JP2009104932A - Fuel cell separator and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell separator improved in adhesion between a separator substrate and a conductive layer. <P>SOLUTION: The fuel cell separator 22 to separate gas between adjoining fuel battery cells comprises: a separator substrate 24 formed by a titanium material or stainless steel; an oxide layer 26 which is formed on the separator substrate 24 and composed of a titanium oxide or a chromium oxide; and a conductive layer 28 which is formed on the oxide layer and composed of gold (Au) and the like. The oxide layer 26 is preferably formed by oxidizing the separator substrate 24. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fuel cell separator and a method for manufacturing the same, and more particularly to a fuel cell separator for separating gas between adjacent fuel cell cells and a method for manufacturing the same.

  In recent years, fuel cells have attracted attention as batteries having high efficiency and excellent environmental characteristics. 2. Description of the Related Art In general, a fuel cell generates electric energy by electrochemically reacting hydrogen, which is a fuel gas, with oxygen in the air, which is an oxidant gas. As a result of the electrochemical reaction between hydrogen and oxygen, water is generated.

  Types of fuel cells include phosphoric acid type, molten carbonate type, solid electrolyte type, alkali type, and solid polymer type. Among these, solid polymer fuel cells that have advantages such as startup at normal temperature and quick startup time have been attracting attention. Such a polymer electrolyte fuel cell is used as a power source for a moving body, for example, a vehicle.

  A polymer electrolyte fuel cell is assembled by laminating a plurality of single cells, current collector plates, end plates, and the like. The fuel cell includes an electrolyte membrane, a catalyst layer, a gas diffusion layer, and a separator.

  Patent Document 1 discloses a fuel cell gas separator and the like, and a base material portion obtained by laminating a base material plate formed of a stainless steel plate has a first coat layer which is a tin plating layer on the surface thereof. It is described that the first coat layer is further covered with a second coat layer made of thermally expanded graphite, and the gas separator for a fuel cell is provided with sufficient corrosion resistance by the second coat layer.

JP 2000-138067 A

  By the way, when manufacturing a separator for a fuel cell with a metal material such as titanium, generally, a conductive material such as gold (Au) having high electrical conductivity is plated on the surface to form a gas diffusion layer or the like. The contact resistance between them is reduced. Here, if the separator substrate made of titanium or the like is directly plated with a conductor such as gold (Au), the conductive layer peels off because the adhesion between the conductive layer formed of the conductor and the separator substrate is weak. There is a case.

  Accordingly, an object of the present invention is to provide a fuel cell separator and a method for producing the same, in which the adhesion between the separator substrate and the conductive layer is further improved.

  A fuel cell separator according to the present invention is a fuel cell separator that separates gas between adjacent fuel cell cells, and is formed on a separator substrate formed of a titanium material or stainless steel, and the separator substrate. It has an oxide layer and a conductive layer formed on the oxide layer.

  In the fuel cell separator according to the present invention, the oxide layer is formed by oxidizing the surface of the separator substrate.

  In the fuel cell separator according to the present invention, the separator base is formed of a titanium material, and the oxide layer is formed of titanium oxide.

  In the fuel cell separator according to the present invention, the thickness of the oxide layer formed of titanium oxide is 2 nm or more and 400 nm or less.

  In the fuel cell separator according to the present invention, the separator base is formed of stainless steel, and the oxide layer is formed of chromium oxide.

  In the fuel cell separator according to the present invention, the conductive layer is formed of gold.

  In the fuel cell separator according to the present invention, the conductive layer formed of gold has a thickness of 2 nm to 100 nm.

  A fuel cell separator manufacturing method according to the present invention is a fuel cell separator manufacturing method for separating gas between adjacent fuel cell cells, wherein the separator substrate is formed of titanium material or stainless steel. It has a shaping | molding process, the oxide layer formation process which forms an oxide layer in a separator base | substrate, and the conductive layer formation process which forms a conductive layer on an oxide layer, It is characterized by the above-mentioned.

  In the method for manufacturing a separator for a fuel cell according to the present invention, the oxide layer forming step is characterized by oxidizing the surface of the separator substrate to form an oxide layer.

