JP5564068B2 - Fuel cell separator and manufacturing method thereof - Google Patents

Description

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

  The fuel cell can continuously extract power by continuously supplying a fuel such as hydrogen and an oxidant such as oxygen. Also, unlike primary batteries such as dry batteries and secondary batteries such as lead-acid batteries, fuel cells have high power generation efficiency, are not significantly affected by the size of the system, and are less affected by noise and vibration. It is expected as an energy source to cover

  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 compact fuel cell (SOFC), biofuel cell, etc. In particular, solid polymer fuel cells are being developed for portable devices such as fuel cell vehicles, household fuel cells (household cogeneration systems), mobile phones and personal computers.

  A general polymer electrolyte fuel cell (hereinafter referred to as a fuel cell) is formed by stacking a plurality of single cells. A single cell is a separator (also referred to as a bipolar plate) in which a solid polymer electrolyte membrane is sandwiched between an anode electrode and a cathode electrode, and grooves are formed as gas (hydrogen, oxygen, etc.) flow paths. It is formed between. A single cell is also called a unit cell or a cell, and a stack of a plurality of single cells is called a stack or a cell stack. The PEFC can increase the output by increasing the number of single cells per stack.

The fuel cell separator is also a component for efficiently collecting the generated electricity and taking it out of the fuel cell. Therefore, the material is required to have a characteristic that the contact resistance (initial contact resistance) is low and that it is maintained for a long time during use as a separator (such a characteristic can be evaluated as a contact resistance after an accelerated durability test). . The contact resistance means that a voltage drop occurs due to an interface phenomenon between the electrode and the separator surface.
Furthermore, since the inside of the fuel cell is in an acidic atmosphere, the separator is also required to have high corrosion resistance.

  In order to satisfy these requirements, various separators have been proposed which are formed by cutting a graphite powder molded body or a mixture of graphite and resin mixture. Although these have excellent corrosion resistance, they are inferior in strength and toughness, and therefore may be damaged when subjected to vibration or impact. Therefore, various separators based on metal materials have been proposed and variously proposed.

  Examples of the metal material having both corrosion resistance and conductivity include Au and Pt. Conventionally, a metal material such as an aluminum alloy, stainless steel, nickel alloy, titanium alloy, etc., which can be thinned and has excellent workability and high strength, is coated with a noble metal such as Au or Pt. A separator imparted with corrosion resistance and conductivity has been studied. However, these noble metal materials are very expensive and therefore expensive.

In order to solve such a problem, a metal separator not using a noble metal material and a manufacturing method thereof have been proposed.
For example, in Patent Documents 1 to 3, a resin in which a carbon-based conductive material is dispersed is coated on the surface of a stainless steel substrate by a method such as an electrodeposition method, and cured by heating at a temperature lower than the decomposition temperature of the resin. A metal separator in which a carbon-based conductive layer is coated on the surface of a metal substrate and a manufacturing method thereof have been proposed.

  Specifically, Patent Document 1 includes a protective layer formed by electrodeposition so as to cover a base material, and the protective layer is a carbon-rich layer obtained by carbonizing a resin layer, and carbon. A separator for a fuel cell containing a conductive material such as particles and a method for producing the same are described. In Patent Document 1, it is described that the carbonization treatment is within the range of T + 30 ° C. to 500 ° C. when the 5% mass reduction temperature of the resin layer material is T ° C.

  Patent Document 2 discloses a fuel in which a resin layer is formed by electrodeposition of an electrodeposition liquid in which a conductive material such as carbon particles is dispersed in a resin having electrodeposition properties on a base material and performing a thermosetting treatment. A battery separator and a method for manufacturing the same are described.

  In Patent Document 3, the surface of a substrate is coated with a composition containing a binder resin, carbon particles, and a solvent, and dried at a temperature below the thermal decomposition temperature of the binder resin and above the boiling point of the solvent to form a coating layer. A fuel cell metal separator and its manufacturing method are described.

JP 2008-41269 A JP 2009-199849 A Special table 2011-508376 gazette

  As described above, the fuel cell separator has a role of efficiently collecting electricity generated in each single cell. Therefore, the contact resistance with the gas diffusion layer such as carbon paper with which the fuel cell separator contacts must be low. Further, it is necessary to maintain high conductivity (low contact resistance) for a long time even in a high temperature / acid atmosphere inside the cell stack. That is, the initial contact resistance and the contact resistance after the accelerated durability test must be low.

