JP5753830B2 - Fuel cell separator and manufacturing method thereof - Google Patents

Description

  The present invention relates to a titanium-based fuel cell separator used in fuel cells and a method for producing the same.

  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 solid polymer electrolyte membrane is sandwiched between an anode electrode and a cathode electrode, and has a groove serving as a flow path for gas (hydrogen, oxygen, etc.). A plurality of the single cells are overlapped through a formed separator (also called a bipolar plate).

  Since the separator is also a component for extracting the current generated in the fuel cell to the outside, a material with low contact resistance (which means that a voltage drop occurs due to an interface phenomenon between the electrode and the separator surface) is applied. Is done. In addition, the separator is required to have high corrosion resistance because the inside of the fuel cell is in an acidic atmosphere having a pH of about 2 to 4, and also has a characteristic that the low contact resistance is maintained for a long time during use in this acidic atmosphere. Is done. Therefore, conventionally, a carbon separator produced by a method such as cutting out a molded product of graphite powder or forming a molded product of graphite and resin has been applied. However, such a carbon separator is inferior in strength and toughness and may be destroyed when vibration or impact is applied to the fuel cell. Then, the separator using metal materials, such as aluminum, titanium, nickel excellent in workability and intensity | strength, the alloy based on them, or stainless steel, is examined.

  When aluminum, stainless steel, or the like is applied to the separator, it corrodes in an acidic atmosphere inside the fuel cell and metal ions are eluted, so that the solid polymer electrolyte membrane and the catalyst are deteriorated at an early stage. On the other hand, a metal having good corrosion resistance such as titanium forms a passive film having low conductivity in a corrosive environment, so that the contact resistance is deteriorated (increased). For these reasons, separators have been developed in which a metal material is used as a base material and the surface thereof is coated with a conductive film that can be maintained for a long period of time to provide corrosion resistance and conductivity.

  Examples of the coating material having conductivity and corrosion resistance include noble metals or noble metal alloys such as Au and Pt. However, if the separator is coated with such a noble metal material, the cost increases. Therefore, a technique of a separator in which a carbon material is applied as an inexpensive material having conductivity and corrosion resistance and a film containing the carbon material is provided on the surface of a metal substrate is disclosed. For example, the separators disclosed in Patent Document 1 and Patent Document 2 are based on an austenitic or austenitic ferrite two-phase stainless steel to which Cr, Ni, which has high acid resistance among stainless steels, is added. Carbon particles are dispersed and adhered, and Patent Document 1 is brought into close contact with the substrate by pressure bonding and Patent Document 2 is heat-treated.

  However, since these separators have carbon particles adhering in an island shape, the base material is partially exposed, and even when a stainless steel base material with high acid resistance is used in a fuel cell, There is a risk of elution of iron ions. Therefore, by applying titanium having excellent corrosion resistance to the base material, a separator that does not cause corrosion of the base material has been developed regardless of the environmental shielding property (barrier property) of the conductive film on the surface.

  The separator disclosed in Patent Document 3 increases the conductivity by forming a carbon film covering the surface at a high temperature by a chemical vapor deposition (CVD) method or a sputtering method and making it amorphous. Therefore, the separator has a low contact resistance. Further, the separator disclosed in Patent Document 4 leaves an oxide film of a metal base for improving corrosion resistance, and in order to provide adhesion between the oxide film and a conductive thin film made of carbon covering the surface, Ti , Zr, Hf, Nb, Ta, Cr, etc., and an intermediate layer made of a metal element such as Si or a semi-metal element such as Si, and further compounded from the metal element to carbon at the interface from the intermediate layer to the conductive thin film The ratio is changing. In the separator disclosed in Patent Document 5, a diamond-like carbon layer is formed on the surface of a metal base material in order to impart corrosion resistance, and a conductive part in which graphite particles are dispersed and adhered is formed on an arc ion plate. It is formed by a Ting (AIP) apparatus.

  However, since the separators described in Patent Documents 3 to 5 include an amorphous carbon film formed by a CVD method or a sputtering method, the barrier property is insufficient, and the base material is a passive film. Although it does not corrode, the conductivity deteriorates, and the adhesion between the carbon film and its base (metal substrate or intermediate layer) is insufficient. Further, according to the CVD method or the like, the processing time is required to form the carbon film with a sufficient film thickness, so that the productivity is inferior.

  Therefore, the present inventors have developed a separator in which an intermediate layer having titanium carbide is formed between the substrate and the carbon layer by heat treatment after forming the carbon layer on the titanium substrate (patent) Reference 6). In this way, by forming the intermediate layer by reacting the base material titanium and the carbon layer carbon, the carbon layer and the base material are excellent in adhesion, and the conductive titanium carbide is used as a low-resistance separator. Become.

