JP2008108490A - Manufacturing method of fuel cell separator, fuel cell separator, and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a fuel cell separator capable of manufacturing the fuel cell separator formed of Ti or a Ti alloy which is excellent in corrosion resistance, low in contact resistance, and furthermore excellent in productivity. <P>SOLUTION: The manufacturing method of the fuel cell separator 1 includes a recessed part forming process S1 for forming a recessed part in order to form a gas flow passage 11 through which gas is circulated in at least a part of the surface of a substrate 2 as the fuel cell separator formed of Ti or a Ti alloy, a plating layer forming process S2 in which at least one plating layer 3 formed by containing a noble metal such as Au and/or Pt is formed by electroplating on the surface of the substrate 2 in which the recessed part is formed, and a heat treatment process S3 wherein the substrate 2 on which the plating layer 3 is formed in the plating layer forming process S2 is heat-treated at a heat treatment temperature of 300 to 800°C. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a separator for a fuel cell made of Ti or Ti alloy for a polymer electrolyte fuel cell used for portable devices such as mobile phones and personal computers, household fuel cells, fuel cell vehicles, etc. The present invention relates to a battery separator and a fuel cell.

In recent years, fuel cells are expected as an energy source for solving global environmental problems and energy problems.
In particular, polymer electrolyte fuel cells can be operated at low temperatures, and can be reduced in size and weight, so they can be applied to household cogeneration systems, power supplies for portable devices, and fuel cell vehicles. It is being considered.

  Here, a general solid polymer type fuel cell is a single cell in which a solid polymer electrolyte membrane is sandwiched between an anode electrode and a cathode electrode, and is connected via an electrode called a separator (or bipolar plate). A plurality of cells are overlapped.

  This separator is required to have a characteristic that the contact resistance is low, and the low contact resistance is maintained for a long time during use of the fuel cell. Therefore, conventionally, application of metal materials such as aluminum alloy, stainless steel, nickel alloy, titanium alloy and the like has been studied as a material for the separator in view of workability and strength.

  However, when these metal materials are used as a separator for a fuel cell, the conductivity tends to be significantly deteriorated due to an oxide film (passive film) formed on the surface thereof. For this reason, even if the contact resistance at the beginning of use is low, this low contact resistance cannot be maintained for a long time during use, and there is a problem that the contact resistance rises with time and causes current loss. . In addition, there is a problem that the electrolyte membrane is deteriorated by metal ions eluted from the metal material due to corrosion.

In order to solve such a problem, a technique for suppressing the increase in contact resistance and maintaining conductivity has been conventionally proposed.
For example, the surface of a separator made of metal such as stainless steel or Ti is plated with gold (for example, see Patent Document 1), and the surface of a separator such as stainless steel or Ti is coated with a surface oxide film (passive film). After the removal, a noble metal or a noble metal alloy adhered by ion vapor deposition or plating (see, for example, Patent Document 2), the surface of the Ti separator is removed from the surface oxide film (passive film), and then the island The thing which gold-plated in the shape (for example, refer patent document 3) is proposed.
JP-A-10-228914 JP 2001-6713 A JP 2006-97088 A

  However, the invention described in Patent Document 1 not only deteriorates the adhesion of gold unless the surface passive film is removed, but also increases the contact resistance due to this passive film (that is, the conductivity is low). Lower). Therefore, the passive film is removed by performing the surface activation process, but since the passive film is formed in the cleaning process performed before the plating process, there is a drawback that sufficient adhesion cannot be obtained. There is a disadvantage that the contact resistance cannot be lowered.

  Moreover, the invention described in Patent Document 2 performs a process of precipitating Pt as a noble metal by a corrosion reaction while mechanically polishing the surface of stainless steel or Ti. When such a treatment is performed, Pt is deposited on the portion where the passive film has been removed, so that the contact resistance decreases (that is, the conductivity increases), but the pinhole (where the substrate partially appears on the surface) In other words, stainless steel and Ti are eluted from the pinhole when used in an acidic atmosphere such as a fuel cell, and the power generation characteristics of the fuel cell deteriorate. There are drawbacks. In addition, although a method of blasting with glass beads plated with precious metal has been proposed, since the separator is required to have high dimensional accuracy, there is a drawback that it becomes difficult to use due to deformation that can occur by blasting. .

  In the invention described in Patent Document 3, island-shaped gold plating is performed after removing the passive film on the surface of Ti in order to increase the adhesion and conductivity of gold plating. The formed passive film has insufficient corrosion resistance, and when exposed to an acidic atmosphere for a long time, the passive film becomes thicker over time and the conductivity deteriorates, or there is a plating defect such as pinholes. Metal elution may occur from the non-plated part of the generated part, and the gold-plated part may fall off.

In addition to plating, there is a method of providing a high corrosion resistance by forming a noble metal film on a stainless steel or Ti substrate by a vapor deposition method such as sputtering, vacuum deposition, or ion plating.
In such a method, in order to improve the adhesion of the noble metal layer, the substrate is irradiated with an argon ion beam in a low gas pressure argon gas atmosphere before the noble metal layer is formed, or a negative bias is applied to the substrate. It is common to form a noble metal layer after removing dirt, a passive film, etc. on the surface of the substrate by generating argon plasma by applying it and causing argon ions to collide with the substrate. According to this method, since the passive film is removed, a sufficiently low contact resistance can be obtained. However, it takes a long time to remove the passive film by such a method, so that there is a disadvantage that productivity is lowered.

  The subject of this invention is providing the manufacturing method of the separator for fuel cells which can manufacture the separator for fuel cells made from Ti or Ti alloy which was excellent in corrosion resistance, was low in contact resistance, and was excellent in productivity. An object of the present invention is to provide a fuel cell separator manufactured thereby and a fuel cell using the fuel cell separator.

