
As shown in FIG. 1, two opposing sides each
Manifold for supplying and discharging hydrogen gas, cooling water and air
Shield holes 4 were provided.

Next, as shown in FIG. 2A, a gas is guided to the separator on the hydrogen side from the manifold hole to the gas flow groove formed by processing the metal plate by the convex portion 5 made of phenol resin. Groove 6 is provided. In addition, the protrusions 5 made of a phenol resin are overlapped so that the two grooves are adjacent to each other and are curved and connected.

The projection made of phenolic resin had a thickness of about 1 mm and was the same as the height of the groove of the separator plate. The gasket 7 is formed in the same manner on the outer peripheral portion of the separator plate and around the manifold hole to correspond to the shape of the metal plate.

Further, as shown in FIG. 2B, in the separator on the air side, six adjacent grooves are curved to form a continuous gas flow groove. The structure is changed between the air side and the hydrogen gas side because the gas flow rate differs between the air side and the hydrogen gas side by about 25 times. Conversely, in such a structure, it is possible to obtain an optimum gas flow rate and gas pressure loss by changing the shape of the resin gas flow groove in accordance with the gas flow rate.

Next, as shown in FIG. 3, the MEA 8 was sandwiched by these two types of separators and gaskets to form a structural unit of a battery. As shown in FIG. 3, the positions of the gas flow grooves 9 on the hydrogen side and the gas flow grooves 10 on the air side were configured to correspond to each other so that excessive sending force was not applied to the electrodes. A cooling unit 11 for flowing cooling water was provided for every two cells stacked. SUS316 metal mesh 12 is used for the cooling section to ensure conductivity and cooling water flow,
A gasket 7 made of phenol resin was provided on the outer peripheral portion and the gas manifold portion to form a seal portion. Grease 13 is applied thinly to portions requiring gas sealing, such as the gasket and MEA, the separator plate and the separator plate, and the gasket and the separator plate, so that the sealing properties are secured without significantly lowering the conductivity.

After stacking 50 cells of the above MEA, the MEA was fastened with a stainless steel plate and a fastening rod via a current collector plate and an insulating plate at a pressure of 20 kgf / cm ² . If the fastening pressure is too small, gas leaks and the contact resistance is large, so the battery performance will be reduced.On the contrary, if it is too large, the electrode will be damaged or the separator plate will be deformed. It was important to change the fastening pressure.

As the battery of the comparative example, a battery having a conductive separator made of a SUS316 plate having no surface coating as in the batteries of the above examples was manufactured. In the battery of the comparative example, the configuration was the same as that of the above example except for the conductive separator.

The polymer electrolyte fuel cells of the present example and the comparative example thus produced were maintained at 85 ° C., and hydrogen gas humidified and heated to a dew point of 83 ° C. was applied to one electrode side. Humidified and heated air was supplied to the other electrode side so as to have a dew point of 78 ° C. As a result, a battery open-circuit voltage of 50 V was obtained when there was no load in which no current was output to the outside.

The battery was subjected to a continuous power generation test under the conditions of a fuel utilization of 80%, an oxygen utilization of 40%, and a current density of 0.5 A / cm ² , and the change over time in the output characteristics is shown in FIG. As a result, it was confirmed that the output of the battery of the comparative example decreased with the driving time, while the battery of the present example maintained the battery output of 1000 W (22 V-45 A) for 8000 hours or more.

In this embodiment, the case where the gas flow groove is a plurality of parallel straight lines is tried. However, as shown in FIG. 4, the gas discharge manifold hole is passed from the gas supply manifold to the gas discharge manifold hole through the twice curved portion 14 as shown in FIG. Various structures are also possible, such as a connection structure and a structure in which a central manifold hole and an outer manifold hole are connected by a gas flow groove like a snail shell.

(Embodiment 2) In the first embodiment, a SUS plate having a tin oxide layer formed by in-forming In was formed on the surface of the SUS plate as a conductive separator. In this embodiment, the surface of the SUS plate on which Pb was deposited was used. The following shows an example in which a lead oxide layer is formed.
In this example, the battery configuration other than the material of the conductive separator and the conditions for evaluating the characteristics of the battery were all the same as those in Example 1.