Japanese Patent No. 3904690 Japanese Patent No. 3904696 JP 2007-207718 A Japanese Patent No. 4147925 JP 2008-204876 A Japanese Patent No. 4886885

Here, among the separators, the separator disposed on the hydrogen electrode (fuel electrode, negative electrode) side of the fuel cell in particular is exposed to a high-temperature hydrogen gas (H ₂ ) atmosphere, so the metal applied to such a separator. There is a problem that the material absorbs hydrogen and the mechanical properties deteriorate (brittle). In particular, titanium and titanium alloys are relatively easy to absorb hydrogen, and a problem that mechanical properties deteriorate (brittle) tends to occur.
However, the separators described in Patent Documents 1 to 6 have insufficient shielding properties against hydrogen regardless of whether the carbon film is amorphous or graphite, and the intermediate layer of the separator described in Patent Document 6 is also included. There was room for improvement in shielding properties against hydrogen.

  The present invention has been made in view of the above problems, and a low-cost carbon layer is formed with good adhesion on a lightweight titanium substrate having excellent corrosion resistance. In addition to maintaining conductivity, hydrogen resistance It is an object of the present invention to provide a fuel cell separator that can be used as a separator disposed on the hydrogen electrode side of a fuel cell due to its excellent absorbability and a method for manufacturing the same.

  As a result of earnest research on the intermediate layer formed between the titanium base material and the carbon layer in the same manner as in Patent Document 6, the present inventors focused on the point that the titanium oxide has hydrogen absorption resistance. The inventors have conceived that the intermediate layer has a two-layer structure of a titanium carbide-containing layer and a titanium oxide layer, and have found an intermediate layer structure that achieves both maintenance of conductivity and improvement of hydrogen absorption resistance.

That is, the fuel cell separator according to the present invention includes a base material made of titanium or a titanium alloy, and a conductive carbon layer covering the surface of the base material, and an interface between the base material and the carbon layer. A fuel cell separator in which an intermediate layer is formed, wherein the intermediate layer has a two-layer structure, the carbon layer side is a titanium oxide layer, and the base material side is a layer containing titanium carbide, In the portion where the intermediate layer is formed on the substrate, the thickness of the titanium oxide layer is 1 to 40 nm and is 50% or less of the total thickness of the intermediate layer. To do.
In the fuel cell separator according to the present invention, the carbon layer is preferably graphite.

In this way, the intermediate layer containing titanium carbide composed of both the base material and the carbon layer is formed between the base material and the carbon layer, so that the base material and the carbon layer are firmly bonded. Thus, adhesion between the substrate and the carbon layer and barrier properties to the substrate are obtained. Furthermore, since the intermediate layer has a two-layer structure of a titanium oxide layer and a layer containing titanium carbide, the hydrogen absorption resistance can be improved in addition to maintaining the conductivity, and the base material is hydrogen-brittle. It becomes a fuel cell separator that is difficult to be converted and has excellent durability.
Further, since the carbon layer is crystalline graphite, the conductivity is further improved, and the fuel cell separator can be maintained for a long time even in the internal environment of the fuel cell.

  The method for producing a fuel cell separator according to the present invention is a method for producing the fuel cell separator, comprising: forming the carbon layer on the substrate; and deoxidizing the substrate on which the carbon layer is formed. A step of heat-treating at a temperature of 300 to 850 ° C. in an atmosphere; and a step of heat-treating the base material heat-treated in the non-oxidizing atmosphere at a temperature of 200 to 550 ° C. in an oxidizing atmosphere. .

  In this way, a fuel cell separator having an intermediate layer having a predetermined structure can be manufactured by subjecting the base material on which the carbon layer is formed to heat treatment under two kinds of conditions.

According to the fuel cell separator of the present invention, a low-cost carbon layer is formed with good adhesion on a lightweight titanium substrate having excellent corrosion resistance, and in addition to maintaining conductivity, it also has excellent hydrogen absorption resistance. . As a result, the fuel cell separator according to the present invention can be used as a separator disposed on the hydrogen electrode side of fuel electricity.
Further, according to the method for manufacturing a fuel cell separator according to the present invention, a fuel cell separator including an intermediate layer having a predetermined structure can be manufactured. As a result, the fuel cell separator manufactured by the manufacturing method is excellent in hydrogen absorption resistance in addition to maintaining conductivity, and can be used as a separator disposed on the hydrogen electrode side of fuel electricity.

It is a schematic diagram explaining the laminated structure of the fuel cell separator which concerns on one Embodiment of this invention, Comprising: It is an expanded sectional view. It is a schematic diagram explaining the measuring method of contact resistance. It is a TEM observation image of the intermediate | middle layer of a fuel cell separator, (a) is test body No.2. No. 1 TEM observation image, (b) is the specimen No. 4 is a TEM observation image of No. 4; It is a flowchart for demonstrating the process of the manufacturing method of the fuel cell separator which concerns on one Embodiment of this invention.

