JP2015069692A - Fuel battery separator, and method for hydrophilic treatment thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for imparting a hydrophilic property to a fuel battery separator having a metal base, and on its surface, a conductive layer of carbon superior in corrosion resistance and conductivity.SOLUTION: A method for a hydrophilic treatment of a fuel battery separator comprises the step of performing a thermal treatment on a fuel battery separator having a graphite-containing conductive layer on its surface at 150-500°C under an atmosphere with an oxygen density of 1% or more. As a result of the thermal treatment like this, oxygen atoms are bound to carbon atoms of part of crystalline graphite, and a hydrophilic property is imparted to the fuel battery separator while keeping the conductivity.

Description

  The present invention relates to a method for imparting hydrophilicity to the surface of a fuel cell separator used in a fuel cell, and more particularly to hydrophilicization of a fuel cell separator having graphite as a conductive material on the surface.

  Unlike primary batteries such as dry batteries and secondary batteries such as lead-acid batteries, fuel cells that can continuously extract power by continuing to supply fuel such as hydrogen and oxidants such as oxygen have high power generation efficiency. Since it is not affected by the size of the system, and it has little noise and vibration, it is expected to be an energy source covering various applications and scales. Specifically, the fuel cell includes a polymer electrolyte fuel cell (PEFC), an alkaline electrolyte fuel cell (AFC), a phosphoric acid fuel cell (PAFC), a molten carbonate fuel cell (MCFC), and a solid oxide. It has been developed as a type fuel cell (SOFC) and biofuel cell. In particular, solid polymer fuel cells are being developed for use in fuel cell vehicles, home cogeneration systems, mobile devices such as mobile phones and personal computers.

  A polymer electrolyte fuel cell (hereinafter referred to as a fuel cell) is a single cell in which a polymer electrolyte membrane is sandwiched between an anode and a cathode, and a groove serving as a gas (hydrogen, oxygen, etc.) channel is formed. A plurality of the single cells are overlapped via a separator (also called a bipolar plate).

  Since the separator is also a part for taking out the current generated in the fuel cell to the outside, a material having a low contact resistance (which means that a voltage drop occurs due to an interface phenomenon between the electrode and the separator surface). Applied. In addition, the separator is required to have high corrosion resistance because the inside of the fuel cell is an acidic atmosphere having a pH of about 2 to 4, and the low contact resistance (conductivity) is maintained for a long time during use in this acidic atmosphere. The characteristic that An example of a material applied to satisfy these requirements is carbon. Specifically, a carbon separator (for example, Patent Documents 1 to 3), such as a graphite powder produced by cutting out a molded product of graphite powder, or a mixture of graphite and resin, titanium, stainless steel, etc. A separator in which carbon particles are attached to a base material made of the above metal material (for example, Patent Documents 4 to 7) or a carbon film is formed by a chemical vapor deposition (CVD) method or the like has been studied.

  Further, in addition to maintaining the conductivity and high corrosion resistance, it is preferable that the separator disposed on the cathode (air electrode) side of the fuel cell has a hydrophilic surface. Specifically, as the fuel cell generates power, water is generated on the cathode (air electrode) side, and if this generated water remains attached to the surface of the separator, the power generation performance deteriorates. As a result, it is preferable to drain the generated water quickly. However, carbon materials generally have water repellency. Therefore, a technique related to a hydrophilic treatment for imparting hydrophilicity to the surface of a separator having a carbon material has been developed.

  Known as hydrophilic treatments for carbon materials are ozone treatment, ultraviolet (UV) treatment, plasma treatment, etc., but these treatments have insufficient sustainability to be applied to fuel cell separators. It is said that it is. Thus, for example, Patent Document 1 discloses a method of manufacturing a separator imparted with hydrophilicity by mixing a carbon powder with a hydrophilic substance such as silicon oxide and molding the carbon powder. Patent Document 2 discloses a method of hydrophilizing a surface by exposing a carbon molded body to a mixed gas atmosphere containing fluorine and oxygen to treat the surface. Patent Document 3 discloses a method of coating the surface of a carbon molded body with a silica thin film.

Japanese Patent Laid-Open No. 10-3931 Japanese Patent No. 4075343 JP 2005-162550 A Japanese Patent No. 3904690 Japanese Patent No. 3904696 Japanese Patent No. 4886885 Japanese Patent No. 5108986

  However, in the method described in Patent Document 1, since the insulating silicon oxide or the like is mixed, the conductivity of the carbon molded body (fuel cell separator) is lowered. Since the method described in Patent Document 2 uses highly reactive fluorine, it can be applied to a fuel cell separator provided with a base material made of a metal material as described in Patent Documents 4 to 7. In addition, processing chambers exposed to fluorine are likely to deteriorate. In the method described in Patent Document 3, the hydrophilicity is easily lost due to peeling of the silica thin film on the surface and does not last for a long period of time. In addition, the polycondensate solution of silicon alkoxide for forming the silica thin film contains acid such as hydrochloric acid. Since the catalyst is added, it cannot be applied to a fuel cell separator provided with a base material made of a metal material, as in Patent Document 2.

