JP2018159116A - Fuel cell separator and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell separator provided with a carbon film having excellent adhesion and conductivity, and a method for producing the same. SOLUTION: A step of forming a relaxation layer 29 on at least one surface of a base material 25 by electrolytic deposition using an aqueous solution containing an organic additive, and the base material 25 on which the relaxation layer 29 is formed under a hydrogen atmosphere. The heat treatment step and the step of coating the surface of the relaxation layer 29 with the carbon film 30 by electrolytic deposition are performed. In the step of forming the relaxation layer 29, the organic additive is a carboxylate salt or a sulfonate salt. An organic compound having a basic structure of at least one selected from the group consisting of a sulfate ester salt, an amine salt, a quaternary ammonium salt, and a betaine-type compound, and having 25 or less carbon atoms with a single hydrocarbon molecular chain bonded In the step of forming a relaxation layer 29 having a thickness of 0.1 μm or more and 5 μm or less and coating with a carbon film 30, the thickness is 0.1 μm or more and 10 μm or more. The following carbon coating 30 is used for coating. [Selection diagram] Figure 2

Description

  The present invention relates to a fuel cell separator and a method for producing the same.

  A fuel cell reacts hydrogen and oxygen to convert chemical reaction energy into electrical energy. A fuel cell includes an electrolyte, two electrodes, and two separators. A configuration in which electrodes are arranged on both sides of the electrolyte and separators are arranged on both sides of the electrodes is called a cell. Among a plurality of types of fuel cells depending on the type of electrolyte, a polymer electrolyte fuel cell (PEFC or PEMFC: Polymer Electrolyte Fuel Cell, Proton Exchange Membrane Fuel Cell) has a lower power generation temperature (from room temperature to about 100). Because it can generate electricity at ℃), it is attracting attention.

  The PEFC has a basic structure in which a membrane-electrode assembly (MEA) is sandwiched between separators, and generates an electromotive force between the separators. Usually, PEFC is used by connecting a plurality (hundreds) of fuel cells of the above basic structure in series.

  In addition to partitioning the fuel cells, the separator plays a role of flowing hydrogen and oxygen over the entire surface of the gas diffusion layer and flowing the generated current to the adjacent fuel cells. Therefore, the separator is required to have properties such as conductivity, corrosion resistance (acid, humidity, etc.), gas barrier properties, and mechanical properties.

  The separator has good electronic conductivity, good separation between oxygen and hydrogen at both electrodes, low contact resistance with MEA, and good durability in the environment inside the fuel cell. Something is required. A gas diffusion layer (Gas Diffusion Layer, GDL) of MEA is generally composed of carbon paper in which carbon fibers are integrated. Therefore, the separator is required to have good conductivity with respect to carbon.

  The separator includes a carbon separator and a metal separator, and the carbon separator is the mainstream. A metal separator has higher strength and ductility than a brittle carbon separator, and is excellent in workability. Therefore, the metal separator can be mass-produced because the gas flow path (protrusions and grooves) can be formed by press working without cracking the material for the metal separator.

  In addition, since the metal separator has higher strength and ductility than the carbon separator and is excellent in workability, it can be thinned. Therefore, since the metal separator can make the fuel cell compact, the practical use of a metal separator having good conductivity with respect to carbon is indispensable for mass production and spread of the fuel cell.

  As a material for the metal separator, stainless steel and titanium are known. However, since the contact resistance against carbon is large as it is, many techniques for reducing this have been proposed (for example, see Patent Document 1). . Examples of the metal separator include those using a noble metal such as Au and Pt, those plated with the noble metal on the surface, and those not using the noble metal.

  As shown in FIG. 3, as a metal separator that does not use a noble metal, a titanium alloy foil 101, a non-conductive film 102 formed on the surface of the titanium alloy foil 101, and a resin layer 103 formed on the surface of the non-conductive film 102, (For example, patent document 2) is disclosed. In the above-mentioned Patent Document 2, the surface of the titanium alloy foil 101 is treated under a predetermined condition to generate TiO in the nonconductive film 102 to form a conductive film. Further, the resin layer 103 includes conductive particles such as Ag, and has improved corrosion resistance.

  Further, as a metal separator not using a noble metal, as shown in FIG. 4, a titanium base material 106, a carbon solid solution layer 107 formed on the surface of the titanium base material 106, and a surface of the carbon solid solution layer 107 are formed. A metal separator 105 including the carbon layer 108 is disclosed (for example, Patent Document 3). In Patent Document 3, a carbon solid solution layer 107 is formed by solid-dissolving carbon element on the surface of a titanium substrate 106 by plasma carburization, and carbon is formed on the surface of the carbon solid solution layer 107 using plasma CVD. A structure in which adhesion is improved by forming the layer 108 is disclosed.