  As described above, according to the fuel cell separator and the method for manufacturing the same according to the present invention, the adhesion between the separator substrate and the conductive layer is further improved by providing the oxide layer between the separator substrate and the conductive layer. be able to.

  Embodiments according to the present invention will be described below in detail with reference to the drawings. First, the configuration of the fuel cell unit will be described. FIG. 1 is a view showing a cross section of a fuel cell 10. A fuel cell 10 includes a membrane electrode assembly 18 (MEA) that forms an electrode of a fuel cell by integrating an electrolyte membrane 12, a catalyst layer 14, and a gas diffusion layer 16, and a gas flow path. The expanded molded body 20 that is a gas flow path structure that forms a gas and a separator 22 that separates fuel gas or oxidant gas between adjacent cells (not shown).

  The electrolyte membrane 12 has a function of moving hydrogen ions generated on the anode electrode side to the cathode electrode side. As the material of the electrolyte membrane 12, a chemically stable fluorine-based resin, for example, an ion exchange membrane of perfluorocarbon sulfonic acid is used.

  The catalyst layer 14 has a function of promoting a hydrogen oxidation reaction on the anode electrode side and an oxygen reduction reaction on the cathode electrode side. The catalyst layer 14 includes a catalyst and a catalyst carrier. In order to increase the electrode area to be reacted, the catalyst is generally used in the form of particles and attached to the catalyst support. As the catalyst, platinum, which is a platinum group element having a smaller activation overvoltage, is used for the oxidation reaction of hydrogen and the reduction reaction of oxygen. As the catalyst carrier, a carbon material such as carbon black is used.

  The gas diffusion layer 16 has a function of diffusing hydrogen gas, which is a fuel gas, and air, which is an oxidant gas, into the catalyst layer 14, a function of moving electrons, and the like. The gas diffusion layer 16 is made of carbon fiber woven fabric, carbon paper or the like, which is a conductive material.

  The expanded molded body 20 is laminated on both surfaces of the membrane electrode assembly 18 and has a function as a gas flow path structure that forms a gas flow path. The expanded molded body 20 is laminated in contact with the gas diffusion layer 16 of the membrane electrode assembly 18 and the separator 22, and is electrically connected to the membrane electrode assembly 18 and the separator 22. Since the expanded molded body 20 has a mesh structure composed of a large number of openings, more fuel gas or the like comes into contact with the membrane electrode assembly 18 and chemically reacts to increase the power generation efficiency of the fuel cell 10. Can do.

For the expanded molded body 20, for example, an expanded metal shown in JIS G 3351, a metal lath or a metal porous body shown in JIS A 5505, or the like is used. The expanded molded body 20 is preferably molded from titanium or a titanium alloy titanium material, stainless steel such as SUS316L or SUS304, or the like. These metal materials have high mechanical strength and are inert on the surface such as passive films made of stable oxides (TiO, Ti ₂ O ₃ , TiO ₂ , CrO ₂ , CrO, Cr ₂ O _3, etc.). This is because the film is formed and thus has excellent corrosion resistance. As the stainless steel, austenitic stainless steel, ferritic stainless steel, or the like can be used.

  The separator 22 is stacked on the expanded molded body 20 and has a function of separating fuel gas and oxidant gas in an adjacent cell (not shown). The separator 22 has a function of electrically connecting adjacent cells (not shown). The separator 22 includes a separator base 24 formed of titanium material or stainless steel, an oxide layer 26 formed on the separator base 24, and a conductive layer 28 formed on the oxide layer 26. Yes.

  The separator substrate 24 is formed of titanium or a titanium material of titanium alloy, or stainless steel of SUS316L and SUS304. This is because these metal materials have high mechanical strength and have an excellent corrosion resistance because an inert film such as a passive film made of a stable oxide is formed on the surface thereof. As the stainless steel, austenitic stainless steel, ferritic stainless steel, or the like can be used.

The oxide layer 26 is preferably composed of an oxide formed by oxidizing the surface of the separator substrate 24. This is because the oxide formed by oxidizing the surface of the separator substrate 24 is excellent in adhesion to the separator substrate 24. When the separator substrate 24 is formed of a titanium material, the oxide layer 26 is preferably formed of titanium oxide (TiO, Ti ₂ O ₃ , TiO ₂ or the like). When the separator base 24 is formed of stainless steel, the oxide layer 26 is preferably formed of chromium oxide (CrO ₂ , CrO, Cr ₂ O _3, etc.). Of course, depending on other conditions, the oxide layer 26 may be composed of an oxide other than the oxide formed by oxidizing the surface of the separator substrate 24.

