JP2001357859A - Separator for fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for a metallic fuel cell having excellent corrosion resistance. SOLUTION: This separator is formed of metal base material and has a contact surface to an electrode or a collector, and a reaction gas vent slot. A conductive film containing a metal, an oxide, a nitride, a carbide or carbon as a main constituent is formed on the contact surface. The structure or the function of the conductive film is continuously changed between the contact interface with the metal base material and the contact interface with the electrode or the collector.

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 a vehicle-mounted fuel cell for powering an automobile.

[0002]

2. Description of the Related Art Fuel cells have attracted attention as next-generation power generators because of their high energy conversion efficiency from fuel to electricity and no emission of harmful substances. In particular, polymer ion exchange membrane fuel cells that operate in a temperature range of 150 ° C. or less are being actively studied, and are expected to be put into practical use in several years. This fuel cell can be operated at a relatively low temperature, has a high power generation output density, and can be downsized, so that it is suitable as a home or vehicle fuel cell.

In a polymer ion exchange membrane fuel cell, a fuel electrode and an oxygen electrode (air electrode) are usually provided on both surfaces of a solid electrolyte membrane.
Are fixed to form a unit cell (cell), which is laminated via a plate-shaped separator provided with a ventilation groove for supplying fuel gas and air. In general, a fluororesin-based ion exchange membrane having a sulfonic acid group or the like is used as the solid electrolyte membrane, 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, protons generated by oxidizing hydrogen gas enter the electrolyte, combine with water molecules to form H ₃ O ⁺ , and move 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 form water. By continuing these reaction processes, electric energy can be continuously taken out. The theoretical electromotive force of this cell is
Although it is 1.2V, it is actually caused by electrode polarization, reaction gas crossover (phenomenon of fuel gas passing through the electrolyte and leaking to the air electrode), voltage drop due to contact resistance between electrode and current collector, etc. The output voltage is about 0.6-0.8V. Therefore,
To obtain a practical output, it is necessary to stack dozens of cells via a separator and connect them in series.

As can be understood from the above-described power generation principle, a large amount of H ⁺ is present in the electrolyte, so that the electrolyte becomes strongly acidic inside the electrolyte where a large amount of water or water vapor is present and near the electrodes. In addition, oxygen is combined with H ⁺ on the positive electrode side to generate water, but hydrogen peroxide may be generated depending on the operation state of the battery. Since the separator is incorporated in such an environment, it is required to have high chemical / electrochemical stability (corrosion resistance) in addition to electric conductivity and airtightness.

Many conventional fuel cell separators are obtained by machining a graphite plate. Graphite separators have low electrical resistance and high corrosion resistance, but have low mechanical strength and high processing costs. Since it is required that a separator used for an in-vehicle fuel cell has high mechanical strength and can be processed at low cost, it is difficult to apply a current graphite separator to an in-vehicle fuel cell as it is. In recent years, a method of manufacturing a separator by mixing graphite powder with a resin, injection molding and firing at a high temperature has been studied, but there is a problem that the density of the obtained fired body is low and airtightness is poor.
It is possible to increase the density by immersing this separator in a resin and carbonizing and refiring, but the manufacturing process becomes complicated. In addition, the contact electric resistance of the separator thus manufactured is several times higher than that of the conventional graphite separator, and a decrease in the output voltage of the battery is inevitable.

[0006] In addition to the graphite separator, a separator made of metal has been studied. Metal separators have low bulk electrical resistance, high airtightness and mechanical strength, and are easy to reduce processing costs. In addition, since the thickness of the separator can be reduced, miniaturization is easy. Further, when a low specific gravity metal material such as aluminum is used, the weight of the fuel cell can be further reduced. However, the metal separator has a problem that the base metal itself is easily corroded. In particular, it has been reported that the aluminum base metal has a very high corrosion rate (RL Rorup, et al., Mate
r. Res. Soc. Symp. Proc., 393 (1995)). Also, when metal ions generated by corrosion enter the electrolyte membrane,
The ionic conductivity of the membrane may be reduced and affect the performance of the battery.