In order to solve the above-described problems, a method for manufacturing a fuel cell separator according to the present invention includes a recess forming step, a plating layer forming step, and a heat treatment step.
As described above, in the method for manufacturing a fuel cell separator according to the present invention, a gas flow path for allowing gas to flow through at least a part of the surface of the substrate as a fuel cell separator made of Ti or Ti alloy is formed by the recess forming step. In the plating layer forming process, at least one plating layer containing Au and / or Pt noble metal is formed on the surface of the substrate on which the recess has been formed by a plating layer forming step. Then, in the heat treatment step, the substrate on which the plating layer is formed is heat treated at a heat treatment temperature of 300 to 800 ° C., so that one of oxygen in the amorphous passive film existing at the interface between the plating layer and the substrate is obtained. The part diffuses into the substrate made of Ti or Ti alloy, and the passive film becomes thin. Alternatively, the film structure of the passive film disappears, and a diffusion layer in which the metal element constituting the plating layer and the Ti of the substrate are diffused to each other is formed. Due to the thinning or disappearance of such a passive film, the conductivity is increased.
Therefore, the fuel cell separator manufacturing method of the present invention is excellent in corrosion resistance and has low contact resistance by performing a heat treatment step after the plating layer forming step by electroplating without performing complicated steps. Can be easily produced with good productivity.

The method for manufacturing a fuel cell separator according to the present invention includes a recess for forming a gas flow path for allowing a gas to flow through at least a part of a surface of a substrate as a fuel cell separator made of Ti or Ti alloy by a recess forming step. In the plating layer forming step, at least one plating layer containing Au and / or Pt noble metal is formed by electroplating on the surface of the substrate on which the concave portion is formed. Then, in the heat treatment step, the substrate on which the plating layer is formed is heat treated at a heat treatment temperature of 300 to 800 ° C., so that one of oxygen in the amorphous passive film existing at the interface between the plating layer and the substrate is obtained. The part diffuses into the substrate made of Ti or Ti alloy, and the passive film becomes thin. Alternatively, the film structure of the passive film disappears, and a diffusion layer in which the metal element constituting the plating layer and the Ti of the substrate are diffused to each other is formed. Further, by forming an oxide film containing crystalline titanium oxide in a portion where there is no plating in which plating defects such as pinholes are present, the corrosion resistance of the portion where there is no plating on the surface of the substrate is improved. By reducing the thickness or disappearance of the passive film, the conductivity is increased, and the corrosion resistance is improved by forming an oxide film containing crystalline titanium oxide in a portion where there is no plating on the substrate surface.
Therefore, the manufacturing method of the separator for a fuel cell according to the present invention is for a fuel cell having excellent corrosion resistance and low contact resistance by performing a heat treatment step after the plating layer forming step by electroplating without performing a complicated step. The separator can be easily manufactured with high productivity.

In order to solve the above-described problems, the fuel cell separator according to the present invention is manufactured by the above-described fuel cell separator manufacturing method.
Thus, the corrosion resistance and electrical conductivity increase by manufacturing the separator for fuel cells of this invention by an above described manufacturing method.

The fuel cell separator according to the present invention is formed on the surface of a substrate as a fuel cell separator made of Ti or Ti alloy in which a recess for forming a gas flow path for allowing gas to flow through at least a part of the surface is formed. An oxide film containing crystalline titanium oxide is formed in a plating layer containing a noble metal of Au and / or Pt and a portion where there is no plating in which plating defects have occurred on the surface of the substrate. Yes.
As described above, the separator for a fuel cell of the present invention has improved conductivity by forming a plating layer, and corrosion resistance by forming an oxide film containing crystalline titanium oxide in a portion where there is no plating on the substrate surface. Will increase.

The separator for a fuel cell according to the present invention is formed at a site where the thickness of an oxide film containing crystalline titanium oxide present at the interface between the plating layer and the substrate is 10 nm or less and no plating is present. The thickness of the oxide film containing crystalline titanium oxide is preferably 10 to 100 nm.
Thus, the conductivity of the fuel cell separator of the present invention is increased by regulating the thickness of the oxide film containing crystalline titanium oxide present at the interface between the plating layer and the substrate to a predetermined value or less. Further, the corrosion resistance is enhanced by defining the thickness of the oxide film containing crystalline titanium oxide formed at a site where plating is not present within a predetermined range.

The fuel cell separator according to the present invention has a deposition amount of Au and / or Pt of 0.1 to 5.0 at% when SEM / EDX analysis is performed under the conditions of an acceleration voltage of 20 kV and a magnification of 50 times. preferable.
The separator for a fuel cell of the present invention has a crystallinity existing at the interface between the plating layer and the substrate by defining the precipitation amount of Au and / or Pt in a predetermined range when SEM / EDX analysis is performed under a predetermined condition. The oxide film containing titanium oxide is less likely to be thick and the conductivity is increased.

  The fuel cell according to the present invention preferably uses the above-described fuel cell separator. Since the fuel cell of the present invention uses the fuel cell separator described above, it has excellent corrosion resistance, low contact resistance, and excellent productivity.

The method for producing a fuel cell separator according to the present invention can produce a fuel cell separator made of Ti or Ti alloy having excellent corrosion resistance, low contact resistance, and excellent productivity.
In addition, the fuel cell separator according to the present invention has excellent corrosion resistance, low contact resistance, and excellent productivity.
The fuel cell according to the present invention has excellent corrosion resistance, low contact resistance, and excellent productivity.

Next, the best mode for carrying out the method for manufacturing a fuel cell separator, the fuel cell separator and the fuel cell according to the present invention will be described with reference to the drawings as appropriate. In the drawings to be referred to, FIG. 1 is a flowchart for explaining the steps of the method for manufacturing a fuel cell separator according to the present invention. FIG. 2 is a cross-sectional view of a fuel cell separator according to the present invention. FIG. 3 is an explanatory diagram for explaining a method of measuring contact resistance. FIG. 4 is a diagram showing an example of the shape of the gas flow path formed on the surface of the substrate. FIG. 5 is a diagram showing a state in which a part of a fuel cell using the fuel cell separator of the present invention is developed.
In the drawings to be referred to, reference numeral S1 denotes a recess forming process, reference numeral S2 denotes a plating layer forming process, reference numeral S3 denotes a heat treatment process, reference numeral 1 denotes a fuel cell separator, reference numeral 2 Indicates a substrate, reference numeral 3 indicates a plating layer, reference numerals 4a and 4b indicate oxide films containing crystalline titanium oxide, reference numeral 5 indicates a non-plated portion, and reference numeral 10 indicates a single cell. Reference numeral 11 indicates a gas flow path, reference numeral 12 indicates a gas diffusion layer, reference numeral 13 indicates a solid polymer film, and reference numeral 20 indicates a fuel cell.

