WO2015059857A1 - 固体高分子形燃料電池のセパレータ用ステンレス箔 - Google Patents
固体高分子形燃料電池のセパレータ用ステンレス箔 Download PDFInfo
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- WO2015059857A1 WO2015059857A1 PCT/JP2014/004509 JP2014004509W WO2015059857A1 WO 2015059857 A1 WO2015059857 A1 WO 2015059857A1 JP 2014004509 W JP2014004509 W JP 2014004509W WO 2015059857 A1 WO2015059857 A1 WO 2015059857A1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/02—Details
- H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
- H01M8/0204—Non-porous and characterised by the material
- H01M8/0223—Composites
- H01M8/0228—Composites in the form of layered or coated products
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C19/00—Alloys based on nickel or cobalt
- C22C19/03—Alloys based on nickel or cobalt based on nickel
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
- C25D11/02—Anodisation
- C25D11/34—Anodisation of metals or alloys not provided for in groups C25D11/04 - C25D11/32
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D3/00—Electroplating: Baths therefor
- C25D3/02—Electroplating: Baths therefor from solutions
- C25D3/12—Electroplating: Baths therefor from solutions of nickel or cobalt
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D3/00—Electroplating: Baths therefor
- C25D3/02—Electroplating: Baths therefor from solutions
- C25D3/30—Electroplating: Baths therefor from solutions of tin
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D3/00—Electroplating: Baths therefor
- C25D3/02—Electroplating: Baths therefor from solutions
- C25D3/38—Electroplating: Baths therefor from solutions of copper
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D3/00—Electroplating: Baths therefor
- C25D3/02—Electroplating: Baths therefor from solutions
- C25D3/46—Electroplating: Baths therefor from solutions of silver
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D3/00—Electroplating: Baths therefor
- C25D3/02—Electroplating: Baths therefor from solutions
- C25D3/48—Electroplating: Baths therefor from solutions of gold
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
- C25D5/10—Electroplating with more than one layer of the same or of different metals
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
- C25D5/10—Electroplating with more than one layer of the same or of different metals
- C25D5/12—Electroplating with more than one layer of the same or of different metals at least one layer being of nickel or chromium
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
- C25D5/34—Pretreatment of metallic surfaces to be electroplated
- C25D5/36—Pretreatment of metallic surfaces to be electroplated of iron or steel
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D7/00—Electroplating characterised by the article coated
- C25D7/06—Wires; Strips; Foils
- C25D7/0614—Strips or foils
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/02—Details
- H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
- H01M8/0204—Non-porous and characterised by the material
- H01M8/0206—Metals or alloys
- H01M8/0208—Alloys
- H01M8/021—Alloys based on iron
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/10—Fuel cells with solid electrolytes
- H01M8/1016—Fuel cells with solid electrolytes characterised by the electrolyte material
- H01M8/1018—Polymeric electrolyte materials
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D3/00—Electroplating: Baths therefor
- C25D3/02—Electroplating: Baths therefor from solutions
- C25D3/56—Electroplating: Baths therefor from solutions of alloys
- C25D3/60—Electroplating: Baths therefor from solutions of alloys containing more than 50% by weight of tin
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/10—Fuel cells with solid electrolytes
- H01M2008/1095—Fuel cells with polymeric electrolytes
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/50—Fuel cells
Definitions
- the present invention relates to a stainless steel foil for a separator of a polymer electrolyte fuel cell excellent in corrosion resistance and adhesion.
- the polymer electrolyte fuel cell is compared with other fuel cells.
- the power generation temperature is about 80 ° C, and power generation is possible at a significantly lower temperature
- the fuel cell body can be reduced in weight and size.
- It can be started up in a short time, and has advantages such as high fuel efficiency and high power density. For this reason, the polymer electrolyte fuel cell is expected to be used as a power source for mounting an electric vehicle, a stationary generator for home use or business use, and a small portable generator.
- the polymer electrolyte fuel cell takes out electricity from H 2 and O 2 through a polymer membrane.
- the membrane-electrode assembly 1 is connected to gas diffusion layers 2 and 3 (for example, Carbon paper or the like) and separators 4 and 5 to form a single component (so-called single cell). Then, an electromotive force is generated between the separator 4 and the separator 5.
- the membrane-electrode assembly 1 is called an MEA (Membrance-Electrode Assembly), which integrates a polymer membrane and an electrode material such as carbon black carrying platinum-based catalysts on the front and back surfaces of the membrane. The thickness is several tens of ⁇ m to several hundreds of ⁇ m. Further, the gas diffusion layers 2 and 3 are often integrated with the membrane-electrode assembly 1.
- a fuel cell stack is generally configured by using several tens to several hundreds of single cells as described above in series.
- the separators 4 and 5 include (a) In addition to serving as a partition wall that separates single cells, (b) a conductor carrying the generated electrons, (c) Air flow path 6 through which O 2 (air) and H 2 flow, hydrogen flow path 7, (d) Discharge path for discharging generated water and gas (air flow path 6 and hydrogen flow path 7 are combined) Therefore, excellent durability and electrical conductivity are required.
- the separator is required to have corrosion resistance that can withstand long-time power generation. The reason is that when metal ions are eluted by corrosion, proton conductivity of the polymer membrane (electrolyte membrane) decreases.
- the contact resistance between the separator and the gas diffusion layer is as low as possible. The reason is that when the contact resistance between the separator and the gas diffusion layer increases, the power generation efficiency of the polymer electrolyte fuel cell decreases. That is, it can be said that the smaller the contact resistance between the separator and the gas diffusion layer, the better the power generation characteristics.
- Patent Document 1 discloses a technique in which a metal that easily forms a passive film such as stainless steel or titanium alloy is used as a separator.
- a metal that easily forms a passive film such as stainless steel or titanium alloy is used as a separator.
- the formation of a passive film leads to an increase in contact resistance, leading to a decrease in power generation efficiency.
- these metal materials have problems to be improved such as a contact resistance larger than that of a graphite material and inferior in corrosion resistance.
- Patent Document 2 discloses a technique for reducing contact resistance and ensuring high output by performing gold plating on the surface of a metal separator such as austenitic steel plate (SUS304).