JP-A-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 is not practical because it increases the cost. In order to reduce costs, it is necessary to reduce the thickness of the noble metal plating layer. However, if the thickness is reduced during wet plating, fine pinholes are generated and cause corrosion, and dry plating (evaporation, sputtering, etc.) produces The efficiency is poor, and the uniformity of the coating is also deteriorated.

[0008]

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

[0009]

Means for Solving the Problems In view of the above problems, as a result of intensive studies, the present inventors have found that a metal fuel cell separator having a conductive coating whose structure or function changes continuously has excellent corrosion resistance. And found the present invention.

That is, the fuel cell separator of the present invention is made of a metal base material, has a contact surface with an electrode or a current collector and a reactive gas ventilation groove, and has a metal surface on the contact surface with the electrode or the current collector. , An oxide, a nitride, a carbide, or a conductive film mainly containing carbon is formed, and the structure or function of the conductive film is changed from a contact interface with a metal base material to a contact interface with an electrode or a current collector. Characterized by a continuous change between.

In a preferred embodiment of the fuel cell separator of the present invention, for example, the composition (A)
The crystal structure or (C) porosity continuously changes from the contact interface with the metal base material to the contact interface with the electrode or the current collector.

In the case of the above (A), the composition of the conductive film at the contact interface with the metal base material preferably contains at least 20% by weight of the constituent elements of the metal base material. Further, the composition of the conductive film at the contact interface with the electrode or current collector is Au, Pt, Pd, Ir or
It is preferable to contain Rh by 30% by weight or more.

In the case of the above (B), the crystal structure of the conductive film at the contact interface with the metal base material is an amorphous structure or a quasi-amorphous structure, and the conductive film at the contact interface with the electrode or the current collector is formed. Preferably, the crystalline structure of the coating is a crystalline structure. In this case, the main component of the conductive coating is preferably carbon, and the half-value width of the peak observed at 30 to 50 ° in 2θ of the X-ray diffraction pattern of the conductive coating at the contact interface with the metal base material. Is preferably 5.84 ° or less.

In the case of (C), the porosity of the conductive film at the contact interface with the metal base material is 5% or less, and the porosity of the conductive film at the contact interface with the electrode or current collector is 20%.
It is preferable that this is the case.

The thickness of the conductive film is preferably 0.5 to 30 μm. Further, the metal base material is preferably a metal plate made of aluminum or an aluminum alloy, and in that case, it is preferable to form an alumite film on the surface of the reaction gas ventilation groove.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The fuel cell separator of the present invention is made of a metal base material, and has a contact surface with an electrode or a current collector and a reactive gas vent groove. A conductive coating is formed on the surface of the separator that contacts the electrode or current collector. INDUSTRIAL APPLICABILITY The separator of the present invention can be used for various fuel cells, and can be particularly suitably used for an in-vehicle fuel cell for driving an automobile. Hereinafter, the fuel cell separator of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited thereto, 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 the fuel cell separator of the present invention. The fuel cell shown in FIG. 1 has a solid electrolyte 2 and anodes 3 provided on both sides thereof.
And a unit cell 1 including a cathode 4 and a separator 5 interposed therebetween. Both ends of the stack are connected to an external circuit (not shown). A current collector may be provided between the electrode and the separator. Hereinafter, each component of the separator of the present invention will be described.

[1] Metal Base Material In the present invention, a metal base material is used as a separator base material. A general metal plate such as a carbon steel plate and a SUS steel plate may be used as the metal base material. When the separator is applied to an in-vehicle fuel cell of an automobile, it is preferable to use a metal plate made of a lightweight metal having a high specific strength such as aluminum, titanium, and magnesium, or an alloy thereof as a metal base material. Among them, a metal plate made of aluminum or an aluminum alloy is particularly preferable. In order to prevent the crossover of the reaction gas (the phenomenon in which the fuel gas permeates the electrolyte and leaks to the air electrode), it is preferable to use a metal plate free from defects such as through holes. The thickness of the metal base material is not particularly limited, but is preferably 0.5 to 3 mm when used for an in-vehicle fuel cell.

[2] Contact Surface with Electrode or Current Collector The separator of the present invention has a contact surface with the electrode or current collector. The shape of the contact surface may be any shape suitable for contacting the electrode of the fuel cell or the carbon paper or carbon cloth of the primary current collector, and is not limited by the drawings.

