JP6308330B2 - Titanium alloy, titanium material, separator, cell, and polymer electrolyte fuel cell - Google Patents

Description

  The present invention relates to a titanium alloy, a titanium material including the titanium alloy, a solid polymer fuel cell separator including the titanium material, a cell including the separator, and a solid polymer fuel cell including the cell.

  A fuel cell uses energy generated during a binding reaction between hydrogen and oxygen. Therefore, introduction and spread of fuel cells are expected from both aspects of energy saving and environmental measures. There are various types of fuel cells such as a solid electrolyte type, a molten carbonate type, a phosphoric acid type, and a solid polymer type.

  Among these, the polymer electrolyte fuel cell has a high output density and can be miniaturized. The polymer electrolyte fuel cell operates at a lower temperature than other types of fuel cells, and is easy to start and stop. Because of these advantages, the polymer electrolyte fuel cell is expected to be used for automobiles, small cogeneration for home use, and the like, and has attracted particular attention in recent years.

  FIG. 1A is a perspective view of a polymer electrolyte fuel cell (hereinafter, also simply referred to as “fuel cell”), and FIG. 1B is an exploded perspective view of a single cell used in the fuel cell.

  As shown in FIG. 1A, the fuel cell 1 is an assembly (stack) of single cells. In the single cell, as shown in FIG. 1B, an anode-side gas diffusion electrode membrane (also referred to as “fuel electrode membrane”; hereinafter referred to as “anode”) 3 is formed on one surface of the solid polymer electrolyte membrane 2. , Cathode side gas diffusion electrode films (also referred to as “oxidant electrode films”; hereinafter referred to as “cathodes”) 4 are laminated. Separators (bipolar plates) 5a and 5b are stacked on both sides of the laminate.

  Some fuel cells are provided with a separator having a cooling water flow path between two adjacent single cells or every several single cells. The present invention is also directed to a titanium material used for such a water-cooled fuel cell separator.

  As the solid polymer electrolyte membrane 2, a fluorine-based proton conductive membrane having a hydrogen ion (proton) exchange group is mainly used.

  Both the anode 3 and the cathode 4 are mainly composed of a carbon sheet in which conductive carbon fibers are formed into a sheet shape. Instead of the carbon sheet, carbon paper thinner than the carbon sheet, or thinner carbon cloth may be used. The anode 3 and the cathode 4 may be provided with a catalyst layer made of a particulate platinum catalyst, graphite powder, and, if necessary, a fluorine resin having a hydrogen ion (proton) exchange group.

  In the separator 5a, a groove-like flow path 6a is formed on the surface on the anode 3 side. A fuel gas (hydrogen or hydrogen-containing gas) A flows through the flow path 6a, and hydrogen is supplied to the anode 3. The separator 5b has a groove-like channel 6b formed on the surface on the cathode 4 side. An oxidizing gas B such as air flows through the flow path 6 b and oxygen is supplied to the cathode 4. By supplying these gases, an electrochemical reaction occurs and DC power is generated. When a catalyst layer is provided on the anode 3 and the cathode 4, the fuel gas or oxidizing gas and the catalyst layer come into contact with each other to promote the reaction.

The main functions required for a separator of a polymer electrolyte fuel cell are as follows.
(1) Function as a “flow path” for uniformly supplying fuel gas or oxidizing gas into the battery surface (2) Water generated on the cathode side together with a carrier gas such as air and oxygen after reaction, Function as a “flow path” for efficiently discharging from the fuel cell to the outside of the system (3) Contact with the electrode membrane (anode 3, cathode 4) to form an electrical path, and further, electricity between two adjacent single cells (4) Function as a “partition” between the anode chamber of one cell and the cathode chamber of the other cell between adjacent cells (5) In a water-cooled fuel cell, Function as a “partition wall” between adjacent cells

  The base material of the separator used in the polymer electrolyte fuel cell needs to be able to fulfill such a function. Substrate materials are roughly classified into metal materials and carbon materials.

  The carbon-based material has an advantage that the weight of the separator can be reduced due to its small specific gravity, but has a problem that it has gas permeability and a low mechanical strength.

  For example, titanium is used as the metal material. A separator made of a metal material is obtained by molding a metal material by press working or the like. Metallic materials are excellent in workability as a characteristic property of metals. A separator made of a metal-based material has an advantage that the thickness can be reduced and the weight of the separator can be reduced. However, there is a problem that the electrical conductivity of the separator decreases due to oxidation of the separator surface, and the contact resistance between the separator and the electrode film can increase. The following measures have been proposed for this problem.

  In Patent Document 1, in order to improve corrosion resistance (oxidation resistance), a passive film is removed from a surface in contact with an electrode in a titanium separator, and then the surface is plated with a noble metal such as gold (Au). It has been proposed to form a thin film layer consisting of However, the use of a large amount of a noble metal such as gold in a fuel cell for a moving body such as an automobile or a stationary fuel cell is problematic from the viewpoint of economy and the amount of resources. For this reason, the titanium separator proposed in Patent Document 1 is not widespread.