First, the manufacturing method of the separator for fuel cells of this invention is demonstrated.
As shown in FIG. 1, the manufacturing method of the fuel cell separator 1 of the present invention includes a recess forming step S1, a plating layer forming step S2, and a heat treatment step S3.

The recess forming step S1 is a gas flow path 11 for circulating a gas such as hydrogen gas or air over at least a part of the surface of the substrate 2 as a fuel cell separator made of Ti or Ti alloy (see FIGS. 4 and 5). A recess for forming the is formed. Here, the surface of the substrate 2 refers to a surface that forms the outside of the substrate 2, and includes a so-called front surface, back surface, and side surface.
Here, the apparatus for forming the gas flow path on at least a part of the surface of the substrate 2 is not particularly limited, and a conventionally known apparatus capable of achieving a predetermined purpose can be appropriately used. .

  The plating layer forming step S2 includes a noble metal of Au and / or Pt on the surface of the substrate 2 made of Ti or Ti alloy having the recesses (the entire surface of the substrate 2 or at least a part of the surface) by electroplating. At least one plating layer is formed.

  Examples of the substrate 2 include 1 to 4 types of pure Ti substrates stipulated in JIS H 4600, and substrates of Ti alloys such as Ti—Al, Ti—Ta, Ti-6Al-4V, and Ti—Pd. However, from the viewpoint of cost and workability, it is preferable to use one or two kinds of pure Ti or α alloy specified in JIS H 4600. However, the substrate 2 that can be used in the present invention is not limited to these, and even Ti alloys containing other metal elements can be suitably used.

  Since noble metals such as Au and Pt do not form an oxide film on the surface even when heat-treated in an oxygen-existing atmosphere, they exhibit low contact resistance even when heat treatment is performed in air. In addition, if the amount of precious metal deposited is above a certain level, it is not necessary to adjust the atmosphere as in vacuum heat treatment and atmospheric heat treatment, so a large amount of processing can be performed in a short time, productivity is high, and processing costs are low. It is also a feature. Moreover, these noble metals are also excellent in corrosion resistance. Therefore, good corrosion resistance and conductivity can be provided by forming a plating layer containing these noble metals.

In the plating layer forming step S2, the plating layer 3 containing a precious metal of Au and / or Pt is formed by electroplating using an electroplating method. In the electroplating method, first, before the plating layer forming step S2, the Ti or Ti alloy substrate 2 cut into a desired shape and size is subjected to ultrasonic cleaning in an organic solvent such as acetone as necessary. The surface of the substrate 2 is degreased by cleaning. Thereafter, the passive film on the surface of the substrate 2 is removed using a nitric hydrofluoric acid aqueous solution, which is a mixed aqueous solution of hydrofluoric acid and nitric acid (passive film removing step (not shown)), and a commercially available plating layer forming step S2 is used. A plating layer 3 containing Au and / or Pt is formed by electroplating using a plating solution. In addition, the plating layer 3 may contain Au and Pt, respectively, or may contain Au and Pt mixed.
Further, the number of plating layers 3 is not particularly specified. The plating layer 3 may be formed in at least one layer, or may be a multilayer in which a plurality of layers are formed.

  In performing the plating layer forming step S2, if the substrate 2 is cleaned in advance using an organic solvent such as acetone, ultrasonic cleaning or the like may cause pinhole formation or poor adhesion due to contamination on the surface of the substrate 2. Can be reduced, which is preferable.

  Next, in the heat treatment step S3, the substrate 2 on which the plating layer 3 is formed in the plating layer formation step S2 is heat-treated at a heat treatment temperature of 300 to 800 ° C. to manufacture the fuel cell separator 1.

As described above, the passive film is removed in advance before the plating process in the plating layer forming step S2, and the substrate 2 has a passive film removing step for removing the passive film and a plating layer forming step. In the portion where the plating layer 3 containing Au and / or Pt is formed during exposure to air during S2, the interface between the plating layer 3 and the substrate 2 (hereinafter, “between the plating layer 3 and the substrate 2”). A thin passive film is formed.
The passive film is an amorphous oxide film before heat treatment (hereinafter the same).

  Here, a part or all of the passive film formed between the plating layer 3 and the substrate 2 before the heat treatment is crystallized by the heat treatment. During the crystallization, the passive film formed between the plating layer 3 and the substrate 2 is thinned by diffusion of oxygen into the Ti base material because the supply of oxygen is blocked by the plating layer 3. And it changes to titanium oxide deficient in oxygen (titanium oxide having an oxygen-deficient gradient structure). This crystallized titanium oxide becomes an n-type semiconductor whose conductivity is increased when oxygen is deficient than the stoichiometric ratio. That is, the conductivity of the passive film formed between the plating layer 3 and the substrate 2 can be improved by heat treatment. Further, by continuing the heat treatment or raising the heat treatment temperature, the passive film before the heat treatment and the highly conductive titanium oxide layer formed as described above are thinned or disappeared. In addition, a diffusion layer (not shown) in which a noble metal element and Ti are mutually diffused may be formed between the plating layer 3 and the substrate 2.