  The conductive layer 28 is formed of a metal material such as gold (Au), silver (Ag), copper (Cu), platinum (Pt), rhodium (Rh), iridium (Ir), palladium (Pd), which is a conductor. The This is because these metal materials have high electrical conductivity, so that the contact resistance can be further reduced. Among these metal materials, gold (Au) is preferable as a metal material for forming the conductive layer 28 because it is excellent in corrosion resistance and has high electric conductivity. The conductive layer 28 may be formed of an alloy such as gold (Au) or platinum (Pt).

  Next, a method for manufacturing the fuel cell separator 22 will be described.

  FIG. 2 is a flowchart showing a method for manufacturing the separator 22. The manufacturing method of the separator 22 includes a separator substrate forming step (S10), a cleaning step (S12), a neutralization step (S14), a pickling step (S16), an oxide layer forming step (S18), And a layer forming step (S20).

  The separator substrate forming step (S10) is a step of forming the separator substrate 24 by processing a titanium material or stainless steel. The separator base 24 is formed by, for example, rolling a titanium material or stainless steel. Generally, a processing apparatus used for a rolling process or a press process of a metal material is used as a processing apparatus for titanium material or stainless steel.

  The cleaning step (S12) is a step of cleaning the separator substrate 24. The separator substrate 24 is cleaned by, for example, alkali dipping degreasing. An alkaline solution such as caustic soda is used for the alkaline immersion degreasing. By washing the separator substrate 24 by alkali immersion degreasing or the like, oil or the like attached to the surface of the separator substrate 24 is removed.

  The neutralization step (S14) is a step of neutralizing and removing the alkaline solution remaining on the separator substrate 24 after washing. The neutralization treatment is performed by immersing the separator substrate 24 after washing in a neutralization solution. As the neutralizing solution, a sulfuric acid solution, a hydrochloric acid solution, a nitric acid solution, or the like is used. Then, the separator substrate 24 taken out from the neutralized solution is washed with deionized water or the like.

  The pickling step (S <b> 16) is a step of pickling the separator substrate 24 that has been subjected to neutralization or the like to remove oxide from the surface of the separator substrate 24. Before the oxide layer forming step (S18), which will be described later, the oxide generated during the molding process is removed from the surface of the separator base 24, so that in the oxide layer forming step (S18), the oxide layer 26 is further removed. It can be formed uniformly. The pickling treatment is performed by immersing the separator substrate 24 in a solution containing fluoride such as a nitric hydrofluoric acid solution or a hydrofluoric acid solution. When the separator substrate 24 is immersed in a solution containing fluoride, the oxide generated on the surface of the separator substrate 24 is etched. The separator substrate 24 taken out of the fluoride-containing solution is washed with deionized water or the like.

  The oxide layer forming step (S18) is a step of forming the oxide layer 26 on the separator substrate 24 that has been pickled. The oxide layer 26 is preferably formed by drying the separator substrate 24 with hot air or firing. This is because the surface of the separator substrate 24 is oxidized and the oxide layer 26 is formed, so that the adhesion between the separator substrate 24 and the oxide layer 26 is improved. For example, a hot gun or the like is used for hot air drying of the separator substrate 24. Further, for firing the separator substrate 24, for example, a general firing furnace or the like is used. The oxide layer 26 is formed to have a predetermined thickness by adjusting the hot air drying temperature, the hot air drying time, the firing temperature, the firing time, and the like. Of course, depending on other conditions, the oxide layer 26 may be formed on the separator substrate 24 by sputtering, ion plating, or the like.

  When the separator substrate 24 is formed of a titanium material, the thickness of the titanium oxide layer 26 is preferably 2 nm or more and 400 nm or less. This is because when the thickness of the titanium oxide layer 26 is smaller than 2 nm, sufficient adhesion between the separator substrate 24 and the conductive layer 28 cannot be obtained. Further, when the thickness of the titanium oxide layer 26 is smaller than 2 nm, the corrosion resistance (oxidation resistance) of Ti is inferior. And when the thickness of the titanium oxide layer 26 is larger than 400 nm, the contact resistance of the separator increases and the electrical conductivity decreases.

