Method for manufacturing a fuel cell separator, fuel cell separator and fuel cell

Abstract

The invention relates to a method for producing a fuel cell separator in which corrosion resistance can be improved. A method for producing a fuel cell separator (22) that separates the adjacent cells (10) of a fuel cell from one another, the method comprising the step of subjecting a separator substrate (24) made of a metal material to pre-gold plating, thereby forming a first gold plating layer with a thickness of 10 to 200 nm. Additional gold plating is preferably performed on top of the first gold plating layer formed by the pre-gold plating, thereby forming a second gold plating layer.

Description

Technical area

[0001] The present invention relates to a method for manufacturing a fuel cell separator, a fuel cell separator and a fuel cell, and more particularly relates to a method for manufacturing a fuel cell separator that separates adjacent cells of a fuel cell from each other, a fuel cell separator and a fuel cell. Technical background

[0002] Fuel cells have recently received considerable attention as cells that exhibit high efficiency and excellent ecological performance. In a fuel cell, oxygen in the air, which serves as an oxidizing gas, generally undergoes an electrochemical reaction with hydrogen, which serves as a fuel gas, thereby generating electrical energy. Water is produced as a result of the electrochemical reaction between hydrogen and oxygen.

[0003] Variations of fuel cells include phosphoric acid fuel cells, molten carbonate fuel cells, solid electrolyte fuel cells, alkaline fuel cells, and solid polymer fuel cells. Of these, solid polymer fuel cells receive particular attention because they offer distinct advantages, such as startup at ambient temperature and a short startup time. Such a solid polymer fuel cell can be used as a power source for moving objects, such as vehicles.

[0004] A solid polymer fuel cell is assembled by stacking a plurality of cell units, a current collector, an end plate, and the like. Each cell of the fuel cell includes an electrolyte membrane, a catalyst layer, a gas diffusion layer, and a separator.

[0005] JP S61 - 243 193 A discloses a method for using gold plating to impart excellent soldering and wire bonding properties to stainless steel at low cost, wherein, in a pretreatment, the surface of the stainless steel is strongly activated by subjecting the stainless steel to cathodic electrolysis in electrolysis baths containing an inorganic acid and an organic acid in two separate process steps, so that tiny pinholes and the like do not occur during the gold plating process and the adhesive strength or adhesion of the plating is significantly improved.

[0006] JP 2004 - 71 321 A discloses a metal separator for a fuel cell in which a portion of the stainless steel is plated under the premise that a significant increase in manufacturing costs can be prevented, the separator having excellent contact resistance with the gas diffusion electrode and excellent corrosion resistance that prevents premature shortening of the service life required of a separator, and a conductive inclusion is exposed through the corrosion-resistant surface and the portion of the surface where the conductive inclusion is not exposed is plated with gold.

[0007] JP 2006 - 236 740 A discloses a method for manufacturing a fuel cell in which the anode plate and / or the cathode plate are gold-plated, with the same method being used to form the 0.3 µm-thick layers. A two-step process for applying a gold coating is disclosed in DE 698 20 233 T2. Finally, US Pat. No. 6,203,936 B1 discloses a gold coating with a combined layer thickness of approximately 20 µm. Disclosure of the inventionTask of the invention

[0008] However, in cases where a fuel cell separator is made of a metal material such as titanium, a conductor or conductive element with high electrical conductivity, such as the aforementioned gold, is generally used to coat the separator surface, thereby reducing the contact resistance with the gas diffusion layer and the like. If the coating film of the conductor or conductive element is not densely formed, corrosion of the separator may occur due to fluorine (F) or chlorine (Cl) and the like generated in the fuel cell power generation environment.

[0009] The present invention provides a method for producing a fuel cell separator having significantly improved corrosion resistance, a fuel cell separator, and a fuel cell comprising the fuel cell separator. Means of solving the problem

[0010] The present invention provides a method for manufacturing a fuel cell separator that separates adjacent cells of a fuel cell from each other, the method comprising a step of: subjecting a separator substrate made of a metal material to pre-gold plating, thereby forming a first gold plating layer having a thickness of approximately 10 nm to approximately 200 nm.