When such a heat treatment is performed, even if the passive film remains, dirt such as hydrocarbons existing on the passive film is decomposed by heat and diffused into the plating layer 3. The plating layer 3 is brought into contact with the surface of the clean passive film and / or the oxide film 4a containing crystallized crystalline titanium oxide (that is, oxygen-deficient titanium oxide) as well as a clean surface. Thus, it is considered that the consistency between the crystallized oxide film 4a containing crystalline titanium oxide and the crystal lattice of the noble metal is improved, and the adhesion between the plating layer 3 and the substrate 2 is improved.
Further, when the heat treatment is performed at a high temperature or for a long time, the passive film disappears completely, and a diffusion layer in which the elements of the plating layer 3 and Ti of the substrate 2 are diffused is formed between the plating layer 3 and the substrate 2. The

  Therefore, the manufacturing method of the separator for a fuel cell of the present invention does not perform a complicated process, but simply performs the heat treatment step S3 after the plating layer forming step S2 by electroplating, and the passive film remains passive. A part or all of the film can be made into an oxide film 4a containing crystallized crystalline titanium oxide having oxygen-deficient conductivity, and if no passive film remains, plating is performed. Since the diffusion layer of the element of the layer 3 and Ti of the substrate 2 can be formed, the fuel cell separator 1 having low contact resistance can be easily manufactured with high productivity.

The heat treatment temperature in the heat treatment step S3 is set to 300 to 800 ° C.
By performing the heat treatment at 300 to 800 ° C., as described above, a part of oxygen in the passive film between the plating layer 3 and the substrate 2 diffuses into the substrate 2 made of Ti or Ti alloy, and becomes non-conductive. The dynamic film becomes thinner. Depending on the heating conditions, the film structure of the passive film may disappear, and a diffusion layer may be formed in which the metal element constituting the plating layer 3 and Ti of the substrate 2 are mutually diffused. Due to the thinning or disappearance of such a passive film, the conductivity is increased.

  When the heat treatment temperature is less than 300 ° C., the diffusion rate of oxygen in the substrate 2 is slow, and the passive film is less likely to be thinned or lost. On the other hand, when the temperature exceeds 800 ° C., even if a diffusion layer between the plating layer 3 and the substrate 2 is formed, oxidation by oxygen in the atmosphere is promoted, and below this diffusion layer (between the diffusion layer and the base material 2). An oxide film 4a containing crystalline titanium oxide is formed, and the conductivity is lowered. Even if the diffusion layer is not formed, the oxide film 4a containing crystalline titanium oxide formed between the plating layer 3 and the substrate 2 becomes thick and the conductivity is lowered.

  Furthermore, when the heat treatment temperature exceeds 800 ° C., the diffusion is too fast, so that the noble metal element and Ti of the substrate 2 diffuse too much to each other, and titanium diffuses to the outermost surface of the plating layer 3 and oxygen in the heat treatment atmosphere. May form a titanium oxide layer (oxide film). When an oxide film is formed, although corrosion resistance is higher than that of a passive film, it is not preferable because contact resistance increases. The heat treatment temperature is more preferably 350 to 750 ° C, and most preferably 380 to 730 ° C. Even in such a temperature range, if heat treatment is performed for a long time, titanium may diffuse to the surface and an oxide film may be formed. Therefore, it is preferable to appropriately adjust the heat treatment time with respect to the heat treatment temperature.

Although the heat treatment time in the heat treatment step S3 depends on the heat treatment temperature, the passive film existing between the plating layer 3 and the substrate 2 is crystallized to reduce the contact resistance (that is, improve the conductivity), or passivate film. Is preferably 1 to 60 minutes, more preferably 5 to 50 minutes, in order to remove or sufficiently thin the film.
If the heat treatment time is less than 1 minute, the conductivity of the passive film may not be improved and the passive film may not be removed sufficiently. Therefore, the contact resistance cannot be lowered.
On the other hand, when the heat treatment time exceeds 60 minutes, although depending on the heat treatment temperature and the thickness of the plating layer 3, the noble metal element and Ti of the substrate 2 may diffuse excessively to form an oxide film on the outermost surface. It becomes easy to be done. As described above, the formation of an oxide film is not preferable because the contact resistance tends to increase.

  As described below, the heat treatment of the substrate 2 on which the plating layer 3 is formed by the electroplating method forms an oxide film 4b containing crystalline titanium oxide in a portion where the plating layer 3 on the surface of the substrate 2 does not exist. Perform in an air atmosphere. Here, since Au and Pt are not oxidized, they can be heat-treated in an air atmosphere. Further, when the plating thickness is thin (precious metal deposition amount is about 0.1 to 0.5 at%), it is preferable to perform heat treatment at a low oxygen partial pressure such as a vacuum atmosphere.

Here, even if the plating layer 3 is formed by the plating layer forming step S2, a pinhole or the like is generated in the plating layer 3, so that the plating of the plating layer 3 does not exist on the surface of the substrate 2. Part 5 is produced.
In such a non-plated portion 5, the substrate 2 made of Ti or Ti alloy is exposed, and this portion is an oxide film containing crystalline titanium oxide when the heat treatment is performed in the heat treatment step S3. 4b is formed. In general, the Ti passive film has an amorphous structure, but the oxide film 4b containing crystalline titanium oxide formed by high-temperature oxidation has a crystalline structure and has higher corrosion resistance than the passive film. Therefore, the portion of the plating layer 3 where the noble metal particles are bonded to the substrate 2 becomes a conductive path, and the other portion exhibits corrosion resistance by the oxide film 4b containing crystalline titanium oxide, thereby achieving both conductivity and corrosion resistance. An improved separator can be provided.