  However, the separators disclosed in Patent Documents 1 to 3 are not carbonized or insufficiently carbonized, so that a carbon-based conductive layer contains a large amount of resin components. For this reason, there is a problem that the electric resistance of the carbon-based conductive layer is not sufficiently low, and the contact resistance with the carbon paper as the gas diffusion layer is not sufficiently low. That is, there is a problem that the initial contact resistance and / or the contact resistance after the accelerated durability test is not sufficiently lowered.

  The present invention has been made in view of the above problems, and is provided with a carbon-based conductive layer, and provides a fuel cell separator having a low initial contact resistance and a contact resistance after an accelerated durability test, and a method for manufacturing the same. Is an issue.

The present invention that has solved the above problems is a fuel cell separator in which a carbon-based conductive layer in which a carbon-based conductive material is dispersed is coated on a substrate made of pure titanium or a titanium alloy, When analyzed by Raman spectroscopy, a peak of D band and G band is obtained, and a peak intensity ratio (D / G ratio) of the obtained D band and G band is 0.10 or more and 1.0 or less, and the D band The full width at half maximum is 98 cm ⁻¹ or more.

When the peak intensity ratio of the D band and the G band of the carbon-based conductive layer is 0.10 or more and 1.0 or less, it indicates that the carbon-based conductive layer contains a sufficiently large amount of graphite component. The graphite component is excellent in conductivity and corrosion resistance. Further, when the half width of the D band is 98 cm ⁻¹ or more, it indicates that most of the matrix phase of the carbon-based conductive layer is inorganic amorphous carbon (diamond-like carbon). Amorphous carbon is not only excellent in conductivity, but is stable and resistant to chemical changes even at high temperatures and in an acidic atmosphere. Therefore, the carbon-based conductive layer that satisfies the above-described conditions is excellent in conductivity and corrosion resistance. That is, the initial contact resistance of the fuel cell separator and the contact resistance after the accelerated durability test can be lowered.

  In the present invention, it is preferable that an intermediate layer containing titanium carbide is formed at the interface between the base material and the carbon-based conductive layer.

  Since titanium carbide has conductivity, the electrical resistance at the interface between the base material and the carbon-based conductive layer is reduced, and the conductivity is improved. Moreover, since the intermediate layer containing titanium carbide is formed by the reaction between the base material and the carbon-based conductive layer, the adhesion between the base material and the carbon-based conductive layer is improved. Therefore, a more preferable fuel cell separator can be obtained.

The present invention that has solved the above problems is a method of manufacturing a fuel cell separator for manufacturing the above-described fuel cell separator, wherein a conductive paint containing a thermosetting resin and a carbon-based conductive material is applied on the base material. and coating drying step of then drying, after the coating drying process, characterized by comprising a non-oxidizing atmosphere the substrate, a heat treatment step of heat-treating at a temperature of 7 fifty to eight hundred and fifty ° C., the.

In the heat treatment step under a non-oxidizing atmosphere, by heat treatment at a high temperature of 7 50-850 ° C., it is possible to carbonize the thermosetting resin almost completely. That is, most of the matrix phase of the carbon-based conductive layer can be made of amorphous carbon. As described above, amorphous carbon is not only excellent in conductivity, but also stable because it does not easily undergo chemical changes even at high temperatures and in an acidic atmosphere. Therefore, in combination with the graphite component contained in the carbon-based conductive layer, a fuel cell separator having excellent conductivity and corrosion resistance can be produced. That is, a fuel cell separator having a low initial contact resistance and a low contact resistance after the accelerated durability test can be manufactured.

In this invention, it is preferable that the said thermosetting resin is 1 or more types selected from a phenol resin, a melamine resin, a urea resin, and an epoxy resin.
When these resins are used, the resin component can be changed to amorphous carbon by the heat treatment step described above.

In the present invention, the carbon-based conductive material is preferably carbon black powder, acetylene black powder, graphite powder or a mixed powder thereof.
Since these contain a graphite component, conductivity and corrosion resistance can be reliably improved.

  In this invention, it is preferable that the mass ratio of the said carbon-type electrically-conductive material is 3-20 mass% among all the solid components contained in the said conductive paint.

  If the carbon-based conductive material is included at such a mass ratio, it not only has sufficient conductivity, but also can maintain adhesion with the substrate.

  According to the present invention, it is possible to provide a fuel cell separator coated with a carbon-based conductive layer and having a low initial contact resistance and a low contact resistance after an accelerated durability test, and a method for manufacturing the same.

It is a schematic sectional drawing of the fuel cell separator which concerns on one Embodiment of this invention. It is a schematic sectional drawing of the fuel cell separator which concerns on other embodiment of this invention. It is the schematic explaining a contact resistance measuring apparatus. It is a flowchart explaining the content of the manufacturing method of the fuel cell separator which concerns on one Embodiment of this invention.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments (embodiments) for carrying out the present invention will be described in detail with reference to the drawings as appropriate.