As shown in FIG. 1, a conductive film 7 is formed on the surface of the separator base material that contacts the electrode or current collector.
The conductive film may be formed only on the contact surface, or may be formed on the entire surface of the separator base material. The conductive coating is metal,
Oxide, nitride, carbide or carbon as a main component.
Mixtures containing these materials may be used. These are not particularly limited as long as they are conductive materials. Oxides that can be used as conductive coating materials include ITO and Z.
nO, SnO ₂ , In ₂ O _{3 and the} like. As the carbide, silicon carbide, niobium carbide, tungsten carbide and the like can be used. Since the carbide conductive film has low contact resistance and good corrosion resistance and oxidation resistance, it also acts as a protective film for the separator. As the carbon, a graphite film by CVD, a DLC film (diamond-like carbon film) or the like can be used. Further, 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, the use of a carbon coating provides good contact familiarity.

In the present invention, the structure or function of the conductive film continuously changes from the contact interface with the metal base material to the contact interface with the electrode or the current collector. That is, in the separator of the present invention, the functions such as corrosion resistance and conductivity are changed by changing the composition, crystal structure, porosity and the like of the conductive film between the metal base material side and the electrode (current collector) side. Let it. The “continuous change” in the present invention includes a quasi-continuous change including a stepwise change in part. When a film whose composition or the like is continuously changed is formed, unlike the method of laminating one layer at a time, a gap or corrosion between layers is hardly generated.

The thickness of the conductive film is preferably 0.5 to 30 μm, more preferably 1 to 20 μm. Film thickness
If it is smaller than 0.5 μm, the corrosion resistance of the metal base material becomes insufficient,
If it is larger than 30 μm, the coating is apt to peel off, which is not preferable. Hereinafter, as a preferred embodiment of the separator according to the present invention, (A) composition of the conductive coating, (B) crystal structure, or
(C) An example in which the porosity changes between the contact interface with the metal base material and the contact interface with the electrode or current collector will be described in detail.

(A) Composition When metal materials or conductive materials are brought into contact with each other, an electric resistance is generated. This electric resistance includes the bulk resistance of each material and the contact resistance of the contact interface. For most conductive materials,
The bulk electric resistance is not so high and the electric resistance at the contact interface is high. This is because an oxide layer is always present on the surface of the conductive material, a potential barrier is generated by the surface energy of a different material, and the surface composition is different from that of the bulk.

In the present invention, as shown in FIG. 2 as an example, the conductive film 7 is provided with a lowermost portion 7a on the contact interface side with the metal base material, intermediate portions 7b to 7e, and an uppermost portion 7f on the contact interface side with the electrode. May be used. It is preferable that the lowermost portion 7a and its vicinity include a material A having excellent corrosion resistance as a main component, and the uppermost portion 7f and its vicinity preferably include a material B having a low contact resistance as a main component. The contact resistance of the material A may be high. Also, the bottom 7a
It is preferable to form the base material and the vicinity thereof from a dense material having good adhesion to the base material of the separator because corrosion of the base material due to pinholes and surface defects can be significantly reduced. in this way,
Since the composition of the conductive film formed on the separator of the present invention can be appropriately selected from various materials depending on the purpose, both improvement in corrosion resistance and reduction in contact resistance can be achieved. Note that FIG.
In the drawings, each part 7a to 7f is schematically shown as if they are stacked stepwise, but in fact, these are simply those whose composition continuously changes from the metal base material side to the electrode or current collector side. One film. Hereinafter, the portion of the conductive film that is in contact with the metal base material is the “bottom”, and the portion that is in contact with the electrode or current collector is the “top”.
, But do not represent layers that are layered in a step-by-step manner, but rather a portion of a single coating that has a continuous change in structure or function.

