JP2005347282A - Separator for solid polymer fuel cell and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-cost solid polyelectrolyte fuel cell of which the metal separator is made highly corrosion-resistant and cell performance is maintained for a long time, and a solid polyelectrolyte fuel cell using the same. <P>SOLUTION: In the solid polymer fuel cell composed of a metal layer 1 and a coating layer 2 with conductivity, the metal layer 1 is made of at least one kind of metal selected from iron, aluminum, copper, titanium magnesium, zirconium, tantalum, niobium, tungsten, nickel, chromium and an alloy thereof, and the outer surface of the metal layer 1 is structured of metal selected from titanium, zirconium, tantalum, niobium and an alloy thereof, while the coating layer 2 is structured of at least one kind of a conductive material 3 selected from carbon, conductive ceramic and metal powder, and a resin binder 5 for fixing the conductive material 3. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a separator and a polymer electrolyte fuel cell which are constituent members of a polymer electrolyte fuel cell.

  Separator materials used in polymer electrolyte fuel cells are broadly divided into carbon and metal types. In the case of carbon, for example, a dense graphite material is cut to form a flow path and a manifold. For this reason, there is a problem that not only material costs but also processing costs are high.

  In order to solve this, for example, there is a method in which a resin is mixed with graphite and a separator is completed by means of heat compression molding or injection molding. Since this method is easy to mold, the cost can be remarkably reduced as compared with the above-described dense graphite cutting.

  Metals satisfy the impermeability of reactive gases (a general term for fuel gas and oxidant gas), which is one of the functions required of separators, and there are differences in thermal conductivity and electrical conductivity depending on the type of metal. Generally larger than graphite. In addition, the strength, toughness, and ductility of metals are superior to those of graphite materials, and they also excel in functions as structural materials and functions as workpieces.

  If the metal used as the separator is a general-purpose general-purpose metal, the material can be easily obtained and the material cost is low. Therefore, it is expected that the cost can be further reduced as compared with a separator formed by mixing graphite and resin.

  However, metals have the disadvantage of being easily corroded, not found in carbon-based materials. Except for precious metals such as platinum and gold, most metals are at risk for corrosion.

  The polymer electrolyte fuel cell is operated at a temperature of about 70 ° C., and the separator on the fuel electrode side may contain vapor (water) of humidified components such as carbon dioxide gas and a small amount of carbon monoxide gas in addition to hydrogen gas. ). The other air electrode side separator is exposed to air containing steam and moisture.

  Normally, if the metal has a corrosion resistance higher than that of stainless steel, it will not be corroded in such an environment, but a phenomenon called polarization unique to the battery is imposed on the separator. This is because there is electrical continuity between the electrode and the separator. When materials having different potentials are brought into electrical contact, they are polarized according to the strength of the electrochemical reaction (speed of reaction rate) and the area. At this time, ionic conductivity is required between the separator and the electrode.

  The substance that controls ionic conductivity is thought to be mainly condensed water. When water is present between the separator and the electrode, an ion passage is formed. Since the shortest distance from the separator surface to the electrode is as short as several hundred μm and the temperature is high, even with pure water, the iR drop is about several tens of mV, so there is a sufficient potential to polarize the separator. It is believed that it can be applied.

  When the separator is polarized and the potential resulting from the polarization hits the active state region or the hyperpassive region of the metal, the corrosion of the metal is accelerated, the contact resistance between the separator and the diffusion layer increases, or the corrosion product May be trapped by the electrolyte membrane as an ion, and as a result, the ionic conductivity of the ion exchange membrane may be reduced.

  When the potential at which the separator is polarized is in the passive region, the occurrence of corrosion is very small, but the passive film grows. Ordinary passive films are composed of oxyhydroxides, oxides, etc. starting from hydroxides. Since most of these compounds have poor electrical conductivity, as the passive film of the metal separator grows thicker, the electrical resistance increases, leading to deterioration in battery performance.

  The corrosion resistance of the metal is maintained by the passive film, but this also causes performance deterioration.

  In addition, an oxide film may grow or corrode due to a current flowing through the separator. This phenomenon is particularly noticeable when the contact resistance in the separator / diffusion layer is large, and this phenomenon is particularly likely to occur in the separator on the anode side. This phenomenon is similar to a kind of stray current corrosion (electric corrosion) or galvanic corrosion, and the higher the current density, the greater the corrosion.

  Many inventions related to prevention of high resistance and corrosion when a metal separator is used have been disclosed from the background that electrical resistance increases or corrosion occurs when a metal is used as a separator.

  Although it is not a separator, Japanese Patent No. 3,211,378 or Japanese Patent Laid-Open No. 4-159227 (Patent Document 1) uses a foamed metal such as nickel, aluminum or copper as a diffusion layer, and corrosion resistance such as platinum or gold. The material is coated.

  The bipolar plate (separator) of Japanese Patent No. 2,953,555 or Japanese Patent Application Laid-Open No. 6-092637 (Patent Document 2) is aluminum, titanium, zirconium, niobium, tantalum and alloys thereof, or stainless steel, high alloy. It is made of steel and nickel-chromium alloy, and its surface is coated with a conductive material.

  In JP-A-8-190883 (Patent Document 3), a noble metal layer is formed on a corrugated separator made of stainless steel or titanium alloy to suppress an increase in resistance.

  In JP-A-8-222237 (Patent Document 4), a large number of protrusions are arranged on the front and back surfaces of a metal separator, and the surface is provided with an electrically conductive coating.

  In JP-A-9-298064 (Patent Document 5), a water repellent layer is formed on a metal, and this water repellent layer is used as a gold plating layer or the like.

  In Japanese Patent Application Laid-Open No. 10-228914 (Patent Document 6), a gold plating layer having a thickness of 0.01 to 0.06 μm is formed on a surface of a metal such as stainless steel in contact with the electrode.

  In JP-A-10-255823 (Patent Document 7), a conductive carbon material is formed on a metal containing 80% by weight or more of aluminum or titanium. Similarly, in Japanese Patent Laid-Open No. 11-162479 (Patent Document 8), a metal film in which conductive ceramics are dispersed is formed.