  The present invention has been made in view of the above-mentioned problems, and is easier to make thinner than a fuel cell separator having carbon as a conductive material having excellent conductivity and corrosion resistance, particularly a carbon separator. An object of the present invention is to provide a method for imparting hydrophilicity to the surface of a separator including a base material made of a metal material.

  As a result of intensive research, the present inventors have applied crystalline graphite having relatively high conductivity among carbon materials, and by conducting heat treatment in a low temperature region in an oxygen-containing atmosphere such as the atmosphere, the hydrophilicity is maintained while maintaining conductivity. It was found that sex is imparted.

  That is, the method for hydrophilizing a fuel cell separator according to the present invention is characterized in that the surface of the fuel cell separator is provided with a conductive layer containing graphite on the surface and the conductive layer is coated with a metal substrate. The fuel cell separator is subjected to a heat treatment at 150 to 500 ° C. in an atmosphere having an oxygen concentration of 1% or more.

  In this way, hydrophilicity is imparted to graphite, which is inherently water-repellent, while maintaining conductivity by heat treatment at a temperature within a predetermined range. Furthermore, since the temperature of the heat treatment is not too high, and a metal material such as titanium is hardly changed, it can be applied to a fuel cell separator using the metal material as a base material.

  The fuel cell separator according to the present invention has a conductive layer containing graphite on the surface, the conductive layer covers a base material made of metal, and water is dropped on the surface in an environment of 25 ° C. The contact angle is 70 ° or less. Furthermore, in the fuel cell separator according to the present invention, it is preferable that the base material is made of titanium or a titanium alloy, and an intermediate layer containing titanium carbide is formed between the base material and the conductive layer.

  Thus, by providing a base material made of a metal, the thickness is reduced, and by forming a conductive layer with crystalline graphite and covering the surface, the conductivity is maintained for a long time, and the contact angle of water on the surface is further increased. By defining the fuel cell separator, the produced water is easily drained. Furthermore, the base material is made of titanium or a titanium alloy, so that it is made thinner and lighter, and an intermediate layer containing titanium carbide composed of both components of the base material and the conductive layer is formed. Thus, the adhesion between the base material and the conductive layer and the barrier property to the base material are obtained, so that the fuel cell separator is excellent in durability in the internal environment of the fuel cell.

  According to the method for hydrophilizing a fuel cell separator according to the present invention, hydrophilicity can be imparted to the fuel cell separator provided with carbon, which is inherently water repellent, by a simple method, particularly based on a metal material. The present invention can also be applied to a fuel cell separator provided in the material. In addition, the fuel cell separator according to the present invention can be thinned, can maintain a low contact resistance for a long time with a conductive layer containing graphite, and is preferably used on the cathode (air electrode) side of the fuel cell. Can do.

It is a schematic diagram explaining the measuring method of contact resistance. It is a graph which shows the temperature dependence in the hydrophilization process of the water contact angle and contact resistance of the test material of the fuel cell separator which concerns on an Example. It is a graph which shows the oxygen concentration dependence in the hydrophilization of the water contact angle and contact resistance of the test material of the fuel cell separator which concerns on an Example.

Hereinafter, embodiments of the present invention will be described in detail.
The fuel cell separator according to the present invention, and the fuel cell separator having hydrophilicity imparted to the surface by the hydrophilization method of the fuel cell separator according to the present invention are used for general fuel cells (solid polymer fuel cells). Therefore, the separator is a plate-like separator in which grooves serving as flow paths for hydrogen, oxygen, and the like are formed (not shown).

[Fuel cell separator]
The fuel cell separator according to the present invention is obtained by coating a metal base material with a conductive layer containing graphite (hereinafter referred to as a carbon layer), and the surface, that is, the carbon layer has hydrophilicity. The hydrophilic surface of the fuel cell separator refers to a region (including both side surfaces and end surfaces) exposed to the atmosphere inside the fuel cell when used in a fuel cell. Hereinafter, each element which comprises the fuel cell separator which concerns on embodiment of this invention is demonstrated.

(Base material)
The base material is obtained by forming a plate material into the shape of the fuel cell separator as the base material of the fuel cell separator. A metal material such as aluminum, titanium, nickel, an alloy based on them, or stainless steel excellent in workability and strength can be applied to the substrate. In particular, titanium (pure titanium) is suitable for reducing the thickness and weight of the fuel cell separator, and has sufficient acid resistance against the acidic atmosphere inside the fuel cell when the fuel cell separator is used in a fuel cell. ) Or a titanium alloy. This is because, as will be described later, in this embodiment, the carbon layer may not be a completely continuous film, and the portion of the base material surface where there is no carbon layer is exposed to the atmosphere inside the fuel cell. is there. The fuel separator according to this embodiment will be described as a configuration in which the base material is made of titanium or a titanium alloy.