[Fuel cell separator]
The fuel cell separator according to the present invention will be described in detail with reference to FIG.
A fuel cell separator 10 according to an embodiment of the present invention is a plate-like separator used for a general fuel cell (solid polymer fuel cell), and has a groove serving as a flow path for hydrogen, oxygen, or the like. (Not shown).
Here, the fuel cell separator 10 includes a fuel cell separator material (plate material) before the grooves are formed, and a fuel cell separator after the grooves are formed.

As shown in FIG. 1, the fuel cell separator 10 includes a base material 1 made of titanium (pure titanium) or a titanium alloy, a carbon layer 2 provided on the surface of the fuel cell separator 10, and a base material 1 and a carbon layer 2. And an intermediate layer 3 formed therebetween. In the intermediate layer 3, the carbon layer 2 side is a titanium oxide layer 32 (hereinafter, appropriately referred to as a titanium oxide layer), and the base material 1 side is a layer 31 containing titanium carbide (hereinafter, appropriately referred to as a titanium carbide layer). ). Here, the surface of the fuel cell separator 10 may be a surface on one side or surfaces on both sides, and when used in a fuel cell, it is exposed to the atmosphere inside the fuel cell. It may be a region (including an end face).
Hereafter, each element which comprises a fuel cell separator is demonstrated in detail.

(Base material)
The base material 1 is a base material of the fuel cell separator 10, and the shape is not particularly limited, and is, for example, a plate shape. The base material 1 is particularly suitable for thinning and reducing the weight of the fuel cell separator 10, and when the fuel cell separator 10 is used for a fuel cell, it is sufficient for the acidic atmosphere inside the fuel cell. It is made of acid-resistant titanium (pure titanium) or a titanium alloy. For example, one to four kinds of pure titanium specified in JIS H 4600 and titanium alloys such as Ti-Al, Ti-Ta, Ti-6Al-4V, and Ti-Pd can be applied. Titanium is preferred. 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 that can be applied in the present invention is not limited to these, and has any composition equivalent to the above-mentioned pure titanium or titanium alloy containing other metal elements. Can be suitably 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 the base material 1 is not particularly limited, the base material 1 of the fuel cell separator 10 is preferably 0.05 to 1.0 mm. If the thickness of the base material 1 is in such a range, the fuel cell separator 10 satisfies the requirements for weight reduction and thickness reduction, has strength and handling properties as a plate material, and is formed on the plate material having such a thickness. This is because (rolling) is easy, and after forming the carbon layer 2, processing such as formation of grooves becomes relatively easy.

  As an example of the manufacturing method of the base material 1, the above-described titanium or titanium alloy is cast and hot-rolled by a known method, and if necessary, annealing / pickling treatment is performed between them, and cold rolling is performed. There is a method of rolling to a desired thickness and manufacturing it as a plate (strip) material. In addition, although it is preferable that the base material 1 is annealed after cold rolling, the finish state is not ask | required, For example, it may be pickled after the said annealing, or vacuum heat treatment finishing, bright annealing finishing, etc. Any finish state may be used.

(Carbon layer)
The carbon layer 2 is provided on the surface of the fuel cell separator 10 so as to cover the substrate 1, and imparts conductivity to the fuel cell separator 10 in a corrosive environment. The structure of the carbon layer 2 is not particularly limited as long as it is formed of carbon (C) having corrosion resistance and has conductivity, but has a hexagonal graphite structure. Specifically, a large number of graphene sheets are stacked in layers. It is preferably a hexagonal plate crystal. 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 2 made of graphite can be formed by adhering (coating) a carbon powder such as graphite (graphite) or carbon black formed into a granular or powder form to a substrate (compression bonding) ( This will be described in detail in the fuel cell separator manufacturing method described later). In addition, the carbon layer 2 may have an amorphous (amorphous) structure in which a fine graphite structure and a cubic diamond structure are mixed, such as so-called charcoal.

  The fuel cell separator 10 has a higher conductivity on the entire surface (including both side surfaces and end surfaces) exposed to the atmosphere inside the fuel cell, as the area ratio covered by the carbon layer 2 is higher. Therefore, it is most preferable that the carbon layer 2 covers the entire surface, but the carbon layer 2 may be formed to be 40% or more, and preferably 50% or more. In the fuel cell separator 10 according to the present invention, as described above, since the base material 1 forms a passive film under a corrosive environment, the base material 1 itself has corrosion resistance and hydrogen resistance absorption, so that it is exposed. There is no corrosion or embrittlement. Therefore, the carbon layer 2 does not need to be a completely continuous film, and can be formed by press-bonding the carbon powder formed into a granular or powder form to the substrate 1 as described above. By being formed by such a method, the carbon layer 2 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 2 is not particularly limited, but if it is extremely thin, sufficient conductivity cannot be obtained. Further, such a thin film has a small amount of carbon powder per area at the time of formation, that is, the number of carbon powders, so that the carbon layer 2 becomes a film with many gaps and a sufficient barrier property cannot be obtained. The area that is finely exposed increases, and a passive film is formed in the area, so that the conductivity of the fuel cell separator 10 is further deteriorated. In order for the carbon layer 2 to impart sufficient conductivity to the fuel cell separator 10, it is preferably ² μg / cm ² or more, more preferably 5 μg / cm ² or more in terms of the amount of carbon attached. On the other hand, even if the carbon adhesion amount of the carbon layer 2 exceeds 1 mg / cm ² , the conductivity is not further improved, and it is difficult to press-bond a large amount of carbon powder to form the carbon layer 2, Furthermore, if the carbon layer 2 is made extremely thick, it becomes easy to peel off by a heat treatment or the like described later due to the difference in thermal expansion coefficient with the base material 1, so that the carbon adhesion amount may be 1 mg / cm ² or less. preferable. The thickness of the carbon layer 2 and the amount of carbon attached can be controlled by the amount of carbon powder applied to the substrate 1 in the formation of the carbon layer 2.