  In JP-A-11-345618 (Patent Document 9), a conductive coating film is formed on a stainless steel substrate in a thickness of 3 to 20 μm, and this coating film is a mixed powder containing graphite and carbon black.

  In Japanese Patent Application Laid-Open No. 11-144744 (Patent Document 10), a coating material in which carbon is dispersed is applied on a stainless steel substrate, and after rolling, this is heated to form a carbon layer.

  Japanese Patent Laid-Open No. 2000-036309 (Patent Document 11) has a structure in which a metal is composite-plated with fluorinated graphite particles and a noble metal.

  Japanese Patent Laid-Open No. 2000-123850 (Patent Document 12) has a configuration in which a noble metal plating layer is provided on either stainless steel, titanium, or a titanium alloy.

  In JP 2000-138067 A (Patent Document 13), first and second coat layers are formed on a metal substrate, a conductive material other than carbon is formed on the first coat layer, and a second coat layer is formed on the second coat layer. Is a separator made of carbon material, and has achieved high corrosion resistance.

  In Japanese Unexamined Patent Publication No. 2000-155742 (Patent Document 14), an anion trapping layer containing an anion trapping substance is formed on the surface of a metal, and the anionic substance is trapped and corroded before the corrosive substance reaches the metal. To prevent.

  In JP 2000-164228 (Patent Document 15), a plurality of layers of stainless steel, copper, aluminum, titanium and their alloys or composite materials are formed on a separator to obtain peeling resistance, conductivity, and corrosion resistance. Yes.

  In Japanese Patent Laid-Open No. 2000-260441 (Patent Document 16), conductive particles are arranged in a portion of a metal gas flow path plate (separator) in contact with a diffusion layer, and the hardness of the conductive particles is determined by the separator. It hardens and breaks the oxide film to form a conductive path.

  In Japanese Patent Laid-Open No. 2000-307747 (Patent Document 17), a metal coat layer that is melt-formed is provided on a substrate metal, and a corrosion-resistant coat layer made of a carbon material or the like is further formed to improve the corrosion resistance.

  In Japanese Unexamined Patent Publication No. 2000-353531 (Patent Document 18), a metal nitride layer such as titanium, aluminum, chromium, copper, alloys thereof, and stainless steel is formed.

JP-A-4-159227 Japanese Patent Laid-Open No. 6-092637 JP-A-8-190883 JP-A-8-222237 JP-A-9-298064 JP-A-10-228914 JP-A-10-255823 JP-A-11-162479 JP-A-11-345618 Japanese Patent Laid-Open No. 11-144744 JP 2000-036309 A JP 2000-123850 A JP 2000-138067 A JP 2000-155742 A JP 2000-164228 A JP 2000-260441 A JP 2000-307747 A JP 2000-353531 A

  The above-mentioned invention is mainly intended to improve the corrosion resistance by forming a coating layer on the surface of the metal, which reliably improves the corrosion resistance of the metal and extends the power generation life of the battery compared to when used alone. It was possible.

  However, the manufacturing process becomes too complicated, continuous production is difficult, or even if the effect of improving the corrosion resistance is great, the cost of materials is high, and thus high costs cannot be avoided. Alternatively, even if the corrosion resistance can be increased at a low cost, the sustainability of the effect may be insufficient.

  For example, considering that the battery life generally required is 5000 hours or more for in-vehicle use and 40,000 to 90,000 hours for home use or distributed power supply, it is necessary to provide sufficient corrosion resistance. Yes, life extension is a major issue when metals are used.

  In order to maintain the anti-corrosion and high resistance prevention functions of the coating layer for a long time, it is necessary to block water and air that permeates the coating layer, and to select a metal that does not elute as ions even if the outer surface metal is oxidized. We thought that it was important and came to obtain the present invention.

  In order to actually form the separator, it is necessary to consider the workability of the substrate metal in addition to the corrosion resistance. The characteristics of metal are sufficient strength and ease of plastic working, but even a number of metals are excellent in plastic working like aluminum and copper, and corrosion resistance such as nickel-chromium-molybdenum alloy and titanium alloy Even if it is good, there is a wide range of metals that are not suitable for plastic working. In this invention, the separator which implement | achieves high corrosion resistance with the metal excellent also in workability is provided.

  In order to achieve the above object, the gist of the present invention is as follows.

  (1) In a polymer electrolyte fuel cell separator comprising a metal layer and a conductive coating layer, the metal layer comprises iron, aluminum, copper, titanium, magnesium, zirconium, tantalum, niobium, tungsten, nickel, chromium and The outer surface of the metal is made of titanium, zirconium, tantalum, niobium, or a metal selected from these alloys, and the coating layer is made of carbon, conductive. It is characterized in that a coating layer composed of at least one conductive material selected from ceramics and metal powder and a resin binder for fixing the conductive material is formed.

  (2) The metal layer is formed of a three-layer structure of outer layer / intermediate layer / outer layer, and the intermediate layer is formed of a metal selected from iron, copper, aluminum, magnesium and alloys thereof. It is in the separator for fuel cells.

  (3) The polymer electrolyte fuel cell separator has an intermetallic compound composed of adjacent metals formed between the outer layer / intermediate layer / outer layer of the metal layer.

  (4) The metal layer is formed of a three-layer structure of outer layer / intermediate layer / outer layer, and a solid whose hardness of the metal of the outer layer is 1/3 to 3/1 with respect to the hardness of the metal of the intermediate layer It is in the separator for polymer fuel cells.

  (5) The metal layer is formed of a three-layer structure of outer layer / intermediate layer / outer layer, the intermediate layer is a metal layer made of aluminum or aluminum alloy, and the portion where the aluminum or aluminum alloy is exposed is anodized Or it exists in the separator for polymer electrolyte fuel cells coat | covered with the boehmite membrane | film | coat.

  (6) The outer surface of the metal is titanium or a titanium alloy, and the impurity concentration in titanium is 0.05 ppm or less of hydrogen, 0.2 ppm or less of oxygen, 0.25 ppm or less of iron, 0.05 ppm or less of nitrogen, Or it exists in the separator for polymer electrolyte fuel cells which the hardness of the said titanium or titanium alloy exists in the range of 72-112 in Vickers hardness.