As described above, there is known a method of plating a metal base material with a platinum group noble metal coating to improve corrosion resistance.
In this method, it is necessary to reduce the thickness of the platinum group noble metal coating in order to reduce the cost. However, if the noble metal plating layer is thin, sufficient corrosion resistance cannot be obtained due to generation of pinholes. That is, if the base material surface is completely covered with the noble metal film, the corrosion of the base material is suppressed by the chemical stability of the noble metal, but if the film has pinholes or defects, the electrode potential difference between the base material and the film is large. Since the catalytic activity of the noble metal is high, the reduction reaction proceeds very easily, and corrosion of the separator is inevitable. In the present invention, the uppermost main component is a noble metal, and the main component of the portion between the uppermost portion and the metal base material is made of a material having excellent corrosion resistance. The potential difference can be reduced and the corrosion rate can be reduced. As a result, corrosion of the base material due to pinholes or surface defects can be significantly reduced. That is, in the present invention,
Simply by physically isolating, corrosion can be suppressed, and also corrosion resistance can be electrochemically improved.

The lowermost portion and its vicinity are composed of Pd, Ru, Ag,
It is preferable to use a metal selected from the group consisting of Zr, Cr, B, Ni, Ti and Sn or an alloy, oxide, nitride, carbide, or carbon thereof as a main component. By using such a material, the coating cost can be significantly reduced. The lowermost composition preferably contains the constituent elements of the metal base material in an amount of 20% by weight or more, more preferably 30% by weight or more. Thereby, the peeling of the conductive film can be suppressed, and the corrosion resistance of the contact surface of the separator electrode can be improved and the cost can be reduced.

On the other hand, it is more preferable that the uppermost portion and the vicinity thereof contain a material having a low contact resistance with an electrode and a high corrosion resistance as a main component. Such materials include Au, Pt, P
Metals selected from the group consisting of d, Ir, Ru, Rh and Ag, or alloys thereof, carbides, carbons and the like can be mentioned. The uppermost composition preferably contains Au, Pt, Pd, Ir or Rh in an amount of 20% by weight or more, particularly preferably 30% by weight or more.

Separators in which the composition of the conductive coating continuously changes from the contact interface with the metal base material to the contact interface with the electrode or current collector may be, for example, a bath solution containing two or more coating compositions. It can be prepared by immersing a metal base material in the inside, and applying wet electrolytic plating while changing the duty ratio by cyclically applying two or more kinds of deposition electrolysis voltages. Further, as the dry process, a method of continuously changing the ratio of the evaporation amount from a source (eg, a target in sputtering) of the film composition can be applied.

In a particularly preferred embodiment of the separator in which the composition of the conductive film is continuously changed, the metal base material is made of aluminum, and the lowermost Al content of the conductive film is 30% by weight or more. The uppermost Au content is 30% by weight or more. According to such a fuel cell separator, the size and weight of the battery cell can be reduced, and in addition, the electrode contact resistance can be significantly reduced, the corrosion resistance can be improved, and the cost can be reduced.

(B) Crystal Structure When the crystal structure of the conductive film is continuously changed between the contact interface with the metal base material and the contact interface with the electrode or current collector, the crystal structure at the contact interface with the metal base material is changed. It is preferable that the crystal structure of the conductive film be an amorphous structure or a quasi-amorphous structure, and the crystal structure of the conductive film at a contact interface with an electrode or a current collector be a crystalline structure. In the present invention, "quasi-amorphous"
Means that there is no clear crystal peak in the X-ray diffraction pattern, but some broad diffraction peaks can be obtained. In this case, the main component of the conductive film is preferably carbon. For example, the lowermost portion and its vicinity may be formed of dense and semi-amorphous hard carbon having slightly lower conductivity, and the crystallinity may be sequentially increased, and the uppermost portion and its vicinity may be made of crystalline graphite carbon. At this time, the X-ray diffraction pattern of the lowermost portion of the carbon conductive film was 30 to 50 at 2θ.
The half width of the peak observed at ° is preferably 5.84 ° or less. That is, the corrosion resistance is secured by amorphous or quasi-amorphous hard carbon, and the contact resistance with the electrode can be reduced by using crystalline graphite carbon at the top.

Such a conductive film can be formed by adjusting film forming conditions for a gas phase reaction such as plasma CVD.

(C) Porosity The great effect can be obtained also by continuously changing the porosity of the conductive film from the contact interface with the metal base material to the contact interface with the electrode or the current collector. That is, when the thickness of the conductive film is increased to avoid the influence of the film defect, peeling or cracking of the film is likely to occur due to film distortion, but the conductive film has a dense structure in the vicinity of the metal plate and is sequentially made porous. Thus, film distortion can be suppressed without causing an interlayer interface in the film.