- a metal separator such as austenitic steel plate (SUS304).
- SUS304 austenitic steel plate
- Patent Document 3 a film having a Sn alloy layer is formed on the surface of a metal substrate, and conductive particles are contained in the film.
- a metal plate for a separator of a polymer electrolyte fuel cell was proposed.
- Patent Document 4 After performing the anode electrolytic treatment in which the Cr transpassive dissolution reaction occurs without performing the intermediate layer forming treatment on the base surface of the base made of high Cr stainless steel, A surface treatment method for a separator for a fuel cell in which a Ni 3 Sn 2 layer was immediately formed was proposed. As a result, a polymer electrolyte fuel cell separator having excellent corrosion resistance can be obtained even when a film made of an Sn alloy layer such as a Ni 3 Sn 2 layer (hereinafter also referred to as an Sn alloy layer film) is thinned. It became so.
- an Sn alloy layer film an Sn alloy layer film
- the present invention was developed in view of the above-mentioned present situation, and it is needless to say that it has excellent electrical conductivity. Even when the Sn alloy layer film is thinned, the separator is used in a polymer electrolyte fuel cell. It is an object of the present invention to provide a stainless steel foil for a separator of a polymer electrolyte fuel cell that can simultaneously obtain excellent corrosion resistance and excellent adhesion between a substrate and a Sn alloy layer film.
- the inventors used a stainless steel foil as a material for the separator for a polymer electrolyte fuel cell, and intensively studied various film forming treatments for the stainless steel foil. As a result, the following knowledge was obtained.
- strike plating comprising a pure metal layer such as Ni or Cu as a base film on the surface of a stainless steel foil substrate prior to the formation of the Sn alloy layer coating. An attempt was made to form a layer. As a result, it was found that the adhesion of the Sn alloy layer coating is greatly improved by providing a strike plating layer as a base coating on the surface of the stainless steel substrate. However, providing such a strike plating layer is disadvantageous in terms of compactness.
- the inventors have further studied to prevent the deterioration of the corrosion resistance that occurs when the Sn alloy layer film is thinned.
- the continuous corrosion of the strike plating layer is suppressed by controlling the above-mentioned strike plating layer adhesion amount within a range of 0.001 to 1 g / m 2 , which is smaller than the conventional one. It was found that the corrosion resistance deterioration due to peeling can be effectively prevented, and that adhesion deterioration does not occur.
- the inventors consider the reason why the continuous corrosion of the strike plating layer can be suppressed by controlling the amount of the strike plating layer to be within a range of 0.001 to 1 g / m 2 . Yes.
- a discontinuous portion such as a non-plated region of the strike plating layer is generated on the surface of the stainless steel foil substrate, and the discontinuous portion of the strike plating layer is formed. It acts as an area that prevents the progress of corrosion. As a result, even when the Sn alloy layer film is thinned, it is considered that continuous corrosion of the strike plating layer is suppressed.
- the inventors may use a pure metal layer such as Au, Ag, Cu or Ni as the strike plating layer, or an alloy layer containing at least one selected from these elements.
- a Ni-P strike plating layer made of an alloy layer of Ni and P is suitable as a strike plating layer because of its low material cost and excellent corrosion resistance.
- the inventors in particular, by controlling the P content in this Ni-P strike plating layer in the range of 5 to 22% by mass, was excellent even when exposed to a high potential for a long time in the separator environment. It was found that the corrosion resistance can be maintained more stably.
- the inventors have formed a more stable Ni-P compound in the usage environment of the separator by controlling the P content in the Ni-P strike plating layer in the range of 5 to 22% by mass, This is considered to be because corrosion of the strike plating layer is further suppressed.
- the inventors have obtained knowledge that the corrosion resistance can be further improved by coating the surface of the Sn alloy layer film with an oxide layer containing Sn.
- the reason for this is that, since the oxide layer containing Sn is extremely stable in the usage environment of the separator, the surface of the Sn alloy layer film is coated with the oxide layer containing Sn, whereby the Sn alloy layer It is considered that corrosion of the film is effectively suppressed. And it is thought that corrosion resistance improves further by such an effect.
- the present invention is based on the above findings.
- the gist configuration of the present invention is as follows. 1. A base made of stainless steel foil, and an Sn alloy layer film coated on the surface of the base through a strike plating layer, A stainless steel foil for a separator of a polymer electrolyte fuel cell, wherein the amount of the strike plating layer deposited is 0.001 to 1 g / m 2 .
- a fuel cell separator excellent in corrosion resistance and adhesion can be obtained without impairing compactness, and in turn, a solid polymer fuel cell excellent in durability can be obtained at low cost. Can do.
- the stainless steel foil used as a substrate is not particularly limited, but a stainless steel plate excellent in corrosion resistance (ferritic stainless steel plate, austenitic stainless steel plate, duplex stainless steel plate) is particularly advantageous. Fits.
- SUS447J1 (Cr: 30% by mass), SUS445J1 (Cr: 22% by mass), SUS316L (Cr: 18% by mass) can be preferably used.
- SUS447J1 containing about 30% by mass of Cr is particularly suitable as a solid polymer fuel cell separator substrate used in an environment where severe corrosion resistance is required because of its high corrosion resistance.
- the thickness of the separator stainless foil is preferably in the range of 0.03 to 0.3 mm.
- the thickness of the stainless steel foil for the separator is 0.03 mm or less, the production efficiency of the stainless steel foil is lowered.
- the mounting space and weight when stacked will increase. More preferably, it is in the range of 0.03 to 0.1 mm.
- the Sn alloy layer coating on the surface of the substrate is corrosion resistant in the use environment (pH: 3 (sulfuric acid environment), use temperature: 80 ° C) of the separator for polymer electrolyte fuel cells. It is preferable to use a Sn alloy containing Ni or Fe, which is excellent in heat resistance. More preferably, it is Ni 3 Sn 2 , Ni 3 Sn 4 , SnFe or SnFe 2 . Particularly preferred is Ni 3 Sn 2 which is an intermetallic compound.
