JP3387046B2 - Fuel cell separator - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell separator, and more particularly to a separator that can be used in an on-vehicle fuel cell for powering an automobile.

[0002]

2. Description of the Related Art A fuel cell has a high efficiency of energy conversion from fuel to electricity and does not emit harmful substances, and therefore has attracted attention as a next-generation power generation device. In particular, polymer ion-exchange membrane fuel cells that operate in the temperature range of 150 ° C. or less have been actively researched and are expected to be put into practical use in a few years.
This fuel cell can be operated at a relatively low temperature, has a high power generation density of power generation, and can be miniaturized, and thus is suitable as a fuel cell for home use or on-vehicle use.

Generally, a polymer ion exchange membrane fuel cell is
Fuel cells and oxygen electrodes (air electrodes) are fixed on both sides of the solid electrolyte membrane to form single cells (cells), which are laminated via plate-like separators provided with ventilation grooves for supplying fuel gas and air. It is composed of As the solid electrolyte membrane, a fluororesin-based ion exchange membrane having a sulfonic acid group or the like is used, and the electrode is formed of carbon black in which a water repellent material PTFE and a noble metal fine particle catalyst are dispersed. When the hydrogen-oxygen fuel cell operates, the protons generated by the oxidation of hydrogen gas enter the electrolyte and bond with water molecules.
It becomes H ₃ O ⁺ and moves to the positive electrode side. On the positive electrode side, oxygen introduced from the ventilation groove obtains electrons generated by the oxidation reaction of hydrogen, and combines with protons in the electrolyte to become water. By continuing these reaction processes, electric energy can be continuously taken out. The theoretical electromotive force of this cell is 1.
Although it is 2 V, due to the polarization of the electrodes, the crossover of the reaction gas (the phenomenon that the fuel gas permeates the electrolyte and leaks to the air electrode), the voltage drop due to the contact resistance of the electrode and the current collector, etc., The output voltage is about 0.6 to 0.8 V. Therefore,
In order to obtain a practical output, it is necessary to stack dozens of unit cells via a separator and connect them in series.

As can be seen from the above-mentioned power generation principle, since a large amount of H ⁺ is present in the electrolyte, it becomes strongly acidic inside the electrolyte and in the vicinity of the electrode where a large amount of water or water vapor is present. On the positive electrode side, oxygen combines with H ⁺ to generate water, but hydrogen peroxide may be generated depending on the operating state of the battery. Since the separator is incorporated in such an environment, it is required to have high chemical and electrochemical stability (corrosion resistance) in addition to electrical conductivity and airtightness.

Most of the conventional fuel cell separators are machined graphite plates. The graphite separator has low electric resistance and high corrosion resistance, but has low mechanical strength and high processing cost. Since a separator used for an on-vehicle fuel cell is required to have high mechanical strength and can be processed at low cost, it is difficult to apply the current graphite separator as it is to an on-vehicle fuel cell. In recent years, a method of manufacturing a separator by mixing graphite powder with a resin, injection-molding the mixture, and further firing it at a high temperature has been studied. However, there is a problem that airtightness is poor because the density of the obtained fired body is low.
It is possible to increase the density by immersing this separator in resin and carbonizing it again, but the manufacturing process becomes complicated. In addition, the contact electric resistance of the separator manufactured in this way is several times higher than that of the conventional graphite separator, and the decrease in the output voltage of the battery cannot be avoided.

In addition to graphite separators, separators made of metal have been investigated. The metal separator has low bulk electric resistance, high airtightness and mechanical strength, and is easy to reduce the processing cost. Moreover, since the thickness of the separator can be reduced, the size can be easily reduced. Further, the fuel cell can be further reduced in weight by using a low specific gravity metal material such as aluminum. However, the metal separator has a problem that the metal itself of the base material is easily corroded. In particular, aluminum substrates have been reported to have very high corrosion rates (RL Rorup, et al., Mate
r. Res. Soc. Symp. Proc., 393 (1995) etc.). Also, when metal ions generated by corrosion enter the electrolyte membrane,
The ionic conductivity of the membrane may be reduced, which may affect battery performance.