[Fuel cell separator]
As shown in FIG. 1, a fuel cell separator 1 according to an embodiment of the present invention (hereinafter, appropriately referred to as a separator 1) covers a base material 2 made of pure titanium or a titanium alloy and the base material 2. And a carbon-based conductive layer 3.

(Base material)
The base material 2 is made of metal from the viewpoint of workability, gas barrier property, conductivity and heat conductivity necessary for forming a groove that becomes a flow path of gas such as oxygen (air) or hydrogen. The substrate 2 is preferably used. The pure titanium and titanium alloy materials described above are very preferable as the base material 2 in the present invention because they are lightweight, excellent in corrosion resistance, excellent in strength and toughness.

  The base material 2 can be manufactured by a conventionally known method, for example, a method of melting and casting pure titanium or a titanium alloy to form an ingot, hot rolling, and then cold rolling. In addition, although it is preferable that the base material 2 is annealed, the finishing state is not ask | required. For example, any finish state such as “annealing + pickling finish”, “vacuum heat treatment finish”, “bright annealing finish”, or the like can be used.

  In addition, although the base material 2 is not limited to pure titanium or a titanium alloy having a specific composition, it is easy to cold-roll a titanium material (base material) (total rolling reduction of 35% or more without intermediate annealing). From the viewpoint of securing the subsequent press formability, 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, with the balance consisting of Ti and inevitable impurities is preferable. For example, a JIS type 1 cold rolled sheet can be used.

  By using the base material 2 made of pure titanium or a titanium alloy, the strength and toughness of the separator 1 are improved, and the base material 2 itself has high corrosion resistance. Therefore, in the fuel cell, the carbon-based conductive layer 3 It is possible to prevent the base material 2 from being eluted from a portion not covered with (that is, a portion where the base material 2 is exposed). Furthermore, since it is lightweight, it is particularly easy to use for automobile applications.

  The plate thickness of the substrate 2 is preferably 0.05 to 1.0 mm. If the plate thickness is less than 0.05 mm, the strength required for the substrate 2 cannot be ensured, and if it exceeds 1.0 mm, the workability deteriorates.

(Carbon-based conductive layer)
The carbon-based conductive layer 3 is formed using a thermosetting resin in which a carbon-based conductive material is dispersed.

  Here, the carbon-based conductive material is preferably carbon black powder, acetylene black powder, graphite powder, or a mixed powder thereof. Since these powders contain a graphite component, they have good conductivity and corrosion resistance, and are inexpensive materials that are convenient for production.

  The particle size of the carbon-based conductive material is preferably 50 μm or less. This is because, when the particle diameter exceeds 50 μm, the carbon-based conductive material is likely to fall off during the pressing process performed to form the groove serving as the flow path on the separator 1. On the other hand, the lower limit of the particle size is not particularly specified, but the particle size of a general-purpose carbon-based conductive material is approximately 0.02 μm or more, and those having a particle size of less than this are difficult to obtain and are available. However, since it becomes expensive, it is not preferable.

  The thermosetting resin is preferably at least one selected from a phenol resin, a melamine resin, a urea resin, and an epoxy resin. If it is the coating material containing 1 or more types selected from these, the organic resin component can be changed into inorganic amorphous carbon (diamond-like carbon) by heat processing process S2 mentioned later. In addition, when thermoplastic resins, such as an acrylic resin, are used, a resin component will decompose | disassemble by the heat processing in heat processing process S2 mentioned later. As a result, the carbon-based conductive layer 3 becomes very brittle and is easily removed from the substrate 2, which is not preferable.

  As shown in FIG. 1, a carbon-based conductive layer 3 having conductivity and corrosion resistance is coated on the substrate 2. The carbon-based conductive layer 3 preferably covers one surface or both surfaces (including end surfaces as necessary) of the base material 2, but does not necessarily need to cover the entire surface. In order to ensure the electrical conductivity and corrosion resistance required for the fuel cell separator, it is sufficient that the surface is covered by 50% or more, preferably 60% or more. Moreover, you may make it coat | cover only the arbitrary locations required in order to ensure the electroconductivity and corrosion resistance required as a fuel cell separator. In addition, since the passive film of titanium is formed in the surface of the base material 2 in which the carbon-type conductive layer 3 is not formed, reactions, such as oxidation of the base material 2, can be suppressed.