[0011] In the above method for manufacturing a fuel cell separator, additional gold plating is further performed on top of the first gold plating layer formed by the pre-gold plating, thereby forming a second gold plating layer with a thickness of approximately 100 nm to approximately 20 µm. The separator substrate is formed from titanium or stainless steel.

[0012] In the above method for manufacturing a fuel cell separator, it is also preferable to form the first gold plating layer with a thickness of not less than approximately 70 nm and not more than approximately 120 nm.

[0013] Furthermore, in the above method for manufacturing a fuel cell separator, the first gold plating layer is preferably formed to a thickness of not less than approximately 70 nm and not more than approximately 100 nm.

[0014] In addition, the present invention also provides a fuel cell separator manufactured using the above method for manufacturing a fuel cell separator.

[0015] Apart from this, the present invention also provides a fuel cell having a fuel cell separator manufactured using the above method for manufacturing a fuel cell separator. Effect of the invention

[0016] As described above, in a method for manufacturing a fuel cell separator according to the present invention and in a fuel cell separator and a fuel cell according to the present invention, corrosion resistance can be further improved because gold can be deposited or formed more densely on the surface of the fuel cell separator. Short description of the drawing Fig. 1 is a diagram showing a cross section of a cell of a fuel cell according to an embodiment of the present invention. Fig. 2 is a flowchart showing a method for manufacturing a separator according to an embodiment of the present invention. Fig. 3A to 3C are schematic diagrams showing the formation of a first gold plating layer of a predetermined thickness on a separator substrate according to an embodiment of the present invention. Fig. 4 is a diagram showing a testing apparatus used in performing a high-temperature electrochemical corrosion test in an embodiment of the present invention. Fig. 5 is a graph showing the results of a corrosion evaluation test in an embodiment of the present invention. Fig. 6 is a graph showing the results of a corrosion resistance evaluation test in an embodiment of the present invention. Fig. 7 is a diagram showing the result of examining a cross-sectional area of ​​a separator test piece of Comparative Example 1 in an embodiment of the present invention. Fig. 8 is a diagram showing the result of examining a cross-sectional area of ​​a separator test piece of Example 1 in an embodiment of the present invention. List of reference symbols 10 cells of a fuel cell 12 Electrolyte membrane 14 Catalyst layer 16 Gas diffusion layer 18 Membrane electrode assembly 20 Stretch molding or expanded molding 22 Separator 24 Separator substrate 26 Conductive layer 28 First gold plating layer 30 Second gold plating layer Best mode for carrying out the invention

[0017] With reference to the drawings, a detailed description of the embodiments according to the present invention will be given below. First, a description will be given of the structure of a cell of a fuel cell. Fig. 1 is a diagram showing a cross-section of a fuel cell cell 10. The fuel cell cell 10 includes a membrane electrode assembly (MEA) 18, which integrates an electrolyte membrane 12, a catalyst layer 14, and a gas diffusion layer 16 and forms an electrode of the fuel cell, a stretch-molded part 20, which is a gas passage structure in which gas passages are formed, and a separator 22, which separates the fuel gas or oxidizing gas from an adjacent cell (not shown in the drawing). The fuel cell cell 10, which is Fig. 1 is only an example, and the cell structure is not limited to this structure.

[0018] The electrolyte membrane 12 functions to transport the hydrogen ions generated on the anode electrode side to the cathode electrode side. A chemically stable fluororesin, such as a perfluorocarbon-sulfuric acid ion exchange membrane or the like, can be used as the material for the electrolyte membrane 12.

[0019] The catalyst layer 14 functions to accelerate the oxidation reaction of hydrogen on the anode electrode side and the reduction reaction or reduction of oxygen on the cathode electrode side. The catalyst layer 14 comprises a catalyst and a catalyst support. To increase the surface area of ​​the electrode available for the reaction, the catalyst is generally in the form of particles adhered to the catalyst support. A platinum group element with a low activation overvoltage, such as platinum and the like, can be used as the catalyst for the oxidation reaction of hydrogen and the reduction reaction or reduction of oxygen. A carbon material, such as carbon black or the like, can be used as the catalyst support.