(Middle layer)
The intermediate layer 3 is a layer formed by diffusing C and Ti at the interface between the carbon layer 2 and the substrate 1 after forming the carbon layer 2 on the substrate 1. The intermediate layer 3 has a two-layer structure in which the carbon layer 2 side is the titanium oxide layer 32 and the base material 1 side is the titanium carbide layer 31.
In the titanium carbide layer 31 of the intermediate layer 3, at least part of the Ti and C is present as titanium carbide (titanium carbide, TiC). Thus, in the titanium carbide layer 31 of the intermediate layer 3, C of the carbon layer 2 and Ti of the base material react to form titanium carbide, so that the carbon layer 2 and the base material are interposed via the intermediate layer 3. The carbon layer 2 and the base material 1 are electrically connected with low resistance by the intermediate layer 3 that is firmly bonded to 1 and contains titanium carbide.

If the components of the intermediate layer 3 are only Ti and C, sufficient shielding properties against hydrogen cannot be obtained, and the base material 1 (Ti base material) absorbs the infiltrated hydrogen and becomes brittle. Therefore, in order to avoid such a situation, the intermediate layer 3 has a two-layer structure by forming the titanium oxide layer 32 on the carbon layer 2 side of the titanium carbide layer 31. That is, by providing the titanium oxide layer 32 as the intermediate layer 3, the hydrogen adsorption resistance is improved, and the base material 1 is difficult to be hydrogen embrittled.
As the thickness of the titanium oxide layer 32 of the two intermediate layers 3 increases, the conductivity decreases, and sufficient conductivity as the fuel cell separator 10 cannot be obtained. Therefore, the titanium oxide layer 32 has a thickness of 1 to 40 nm and preferably 50% or less of the total thickness of the intermediate layer 3, and has a thickness of 2 to 35 nm and 40% or less of the total thickness of the intermediate layer 3. More preferably, the thickness is 3 to 30 nm, and 30% or less of the total thickness of the intermediate layer 3 is more preferable.
Such an intermediate layer 3 is formed by forming a carbon layer 2 on a substrate 1 and then performing a heat treatment in a non-oxidizing atmosphere and then performing a heat treatment in an oxidizing atmosphere (for example, an air atmosphere) (the fuel described later) This will be described in detail in the battery separator manufacturing method).

As described above, when the carbon layer 2 is formed by pressure bonding the carbon powder to the base material 1, at this point, the carbon layer 2 is only attached by being pressed against the hard base material 1, Adhesiveness with the material 1 is insufficient, and a passive film (oxide film) is formed on the surface of the base material 1, that is, the interface with the carbon layer 2, regardless of the finished state of the base material 1 (with or without pickling). Exists. If heat treatment is performed in a non-oxidizing atmosphere in this state, the thickness of the passive film on the surface of the substrate 1 becomes thin and may eventually disappear. This is because oxygen (O) in the passive film (TiO ₂ ) diffuses inward into the base material (Ti) of the base material 1 or reacts with C in the carbon layer 2 to generate carbon dioxide (CO ₂ ). It is estimated that it is released as When the carbon layer 2 is in contact with the base material (Ti) of the base material 1, C and Ti are diffused and react with each other by heat treatment at the contacted interface, and titanium carbide is generated. . Thus, in the intermediate layer 3 formed by performing the heat treatment in the non-oxidizing atmosphere after the formation of the carbon layer 2, titanium carbide (TiC) is generated in a granular form. As an example, the base layer 1, the carbon layer 2, Are formed in one or a plurality of layers.
Next, when heat treatment is performed in an oxidizing atmosphere (for example, air atmosphere), the carbon layer 2 side of the intermediate layer 3 is slightly oxidized, and the intermediate layer 3 has a two-layer structure of a titanium oxide layer 32 and a titanium carbide layer 31. .