  The conductive layer forming step (S20) is a step of forming the conductive layer 28 on the oxide layer 26. The conductive layer 28 is formed by coating a conductor such as gold (Au). For the coating of gold (Au) or the like, for example, an electrolytic plating method can be used. A gold plating bath containing potassium gold cyanide, sodium gold sulfite, or the like is used for the electrolytic plating method of gold (Au). In addition, an acidic, neutral or alkaline plating bath is used as the gold plating bath. The conductive layer 28 is formed to a predetermined thickness by adjusting the plating time and the like. Of course, depending on other conditions, the conductive layer 28 may be formed by a coating method, an inkjet method, or the like.

  When the conductive layer 28 is formed of gold, the thickness of the conductive layer 28 is preferably 2 nm or more and 100 nm or less. This is because when the thickness of the conductive layer 28 is smaller than 2 nm, the contact resistance of the separator increases. Further, when the thickness of the conductive layer 28 is larger than 100 nm or less, the manufacturing cost increases because the conductive layer 28 is formed of expensive gold. In addition, when the conductive layer 28 is formed of gold, the thickness of the conductive layer 28 is more preferably 2 nm or more and 20 nm or less. Thus, the manufacture of the fuel cell separator 22 is completed.

  According to the above configuration, by providing the oxide layer between the separator base and the conductive layer, adhesion between the separator base and the conductive layer is improved, so that peeling of the conductive layer can be suppressed.

  According to the said structure, the adhesiveness of a separator base | substrate and an oxide layer can be improved more by oxidizing the surface of a separator base | substrate and forming an oxide layer.

(Example)
A separator specimen was prepared by changing the film thickness of the oxide layer, and the electrical conductivity was evaluated.

  First, a method for producing a separator specimen will be described. A pure titanium material was roll-rolled to form a titanium sheet. The titanium sheet was degreased by alkali soaking and washed to remove oil adhering to the titanium sheet. The titanium sheet washed with alkali degreasing was neutralized by dipping in a sulfuric acid solution. Next, the titanium sheet was dipped in a nitric hydrofluoric acid solution and pickled, and the oxide formed on the surface of the titanium sheet was removed by etching.

The surface of the pickled titanium sheet was oxidized to form a titanium oxide layer (TiO ₂ layer). The thickness of the titanium oxide layer was in the range of 2 nm to 800 nm. The titanium oxide layer was formed by changing the temperature and time by hot air drying or firing. For example, when the thickness of the titanium oxide layer is 2 nm, hot air drying is performed at 60 ° C. to 80 ° C. for 5 seconds. When the titanium oxide layer is formed with a thickness of 400 nm, baking is performed at 300 ° C. for 30 minutes, and when the titanium oxide layer is formed with a thickness of 800 nm, baking is performed at 600 ° C. for 30 minutes. went. And the gold plating layer which is a conductive layer was formed on the titanium oxide layer. The gold plating layer was formed by an electrolytic plating method using an alkaline gold plating bath. The thickness of the gold plating layer was set to 10 nm for all separator specimens.

  The contact resistance of the produced separator specimen was measured. FIG. 3 is a diagram illustrating a method for measuring contact resistance. After the gas diffusion layer material 32 was attached to the metal jig 30, a separator specimen as a test piece 34 was sandwiched between the two gas diffusion layer materials 32, and a predetermined surface pressure was applied to bring them into close contact. The voltage between the test piece 34 and the gas diffusion layer material 32 when a current of 1 A was passed was measured to determine the contact resistance.

FIG. 4 is a graph showing measurement results of contact resistance in the separator specimen. As shown in FIG. 4, the horizontal axis represents the thickness (nm) of the titanium oxide layer, the vertical axis represents the contact resistance (mΩ · cm ² ), and the contact resistance value for each film thickness is indicated by a black rhombus. . In the separator specimen in which the thickness of the titanium oxide layer was larger than 400 nm, the contact resistance rapidly increased. A separator specimen having a titanium oxide layer thickness of 2 nm or more and 400 nm or less exhibited a low contact resistance and good electrical conductivity. Note that the thickness of the titanium oxide layer is preferably 2 nm to 200 nm, and more preferably 2 nm to 10 nm. By setting the film thickness of the titanium oxide layer in the above range, the contact resistance can be further reduced and the electrical conductivity can be further increased while ensuring the inherent corrosion resistance (oxidation resistance) of Ti.