- the reason why the above-described Sn alloy is excellent in corrosion resistance in the usage environment of the separator for the polymer electrolyte fuel cell is considered as follows. That is, the bond in the Sn alloy, for example, the Sn—Ni or Sn—Fe bond is more stable than the Sn—Sn bond in the metal Sn simple substance, and the corrosion resistance is improved.
- Ni 3 Sn 2 has excellent corrosion resistance because the formation temperature is 790 ° C or higher and the Sn-Ni bond is very stable according to the Ni-Sn binary alloy phase diagram. Is considered to be obtained.
- the film thickness of the Sn alloy layer film be 5 ⁇ m or less in consideration of the mounting space and weight when the fuel cell stack is stacked.
- the film thickness of the Sn alloy layer film is preferably 0.1 ⁇ m or more. More preferably, it is in the range of 0.5 to 3 ⁇ m.
- the Sn alloy layer film on the surface of the stainless steel foil substrate it is preferable to use a plating method.
- a plating bath adjusted to a predetermined composition by a conventionally known plating method.
- the substrate may be dipped in and electroplated.
- the adhesion between the coating and the substrate is improved by providing a strike plating layer between the stainless steel foil substrate and the Sn alloy layer coating.
- the inventors consider the reason why the adhesion between the coating and the substrate is improved by providing a strike plating layer between the stainless steel foil substrate and the Sn alloy layer coating as follows. That is, when there is no strike plating layer, an inert passive film or the like is easily formed on the surface of the stainless steel foil substrate, and high adhesion is not always obtained.
- the strike plating layer when the strike plating layer is provided, the formation of the above-described passive film or the like is suppressed and the stainless steel foil substrate surface is hardly made inactive, and as a result, the adhesion between the substrate and the Sn alloy layer film is improved. I believe that. If the strike plating layer has irregularities or the like, it is more advantageous because the adhesion is further improved by the anchor effect.
- Amount of strike plating layer 0.001 to 1 g / m 2
- the strike plating layer between the stainless steel foil substrate and the Sn alloy layer coating corrodes continuously and uniformly widely in the plane direction through the above defects, and the upper Sn alloy layer coating is removed from the stainless steel foil substrate. It will peel off.
- the Sn alloy layer film is peeled off, the stainless steel substrate is exposed in the environment where the separator is used, so that the corrosion resistance is lowered.
- the amount of the strike plating layer is controlled within a very small range, the strike plating layer is formed discontinuously or non-uniformly on the substrate surface, in other words, the strike plating layer is not plated on a part of the substrate surface. A discontinuous part such as a region is generated.
- This discontinuous portion of the strike plating layer acts as a region that prevents the progress of corrosion, and even when the Sn alloy layer film is thinned, the continuous and uniform corrosion of the strike plating layer is suppressed. it can. As a result, deterioration of corrosion resistance can be prevented.
- the adhesion amount of the strike plating layer is controlled in the range of 0.001 to 1 g / m 2 .
- the adhesion amount of strike plating is controlled in the range of 0.003 ⁇ 0.5g / m 2, more preferably in the range of 0.003 ⁇ 0.3g / m 2, more preferably in the range of 0.005 ⁇ 0.05g / m 2.
- the strike plating layer is preferably a pure metal layer such as Au, Ag, Cu or Ni, and further preferably an alloy layer containing at least one selected from these elements, considering the material cost More preferably, Ni strike plating or Ni—P strike plating made of an alloy layer of Ni and P is applied. In particular, when performing Ni-P strike plating, it is more preferable to control the P content in the Ni-P strike plating layer in the range of 5 to 22% by mass.
- P content in Ni-P strike plating layer 5-22% by mass
- the P content in the Ni-P strike plating layer is preferably controlled in the range of 5 to 22% by mass. More preferably, it is in the range of 7 to 20% by mass, and further preferably in the range of 10 to 18% by mass.
- the strike plating layer may be formed by electroplating or electroless plating in a plating bath adjusted to an appropriate composition by a conventionally known plating method. Moreover, the adhesion amount of the strike plating layer can be adjusted by the residence time in the plating bath, that is, the plating time. The P content in the Ni-P strike plating layer can be adjusted by the P concentration in the plating bath, the current density during electroplating, and the like.
- the surface of the Sn alloy layer film is covered with an oxide layer containing Sn.
- the corrosion resistance at the time of using for a long time under the use environment of a separator can be improved further.
- the Sn-containing oxide layer covering the surface of the Sn alloy layer film is not a natural oxide film formed in the atmospheric environment, but is intentionally formed by treatment such as immersion in an acidic solution. This refers to the oxidized film.
- the film thickness of the natural oxide film is usually about 2 to 3 nm.
- the oxide layer containing Sn As a main component of the oxide layer containing Sn, SnO 2 is preferable.
- the film thickness is desirably in the range of 5 to 50 nm. More preferably, it is in the range of 10 to 30 nm. This is because if the oxide layer containing Sn becomes too thick, it causes a decrease in conductivity. On the other hand, if the oxide layer containing Sn is too thin, the effect of improving the corrosion resistance in the use environment of the separator cannot be obtained.
- the corrosion resistance when used for a long time in the separator usage environment is improved because the Sn-containing oxide layer is Since it is extremely stable in the use environment, it is considered that the corrosion of the Sn alloy layer film is effectively suppressed by forming this Sn-containing oxide layer on the surface of the Sn alloy layer film.
- the purpose of forming an oxide film intentionally by immersing it in an acidic solution instead of a natural oxide film is that the oxide film is applied to the surface of the Sn alloy layer film by such treatment. This is because it can be formed uniformly and densely, and corrosion of the Sn alloy layer film can be extremely effectively suppressed.
- Examples of the formation of the oxide layer containing Sn include a method of immersing in an acidic aqueous solution having an oxidizing property such as hydrogen peroxide and nitric acid, and a method of electrochemically performing anodic electrolysis.
- an acidic aqueous solution having an oxidizing property such as hydrogen peroxide and nitric acid
- electrochemically performing anodic electrolysis For example, the above-mentioned Sn alloy layer coating-formed stainless steel foil for separator is energized for 5 minutes at a current density of +1 mA / cm 2 in a sulfuric acid aqueous solution at a temperature of 60 ° C. and a pH of 1 to oxidize the Sn as described above.