  Two such intermediate layers 3 are formed between the substrate 1 and the carbon layer 2, the thickness of the titanium oxide layer 32 is 1 to 40 nm, and 50% or less of the total thickness of the intermediate layer 3. If it is, low contact resistance is obtained as a laminated body of the base material 1, the intermediate | middle layer 3, and the carbon layer 2. FIG. Furthermore, although the intermediate layer 3 is formed, the base material 1 and the carbon layer 2 are firmly bonded via the intermediate layer 3, and the thickness of the titanium oxide layer 32 in the intermediate layer 3 is When the thickness is 40 nm or less and 50% or less of the total thickness of the intermediate layer 3, the adverse effect on the adhesion between the substrate 1 and the carbon layer 2 is small. As a result, the fuel cell separator 10 is unlikely to peel off the carbon layer 2 when the fuel cell separator 10 is molded or used in a fuel cell. Furthermore, in the fuel cell separator 10, the titanium oxide layer 32 in the intermediate layer 3 acts as a hydrogen intrusion barrier, so that the hydrogen gas atmosphere inside the fuel cell enters and contacts the surface of the substrate 1. Since there is no fear, hydrogen is not absorbed by the base material 1 (base material), and durability is improved.

The intermediate layer 3 is most preferably formed at all (interface) between the substrate 1 and the carbon layer 2, but if formed at 50% or more of the interface, the substrate 1 and the carbon layer 2. Adhesion with is sufficiently obtained. Further, the thickness of the intermediate layer 3 is not particularly limited, but if it is 10 nm or more, the adhesion between the substrate 1 and the carbon layer 2 is sufficiently obtained, which is preferable. On the other hand, even if the thickness of the intermediate layer 3 exceeds 500 nm, the adhesion between the base material 1 and the carbon layer 2 is not further improved, and the heat treatment time becomes longer and the productivity is lowered. Is preferable, and 200 nm or less is more preferable.
The thickness of the intermediate layer 3 can be controlled by the heat treatment temperature and the heat treatment time in the heat treatment step S2 in the non-oxidizing atmosphere described later.
Further, the thickness of the titanium oxide layer 32 and the ratio of the titanium oxide layer 32 to the entire thickness of the intermediate layer 3 are the oxygen partial pressure, the heat treatment temperature, and the heat treatment time in the heat treatment step S3 in the oxidizing atmosphere described later. Can be controlled.

The method for measuring the thickness of the titanium oxide layer 32 of the intermediate layer 3 and the method for calculating the ratio to the thickness of the entire intermediate layer 3 are as follows.
First, the cross section of the fuel cell separator 10 is processed by an ion beam processing apparatus or the like to expose the observation surface. And while observing the interface vicinity of the base material 1 and the carbon layer 2 among this observation surface with a transmission electron microscope (TEM: Transmission Electron Microscope) at a magnification of 750,000 times, for example, energy dispersive X-rays Analysis (EDX: Energy dispersive X-ray spectrometry) and electron diffraction. Then, EDX analysis and electron diffraction analysis are performed on any three points (or three or more points) of each layer to determine whether it is the titanium oxide layer 32 or the titanium carbide layer 31, and TEM observation is performed. The thickness of the titanium oxide layer 32 is measured from the image, and the ratio of the thickness of the titanium oxide layer 32 to the total thickness of the intermediate layer 3 (= thickness of the titanium oxide layer 32 / the total thickness of the intermediate layer 3). × 100) was calculated.
In the first place, the portion where the intermediate layer 3 is not formed on the base material 1 is not subject to the measurement / calculation. That is, the thickness of the titanium oxide layer 32 is specifically the average thickness of the titanium oxide layer 32 in the portion where the intermediate layer 3 is present on the base material 1, and the intermediate thickness of the titanium oxide layer 32. Specifically, the ratio to the thickness of the entire layer 3 is an average ratio of the titanium oxide layer 32 to the entire thickness of the intermediate layer 3 in the portion where the intermediate layer 3 exists on the substrate 1.

[Method for producing fuel cell separator]
Next, an example of the manufacturing method of the fuel cell separator according to the present invention will be described.
As shown in FIG. 4, the fuel cell separator manufacturing method according to the present invention includes a carbon layer forming step S1 for forming a carbon layer, a heat treatment step S2 for heat treatment in a non-oxidizing atmosphere, and a heat treatment for heat treatment in an oxidizing atmosphere. Step S3 is included.

(Substrate manufacturing process)
In the base material 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 the base material 1. 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)
In carbon layer formation process S1, the carbon powder for forming the carbon layer 2 is made to adhere to the surface (one side or both sides) of the base material 1. FIG. The attachment method is not particularly limited, but if carbon powder is directly attached to the substrate, or a slurry in which carbon powder is dispersed in an aqueous solution such as carboxymethyl cellulose or a resin component is applied to the substrate 1. Good. Alternatively, a carbon powder-containing film prepared by kneading carbon powder and a resin is attached to the base material 1, the carbon powder is driven onto the surface of the base material 1 by shot blasting, and supported on the base material 1. And a method in which resin powder is mixed and adhered to the substrate 1 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 2 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 base material 1, and it is also difficult to adhere to the base material 1 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 1 in the press-bonding to the base material 1 by rolling becomes weak, so that it is difficult to adhere to the base material 1.