The carbon-based conductive layer 3 formed on the substrate 2 contains a graphite component. When the carbon-based conductive layer 3 is analyzed by Raman spectroscopy, peaks of D band and G band are obtained. In the present invention, the peak intensity ratio (D / G ratio) between the D band and the G band is 0.10 or more and 1.0 or less, and the half width of the D band is 60 cm ⁻¹ or more.
Analysis by Raman spectroscopy can be performed using a conventionally known laser Raman spectrometer or the like.

The D band is observed due to point defects, crystal edge defects, and the like, and has a peak in the vicinity of 1350 cm ⁻¹ . The peak intensity of the D band refers to the peak intensity observed in the D band.

The G band is observed due to graphite and has a peak in the vicinity of 1590 cm ⁻¹ . The peak intensity of the G band refers to the peak intensity observed in the G band. Graphite is a material that is particularly excellent in conductivity and corrosion resistance among carbon-based conductive materials. When graphite is analyzed by Raman spectroscopic analysis, the peak of the G band is strongly detected.

  A D / G ratio smaller than 1.0 indicates that the peak intensity of the G band is larger than the peak intensity of the D band and contains a large amount of graphite components. Such a conductive layer is preferable because of its excellent conductivity and excellent corrosion resistance. If the D / G ratio exceeds 1.0, the conductivity and corrosion resistance will be insufficient. A preferable value of the D / G ratio is 0.90 or less, more preferably 0.80 or less, and still more preferably 0.60 or less.

  When the carbon-based conductive material used is only graphite powder, the D / G ratio is 0.30 or less, and high conductivity can be obtained. However, the separator 1 according to the embodiment does not include only the G band because the carbon-based conductive layer 3 is formed using a paint containing a thermosetting resin. Even when the D / G ratio is the lowest (when the carbon-based conductive material dispersed in the thermosetting resin is only graphite), it becomes 0.10 or more as described above.

Further, the half-value width of the D band obtained when the carbon-based conductive layer 3 is analyzed by Raman spectroscopy is 60 cm ⁻¹ or more. It is difficult for the carbon-based conductive material to be coated on the base material 2 with good adhesion as it is. Therefore, in general, a carbon-based conductive material is dispersed in a paint containing a thermosetting resin to form a conductive paint, which is applied onto the substrate 2 and then cured to form a layer.

  Since no peak is obtained even if the paint itself that does not contain carbon powder is analyzed by Raman spectroscopy, when applying a conductive paint with dispersed carbon powder analyzed by Raman spectroscopy, derived from the added carbon powder Only the peak of is obtained. Therefore, the state of the conductive layer defined in this patent cannot be obtained only by selecting the type of paint to be used.

  A coating film with a conductive paint applied or a layer that is insufficiently treated in the heat treatment step S2 described below contains a large amount of organic resin components, and therefore has low conductivity, and is also in a high temperature / acid atmosphere inside the fuel cell. Then, an organic component will deteriorate over time.

However, the separator 1 according to the present invention includes the coating / drying step S1 using the above-described coating material including the resin and the heat treatment step S2 performed subsequently (the coating / drying step S1 and the heat treatment step S2 will be described later). The organic component constituting the matrix phase of the carbon-based conductive layer 3 changes to inorganic amorphous carbon (diamond-like carbon). Accordingly, the matrix phase itself exhibits conductivity, and exhibits stable properties even in a high temperature / acidic atmosphere.
Further, due to the change from organic resin to inorganic amorphous carbon (diamond-like carbon), the half-value width of the D band obtained when analyzed by Raman spectroscopy is changed in a widening direction. When the half width of the D band is 60 cm ⁻¹ or more, good conductivity can be obtained. When the half width of the D band is lower than 60 cm ⁻¹ , good conductivity cannot be obtained. A preferable value of the half-width of the D band is 65 cm ⁻¹ or more, more preferably 80 cm ⁻¹ or more, still more preferably 90 cm ⁻¹ or more, and even more preferably 100 cm ⁻¹ or more.
On the other hand, the upper limit of the full width at half maximum of the D band is not particularly defined, but is preferably 300 cm ⁻¹ or less.

(Middle layer)
As shown in FIG. 2, in the separator 1, an intermediate layer 4 is preferably formed between the base material 2 and the carbon-based conductive layer 3. In particular, the intermediate layer 4 is preferably a layer containing titanium carbide formed by the reaction of the substrate 2 and the carbon-based conductive layer 3. Since titanium carbide has conductivity, the electrical resistance at the interface between the substrate 2 and the carbon-based conductive layer 3 is reduced, and the conductivity is improved. Further, since the base material 2 and the carbon-based conductive layer 3 are formed by reaction, the adhesion between the base material 2 and the carbon-based conductive layer 3 is improved.

