Separator for fuel cell

Abstract

To provide an inexpensive separator with high corrosion resistance.SOLUTION: A fuel cell separator includes a base material containing iron and a surface layer provided on a surface of the base material. The surface layer contains an iron capture material and resin.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a separator, specifically a separator for a fuel cell.

Background Art

[0002] A fuel cell has a stack structure in which a predetermined number of single cells that generate electric power by the reaction of a fuel gas (hydrogen) and an oxidant gas (oxygen) are stacked. A single cell has a membrane electrode assembly including anode and cathode electrode layers (catalyst layer and gas diffusion layer) on both sides of an electrolyte membrane, and separators disposed on both sides of the membrane electrode assembly, respectively.

[0003] A separator for a fuel cell has a function of electrically connecting single cells in series and a function as a partition wall that blocks a fuel gas, an oxidant gas, and cooling water from each other.

[0004] Therefore, since a separator for a fuel cell also plays a role of flowing the generated current to an adjacent cell, the base material constituting the separator for a fuel cell is required to have high conductivity and conductive durability in which the high conductivity is maintained for a long time even in a high-temperature and acidic atmosphere inside the fuel cell. Here, high conductivity and conductive durability mean low contact resistance. Further, contact resistance means that a voltage drop occurs due to an interfacial phenomenon between an electrode and the surface of a separator.

[0005] Therefore, pure titanium or a titanium alloy is often used as the base material constituting the separator for a fuel cell, which is one of the major factors contributing to the cost increase in the manufacture of the separator for a fuel cell.

[0006] Various studies have been conducted to manufacture such a separator for a fuel cell at low cost.

[0007] For example, Patent Document 1 discloses a surface treatment method for forming an iron hydroxide film on the surface of a substrate made of stainless steel by cathodic electrolysis in an alkaline treatment solution. In this method, for the substrate made of stainless steel, a conductor containing at least no chromium is used as the counter electrode. Further, a separator for a fuel cell manufactured by using this surface treatment method is disclosed.

[0008] Patent Document 2 discloses a separator made of a separator material including a substrate made of stainless steel or iron, a titanium layer on the surface of the substrate, and a mixed layer of conductive particles and titanium oxide on the surface of the titanium layer.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0010] However, the inventors of the present application have discovered that in an inexpensive separator for a fuel cell manufactured by performing a surface treatment on a substrate containing iron as disclosed in Patent Documents 1 and 2, iron ions eluted from the substrate may deteriorate the electrolyte membrane of the fuel cell.

[0011] Therefore, an object of the present invention is to provide an inexpensive separator with high corrosion resistance.

Means for Solving the Problems

[0012] For example, Japanese Patent Application Laid-Open No. 2010-138252 describes a method for producing a polymer electrolyte membrane precursor, which includes emulsion polymerizing a mixture containing a fluorine-containing monomer having radical polymerizability, an emulsifier, and a polymerization initiator to capture radicals generated in the polymer electrolyte membrane used in a fuel cell, adding a coagulant to the obtained polymer dispersion to obtain a polymer, wherein at least one of the emulsifier, the polymerization initiator, and the coagulant contains a compound containing a metal selected from the group consisting of Ce, Tl, Mn, and Yb, and the total content of the compound containing the metal in each of the emulsifier, the polymerization initiator, and the coagulant is 30 mol% or more.

[0013] However, the metals that can be introduced into the polymer electrolyte membrane to impart radical resistance in Japanese Patent Application Laid-Open No. 2010-138252 may reduce the output of the fuel cell. This is because when a part of the hydrogen atoms of the sulfonic acid groups contained in a perfluorinated membrane, which is a general polymer electrolyte membrane, such as a sulfonated polyphenylene sulfide membrane, is substituted by a metal such as Ce, although the oxidation resistance is improved and the durability is improved, the proton conductivity decreases.

[0014] Therefore, as a result of various studies on means for solving the above problems, the inventors of the present invention have found that in a method for manufacturing a separator having a surface treatment step, by using a substrate containing iron as a substrate and forming a surface layer containing an iron scavenger on the surface of the substrate, iron ions eluted from the substrate can be captured by the iron scavenger to form a stable salt and rendered harmless, and thus completed the present invention.

[0015] That is, the gist of the present invention is as follows. (1) A fuel cell separator including a substrate containing iron and a surface layer provided on the surface of the substrate, wherein the surface layer includes an iron scavenger and a resin. (2) The fuel cell separator according to (1), wherein the iron scavenger includes at least one selected from the group consisting of an iron hydroxide ceramic carrier, sodium hydroxide, calcium hydroxide, and calcium carbonate. (3) The fuel cell separator according to (1) or (2), wherein the resin contains an epoxy resin.

Advantages of the Invention

[0016] The present invention provides an inexpensive separator with high corrosion resistance.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0018] Hereinafter, preferred embodiments of the present invention will be described in detail. In this specification, the features of the present invention will be described with reference to the drawings as appropriate. In the drawings, the dimensions and shapes of each part are exaggerated for clarity and do not accurately depict the actual dimensions and shapes. Therefore, the technical scope of the present invention is not limited to the dimensions and shapes of each part shown in these drawings. Note that the separator for a fuel cell of the present invention is not limited to the following embodiments, and can be implemented in various forms with modifications and improvements that can be made by those skilled in the art without departing from the gist of the present invention.