Hereinafter, a manufacturing process of the conductive separator will be described. First, a Pb layer having a thickness of 1 μm was formed on a surface of a SUS316 plate having a thickness of 0.3 mm by a vacuum heating evaporation method. The deposition conditions at this time were 1 × 10 ⁻⁷ Torr Ar
(99.9999%) atmosphere, and the substrate temperature was 200 ° C. Next, Pb is deposited on the Pb-deposited surface of this Pb-deposited SUS plate.
The bO layer was formed by a sputtering method. The formation conditions were as follows: an Ar (99.9999%) atmosphere having an oxygen partial pressure of 2 × 10 ⁻⁴ Torr; a substrate temperature of 200 ° C .; In the structural analysis of the obtained sputtered layer, PbO was identified by X-ray diffraction. The specific resistance of the PbO layer formed by the above method is 5 × 1
It was 0 ^-5 Ωcm.

As in the first embodiment, the fuel cell was maintained at 85.degree. C., hydrogen gas humidified and heated to a dew point of 83.degree. C. was applied to one electrode, and 78 was applied to the other electrode.
Supply air humidified and heated to a dew point of ° C, fuel utilization 80%, oxygen utilization 40%, current density 0.5A
The battery output at the initial stage (after 10 hours from the start of operation) when the continuous power generation test was performed under the conditions of / cm ² and at the time when the operation time had passed 8000 hours were shown. The results are shown in Table 1.

The PbO ₂ layer was formed to a thickness of 1 μm by controlling the sputtering conditions. The characteristics of the battery using this were also good, and the results are shown in Table 1. The sputtering conditions were as follows: the substrate temperature was 40 ° C., the sputtering gas was 3 × 10 ⁻⁴ Torr with oxygen,
The deposition rate was 2 μm / hour.

(Embodiment 3) In this embodiment, an example in which TiN which is a conductive nitride is used as a conductive inorganic compound will be described. In this example, the battery configuration other than the material of the conductive separator and the conditions for evaluating the characteristics of the battery were all the same as those in Example 1.
And the same.

Hereinafter, a manufacturing process of the conductive separator will be described. A TiN layer having a thickness of 1 μm was formed on a surface of a 0.3 mm-thick Ti plate by a sputtering method using an RF-plana magnetron. At this time, the target is T
iN (99%) was used, and the substrate temperature was 500 ° C. The sputtering atmosphere was 4 × 10 ⁻² Torr of Ar (99.999
9%), the sputtering power was set to 400 W, and the formation rate was controlled to 1.5 μm / hour. In the structural analysis of the obtained sputtered layer, TiN was identified by X-ray diffraction. The specific resistance of the TiN layer formed by the above method is 2 × 1
It was 0 ^-4 Ωcm.

As in Example 1, the fuel cell was maintained at 85.degree. C., and hydrogen gas humidified and heated to a dew point of 83.degree. C. was applied to one electrode side, and 78% was applied to the other electrode side.
Supply air humidified and heated to a dew point of ° C, fuel utilization 80%, oxygen utilization 40%, current density 0.5A
/ Cm ² shows the battery output at the initial time when the continuous power generation test was performed under the condition of / cm ² , and also when the operation time has passed 8000 hours. The results are shown in Table 1.

In this embodiment, the thickness of the TiN layer is set to 1 μm. However, when the thickness is reduced, the impedance as a battery is reduced, and the output characteristics are improved accordingly, but the long-term stability is impaired. The disadvantage occurs. Further, if the film thickness is too large, the reliability is increased, but there is a problem that the film formation time is lengthened and the productivity is reduced. Thus, in this example, when the thickness of the TiN layer was examined, it was practically about 1 μm.

Also, instead of TiN, Ti-Al-N
Was coated using an Al plate as a substrate, and similar excellent characteristics were obtained. The results are shown in Table 1. The film forming conditions are shown below.

The surface of the 0.3 mm thick Al plate was RF-
By a sputtering method using a diode, Ti-Al-N
The layer was formed with a thickness of 1.2 μm. At this time, the target used was Ti-Al-N (99%), and the substrate temperature was 3
The temperature was set to 00 ° C. The sputtering atmosphere is 4 × 10 ^-2 Torr A
r (99.999%), the sputtering power was set to 300 W, and the formation rate was controlled to be 1.0 μm / hour. The specific resistance of the Ti—Al—N layer formed by the above method was 1 × 10 ⁻³ Ωcm.