  Whether or not the intermediate layer 4 contains titanium carbide can be confirmed by observing the interface between the substrate 2 and the carbon-based conductive layer 3 using a transmission electron microscope or the like. it can.

(Contact resistance)
In an actual fuel cell, the separator is in contact with a gas diffusion layer such as carbon paper and is clamped at a pressure of approximately 10 kg / cm ² .
Accordingly, in any of the separators 1 shown in FIGS. 1 and 2, the carbon-based conductive layer 3 is coated on both surfaces of the base material 2, and the base material 2 (separator 1) is sandwiched between the two carbon papers 11. The contact resistance measured with the contact resistance measuring device 10 (contact area 1 cm ² of the copper electrode 12) shown in FIG. 3 is 12 mΩ · cm ² or less while applying pressure from the side of the electrode at a surface pressure of 10 kg / cm ² . Is preferred.

If the value of the contact resistance is too large, the current loss when used as a separator in the fuel cell increases, and the performance as a fuel cell is lowered, which is not preferable. Therefore, it is preferable contact resistance between the separator 1 and the carbon paper 11 is 12mΩ · cm ² or less, more preferably 10 m [Omega · cm ² or less, more preferably 8.0mΩ · cm ² or less, even more preferably 6. 0 mΩ · cm ² or less.

[Method for producing fuel cell separator]
Next, with reference to FIG. 4, the manufacturing method of the fuel cell separator which concerns on one Embodiment of this invention is demonstrated.
As shown in FIG. 4, the method for manufacturing a fuel cell separator according to one embodiment of the present invention includes a coating drying step S1 and a heat treatment step S2. The separator 1 described with reference to FIGS. 1 and 2 can be manufactured by performing these steps in this order in the manufacturing method.

(Coating drying process)
The coating drying step S1 is a step of applying and drying a conductive paint containing a thermosetting resin and a carbon-based conductive material on the substrate 2.
Here, what was mentioned above can be used suitably for the base material 2, the thermosetting resin, and the carbon-based conductive material. Since these are already described in detail, they will be omitted.

  In addition, the ratio of the resin component contained in the conductive paint is preferably 5 to 30% by mass. If the ratio exceeds 30% by mass, the viscosity of the coating is too high, and it becomes difficult to apply the coating on the substrate 2 with a uniform thickness. On the other hand, when the ratio is less than 5% by mass, the viscosity is too low and it is difficult to apply the film with a uniform thickness.

  In addition, it is preferable that the mass ratio of a carbon-type electrically-conductive material is 2-30 mass% among all the solid components contained in a conductive paint. When the mass ratio is less than 2 mass%, the conductivity of the carbon-based conductive layer 3 becomes insufficient. On the other hand, when the mass ratio exceeds 30% by mass, the effect of increasing the conductivity is saturated, while the carbon-based conductive layer 3 obtained after the heat treatment becomes brittle and easily peels from the substrate 2. For this reason, in order to make electroconductivity and the adhesiveness of the carbon-type conductive layer 3 compatible, it is preferable to set it as 2-30 mass%. A more preferable range is 4 to 28% by mass, and a further preferable range is 5 to 25% by mass. Examples of the remaining components of the conductive paint include a solvent.

  As a method for applying the conductive paint to the surface of the substrate 2, any of conventionally known bar coaters, roll coaters, reverse roll coaters, gravure coaters, die coaters, kiss coaters, rod coaters, dip coaters, and spray coaters can be applied. be able to. By using the various coaters described above, a slurry (conductive paint) can be appropriately continuously applied to the surface of the base material 2, and productivity can be improved.

  In addition, what is necessary is just to make the application | coating thickness of an electroconductive coating material be 0.5-20 micrometers in thickness of the carbon-type conductive layer 3 after heat processing process S2 mentioned later. Such a coating thickness can be appropriately changed and set in relation to the heat treatment step S2.

  The conductive coating is dried by natural drying or forced drying by applying warm air, and the method and temperature may be appropriately selected depending on the type of solvent used in the coating and the desired drying time. If it is a roll-to-roll type coating apparatus, it will be continuously sent to a drying process after a coating process, and will be wound up in coil shape after drying.

(Heat treatment process)
The heat treatment step S2 is a step of heat-treating the substrate 2 at a temperature of 550 to 850 ° C. in a non-oxidizing atmosphere after the coating drying step S1. By performing such a heat treatment, the conductivity of the carbon-based conductive layer 3 can be increased, and the bond between the carbon-based conductive layer 3 and the substrate 2 can be made stronger. The intermediate layer 4 described above can be formed by performing this heat treatment step S2.