  (7) In the separator for a solid polymer fuel cell, the thickness of the outermost layer of the metal layer is 10 μm or more, and the ratio of the thickness of the outermost layer to the thickness of the metal layer is 30% or less.

  (8) The coating layer is in a polymer electrolyte fuel cell separator having a thickness of 10 to 100 μm, preferably 40 to 70 μm.

  (9) The coating layer is composed of a carbon-based conductive material containing graphite and carbon black and a binder, and the mixing ratio of the carbon-based conductive material and the binder is 15:85 to 90:10 by weight. Preferably, the ratio is 35:65 to 55:45, and the blend ratio of graphite and carbon black of the carbon-based conductive material is 30:70 to 90:10 by weight ratio in the polymer electrolyte fuel cell separator.

  (10) The binder of the coating layer is at least one of fluorine resin, silicon resin, phenol resin, epoxy resin, polyimide resin, polyamide resin, polyolefin resin, furan resin, and rubber resin. In the separator for a polymer electrolyte fuel cell.

  (11) The binder of the coating layer is a copolymer (PVDF-HFP copolymer) of polyvinylidene fluoride (PVDF) and hexafluoropropylene (HFP), and the propylene hexafluoride is a binder. The solid polymer fuel cell separator is in the range of 5 to 30% by weight.

  (12) In the polymer electrolyte fuel cell having a separator having an electrode, a gas diffusion layer, and a manifold on both surfaces of the polymer electrolyte having ionic conductivity, any one of (9) to (11) It is in the separator for polymer electrolyte fuel cells which formed the coating layer of description.

  (13) In a polymer electrolyte fuel cell having a polymer electrolyte having ionic conductivity and electrodes formed on both sides of the polymer electrolyte, and having a gas diffusion layer and a separator, the separators are (1) to (12). The polymer electrolyte fuel cell is a separator according to any one of the above.

  According to the present invention, a coating layer composed of a conductive material such as carbon and a resin binder for fixing the conductive material is formed on a metal layer having titanium, zirconium, tantalum, niobium, and tungsten as the outermost layer. As a result, it is possible to provide a metal separator for a solid polymer electrolyte fuel cell that maintains the corrosion resistance of the metal layer for a long period of time and suppresses an increase in resistance, and a solid polymer electrolyte fuel cell.

  The present inventors first tried to select a material suitable as a metal separator material. As the method, the change in weight before and after the immersion test in a sulfuric acid aqueous solution at room temperature, the current density obtained from the polarization curves of sulfuric acid (pH about 1.2) and aqueous sodium sulfate (pH about 6.8) at 30 ° C., The current density and the amount of eluted metal in a constant potential holding test in a sodium sulfate aqueous solution at 70 ° C. were used.

  Although there are many unclear points about the actual battery environment to which the separator is exposed, it was considered possible to make a relative comparison of the corrosion resistance between materials by carrying out the above test.

  As a result of conducting various tests on pure metals, the following knowledge was obtained. The behavior of corrosion resistance in sulfuric acid aqueous solution is roughly classified into three.

Category 1: Both the anode and cathode have excellent corrosion resistance. Category 2: The anode has excellent corrosion resistance. Category 3: Both the anode and cathode have poor corrosion resistance. The metals belonging to the above category 1 are as follows. It was.

  Elements belonging to category 1: titanium, zirconium, tantalum, niobium, tungsten, gold, platinum, lead, silicon, graphite.

  In these materials, these metal components contained in the test solution after the end of the polarization curve and the test solution for the constant potential holding test were extremely small, and the values were about three orders of magnitude lower than those of other metals. Therefore, it is expected that there is little possibility of adverse effects on the electrode and the electrolyte.

However, since a certain amount of current flows at the time of polarization, it is considered that most of this current was used for film growth. Most of the metals listed above are valve metals except for noble metals such as gold. Therefore, although corrosion resistance is good, there is a concern that the surface resistance of the metal increases with the passage of time. In fact, in the case of titanium, the initial sheet resistance was 0.3 mΩ · cm ² (plate thickness 4 mm), but increased to 100 mΩ · cm ^{2 on the} order of several tens of hours. That is, these metals other than noble metals also need to be subjected to some surface treatment.

  Stainless steel, which is generally called a corrosion-resistant metal, is a widely used metal, is inexpensive, and has excellent workability. Therefore, it is expected as a material for a separator, but the corrosion resistance is particularly poor in the cathode potential region. Stainless steel is thought to be because its components, chromium and nickel, dissolve in a high potential region. Actually, constituent element ions of stainless steel were detected in the test solution after the constant potential holding test.

  Pure chromium and pure nickel are just equivalent to the hyperpassive region in the cathode potential region of the fuel cell. Therefore, it is considered that the stainless steel (especially austenite type) containing chromium and nickel as main constituents also has an increased current in the cathode potential region and an increased amount of dissolution.

  Therefore, high chromium, high nickel stainless steel, such as SUS309S and SUS310S, was poorer in corrosion resistance than SUS304. Molybdenum has been added to stainless steel as an element imparting high corrosion resistance, but molybdenum did not show any passivation in an aqueous sulfuric acid environment. Therefore, the SUS310 series alloy to which molybdenum is added is inferior in corrosion resistance to SUS304, though only slightly. Copper as an additive element was the same as molybdenum.

  For the same reason, the nickel base alloy has poor corrosion resistance on the cathode side. In chemical plants that handle strongly acidic solutions such as hydrochloric acid and sulfuric acid, nickel-based alloys are used as structural materials, but they are considered difficult to use in fuel cell environments.

  However, since these materials showed excellent corrosion resistance in the anode potential region, there is a possibility that the corrosion resistance can be improved by surface treatment.

  Considering the price and corrosion resistance of the materials, austenitic SUS304 steel, SUS316 steel, and ferritic SUS430 were excellent overall. Double-layer stainless steel (SUS329 or the like) is excellent from the standpoint of corrosion resistance alone, but this material is also promising if the material cost can be reduced. In addition, titanium is a metal whose price is about one digit higher than that of SUS304 steel. However, if it is a composite metal material in which a thin layer of titanium is coated with an inexpensive metal, it is a metal that can be expected because it is inexpensive.