Japanese Unexamined Patent Publication (Kokai) No. 11-162478 discloses a method of improving corrosion resistance by plating a noble metal on the entire surface of a metal separator. Although this method has no problem with respect to the separator performance, it causes high cost and is not practical. It is necessary to thin the precious metal plating layer to reduce the cost, but if the layer thickness is thinned during wet plating, fine pinholes will be generated and cause corrosion, and it will be produced by dry plating (evaporation, sputtering, etc.). The efficiency is poor and the uniformity of the coating is also poor.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a metal fuel cell separator having excellent corrosion resistance.

[0009]

As a result of earnest research in view of the above problems, the inventors of the present invention have shown that a metal fuel cell separator partially provided with an alumite coating and a polymer heat resistant coating exhibits excellent corrosion resistance. After discovering this, the present invention was conceived.

That is, the fuel cell separator of the present invention is made of a metal plate and has a contact surface with an electrode or a current collector and a reaction gas ventilation groove, and the surface of the reaction gas ventilation groove has an armature.
Coating film is formed and polymer heat resistance on the alumite coating
It is characterized in that a coating is formed. Anodized
The porosity of the membrane is preferably 5% or more. See also Alma
Coating is a dense alumite coating with a porosity of less than 5%.
And porous alumite with a porosity of 5% or more formed on it
It is also preferable that it is composed of a coating film.

[0011]

[0012]

[0013]

[0014]

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The fuel cell separator of the present invention is made of a metal plate and has a contact surface with an electrode or a current collector and a reaction gas ventilation groove. A polymer heat resistant coating is formed on the surface of the reaction gas ventilation groove. INDUSTRIAL APPLICABILITY The separator of the present invention can be used for various fuel cells, and is particularly suitable for on-vehicle fuel cells for powering automobiles.

The metal plate used as the separator substrate preferably has a dense structure. Here, "dense" means that the reaction gas does not permeate the metal plate to cause crossover because there is substantially no through hole or the like. As the separator base material, it is preferable to use one made of a metal having high electrical conductivity and seismic resistance. In addition, since it is necessary to reduce the weight of the separator when used as an in-vehicle fuel cell for automobiles, it is preferable to use a light metal such as aluminum, titanium, or magnesium as a base material or an alloy thereof, and it is preferable to use aluminum or an aluminum alloy. More preferable. The thickness of the base material is not particularly limited,
When used in an on-vehicle fuel cell, it is preferably 0.5 to 3 mm. Since the shape and manufacturing method of the separator in the present invention, the material and the forming method of the polymer heat resistant coating are basically the same when using any metal as the base material,
The fuel cell separator according to the present invention using an aluminum metal plate as a substrate will be described with reference to the drawings.
The present invention is not limited to these, and various changes can be made without changing the gist of the present invention.

FIG. 1 is a partial schematic view showing an example of a fuel cell including a fuel cell separator according to an embodiment of the present invention. The fuel cell of FIG. 1 includes a unit cell 1 including a solid electrolyte 2 and anodes 3 and cathodes 4 provided on both sides of the solid electrolyte 2.
It is configured by stacking via a separator 5. Both ends of the stack are connected to an external circuit (not shown).

As shown in FIG. 1, the separator 5 of the present invention.
Has reaction gas vent grooves 9 and 10. Normally, the fuel gas is supplied to the passage formed by the reaction gas ventilation groove 10 and the anode 3, and the oxidant gas is supplied to the passage formed by the reaction gas ventilation groove 9 and the cathode 4. The reaction gas ventilation grooves 9 and 10 may be formed in a predetermined pattern by a method such as machining, pressing, precision casting, chemical polishing (etching), and electrolytic polishing. Although the shape of the reaction gas ventilation groove is U-shaped in FIG. 1, it is not particularly limited as long as the reaction gas passage can be formed in the portion in contact with the electrode, and the reaction gas ventilation resistance is small and the power generation efficiency is high. It is preferable to set so that Normally, the depth of each reaction gas ventilation groove is 0.2-2m
It is preferably m, and the width is preferably 0.5 to 5 mm.