When the heat treatment temperature is less than 550 ° C., the conductivity of the carbon-based conductive layer 3 is insufficient, and the contact resistance with the carbon paper described above is not sufficiently low. On the other hand, if the heat treatment temperature exceeds 850 ° C., the mechanical properties of the substrate 2 may be deteriorated, which is not preferable. A preferable range of the heat treatment temperature is 600 to 800 ° C, and a more preferable range is 650 to 750 ° C.
The change of the matrix phase of the carbon-based conductive layer 3 to inorganic amorphous carbon (diamond-like carbon) is further promoted by setting the heat treatment temperature to 600 ° C. or higher, more preferably 700 ° C. or higher. Therefore, it is preferable that the temperature be higher than these temperatures.

  Note that the non-oxidizing atmosphere refers to an atmosphere having a low oxygen partial pressure, preferably an atmosphere having an oxygen partial pressure of 10 Pa or less. When the atmosphere is not a non-oxidizing atmosphere, carbon in the carbon conductive layer reacts with oxygen in the atmosphere (causes a combustion reaction). Thereby, the base material 2 is oxidized, and the conductivity is deteriorated.

  The heat treatment time is preferably 0.5 to 60 minutes. The time may be appropriately adjusted depending on the temperature, such as a long time treatment when the heat treatment temperature is low and a short time treatment when the heat treatment temperature is high.

  This heat treatment can be performed by using an electric furnace, a gas furnace or the like, but any heat treatment furnace can be used as long as the heat treatment can be performed at a heat treatment temperature of 550 to 850 ° C. and the atmosphere can be adjusted. It can also be used in a furnace.

In the conventional technique using a conductive paint, after a conductive layer is formed on the substrate 2 by various methods using the conductive paint, a heat treatment at about 200 ° C. or less is performed to cure the paint. Often. However, in such a case, since a large amount of the organic resin component remains in the conductive layer, the conductivity is insufficient, and there is a concern about deterioration of the organic component under high temperature / acid atmosphere inside the fuel cell. .
However, since the carbon-based conductive layer 3 of the separator 1 according to the present invention is heat-treated at a higher temperature than before in a non-oxidizing atmosphere, the resin component is not organic but inorganic amorphous carbon (diamond-like carbon). To change. Therefore, it becomes excellent in electroconductivity and corrosion resistance. The separator 1 according to the present invention is superior in these respects to a separator treated with a conventional conductive paint.

The thickness of the carbon-based conductive layer 3 after the heat treatment step S2 is preferably 0.5 to 20 μm. When the thickness is less than 0.5 μm, the conductivity is insufficient and the contact resistance with the carbon paper tends to be high. On the other hand, when the thickness exceeds 20 μm, it is easy to peel off in the carbon-based conductive layer 3 when a groove serving as a gas flow path is formed by press molding. The preferable thickness range of the carbon-based conductive layer 3 is 0.8 to 18 μm, more preferably 1 to 15 μm.
By the heat treatment, the thickness of the carbon-based conductive layer 3 changes in a decreasing direction. In order to adjust the thickness of the carbon-based conductive layer 3 after the heat treatment within the above range, the thickness at the time of applying the conductive paint may be appropriately adjusted.

The manufacturing method of the fuel cell separator according to the embodiment described above can perform steps other than these.
For example, after the heat treatment step S <b> 2, a press forming step of forming a groove serving as a gas flow path by press forming can be performed. In this press molding step, it can be molded into a desired shape by cutting, pressing, or the like.
Moreover, the surface finishing process (illustration omitted) which finishes the surface of the base material 2 to arbitrary states can be performed before coating drying process S1.
Examples of the surface finishing process include annealing, pickling, vacuum heat treatment finishing, and bright annealing finishing of the surface of the substrate 2, but are not limited to these, and other surface finishing. It can also be.

(Press molding process)
When using the separator 1 as a separator of a fuel cell, it is preferable to perform the press molding step (not shown in FIG. 4). In press molding, lubricating oil may be used. However, since the carbon-based conductive layer 3 on the substrate 2 acts as a lubricant, press molding is possible even without lubricating oil. Therefore, even if press molding is performed without lubricating oil, the carbon-based conductive layer 3 hardly peels after press molding. When press molding without lubricating oil, the degreasing cleaning after press molding is not necessary, so that the productivity of the separator 1 is improved.
In addition, this press molding process can also be performed before the coating drying process S1 or between the coating drying process S1 and the heat treatment process S2.