- a physical layer can be formed.
- the method for forming an oxide layer containing Sn is not limited to the above-described method, and a physical vapor deposition method (PVD method) or a chemical vapor deposition method (CVD method). Moreover, the coating method etc. are also mentioned.
- the surface of a stainless steel foil substrate is coated with a Sn alloy layer film via a strike plating layer, or a strike plating layer is provided.
- a conductive layer having a low electrical resistance can be further coated on the Sn alloy layer coating or the Sn-containing oxide layer.
- a pure metal layer, a conductive polymer layer, an alloy layer containing conductive particles, or a polymer layer containing conductive particles is contained on the Sn alloy layer film or Sn. You may coat
- the polymer electrolyte fuel cell separator is required to have excellent corrosion resistance since it is used in a severe environment of temperature: 80 ° C. and pH: 3. Further, in the manufacturing process of the fuel cell, for example, in the process of processing the separator into a desired shape or the process of assembling the fuel cell, the stainless steel foil base and the Sn alloy layer film are not separated from the stainless steel foil base. High adhesion is required between the two. Furthermore, it is required to improve the compactness of the fuel cell by reducing the plate thickness increase rate after the coating is formed on the surface of the stainless steel foil substrate. Therefore, in view of these required characteristics, the following three evaluations were performed on the samples described later.
- ⁇ (unacceptable) Current density over 20 hours 0.2 ⁇ A / cm 2 or more
- the ratio of the current density after 50 hours to the current density after 20 hours [(current density after 50 hours) / (current density after 20 hours) ⁇ 100] was determined. Based on the ratio of the current density at the time of 50 hours to the current density at the time of 20 hours, the corrosion resistance at the time of 50 hours in the separator use environment was evaluated according to the following criteria. ⁇ (Passed, especially excellent): Ratio of current density after 50 hours to current density after 20 hours less than 80% ⁇ (Pass): Ratio of current density after 50 hours to current density after 20 hours 80% or more and less than 100% ⁇ (failed): Ratio of current density after 50 hours to current density after 20 hours 100% or more
- FIG. 2 11 is a sample, 12 is a stainless steel foil substrate, 13 is a strike plating layer, 14 is a Sn alloy layer film, 15 is a cold-rolled steel sheet, 16 is an adhesive, and 17 is an oxide layer containing Sn.
- the test piece for adhesion evaluation thus obtained was pulled from both sides with a tensile tester to determine the tensile strength (peel strength) when the substrate and the film peeled, and the film adhesion was evaluated according to the following criteria. .
- Thickness increase rate [([film thickness per side] ⁇ 2) / [film thickness of stainless steel foil substrate]] ⁇ 100 ⁇ (Pass): Plate thickness increase rate 20% or less ⁇ (Fail): Plate thickness increase rate> 20% Note that the film thickness here refers to the average thickness and Sn of the strike plating layer converted from the amount of adhesion. The total film thickness of the alloy layer film or the average film thickness of the strike plating layer converted from the amount of adhesion and the total film thickness of the Sn alloy layer film and the oxide layer containing Sn.
- Example 1 After using SUS447J1 (Cr: 30% by mass), SUS445J1 (Cr: 22% by mass), and SUS316L (Cr: 18% by mass) with a thickness of 0.05mm as the stainless steel foil substrate, appropriate pretreatment such as degreasing was performed.
- a strike plating layer having an adhesion amount shown in Table 1 was formed on a stainless steel foil substrate with the following plating bath composition and plating conditions.
- an Sn alloy layer film having an average film thickness shown in Table 1 was formed on the stainless steel foil substrate subjected to the strike plating layer under the following plating bath composition and plating conditions to obtain a stainless steel foil for a separator. .
- the separator stainless steel foil obtained as described above was energized for 5 minutes at a current density of +1 mA / cm 2 in a sulfuric acid aqueous solution at a temperature of 60 ° C. and a pH of 1; An oxide layer containing Sn was formed on the surface of the Sn alloy layer coating.
- various characteristics were evaluated as described above.
- the amount of strike plating layer deposited, the average thickness of the Sn alloy layer film, and the average thickness of the oxide layer containing Sn are controlled in advance by examining the relationship with the plating time or anode electrolysis time. did.
- a stainless steel foil for a separator that was not provided with a strike plating layer was also prepared, and various characteristics were evaluated in the same manner as described above.
- the adhesion amount of the strike plating layer was measured by the following method. First, a sample having a strike plating layer formed on the surface of a substrate (thickness: 0.05 mm) was cut into about 50 mmW ⁇ 50 mmL, the length of two sides was measured with calipers, and the sample area was calculated.
- a solution capable of dissolving the strike plating layer (hereinafter, a known stripping solution may be used, for example, 30% nitric acid for Ni, Ni-P and Cu strike plating, 90% sulfuric acid + 10% nitric acid for Ag strike plating)
- a known stripping solution may be used, for example, 30% nitric acid for Ni, Ni-P and Cu strike plating, 90% sulfuric acid + 10% nitric acid for Ag strike plating
- the sample is immersed in sodium cyanide 30g / L + hydrogen peroxide 40mL / L for 10 minutes to dissolve the strike plating layer, and the strike plating layer constituent element dissolved in the solution is ICP (Inductively Coupled Plasma) )
- the amount of plating adhesion (g / m 2 ) was calculated by quantifying with an emission spectroscopic analyzer and dividing the sample area.
- the average film thickness of the strike plating layer was calculated
- the column for the amount of strike plating layer deposition and the converted average film thickness is “-”.
- the average film thickness of the Sn alloy layer film was measured by the following method. First, a sample in which a strike plating layer and a Sn alloy layer film were formed on the surface of a substrate (thickness: 0.05 mm) was cut to about 10 mmW ⁇ 15 mmL. Next, after embedding the sample in resin and polishing the cross section, the film thickness of the Sn alloy layer film was measured by observing with a scanning electron microscope (SEM). In addition, the measurement of the film thickness of the Sn alloy layer film was performed for each of the ten samples cut into the above shape from the same sample on which the Sn alloy layer film was formed, and the average value of these was calculated as the average film of the Sn alloy layer film. Thickness.