In the heat treatment step S3, the heat treatment for thinning or eliminating the passive film and forming the oxide film 4b containing crystalline titanium oxide on the surface of the substrate 2 of the non-plated portion 5 is performed at 300 to 800 ° C. Is good. That is, by setting the heat treatment temperature in the heat treatment step S3 to 300 to 800 ° C., as described above, the passive film formed between the plating layer 3 and the substrate 2 is made thin or disappeared, and the non-plated portion 5 An oxide film 4 b containing crystalline titanium oxide is formed on the surface of the substrate 2.
In the heat treatment in the heat treatment step S3, as long as oxygen is present in the atmosphere, Ti is oxidized to form an oxide film 4b containing crystalline titanium oxide. If the heat treatment temperature is less than 300 ° C., the non-plated portion 5 In addition to the fact that the oxide film 4b containing crystalline titanium oxide is not formed to a sufficient thickness, the crystallization does not proceed at a temperature lower than 300 ° C. and remains amorphous after the heat treatment, and the crystalline titanium oxide having high corrosion resistance. Therefore, although the conductivity is not lowered, the corrosion resistance is not ensured. Further, as described above, it is difficult for the passive film to be thinned and lost. On the other hand, when the heat treatment temperature exceeds 800 ° C., the oxide film 4b containing the crystalline titanium oxide in the non-plated portion 5 becomes too thick and the conductivity is lowered. Further, as described above, when the diffusion layer is formed, the oxide film 4a containing crystalline titanium oxide is formed between the diffusion layer and the substrate 2, the conductivity is lowered, and the diffusion layer is not formed. However, the oxide film 4a containing crystalline titanium oxide formed between the plating layer 3 and the substrate 2 becomes thick, and the conductivity is lowered. Further, Ti of the substrate 2 may diffuse up to the outermost surface of the plating layer 3, and an oxide film may be formed there.

Next, the fuel cell separator 1 according to the present invention manufactured by the method for manufacturing the fuel cell separator of the present invention will be described in detail.
As shown in FIG. 2, the fuel cell separator 1 according to the present invention includes, as described above, Ti or Ti having a recess for forming a gas flow path 11 through which gas flows at least part of the surface. A plating layer 3 containing Au and / or Pt noble metal is formed on the surface of a substrate 2 as an alloy fuel cell separator. In addition, an oxide film 4b containing crystalline titanium oxide is formed on a portion of the surface of the substrate 2 where plating by the plating layer 3 does not exist. Here, there may be an oxide film 4 a containing crystalline titanium oxide between the plating layer 3 and the substrate 2.
More specifically, the fuel cell separator 1 according to the present invention has a configuration in which at least one plating layer 3 containing a precious metal of Au and / or Pt is formed on the surface of the substrate 2 by electroplating. ing. Further, the substrate on which the plating layer 3 is formed is heat-treated at a heat treatment temperature of 300 to 800 ° C., and an oxidation containing crystalline titanium oxide is performed on the surface of the substrate 2 where no plating by the plating layer 3 exists. The film 4b is formed. An oxide film 4 a containing crystalline titanium oxide may exist between the plating layer 3 and the substrate 2.
The significance of performing electroplating by the electroplating method and defining the heat treatment temperature of the heat treatment has already been described in detail and will not be described.
In addition, the fuel cell separator 1 according to the present invention may not be based on the manufacturing method described above.

Here, the thickness of the oxide film 4a containing crystalline titanium oxide formed between the plating layer 3 containing Au and / or Pt and the substrate 2 is preferably 10 nm or less. In terms of conductivity, it is preferable that the oxide film 4a containing crystalline titanium oxide does not exist. However, even when it is formed, it is known that the film has a certain thickness, and the film thickness is , About 10 nm or less.
Therefore, the thickness of the oxide film 4a containing crystalline titanium oxide formed between the plating layer 3 and the substrate 2 is preferably 10 nm or less, and more preferably 5 nm or less.

Moreover, the thickness of the oxide film 4b containing crystalline titanium oxide formed in the non-plated portion 5 such as the pinhole portion of the plated layer 3 is preferably in the range of 10 to 100 nm. The non-plated portion 5 is required to have corrosion resistance that can withstand an acidic atmosphere of about pH 2. In the case of the oxide film 4b containing crystalline titanium oxide formed by high-temperature oxidation, the corrosion resistance is generally higher than that of the passive film, but if it is less than 10 nm, it is said to be high temperature (60 to 80 ° C.) and acidic (pH 2). Corrosion resistance in the atmosphere inside the fuel cell is not sufficient. In addition, when heat treatment is performed under conditions (high temperature and long time) in which the oxide film 4b containing crystalline titanium oxide in the non-plated portion 5 exceeds 100 nm, oxygen flows into the interface between the plating layer 3 and the substrate 2 and the plating layer 3 There is a possibility that the oxide film 4a containing crystalline titanium oxide between the substrate 2 and the substrate 2 becomes thick and the conductivity is deteriorated.
Therefore, the oxide film 4b containing crystalline titanium oxide formed on the non-plated portion 5 is preferably in the range of 10 to 100 nm.

  The film thickness of the oxide film 4b containing crystalline titanium oxide is controlled by adjusting the temperature and time during the heat treatment. The thickness of the oxide film 4a containing crystalline titanium oxide between the plating layer 3 and the substrate 2 and the thickness of the oxide film 4b containing crystalline titanium oxide formed on the non-plated portion 5 were measured by cross-sectional TEM observation. It can be carried out.

  The precipitation amount of Au and / or Pt on the surface of the substrate 2 can be measured using SEM / EDX. Here, when the SEM / EDX analysis is performed under the conditions of an acceleration voltage of 20 kV and a magnification of 50 times (field of view: approximately 2 × 1.5 mm), the precipitation amount of Au or Pt is 0.1 to 5.0 at%. Is preferable, and it is more preferable to set it as 1.0-3.0 at%.

  Here, when the precipitation amount of Au and / or Pt is 1.0 to 5.0 at%, the plating layer 3 has a substantially layered structure. When such a structure is used, the heat treatment causes the passivation film to become thin or disappear as described above, and good conductivity can be obtained. Furthermore, since the oxide film 4b containing crystalline titanium oxide is formed in a portion where the substrate 2 is exposed, such as a pinhole portion, the corrosion resistance is improved, and metal elution from the substrate 2 does not occur even in an acidic atmosphere. Conductivity is stably maintained.