  The manufacturing method of the fuel cell separator according to one embodiment of the present invention is a process other than the coating drying step S1 and the heat treatment step S2, for example, the press molding step, the step of allowing the separator to cool after the heat treatment step S2, and the like. May be included.

  In the fuel cell separator 1 manufactured by the above manufacturing method, the carbon-based conductive layer 3 having excellent conductivity and corrosion resistance is formed on the surface of the base 2, and the carbon-based conductive layer 3 is firmly on the base 2. Therefore, the substrate 2 has a high environmental shielding property (barrier property) for shielding the substrate 2 from the in-cell environment of the fuel cell, and excellent conductivity can be maintained for a long time.

  As mentioned above, although one Embodiment of this invention was described, this invention is not limited to the said embodiment, A design change is possible suitably in the range which does not deviate from the summary of this invention described in the claim.

  Hereinafter, the fuel cell separator and the manufacturing method thereof according to the present invention will be described in detail by way of examples that achieve the desired effects of the present invention and comparative examples that do not.

1. Preparation of test body JIS 1 type titanium base material (annealing pickling finish) was used for the base material.
The chemical composition of the substrate (annealed pickling finish) was O: 450 ppm, Fe: 250 ppm, N: 40 ppm, the balance being Ti and inevitable impurities. The thickness of the substrate was 0.1 mm, and the size was 50 × 150 mm. The base material is obtained by subjecting a titanium raw material to a conventionally known melting step, casting step, hot rolling step, and cold rolling step.

2. Application / Drying of Conductive Paint A thermosetting resin shown in Table 1 was dissolved in an organic solvent, and a carbon-based conductive material was dispersed therein to produce a conductive paint. As carbon-based conductive materials, acetylene black powder (manufactured by Strem Chemicals, Inc., average particle size 50 nm, purity 99.99%), graphite powder (manufactured by SEC Carbon, SNE-6G, average particle size 7 μm, (Purity 99.9%), carbon black powder (Tokai Carbon Co., Ltd., Toka Black # 4500, average particle size 40 μm, purity 99.9%) was used.

  In addition, using the organic solvent for dissolving in the thermosetting resin, the resin component (solid content) in the coating is about 20% by mass, and the mass ratio of the carbon-based conductive material in the solid content is 5%. Each conductive paint was prepared so that it might become -22 mass%. The paint was applied to the substrate using a bar coater (# 20) and dried. In this way, a layer having a thickness of about 5 μm was formed on both surfaces of the substrate.

3. Next, the base material (test body) on which the layer having a thickness of about 5 μm was formed was 6.7 × 10 ⁻³ Pa in a vacuum atmosphere (oxygen partial pressure 1.3 × 10 ⁻³ Pa) or oxygen concentration. Was subjected to a heat treatment at a temperature shown in Table 1 for 3 minutes in an Ar gas atmosphere of 10 ppm (corresponding to an oxygen partial pressure of 1.0 Pa). For comparison, some specimens were not heat-treated. “-” In Table 1 indicates that neither a vacuum atmosphere of 6.7 × 10 ⁻³ Pa nor an Ar gas atmosphere was used, that is, the atmosphere. The temperature “None” indicates that no heat treatment was performed. That is, no heat treatment was performed on the test body 11 after the conductive paint was applied and dried.

  For the test specimens 1 to 13 thus produced, measurement by Raman spectroscopy, adhesion of the carbon-based conductive layer, initial contact resistance, and contact resistance after the accelerated durability test were evaluated. These evaluations were performed as follows.

(1) Measurement by Raman spectroscopy The Raman spectrum analysis of carbon was performed on each specimen using a microscopic laser Raman spectroscopy analyzer. Peak of D band at about 1350 cm ^-1, a peak of G-band was obtained at about 1590 cm ^-1. And the peak intensity ratio (D / G ratio) of D band and G band was calculated | required from each peak intensity.
Moreover, the half width of D band obtained by the same analysis was calculated | required.

(2) Adhesion of carbon-based conductive layer After applying a tape (Sumitomo 3M Mending Tape 12mm width) on the surface of the carbon-based conductive layer of each specimen, the tape is perpendicular to the surface of each specimen. The carbon-based conductive layer was evaluated for adhesion. The case where the carbon-based conductive layer peels off from the interface with the base material is indicated as x, the case where the carbon-based conductive layer peels off is indicated as △, and the case where the tape adhesive remains on the surface of the carbon-based conductive layer is indicated as ○. . In this evaluation, Δ and ○ were regarded as acceptable.