  In the carbon layer forming step S1, the base material 1 to which the carbon powder is attached is further cold-rolled to cause the carbon powder to be pressure-bonded to the base material 1 (hereinafter, appropriately referred to as rolling pressure bonding). The film-like carbon layer 2 is formed by bonding. Cold rolling at this time can be performed by a rolling mill in the same manner as normal cold rolling when the base material 1 is manufactured. However, since carbon powder has the same effect as a lubricant, Does not need to be lubricated. 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 1 + the carbon layer (adhered 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 joined together to form a film-like carbon layer 2 and adhere to the substrate 1. 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 substrate 1 at the completion of the substrate manufacturing process. However, since warping and undulation occur when the total rolling rate is excessive for the base material 1, the total rolling rate of the base material 1 (the plate thickness change of the base material 1 due to the rolling pressure bonding with respect to the thickness of the base material 1 before the rolling pressure bonding) Rate) is preferably 50% or less.

  Thus, the carbon layer 2 is formed by press-bonding the carbon powder, so that the soft carbon powders are joined together to form an integral film, but the carbon layer 2 is attached to the hard base material 1 by being pressed. Therefore, the adhesion to the substrate 1 is insufficient immediately after the formation of the carbon layer 2. Further, as described above, since the passive film is formed on the surface of the base material 1, that is, the interface with the carbon layer 2, the contact resistance as a whole is high. Therefore, the passive film on the surface of the substrate 1 is eliminated by the following heat treatment, and the intermediate layer 3 is formed between the carbon layer 2 and the intermediate layer 3.

(Heat treatment process: non-oxidizing atmosphere)
In the heat treatment step S2, the base material 1 on which the carbon layer 2 is formed is first subjected to a heat treatment in a non-oxidizing atmosphere, so that the passive film of the base material 1 is thinned and at least a part thereof disappears. The carbon layer 2 is brought into contact with the base material (Ti), and titanium carbide is generated at the contacted interface to form the intermediate layer 3. The heat treatment temperature 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 1 and the carbon layer 2 does not proceed, so that the intermediate layer 3 is not formed. Time can be shortened. However, if the heat treatment temperature is too high, a phase transformation of Ti occurs, and the mechanical properties of the substrate 1 may change. The heat treatment time may be set in the range of 0.5 to 60 minutes according to the heat treatment temperature.
This heat treatment step S2 is preferably performed in the above temperature range in a vacuum or in a non-oxidizing atmosphere such as an Ar gas atmosphere. The non-oxidizing atmosphere in the heat treatment is an atmosphere having a low oxygen partial pressure, for example, a vacuum atmosphere having a degree of vacuum of 10 Pa or less, that is, an oxygen partial pressure of 2 Pa or less, or an inert gas atmosphere having an oxygen concentration of 100 volume ppm or less ( For example, an Ar gas or nitrogen gas atmosphere is preferable. If the oxygen partial pressure is high, the carbon in the carbon layer reacts with oxygen in the atmosphere, resulting in carbon dioxide (causing a combustion reaction), reducing the amount of carbon that improves conductivity and corrosion resistance. Because it will end up. Moreover, since metal powder and the base-material surface will be oxidized simultaneously, there exists a possibility that electroconductivity may fall.

(Heat treatment process: oxidizing atmosphere)
In the heat treatment step S3, an intermediate layer 3 containing titanium carbide is formed at the interface between the base material 1 and the carbon layer 2, and then heat treatment is performed in an oxidizing atmosphere in which oxygen is present. Then, a titanium oxide layer 32 is formed.
The heat treatment temperature at this time is preferably in the range of 200 to 550 ° C. If the heat treatment temperature is too low, the titanium oxide layer 32 is not formed. If the heat treatment temperature is too high, the oxidation proceeds too quickly, and the entire intermediate layer 3 becomes the titanium oxide layer 32, resulting in a decrease in conductivity and the carbon layer. Since 2 is oxidized to carbon dioxide, it is not preferable. The heat treatment time may be appropriately set in accordance with the heat treatment temperature in the range of 5 seconds to 10 minutes.
This second heat treatment step is preferably performed in the above temperature range in an oxidizing atmosphere containing oxygen. The oxidizing atmosphere in the heat treatment is preferably an atmosphere having an oxygen partial pressure of 20 Pa or more (for example, a vacuum atmosphere or an oxygen-containing atmosphere). More simply, the heat treatment may be performed in an air atmosphere.
In the heat treatment in an oxidizing atmosphere, when the oxygen concentration in the atmosphere is high, the heat treatment temperature is adjusted to a low temperature in order to reduce the rate of progress of oxidation, while when the oxygen concentration in the atmosphere is low, the heat treatment temperature is increased. The treatment temperature and time are appropriately adjusted depending on the oxygen concentration.