  Next, a separator specimen was prepared by changing the film thickness of the conductive layer, and the electrical conductivity was evaluated.

  First, a method for producing a separator specimen will be described. A separator specimen was produced by the same method as the production method described above. However, the titanium oxide layer was formed to 8 nm by oxidizing the surface of the titanium sheet by hot air drying. Then, a gold plating layer was formed on the titanium oxide layer by an electrolytic plating method using an alkaline gold plating bath. The film thickness of the gold plating layer was 2 nm to 20 nm.

The contact resistance of the produced separator specimen was measured. The contact resistance was measured by the contact resistance measuring method shown in FIG. FIG. 5 is a graph showing the results of contact resistance measurement in the separator specimen. As shown in FIG. 5, the horizontal axis represents the film thickness (nm) of the gold plating layer, the vertical axis represents the contact resistance (mΩ · cm ² ), and the contact resistance value for each film thickness is indicated by a black square. As is clear from FIG. 5, the contact resistance of the separator specimens produced with any film thickness was small and good electrical conductivity was obtained. Further, when the thickness of the gold plating layer was larger than 10 nm, the rate of decrease in contact resistance was reduced. Since gold is expensive, it is preferable in terms of manufacturing cost to form a gold plating layer with a thickness of 10 nm or less.

Next, the cross section of the separator specimen was observed. The separator specimen for cross-sectional observation was prepared by the same method as the separator specimen described above, with the titanium oxide layer having a thickness of 8 nm and the gold plating layer having a thickness of 80 nm. The cross section of the separator specimen was observed with a transmission electron microscope (TEM). FIG. 6 is a photograph showing a transmission electron microscope image of a cross section of the separator specimen. As shown in FIG. 6, it was observed that the TiO ₂ layer is formed is titanium oxide layer between the gold plating layer and a titanium sheet.

  Next, two types of fuel cell separators were manufactured, and adhesion and corrosion resistance were evaluated.

First, the manufacturing method of the separator in Example 1 is demonstrated. Pure titanium was used as the metal material for forming the separator substrate. A pure titanium material was roll-rolled to form a titanium sheet. The titanium sheet was washed by alkali soaking and degreasing, and the alkali degreasing washed titanium sheet was soaked in a sulfuric acid solution for neutralization. Next, the titanium sheet was dipped in a nitric hydrofluoric acid solution and pickled, and the oxide formed on the surface of the titanium sheet was removed by etching. A titanium oxide layer (TiO ₂ layer) was formed by oxidizing the titanium sheet by hot air drying at 60 ° C. to 80 ° C. to form 8 nm. And the gold plating layer which is a conductive layer was formed on the titanium oxide layer. The film thickness of the gold plating layer was 10 nm. The gold plating layer was formed by an electrolytic plating method using an alkaline gold plating bath.

The manufacturing method of the separator in the comparative example 1 is demonstrated. The separator in Comparative Example 1 was manufactured by the same manufacturing method as that of the separator of Example 1 except that the titanium oxide layer (TiO ₂ layer) was not formed on the titanium sheet.

An adhesion test was performed on the manufactured separator. The separator adhesion test was performed in accordance with JIS standards. FIG. 7 is a graph showing the separator adhesion test results. As shown in FIG. 7, the horizontal axis indicates the type of separator, the vertical axis indicates the adhesion strength (N / cm ² ), and the adhesion strength of each separator is indicated by a bar graph. As is clear from FIG. 7, the adhesion strength of the separator of Example 1 was higher than the adhesion strength of the separator of Comparative Example 1. By providing the titanium oxide layer between the titanium sheet and the gold plating layer, the adhesion between the titanium sheet and the gold plating layer was improved.