[0020] The gas diffusion layer 16 has the function of diffusing the fuel gas, such as hydrogen gas, and the oxidizing gas, such as air, to the catalyst layer 14, as well as the function of transporting electrons. For the gas diffusion layer 16, a conductive material such as a carbon fiber fabric or carbon paper, etc., can be used.

[0021] The expanded molding 20 is layered on both surfaces of the membrane electrode assembly 18 and functions as a gas passage structure in which gas passages are formed. The expanded molding 20 is layered in such a way that it contacts 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. The expanded molding 20 has a mesh structure with a plurality of openings, and thus, a larger amount of fuel gas or the like can come into contact with the membrane electrode assembly 18 and undergo a chemical reaction, which means that the power generation efficiency of the cell 10 of the fuel cell can be improved.

[0022] For the expanded metal part 20, expanded metals conforming to JIS G 3351, or metal strips or porous metal materials conforming to JIS A 5505, or the like can be used. The expanded metal part 20 is preferably formed from titanium, a titanium alloy, or stainless steel, or the like. These materials are preferred because they have high mechanical strength and contain an inactive coating, such as a passivation film containing a stable oxide (such as TiO, Ti2O3, TiO2, CrO2, CrO, or Cr2O3) on the metal surface, thus providing excellent corrosion resistance. Instead of stainless steel, austenitic stainless steel, ferritic stainless steel, and the like can also be used.

[0023] The separator 22 is layered on the expanded metal part 20 and functions to separate the fuel gas and the oxidizing gas in the adjacent cells (not shown in the drawing). Furthermore, the separator 22 also functions to electrically connect the adjacent cells (not shown in the drawing). The separator 22 includes a separator substrate 24 and a conductive layer 26 formed on the separator substrate 24.

[0024] The separator substrate 24 is preferably formed of titanium, a titanium alloy, or stainless steel, or the like. As described above, the reason why these materials are preferred is that titanium materials and stainless steel have high mechanical strength and include an inactive coating, such as a passivation film comprising a stable oxide formed on the metal surface, and therefore have excellent corrosion resistance.

[0025] The conductive layer 26 functions to reduce the contact resistance between the expanded molded part 20 and the separator substrate 24. The conductive layer 26 is formed using gold (Au) as the conductor. Gold (Au) exhibits excellent corrosion resistance and high electrical conductivity.

[0026] The conductive layer 26 includes a first gold plating layer 28 and a second gold plating layer 30. As described above, the first gold plating layer 28 is formed on the surface of the separator substrate 24 using a pre-gold plating method, whereas the second gold plating layer 30 is formed on top of the first gold plating layer 28 using a thick gold plating method or the like. By forming the first gold plating layer 28 by pre-gold plating, a denser coating film can be formed. Furthermore, by forming the layer using pre-gold plating, improved adhesion between the separator substrate 24 and the first gold plating layer 28 can also be achieved.

[0027] Next, a description will be given of the manufacturing process of the fuel cell separator 22.

[0028] Fig. 2 is a flowchart showing a method for manufacturing the separator 22. The method for manufacturing the separator 22 includes a separator substrate forming step (S10), a cleaning step (S12), a neutralization step (S14), an acid rinsing step (S16), a first gold plating layer forming step (S18), and a second gold plating layer forming step (S20). A fuel cell separator with only the first gold plating layer 28 formed on the separator substrate 24 can also be manufactured by omitting the second gold plating layer forming step (S20) shown in the flowchart of Fig. 2 is omitted and thereafter the separator substrate forming step (S10), the cleaning step (S12), the neutralization step (S14), the acid rinsing step (S16) and the first gold plating layer forming step (S18) are carried out.

[0029] The separator substrate forming step (S10) is a step in which the separator substrate 24 is formed from a metal material. As mentioned above, titanium, stainless steel, or the like can be used as the metal material. The separator substrate 24 is formed into a sheet-like shape, for example, by subjecting the titanium or stainless steel to rolling or pressing.