  Further, as shown in FIG. 5, a metal structure 110 is known in which the surface of the metal foil 111 is covered with a carbon layer 112 and functions such as corrosion resistance and conductivity are imparted. Patent Document 4 discloses that the carbon layer 112 can be formed on the surface of the metal foil 111 by an electrochemical process using a molten salt, a normal pressure, a low voltage, a simple and inexpensive manufacturing apparatus, and in principle. It is disclosed that a carbon layer 112 containing no hydrogen can be obtained, and as a result, high conductivity and adhesion can be obtained.

JP 2007-5084 A Japanese Patent No. 5888473 JP 2010-248572 A JP 2009-120860 A

  However, in the case of the above-mentioned Patent Document 2, the generation of TiO is limited to the case where a titanium component is present in the surface component, and in order to maintain the durability of the separator in a corrosive environment, the surface of such a titanium alloy is used. It is necessary to use a resin (binder) that has high affinity with the resin, and from the viewpoint of adhesion and corrosion resistance, a primer treatment and an adhesive layer are required between the metal and the resin, resulting in a high electrical resistance. There is.

  In the case of Patent Document 3, the vapor phase growth method such as CVD or PVD has a problem that the condition control in a large chamber is complicated and batch production is unsuitable for mass production. Moreover, since the raw material basically uses hydrocarbons, it is easy to obtain a carbonaceous film containing hydrogen, and there is a problem that the adhesion of the film is lowered.

  In addition, the present inventors conducted a follow-up experiment for forming a carbon film by an electrochemical process using the molten salt described in Patent Document 4 described above, and although the electrical resistance was lowered and the conductivity was improved, the change in cooling and heating was repeated. It has been found that good adhesion cannot be obtained in an environment, and the durability to maintain conductivity cannot be secured. The cause of this is thought to be due to the effect of the difference in thermal expansion between the metal foil and the carbon film. Therefore, it is important to reduce the difference in thermal expansion between the metal foil and the carbon film and suppress the decrease in adhesion. .

  Therefore, the present inventors have developed a method of reducing the difference in thermal expansion between the metal foil and the carbon film by forming a conductive metal layer that is in the range between the thermal expansion of the metal foil and the carbon film. I thought.

  However, after the step of forming the relaxation layer, when it was covered with a carbon film, it became clear that the carbon film was burned and the adhesion decreased. The reason for this is that when an aqueous solution is used for plating to form a relaxation layer, various organic additives are generally used to obtain a stable film, and these organic additives are incorporated into the plating film. It has been known. It was found that the organic additives in these films were burned during the process of coating with a carbon film by an electrochemical process using a high-temperature molten salt.

  As a result of diligent efforts, the inventors of the present invention have conceived that the organic additive remaining in the relaxation layer after the formation of the relaxation layer is removed by heat treatment in a hydrogen atmosphere, and more efficiently removed. The relaxation layer forming method and its structure were found.

  An object of this invention is to provide the separator for fuel cells provided with the carbon membrane excellent in adhesiveness and electroconductivity, and its manufacturing method.

  The method for producing a separator for a fuel cell according to the present invention includes a step of forming a relaxation layer on at least one surface of a substrate by electrolytic deposition using an aqueous solution containing an organic additive, and a substrate on which the relaxation layer is formed. And a step of coating the surface of the relaxation layer with a carbon film by electrolytic deposition, wherein the step of forming the relaxation layer includes the step of forming the relaxation layer with the organic additive being a carboxylate salt or sulfone salt. Having at least one basic structure selected from the group consisting of acid salts, sulfuric acid ester salts, amine salts, quaternary ammonium salts, and betaine type compounds, and having 25 or less carbon atoms in which hydrocarbon molecular chains are bonded in a single chain The step of forming the relaxation layer having an addition amount of 0.1 to 15 g / L using an organic compound and having a thickness of 0.1 μm to 5 μm and covering with the carbon film has a thickness of 0.1 μm. The carbon film of 10 μm or less To cover.

A fuel cell separator according to the present invention is a fuel cell separator comprising a base material, a relaxation layer on one surface of the base material, and a carbon film covering the surface of the relaxation layer. The thickness is 0.1 μm or more and 5 μm or less, the thickness of the carbon film is 0.1 μm or more and 10 μm or less, the carbon film is not peeled by a tape test, and the contact resistance of the surface is 20 mΩ · cm ² or less.

  According to the present invention, since defects such as burns do not occur in the carbon film, it is possible to obtain a fuel cell separator provided with a carbon film having excellent adhesion and conductivity between the relaxing layer and the carbon film.