  Examples of titanium and titanium alloys used for the base material include 1 to 4 types of pure titanium specified in JIS H 4600, and Ti alloys such as Ti-Al, Ti-Ta, Ti-6Al-4V, and Ti-Pd. Pure titanium that can be applied and particularly suitable for thinning is preferable. In particular, from the viewpoint of ease of cold rolling of a titanium material (base material) (cold rolling with a total rolling reduction of 35% or more can be performed without intermediate annealing) and subsequent press formability securing, O: 1500 ppm Or less (more preferably 1000 ppm or less), Fe: 1500 ppm or less (more preferably 1000 ppm or less), C: 800 ppm or less, N: 300 ppm or less, H: 130 ppm or less, and the balance consisting of Ti and inevitable impurities is preferable. For example, a JIS type 1 cold rolled sheet can be used. However, the pure titanium or titanium alloy used for the base material is not limited to these, as long as it has a composition equivalent to the above pure titanium or titanium alloy containing other metal elements and the like. Can be preferably used. Hereinafter, in the present specification, titanium and carbon as components and elements are represented as “Ti” and “C”, respectively.

  Although the thickness (plate thickness) of a base material is not specifically limited, As a base material of a fuel cell separator, it is preferable that it is 0.05-1.0 mm. If the thickness of the base material is within such a range, the requirements for weight reduction and thinning of the fuel cell separator are satisfied, the strength and handling properties of the plate material are provided, and the plate material having such a thickness is formed (rolled) ), And after forming the carbon layer, it is relatively easy to process the fuel cell separator.

  As an example of the manufacturing method of the base material, the above-mentioned titanium or titanium alloy is cast and hot-rolled by a known method, and if necessary, annealed / pickled, etc., and cold-rolled as desired. It can be rolled to a thickness of 10 mm to produce a plate (strip) material. The base material is preferably annealed after cold rolling, but the finish state is not limited, for example, it may be pickled after the annealing, vacuum heat treatment finish, bright annealing finish, etc. Any finished state may be used.

(Carbon layer)
The carbon layer covers the base material and is provided on the surface of the fuel cell separator, and imparts conductivity to the fuel cell separator in a corrosive environment. The carbon layer is formed of corrosion-resistant carbon (C), particularly graphite, and the structure thereof is not particularly limited as long as it has conductivity, but has a hexagonal graphite structure. Specifically, the graphene sheet is layered. It is preferable that the hexagonal plate crystals are stacked in large numbers. Crystalline graphite is excellent in conductivity and excellent in durability in the internal environment of the fuel cell in a high temperature and acidic atmosphere, so that the conductivity can be maintained. Such a carbon layer, which is graphite, can be formed by adhering (coating) a carbon powder such as graphite or carbon black formed into a granular or powder form to a substrate (described later). The fuel cell separator manufacturing method will be described in detail). In addition, the carbon layer may have an amorphous (amorphous) structure in which a fine graphite structure and a cubic diamond structure are mixed like so-called charcoal.

  The conductivity of the fuel cell separator increases as the area ratio covered by the carbon layer increases on the entire surface (including both side surfaces and end surfaces) exposed to the atmosphere inside the fuel cell. Therefore, it is most preferable that the carbon layer covers the entire surface, but it may be formed to be 40% or more, and is preferably formed to 50% or more. In the fuel cell separator according to the present embodiment, as described above, the base material is made of titanium or a titanium alloy, and forms a passive film in a corrosive environment. Therefore, even if the base material itself has corrosion resistance, it is exposed. There is no corrosion. Therefore, the carbon layer does not need to be a completely continuous film, and can be formed by press-bonding the carbon powder formed in a granular or powder form to the substrate as described above. By being formed by such a method, the carbon layer is formed to a sufficient thickness with high productivity, and excellent conductivity can be obtained by graphite or carbon black.

The thickness (film thickness) of the carbon layer is not particularly limited, but if it is extremely thin, sufficient conductivity cannot be obtained, and such a thin film has a small amount of carbon powder, that is, the number of carbon powders per area when formed. For this reason, the carbon layer becomes a film with many gaps, and sufficient barrier properties are not obtained, and there are many areas that are finely exposed on the surface of the base material, and a passive film is formed in such areas. The conductivity of the battery separator is further deteriorated. In order for the carbon layer to impart sufficient conductivity to the fuel cell separator, it is preferably ² μg / cm ² or more, more preferably 5 μg / cm ² or more, in terms of the amount of carbon deposited. On the other hand, even if the carbon adhesion amount of the carbon layer exceeds 1 mg / cm ² , the conductivity is not further improved. In addition, it is difficult to form a carbon layer by pressing a large amount of carbon powder, and when the carbon layer is extremely thick, it peels off due to the difference in thermal expansion coefficient with the base material due to the heat treatment described later. Since it becomes easy, it is preferable that the adhesion amount of carbon is 1 mg / cm < ² > or less. The thickness of the carbon layer and the amount of carbon attached can be controlled by the amount of carbon powder applied to the substrate in forming the carbon layer.