  From the above, metals that can be used in the separator as a single metal are difficult except for noble metals. Since the use of noble metals is economically out of the question, some surface treatment means such as suppressing an increase in electrical resistance or imparting corrosion resistance to other inexpensive metals is necessary.

  Furthermore, the following experiment was conducted and it was found that the substrate metal needs to be insoluble even when it is corroded.

The test piece was made of metal / carbon paper / metal (contact area 10 cm ² ), and lead wires were attached to the metal at both ends of the test piece. This test simulates a separator and carbon diffusion layer in a fuel cell. This test piece was immersed in a neutral 0.05M Na ₂ SO ₄ aqueous solution (open to the atmosphere, 2 L) at 70 ° C., and a current (0.1 A / cm ² , lead) was forced between both electrodes using a galvanostat. The voltage between the metals after correcting the iR drop such as a line was about 1.0 V).

  As a result, in an alloy containing Ni or Cr such as stainless steel or nickel base alloy, the test solution after 100 hours contained Ni or Cr in the order of ppm. The observed surface after the test exhibited both positive and negative corrosion, and the positive electrode was particularly remarkable. When the metal was titanium, elution of the titanium component into the test solution was not observed.

  As described above, the elution component from the metal causes deactivation of the electrode and a decrease in the ionic conductivity of the polymer electrolyte membrane, so that the dissolved component from the metal must be suppressed. Also from the above experiments, the elements belonging to category 1, ie, titanium, zirconium, tantalum, niobium, tungsten, gold, platinum, lead, silicon, and graphite, are effective as the substrate metal.

  Among these, practical metals are titanium, zirconium, tantalum, niobium, and tungsten, and it is desirable that the outermost surface of the metal layer be these metals. However, in addition to the disadvantage that these metals are expensive, they have the disadvantage of being inferior in formability.

  Since the separator plays a role of efficiently supplying the reaction gas to the electrode, a complicated groove shape, dimple processing, or embossing is usually performed. In the present invention, although corrosion resistance such as iron, copper, aluminum, and magnesium is inferior, a metal having good workability is placed in the intermediate layer, and both surfaces thereof are covered with the above metal such as thin titanium to form an outer layer / intermediate layer / outer layer.

  As a method for forming this material, there are an explosion method, a rolling method, an adhesion method, and the like. For this reason, it is necessary to select an appropriate one for the properties of the outer layer and the intermediate layer.

  Next, various surface treatment methods were examined. In addition, as a test method, in order to quickly determine the effect of the coating layer, various surface treatment methods are applied to carbon steel (SS400) with poor corrosion resistance, and corrosion prevention is performed through polarization curves and constant-potential immersion tests (implemented by simple immersion tests). The function was evaluated.

  Typical plating methods include chrome plating, nickel plating, and gold plating. As described above, since chromium and nickel have poor corrosion resistance, electrolytic gold plating was employed. As a result, the plating was divided into two stages, and unless the thickness of the plating layer was increased to 0.1 μm or more, pinholes could not be eliminated and sufficient corrosion resistance could not be obtained. In addition, gold plating requires many processes such as pretreatment and increases the cost.

  A material obtained by depositing conductive ceramics by a dry process such as ion plating or sputtering could not obtain satisfactory corrosion resistance. In addition to the fact that the membrane is porous, depending on the ceramic used, the ceramic itself may change and dissolve in an electrochemical reaction.

Next, application of a conductive paint was attempted as a surface treatment method. When carbon steel was coated with a paint in which a conductive material such as graphite was mixed with a resin binder, this had the highest anticorrosion effect and resistance increase suppression effect. However, the effect of anticorrosion varies greatly depending on the kind of binder (binder) and the concentration of the conductive material, and it is necessary to obtain an optimum composition.
[Example 1]
This embodiment will be described with reference to the drawings. In this example, the corrosion resistance of various materials was compared for the coating layer.

  The substrate metal uses a multiphase metal composed of titanium, zirconium, tantalum, niobium, and tungsten as an outer layer and an intermediate layer of iron, copper, aluminum, and magnesium. Thereby, a substrate metal excellent in corrosion resistance and workability can be obtained. Here, titanium / copper / titanium is used as an example.

  As for the titanium / copper / titanium material, three sheets of titanium and copper having an appropriate thickness were stacked and rolled cold or hot to finally obtain a sheet thickness of 0.2 to 0.3 mm. In the case of hot rolling, the temperature was set to 400 to 600 ° C., and the oxide film formed on the surface was removed with emery paper.

  As the coating layer, a carbon / binder / solvent mixture having various compositions was used. Carbon used was graphite or carbon black added thereto. As the binder, fluorine resin, silicon resin, phenol resin, epoxy resin, polyimide resin, polyamide resin, polyolefin resin, furan resin, rubber resin, and some of these mixtures were used. .

  The method for preparing the mixture is as follows. The binder is dissolved in various solvents (an appropriate solvent is selected according to the binder material), and graphite having an average particle size of about 4 μm and furnace black having an average particle size of 0.02 μm are added thereto, and dispersed with a roll. To obtain a mixture. The blending ratio of graphite and furnace black was 80:20 by weight.

  When the mass ratio of graphite: furnace black affecting resistance was tested in another test, the mass ratio of graphite: furnace black was 30:70 to 90:10, and the resistance could be made smaller than that of graphite alone, especially graphite: furnace black. The composition ratio was selected because the resistance was the smallest at a mass ratio of 80:20.

  This mixture was applied by screen printing on a titanium / copper / titanium material cut to 20 × 50 mm. The screen thickness was selected so that the film thickness after drying was about 50 μm. After coating, it was dried in accordance with the characteristics of each solvent and binder. Furthermore, this test piece left one side of 20 × 50 mm, and the other part was covered with silicon resin so that the exposed surface was finally about 16 mm × 46 mm.

  The metal used in the test was also applied to an SS400 (carbon steel) metal plate of the same size as titanium / copper / titanium in order to examine only the corrosion resistance of the coating layer, and the anticorrosion performance was compared.