It is a schematic diagram which shows the basic composition of a fuel cell. It is a longitudinal cross-sectional view which shows the structure of the separator for fuel cells, FIG. 2A is this embodiment, FIG. 2B is a modification. It is a longitudinal cross-sectional view which shows the structure of a well-known metal separator (1). It is a longitudinal cross-sectional view which shows the structure of a well-known metal separator (2). It is a longitudinal cross-sectional view which shows the structure of a well-known metal structure material.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(overall structure)
As shown in FIG. 1, the fuel cell includes a plurality of fuel cells 10 each having an electrolyte 12, two electrodes 11 and 13, and two fuel cell separators (hereinafter referred to as “separators”) 22 and 24. , Convert chemical reaction energy into electrical energy. The electrodes 11 and 13 have catalyst layers 14 and 16 and gas diffusion layers 18 and 20, respectively. The fuel cell 10 has a configuration in which electrodes 11 and 13 are disposed on both sides of the electrolyte 12, and separators 22 and 24 are disposed on both sides of the electrodes 11 and 13.

  As shown in FIG. 2A, the separators 22 and 24 include a plate-like base material 25, at least one surface of the base material 25, in the case of this figure, a relaxation layer 29 formed on both surfaces, and carbon that covers the relaxation layer 29. And a coating 30. As shown in FIG. 2B, the separators 22 and 24 may have a flow path layer 32 having gas flow paths 26 and 28 on the surface of the carbon film 30. The flow path layer 32 may be formed of a conductive resin that can be easily processed.

The substrate 25 has resistance to molten salt heat treatment and hydrogen resistance when coated with the carbon film 30. Furthermore, the base material 25 is preferably excellent in conductivity. The substrate 25 is made of, for example, Al, Ag, Au, Be, Ca, Cd, Co, Cu, Fe, In, Ir, Li, Mg, Mo, Na, Ni, Os, Pd, Pt, Rh, Ru, Sn , W, Zn, or alloys thereof. In addition, the base material 25 has Al, Ag, Au, Be, Ca, Co, Cu, Fe, In, Ir, and Mg in consideration of the thermal expansion coefficient (about 4 × 10 ⁻⁶ / K) of the carbon film 30. Mo, Ni, Os, Pd, Pt, Rh, Ru, Sn, W, or an alloy thereof is more preferable. The base material 25 is made of Al, Ag, Au, Co, Cu, Fe, In, Ir, Mg, Mo, Ni, Os, Pd, Pt, Rh, Ru, Sn, W, or these because of their availability. More preferred are alloys. The substrate 25 is most preferably Al, Cu, Fe, Mg, Ni, Sn, or an alloy thereof. The maximum height Rmax of the surface roughness of the substrate 25 is preferably less than 5 μm. When the maximum height Rmax of the surface roughness of the substrate 25 is 5 μm or more, an uncoated portion of the relaxing layer 29 is likely to occur. The maximum height Rmax of the surface roughness of the substrate 25 is a value measured with a laser microscope.

  The relaxing layer 29 has a role of suppressing a decrease in adhesion between the base material 25 and the carbon film 30 due to a difference in thermal expansion between the base material 25 and the carbon film 30. The relaxation layer 29 can be selected from Ag, Au, Cu, Fe, In, Ni, Pd, Pt, Rh, Ru, and Sn. The relaxation layer 29 is preferably any one of Ag, Au, Cu, Fe, Ni, Pd, Pt, Rh, and Ru in order to more reliably suppress the decrease in adhesion. The relaxation layer 29 is more preferably one of Ag, Au, Cu, Ni, Pd, Pt, Rh, and Ru from the viewpoint of hydrogen resistance. The relaxation layer 29 is most preferably Cu or Ni from the viewpoint of availability.

  The thickness of the relaxing layer 29 is not less than 0.1 μm and not more than 5 μm. If the thickness of the relaxation layer 29 is less than 0.1 μm, the effect of relaxation of thermal expansion cannot be obtained, but if the thickness is 0.1 μm or more, the thermal expansion difference between the substrate 25 and the carbon film 30 is not achieved. Can be relaxed. When the thickness of the relaxation layer 29 is 5 μm or less, the organic additive remaining in the film can be removed by subsequent hydrogen heat treatment while obtaining the effect of thermal expansion relaxation. When the thickness exceeds 5 μm, the organic compound remains in the relaxation layer 29 even after the heat treatment, and burns occur with high probability in the molten salt heat treatment when the carbon film 30 is coated. Here, “discoloration” refers to a phenomenon in which the film becomes dark. The thickness of the relaxation layer is 3 times 5000 times with a scanning electron microscope (SEM) using a sample in which the base material after layer formation is embedded in resin and then polished in a direction perpendicular to the surface of the base material. Observe the field of view, measure any three locations in each field of view image, and average the thickness of a total of nine locations.

  The maximum height Rmax of the surface roughness of the relaxing layer 29 is preferably 0.1 μm or more and 10 μm or less. The relaxation layer 29 can improve the adhesion with the carbon film 30 by having the surface roughness within the above range. The maximum height Rmax of the surface roughness of the relaxing layer 29 is a value measured with a laser microscope.