  The surface of the fuel cell separator according to the present embodiment, that is, the carbon layer has hydrophilicity at least on the surface. This is because oxygen (O) is maintained while some carbon atoms (C) of the carbon layer maintain bonds with other carbon atoms by the method for hydrophilizing a fuel cell separator according to the present invention described later. It is presumed that this is due to bonding in the form of> C—O—C <,> C═O. The carbon layer (graphite) has little influence on conductivity even when oxygen is bonded in this way, and there is no problem as a conductive material for the fuel cell separator. Furthermore, having hydrophilicity specifically means that the contact angle when water is dropped on the surface of the fuel cell separator in an environment of 25 ° C. is 70 ° or less, preferably the contact angle is It is less than 50 °.

(Middle layer)
As described above, the carbon layer formed of carbon powder is only adhered by being pressed against the base material by being pressed onto the hard base material, and the adhesion with the base material is insufficient. is there. In addition, since a passive film of titanium (titanium dioxide, TiO ₂ ) is formed on the surface of the substrate, that is, the interface with the carbon layer, regardless of the finished state of the substrate (whether or not pickling), the fuel cell separator The conductivity of the is lowered. Therefore, the fuel cell separator according to the present embodiment has a layer (intermediate layer) containing Ti and C at the interface between the carbon layer and the base material. In the intermediate layer, the Ti and C are present as titanium carbide (titanium carbide, TiC) or, further, carbon solid solution titanium. Such an intermediate layer is formed by diffusing C and Ti at the interface by performing a heat treatment in a non-oxidizing atmosphere (low oxygen atmosphere) after forming a carbon layer on the substrate (described later). This will be described in detail in the fuel cell separator manufacturing method).

Here, that the intermediate layer is formed, that is, the presence of titanium carbide at the interface between the base material and the carbon layer means that there is no passive film on the surface of the base material. When heat treatment is performed in a non-oxidizing atmosphere at the time when a carbon layer is formed by press-bonding carbon powder to the substrate, the thickness of the passive film on the surface of the substrate decreases, and finally Can disappear. This is because oxygen (O) in the passive film (TiO ₂ ) diffuses inward into the base material (Ti) of the base material or reacts with C in the carbon layer and is released as carbon dioxide (CO ₂ ). It is presumed that When the carbon layer comes into contact with the base material (Ti) of the base material, C and Ti diffuse and react with each other by heat treatment at the contacted interface, and titanium carbide is generated.

  Therefore, the region where the intermediate layer (titanium carbide) is formed is a region where the passive film of the substrate has disappeared. In such a region, the carbon layer covers the base material (base material) only through the conductive intermediate layer, and the carbon layer and the base material are electrically connected with low resistance. As a result, the fuel cell separator has a low contact resistance as a laminate of the base material, the intermediate layer, and the carbon layer. Furthermore, by forming the intermediate layer, the base material and the carbon layer are firmly bonded via the intermediate layer. As a result, when the fuel cell separator is molded into the fuel cell separator or used in the fuel cell, not only does the carbon layer not peel off, but also no gap is formed between the substrate and the carbon layer. Therefore, the acidic atmosphere inside the fuel cell does not enter and contact the surface of the base material, and an increase in contact resistance due to the formation of a new passive film is suppressed and durability is improved.

  The intermediate layer is most preferably formed at all (interface) between the substrate and the carbon layer. However, if the intermediate layer is formed at 50% or more of the interface, the adhesion between the substrate and the carbon layer is improved. Fully obtained. Further, the thickness of the intermediate layer is not particularly limited, but if it is 10 nm or more, the adhesion between the base material and the carbon layer can be sufficiently obtained, which is preferable. On the other hand, even if the thickness of the intermediate layer exceeds 500 nm, the adhesion between the base material and the carbon layer is not further improved, and the heat treatment time is prolonged and the productivity is lowered. More preferably, it is 200 nm or less.

  As described above, since the fuel cell separator according to the embodiment of the present invention includes a metal material having high strength and excellent workability in the base material, the fuel cell separator can be easily thinned and is inherently water-repellent. However, the surface is provided with hydrophilic graphite while maintaining its electrical conductivity, so even if it is applied to a separator placed on the cathode (air electrode) side of the fuel cell, it generates power generation performance. It is not lowered by.

[Method for producing fuel cell separator]
Next, the method for hydrophilizing the fuel cell separator according to the present invention will be described together with the method for producing the fuel cell separator.