If the porosity of the conductive film at the contact interface with the metal base material is set to 5% or less and the porosity of the conductive film at the contact interface with the electrode or current collector is set to 20% or more, the distortion of the film is reduced. This is preferable because it can greatly reduce the occurrence of film peeling and cracks.

Such a conductive film can be formed by adjusting film forming conditions such as sputtering.

[3] Reactive Gas Vent Groove As shown in FIG. 1, the fuel cell separator 5 of the present invention has reactive gas vent grooves 8 and 9. Usually, a fuel gas is supplied to a passage formed by the reaction gas ventilation groove 9 and the anode 3, and an oxidizing gas is supplied to a passage formed by the reaction gas ventilation groove 8 and the cathode 4. The reactive gas ventilation groove 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 the figure, it is not particularly limited as long as the reaction gas passage can be formed in a 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 Usually, the depth of each reaction gas ventilation groove is preferably 0.2 to 2 mm, and the width is preferably 0.5 to 5 mm.

As shown in FIG. 1, in order to improve the corrosion resistance and oxidation resistance of the separator, it is preferable to form a ventilation groove protective film 6 on the surface of the reactive gas ventilation grooves 8 and 9.
Forming the lowermost part of the conductive film on the entire surface of the separator,
It may be a ventilation groove protective film. The ventilation groove protective film can be formed by oxidizing a metal base material or laminating a corrosion resistant substance by a wet plating method, a thermal spraying method, a sputtering method, an ion plating method, a CVD method, or the like. The thickness of the ventilation groove protective film is 0.5 to 20
It is preferably set to μm.

When a metal plate made of aluminum or an aluminum alloy is used as the metal base material, it is preferable to form a chemically and physically stable alumite film as a ventilation groove protective film on the surface of the above-mentioned reaction gas ventilation groove. . The alumite film can be formed by an anodization method or the like. For example, the γ-alumina film may be formed on the surface of the base material by electrolysis using an aqueous solution of oxalic acid, sulfuric acid, chromic acid or the like as an electrolytic solution.

[0038]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited thereto.

Example 1 Each separator base material shown in Table 1 (1 mm × 150 mm × 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. Next, this is degreased and washed, and after passing through steps such as pre-treatment, the weight ratio of Au / Ni is adjusted to 0/100 (bottom) by performing electroplating while adjusting the electrolysis voltage and the duty ratio of the electrolysis pulse. From 100 to 0/0 (uppermost) to form a gradient composition coating of Au-Ni, thereby producing a separator of the present invention. The thickness of the Au-Ni gradient composition coating is about 5
μm. In this example, an Au—Ni gradient composition coating was similarly formed on the inner surface of the gas vent groove of the separator.

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 (registered trademark) particles (average particle size: 0.2 μm) were further added to a water repellent. To prepare a paste for an electrode. This electrode paste is mixed with a proton-conductive polymer solid electrolyte membrane (Na
fion) and dried. This was sandwiched between carbon cloths, and further sandwiched between the two separators, to produce fuel cells (unit cells) 1a and 1b each containing the separator of the present invention. The tightening pressure of the separator was 10 kg / cm ² .

In place of the Au-Ni gradient composition coating, the weight ratio A
u / Ni is 0/100, 25/75, 50/50, 75/25, 100/0 A
Fuel cells 1a 'and 1b' for comparison were produced in the same manner as the above fuel cells 1a and 1b, except that an Au-Ni laminated film in which u-Ni layers were sequentially laminated from the base material side was formed. In addition, a comparative fuel cell 1 using a conventional graphite separator (without conductive coating)
c ′ was similarly prepared.

With respect to the obtained fuel cell, a simulated fuel gas (70% H ₂ , 15%
CO ₂ , 15% H ₂ O) was supplied, and air was supplied as an oxidant to the cathode side ventilation groove to evaluate the power generation performance stability. In this example, the fuel cell was driven in a cycle of stopping for one hour after operating for two hours, and the evaluation was performed for about 25 days. Table 1 also shows the separator base material, the type of conductive film, the initial power generation voltage, the power generation voltage after 25 days of operation, and the corrosion resistance of the separator electrode contact surface after 25 days of operation for each fuel cell.