  When the Au and / or Pt deposition amount is less than about 1.0 at%, the plating layer 3 has a structure in which noble metal particles of Au and / or Pt are scattered in an island shape on the substrate 2. Even in an island shape, if noble metal particles are present at a certain density or higher, it is possible to ensure conductivity. However, when the precipitation amount of Au and / or Pt is less than 0.1 at%, the noble metal particles are small and sparsely exist. When the noble metal particles are small, the oxide film 4a containing crystalline titanium oxide flows between the noble metal particles and the substrate 2 during the heat treatment after the plating process, and the oxide film 4a containing crystalline titanium oxide is likely to grow. As a result, conductivity cannot be secured.

On the other hand, there is no upper limit on the amount of precipitation of Au and / or Pt to be measured, but it is preferably 5.0 at% or less from the viewpoint of cost.
Therefore, judging from the aspects of conductivity, cost, etc., the precipitation amount of Au and / or Pt is preferably 0.1 to 5.0 at%, more preferably 1.0 to 3.0 at%. preferable.

Next, the fuel cell according to the present invention will be described with reference to the drawings as appropriate.
As shown in FIG. 5, the fuel cell 20 according to the present invention is manufactured using the above-described fuel cell separator 1 according to the present invention, and can be manufactured as follows.
For example, a predetermined number of substrates 2 made of Ti or Ti alloy are prepared, and the predetermined number of substrates 2 is set to a predetermined size of 95.2 mm in length × 95.2 mm in width × 19 mm in thickness, and the surface of the substrate 2 For example, a recess having a groove width of 0.6 mm and a groove depth of 0.5 mm is formed in the central portion by machining or etching to form a gas flow path 11 having a shape as shown in FIG.

  Then, after ultrasonically cleaning the substrate 2 in which the recesses are formed with an organic solvent such as acetone, the passive film on the surface of the substrate 2 is removed using a nitric hydrofluoric acid aqueous solution that is a mixed aqueous solution of hydrofluoric acid and nitric acid. Then, the plating layer 3 containing Au and / or Pt is formed on the substrate 2 using a commercially available plating solution. Thus, the board | substrate 2 in which the plating layer 3 was formed is put into a heat treatment furnace, the heat processing which heats at 500 degreeC for 5 minute (s) is performed, and the separator 1 for fuel cells 1 is manufactured.

  Note that productivity can be improved by preparing a large number of substrates 2 in advance and collectively forming the plating layer 3 and performing heat treatment. Further, since Au or Pt is used as a noble metal, it is not necessary to draw a vacuum, and heat treatment can be performed with an oxygen partial pressure at atmospheric pressure, so that productivity can be further improved.

  Next, as shown in FIG. 5, for example, two fuel cell separators 1 that are manufactured in a predetermined number are disposed so that the surfaces on which the gas flow paths 11 are formed face each other, and the gas flow paths 11 are formed. A gas diffusion layer 12 such as carbon cloth C for uniformly diffusing the gas on the film is disposed on each surface, and a platinum catalyst is placed on the surface between one gas diffusion layer 12 and the other gas diffusion layer 12. The single cell 10 is produced with the solid polymer film 13 applied therebetween. Similarly, by stacking a plurality of unit cells 10 to form a cell stack (not shown) and attaching and connecting other predetermined parts necessary for the fuel cell, it has good corrosion resistance and conductivity. The fuel cell (solid polymer fuel cell) 20 according to the present invention having the characteristics can be produced.

  The solid polymer membrane 13 used in the fuel cell 20 can be used without particular limitation as long as it has a function of moving protons generated at the cathode electrode to the anode electrode. A fluorine-based polymer film having a group can be preferably used.

  The fuel cell 20 thus manufactured introduces fuel gas (for example, hydrogen gas with a purity of 99.999%) into the fuel cell separator 1 arranged as an anode electrode through the gas flow path 11. Air is introduced into the fuel cell separator 1 arranged as the cathode electrode through the gas flow path 11. At this time, the fuel cell 20 is preferably heated and kept at about 80 ° C., and the dew point temperature is preferably adjusted to 80 ° C. by passing the hydrogen gas and air through the heated water. The fuel gas (hydrogen gas) and air may be introduced at a pressure of 2026 hPa (2 atm), for example.

The fuel cell 20 is uniformly supplied to the solid polymer film 13 by the gas diffusion layer 12 by introducing hydrogen gas into the anode electrode in this way, and the solid polymer film 13 uses the following formula (1). Reaction occurs.
H ₂ → 2H ⁺ + 2e ⁻ (1)
On the other hand, the fuel cell 20 is uniformly supplied to the solid polymer film 13 by the gas diffusion layer 12 by introducing air into the cathode electrode, and the reaction of the following formula (2) is performed in the solid polymer film 13. Arise.
4H ⁺ + O ₂ + 4e ⁻ → H ₂ O (2)
As described above, the reaction of the above formulas (1) and (2) occurs in the solid polymer film 13, so that a voltage of about 1.2V is theoretically obtained.

  Here, as described above, the fuel cell 20 according to the present invention uses the fuel cell separator 1 according to the present invention in which the plating layer 3 containing a noble metal of Au and / or Pt is formed. Compared with a fuel cell using a conventional metal separator, it is possible to have good corrosion resistance and conductivity.

  Next, the fuel cell separator manufacturing method, fuel cell separator, and fuel cell of the present invention will be described in detail by comparing an example that satisfies the requirements of the present invention with a comparative example that does not satisfy the requirements of the present invention. To do.

<Example A>
A Ti substrate (width 2 cm × 5 cm, thickness 1 mm) made of one kind of pure Ti as defined in JIS H 4600 was ultrasonically cleaned with acetone, and then the substrate was mixed with hydrofluoric acid and nitric acid (0. The substrate was dipped in 5% hydrofluoric acid and 4% nitric acid for 5 minutes at room temperature to remove the passive film on the substrate surface. Thereafter, a plating process was performed for 20 seconds in a commercially available Au plating solution or Pt plating solution under conditions of room temperature and a current density of 6 A / dm ² . Thereafter, the substrate on which the Au or Pt plating layer was formed was heat-treated at 250, 300, 500, 700, 800, and 850 ° C. for 5 minutes in the air. The test plate 9 was not heat-treated.