The following method was used for the corrosion test. After inserting the test piece into the glass container (volume 2L) of the loop type tester, 0.05M Na ₂ SO ₄ aqueous solution was introduced, and the test solution in the container had dissolved oxygen concentration <10 ppb, dissolved hydrogen concentration about 30 ppb, pH 6 After reaching 0.8 to 7.2, the temperature was raised to 70 ° C. in 30 minutes, and the outlet valve of the glass container was closed.

  The test solution in the container was sampled periodically, and the metal components contained in the test solution were quantified by ICP. The test time was 100 hours.

  Table 1 shows the details of the coating layer used in this example and the results of the corrosion test. The conductive material (wt%) in the table represents the ratio of the amount of conductive material after drying.

  No2-No14 is the result of investigating the anticorrosion performance of the coating layer. As the conductive material increases, the elution rate of iron increases. In particular, when the proportion of the conductive material is 90 wt%, although the corrosion resistance is improved compared to the bare SS400 (No. 1) in which the coating layer is not formed, the corrosion amount increases to about 1/10 of SS400.

Conversely, when the proportion of the conductive material is reduced, the amount of corrosion decreases, but when the sheet resistance of No3 was measured in another test, it reached 1 Ω · cm ² . For example, if the current value of the fuel cell is about 0.5 A / cm ² , this resistance value corresponds to an iR drop of 0.5 V, and 80% of the voltage obtained by power generation results in a loss of resistance. It was not a good value.

In order to keep the efficiency of the battery high, it is important to make iR drop as small as possible. In this case, the resistance of the separator needs to be 30 mΩ · cm ² or less. The ratio of conductive material: binder satisfying this value was 35:65 to 55:45.

  In summary, the blending ratio of the conductive material and the binder is 15:85 to 90:10, and an improvement in corrosion resistance can be expected. However, in order to bring out more functions as the conductive material in the separator, the conductive material: binder The ratio was found to be 35:65 to 55:45.

  It was also found that the thickness of the coating layer has a great influence on the corrosion resistance. FIG. 2 shows the relationship between the film thickness of the coating layer and the corrosion rate. If the film thickness is 10 μm or more, the effect of improving the corrosion resistance appears. In particular, when the thickness is 40 μm or more, the SS400 of the substrate is not corroded.

  On the other hand, when the film thickness is 100 μm or more, the film thickness becomes non-uniform, which causes drying unevenness and a phenomenon that a part of the coating layer swells in a balloon shape. The coating layer was not formed in the balloon-swelled portion.

  When the average film thickness was 70 μm or less, this phenomenon could be completely suppressed. Accordingly, the film thickness is suitably 10 to 100 μm, preferably 40 to 70 μm.

  No12 and No15-No22 are the results of examining the influence of the binder. Even if any binder is used, SS400 (No. 1) has the effect of increasing the corrosion resistance, but the binder having the largest anticorrosion effect is a fluororesin such as PVDF or PTFE. It is considered that these resins are particularly excellent in hydrophobicity and have small water permeation.

  Furthermore, regarding PVDF, a copolymer with HFP, which is expected to be able to improve the adhesion to metal, was also tested. No. 6 to No. 11 are results when the composition of the PVDF-HFP (vinylidene fluoride-6-fluorinated polypropylene) copolymer is changed from 0 to 50%. Although the difference in effect is small, the anticorrosion performance can be improved when the HFP ratio is in the range of 5 to 30%.

No25 is a state of pure titanium / copper / titanium, and No26 is a case where a PVDF-based coating layer having a conductive material amount of 45 wt% is formed on a titanium / copper / titanium metal layer. In either case, no titanium is present in the test solution and is the best. However, as will be described later in detail, it is found that when titanium / copper / titanium is used as a solid separator as a separator, sufficient power generation performance cannot be obtained due to the growth of an oxide film, and formation of a coating layer is essential. It was.
[Example 2]
In this example, the metal layer has a structure of outer layer / intermediate layer / outer layer, and a separator provided with a coating layer composed of the graphite-based conductive material and the PVDF-based binder described in Example 1 on both surfaces. Will be described.

  The intermediate layer is selected from copper, iron, aluminum and magnesium, or alloys thereof. This is because these metals are low in cost and excellent in press formability. Any of these metals may be used, but copper was selected because it is particularly excellent in electrical conductivity, thermal conductivity, and composition workability.

  Moreover, it is excellent also in the adhesiveness and affinity with titanium described below. Titanium, zirconium, tantalum, niobium and tungsten are suitable for the outer layer, but the most versatile titanium among these metals was selected. By using such a metal layer formed with an outer layer / intermediate layer / outer layer, the amount of expensive titanium, zirconium, tantalum, niobium, and tungsten used can be suppressed, and the cost can be reduced.

  In addition, titanium, zirconium, tantalum, niobium, and tungsten have poor workability, and it was difficult to perform plastic processing such as press working alone. However, by adopting such an outer layer / intermediate layer / outer layer structure, The plastic workability is improved.

  For example, the most effective effect was when the separator flow path was pressed, and the thickness of the rib 21 as shown in FIG. 3 is 0.3 / mm or titanium / copper / titanium or titanium / aluminum / titanium. When press-molded into a corrugated separator 6 having a width of 1 mm, an opening width of the groove 22 of 1.5 mm, and a depth of the groove 22 of 0.5 mm, the warp size was 1/100, whereas titanium The single unit (JIS TP270H) was as large as 1/20. In addition, cracks were observed at the corners.

  Thus, the workability could be improved by using the metal layer 1 as the outer layer / intermediate layer / outer layer.

  FIG. 1 is an enlarged cross-sectional view of a separator 6 in which a straight channel is formed by pressing a 0.3 mm thick titanium / copper / titanium material as the metal layer 1 and a coating layer 2 is formed thereon.

  The titanium / copper / titanium material used here has the following characteristics. Titanium / copper / titanium is a material joined by cold rolling. However, since titanium and copper have different deformation resistances, it is necessary to match the hardness of each metal as much as possible. In general, copper as an intermediate layer is a soft metal, and titanium as an outer layer is hard. When the hardness of the intermediate layer and the outer layer was variously changed and the adhesive strength after completion was evaluated by a bending test of the plate, the hardness ratio between the outer layer and the intermediate layer was in the range of 1/3 to 3/1. Titanium / copper / titanium did not peel even in the 90-degree bending test.