In order to secure the corrosion resistance of the metal separator, a polymer heat resistant coating 6 is formed on the surfaces of the reaction gas ventilation grooves 9 and 10 which do not come into contact with the electrodes or the like (see FIG. 1). The polymer heat resistant coating preferably has a dense structure. Here, the "dense structure" means a structure in which a gas such as water or water vapor does not permeate.

The polymer heat resistant coating preferably has water repellency. When it has water repellency, the retention of water is suppressed and the corrosion of the base material is suppressed, so that the corrosion resistance of the separator can be greatly improved. In the present invention, "having water repellency" means that there is no attachment or retention of water, and for example, the contact angle when a liquid is brought into contact with the solid-gas interface of the coating to replace the solid-liquid interface is 90 °. That is the above. Also, since the operating temperature of fuel cells is usually 80 to 120 ° C, the softening point of the material used for the polymer heat resistant coating is 120 ° C considering the long-term stability.
The above is preferable.

As the polymer material forming the polymer heat resistant coating, vinyl resins such as polyvinyl butyral (PVB), polyvinyl chloride (PVC), polytetrafluoroethylene (P
TFE), polyvinylidene fluoride, aromatic polyamide, polyimide, polycarbonate, polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polyester, polystyrene or its derivatives, copolymers of styrene and other monomers, polyethylene, polypropylene, It is preferable to use polyurethane, silicone resin, polysulfone, polyether sulfone, rayon, cupra, acetate resin, promix, vinylon, vinylidene resin and / or acrylic.

The polymer heat resistant coating preferably has a multilayer structure composed of two or more layers. For example, as shown in FIG. 2, the polymer heat resistant coating is composed of two polymer heat resistant coatings 6,
It may be a two-layer structure composed of 6 '. In this case, the polymer heat-resistant coating 6 is formed of a polymer material having excellent adhesion to a metal substrate, and the polymer heat-resistant coating 6'is formed of a polymer material having excellent waterproofness. Particularly preferred from the viewpoint of improvement.

The method for forming the polymer heat resistant coating is not particularly limited. For example, the polymer material as described above may be dissolved in an appropriate organic solvent, the separator may be dipped in the resulting solution, and then dried to form the separator. It is also possible to coat the separator with a thin polymer film and heat-bond it to form the separator.

In order to further improve the corrosion resistance, the surface of the reaction gas ventilation groove is appropriately treated. As shown in FIG. 3, when a metal plate of aluminum or aluminum alloy is used as the base material, a chemically and physically stable alumite coating 7 is formed on the surface inside the reaction gas ventilation grooves 9 and 10. A polymer heat resistant coating 6 is formed on top. It is considered that the cause of the deterioration of the corrosion resistance of the separator formed with the alumite coating is cracking or peeling that occurs when the alumite coating swells and grows in water vapor and causes film distortion. Particularly in the case of a fuel cell mounted in an automobile, the alumite coating is placed in an environment where the temperature and humidity change greatly, so that film distortion is likely to occur. In the present invention, since the waterproof polymer heat resistant coating is formed on the alumite coating, such deterioration of the alumite coating due to water vapor can be suppressed.

The alumite coating can be formed by an anodic oxidation method or the like. For example, the γ-alumina coating may be formed on the surface of the substrate by electrolysis using an aqueous solution of oxalic acid, sulfuric acid, chromic acid or the like as the electrolytic solution. From the viewpoint of corrosion resistance, the film thickness of the alumite coating is preferably 5 to 50 μm, and more preferably 10 to 30 μm.

By appropriately adjusting the anodizing conditions,
A fine hard alumite coating can be formed, and the corrosion resistance is further improved. Further, after anodizing treatment, by treating with boiling water or steam, it is possible to close the fine pores peculiar to the alumite coating.