  The relaxation layer 29 preferably has a coverage of 55% or more with respect to the substrate 25, and most preferably 100%. The coverage is measured by immersing the base material 25 after forming the relaxation layer 29 in an acidic aqueous solution (such as dilute hydrochloric acid) for 5 minutes or more, and then observing with an optical microscope or a scanning electron microscope (SEM). The area ratio, which is calculated based on an image obtained by taking in 1-cm square image data and binarized, is defined as a surface area of the uncovered portion with respect to the surface area of the base material 25. The average value of values calculated at any three locations for one base material 25 is defined as the coverage of the base material 25.

  The relaxation layer 29 preferably has a crystal grain size of 30 nm or more. The organic compound is presumed to remain between crystal grains (grain boundaries). For this reason, the larger the crystal grain size, the fewer the grain boundaries, and the easier access and desorption of the gas facilitates removal of the organic compound. The crystal grain size of the relaxation layer 29 is 5 μm or less, similar to the upper limit of the thickness.

  The carbon film 30 needs to have a coverage of 100% with respect to the relaxation layer 29 in order to obtain good corrosion resistance. The thickness of the carbon film 30 is 0.1 μm or more and 10 μm or less. When the carbon film 30 has a thickness of less than 0.1 μm, the coverage of the relaxing layer 29 may not be 100%. When the thickness of the carbon film is more than 10 μm, the unevenness of the surface becomes large, which is inappropriate as the separators 22 and 24. The thickness of the carbon film was determined by observing 3 fields of view 5000 times by SEM using a sample polished in the direction perpendicular to the surface of the substrate after embedding the coated substrate in resin, and in each field image Each of these three locations is measured, and the total thickness at 9 locations is averaged.

  When the relaxation layer 29 is formed on the substrate 25 by electrolytic plating, it is necessary to add an organic additive containing an organic compound to the plating bath in order to obtain a stable plating film. A part of the organic compound contained in the organic additive remains in the relaxing layer 29. The organic compound remaining in the relaxation layer 29 causes defects such as burns in the carbon film 30 when the carbon film 30 is coated in high-temperature molten salt electrolysis. Such a defect causes a decrease in adhesion between the base material 25 and the carbon film 30 and an increase in surface contact resistance in the separators 22 and 24.

In the separators 22 and 24 of the present embodiment, since the organic compound content is 1.0 mg / cm ² or less, the carbon film 30 does not have defects such as burns, and the relaxation layer 29 and the carbon film 30 are in close contact with each other. Can be improved. Content of the organic compound is determined by heating the separators 22 and 24 from room temperature to 1000 ° C. in an air atmosphere by temperature-programmed desorption gas mass spectrometry, and desorbing the amount of carbon (converted to molecules) at that time in unit area ( 1 cm ² ).

Since the separators 22 and 24 of the present embodiment are free from defects such as burns, the surface contact resistance can be reduced to ²⁰ mΩ · cm ² or less. The contact resistance is obtained by stacking carbon paper constituting the gas diffusion layer on the separators 22 and 24, sandwiching it from both sides with an Au-plated copper plate, and applying a load of 10 kg / cm ^{2 with} a surface pressure of 10A by the 4-terminal method. The value obtained from the voltage measured by applying.

(Production method)
Next, a method for manufacturing the separators 22 and 24 will be described. The separators 22 and 24 include a step of forming a relaxation layer 29 on the surface of the substrate 25, a step of heat-treating the substrate 25 on which the relaxation layer 29 is formed in a hydrogen atmosphere, and a surface of the relaxation layer 29 with a carbon film 30. It can manufacture by the process to coat | cover.

  First, the process of forming the relaxation layer 29 on the surface of the substrate 25 will be described. The relaxation layer 29 can be formed by electrolytic deposition. A plating bath used for electrolytic deposition uses an aqueous solution containing an organic additive.

  Organic additives improve the wettability of the substrate surface (plated surface) and prevent the non-plated part (pit defects) by improving the detachability of hydrogen gas generated on the substrate surface, and molecules adsorb and desorb gently on the plated surface. By doing so, there is an effect of obtaining a stable plating layer by generating a composite action of controlling the plating reaction. Since the surface of the substrate has a lot of irregularities that become surface roughness, the plating reaction control as described above causes the precipitation reaction and nucleation to proceed in the recesses, and the formation of a uniform and smooth film by suppressing the precipitation of the protrusions. A stable plating layer can be obtained. As the molecules that can obtain this effect, surfactants (categorized into cationic, anionic, amphoteric, nonionic, etc.) and polymer compounds (gelatin, polyethylene glycol, etc.) are mainly known. Since a relatively large molecule tends to remain in the relaxation layer 29, it needs to be a low molecular weight surfactant.

  That is, the organic additive has at least one basic structure selected from the group consisting of carboxylate, sulfonate, sulfate ester salt, amine salt, quaternary ammonium salt, and betaine type compound, and the hydrocarbon molecular chain is An organic compound having a carbon number of 25 or less bonded in a single chain is used. More preferably, the organic additive has 5 or less double bonds per molecular weight.