  Similarly, no peeling occurred in titanium / iron / titanium. Titanium / aluminum / titanium and titanium / magnesium / titanium were peeled off by bending. As a means for solving this, when the steel was heated to about 400 ° C. after cold rolling, an intermetallic compound was generated between adjacent metals, and the adhesive force was improved. Such an effect was obtained in the same way with titanium / copper / titanium and titanium / iron / titanium. As described above, these metals can be bonded only by cold rolling, but when heat treatment is performed and a metal compound is generated between the layers, the bonding strength becomes stronger. In addition to adhesive strength, the electrical resistance of the material was also reduced. It is considered that the contact resistance could be reduced because the layers were more closely adhered.

  In this example, copper is used for the intermediate layer. However, since this is a soft metal, titanium used for the outer layer was selected so that the deformation resistance difference does not increase. There are about 10 types of titanium and titanium alloys as defined in JIS and ASTM standards.

  Among these, the metal having the best adhesive strength with copper, iron, aluminum, and magnesium of the intermediate layer is that the impurity concentration of titanium is 0.05 ppm or less of hydrogen, oxygen is 0.2 ppm or less, iron is 0.25 ppm or less, and nitrogen is It was 0.05 ppm or less, or titanium whose titanium or titanium alloy had a Vickers hardness in the range of 72 to 112.

  This titanium has a deformation resistance close to that of copper, iron, aluminum, and magnesium. Therefore, when rolled, both the outer layer titanium and the intermediate layer copper, iron, aluminum, and magnesium could be rolled almost uniformly.

  When the impurity concentration of titanium deviated from the above, the titanium became hard and only the intermediate layer was preferentially rolled during rolling, and a multilayer metal having a uniform thickness could not be obtained. This was particularly remarkable when aluminum or magnesium was used as the intermediate layer.

  Even when titanium is in the above composition range, it may be impossible to make uniform when aluminum or magnesium is used as the intermediate layer. Therefore, it is preferable to use an aluminum-copper alloy or an aluminum-magnesium alloy.

  The thickness of the titanium layer in the titanium / copper / titanium material needs to be 10 μm or more. This is because the crystal grain size of titanium is around 10 μm. This is because when the thickness of the titanium layer is approximately the same as the thickness of the crystal grain size, when the bending stress during pressing is applied to the titanium of the outer layer, the titanium layer is easily broken from the grain boundary. Moreover, even if the thickness of titanium as the outer layer is increased excessively, it is not preferable in terms of workability.

  If the thickness ratio of the outer layer of the metal layer is 30% or less, the excellent workability of the intermediate layer is not impaired, and composition processing is possible as in the case where the metal of the intermediate layer is a single body. When the thickness of the outer layer exceeded 30%, the mechanical properties of titanium became obvious and the plastic deformability deteriorated. Therefore, the thickness of the outer layer is preferably 10 μm or more, and the ratio of the thickness of the outer layer to the thickness of the metal layer is preferably 30% or less.

  The covering layer 2 shown in FIG. 1 is composed of the material No. 8 shown in Table 1. PVDF-HFP (10 wt%) copolymer as a binder is dissolved in NMP (N-methylpyrrolidone), and graphite having an average particle diameter of about 4 μm and furnace black having an average particle diameter of 0.02 μm are added thereto. The mixture was obtained by dispersing with a roll. The blending ratio of graphite and furnace black was 80:20 by weight. Finally, two types of mixtures having a mass ratio (solid content) of the conductive material + binder to the mixture of 25 wt% and 40 wt% were prepared.

  As shown in FIG. 4, the cross section of the flow path of the separator 6 is trapezoidal, the width of the rib in contact with the diffusion layer 9 is 1 mm, the width of the groove opening is 1.5 mm, and the flow path depth is 0.5 mm. The coating layer 2 in FIG. 1 is of two types, a dip coating method and a screen printing method.

  The dip coating method was performed by dipping the separator 6 in a mixture having a solid content (conductive material + binder) of 25 wt% at room temperature for about 10 seconds and pulling it up at a speed of 10 mm / second. This was heated to 140 ° C. with a vacuum dryer and dried for 3 hours. The coating layer 2 obtained by this method had an average thickness of 60 μm.

  Screen printing uses a stainless steel mesh size # 100 screen with a final coating layer 2 (see FIG. 1) thickness of 60 μm, and a silicon rubber blade is used to print and apply a 40 wt% solid content mixture. did. In the screen printing method, the coating layer 2 is formed on the entire surface of the separator 6 by the dip coating method, whereas the coating layer 2 can be formed only on the rib surface (the current-carrying surface through which electricity flows) of the separator 6. However, the coating layer 2 was formed by brushing the portion of the metal layer 1 where the copper around the plate was exposed. This separator 6 was dried by heating at 140 ° C. for 3 hours in a vacuum dryer. The average thickness of the coating layer 2 was 60 μm.

The conductive materials exemplified in the present embodiment are graphite and furnace black, but are not limited thereto, and may be fullerene, carbon tube or the like, and conductive ceramics such as tungsten carbide or titanium nitride. It may be a mixture. Furthermore, the same effect can be obtained even with a metal powder.
Example 3
This embodiment will be described with reference to the drawings. In this example, an example in which the separator of Example 2 is used for a single cell fuel cell is shown.

  FIG. 4 is a schematic cross-sectional view of a unit cell power generation test cell 7 provided with this separator 6. In the single cell power generation test cell 7, a MEA (Membran Electrode Assembly; PRIME 5510) 8 manufactured by Goretech Japan is sandwiched between two sheets of diffusion layers (CARBEL-CF) 9 manufactured by the same company, and further sandwiched by a separator 6.

  The separator 6 is a plate material having a thickness of 0.3 mm and has a power generation surface (contact surface with the diffusion layer 9) of 30 mm × 30 mm, and a straight flow path is formed in this portion. Further, the separator 6 is housed in a holder 10 made of dense graphite.

  The surface treatment layer 2 used was of three types: a type formed on the entire outer surface of the separator 6, a type formed only on the rib surface, and a type not formed with the surface treatment layer 2.