It is also possible to form fine vertical pores or a spongy porous layer in the alumite coating by appropriately selecting the electrolysis conditions for anodic oxidation. As shown in FIG. 3, by making the alumite coating 7 a porous alumite coating 11, the adhesion of the polymer coating 6 can be improved. The porosity of the porous alumite coating is preferably 5
% Or more, more preferably 10% or more.

As shown in FIG. 4, when the alumite coating 7 is composed of a dense alumite coating 12 having a porosity of less than 5% and a porous alumite coating 11 having a porosity of 5% or more formed thereon, the above corrosion resistance is improved. The effect and the effect of improving the adhesiveness are simultaneously obtained, which is preferable. In such a case, the porosity of the porous alumite coating is particularly preferably 20% or more. The film thickness of the dense alumite coating is preferably 2 to 30 μm, and the film thickness of the porous alumite coating is 5 to 5 μm.
It is preferably 50 μm.

If the aluminum or aluminum alloy used as the substrate contains a large amount of impurities, the uniformity of the alumite coating deteriorates and the density becomes low. Further, in such a case, once the alumite coating is formed, the effect of the densification treatment using boiling water, steam or the like becomes small. Therefore, the purity of the aluminum or aluminum alloy used in the separator of the present invention is preferably 99.5% or more, more preferably 99.9% or more.

The separator of the present invention has a contact surface with an electrode or a current collector. The shape of the contact surface may be any shape suitable for contacting the electrodes of the fuel cell or the carbon paper, carbon cloth, etc. of the primary current collector, and is not limited by the drawings.

As shown in FIGS. 1 to 4, it is preferable to form a conductive film 8 on the contact surface (electrically conductive surface) with the electrode or the current collector. In the separator of the present invention, it is preferable to cover the entire surface with the polymer heat resistant coating and the conductive coating. That is, only a portion that contacts the electrode and conducts electricity is coated with a noble metal or the like having good electrical conductivity, and a chemically or physically stable polymer heat resistant coating is formed on the surface in the ventilation groove,
It is preferable to make both the corrosion resistance and the electrical conductivity of the base material compatible with each other.

The conductive film is preferably formed by using a material having good electrical conductivity and corrosion resistance, such as Pt, Au, Pd,
More preferably, it is formed of a metal selected from the group consisting of Ru, Rh, Ir and Ag, an alloy thereof, carbon, or a conductive carbide. Noble metal coatings such as Au, Ag, Pt and Pd have low contact resistance and extremely good corrosion resistance. The carbon is preferably a graphite film formed by CVD, a DLC film (diamond-like carbon film), or the like. Alternatively, graphite powder to which a water repellent is added may be applied. When the electrode is made of carbon black to which a small amount of Pt is added or the like, the use of a carbon coating provides good contact familiarity. Silicon carbide, niobium carbide, tungsten carbide and the like are preferable as the conductive carbide. The carbide coating not only has a low contact resistance, but also has good corrosion resistance and oxidation resistance, and therefore functions as a protective film for the separator.

The conductive film can be formed by a method such as a sputtering method, electroplating, wet plating or CVD. The thickness of the conductive coating is preferably 0.01-5 μm. Film thickness
If it is smaller than 0.01 μm, the film strength is weak and unstable, and it is 5 μm
If it is larger, the cost becomes higher, which is not preferable.

[0034]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

Reference Example 1 Each separator substrate shown in Table 1 (1 mm x 150 mm x 150 mm)
Then, a reaction gas ventilation groove having a depth of 1.0 mm and a width of 3.0 mm was formed by pressing. Add 15 parts by weight of polyvinyl butyral (PV
B) About 1 after dipping into a solution of powder
Cure treatment was performed at 50 ° C. to form a polymer heat resistant coating on the entire surface. Next, in order to improve the flatness of the electrode contact surface of each separator, the electrode contact surface was lapped and cleaned. Through this step, the polymer heat resistant coating made of PVB formed on the electrode contact surface was removed. Then, 5mTor
In a pure argon gas atmosphere of r, the substrate temperature was set to 200 ° C. and Au was sputtered on the electrode contact surface to form a conductive film, and each separator according to the present invention was produced. The thickness of the Au conductive coating was about 1 μm.