  Any heat treatment furnace such as an electric furnace or a gas furnace can be used for the heat treatment in the heat treatment steps S2 and S3 as long as the heat treatment can be performed at a desired heat treatment temperature within the above range and the atmosphere can be adjusted. be able to. Moreover, if it is a continuous heat processing furnace, the base material 1 in which the carbon layer 2 was formed can be heat-processed with a coil-shaped strip. On the other hand, when a batch-type heat treatment furnace is used, the heat treatment may be performed after cutting into a length that can be accommodated in the furnace or into a predetermined shape.

(Molding process)
In the forming step, the base material 1 on which the carbon layer 2 and the intermediate layer 3 are further formed is formed into a desired shape by cutting, pressing or the like. In addition, a shaping | molding process can also be performed before a heat treatment process. That is, even before the intermediate layer 3 is formed, it is sufficient that the carbon layer 2 is in close contact with the base material 1 so as not to be peeled off by processing or the like. Moreover, it may replace with rolling crimping | compression-bonding, and carbon powder may be crimped | bonded simultaneously with the press work of the base material 1, and the carbon layer 2 may be formed.

The fuel cell separator according to the present invention is not limited to the manufacturing method described above. For example, the chemical vapor deposition (CVD) method, the sputtering method, or the like is used to form the intermediate layer 3 (titanium carbide layer 31, The titanium oxide layer 32) and the carbon layer 2 may be successively formed in order. The titanium carbide layer 31 can be formed by sputtering using a direct current power source or an RF power source with titanium carbide as a target. The titanium oxide layer 32 can be formed by sputtering using an RF power source with titanium oxide as a target. Subsequently, the atmosphere and applied voltage are switched, and the carbon layer 2 is formed by a plasma CVD method or the like. The carbon layer 2 formed by the CVD method is usually an amorphous film.
In addition, in such a manufacturing method, the heat treatment (heat treatment in a non-oxidizing atmosphere) for forming the intermediate layer 3 is not necessary, so that the substrate 1 is irradiated by ion beam irradiation before the formation of the intermediate layer 3 or the like. Alternatively, the surface may be pickled to remove the passive film on the surface.

  As mentioned above, although the form for implementing this invention was demonstrated about the fuel cell separator which concerns on this invention, the Example which confirmed the effect of this invention is compared with the comparative example which does not satisfy | fill the requirements of this invention below. I will explain. 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]
JIS 1 type as the base material, chemical composition: O: 450 ppm, Fe: 250 ppm, N: 40 ppm, C: 200 ppm, H: 30 ppm, the balance is Ti and unavoidable impurities pure titanium, Casting, hot rolling, and cold rolling were performed to produce a strip having a thickness of 0.1 mm, which was cut into 50 mm × 150 mm and used as a substrate.

As the carbon powder, expanded graphite powder having an average particle size of 7 μm and a purity of 99.9% (manufactured by SEC Carbon Co., SNE-6G) was used, and the graphite powder was added in an amount of 8% by mass in a 0.8% by mass carboxymethylcellulose aqueous solution. A slurry was prepared by dispersing so as to be. Then, the slurry above the 200 [mu] g / cm ² (after drying basis) on both sides of the substrate (cold rolled finish pure titanium material) was applied using a bar coater No. 10 count, then air dried. 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. ) A carbon layer was formed by cold rolling of 1.0%.

The base material on which the carbon layer was formed was heat-treated by being held at 700 ° C. for 2 minutes in a vacuum atmosphere of 6.7 × 10 ⁻³ Pa. Then, after the furnace was cooled until the temperature of the substrate became 100 ° C. or lower, the inside of the furnace was opened to the atmosphere, and the substrate was taken out. Next, the base material subjected to the vacuum heat treatment was heat-treated under various conditions in an air atmosphere to obtain a test material.

(Structure observation between substrate and carbon layer)
A test material for the fuel cell separator was cut out, and the cross section was processed with an ion beam processing apparatus (Hitachi focused ion beam processing observation apparatus, FB-2100) to obtain an observation surface. While observing the vicinity of the interface between the substrate and the carbon layer with a transmission electron microscope (TEM: Transmission Electron Microscope, Hitachi Field Emission Analysis Electron Microscope, HF-2200) at a magnification of 750,000 times, Energy dispersive X-ray analysis (EDX) and electron diffraction were performed.
Specifically, in the cross section of the test material, the layer structure of the intermediate layer existing between these was observed with the region made of titanium alone as the base material and the region made of carbon alone as the carbon layer. And about arbitrary 3 points | pieces of each layer, while performing an EDX analysis and an electron beam diffraction analysis, it is judged whether it is a titanium oxide layer or a titanium carbide layer, and thickness of a titanium oxide layer from a TEM observation image Was measured, and the ratio of the thickness of the titanium oxide layer to the thickness of the entire intermediate layer was calculated.
The titanium oxide layer was measured only for the portion where the intermediate layer was formed.