[0043]

[Table 1]

From Table 1, it can be seen that the separator (fuel cells 1a 'and 1b') having a conductive film in which layers having different compositions were laminated showed corrosion and peeling of the film, whereas the composition of the conductive film The separator of the present invention in which is continuously changed shows good corrosion resistance, and the fuel cells 1a and 1b using the separator
It can be seen that has excellent power generation performance equivalent to that of the fuel cell 1c 'using the conventional graphite separator.

Example 2 An aluminum metal plate having a purity of 99.6% (1 mm × 150 mm × 150 m
m), a reaction gas ventilation groove having a depth of 1.0 mm and a width of 3.0 mm was formed by press working. This was anodized in an oxalic acid aqueous solution, then immersed in boiling water for 30 minutes, and dried to form a 12 μm-thick alumite film as a ventilation groove protective film on the surface of the base material. Next, in order to improve the flatness of the electrode contact surface of the separator, the electrode contact surface was lapped and polished and washed. By this step, the insulating alumite film formed on the electrode contact surface was removed. Subsequently, the conductive films shown in Table 2 were formed only on the electrode contact surfaces by the same method as in the case of the separators used in the fuel cells 1a and 1b, and the separators of the present invention were produced. However, when using carbide, oxide or carbon, RF using target
A conductive film was formed by a sputtering method. In addition,
In Table 2, for example, when "lower part: Ni, uppermost part: Au" is indicated, the composition of the portion of the conductive film in contact with the aluminum base material is Ni, and the composition ratio of Ni is continuous as approaching the electrode contact interface. At the same time, the Au composition ratio continuously increases, and the composition of the coating in the portion in contact with the electrode is Au. Using the obtained separator of the present invention, fuel cells 2a to 2p were produced in the same manner as in Example 1 above.

The stability of the power generation performance of the obtained fuel cells 2a to 2p was evaluated in the same manner as in Example 1. However, the evaluation was performed for 14 days. The composition at the bottom of each fuel cell, the composition at the top,
Table 2 also shows the initial generated voltage, the generated voltage after 14 days of operation, and the corrosion resistance of the separator after 14 days of operation.

[0047]

[Table 2]

From Table 2, it can be seen that the separator of the present invention shows excellent corrosion resistance even when an aluminum metal plate is used as the base material of the separator, and that the fuel cell using the separator has high power generation performance.

Example 3 Table 3 shows the Al content at the lowermost part and the Al content at the uppermost part.
Fuel cells 3a to 3p each including the separator of the present invention were produced in the same manner as in Example 2 except that a conductive film made of Al-Au having an Au content was formed. However, Al
The -Au conductive film was formed by dual simultaneous RF sputtering of an Al target and an Au target. At this time, by changing the deposition power and T / S distance of each target,
The composition was controlled so as to change continuously. Pure argon gas was used as a sputtering gas. The composition of the formed conductive film was determined by dissolving the film simultaneously formed on another substrate and performing plasma emission spectroscopy.

The stability of the power generation performance of the obtained fuel cells 3a to 3p was evaluated in the same manner as in Example 1. However, the evaluation was performed for 15 days. Table 3 shows the Al content at the bottom of the conductive coating, the Au content at the top, the initial voltage, the voltage generated after 15 days of operation, and the corrosion resistance of the separator after 15 days of operation for each fuel cell. Shown.

[0051]

[Table 3]

According to Table 3, in the separator of the present invention using an aluminum metal plate as the base material, the Al content at the lowermost portion of the conductive film is preferably at least 16.81% by weight, more preferably at least 28.90% by weight. It can be seen that good adhesion can be obtained. The Au content at the top was 29.4
When the content is 8% by weight or more, good power generation performance stability can be obtained, and it is understood that it is very preferable.

Example 4 A Pt-Ir (30% by weight) conductive film having the porosity shown in Table 4 was formed in the same manner as in Example 2 except that the conductive film was formed by the RF sputtering method as in Example 3. Fuel cells 4a to 4d including the separator of the present invention and a fuel cell 4a 'for comparison were produced, respectively. However, for example, in Table 4, "0-45%"
(Fuel cell 4a), the lowermost part of the Pt-Ir conductive film is made to have a porosity of 0%, and the porosity is continuously changed by adjusting the sputtering gas pressure and the temperature.
It represents 45%. In the separator used for the fuel cell 4a 'for comparison, the porosity of the lowermost part of the Pt-Ir conductive coating was set to 23.
%.