[0019] The present invention relates to a fuel cell separator including a substrate containing iron and a surface layer provided on the surface of the substrate, wherein the surface layer contains an iron scavenger and a resin.

[0020] The separator in the present invention is a component of a fuel cell (single cell) and is disposed on both sides of a membrane electrode assembly (an electrolyte membrane and electrode layers of an anode and a cathode disposed on both sides of the electrolyte membrane).

[0021] Examples of the base material containing iron include, but are not limited to, plate-shaped base materials made of stainless steel [SUS (iron, chromium, nickel)] or iron, which are base materials made of materials cheaper than titanium.

[0022] Examples of the stainless steel base material (stainless steel substrate) include, but are not limited to, SUS316 with high corrosion resistance, SUS447 which is cheaper than SUS316, and the like.

[0023] By using an inexpensive material as the base material containing iron, the amount of titanium used can be reduced compared to using a titanium base material, and the cost can be lowered.

[0024] The thickness of the base material containing iron is not limited, but is usually 0.05 mm to 0.2 mm, preferably 0.08 mm to 0.12 mm.

[0025] By setting the thickness of the base material containing iron within the above range, it is possible to easily perform press forming while suppressing the raw material cost.

[0026] A surface layer is provided on the base material containing iron, and the surface layer contains an iron capture material.

[0027] The iron capture material means a material that can capture iron ions (Fe 2+ ) that can elute from the base material containing iron, and compounds that react with iron ions to form stable salts, including, but not limited to, for example, iron hydroxide ceramic carriers, bases such as sodium hydroxide, calcium hydroxide, or calcium carbonate, and mixtures of one or more of them.

[0028] The iron hydroxide ceramic carrier is a material having a carrier formed from ceramic or the like and iron hydroxide Fe(OH)2 coated on the surface of the carrier. The iron hydroxide Fe(OH)2 on the surface of the iron hydroxide ceramic carrier adsorbs iron ions (Fe 2+ ), and then, by hydrolysis and air oxidation, the iron ions can be continuously captured.

[0029] The content of the iron scavenger is not limited, but is usually 0.001% by weight to 0.1% by weight, preferably 0.01% by weight to 0.1% by weight, based on the total weight of the surface layer.

[0030] By including an iron scavenger in the surface layer, iron ions that can elute from an iron-containing base material can be converted into a form of salt that is harmless to the fuel cell, suppressing the deterioration of the polymer electrolyte membrane and improving the corrosion resistance of the fuel cell.

[0031] The surface layer further contains a resin.

[0032] Examples of the resin include, but are not limited to, phenol and epoxy resin. Epoxy resin is preferred as the resin.

[0033] The content of the resin is not limited, but is usually 20% by weight to 80% by weight, preferably 30% by weight to 50% by weight, based on the total weight of the surface layer.

[0034] By further including a resin in the surface layer, the iron scavenger can be stably supported (coated) on the surface of the iron-containing base material.

[0035] The surface layer may further contain conductive particles.

[0036] Examples of the conductive particles include, but are not limited to, carbon such as carbon black, antimony-doped tin oxide (ATO), noble metals, tin-doped indium oxide (ITO), LaNiO3, SrMoO3, (La,Sr)CoO3, LaTiO3, MgZnO, Ta2O, ZnMgAlO, SrSnO3, etc. Carbon and antimony-doped tin oxide, which are inexpensive, are preferred as the conductive particles.

[0037] When the conductive particles are present, the content of the conductive particles is not limited, but is usually 20% by weight to 80% by weight, based on the total weight of the surface layer.

[0038] By further including conductive particles in the surface layer, the conductivity of the separator for fuel cells can be ensured.

[0039] The average thickness of the surface layer is not limited. However, when measured by cross-sectional TEM observation, for example, it is usually 1 μm to 20 μm, preferably 5 μm to 10 μm.

[0040] When the average thickness of the surface layer is within the above range, iron ions that can elute from the iron-containing base material can be converted into a harmless salt form for the fuel cell, suppressing the deterioration of the polymer electrolyte membrane and improving the corrosion resistance of the fuel cell.

[0041] In addition to the surface layer, the separator for fuel cells of the present invention may further include a titanium layer for further improving corrosion resistance.

[0042] The titanium layer may be a titanium layer known in the art, for example, a titanium layer formed by sputtering, ion plating, CVD method, etc.

[0043] Furthermore, in addition to the surface layer, the separator for fuel cells of the present invention may further include a conductive layer for further ensuring conductivity.

[0044] Examples of the conductive layer include a carbon layer known in the art, for example, a carbon layer formed by arc ion plating method, etc.