- the composition of the Sn alloy layer film was identified by an energy dispersive X-ray spectrometer (EDX) and an X-ray diffractometer (XRD) which were performed at the time of SEM observation.
- EDX energy dispersive X-ray
- the average film thickness of the oxide layer containing Sn was measured by the following method.
- a thin film for cross-sectional observation was fabricated by processing a sample with an oxide layer containing Sn in addition to the strike plating layer and Sn alloy layer film on the surface of the substrate (thickness: 0.05 mm) with a focused ion beam.
- the average film thickness of the oxide layer containing Sn was measured by observing the produced thin film for cross-sectional observation with a transmission electron microscope (TEM).
- TEM transmission electron microscope
- the film thickness of the oxide layer containing Sn was measured at three points for the film thickness of the oxide layer containing Sn in the produced thin film for cross-sectional observation, and the average value of these was calculated for the oxide layer containing Sn. It was set as the average film thickness.
- the composition of the oxide layer was identified by an energy dispersive X-ray spectrometer (EDX) and X-ray photoelectron spectroscopy (XPS) performed during TEM observation.
- Nickel chloride 240 g / L Hydrochloric acid: 125ml / L Temperature: 50 ° C Current density: 5 A / dm 2 ⁇ Ni-P strike plating> Nickel sulfate: 1 mol / L Nickel chloride: 0.1mol / L Boric acid: 0.5mol / L Sodium phosphite: 0.05 to 5 mol / L Temperature: 50 ° C Current density: 5 A / dm 2 ⁇ Cu strike plating> Copper cyanide: 30g / L Sodium cyanide: 40g / L Potassium hydroxide: 4g / L Temperature: 40 ° C Current density: 5 A / dm 2 ⁇ Ag strike plating> Potassium cyanide cyanide: 2g / L Sodium cyanide: 120 g / L Temperature: 30 ° C Current density: 3 A / dm 2
- samples No. 13 to 23, No. 15b, No. 15c, No. 15d, No. 18a, No. 18b, and No. 19a are all over 20 hours.
- the ratio of the current density after 50 hours to the current density is less than 80%, good corrosion resistance is more stably maintained.
- the tensile strength (peeling strength) necessary for peeling of the film is greatly increased, and the adhesion is greatly improved.
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Abstract
Description
そして、使用される電解質膜の種類に応じて、リン酸形燃料電池、溶融炭酸塩形燃料電池、固体酸化物形燃料電池、アルカリ形燃料電池および固体高分子形燃料電池(PEFC;proton-exchange membrane fuel cellまたはpolymer electrolyte fuel cell)に分類され、それぞれ開発が進められている。
(a) 発電温度が80℃程度であり、格段に低い温度で発電ができる、
(b) 燃料電池本体の軽量化、小型化が可能である、
(c) 短時間で立上げができ、燃料効率、出力密度が高い
等の利点を有している。
このため、固体高分子形燃料電池は、電気自動車の搭載用電源、家庭用または業務用の定置型発電機、携帯用の小型発電機としての利用が期待されている。
なお、上記の膜-電極接合体1は、MEA(Membrance-Electrode Assembly)と呼ばれていて、高分子膜とその膜の表裏面に白金系触媒を担持したカーボンブラック等の電極材料を一体化したものであり、厚さは数10μm~数100μmである。また、ガス拡散層2,3は、膜-電極接合体1と一体化される場合も多い。
ここに、セパレータ4,5には、
(a) 単セル間を隔てる隔壁
としての役割に加え、
(b) 発生した電子を運ぶ導電体、
(c) O2(空気)とH2が流れる空気流路6、水素流路7、