[0030] The cleaning step (S12) is a step in which the separator substrate 24 is cleaned. The separator substrate 24 can be cleaned, for example, by degreasing by immersion in an alkali bath or the like. An alkaline solution or the like of sodium hydroxide or caustic soda can be used for degreasing by immersion in an alkali bath. By cleaning the separator substrate 24 by degreasing by immersion in an alkali bath, oil components and the like adhering to the surface of the separator substrate 24 can be removed.

[0031] The neutralization step (S14) is a step for neutralizing and then removing the residual alkali solution remaining on the separator substrate 24 after the cleaning process. The neutralization treatment can be performed, for example, by immersing the cleaned separator substrate 24 in a neutralizing solution. A sulfuric acid solution, a hydrochloric acid solution, a nitric acid solution, or the like can be used as the neutralizing solution. After the separator substrate 24 is removed from the neutralizing solution, the separator substrate 24 can be rinsed with deionized water or the like.

[0032] The acid rinsing step (S16) is a step in which the separator substrate 24, which has undergone the neutralization treatment and the like, is rinsed with acid, thereby removing oxides and the like formed on the surface of the separator substrate 24. The acid rinsing treatment can be performed, for example, by immersing the separator substrate 24 in a nitric acid-hydrofluoric acid solution or a hydrofluoric acid solution or the like. After the separator substrate 24 is removed from the nitric acid-hydrofluoric acid solution or the like, it can be rinsed with deionized water or the like.

[0033] The first gold plating layer formation step (S18) is a step in which the first gold plating layer 28 is formed on the separator substrate 24 that has undergone the acid rinsing treatment and the like. The first gold plating layer 28 is formed using a pre-gold plating method. The reason why a pre-gold plating method is used is that the first gold plating layer 28 can be formed more densely. Conventionally conducted electrolytic gold plating methods or the like can be used as the pre-gold plating method. A plating bath containing potassium gold cyanide or sodium gold sulfite or the like can be used as the pre-gold plating bath. Further, an alkali bath or an acid bath or the like can be used for the pre-gold plating bath.In a pre-gold plating process, the metal ion concentration is set or adjusted to a lower level than that used in a conventional process for producing a thick gold plating, and the plating process is carried out with a comparatively high electric current density. In this case, the electric current density can, for example, be within a range of approximately 0.2 to approximately 2 A / dm. 2 be set.

[0034] Fig. 3A to 3C are schematic diagrams showing the formation of the first gold plating layer 28 with predetermined thickness values ​​on the separator substrate 25, wherein Fig. 3A is a schematic diagram showing the formation of the first gold plating layer 28 having a thickness of approximately 3 nm, Fig. 3B is a schematic diagram showing the formation of the first gold plating layer 28 with a thickness of approximately 100 nm, and Fig. 3C is a schematic diagram showing the formation of the first gold plating layer 28 having a thickness approximately exceeding 200 nm.

[0035] The first gold plating layer 28 is typically formed to a thickness of not less than approximately 10 nm and not more than approximately 200 nm. The reason why the thickness of the first gold plating layer 28 is not less than approximately 10 nm is that if the first gold plating layer 28 were formed using the pre-gold plating to a thickness of less than approximately 10 nm, the gold plating layer would tend to have an increased number of irregularities and defects, and the gold plating layer would not be dense.The reason why the thickness of the first gold plating layer 28 is not more than approximately 200 nm is that if the first gold plating layer 28 were formed using the pre-gold plating with a thickness of more than approximately 200 nm, the deposited gold particles would be coarser and the density of the gold plating layer would deteriorate. The first gold plating layer 28 is preferably formed with a thickness of not less than approximately 70 nm and not more than approximately 120 nm, and it is even more preferable to form it with a thickness of not less than approximately 70 nm and not more than approximately 100 nm.This is because by forming the first gold plating layer 28 with a thickness of not less than approximately 70 nm and not more than approximately 100 nm, a further improvement in the corrosion resistance of the separator 22 can be achieved.