(Substrate manufacturing process)
As described above, a cold-rolled sheet (strip material) having a desired thickness made of titanium or a titanium alloy is manufactured by a known method, wound around a coil, and used as a base material. Further, if necessary, the cold rolled sheet may be annealed or pickled with a mixed solution of hydrofluoric acid and nitric acid.

(Carbon layer formation process)
Carbon powder for forming a carbon layer is attached to the surface (one side or both sides) of the substrate. The attachment method is not particularly limited, but it is only necessary to apply carbon powder directly to the base material, or apply a slurry in which carbon powder is dispersed in an aqueous solution such as carboxymethyl cellulose or a resin component containing a resin component to the base material. . Alternatively, a carbon powder-containing film prepared by kneading carbon powder and resin is affixed to a base material, carbon powder is shot onto the base material surface by shot blasting, and supported on the base material, or carbon powder and resin powder And a method of adhering to a substrate by a cold spray method. Further, when a solvent is used such as when slurry is applied, it is preferable to perform subsequent pressure bonding after drying by blowing or the like.

  The carbon powder for forming the carbon layer preferably has a powder diameter or particle diameter (diameter) in the range of 0.5 to 100 μm. If the particle size is too large, it is difficult to adhere to the substrate, and it is also difficult to adhere even when crimping to the substrate by rolling. On the other hand, if the particle size is too small, the force with which the carbon powder is pressed against the base material in the press-bonding to the base material by rolling becomes weak, so that it is difficult to adhere to the base material.

  The base material to which the carbon powder is adhered is further cold-rolled, so that the carbon powder is pressure-bonded to the base material (hereinafter referred to as rolling pressure bonding), and the carbon powders are joined to form a film-like carbon layer. . Cold rolling at this time can be performed by a rolling mill in the same manner as normal cold rolling at the time of manufacturing a base material, but since carbon powder has the same effect as a lubricant, Lubricating oil does not have to be applied. The total rolling rate in this rolling and pressing (the rate of change due to rolling and pressing with respect to the total thickness of the base material + carbon layer (attached carbon powder) before rolling and pressing) is preferably 0.1% or more. By such rolling and pressure bonding, the soft carbon powder is deformed and the carbon powders are bonded to each other to form a film-like carbon layer and adhere to the substrate. The upper limit of the total rolling rate is not particularly defined, and may be adjusted so as to be a desired thickness with respect to the thickness of the base material at the completion of the base material manufacturing process. However, since the warpage and undulation occur when the total rolling rate is excessive for the base material, the total rolling rate of the base material (the thickness change rate of the base material due to the rolling pressure bonding with respect to the thickness of the base material before the rolling pressure bonding) is 50. % Or less is preferable.

  In this way, the carbon layer is formed by press-bonding carbon powder, so that soft carbon powders are joined together to form an integral film, but are attached to the hard substrate by being pressed. Therefore, immediately after the formation of the carbon layer, the adhesion to the substrate is insufficient. Further, as described above, since a passive film is formed on the surface of the substrate, that is, the interface with the carbon layer, the contact resistance as a whole is high. Therefore, the passive film on the substrate surface is eliminated by the following heat treatment, and an intermediate layer is formed between the carbon layer and the carbon layer.

(Intermediate layer forming process)
By subjecting the substrate on which the carbon layer is formed to a heat treatment in a non-oxidizing atmosphere, the passive film on the substrate is thinned to at least partially disappear, and the carbon layer is formed on the base material (Ti) of the substrate. In addition, titanium carbide is generated at the contact interface and an intermediate layer is formed. The non-oxidizing atmosphere specifically refers to an oxygen partial pressure of 1.3 × 10 ⁻³ Pa or less, preferably in a vacuum or an inert gas such as nitrogen (N ₂ ) or Ar. If the oxygen partial pressure is not sufficiently low, the carbon of the carbon layer is oxidized by heat treatment and dissociated as carbon dioxide (CO ₂ ), and the film thickness of the carbon layer is reduced.

  The heat treatment temperature in the intermediate layer forming step is preferably in the range of 300 to 850 ° C. If the heat treatment temperature is too low, the reaction between Ti and C at the interface between the base material and the carbon layer does not proceed, so the intermediate layer is not formed. If it is lower, the natural oxide film (passive film) of the base material It remains because the reaction between O in the passive film and C in the carbon layer does not proceed. The higher the temperature, the faster the reaction rate, so the heat treatment time can be shortened. The heat treatment time is set in the range of 0.5 to 120 minutes according to the heat treatment temperature. On the other hand, if the heat treatment temperature is too high, a phase transformation of Ti occurs, which may change the mechanical properties of the substrate.