(d) 生成した水やガスを排出する排出路(空気流路6、水素流路7が兼備)
としての機能が求められるので、優れた耐久性や電気伝導性が必要となる。
しかしながら、自動車などで使用する燃料電池への適用においては、搭載スペースやエネルギー効率の観点から、セパレータを薄くして、一層のコンパクト化を図ることが求められている。
これにより、Ni3Sn2層などのSn合金層からなる皮膜(以下、Sn合金層皮膜ともいう)を薄膜化した場合においても、優れた耐食性を有する固体高分子形燃料電池のセパレータが得られるようになった。
その結果、以下の知見を得た。
(1)まず、発明者らは、密着性の向上を図るため、Sn合金層皮膜の形成に先立ち、ステンレス箔製の基体表面に、下地皮膜としてNiやCuといった純金属層等からなるストライクめっき層の形成を試みた。その結果、ステンレス箔製の基体表面に下地皮膜としてストライクめっき層を設けることで、Sn合金層皮膜の密着性が大きく向上することが判明した。ただし、このようなストライクめっき層を設けることは、コンパクト化の点では不利となる。
その結果、上記のストライクめっき層の付着量を従来よりも少ない0.001~1g/m2の範囲に制御することで、ストライクめっき層の連続的な腐食が抑制され、その結果、Sn合金層皮膜の剥離に伴う耐食性の劣化を効果的に防止でき、しかも密着性の劣化も生じないとの知見を得た。
ここに、上記のストライクめっき層の付着量を0.001~1g/m2の範囲に制御することで、ストライクめっき層の連続的な腐食が抑制できる理由は、発明者らは次のように考えている。
すなわち、ストライクめっき層の付着量を従来よりも少ない範囲で制御することで、ステンレス箔製の基体表面にストライクめっき層の不めっき領域といった不連続部が生じ、このストライクめっき層の不連続部が腐食の進行を阻止する領域として作用する。その結果、Sn合金層皮膜を薄くした場合であっても、ストライクめっき層の連続的な腐食が抑制されるものと考えている。
この理由として、発明者らは、Ni-Pストライクめっき層中のP含有量を5~22質量%の範囲に制御することで、セパレータの使用環境でより安定なNi-P化合物が形成され、これにより、ストライクめっき層の腐食が一層抑制されるためと考えている。
この理由として、発明者らは、Snを含む酸化物層がセパレータの使用環境において極めて安定であるため、Sn合金層皮膜の表面を、Snを含む酸化物層で被覆することにより、Sn合金層皮膜の腐食が効果的に抑制されるものと考えている。そして、このような効果により、耐食性が一層向上するものと考えている。
本発明は、上記の知見に立脚するものである。
1.ステンレス箔製の基体と、該基体表面にストライクめっき層を介して被覆したSn合金層皮膜とをそなえ、
該ストライクめっき層の付着量が0.001~1g/m2である固体高分子形燃料電池のセパレータ用ステンレス箔。
(1)基体として用いる金属板
本発明において、基体として用いるステンレス箔については特に制限はないが、耐食性に優れるステンレス鋼板(フェライト系ステンレス鋼板、オーステナイト系ステンレス鋼板、二相ステンレス鋼板)がとりわけ有利に適合する。
例えば、SUS447J1(Cr:30質量%)、SUS445J1(Cr:22質量%)、SUS316L(Cr:18質量%)などを好適に使用することができる。特に、Crを30質量%程度含有するSUS447J1は、耐食性が高いため、厳しい耐食性が要求される環境下で使用される固体高分子形燃料電池セパレータ基体として、とりわけ有利に適合する。
前記基体の表面に被覆するSn合金層皮膜としては、固体高分子形燃料電池用のセパレータの使用環境(pH:3(硫酸環境)、使用温度:80℃)において耐食性に優れるNiあるいはFeを含むSn合金を使用することが好ましい。より好ましくは、Ni3Sn2、Ni3Sn4、SnFeあるいはSnFe2である。特に好ましくは、金属間化合物のNi3Sn2である。
すなわち、金属Sn単体におけるSn-Sn結合よりも、Sn合金における結合、例えばSn-NiまたはSn-Fe結合のほうが、より安定な結合状態をとるために耐食性が向上する。特にNi3Sn2は、Ni-Snの二元合金状態図によれば形成される温度が790℃以上と高温の領域にあり、Sn-Ni結合が非常に安定であるために、優れた耐食性が得られるものと考えられる。
また、本発明では、ステンレス箔基体とSn合金層皮膜との間にストライクめっき層設けることで、皮膜と基体の密着性を向上させている。ここに、ステンレス箔基体とSn合金層皮膜との間にストライクめっき層設けることで、皮膜と基体の密着性が向上する理由は、発明者らは次のように考えている。
すなわち、ストライクめっき層がない場合、ステンレス箔基体表面に不活性な不動態皮膜等が形成されやすく、高い密着性が得られるとは限らない。一方、ストライクめっき層を設けると、上記の不動態皮膜等の形成が抑制されてステンレス箔基体表面が不活性になり難く、その結果、基体とSn合金層皮膜との間の密着性が向上するものと考えている。
なお、ストライクめっき層に凹凸等がある場合には、アンカー効果により、密着性が一層向上するので、より有利である。
ストライクめっき層の付着量:0.001~1g/m2
ストライクめっき層の付着量を上記の範囲に制御することで、Sn合金層皮膜を薄くした場合であっても、セパレータ使用環境における耐食性を維持することができる。その理由は、発明者らは次のように考えている。
すなわち、通常、Sn合金層皮膜の膜厚の減少に伴って、Sn合金層皮膜から基体に通ずる皮膜中欠陥が増加する。その結果、上記の欠陥を通じて、ステンレス箔基体とSn合金層皮膜との間にあるストライクめっき層が平面方向に連続的かつ均一に広く腐食して、その上層のSn合金層皮膜がステンレス箔基体から剥離してしまう。Sn合金層皮膜が剥離すると、ステンレス鋼基体がセパレータ使用環境下で露出するため、耐食性が低下する。
これに対し、ストライクめっき層の付着量を極めて少ない範囲で制御すると、ストライクめっき層が基体表面に不連続または不均一に形成される、換言すれば基体表面の一部にストライクめっき層の不めっき領域といった不連続部が生じることとなる。そして、このストライクめっき層の不連続部が、腐食の進行を阻止する領域として作用することとなり、Sn合金層皮膜を薄くした場合であっても、ストライクめっき層の連続的かつ均一な腐食が抑制できる。そして、その結果、耐食性の劣化を防止できる。
特に、Ni-Pストライクめっきを施す場合、Ni-Pストライクめっき層中のP含有量を、5~22質量%の範囲に制御することがさらに好ましい。
Ni-Pストライクめっき層中のP含有量を上記の範囲に制御することで、セパレータ環境において長時間高電位にさらされた場合でも、優れた耐食性をより安定して維持できる。その理由は、発明者らは次のように考えている。