  As shown in FIG. 1, the coating layer 2 is composed of a mixture of a resin 5 of polyvinylidene fluoride, and a conductive material 3 of graphite having an average particle diameter of 4 μm and carbon black having an average particle diameter of 0.02 μm. The mass of the conductive material 3 occupying the coating layer 2 is 40%, and the thickness of the coating layer 2 is 60 μm on average.

The continuous power generation test of the single cell power generation test cell 7 formed by these was performed. The power generation test conditions were a cell temperature of 70 ° C., an anode and cathode humidification temperature of 70 ° C., a current density of 0.5 A / cm ^2, and a change in output voltage with time was observed under the conditions of a hydrogen utilization rate of 70% and an oxygen utilization rate of 40%. . Note that pure hydrogen at normal pressure was used as the fuel gas, and dry air was used as the oxidant gas.

  As a result, the voltage at the beginning of the test was 0.68V. Compared with a machine-cut dense graphite separator measured for comparison, the value for titanium was about 0.03 V lower. This is because the resistance of the separator 6 is larger than that of dense graphite.

  In addition, although the initial voltage is lower than that of the graphite separator, the voltage drop rate is -15 mV / 1,000 hours at the time of continuous power generation time of 1,000 hours in the titanium / copper / titanium separator, which is more than 5,000 hours. It can be regarded as a lifetime.

  Regarding the power generation performance, the surface treatment layer 2 was almost the same for both the entire surface formation type of the separator 6 and the rib surface formation type. Therefore, it is sufficient to form the surface treatment layer 2 only on the rib surface. By forming the coating layer 2 only at the necessary locations, the amount of material used can be kept low.

  When a bare titanium / copper / titanium separator 6 without the coating layer 2 was used, the initial voltage was 0.6 V or less, and the voltage drop rate was -1,000 mV / 1,000 hours. The surface of the separator 6 after decomposition has changed to a light purple interference color as a whole, and the increase in resistance due to the growth of the titanium film is considered to cause a large reduction rate.

  For comparison, the same test was performed on stainless steel (SUS304 steel) on which the same surface treatment layer was formed. In the case of stainless steel, the output voltage and the voltage drop rate were 0.68 V and -15 mV / 1,000 hours, respectively, which are almost the same as those of the titanium / copper / titanium separator. The voltage decreased rapidly and became 0.2V or less.

  When the battery using the stainless steel separator was disassembled, the surface treatment layer 2 was removed, and the surface was observed, the rib surface was in the form of overall corrosion.

  Furthermore, as a result of analyzing the element distribution of MEA by TOF-SIMS, nickel, which is a component of stainless steel, was detected in the electrolyte membrane, and in particular, accumulation of iron was observed in the cathode side electrode layer.

  When stainless steel was used as a separator, the elution component from stainless steel caused harmful effects on MEA due to corrosion accompanying power generation, and shortened the life. In the titanium / copper / titanium separator, some titanium was observed by MEA, but the amount was small and did not affect power generation performance.

Thus, the titanium / copper / titanium formed with the coating layer 2 can be used without shortening the battery life.
Example 4
This embodiment will be described with reference to the drawings. In this embodiment, an example of a stacked battery is shown.

  FIG. 5 is a schematic bird's-eye view of the separator 6 used in the stacked battery of this example. In the separator 6, the metal layer 1 is coated with three layers of titanium / aluminum / titanium, and the coating layer 2 is coated on the both surfaces of the titanium / aluminum / titanium three-layered metal layer 1 with the No. 8 mixture shown in Table 1. .

  As the coating method, the dip coating method described in Example 2 was used. The power generation surface of the separator 6 is formed by pressing a straight channel groove and has a channel groove portion of 80 × 150 mm. This flow path portion has a width of 1 mm of the rib 21 (see FIG. 3), an opening width of the groove 22 of 1.5 mm, and a depth of the groove 22 of 0.5 mm. The separator 6 is formed with a manifold 13 which is an inlet / outlet of the reaction gas and the cooling water.

  The separator 6 has a frame 12 made of PPS in which an introduction groove for introducing a reaction gas into the flow path is formed and bonded with a silicon adhesive.

  In the metal layer having the structure of outer layer / intermediate layer / outer layer, the intermediate layer is exposed at the periphery of the separator 6 and at the manifold end face 13. Therefore, if this exposed part is not protected and used as it is, the intermediate layer is selectively corroded, and the corrosion product deteriorates the power generation performance. Therefore, in Example 2, the exposed surface was coated with the same material as that of the protective layer 2, but this may be performed by other methods such as plating or resin coating. When titanium / aluminum / titanium is used as the metal layer 1, alumite treatment is appropriate.

  When this is anodized in a 10 wt% sulfuric acid at room temperature for 15 minutes at a voltage of 15 V, aluminum as an intermediate layer is covered with a dense anodized aluminum film having excellent corrosion resistance. Corrosion resistance after anodizing was improved by about 3 digits.

  Subsequent to the alumite treatment, the corrosion resistance was further improved by sealing with pure water at 95 ° C. for 10 minutes. However, the outer layer of titanium is also oxidized, and a purple insulating film grows. Therefore, this was removed by polishing or the like to obtain a separator.

  FIG. 6 shows a bird's-eye view of the cooling plate 15. A cooling plate (cooling cell) 15 having the same structure as the separator 6 was used. The cooling water frame 16 is sandwiched between two cooling plates 15 having the same shape as the separator 6, and this is used as a unit cooling cell. The cooling water has a structure that flows between the cooling plate 15-a and the cooling plate 15-b.

  The opposing surfaces of the cooling plate 15-a and the cooling plate 15-b are passages for cooling water, whereas the opposite surfaces are electrode surfaces.

  FIG. 7 shows the structure of a stacked battery in which the separators 6 are stacked. Between the separator 6 and the separator 6, two sheets of Gore-Tech Japan MEA (Membran Electrode Assembly; PRIME 5510) 8 and the company's diffusion layer (CARBEL-CF) 9 are sandwiched. This was defined as a unit of power generation cell.

  One unit of cooling cells was repeatedly stacked on three units of power generation cells, and a total of nine units of power generation cells and two units of cooling cells were laminated to form a stacked battery. Carbon paper 17 / nickel current collector 18 / Teflon (registered trademark) insulating plate 19 / end plate 20 are installed on both ends of the laminated body toward the outside.