  The heat treatment in the intermediate layer forming step can be performed in any heat treatment furnace, such as an electric furnace or a gas furnace, as long as it can be performed at a desired heat treatment temperature within the above range and the atmosphere can be adjusted. Moreover, if it is a continuous heat processing furnace, it can heat-process with the base material in which the carbon layer was formed still with a coil-shaped strip. On the other hand, when a batch-type heat treatment furnace is used, it is cut into a length that can be accommodated in the furnace, a predetermined shape for forming a fuel cell separator, or further shaped into a fuel cell separator shape ( Heat treatment may be performed after the molding step described later.

(Molding process)
The base material on which the carbon layer and the intermediate layer are formed is formed into a desired shape by cutting, pressing, or the like to obtain a fuel cell separator (before hydrophilization treatment). In addition, a shaping | molding process can also be performed before a heat treatment process. That is, even before the intermediate layer is formed, it may be in close contact with the substrate to such an extent that the carbon layer does not peel off due to processing or the like. Moreover, it may replace with rolling crimping | compression-bonding and may press-bond carbon powder simultaneously with the press processing of a base material, and may form a carbon layer.

(Hydrophilic treatment process)
In the method for hydrophilizing a fuel cell separator according to the present invention, a heat treatment at 150 to 500 ° C. in an atmosphere having an oxygen (O ₂ ) concentration of 1% or more is applied to a fuel cell separator having a carbon layer on the surface of a metal substrate. Apply. Hereinafter, as an embodiment, a hydrophilic treatment method for a fuel cell separator in which a carbon layer and an intermediate layer between the base material and the carbon layer are formed on a base material made of titanium or a titanium alloy by the manufacturing method described above. Will be described in detail.

In the hydrophilic treatment step, heat treatment is performed in an atmosphere containing oxygen (O ₂ ). O ₂ may be mixed with an inert gas such as N ₂ or Ar, or a normal air atmosphere (O ₂ concentration of about 21%) may be used. It is assumed that the fuel cell separator is subjected to heat treatment in such an atmosphere, whereby oxygen (O) is bonded to the carbon layer (graphite) on the surface, and the carbon layer becomes hydrophilic. O The ₂ concentration of less than 1% atmosphere, too slow the progress of hydrophilic carbon layer, it is difficult to productivity to impart sufficient hydrophilicity may decrease, most hydrophilic More O ₂ concentration is lower do not do. Therefore, the O ₂ concentration in the heat treatment atmosphere is 1% or more, preferably 5% or more. On the other hand, the upper limit of the O ₂ concentration is not particularly defined, but even if it exceeds 10%, no further improvement effect of hydrophilization can be obtained. Therefore, the upper limit of the O ₂ concentration should be less than or equal to the atmospheric atmosphere (O ₂ concentration about 21%). Is preferred.

The heat treatment temperature in the hydrophilization treatment step is in the range of 150 to 500 ° C. If the heat treatment temperature is less than 150 ° C., the progress of hydrophilization is too slow, and it becomes difficult to lower the productivity or impart sufficient hydrophilicity. The heat treatment temperature is preferably 200 ° C. or higher, more preferably 230 ° C. or higher, and further preferably 250 ° C. or higher. On the other hand, the higher the heat treatment temperature, the faster the carbon layer becomes hydrophilic. However, the conductivity of the fuel cell separator deteriorates at a certain high temperature. This is because when the temperature is high, the metal on the surface of the base material reacts with oxygen (O), that is, oxidizes, and particularly in the fuel cell separator according to this embodiment, O is introduced into the intermediate layer and further onto the base material surface layer. Thus, it is presumed that the conductivity of the intermediate layer or the like is lowered. In particular, when the heat treatment temperature exceeds 500 ° C., the deterioration of conductivity tends to become remarkable. Further, when the temperature is high, carbon in the carbon layer is oxidized and dissociated as carbon dioxide (CO ₂ ), and the film thickness of the carbon layer is reduced. The heat treatment temperature is preferably 450 ° C. or less, more preferably 400 ° C. or less, and further preferably less than 400 ° C. The heat treatment time is preferably in the range of about 5 seconds to 10 minutes, and is set according to the heat treatment temperature.

  The heat treatment in the hydrophilization treatment step can be performed in any heat treatment furnace such as an electric furnace or a gas furnace as long as the fuel cell separator is accommodated in the furnace and can be performed at a desired heat treatment temperature within the above range. Can be used.

As described above, since the intermediate layer forming step can be performed after the molding step, the intermediate layer forming step and the hydrophilization processing step may be performed successively using, for example, a batch heat treatment furnace capable of adjusting the atmosphere. . Specifically, after the intermediate layer forming step is performed by heat treatment in a non-oxidizing atmosphere, the temperature is lowered while the fuel cell separator is housed in the furnace to be in the range of 150 to 500 ° C., or After performing the heat treatment in the intermediate layer forming step at 500 ° C. or lower, the temperature is kept, and oxygen (O ₂ ) is introduced into the furnace to perform a hydrophilization treatment step with a desired O ₂ concentration.