[0036] The second gold plating layer formation step (S20) is a step in which the second gold plating layer 30 is formed on the separator substrate 24 on which the first gold plating layer 28 is formed. The second gold plating layer 30 can be formed, for example, using a thick gold plating method or the like. As the thick gold plating method, a conventionally conducted electrolytic plating method or the like can be used. As the gold plating bath, a plating bath containing potassium gold cyanide or sodium gold sulfite or the like can be used. Furthermore, an alkali bath, a neutral bath, an acid bath or the like can be used instead of the gold plating bath.The second gold plating layer 30 is formed on the first gold plating layer 28, for example, with a thickness within a range of approximately 100 nm to approximately 20 µm.

[0037] According to the configuration described above, by forming the first gold plating layer on the separator substrate 24 using a pre-gold plating method, the first gold plating layer can be formed more densely, thereby improving the corrosion resistance of the first gold plating layer and, consequently, the corrosion resistance of the fuel cell separator. Furthermore, by forming the second gold plating layer on the densely formed first gold plating layer, the corrosion resistance of the conductive layer comprising the first gold plating layer and the second gold plating layer can be further improved, which means that the corrosion resistance of the fuel cell separator can be further improved. Examples

[0038] A more detailed description of the details of the present invention will be given below based on examples and comparative examples, although the invention is by no means limited to the examples given below.

[0039] The thickness of the pre-gold plating layer of the first gold plating layer 28 is varied, and the corrosion resistance is evaluated. The corrosion resistance evaluation is carried out by forming only the pre-gold plating layer on a titanium layer serving as the separator substrate 24. The titanium layer is first subjected to an alkaline degreasing rinse, followed by a neutralization treatment with sulfuric acid and an acid rinse treatment with nitric-hydrofluoric acid solution. Subsequently, the acid-rinsed titanium layer is subjected to pre-gold plating. An alkaline non-cyanide gold plating bath is used as the pre-gold plating. Then, at a pressure of 1 A / dm 2a pre-gold plating layer is formed at a set or adjusted electric current density, wherein the plating time is adjusted so that a pre-gold plating layer with a density of 2 nm to 200 nm (3 nm, 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 100 nm, 120 nm, 140 nm, 160 nm, 180 nm or 200 nm) is formed.

[0040] The corrosion test is carried out according to the electrochemical high-temperature corrosion test method for metal materials according to Japanese Industrial Standard JIS Z2294. Fig. Figure 4 is a diagram showing the test apparatus used for conducting the high-temperature electrochemical corrosion test. The test is conducted in an open-atmosphere system. The solution used in the test is a sulfuric acid-based solution. The temperature of the test solution is set to 50°C. The corrosion test is conducted for a period of 50 hours while a fixed potential is applied. The corrosion resistance is assessed by determining the corrosion initiation time based on observation of the external appearance and the corrosion-generating current.

[0041] Fig. Figure 5 is a diagram showing the results of the corrosion evaluation test. As can be seen from Fig. As can be seen in Figure 5, the thickness of the pre-gold plating layer is plotted along the abscissa, and the corrosion initiation time is plotted along the ordinate, while the corrosion initiation time data for each of the pre-gold plating layers with different thicknesses are indicated by black diamonds. When the thickness of the pre-gold plating layer is less than 10 nm, the corrosion initiation time is less than 500 hours, and satisfactory corrosion resistance cannot be achieved.When the thickness of the pre-gold plating layer is increased from 10 nm to 70 nm, the corrosion initiation time gradually increases. When the thickness of the pre-gold plating layer is increased from 70 nm to 100 nm, the corrosion initiation time rapidly increases. Finally, when the thickness of the pre-gold plating layer is increased from 100 nm to 200 nm, the corrosion initiation time gradually shortens. Accordingly, when the thickness of the gold plating layer is within a range of 10 nm to 200 nm, the corrosion initiation time only occurs after 500 hours, indicating that favorable corrosion resistance can be obtained.