(1) About these test plates 1-13, the initial contact resistance of the test plate was measured with the load 98N (10 kgf) using the contact resistance measuring apparatus 30 shown in FIG. That is, each of the test plates 1 to 13 is sandwiched between carbon cloths C and C, and the outside is pressurized with 98 N using copper electrodes 31 and 31 having a contact area of 1 cm ² , and a direct current power source 32 is used. 1A was energized, the voltage applied between the carbon cloths C and C was measured with a voltmeter 33, and the contact resistance was calculated.
(2) Further, after each of the test plates 1 to 13 was immersed in an aqueous sulfuric acid solution (pH 2) at 80 ° C. for 1000 hours, the contact resistance was measured again in the same manner as described above. In addition, the initial stage of (1) and the contact resistance of (2) made 15 mΩ · cm ² or less acceptable.

Table 1 shows the results of (1) initial contact resistance and (2) contact resistance after being immersed in an aqueous sulfuric acid solution (pH 2) at 80 ° C. for 1000 hours (after 1000 hours of sulfuric acid immersion).
In Table 1, the thickness of the oxide film containing crystalline titanium oxide between the plating layer and the substrate and the thickness of the oxide film containing crystalline titanium oxide in the non-plated portion were 750,000 times and 1.5 million by cross-sectional TEM observation. The measurement was conducted by observing at double magnification.
Further, the amount of precious metal deposited on the surface of the Ti substrate was measured by SEM / EDX analysis. The measurement conditions were an acceleration voltage of 20 kV and a magnification of 50 times (field of view 2 × 1.5 mm). The measurement was performed at five locations on the substrate surface, and the average of these values was used as the amount of precious metal deposited.

From the results shown in Table 1, the test plates 1 to 8 were prepared in a thermal processing temperature range of the present invention, the initial contact resistance is at 15mΩ · cm ² or less, even 15mΩ · cm ² The following values after acid immersion for 1000 hours Since it maintained, it turned out that it is excellent in electroconductivity and acid resistance (corrosion resistance).

On the other hand, the test plate 9 not subjected to heat treatment and the test plates 10 and 12 having a heat treatment temperature of 250 ° C. had an initial contact resistance as low as 4.2 to 5.6 mΩ · cm ² , but after 1000 hours of sulfuric acid immersion, It rose remarkably and became a value of 50 mΩ · cm ² or more. This is because the non-plated portion of the titanium oxide layer is not formed to a sufficient thickness, and crystallization does not proceed below 300 ° C., and remains amorphous after heat treatment, and is a crystalline titanium oxide with high corrosion resistance. This is presumably because the acid resistance (corrosion resistance) was insufficient although the initial contact resistance did not decrease because the oxide film did not contain.

Further, the test plates 11 and 13 having a heat treatment temperature of 850 ° C. have an oxide film containing crystalline titanium oxide between the plating layer and the substrate and an oxide film containing crystalline titanium oxide in the non-plated portion being too thick, The initial contact resistance was higher than 15 mΩ · cm ² . The increase in the contact resistance value after 1000 hours of immersion in sulfuric acid is less than that of the test plates 10 and 12, which is considered to be because the oxide film containing crystalline titanium oxide in the non-plated portion is thick.

<Example B>
A Ti substrate (width 2 cm × 5 cm, thickness 1 mm) made of one kind of pure Ti as defined in JIS H 4600 was ultrasonically cleaned with acetone, and then the substrate was mixed with hydrofluoric acid and nitric acid (0. The substrate was dipped in 5% hydrofluoric acid and 4% nitric acid for 5 minutes at room temperature to remove the passive film on the substrate surface. Then, in a commercial Au plating solution or Pt plating solution, at room temperature, the plating treatment at a current density of 6A / dm ² was carried out. The plating amount on the substrate surface was adjusted by changing the plating treatment time as shown in Table 2 with a constant current density. Thereafter, the substrate on which the Au or Pt plating layer was formed was heat-treated at 500 ° C. for 5 minutes in the air.

(1) About these test plates 14-23, the initial contact resistance of the test plate was measured with the load 98N (10 kgf) using the contact resistance measuring apparatus 30 shown in FIG. The measurement method of contact resistance was performed according to <Example A>.
(2) Further, after each of the test plates 14 to 23 was immersed in an aqueous sulfuric acid solution (pH 2) at 80 ° C. for 1000 hours, the contact resistance was measured again in the same manner as described above. In addition, the initial stage of (1) and the contact resistance of (2) made 15 mΩ · cm ² or less acceptable.

Table 2 shows the results of (1) initial contact resistance and (2) contact resistance after being immersed in an aqueous sulfuric acid solution (pH 2) at 80 ° C. for 1000 hours (after 1000 hours of sulfuric acid immersion).
In Table 2, the thickness of the oxide film containing crystalline titanium oxide between the plating layer and the substrate, and the thickness of the oxide film containing crystalline titanium oxide in the non-plated portion were 750,000 times and 1.5 million by cross-sectional TEM observation. The measurement was conducted by observing at double magnification.
Further, the amount of precious metal deposited on the surface of the Ti substrate was measured by SEM / EDX analysis. The measurement conditions were an acceleration voltage of 20 kV and a magnification of 50 times (field of view 2 × 1.5 mm). The measurement was performed at five locations on the substrate surface, and the average of these values was used as the amount of precious metal deposited.

From the results shown in Table 2, the test plates 14 to 21 have an initial contact resistance of 15 mΩ · cm ² or less, and maintain a value of 15 mΩ · cm ² or less even after being immersed in a sulfuric acid aqueous solution (pH 2) at 80 ° C. for 1000 hours. Therefore, it was found that the material is excellent in conductivity and acid resistance (corrosion resistance).

On the other hand, in the test plates 22 and 23 in which the adhesion amount of Au or Pt is less than 0.1 at%, a thick oxide film containing crystalline titanium oxide is formed between the plating layer after the heat treatment at 500 ° C. for 5 minutes and the substrate. The initial contact resistance was higher than 15 mΩ · cm ² .