すなわち、Ni-Pストライクめっき層中のP含有量を5~22質量%の範囲に制御することで、セパレータの使用環境でより安定なNi-P化合物が形成され、これにより、ストライクめっき層の腐食がより長時間、効果的に抑制されるためと考えている。
またNi-Pストライクめっき層中のP含有量は、めっき浴中のP濃度や、電気めっき時の電流密度などで調整することができる。
また、本発明のセパレータ用ステンレス箔では、前記したSn合金層皮膜の表面を、Snを含む酸化物層で被覆することが好適である。これにより、セパレータの使用環境下で長時間使用した際の耐食性を一層向上できる。
ここで、Sn合金層皮膜の表面に被覆するSnを含む酸化物層は、大気環境下で形成される自然酸化皮膜ではなく、酸性溶液に浸漬させる等の処理を施すことで、意図的に形成させた酸化皮膜をいう。なお、自然酸化皮膜の膜厚は通常2~3nm程度である。
なお、自然酸化皮膜ではなく、酸性溶液に浸漬させる等の処理を施すことにより意図的に酸化皮膜を形成するのは、このような処理を行うことによって、酸化皮膜をSn合金層皮膜の表面に均一かつ緻密に形成することができ、Sn合金層皮膜の腐食を極めて効果的に抑制できるからである。
例えば、前記したSn合金層皮膜を形成したセパレータ用ステンレス箔を、温度60℃、pH:1の硫酸水溶液中で電流密度:+1mA/cm2として5分間通電することで、上記したSnを含む酸化物層を形成することができる。
なお、Snを含む酸化物層を形成する手法としては、上記にあげた手法に限定されることはなく、物理的気相成長法(PVD法)や、化学的気相成長法(CVD法)、コーティング法等も挙げられる。
また、セパレータ要求特性の一つである導電性を向上させるため、ステンレス箔製の基体の表面に、ストライクめっき層を介してSn合金層皮膜を被覆した後、あるいはストライクめっき層を介してSn合金層皮膜を被覆しSnを含む酸化物層を形成させた後、さらにこのSn合金層皮膜上あるいはSnを含む酸化物層上に、電気抵抗の低い導電層を被覆することができる。例えば、接触抵抗を低減させる目的で、純金属層、導電性高分子層、導電性粒子を含んだ合金層または導電性粒子を含んだ高分子層を、上記Sn合金層皮膜上またはSnを含む酸化物層上に被覆してもよい。
(a)20時間経過時の耐食性の評価
ステンレス鋼は一般的に、印加される電位が高くなるほど過不動態溶解しやすく、耐食性が劣化しやすい。そこで、セパレータ使用環境において高電位環境にさらされた場合の安定性を評価するため、試料を温度:80℃、pH:3の硫酸水溶液中に浸漬し、参照電極にAg/AgCl(飽和KCl)を用いて、0.9V(vs.SHE)の電位に20時間保持し、20時間経過時の電流密度の値を測定した。この20時間経過時の電流密度の値により、以下の基準で、セパレータ使用環境における20時間経過時の耐食性を評価した。
◎(合格、特に優れる):20時間経過時の電流密度0.015μA/cm2未満
○(合格):20時間経過時の電流密度0.015μA/cm2以上0.2μA/cm2未満
×(不合格):20時間経過時の電流密度0.2μA/cm2以上
さらに、ストライクめっき層としてNi-Pストライクめっき層を形成し、かつ20時間経過時に良好な耐食性が得られた各試料について、以下の評価を実施した。
すなわち、セパレータ使用環境において高電位環境により長時間さらされた場合の安定性を評価するため、試料を温度:80℃、pH:3の硫酸水溶液中に浸漬し、参照電極にAg/AgCl(飽和KCl)を用いて、0.9V(vs.SHE)の電位に50時間保持し、20時間経過時および50時間経過時の電流密度の値を測定した。そして、20時間経過時の電流密度に対する50時間経過時の電流密度の比率[(50時間経過時の電流密度)/(20時間経過時の電流密度)×100]を求めた。この20時間経過時の電流密度に対する50時間経過時の電流密度の比率により、以下の基準で、セパレータ使用環境における50時間経過時の耐食性を評価した。
◎(合格、特に優れる):20時間経過時の電流密度に対する50時間経過時の電流密度の比率80%未満
○(合格):20時間経過時の電流密度に対する50時間経過時の電流密度の比率80%以上100%未満
×(不合格):20時間経過時の電流密度に対する50時間経過時の電流密度の比率100%以上
基体(厚さ:0.05mm)の表面に皮膜を形成した試料を25mmW×80mmLに切断した。ついで、切断した試料と、25mmW×80mmL×1mmtの冷延鋼板とを、皮膜が形成された面で一部が重なるように接合し、図2に示すような密着性評価用の試験片を作製した。ここで、試料と冷延鋼板の接合には、接着剤(サンライズMSI製:E-56)を用い、また接着剤の厚さが2mm、接着面積が25mmW×20mmLとなるように接合した。なお、試料(基体)の板厚が薄いため、上記の冷延鋼板を接着した面と反対側の面にも、別の冷延鋼板(25mmW×80mmL×1mmt)を接合して補強した。
図2中、符号11は試料、12はステンレス箔基体、13はストライクめっき層、14はSn合金層皮膜、15は冷延鋼板、16は接着剤、17はSnを含む酸化物層である。
かくして得られた密着性評価用の試験片を、引張試験機により両側から引っ張り、基体と皮膜が剥離した時の引張強さ(剥離強度)を求め、次の基準で皮膜の密着性を評価した。
◎(合格、特に優れる):剥離強度6MPa以上
○(合格):剥離強度2MPa以上6MPa未満
×(不合格):剥離強度2MPa未満
以下の計算式によって板厚増加率を計算し、次の基準で燃料電池スタック時のコンパクト性を評価した。
板厚増加率(%)=[([片面あたりの皮膜膜厚]×2)/[ステンレス箔基体の膜厚]]×100
○(合格):板厚増加率20%以下
×(不合格):板厚増加率20%超
なお、ここでいう皮膜膜厚とは、付着量から換算したストライクめっき層の平均膜厚とSn合金層皮膜の膜厚の合計、あるいは付着量から換算したストライクめっき層の平均膜厚とSn合金層皮膜およびSnを含む酸化物層の膜厚の合計である。
板厚0.05mmのSUS447J1(Cr:30質量%)、SUS445J1(Cr:22質量%)、SUS316L(Cr:18質量%)をステンレス箔基体として用い、脱脂等の適切な前処理を実施した後、下記のめっき浴組成およびめっき条件で、ステンレス箔基体上に表1に示す付着量となるストライクめっき層を形成した。ついで、下記のめっき浴組成およびめっき条件で、上記ストライクめっき層を施したステンレス箔基体上に、表1に示す平均膜厚となるSn合金層皮膜を形成し、セパレータ用のステンレス箔を得た。