(Embodiment 4) This embodiment shows an example in which n-type SiC which is a conductive carbide is used as the conductive inorganic compound.

Hereinafter, an n-type doped SiC on a metal substrate will be described.
A method for forming a layer will be described. As a film forming method, a high frequency glow discharge decomposition method of 14.56 MHz is used, and gas to be decomposed is silane, methane (CH ₄ ), diborane (PH ₃ ) diluted with hydrogen.
Were mixed at a ratio of P / (Si + C) = 10 at%, and the whole was set to 10 Torr at a substrate temperature of 300 ° C. At this time, by controlling the film formation time, the thickness of the n-type toughened SiC layer was set to 1,000. After film formation,
A gold electrode was deposited on the C layer, and the specific resistance of the SiC layer was measured to be 50 Ωcm.

As in the first embodiment, the fuel cell was maintained at 85 ° C., and hydrogen gas humidified and heated so as to have a dew point of 83 ° C. was applied to one electrode side, and 78% was applied to the other electrode side.
Supply air humidified and heated to a dew point of ° C, fuel utilization 80%, oxygen utilization 40%, current density 0.5A
/ Cm ² shows the battery output at the initial time when the continuous power generation test was performed under the condition of / cm ² , and also when the operation time has passed 8000 hours. The results are shown in Table 1.

[0044]

[Table 1]

[0045]

According to the present invention, as a separator plate, a metal material such as stainless steel can be used without cutting in place of the conventional carbon plate cutting method, so that the cost can be significantly reduced during mass production. Further, the thickness of the separator can be further reduced, which contributes to the compactness of the laminated battery.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a conductive separator used in a fuel cell according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a hydrogen 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 fuel cell stack according to the first embodiment of the present invention;

FIG. 4 is a diagram showing a configuration of another conductive separator that can be used in the fuel cell according to the first embodiment of the present invention.

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Corrugated processing part 2 Groove 3 Crest 4 Manifold hole 5 Phenol convex part 6 Phenol groove 7 Phenol gasket 8 MEA 9 Hydrogen side gas circulation groove 10 Air side gas circulation groove 11 Cooling part 12 Metal mesh 13 Grease 14 Bent part 15 Seam

────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] June 15, 1999 (1999.6.1
5)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0017

[Correction method] Change

[Correction contents]

[0017]

Embedded image

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0019

[Correction method] Change

[Correction contents]

[0019]

Embedded image

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Kazuhito Hato 1006 Kazuma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Kazufumi Nishida 1006 Kadoma, Kadoma, Osaka Pref.Matsushita Electric Industrial Co., Ltd. (72) Inventor Makoto Uchida 1006 Odama, Kadoma, Kadoma, Osaka Pref. Yasushi 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture, Japan Matsushita Electric Industrial Co., Ltd. Address F-term (reference) in Matsushita Electric Industrial Co., Ltd. 5H026 AA01 AA02 AA06 CC03 EE11 EE12

Claims (4)

[Claims] 1. A solid polymer fuel cell comprising a pair of electrodes sandwiching a solid polymer electrolyte membrane, and a unit cell comprising means for supplying and discharging fuel gas to and from the electrodes, with a conductive separator interposed therebetween. In the above, the conductive separator is formed of a metal plate coated with a conductive inorganic compound, and the conductive separator forms a gas flow groove for flowing the fuel gas, and further includes a material having a gas sealing property for the fuel gas. A solid polymer fuel cell, wherein the gas flow groove is connected to a means for supplying and discharging the fuel gas. 2. The polymer electrolyte fuel cell according to claim 1, wherein the conductive inorganic compound is a conductive inorganic oxide, a conductive inorganic nitride, or a conductive inorganic carbide. 3. The polymer electrolyte fuel cell according to claim 1, wherein the gas flow grooves formed in the conductive separator have a plurality of linear shapes parallel to each other. 4. A gas flow groove formed on one surface of a conductive separator, the gas flow groove having a concave portion formed on a back surface of the conductive separator. Or the polymer electrolyte fuel cell according to 3.