  Next, a method for evaluating the corrosion resistance of the separator will be described. The separator was evaluated for corrosion resistance by measuring the contact resistance after the corrosion test. The corrosion test was conducted in accordance with the electrochemical high temperature corrosion test method for metal materials specified in JIS Z 2294. FIG. 8 is a diagram showing a test apparatus used in an electrochemical high temperature corrosion test. The test was conducted in an open air system. The solution used for the test was a sulfuric acid solution. The temperature of the test solution was 50 ° C. Then, a corrosion test was performed by applying a constant potential for 100 hours. After the corrosion test, the contact resistance was measured by the contact resistance measuring method shown in FIG.

FIG. 9 is a graph showing the contact resistance measurement results after the corrosion test on the separator. As shown in FIG. 9, the horizontal axis indicates the type of separator, the vertical axis indicates the contact resistance (mΩ · cm ² ), and the contact resistance after 100 hours of corrosion test in each separator is indicated by a black diamond. The contact resistance of the separator in Example 1 was lower than the contact resistance of the separator in Comparative Example 1. In the separator in Comparative Example 1, since the titanium oxide layer is not provided between the titanium sheet and the gold plating layer, the contact resistance is reduced due to the deterioration of the adhesion of the gold plating layer and the corrosion of the titanium sheet. Increased and the electrical conductivity decreased. On the other hand, in the separator in Example 1, a decrease in electrical conductivity is suppressed due to the improved adhesion between the titanium sheet and the gold plating layer and the titanium oxide layer functioning as a protective film. Good corrosion resistance was obtained.

In embodiment of this invention, it is a figure which shows the cross section of the cell for fuel cells. In embodiment of this invention, it is a flowchart which shows the manufacturing method of a separator. In embodiment of this invention, it is a figure which shows the measuring method of contact resistance. In embodiment of this invention, it is a graph which shows the measurement result of the contact resistance in a separator test piece. In embodiment of this invention, it is a graph which shows the measurement result of the contact resistance in a separator test piece. In embodiment of this invention, it is a photograph which shows the transmission electron microscope image of the cross section in a separator specimen. In embodiment of this invention, it is a graph which shows the adhesive test result of a separator. In embodiment of this invention, it is a figure which shows the test apparatus used by the electrochemical high temperature corrosion test. In embodiment of this invention, it is a graph which shows the contact resistance measurement result after the corrosion test in a separator.

Explanation of symbols

  10 Fuel Cell, 12 Electrolyte Membrane, 14 Catalyst Layer, 16 Gas Diffusion Layer, 18 Membrane Electrode Assembly, 20 Expanded Molded Body, 22 Separator, 24 Separator Base, 26 Oxide Layer, 28 Conductive Layer, 30 Metal Jig , 32 Gas diffusion layer material, 34 test pieces.

Claims (9)

A fuel cell separator for separating gas between adjacent fuel cell cells,
A separator substrate formed of titanium material or stainless steel;
An oxide layer formed on the separator substrate;
A conductive layer formed on the oxide layer;
A fuel cell separator characterized by comprising: The fuel cell separator according to claim 1,
The fuel cell separator, wherein the oxide layer is formed by oxidizing the surface of the separator substrate. The fuel cell separator according to claim 1 or 2,
A separator for a fuel cell, wherein the separator substrate is formed of a titanium material, and the oxide layer is formed of titanium oxide. The fuel cell separator according to claim 3, wherein
A fuel cell separator, wherein the oxide layer formed of titanium oxide has a thickness of 2 nm to 400 nm. The fuel cell separator according to claim 1 or 2,
A separator for a fuel cell, wherein the separator substrate is formed of stainless steel and the oxide layer is formed of chromium oxide. A fuel cell separator according to any one of claims 1 to 5,
The separator for a fuel cell, wherein the conductive layer is made of gold. The fuel cell separator according to claim 6,
A fuel cell separator, wherein the conductive layer formed of gold has a thickness of 2 nm to 100 nm. A method for manufacturing a fuel cell separator for separating gas between adjacent fuel cell cells,
A separator substrate forming step of forming a separator substrate with titanium material or stainless steel;
An oxide layer forming step of forming an oxide layer on the separator substrate;
A conductive layer forming step of forming a conductive layer on the oxide layer;
The manufacturing method of the separator for fuel cells characterized by having. It is a manufacturing method of the separator for fuel cells according to claim 8,
The oxide layer forming step oxidizes the surface of the separator substrate to form an oxide layer.