(3) Initial contact resistance About the test body which the adhesiveness of the carbon-type conductive layer passed, contact resistance was measured using the contact resistance measuring apparatus shown in FIG. Specifically, the load is sandwiched between two sheets of carbon paper 11 on both sides of the specimen (base material 2 (separator 1) in FIG. 3), and further sandwiched between two copper electrodes 12 with a contact area of 1 cm ^2. A pressure of 98 N (10 kgf) was applied, a current of 7.4 mA was applied using a direct current power source, a voltage applied between the carbon papers 11 was measured with a voltmeter, and a contact resistance (initial contact resistance) was obtained.
The initial contact resistance was determined to be acceptable when it was 12 mΩ · cm ² or less, and was rejected when it exceeded 12 mΩ · cm ² .

(4) Contact resistance after accelerated endurance test An accelerated endurance test was performed on the test specimens that passed the adhesion and initial contact resistance of the carbon-based conductive layer. That is, the specimen was immersed in an 80 ° C. sulfuric acid aqueous solution (10 mmol / L) having a specific liquid volume of 20 ml / cm ² , and a potential of +600 mV was applied to the specimen based on the saturated calomel electrode (SCE). Then, after the immersion treatment for 100 hours, the test specimen was taken out from the sulfuric acid aqueous solution, washed and dried, and the contact resistance was measured by the same method as the above (3) initial contact resistance.
The contact resistance after the accelerated durability test was determined to be acceptable when it was ²⁰ mΩ · cm ² or less, and rejected when exceeding ²⁰ mΩ · cm ² .

  Table 2 shows the evaluation for each specimen. In Table 2, “-” indicates that measurement was not performed.

As shown in Table 2, all of the test bodies 1 to 10 had good adhesion of the carbon-based conductive layer, had good initial contact resistance and contact resistance after the accelerated durability test, and were evaluated as passing. In the test bodies 1 to 10, the peak intensity ratio (D / G ratio) between the D band and G band obtained when the carbon-based conductive layer was analyzed by Raman spectroscopy was 1.0 or less, and the D band had a half-value width. The value was 60 cm ⁻¹ or more.

  On the other hand, the test bodies 11 to 13 were evaluated as rejected because the carbon-based conductive layer had poor adhesion, initial contact resistance, or contact resistance after the accelerated durability test.

  Specifically, since the test body 11 was not heat-treated, the heat-treatment temperature of the test body 12 was not sufficiently high. In these, at least one of the peak intensity ratio (D / G ratio) of the D band and the G band and the half-value width of the D band was out of the scope of the present invention.

  Moreover, since the test body 13 was an acrylic resin whose thermoplastic resin was used as the resin component of the paint used, the adhesion of the carbon-based conductive layer was very low and the test piece 13 was rejected. In the test body 13, both the peak intensity ratio (D / G ratio) of the D band and the G band and the half width of the D band were out of the scope of the present invention.

1 Separator (fuel cell separator)
2 Substrate 3 Carbon conductive layer 4 Intermediate layer S1 Coating / drying step S2 Heat treatment step

Claims (6)

A fuel cell separator in which a carbon-based conductive layer in which a carbon-based conductive material is dispersed is coated on a substrate made of pure titanium or a titanium alloy,
When the carbon-based conductive layer is analyzed by Raman spectroscopy, a peak of D band and G band is obtained, and a peak intensity ratio (D / G ratio) of the obtained D band and G band is 0.10 or more and 1.0. A fuel cell separator, wherein the D band has a full width at half maximum of 98 cm ^-1 or less.   The fuel cell separator according to claim 1, wherein an intermediate layer containing titanium carbide is formed at an interface between the base material and the carbon-based conductive layer. A fuel cell separator manufacturing method for manufacturing the fuel cell separator according to claim 1 or 2 ,
On the base material, a coating drying step of applying and drying a conductive paint containing a thermosetting resin and a carbon-based conductive material;
After the coating drying step, a heat treatment step of heat-treating the substrate under a non-oxidizing atmosphere at a temperature of 7 fifty to eight hundred fifty ° C.,
The manufacturing method of the fuel cell separator characterized by including. The method for producing a fuel cell separator according to claim 3 , wherein the thermosetting resin is at least one selected from a phenol resin, a melamine resin, a urea resin, and an epoxy resin. The method for producing a fuel cell separator according to claim 3 or 4 , wherein the carbon-based conductive material is carbon black powder, acetylene black powder, graphite powder, or a mixed powder thereof. Fuel according to any one of the preceding claims 5 to mass ratio of the carbon-based conductive material, characterized in that 3 to 20% by weight of the total solid components contained in the conductive coating A method for producing a battery separator.

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