[0045] In the separator for a fuel cell of the present invention, when a titanium layer and / or a conductive layer is present, the order of the surface layer, the titanium layer, and / or the conductive layer is not limited. For example, the separator for a fuel cell includes a base material containing iron, a titanium layer provided on the surface of the base material, and a surface layer provided on the surface of the titanium layer. For example, the separator for a fuel cell includes a base material containing iron, a conductive layer provided on the surface of the base material, and a surface layer provided on the surface of the conductive layer. For example, the separator for a fuel cell includes a base material containing iron, a titanium layer provided on the surface of the base material, a conductive layer provided on the surface of the titanium layer, and a surface layer provided on the surface of the conductive layer. For example, the separator for a fuel cell includes a base material containing iron, a titanium layer provided on the surface of the base material, a first surface layer provided on the surface of the titanium layer, a conductive layer provided on the surface of the first surface layer, and a second surface layer provided on the surface of the conductive layer.

[0046] The separator for a fuel cell of the present invention can be manufactured by applying a paint containing an iron scavenger onto the surface of a base material containing iron by manual application using a surface treatment method known in the art, such as a brush, a roller brush, a spatula, etc., or by equipment operation using air spraying, airless spraying, dipping, etc., or by apparatus operation using adsorption by electric attraction (electrostatic action).

[0047] FIG. 1 schematically shows an example of a method for manufacturing a separator for a fuel cell of the present invention. In FIG. 1, the separator for a fuel cell is first manufactured by adding an iron scavenger to a resin and uniformly stirring to prepare a paint, and then applying the prepared paint onto the surface of a base material containing iron. In the separator for a fuel cell, Fe ions eluted from the base material containing iron react with the iron scavenger contained in the surface layer and are detoxified by forming a stable salt.

[0048] The separator for a fuel cell according to the present invention can be used in various electrochemical devices such as a polymer electrolyte fuel cell.

Example

[0049] Hereinafter, several embodiments of the present invention will be described, but the present invention is not intended to be limited to those shown in such embodiments.

[0050] 1. Proton (H3O + ) permeation experiment In an apparatus including two chambers capable of accommodating two different solutions and a partition provided between the two chambers, a solution with pH 3 is introduced into one chamber, and a solution with pH 1 is introduced into the other chamber. As the partition, plate-shaped porous glass (pore diameter 4 nm) (hereinafter referred to as "porous glass 4 nm"), plate-shaped porous glass (pore diameter 50 nm) (hereinafter referred to as "porous glass 50 nm"), a material with an epoxy resin coated on one surface of plate-shaped porous glass (pore diameter 50 nm) (hereinafter referred to as "porous glass 50 nm + epoxy resin"), or a material with a Kapton tape attached to one surface of plate-shaped porous glass (pore diameter 50 nm) (hereinafter referred to as "porous glass 50 nm + Kapton tape") is used. By measuring the change in pH of the solution in the chamber into which the solution with pH 3 is introduced over time, the permeation of protons (H3O + ) due to the difference in the type of partition was observed.

[0051] A schematic diagram of this experiment is shown in Figure 2. In this experiment, as shown in Figure 2, a partition with a surface layer (film) on porous glass or on the surface of porous glass is provided between the solution with pH 3 (pH change measurement side) and the solution with pH 1 (low pH side), and by measuring the change in pH of the solution with pH 3 over time, it is possible to observe whether protons (H3O + ) permeate through the surface layer.

[0052] Figure 3 shows the relationship between the elapsed time and pH in each partition in this experiment. From Figure 3, when the partition is made of porous glass 4 nm, porous glass 50 nm, and porous glass 50 nm + epoxy resin, the pH of the solution at pH 3 gradually decreased, while in the case of porous glass 50 nm + Kapton tape, the pH of the solution at pH 3 did not change. Therefore, while there are paths through which protons (H3O + ) can permeate in porous glass 4 nm, porous glass 50 nm, and epoxy resin, it was found that there are no paths through which protons (H3O + ) can permeate in Kapton tape.

[0053] From this experiment, it was found that iron ions (Fe + , ionic radius: about 0.8 Å), which have an ionic radius smaller than that of protons (H3O 2+ , ionic radius: about 2 Å), can permeate through epoxy resin. That is, in a fuel cell separator, if a surface layer containing an iron scavenger is provided on the surface of a substrate containing iron, even if the iron ions contained in the substrate permeate and elute through the epoxy resin or film defects in the surface layer, it was found that they are captured by the iron scavenger present in the surface layer and rendered harmless.

[0054] 2. Manufacture of Fuel Cell Separator A fuel cell separator was manufactured by applying a paint containing calcium carbonate as an iron scavenger in epoxy resin to the surface of a substrate containing iron.

Claims

1. A fuel cell separator comprising a substrate containing iron and a surface layer provided on the surface of the substrate, wherein the surface layer contains an iron scavenger, a resin, and conductive particles, and the iron scavenger contains at least one selected from the group consisting of an iron hydroxide ceramic carrier, sodium hydroxide, calcium hydroxide, and calcium carbonate.

2. The fuel cell separator according to claim 1, wherein the content of the conductive particles is 20% by weight to 80% by weight based on the total weight of the surface layer.

3. The fuel cell separator according to claim 1 or 2, further comprising a conductive layer between the substrate and the surface layer.

4. The fuel cell separator according to any one of claims 1 to 3, wherein the resin contains an epoxy resin.

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