  Between the two end plates 20 provided at both ends of the laminate, the laminate was tightened using bolts and nuts and disc springs. The end plate 20 is provided with a reaction gas and cooling water inlet / outlet connector, through which the reaction gas and the cooling water are introduced into the stacked battery.

This stacked battery was generated under the following conditions. The power generation conditions were: current density 0.3 A / cm ² , battery temperature 70 ° C., anode and cathode humidified water temperature 70 ° C. (reactive gas humidified by external humidifier), hydrogen utilization rate 70% (pure hydrogen), oxygen utilization rate 40 % (Air), gas exhaust pressure and atmospheric pressure.

The open circuit voltage averaged 900 mV per power generation cell, and averaged 0.74 V per power generation cell at 0.3 A / cm ² load. When power was generated up to 1,000 hours, the output voltage only decreased by 0.02 V per power generation cell.

The result of periodically measuring the AC resistance during power generation was 90 mΩ · cm ² without any change until 3,000 hours after the start of power generation. Therefore, the separator itself was not deteriorated at all, and could be a long-life separator.

  The shape of the separator 6 used in the present embodiment, the width of the rib 21, the width of the groove 22, and the depth are merely examples, and the present invention is not limited thereto.

It is a schematic cross-sectional enlarged view of the separator which formed the coating layer in titanium / copper / titanium. It is a graph showing the relationship between the film thickness of a coating layer, and a corrosion rate. It is a bird's-eye view and cross-sectional enlarged view of a press separator. It is a schematic cross section of a single cell power generation test cell. It is a bird's-eye view of the separator used for the laminated type battery. It is a bird's-eye view of the cooling plate used for the laminated battery. It is a schematic cross section showing the structure of a laminated battery.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Metal layer, 2 ... Coating layer, 3 ... Conductive material, 5 ... Resin, 6 ... Separator, 7 ... Single cell power generation test cell, 8 ... MEA, 9 ... Diffusion layer, 10 ... Holder, 12 ... Frame, 13 ... Manifold, 15 ... cooling plate, 16 ... cooling water frame, 17 ... carbon paper, 18 ... current collecting plate, 19 ... insulating plate, 20 ... end plate, 21 ... rib, 22 ... groove.

Claims (13)

  A separator for a polymer electrolyte fuel cell comprising a metal layer and a conductive coating layer, the metal layer comprising iron, aluminum, copper, titanium, magnesium, zirconium, tantalum, niobium, tungsten, nickel, chromium and the metal layer It is made of at least one metal selected from metal alloys, and the outer surface of the metal layer is made of a metal selected from titanium, zirconium, tantalum, niobium and alloys thereof, and the coating layer is made of carbon, conductive A solid polymer fuel characterized in that a coating layer composed of at least one conductive material selected from conductive ceramics and metal powder and a resin binder for fixing the conductive material is formed Battery separator.   2. The solid according to claim 1, wherein the metal layer is formed of a three-layer structure of outer layer / intermediate layer / outer layer, and the intermediate layer is formed of a metal selected from iron, copper, aluminum, magnesium, and alloys thereof. Polymer fuel cell separator.   2. The polymer electrolyte fuel cell separator according to claim 1, wherein an intermetallic compound composed of adjacent metals is formed between the outer layer / intermediate layer / outer layer of the metal layer.   The metal layer is formed in a three-layer structure of outer layer / intermediate layer / outer layer, and the ratio of the hardness of the metal of the outer layer to the hardness of the metal of the intermediate layer is 1/3 to 3/1. Solid polymer fuel cell separator.   The metal layer is formed of a three-layer structure of outer layer / intermediate layer / outer layer, the intermediate layer is a metal layer made of aluminum or an aluminum alloy, and the portion where the aluminum or aluminum alloy is exposed is an alumite or boehmite film The separator for a polymer electrolyte fuel cell according to claim 1, wherein the separator is coated with.   The outer surface of the metal is titanium or a titanium alloy, and the impurity concentration in titanium is 0.05 ppm or less of hydrogen, 0.2 ppm or less of oxygen, 0.25 ppm or less of iron, 0.05 ppm or less of nitrogen, or 2. The solid polymer fuel cell separator according to claim 1, wherein the hardness of titanium or a titanium alloy is in the range of 72 to 112 in terms of Vickers hardness.   2. The separator for a polymer electrolyte fuel cell according to claim 1, wherein a thickness of the outermost layer of the metal layer is 10 μm or more and a ratio of the thickness of the outermost layer to the thickness of the metal layer is 30% or less.   The separator for a polymer electrolyte fuel cell according to claim 1, wherein the coating layer has a thickness of 10 to 100 μm.   The coating layer is composed of a carbon-based conductive material containing graphite and carbon black and a binder, and the mixing ratio of the carbon-based conductive material and the binder is 15:85 to 90:10 by weight, and the carbon-based 2. The solid polymer fuel cell separator according to claim 1, wherein the blending ratio of graphite and carbon black of the conductive material is 30:70 to 90:10 by weight.   The binder of the coating layer includes at least one of fluorine resin, silicon resin, phenol resin, epoxy resin, polyimide resin, polyamide resin, polyolefin resin, furan resin, and rubber resin. Item 10. The polymer electrolyte fuel cell separator according to Item 1.   The binder of the coating layer is a copolymer of polyvinylidene fluoride (PVDF) and propylene hexafluoride (HFP) (PVDF-HFP copolymer), and the propylene hexafluoride is a binder 5 The separator for a polymer electrolyte fuel cell according to claim 1, which is -30% by weight.   12. The coating layer according to claim 9, wherein in a polymer electrolyte fuel cell having a separator having an electrode, a gas diffusion layer, and a manifold on both sides of a polymer electrolyte having ionic conductivity, the coating layer according to claim 9 only on a current-carrying surface. A separator for a polymer electrolyte fuel cell, characterized in that is formed.   13. The polymer electrolyte having ionic conductivity and electrodes formed on both sides of the polymer electrolyte, and having a gas diffusion layer and a separator, the separator is any one of claims 1 to 12. A solid polymer fuel cell comprising a separator of

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