The power generation performance stability of the obtained fuel cells 4a to 4d and 4a 'was evaluated in the same manner as in Example 1. However, the evaluation was performed for 14 days. Table 4 shows the composition of the conductive coating formed on the separator of each fuel cell, the porosity of the conductive coating, the initial power generation voltage, the power generation voltage after 14 days of operation, and the corrosion resistance of the separator after 14 days of operation. Show.

[0055]

[Table 4]

From Table 4, it can be seen that the separator of the present invention in which the porosity of the conductive coating was continuously changed exhibited excellent corrosion resistance.
It can be seen that the fuel cells 4a to 4d using the separator have high power generation performance.

Example 5 A fuel cell 5a including the separator of the present invention and a comparative fuel cell 5a were formed in the same manner as in Example 2 except that a carbon film having a crystal structure shown in Table 5 was formed as the conductive film. 'And 5b' were prepared respectively. However, the carbon film was formed using a plasma CVD apparatus and using CH ₄ as a carbon source. In the separator of the present invention used for the fuel cell 4a, the lowermost portion of the conductive film has a poorer conductivity but has a dense and hard quasi-amorphous structure, and its crystal structure is continuously changed. The upper part was a highly conductive crystalline graphite carbon film.

The stability of the power generation performance of the obtained fuel cells 5a, 5a 'and 5b' was evaluated in the same manner as in Example 1. However, the evaluation was performed for 25 days. For each fuel cell, the crystal structure of the carbon conductive coating, the initial power generation voltage, the power generation voltage after 25 days of operation,
Table 5 also shows the electrode contact surface corrosion resistance of the separator after 25 days of operation.

[0059]

[Table 5]

From Table 5, it can be seen that in the fuel cell 5a 'including the separator on which the dense amorphous carbon film was formed, the power generation performance was deteriorated due to the low conductivity of the carbon film. The formed separator (fuel cell 5b ') has a low film strength and low density, which causes corrosion of the base material, whereas the crystalline structure of the carbon conductive coating changes from a quasi-amorphous structure to a crystalline structure The thus-formed separator of the present invention exhibits excellent corrosion resistance, and it can be seen that the fuel cell 5a using the separator has high power generation performance.

FIG. 3 shows the X-ray diffraction patterns of the amorphous carbon film and the graphite crystal (Graphite) film obtained in this example. The diffraction peak of the amorphous carbon film (around 40 ° at 2θ) is much broader than the diffraction peak of the (003) plane of the graphite crystal structure carbon film seen around 26 to 27 ° at 2θ. Therefore, since a carbon film having low crystallinity has low electron conductivity, it is necessary that the carbon film has appropriate crystallinity (that is, has appropriate electron conductivity) in order to be used as a conductive film. In the separator of the present invention used in the above fuel cell 5a, a hard carbon film having an appropriate electron conductivity is formed at the lowermost portion, and as the uppermost portion is approached, the contact resistance with the electrode is continuously reduced to an extremely small graphite crystal structure film. In this case, good corrosion resistance and reduction of electrode contact resistance can both be achieved.

Example 6 The same as the fuel cell 5a except that the crystal structure at the bottom of the conductive film was changed by adjusting the plasma film forming conditions, and a carbon conductive film having a film thickness of about 6 μm was formed. Then, fuel cells 6a to 6f each including the separator of the present invention were produced. Here, the crystallinity of the lowermost part of the conductive film of the separator used in each fuel cell was evaluated by the half width of the diffraction peak obtained by powder X-ray diffraction (Cu-kα) shown in Table 6.

The stability of power generation performance of the obtained fuel cells 6a to 6f was evaluated in the same manner as in Example 1 above. However, the evaluation was performed for 25 days. Table 6 shows the half width of the powder X-ray diffraction peak at the bottom of the conductive film, the initial power generation voltage, the power generation voltage after 25 days of operation, and the electrode contact surface corrosion resistance of the separator after 25 days of operation for each fuel cell. Are shown together.