  In Patent Document 2, an attempt is made to increase the corrosion resistance (oxidation resistance) of a titanium separator without using a noble metal such as gold. Specifically, Patent Document 2 proposes a titanium separator having a conductive contact layer made of carbon formed on its surface. The conductive contact layer is formed by vapor deposition. However, since it takes a long time to form such a conductive contact layer by vapor deposition, productivity is lowered. Moreover, since a special apparatus is required for vapor deposition, the equipment cost increases. For this reason, the titanium separator proposed in Patent Document 2 is not actively employed at present.

  Patent Document 3 proposes to reduce an increase in contact resistance due to surface oxidation by forming a metal film in which conductive ceramics are dispersed on the surface of a titanium separator. However, when a plate material on which this metal film is formed is press-molded to obtain a separator, ceramics dispersed in the metal film may hinder molding, and cracks or through holes may occur in the plate material during processing. . In addition, since ceramics wear the press die, it is necessary to change the press die to an expensive material such as a cemented carbide. For this reason, the titanium separator proposed in Patent Document 3 has not been put into practical use.

In Patent Document 4, a titanium alloy base material containing a platinum group element is immersed in a solution containing a non-oxidizing acid and an oxidizing acid and pickled, thereby concentrating the platinum group element on its surface, Thereafter, a method of manufacturing a separator titanium material by a process of performing a heat treatment in a low oxygen concentration atmosphere is disclosed. By this process, a mixed layer of a platinum group element and titanium oxide is formed on the surface of the separator titanium material. With this mixed layer, the contact resistance of the titanium material when a current of 7.4 mA is passed with a load of ⁵ kgf / cm ² (4.9 × 10 ⁵ Pa) applied to the titanium material is 10 mΩ · cm ^2. It is supposed to be lower as follows. This technique is also described in Non-Patent Document 1.

  In Patent Document 4, the time for immersing the substrate in the solution for pickling is 10 minutes or 30 minutes in the examples. Thus, in the manufacturing method of the titanium material for separators proposed by patent document 4, since it takes time for pickling and it takes time to adjust so that the atmosphere of heat processing may satisfy predetermined conditions, it is produced. Low.

  In Patent Document 5, a titanium alloy substrate containing a platinum group element is immersed in an acid containing a non-oxidizing acid and pickled to form a separator in which a layer enriched with the platinum group element is formed on the surface thereof. Titanium materials have been proposed. In patent document 5, the time which immerses a base material in a solution for pickling is all made into 5 minutes or more in the Example. For this reason, it is difficult to perform pickling continuously, and it is necessary to perform it by a batch type.

  Moreover, in patent document 5, the heat processing heated to 350-600 degreeC in a vacuum atmosphere (low oxygen concentration atmosphere) is performed for the purpose of the adhesive improvement of the platinum group element component concentrated on the surface after pickling, and a matrix. Is preferred. As described above, the titanium material for a separator proposed in Patent Document 5 requires time for pickling, and it takes time to adjust the heat treatment atmosphere so as to satisfy a predetermined condition. Is difficult and reduces productivity.

  Patent Document 6 discloses a titanium material for a separator of a polymer electrolyte fuel cell, which contains a platinum group element and a rare earth element. Since this titanium material contains rare earth elements, platinum group elements are concentrated on the surface by a short pickling treatment, and the initial titanium material can be obtained without heat treatment in a vacuum (low oxygen concentration atmosphere). It is said that the contact resistance is reduced. Further, in this titanium material, even when the platinum group element content is as small as 0.005 mass%, the effect of reducing the initial contact resistance by concentrating the platinum group element on the surface by pickling can be obtained. Has been.

That is, the following effects (1) to (3) can be obtained with the titanium material of Patent Document 6 based on the techniques of Patent Documents 1 to 5.
(1) Reduction of surface treatment time (2) Reduction of platinum group element content of titanium material (3) Enabling heat treatment in vacuum (low oxygen concentration atmosphere) to be omitted

JP 2003-105523 A Japanese Patent No. 4367062 JP-A-11-162479 Japanese Patent No. 4032068 JP 2006-190643 A JP 2013-108991 A

Toshiki Sato, 3 people, R & D Kobe Steel Engineering Reports, vol.55, No.3 (2005), p.48-51

However, the titanium material of Patent Document 6, for example, has a low initial contact resistance measured by applying a load of 20 kgf / cm ² (1.96 × 10 ⁶ Pa). The problem arises that the resistance increases.

  Furthermore, the titanium material of Patent Document 6 tends to cause rough skin (increase in surface roughness) during molding. In order to secure adhesion between the separator using the titanium material and other members (for example, the anode and the cathode), the surface of the titanium material needs to be flat.