  Specific examples of organic additives having a small molecular weight include sodium formate, sodium acetate, sodium propionate, sodium butyrate, sodium valerate, sodium caproate, sodium enanthate, sodium caprylate, sodium pelargonate, capric acid. Sodium, sodium undecanoate, sodium laurate, sodium tridecanoate, sodium myristate, sodium pentadecanoate, sodium palmitate, sodium margarate, sodium stearate, sodium nonadecanoate, sodium icosanoate, sodium heicosanoate, sodium docosanoate, Sodium tricosanoate, sodium tetracosanoate, sodium pentacosanoate, sodium sulfonate, sodium methanesulfonate, Sodium sulfonate, sodium propanesulfonate, sodium butanesulfonate, sodium pentanesulfonate, sodium hexanesulfonate, sodium heptanesulfonate, sodium octanesulfonate, sodium nonanesulfonate, sodium decanesulfonate, sodium undecanesulfonate, dodecane Sodium sulfonate, sodium tridecane sulfonate, sodium tetradecane sulfonate, sodium pentadecane sulfonate, sodium hexadecane sulfonate, sodium heptadecane sulfonate, sodium octadecane sulfonate, sodium nonadecane sulfonate, sodium icosane sulfonate, Henko Sodium sulfonate, sodium docosan sulfonate, tricosan sulfonate Acid sodium, sodium tetracosansulfonate, sodium pentacosansulfonate, sodium methylbenzenesulfonate, sodium ethylbenzenesulfonate, sodium propylbenzenesulfonate, sodium butylbenzenesulfonate, sodium pentylbenzenesulfonate, sodium hexylbenzenesulfonate, Sodium heptylbenzenesulfonate, sodium octylbenzenesulfonate, sodium nonylbenzenesulfonate, sodium decylbenzenesulfonate, sodium undecylbenzenesulfonate, sodium dodecylbenzenesulfonate, sodium tridecylbenzenesulfonate, sodium tetradecylbenzenesulfonate , Sodium pentadecylbenzenesulfonate, hexadecyl Sodium benzenesulfonate, sodium heptadecylbenzenesulfonate, sodium octadecylbenzenesulfonate, sodium nonadecylbenzenesulfonate, sodium sulfate, sodium methyl sulfate, sodium ethyl sulfate, sodium propyl sulfate, sodium butyl sulfate, sodium pentyl sulfate, hexyl sulfate Sodium, sodium heptyl sulfate, sodium octyl sulfate, sodium nonyl sulfate, sodium decyl sulfate, sodium undecyl sulfate, sodium lauryl (dodecyl) sulfate, sodium tridecyl sulfate, sodium tetradecyl sulfate, sodium pentadecyl sulfate, sodium hexadecyl sulfate, sodium heptadecyl sulfate, octadecyl Sodium sulfate, sodium nonadecyl sulfate, icosanyl sulfate Sodium, sodium heicosanyl sulfate, sodium docosanyl sulfate, sodium tricosanyl sulfate, sodium tetracosanyl sulfate, sodium pentacosanyl sulfate, methylamine hydrochloride, ethylamine hydrochloride, propylamine hydrochloride, butylamine hydrochloride, pentylamine hydrochloride, hexylamine hydrochloride, Heptylamine hydrochloride, octylamine hydrochloride, nonylamine hydrochloride, decylamine hydrochloride, undecylamine hydrochloride, dodecylamine hydrochloride, tridecylamine hydrochloride, tetradecylamine hydrochloride, pentadecylamine hydrochloride, hexadecylamine Hydrochloride, heptadecylamine hydrochloride, octadecylamine hydrochloride, nonadecylamine hydrochloride, icosanylamine hydrochloride, heicosanylamine hydrochloride, docosanylamine hydrochloride Tricosanylamine hydrochloride, tetracosanylamine hydrochloride, pentacosanylamine hydrochloride, dimethylamine hydrochloride, trimethylamine hydrochloride, tetramethylammonium chloride, ethyltrimethylammonium chloride, propyltrimethylammonium chloride, butyltrimethylammonium chloride, chloride Pentyltrimethylammonium chloride, hexyltrimethylammonium chloride, heptyltrimethylammonium chloride, octyltrimethylammonium chloride, nonyltrimethylammonium chloride, decyltrimethylammonium chloride, undecyltrimethylammonium chloride, dodecyltrimethylammonium chloride, tridecyltrimethylammonium chloride, tetradecyltrimethyl chloride Ammonium, pentadecyltrimethylammonium chloride, Hexadecyltrimethylammonium chloride, heptadecyltrimethylammonium chloride, octadecyltrimethylammonium chloride, nonadecyltrimethylammonium chloride, icosyltrimethylammonium chloride, heicosyltrimethylammonium chloride, and docosyltrimethylammonium chloride can be used. In addition, the carboxylic acid, the sulfonic acid, and the sulfate ester are bonded to the quaternary ammonium, and a betaine type compound (for example, octadecylaminomethyl) having a positive charge and a negative charge at non-adjacent positions in the same molecule. Dimethylsulfopropyl betaine etc.) can also be used. A mixture of at least one of these organic additives may be used. In addition, each salt of carboxylate, sulfonate, and sulfate ester salt may be an alkali metal other than sodium. The quaternary ammonium salt is not limited to chloride, but may be bromide or hydroxide. The addition amount of the organic additive is 0.1 to 15 g / L, preferably 0.1 to 5 g / L with respect to the entire plating bath.