  The hydrophilic treatment process is performed after the intermediate layer forming process. This is because if high-temperature heat treatment is performed in a non-oxidizing atmosphere after the hydrophilization treatment step, oxygen (O) bonded to the carbon layer may be dissociated and the hydrophilicity may be lost. Further, since the lubricity of the carbon layer tends to decrease when hydrophilicity is imparted, the hydrophilic treatment process is preferably performed after the molding process, although it depends on the molding specifications and processing amount.

  The hydrophilization treatment of the fuel cell separator may be performed not only by the treatment by the hydrophilization treatment method of the fuel cell separator according to the present invention (heat treatment in an oxygen-containing atmosphere) but also by combining other methods. Specific examples include ozone treatment, UV treatment, and plasma treatment. These treatments are preferably performed after heat treatment in an oxygen-containing atmosphere.

  The method for hydrophilizing a fuel cell separator according to the present invention can be applied not only at the time of production of the fuel cell separator but also to a fuel cell separator whose hydrophilicity has deteriorated after being used in the fuel cell, that is, by use.

  The method for hydrophilizing a fuel cell separator according to the present invention is not limited to a fuel cell separator in which a carbon layer (conductive layer) made of graphite is coated on a base material made of a metal material such as titanium, but from a carbon (graphite) molded body. The present invention can also be applied to a fuel cell separator. In the hydrophilization treatment of the carbon molded body, there is no risk of a decrease in conductivity due to the introduction of oxygen (O) into the metal material of the base material. Further, by such heat treatment, not only the surface layer of the fuel cell separator (carbon molded body) but also the inside is hydrophilized, so that the hydrophilicity is maintained for a long time.

  As mentioned above, although the form for implementing this invention was demonstrated about the fuel cell separator which concerns on this invention, and its hydrophilization processing method, the Example which confirmed the effect of this invention below is the requirements of this invention. This will be described in comparison with a comparative example that is not satisfied. In addition, this invention is not limited to this Example and the said form, It cannot be overemphasized that what was variously changed and modified based on these description is also contained in the meaning of this invention.

[Production of test materials]
(Base material production)
As the base material, JIS 1 type, chemical composition: O: 450 ppm, Fe: 250 ppm, N: 40 ppm, C: 200 ppm, H: 30 ppm, the balance being Ti and inevitable impurities pure titanium were applied. This pure titanium is subjected to known melting, casting, hot rolling, and cold rolling to produce a strip with a thickness of 0.1 mm, and further annealed and pickled, cut into a 50 mm × 150 mm base material It was.

(Carbon layer formation)
As the graphite (graphite) powder forming the carbon layer, scaly graphite powder having an average particle size of 10 μm and a purity of 99.9% (manufactured by SEC Carbon Co., SNO-10) was used. This graphite powder was dispersed in a 1.0% by mass carboxymethylcellulose aqueous solution so as to be 12% by mass to prepare a slurry. And this slurry was apply | coated to both surfaces of the said base material each 200 microgram / cm < ² > (converted after drying) using the 15th count bar coater, and was dried in the dryer which set temperature as 100 degreeC. . Then, the base material was roll-pressed with a load of 2.5 tons using a two-stage rolling mill with a work roll diameter of 200 mm and a lubricant was not applied, and the rolling reduction (= total rolling ratio) in one pass. ) 1.0% cold rolling was applied to form carbon layers on both sides of the substrate.

(Intermediate layer formation)
The base material on which the carbon layer is formed is held at 560 ° C. for 2 hours in a vacuum atmosphere (6.7 × 10 ⁻³ Pa) with an oxygen partial pressure of 1.3 × 10 ⁻³ Pa or less using a heat treatment furnace. Heat treatment was performed. After the heat treatment, the substrate was cooled in a vacuum atmosphere until the temperature of the substrate became 100 ° C. or lower, cut into 40 mm × 30 mm, and used as a fuel cell separator test material (before hydrophilization treatment).

(Hydrophilic treatment)
The obtained fuel cell separator test material was subjected to heat treatment in an atmospheric furnace at the temperature shown in Table 1 for the time shown in Table 1, and subjected to heat treatment. It was set to 2-10. Moreover, the test material which does not give heat processing (hydrophilization treatment) was made into the comparative example (test material No. 1).

Also, using a rapid heating furnace capable of adjusting the atmosphere, heat treatment was performed by holding at 350 ° C. for 60 seconds in an atmosphere in which nitrogen (N ₂ ) was mixed with oxygen (O ₂ ) having the concentration shown in Table 2, and then performing the test. Material No. 11-16.