[Evaluation]
(Evaluation of contact resistance)
The contact resistance of the test material was measured using a contact resistance measuring device 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 DC current power source. The resistance value was calculated by measuring the voltage applied between the carbon cloths with a voltmeter. The obtained resistance values are shown in Table 1 as the initial contact resistance. The electrical conductivity acceptance criterion was a contact resistance of 8 mΩ · cm ² or less.

(Durability evaluation)
By immersing the test material in an aqueous sulfuric acid solution (10 mmol / L) heated to 80 ° C. at a specific liquid volume of 20 ml / cm ² and applying a potential of +0.60 V with respect to the saturated calomel electrode (SCE) for 100 hours. A corrosion resistance test was conducted. For the test material washed and dried after the corrosion resistance test, the contact resistance was measured by the same method as the test material before immersion, and the obtained resistance value is shown in Table 1 as the contact resistance after the durability test. The acceptance criterion for durability was a contact resistance of 15 mΩ · cm ² or less after the corrosion resistance test.

(Evaluation of hydrogen absorption resistance)
The test material is cut into 20 mm × 50 mm, accommodated in a gas phase part of an airtight container filled with water and 0.3 MPa (3 atm) hydrogen gas (H ₂ ), and heated at 150 ° C. A hydrogen gas exposure test was performed by exposing to an atmosphere of pure hydrogen (purity 99.9%) humidified to 1% and exposing in this atmosphere for 500 hours. After the test, the taken-out test material was put into a graphite crucible, and gas was extracted by melting and heating with tin in a gas flow of inert gas (Ar) together with tin. The gas extracted from the test material is passed through a separation column, hydrogen (H ₂ ) is separated from other gases and transported to a thermal conductivity detector, and the change in thermal conductivity due to hydrogen is measured (inert gas melting). - by gas chromatography) to determine the average hydrogen in the test material _{(H 2)} concentration (ppm). Table 1 shows the average H ₂ concentration of the test material. In the titanium material, when the H ₂ concentration exceeds 150 ppm, there is a possibility that the mechanical properties may be deteriorated. Therefore, the pass criterion for hydrogen absorption resistance is set to an average H ₂ concentration of 150 ppm or less.

Table 1 summarizes the heat treatment conditions in the air atmosphere performed after the vacuum heat treatment, the structure of the intermediate layer and the titanium oxide layer, the conductivity and durability evaluation results, and the hydrogen absorption resistance evaluation results.
Specimen No. Although No. 1 had good conductivity and durability (maintenance of conductivity), the hydrogen absorption resistance was rejected because the intermediate layer had no titanium oxide layer.
On the other hand, the specimen No. In No. 8, since the heat treatment temperature in the air atmosphere was high, the thickness of the titanium oxide layer exceeded the specified range of this patent. As a result, it was found that the conductivity and durability (maintenance of conductivity) were poor, which is not preferable as a fuel cell separator material.

In addition, the result of the structure observation (TEM observation) between a base material and carbon layers is shown in FIG. (A) of FIG. 1 is an observed image, and FIG. 4 is an observation image.
As is clear when FIG. 3 (a) and FIG. 4 shows that the titanium oxide layer 32 is formed.

DESCRIPTION OF SYMBOLS 1 Base material 2 Carbon layer 3 Intermediate | middle layer 10 Fuel cell separator (separator)
31 Layer containing titanium carbide (titanium carbide layer)
32 Titanium oxide layer (titanium oxide layer)
S1 Carbon layer formation step S2 Heat treatment step (heat treatment step: non-oxidizing atmosphere)
S3 Heat treatment process (heat treatment process: oxidizing atmosphere)

Claims (3)

A fuel cell separator comprising: a base material made of titanium or a titanium alloy; and a conductive carbon layer covering a surface of the base material, and an intermediate layer formed at an interface between the base material and the carbon layer Because
The intermediate layer has a two-layer structure, the carbon layer side is a layer of titanium oxide, and the base material side is a layer containing titanium carbide,
In the portion where the intermediate layer is formed on the base material, the thickness of the titanium oxide layer is 1 to 40 nm and 50% or less of the total thickness of the intermediate layer. A fuel cell separator.   The fuel cell separator according to claim 1, wherein the carbon layer is graphite. A method of manufacturing a fuel cell separator according to claim 1 or 2,
Forming the carbon layer on the substrate;
Heat-treating the base material on which the carbon layer is formed at a temperature of 300 to 850 ° C. in a non-oxidizing atmosphere;
And a step of heat-treating the substrate heat-treated in the non-oxidizing atmosphere at a temperature of 200 to 550 ° C. in an oxidizing atmosphere.