  The plating bath may further contain saccharin or butynediol as a brightener (smoothing agent). Although the addition amount is not particularly limited, for example, the addition amount of saccharin is several g to several tens g / L, and the addition amount of butynediol is 0.1 to 0.3 g / L.

The composition of the plating bath when forming the relaxation layer 29 made of Ni is nickel sulfate: 240 to 300 g / L, nickel chloride: 45 to 50 g / L, boric acid: 30 to 80 g / L, and the above organic additives. be able to. While stirring the plating bath, plating can be performed under the conditions of a bath temperature of 45 ° C. to 90 ° C. and a current density of ² to 8 A / dm ² . The amount of boric acid added is preferably 40 to 80 g / L because it can more reliably prevent burns. The bath temperature is preferably 60 to 80 ° C.

The composition of the plating bath when forming the relaxation layer 29 made of Cu is copper sulfate: 50 to 200 g / L, sulfuric acid: 50 to 200 g / L, sodium chloride: 60 to 150 mg / L, and the above organic additives. Can do. While stirring the plating bath, plating can be performed under the conditions of a bath temperature of 20 to 50 ° C. and a current density of 0.1 to 8 A / dm ² .

Next, the process of heat-treating the base material 25 on which the relaxation layer 29 is formed in a hydrogen atmosphere will be described. In the heat treatment step, the volume of hydrogen supplied into the reaction vessel is preferably 40 to 3000 mL. For example, a mixed gas of H ₂ and Ar of less than 4 vol% can be supplied as an atmospheric gas at a flow rate of 500 mL / min, and the temperature can be 120 to 1000 ° C. and the time can be 2 minutes to 2.5 hours. When the temperature of the heat treatment is less than 120 ° C., the organic compound hardly reacts with hydrogen, and it becomes difficult to remove H ₂ O generated by the above reaction. When the temperature of the heat treatment exceeds 1000 ° C., the reaction rate between the organic compound and hydrogen reaches the upper limit, leading to wasted heat energy. The temperature of the heat treatment is preferably 700 ° C. or lower in order to prevent deformation such as function deterioration and warping due to a change in the structure of the substrate 25. Note that the mixed gas may be N ₂ or He instead of Ar.

  Next, a process of coating the surface of the relaxing layer 29 with the carbon film 30 will be described. A known method using a molten salt can be applied to the step of coating the surface of the relaxing layer 29 with the carbon film 30. For example, a manufacturing apparatus including an electric furnace, a holder installed in the electric furnace, and an electrolytic cell installed in the holder is used. The manufacturing apparatus further includes an introduction pipe for introducing atmospheric gas into the holder and an exhaust pipe for exhausting the gas in the holder. As the electrolytic cell, a high-purity alumina crucible can be used. In the electrolytic cell, an alkali metal halide or the like is melted. In a state where the atmospheric gas is circulated in the holder, a carbonate ion source (for example, potassium carbonate) or a carbide ion source (for example, calcium carbide) as a raw material for the carbon film 30 is added to the molten salt to form a molten salt bath. . The base material 25 on which the relaxation layer 29 is formed is connected to a working electrode installed in the electrolytic cell, and an electrochemical measuring device is connected to the working electrode, the counter electrode, and the reference electrode. By performing electrolysis in this state, the carbon film 30 is deposited on the surface of the relaxing layer 29. The molten salt in the electrolytic cell is not limited to carbonate, but may be chloride, bromide, or fluoride.

(Example)
A separator was produced according to the procedure of the above production method and evaluated. The configuration of each sample is as shown in Tables 1 to 4. In Examples No. 1 to 55, the heat treatment step is 600 mL of hydrogen volume, the molten salt bath used when coating with a carbon film is 59 mol% LiCl, 41 mol% KCl, and ₂ mol% CaC ₂ as a carbide ion source. What melted the mixture which consists of (outside number) at 450 degreeC was used. The carbon film was formed by electrolytic deposition of a base material on which a relaxation layer was formed on the working electrode, and an aluminum plate connected to the counter electrode.

Examples Nos. 56 to 58 were prepared by melting a mixture of 5 mol% (external number) of K ₂ CO ₃ at 450 ° C. as a carbonate ion source in a molten salt bath when forming a carbon film. Changed. In Examples Nos. 59 to 62, the hydrogen volume in the heat treatment step was changed.