15 parts by weight of Pt paste (Pt: 90% by weight) was added to 100 parts by weight of carbon black, and 15 parts by weight of Teflon particles (average particle size: 0.2 μm) were added as a water repellent. An electrode paste was prepared. This electrode paste was applied to a proton conductive polymer solid electrolyte membrane (Nafion) and dried. This was sandwiched between carbon cloths and further sandwiched between two sheets of the above-mentioned respective separators to fabricate fuel cells (unit cells) 1a to 1d of Reference Example 1, respectively. The tightening pressure of the separator was 10 kg / cm ² .

Comparative fuel cells 1a 'to 1d' were produced in the same manner as the above-mentioned fuel cells 1a to 1d except that the polymer heat resistant coating was not formed. Further, using graphite as a separator base material, a comparative fuel cell 1e ′ having no polymer heat resistant coating was prepared in the same manner as the fuel cells 1a to 1d.

With respect to the obtained fuel cells 1a to 1d of Reference Example 1 and the comparative fuel cells 1a 'to 1e', a simulated fuel gas (70% H ₂ , 15% C
O ₂ and 15% H ₂ O) were supplied, and air was supplied as an oxidant to the cathode side ventilation groove to evaluate the stability of power generation performance. The evaluation was conducted for 13 days. Table 1 also shows the separator base material of each fuel cell, the polymer material used for the polymer heat resistant coating, the initial generation voltage, the generation voltage after 13 days of operation, and the corrosion resistance of the separator after 13 days of operation. .

[0039]

[Table 1]

From Table 1, it can be seen that the separator of the present invention provided with a polymer heat resistant coating exhibits excellent corrosion resistance, and the fuel cells 1a to 1d of Reference Example 1 using the separator exhibit high stability of power generation performance. Recognize.

[0041] Reference Example 2 as a material of the conductive film in the same manner as the method for manufacturing the fuel cell 1a except for using the materials shown in Table 2, the fuel cell of Example 2 including the separator of the present invention 2a~2r Were produced respectively. Also, a comparative fuel cell without a conductive coating
2'was similarly prepared. However, when forming a conductive coating of carbon (2q) and conductive carbide SiC (2r), use a target of the coating composition and use Ar (30 m
Torr) was used. The obtained fuel cells 2a to 2r of Reference Example 2,
Simulated fuel gas (70% H ₂ , 20% CO ₂ , 10% H ₂ O) humidified in the reaction gas ventilation groove on the anode side of the comparative fuel cell 2 ′ and the comparative fuel cell 1 e ′. Was supplied, and air was supplied as an oxidant to the ventilation groove on the cathode side to evaluate the stability of power generation performance. The evaluation was conducted for 12 days. Conductive coating material,
Table 2 also shows the initial generation voltage, the generation voltage after 12 days of operation, and the corrosion resistance of the separator after 12 days of operation.

[0042]

[Table 2]

From Table 2, the aluminum separator according to the present invention having the above-mentioned preferable conductive coating exhibits excellent corrosion resistance, and the fuel cells 2a to 2r of Reference Example 2 using the separator exhibit high stability in power generation performance. I understand.

Example 1 The above fuel cell 1a was prepared, except that an alumite coating having the porosity shown in Table 3 was formed on the surface of the reaction gas vent groove of the aluminum base material, and a polymer heat resistant coating was formed thereon. similar to the manufacturing method, the fuel cell 1 a to 1 i of example 1, including a separator of the present invention were produced. The alumite coating was formed by anodizing in an oxalic acid aqueous solution, then immersing it in boiling water for 30 minutes and then drying it. The thickness of the alumite coating was 15 μm. Moreover, except for not forming the polymeric heat-resistant coating as in the case of the fuel cell 1 a to 1 i of Example 1, were produced fuel cell 3A'～3i 'for comparison. The power generation performance stability of the resulting fuel cell 1 a to 1 i and comparative fuel cell 3a'~3i of Example 1 'was evaluated in the same manner as in Reference Example 2. However, the evaluation was conducted for 48 days. Table 3 also shows the porosity of the alumite coating of each fuel cell, the initial power generation voltage, the power generation voltage after 48 days of operation, and the peeling state of the alumite coating after 48 days of operation.