また、一部の試料では、上記のようにして得られたセパレータ用ステンレス箔を、温度:60℃、pH:1の硫酸水溶液中で電流密度:+1mA/cm2として5分間通電することで、上記Sn合金層皮膜の表面にSnを含む酸化物層を形成した。
かくして得られたセパレータ用のステンレス箔を用いて、上記の要領で各種特性の評価を行った。
なお、ストライクめっき層の付着量、Sn合金層皮膜の平均膜厚及びSnを含む酸化物層の平均膜厚は、あらかじめ、めっき時間あるいはアノード電解時間との関係を調べておくことにより、それぞれ制御した。また、比較のため、ストライクめっき層を設けなかったセパレータ用のステンレス箔についても作製し、上記と同じ要領で、各種特性の評価を行った。
ここで、Sn合金層皮膜の組成は、SEM観察時に実施したエネルギー分散型X線分光器(EDX)およびX線回折装置(XRD)により同定した。
ここで、酸化物層の組成は、TEM観察時に実施したエネルギー分散型X線分光器(EDX)およびX線光電子分光法(XPS)により同定した。
<Niストライクめっき>
塩化ニッケル:240g/L
塩酸:125ml/L
温度:50℃
電流密度:5A/dm2
<Ni-Pストライクめっき>
硫酸ニッケル:1mol/L
塩化ニッケル:0.1mol/L
ホウ酸:0.5mol/L
亜リン酸ナトリウム:0.05~5mol/L
温度:50℃
電流密度:5A/dm2
<Cuストライクめっき>
シアン化銅:30g/L
シアン化ナトリウム:40g/L
水酸化カリウム:4g/L
温度:40℃
電流密度:5A/dm2
<Agストライクめっき>
シアン化銀カリウム:2g/L
シアン化ナトリウム :120g/L
温度:30℃
電流密度:3A/dm2
<Auストライクめっき>
シアン化金カリウム:8g/L
クエン酸ナトリウム:80g/L
スルファミン酸ニッケル:3g/L
酢酸亜鉛:0.3g/L
温度:30℃
電流密度:3A/dm2
<Ni3Sn2>
塩化ニッケル:0.15mol/L
塩化スズ:0.15mol/L
ピロリン酸カリウム:0.45mol/L
グリシン :0.15mol/L
温度:60℃
電流密度:1A/dm2
<Ni3Sn4>
塩化ニッケル:0.15mol/L
塩化スズ:0.30mol/L
ピロリン酸カリウム:0.45mol/L
温度:60℃
電流密度:1A/dm2
<FeSn>
塩化鉄:0.15mol/L
塩化スズ:0.18mol/L
ピロリン酸カリウム:0.45mol/L
温度:60℃
電流密度:1A/dm2
<FeSn2>
塩化鉄:0.15mol/L
塩化スズ:0.36mol/L
ピロリン酸カリウム:0.45mol/L
温度:60℃
電流密度:1A/dm2
なお、本発明において、上記で示しためっき浴組成以外のものであっても、所望のめっきを形成できるならば、公知のめっき方法に従っても良い。
(a) 発明例の試料はいずれも、耐食性評価における20時間経過時の電流密度がいずれも小さく、セパレータ使用環境のような高電位環境に長時間さらされた場合であっても、良好な耐食性が得られている。特にSnを含む酸化物層を形成したNo.6、No.15、No.18、No.19a、No.26、No.28、No.30、No.32、No.34およびNo.36は、優れた耐食性が得られている。
(b) また、ストライクめっき層としてNi-Pストライクめっきを施した発明例の試料はいずれも、耐食性評価における20時間経過時の電流密度に対する50時間経過時の電流密度の比率が100%未満であり、セパレータ使用環境のような高電位環境にさらに長い時間さらされた場合であっても、良好な耐食性が安定して維持されている。特に、Pの含有量が好適範囲となるNo.13~23、No.15b、No.15c、No.15d、No.18a、No.18bおよびNo.19aの試料ではいずれも、20時間経過時の電流密度に対する50時間経過時の電流密度の比率が80%未満と、良好な耐食性がより安定して維持されている。
(c) 発明例の試料はいずれも、皮膜の剥離に必要な引張強さ(剥離強度)が大幅に増加しており、密着性が大幅に向上している。
(d) 発明例の試料はいずれも、板厚増加率が小さく、燃料電池スタック時のコンパクト性に優れている。
(e) 比較例No.1、37、43の試料はいずれも、ストライクめっき層を形成していないため、皮膜の剥離に必要な引張強さ(剥離強度)が低く、所望の密着性を得られない。
(f) 比較例No.11、24の試料は、ストライクめっき層の付着量が適正範囲を超えているため、耐食性評価における20時間経過時の電流密度が大きく、所望の耐食性を得られない。
(g) 比較例No.12の試料は、ストライクめっき層の付着量が適正範囲を超えているもののSn合金層皮膜の膜厚が大きいので、耐食性は確保されているが、板厚増加率が大きく、所望のコンパクト性が得られない。
2,3 ガス拡散層
4,5 セパレータ
6 空気流路
7 水素流路
11 試料
12 ステンレス箔基体
13 ストライクめっき層
14 Sn合金層皮膜
15 冷延鋼板
16 接着剤
17 Snを含む酸化物層
Claims (6)
- ステンレス箔製の基体と、該基体表面にストライクめっき層を介して被覆したSn合金層皮膜とをそなえ、
該ストライクめっき層の付着量が0.001~1g/m2である固体高分子形燃料電池のセパレータ用ステンレス箔。 - 前記Sn合金層皮膜が、NiおよびFeのうちから選んだ少なくとも一種の元素を含有する請求項1に記載の固体高分子形燃料電池のセパレータ用ステンレス箔。
- 前記Sn合金層皮膜が、Ni3Sn2、Ni3Sn4、SnFeおよびSnFe2のうちから選んだ少なくとも一種を含有する請求項1または2に記載の固体高分子形燃料電池のセパレータ用ステンレス箔。
- 前記ストライクめっき層が、Ni、Cu、AgおよびAuのうちから選んだ少なくとも一種の元素を含有する請求項1~3のいずれか1項に記載の固体高分子形燃料電池のセパレータ用ステンレス箔。
- 前記ストライクめっき層がNiとPの合金層からなり、このPの含有量が5~22質量%の範囲にある請求項4に記載の固体高分子形燃料電池のセパレータ用ステンレス箔。
- 前記Sn合金層皮膜の表面に、Snを含む酸化物層をそなえる請求項1~5のいずれか1項に記載の固体高分子形燃料電池のセパレータ用ステンレス箔。
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JP2020506499A (ja) * | 2016-12-22 | 2020-02-27 | ポスコPosco | 接触抵抗が優秀な高分子燃料電池分離板用ステンレス鋼およびその製造方法 |
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