[0064]

[Table 6]

As shown in Table 6, when a carbon conductive film having a continuously changing crystal structure is formed, the half value width of the powder X-ray diffraction peak at the bottom of the conductive film is 5.84 ° or less. It is understood that the angle is preferably 5.25 ° or less.

[0066]

As described above in detail, the fuel cell separator of the present invention uses a metal plate as a base material, and therefore is much lighter than conventional graphite separators, has high mass productivity, and can reduce processing costs. . In addition, in the present invention, on the contact surface with the electrode or the current collector, the conductive or conductive structure whose structure or function continuously changes from the contact interface with the metal base material to the contact interface with the electrode or the current collector By forming the functional coating, a separator having excellent corrosion resistance at low cost can be obtained. The fuel cell using the separator of the present invention has high power generation performance stability.

[Brief description of the drawings]

FIG. 1 is a partial schematic view showing an example of a fuel cell including a fuel cell separator according to one 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 a conductive film thereof.

FIG. 3 is a schematic diagram showing an example of an X-ray diffraction pattern of a carbon film that can be used as a conductive film of the separator of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Single cell 2 ... Solid electrolyte 3 ... Anode 4 ... Cathode 5 ... Separator 6 ... Ventilation groove protective film 7 ... Conductive film 7a ... Lowermost 7b, 7c, 7d, 7e: middle part 7f: top part 8, 9: reaction gas vent groove

Claims (12)

[Claims] 1. A fuel cell separator comprising a metal base material and having a contact surface with an electrode or a current collector and a reactive gas ventilation groove, wherein a metal, an oxide, a nitride,
A conductive film containing carbide or carbon as a main component is formed, and the structure or function of the conductive film is continuously between a contact interface with the metal base material and a contact interface with an electrode or a current collector. A fuel cell separator characterized by a change. 2. The fuel cell separator according to claim 1, wherein a composition of the conductive film continuously changes from a contact interface with the metal base material to a contact interface with the electrode or the current collector. A fuel cell separator, comprising: 3. The fuel cell separator according to claim 2, wherein a composition of the conductive film at a contact interface with the metal base material includes at least 20% by weight of a constituent element of the metal base material. Fuel cell separator. 4. The fuel cell separator according to claim 2, wherein the composition of the conductive film at the contact interface with the electrode or the current collector is Au, Pt, Pd, Ir, or Rh.
A separator for a fuel cell, characterized in that the separator contains not less than% by weight. 5. The fuel cell separator according to claim 1, wherein the crystal structure of the conductive coating is continuously between a contact interface with the metal base material and a contact interface with the electrode or the current collector. A fuel cell separator characterized by a change. 6. The fuel cell separator according to claim 5, wherein a crystal structure of the conductive film at a contact interface with the metal base material is an amorphous structure or a quasi-amorphous structure, and A fuel cell separator, wherein the crystal structure of the conductive coating at the contact interface with the current collector is a crystalline structure. 7. The fuel cell separator according to claim 6, wherein the conductive coating contains carbon as a main component. 8. The fuel cell separator according to claim 7, wherein the X-ray diffraction pattern of the conductive coating at the contact interface with the metal base material has a half value of a peak observed at 30 to 50 ° in 2θ. A fuel cell separator having a width of 5.84 ° or less. 9. The fuel cell separator according to claim 1, wherein the porosity of the conductive coating is continuously between a contact interface with the metal base material and a contact interface with the electrode or the current collector. A fuel cell separator characterized by a change. 10. The fuel cell separator according to claim 9, wherein a porosity of the conductive coating at a contact interface with the metal base material is 5% or less, and a contact interface with the electrode or the current collector. Wherein the porosity of the conductive coating is 20% or more. 11. The fuel cell separator according to claim 1, wherein the conductive coating has a thickness of 0.5.
A separator for a fuel cell, wherein the thickness is up to 30 μm. 12. The fuel cell separator according to claim 1, wherein the metal base material is a metal plate made of aluminum or an aluminum alloy, and an alumite film is formed on a surface of the reaction gas ventilation groove. A fuel cell separator characterized by being formed.