[0042] To subsequently evaluate how the corrosion resistance of the separator changes depending on the presence or absence of the pre-gold plating layer, two types of separator test pieces were prepared and subjected to subsequent corrosion evaluation tests. First, a method for producing a separator test piece according to Example 1 is described. In the method for producing a separator test piece according to Example 1, a titanium layer formed from titanium is first subjected to an alkaline degreasing rinse, followed by a neutralization treatment with sulfuric acid and an acid rinse treatment with a nitric-hydrofluoric acid solution. The acid-rinsed titanium layer is then subjected to pre-gold plating using an alkaline, non-cyanide gold plating bath. The thickness of the pre-gold plating layer is set to 100 nm.A thick gold plating layer is then applied to the pre-gold plating layer using an alkaline, non-cyanide gold plating bath. The thickness of this gold plating layer is set to 20 µm.

[0043] Next, a description will be given of a method for manufacturing a separator test piece according to Comparative Example 1. In the method for manufacturing a separator test piece according to Comparative Example 1, a titanium layer formed of titanium is first subjected to alkaline degreasing rinsing, and then to neutralization treatment and acid rinsing treatment in the same way as in the description of the separator test piece according to Example 1. Subsequently, a thick gold plating layer with a thickness of 20 μm is formed directly on the acid-rinsed titanium layer without first forming a pre-gold plating layer. The thick gold plating is performed using the same method as that described in Example 1.

[0044] The corrosion resistance evaluation tests are conducted on the separator test pieces of Example 1 and Comparative Example 1. The corrosion resistance evaluation tests are conducted according to the Japanese Industrial Standard JIS Z2294 described above. Fig. Figure 6 is a graph showing the results of the corrosion resistance evaluation tests. As can be seen from Fig. As can be seen in Figure 6, the power generation period is plotted along the abscissa and the corrosion-generating current is plotted along the ordinate. The data for the separator specimen of Example 1 are shown as black squares, and the data for the separator specimen of Comparative Example 1 are shown as black diamonds. With the separator specimen of Comparative Example 1, the corrosion-generating current value begins to increase 500 hours after the start of the test, indicating that corrosion is progressing. In contrast, with the separator specimen of Example 1, almost no increase in the corrosion-generating current is observed, even after 2000 hours after the start of the test.

[0045] Subsequently, the separator test pieces, for which 2000 hours have elapsed since the start of the corrosion resistance test, are subjected to an examination of their cross-sectional area using a metallurgical microscope. Fig. Figure 7 is a graph showing the result of the cross-sectional area examination of the separator test piece of Comparative Example 1. In addition, Fig. 8 is a graph showing the result of examining the cross-sectional area of ​​the separator test piece of Example 1. In the separator test piece of Comparative Example 1, corroded areas are observed on the surface. In contrast, in the separator test piece of Example 1, no corroded areas are observed on the surface. Therefore, from these results, it is apparent that corrosion resistance can be improved by providing a pre-gold plating layer on a titanium layer.

Claims

[1] A method for producing a fuel cell separator (22) which separates adjacent cells (10) of a fuel cell from one another, the method comprising the following steps: Subjecting a separator substrate (24) comprising a metal material to pre-gold plating, thereby forming a first gold plating layer (28) having a thickness of approximately 10 nm to approximately 200 nm; and Performing an additional gold plating on top of the first gold plating layer (28) formed by the pre-gold plating, thereby forming a second gold plating layer (30) having a thickness of approximately 100 nm to approximately 20 µm, wherein the separator substrate (24) is formed from titanium or stainless steel. [2] A method for producing a fuel cell separator according to claim 1, wherein the first gold plating layer (28) is formed with a thickness of not less than approximately 70 nm and not more than approximately 120 nm. [3] A method for producing a fuel cell separator according to claim 1, wherein the first gold plating layer (28) is formed with a thickness of not less than approximately 70 nm and not more than approximately 100 nm. [4] A fuel cell separator (22) manufactured using the method for manufacturing a fuel cell separator according to claim 1. [5] A fuel cell comprising a fuel cell separator (22) manufactured using the method for manufacturing a fuel cell separator according to claim 1.