<Example C>
Next, in <Example C>, a power generation test was performed in the case of using a separator manufactured using a Ti substrate made of one kind of pure Ti specified in JIS H 4600.
First, two Ti substrates each having a length of 95.2 mm × width of 95.2 mm × thickness of 19 mm are prepared, and a gas having a groove width of 0.6 mm and a groove depth of 0.5 mm is machined at the center of the surface. The flow path was produced in the shape shown in FIG. Then, on the surface of the Ti substrate on which the gas flow path was formed, a separator was produced by performing a plating process for 20 seconds and a heat treatment under the same method and conditions as in <Example B>.

Then, the produced separator was incorporated into a solid polymer fuel cell (manufactured by Electrochem, fuel cell EFC-05-01SP) as follows, and a power generation test was performed.
First, as shown in FIG. 5, the two separators prepared were placed with the surfaces on which the gas flow paths were formed facing each other, and the carbon cloth was placed on each surface on which the gas flow paths were formed. A fuel cell 20 for power generation test was fabricated by sandwiching a solid polymer film between the carbon cloths.

Hydrogen gas having a purity of 99.999% was used as the fuel gas introduced into the anode electrode side of the fuel cell produced as described above, and air was used as the gas introduced into the cathode electrode side.
The entire fuel cell was heated and maintained at 80 ° C., and hydrogen gas and air were passed through heated water to adjust the dew point temperature to 80 ° C. and introduced into the fuel cell at a pressure of 2 atm. .

And using the system for cell performance measurement (890CL by Scripner), the electric current which flows into a separator was 300 mA / cm < ² >, and it was made to generate electric power for 100 hours, and the change of the voltage was measured.
As a result, the initial voltage of the separator of the Ti substrate made of one kind of pure Ti specified in JIS H 4600 and the voltage after power generation for 100 hours are both 0.61 V, and the change in voltage is I was not able to admit.

In addition, as a comparison object, instead of a Ti substrate separator made of pure Ti as defined in JIS H 4600, a conventionally used graphite separator (manufactured by Electrochem, FC-05-MP) is used. A fuel cell was prepared by placing the battery, and a power generation test was performed under the same conditions as described above.
As a result, the voltage at the initial stage of power generation and the voltage after power generation for 100 hours are both 0.61 V, and the result is exactly the same as that of a Ti substrate separator made of one kind of pure Ti specified in JIS H 4600. It became.

  From the above results, it has been found that the fuel cell separator produced by the method for producing a fuel cell separator of the present invention exhibits the same performance as a graphite separator even though it is a metallic separator.

  The fuel cell separator manufacturing method, the fuel cell separator and the fuel cell according to the present invention have been described in detail with reference to the preferred embodiments and examples. However, the gist of the present invention is limited to the contents described above. The scope of rights should be broadly interpreted based on the claims. Needless to say, the contents of the present invention can be widely modified and changed based on the above description.

It is a flowchart explaining the process of the manufacturing method of the separator for fuel cells which concerns on this invention. It is sectional drawing of the separator for fuel cells which concerns on this invention. It is explanatory drawing explaining the measuring method of contact resistance. It is a figure which shows an example of the shape of the gas flow path formed in the surface of a board | substrate. It is a figure which shows a mode that a part of fuel cell using the separator for fuel cells of this invention was expand | deployed.

Explanation of symbols

S1 Concave formation step S2 Plating layer formation step S3 Heat treatment step 1 Fuel cell separator 2 Substrate 3 Plating layer 4a, 4b Oxide film containing crystalline titanium oxide 5 Non-plated portion 10 Single cell 11 Gas flow path 12 Gas diffusion layer 13 Solid polymer membrane 20 Fuel cell

Claims (7)

A recess forming step for forming a recess for forming a gas flow path for flowing gas on at least a part of the surface of the substrate as a fuel cell separator made of Ti or Ti alloy;
A plating layer forming step of forming at least one plating layer containing Au and / or Pt noble metal by electroplating on the surface of the substrate on which the recess is formed;
A heat treatment step of heat treating the substrate on which the plating layer is formed in the plating layer forming step at a heat treatment temperature of 300 to 800 ° C .;
The manufacturing method of the separator for fuel cells characterized by including these. A recess forming step for forming a recess for forming a gas flow path for flowing gas on at least a part of the surface of the substrate as a fuel cell separator made of Ti or Ti alloy;
A plating layer forming step of forming at least one plating layer containing Au and / or Pt noble metal by electroplating on the surface of the substrate on which the recess is formed;
The substrate on which the plating layer is formed in the plating layer forming step is heat-treated at a heat treatment temperature of 300 to 800 ° C., and crystalline titanium oxide is applied to a portion of the surface of the substrate where plating by the plating layer does not exist. A heat treatment step for forming an oxide film including:
The manufacturing method of the separator for fuel cells characterized by including these.   A fuel cell separator manufactured by the method for manufacturing a fuel cell separator according to claim 1.   A surface of a substrate as a fuel cell separator made of Ti or Ti alloy in which a recess for forming a gas flow path for allowing gas to flow through at least a part of the surface contains a noble metal such as Au and / or Pt. A separator for a fuel cell, wherein an oxide film containing crystalline titanium oxide is formed on a portion of the surface of the substrate where plating by the plating layer does not exist.   The thickness of the oxide film containing crystalline titanium oxide present at the interface between the plating layer and the substrate is 10 nm or less, and is formed in a portion where the plating by the plating layer does not exist on the surface of the substrate. The fuel cell separator according to claim 4, wherein the thickness of the oxide film containing crystalline titanium oxide is 10 to 100 nm.   4. The precipitation amount of Au and / or Pt when SEM / EDX analysis is performed under the conditions of an acceleration voltage of 20 kV and a magnification of 50 times is 0.1 to 5.0 at%. The fuel cell separator according to claim 5.   A fuel cell comprising the fuel cell separator according to any one of claims 3 to 6.

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