[0045]

[Table 3]

From Table 3, it is understood that when the separator of the present invention has an alumite coating, its porosity is preferably 4.82% or more, more preferably 9.84% or more. It was also confirmed that, in comparison with the separator used in the fuel cells 3a ′ to 3i ′, the separator of the present invention can suppress the peeling of the alumite coating by forming the polymer heat resistant coating.

Reference Example 3 Similar to the method for producing the fuel cell 1a of Reference Example 1, except that each material shown in Table 4 was used as the polymer material for forming the polymer heat-resistant coating, the separator of the present invention was included. the fuel cell 3 a~ 3 w of reference example 3 were produced. However, the method for forming the polymer heat resistant coating was appropriately selected from the solution coating method and the heat fusion method depending on the polymer material used. Obtained reference example
The power generation performance stability of 3 of the fuel cell 3 a to 3 w were evaluated in the same manner as in Reference Example 2. Table 4 also shows the polymer material of each fuel cell, the initial power generation voltage, the power generation voltage after 12 days of operation, and the corrosion resistance after 12 days of operation.

[0048]

[Table 4]

From Table 4, all of the separators of the present invention having the above-mentioned preferable polymer heat-resistant coating showed excellent corrosion resistance, and the fuel cell 3 a of Reference Example 3 using the separator was used.
It can be seen that ~ 3 w shows high power generation performance stability.

[0050]

As described in detail above, since the fuel cell separator of the present invention uses a metal plate as a base material, it is much lighter in weight than conventional graphite separators, has high mass productivity, and can reduce processing costs. . In addition, in the present invention, a separator having excellent corrosion resistance can be obtained by forming a polymer heat resistant coating on the surface of the reaction gas ventilation groove. The fuel cell using the separator of the present invention has high power generation performance stability.

[Brief description of drawings]

FIG. 1 is a partial schematic view showing an example of a fuel cell including a fuel cell separator according to an embodiment of the present invention.

FIG. 2 is a schematic view showing a fuel cell separator according to another embodiment of the present invention, and a partially enlarged view showing the structure of the polymer heat resistant coating.

FIG. 3 is a schematic view showing a fuel cell separator according to another embodiment of the present invention, and a partially enlarged view showing the structures of the polymer heat resistant coating and the alumite coating.

FIG. 4 is a schematic view showing a fuel cell separator according to another embodiment of the present invention, and a partially enlarged view showing the structures of the polymer heat resistant coating and the alumite coating.

[Explanation of symbols]

1 ... single battery 2 ... Solid electrolyte 3 ... Anode 4 ... Cathode 5 ... Separator 6,6 '... Polymer heat resistant coating 7 ... Alumite coating 8 ... Conductive coating 9, 10 ... Reactive gas ventilation groove 11 ... Porous alumite coating 12 ... Dense alumite coating

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP 2000-36309 (JP, A) JP 10-12250 (JP, A) JP 9-298064 (JP, A) JP 11-97041 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01M 8/00-8/24

Claims (3)

(57) [Claims] 1. A metal plate which is in contact with an electrode or a current collector.
Fuel cell separator having touch surface and reaction gas ventilation groove
In, the surface of the reaction gas ventilation groove, alumite coating
And a polymer heat resistant coating is formed on the alumite coating.
For a fuel cell, characterized in that
Ta. 2. The fuel cell separator according to claim 1.
In, the alumite coating has a porosity of 5% or more.
Fuel cell separator characterized by a high quality alumite coating
Parator. 3. The fuel cell separator according to claim 1.
In the above, the alumite coating has a porosity of less than 5%.
Dense alumite coating and porosity 5% formed on it
It is characterized by being composed of the above porous alumite coating.
Fuel cell separator to be collected.