[Evaluation]
(Hydrophilic)
Test material No. About 1-16, in a 25 degreeC environment, test material is mounted horizontally, about 0.5 microliters pure water is dripped on the surface, and a contact angle measuring device (the Kyowa Interface Science company make, CA-A) is used. The contact angle (water contact angle) θ was measured. The acceptance criterion for hydrophilicity was a contact angle θ of 70 ° or less. Contact angle θ and test material No. The difference Δθ with respect to 1 is shown in Tables 1 and 2.

(Conductivity)
Test material No. About 1-16, the contact resistance was measured using the contact resistance measuring apparatus shown in FIG. The test material is sandwiched between two carbon cloths from both sides, and the outside is pressurized to a load of 98 N (10 kgf) with a copper electrode with a contact area of 1 cm ² , and a current of 7.4 mA is applied using a direct current power source. The resistance value was calculated by measuring the voltage applied between the carbon cloths with a voltmeter. The obtained resistance value is shown in Table 1 as contact resistance. The electrical conductivity acceptance criterion was a contact resistance of 5 mΩ · cm ² or less.

Test material No. FIG. 2 shows a graph of temperature dependence in the hydrophilization treatment for water contact angles and contact resistances of 1 to 9. The test material No. For No. 1, the heat treatment temperature was 0 ° C. In addition, test material No. FIG. 3 shows a graph of the O ₂ concentration dependency in the hydrophilization treatment for water contact angles and contact resistances of 11 to 16.

  As shown in Table 1 and FIG. For all of Nos. 2 to 10, the test material No. The hydrophilicity was higher than 1. In particular, until the heat treatment temperature was around 350 to 400 ° C. (test material Nos. 6 and 7), the hydrophilicity increased as the temperature increased. Further, even when the heat treatment temperature exceeds 400 ° C., there is almost no change in hydrophilicity, but the contact resistance starts to gradually increase at 300 ° C. or higher, and the test material No. In No. 9, the conductivity was not acceptable. On the other hand, test material No. No. 2 had a low heat treatment temperature and insufficient hydrophilicity. In addition, the test material No. in which the heat treatment temperature was increased at the lower limit (150 ° C.) of the range of the present invention. 10 is a test material No. 10 having the same heat treatment temperature. Compared with 3, the conductivity did not decrease, but the progress of hydrophilization was slow, and the hydrophilicity was not greatly improved.

As shown in Table 2 and FIG. For all of Nos. 12-16, the test material No. The hydrophilicity was higher than 1 (see Table 1). Particularly O ₂ concentration of 5% to (test material No.14), the hydrophilic accordance O ₂ concentration increases is significantly higher, whereas, little change in hydrophilicity beyond the O ₂ concentration of 5% No test material No. which was heat-treated in the air There was almost no difference from 6 (see Table 1). On the other hand, even with the same temperature and holding time, test material No. 1 subjected to heat treatment only in nitrogen (N ₂ ), ie, in a non-oxidizing atmosphere. 11 is a test material No. With respect to 1, the hydrophilicity hardly changed. In addition, test material No. No. 12 had a low O ₂ concentration and insufficient hydrophilization. The contact resistance slightly increased when the O ₂ concentration was 1% or more, but the dependence on the O ₂ concentration was very small.

  In order to observe the effect only on the conductive layer (graphite), heat treatment in the hydrophilization treatment method according to the present invention was performed on a graphite molded body (G347B, manufactured by Toyo Carbon Co., Ltd.) having a thickness of 5 mm as a test material for a fuel cell separator. Was given. Test material No. 1 of Example 1 In the same manner as in Nos. 2 to 10, heat treatment was carried out in the air at 450 ° C. for 180 seconds. It was set to 17. Test material No. For No. 17, the contact angle and the contact resistance were measured in the same manner as in Example 1 before and after the heat treatment, and are shown in Table 3. In Table 3, Δθ is the difference in contact angle θ before heat treatment.

  As shown in Table 3, the hydrophilicity of the fuel cell separator made entirely of graphite was also increased by the heat treatment. On the other hand, even if the heat treatment of Example 1 was a heat treatment at a relatively high temperature for a long time, there was almost no decrease in conductivity.

Claims (3)

A fuel cell separator hydrophilization method for imparting hydrophilicity to the surface of a fuel cell separator comprising a conductive layer containing graphite on the surface and the conductive layer covering a substrate made of metal,
A method for hydrophilizing a fuel cell separator, comprising subjecting the fuel cell separator to a heat treatment at 150 to 500 ° C. in an atmosphere having an oxygen concentration of 1% or more. A fuel cell separator comprising a conductive layer containing graphite on a surface, the conductive layer covering a base material made of metal,
A fuel cell separator having a contact angle of 70 ° or less when water is dropped on the surface in an environment of 25 ° C. The substrate is made of titanium or a titanium alloy,
The fuel cell separator according to claim 2, wherein an intermediate layer containing titanium carbide is formed between the base material and the conductive layer.

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