  The adhesion of the carbon film was evaluated based on the degree of burn by the appearance inspection and the degree of peeling by the cross cut tape test. If there was no burn or peeling, “2 points”. When there was no burn, “1 point” was given, and when burns and peeling occurred, “0 point” was given. In the cross cut tape test, according to “JIS K5400-8.5”, the carbon film formed on the surface of the base material is cross-cut (100 squares) on a cross section of 1 mm × 1 mm, and an adhesive tape (manufactured by Nichiban Co., Ltd., product number) : CT24) was pressure-bonded to the crosscut portion, and then peeled off rapidly to confirm the presence or absence of peeling. In the determination, a case where no film is peeled out of 100 squares is expressed as “1 point” or more, and a case where even one square is peeled is expressed as “0 point”.

The contact resistance was measured by stacking carbon paper on the separators 22 and 24, sandwiching them with Au-plated copper plates from both sides, and applying a current of 1 A while applying a surface pressure of 10 kg / cm ² by the 4-terminal method. Obtained from voltage.

  Corrosion resistance is determined by chlorinating N / 20 hydrochloric acid solution (used in JISG 0578 “Method of Ferric Chloride Corrosion Test for Stainless Steel”) to confirm that the carbon film completely covers the base material and the relaxation layer. Dissolve ferric acid and drop the acidified 6% ferric chloride solution to the surface of the sample so that it has a diameter of more than 1 cm, leave it in a room adjusted to about 20 ° C for 48 hours, and wash it. A test was conducted. When the sample surface after the test did not change from the state before the test, it was set to “2 points”, and when changed, it was set to “0 point”.

  Adhesion after the thermal test is evaluated by the degree of peeling by the cross cut tape test after 20 cycles of the thermal test (−20 ° C. and 200 ° C.). 0/100) is “2 points”, when partial peeling occurs (1-25 / 100) is “1 point”, and when much peeling occurs (26 or more / 100), “0 points” It was.

  In Examples Nos. 1 to 55, in the step of forming the relaxation layer, the organic additive is selected from the group consisting of carboxylate, sulfonate, sulfate ester, amine salt, quaternary ammonium salt, and betaine type compound. Using a plating bath having one or more selected basic structures, an organic compound having a hydrocarbon molecular chain bonded in a single chain and having 25 or less carbon atoms, and an addition amount of 0.1 to 15 g / L Since the relaxation layer having a thickness of 0.1 μm or more and 5 μm or less was formed and coated with the carbon film having a thickness of 0.1 μm or more and 10 μm or less, good results were obtained in the adhesion and contact resistance of the carbon film. was gotten.

  In Examples No. 47 and 48, the maximum height Rmax of the surface roughness of the relaxation layer was outside the range of 0.1 μm or more and 10 μm or less, and thus the adhesion decreased after the cooling test.

From the results of Example Nos. 56 to 58, it was confirmed that good results were obtained in the adhesion and electric resistance of the carbon film even when K ₂ CO ₃ was used as the carbonate ion source.

  From the results of Example Nos. 59 to 62, it was confirmed that good results can be obtained in the adhesion and electrical resistance of the carbon film by performing the heat treatment step in the range of 40 to 3500 mL of hydrogen volume. did it.

  Comparative Examples Nos. 1 to 3 and 20 were not used with an additive, or because the concentration of the additive was less than the lower limit to form a relaxation layer, so that charring due to current concentration on the convex portion occurred in the relaxation layer, and the carbon film At least one of the adhesiveness and the electrical resistance decreased.

  In Comparative Examples No. 4 to 9, since the concentration of the additive exceeded the upper limit or the additive was outside the specified range, the organic compound content in the relaxation layer exceeded the upper limit, resulting in burns in the carbon film. .

  In Comparative Example No. 10, since the heat treatment after the formation of the relaxation layer was not performed, organic substances remained in the relaxation layer, and the carbon film was burned.

  In Comparative Example No. 11, since the heat treatment after the formation of the relaxation layer was performed in the air, the relaxation layer was oxidized when the organic substance burned, and the adhesion with the carbon film was reduced.

  In Comparative Example No. 12, since the heat treatment after the formation of the relaxation layer was performed in an Ar atmosphere, the organic matter did not burn, the organic matter remained in the relaxation layer, and the carbon film was burned.

  Since Comparative Examples No. 13 and 14 did not have a relaxation layer, the adhesion after the cooling test decreased due to the difference in thermal expansion between the substrate and the carbon film.

  Since Comparative Example No. 15 did not have a carbon film, Comparative Example No. 21 had a carbon film thickness less than the lower limit, and thus corrosion resistance could not be obtained. In Comparative Examples No. 16 and 18, since the thickness of the relaxation layer was less than the lower limit, the adhesion of the carbon layer and the adhesion after the cooling test were lowered. In Comparative Examples No. 17 and 19, since the thickness of the relaxation layer exceeded the upper limit, the organic matter remained in the relaxation layer, and the carbon film was burnt.

(Modification)
The present invention is not limited to the above-described embodiment, and can be appropriately changed within the scope of the gist of the present invention.

  In the case of the said embodiment, although the separators 22 and 24 demonstrated the case where a relaxation layer and the carbon membrane | film | coat which covers a relaxation layer were provided on both surfaces of a base material, this invention is not limited to this, It relaxes only on one surface. It is good also as providing the carbon film which covers a layer and a relaxation layer.

In the step of heat-treating the base material on which the relaxation layer is formed in a hydrogen atmosphere, it is possible to use 99% or more high-purity H ₂ gas as the atmospheric gas. Further, as a heat treatment method, an inert gas containing 20% by volume of hydrogen may be filled in a 9 L container, and the base material may be placed in the container and held at 200 ° C. for 1 hour.

DESCRIPTION OF SYMBOLS 10 Fuel cell 11 and 13 Electrode 12 Electrolyte 14 and 16 Catalyst layer 18 and 20 Gas diffusion layer 22 and 24 Separator for fuel cells (separator)
25 Base material 26, 28 Gas flow path 29 Relaxation layer 30 Carbon film 32 Flow path layer

Claims (13)

Forming a relaxation layer by electrolytic deposition using an aqueous solution containing an organic additive on at least one surface of the substrate;
Heat-treating the base material on which the relaxation layer is formed in a hydrogen atmosphere;
Coating the surface of the relaxation layer with a carbon film by electrolytic deposition,
The step of forming the relaxation layer includes at least one basic structure in which the organic additive is selected from the group consisting of carboxylate, sulfonate, sulfate ester salt, amine salt, quaternary ammonium salt, and betaine type compound. And an organic compound having a carbon number of 25 or less, in which hydrocarbon molecular chains are bonded in a single chain, the addition amount is 0.1 to 15 g / L, and the thickness is 0.1 to 5 μm. Forming a layer,
The step of coating with the carbon film is a method for manufacturing a fuel cell separator that is coated with the carbon film having a thickness of 0.1 μm or more and 10 μm or less.   The method for producing a fuel cell separator according to claim 1, wherein the base material is any one of an Al alloy, a Cu alloy, a Mg alloy, a Ni alloy, a Sn alloy, steel, and stainless steel. The step of forming the relaxation layer includes:
The aqueous solution containing the organic additive contains 240 to 300 g / L of nickel sulfate, 45 to 50 g / L of nickel chloride, 30 to 80 g / L of boric acid, and the organic additive.
The manufacturing method of the separator for fuel cells of Claim 1 or 2 which sets bath temperature to 45 to 90 degreeC and current density to 2-8 A / dm < ² >, stirring the said aqueous solution. The step of forming the relaxation layer includes:
The aqueous solution containing the organic additive includes copper sulfate 50 to 200 g / L, sulfuric acid 50 to 200 g / L, sodium chloride 60 to 150 mg / L, and the organic additive.
The manufacturing method of the separator for fuel cells of Claim 1 or 2 which sets bath temperature to 20 to 50 degreeC, and sets current density to 0.1-8 A / dm < ² >, stirring the said aqueous solution.   The method for producing a separator for a fuel cell according to any one of claims 1 to 4, wherein in the step of forming the relaxation layer, the organic additive uses an organic compound having 5 or less double bonds per molecular weight. .   The production of the fuel cell separator according to any one of claims 1 to 5, wherein the heat treatment step is carried out at a hydrogen volume of 40 to 3000 mL and 120 to 1000 ° C supplied into the reaction vessel for 2 to 150 minutes. Method.   The fuel cell separator according to any one of claims 1 to 6, wherein the coating with the carbon film uses at least one molten salt bath selected from the group consisting of chloride, bromide, fluoride, and carbonate. Manufacturing method. A separator for a fuel cell comprising a base material, a relaxation layer on one surface of the base material, and a carbon film covering the surface of the relaxation layer,
The thickness of the relaxation layer is 0.1 μm or more and 5 μm or less, and the thickness of the carbon film is 0.1 μm or more and 10 μm or less,
There is no peeling of the carbon film by the tape test,
A fuel cell separator having a surface contact resistance of 20 mΩ · cm ² or less. The fuel cell separator according to claim 8, wherein the content of the organic compound is 1.0 mg / cm ² or less.   The fuel cell separator according to claim 8 or 9, wherein a coverage of the relaxation layer with respect to the base material is 55% or more.   11. The fuel cell separator according to claim 8, wherein the relaxing layer has a maximum surface roughness height Rmax of 0.1 μm to 10 μm.   The fuel cell separator according to any one of claims 8 to 11, wherein the base material is any one of Al alloy, Cu alloy, Mg alloy, Ni alloy, Sn alloy, steel, and stainless steel.   The separator for a fuel cell according to any one of claims 8 to 12, wherein the relaxation layer is any one of Ag, Au, Cu, Fe, Ni, Pd, Pt, Rh, Ru, Sn, and In.

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