  Accordingly, an object of the present invention is to provide a titanium material that has low contact resistance after repeated load application and excellent formability while maintaining the effects (1) to (3). Another object of the present invention is to provide a titanium alloy from which the titanium material can be easily obtained by pickling.

  Still another object of the present invention is to provide a polymer electrolyte fuel cell separator containing the titanium material, a cell including the separator, and a polymer electrolyte fuel cell including the cell.

The titanium alloy of the embodiment of the present invention is
% By mass
Platinum group elements: 0.005% to 0.15%,
Rare earth elements: 0.0005% or more, 0.0019% or less,
Ni: 0 to 1.0%,
Mo: 0 to 0.5%,
V: 0 to 0.5%
Cr: 0 to 0.5%, and W: 0 to 0.5%
And the balance consists of Ti and impurities,
The average crystal grain size of the α phase, 2 7 [mu] m or more and 300μm or less.

The titanium material of the embodiment of the present invention is
A base material made of the above titanium alloy;
A film formed on the surface of the base material and mainly composed of titanium oxide and a platinum group element and having a thickness of 50 nm or less is provided.

A separator for a polymer electrolyte fuel cell according to an embodiment of the present invention includes the titanium material.
A cell for a polymer electrolyte fuel cell according to an embodiment of the present invention includes the separator.
A polymer electrolyte fuel cell according to an embodiment of the present invention includes the cell.

  In the titanium material of the present embodiment, the initial contact resistance is low, and the increase in contact resistance due to repeated load is small. For this reason, the contact resistance after repeatedly applying a load is low. Moreover, since this titanium material is provided with the above-described film, the contact resistance is low. Since the coating is excellent in corrosion resistance, the contact resistance of the titanium material is kept low in the environment inside the polymer electrolyte fuel cell. Furthermore, the formability of the titanium material of the present embodiment is good, and rough skin hardly occurs on the surface of the titanium material at the time of molding. For this reason, when this titanium material is applied to a separator of a polymer electrolyte fuel cell, it has good adhesion to other members such as an anode and a cathode.

  The titanium alloy according to the present embodiment can be pickled under appropriate conditions to concentrate the platinum group element on the surface in a short time and form the film. That is, the titanium material can be easily obtained by pickling the titanium alloy under appropriate conditions.

  The separator of the present embodiment includes the titanium material of the present embodiment, and the cell and the polymer electrolyte fuel cell of the present invention include this separator. Therefore, in these separator, cell, and polymer electrolyte fuel cell, The said effect by the said titanium material is acquired.

FIG. 1A is a perspective view schematically showing a structure of a polymer electrolyte fuel cell. FIG. 1B is an exploded perspective view showing the structure of a single cell constituting the solid polymer fuel cell. FIG. 2 is a diagram for explaining a method of measuring contact resistance.

  As shown in Patent Document 6, the present inventors have confirmed that when a platinum group element and a rare earth element are contained in a titanium alloy, the platinum group element can be concentrated on the surface in a short time and at a high concentration. The titanium material thus obtained has a low initial contact resistance, but it has been found that the contact resistance increases when a repeated load is applied.

  Therefore, further investigations have been made, and it has been found that there is an optimum range for the rare earth element content in order to reduce the contact resistance after repeated loading. This is because when the load is repeatedly applied, the rare earth element near the surface of the titanium material reacts with oxygen to form an oxide, resulting in a decrease in conductivity. Such oxidation occurs even if the rare earth element content is within the solid solubility limit of the rare earth element with respect to the titanium α phase.

  It has also been found that the crystal grain size of the titanium α phase affects the contact resistance. Specifically, the larger the crystal grain size, the smaller the contact resistance. This is presumably because the crystal grain boundaries lower the mobility of electrons.

Furthermore, high rare earth element content, and if the crystal grain size is 2 7 [mu] m or more, surface roughening is likely to occur, it is difficult to the flatness of the titanium material surface after machining to a practical level There was found. This is presumably because the oxide formed by the reaction of the rare earth element with oxygen not only promotes non-uniform deformation during processing but also serves as a starting point for cracking. The present inventors have found that there is a further optimum range for the rare earth element content in order to improve the rough skin without impairing the property that the platinum group element is concentrated on the surface in a short time and at a high concentration. .

  The present invention has been completed based on the above findings. Hereinafter, a titanium alloy, a titanium material, a separator, a cell, and a polymer electrolyte fuel cell according to an embodiment of the present invention will be described in detail. In the following description, “%” for chemical composition means mass%.

1. Titanium alloy 1-1. Chemical composition
1-1-1. Platinum group element In this specification, a platinum group element means Ru, Rh, Pd, Os, Ir, and Pt. The platinum group element is an element having an electric resistivity lower than that of Ti, and does not cause oxidation and corrosion in the operating environment of the polymer electrolyte fuel cell and does not increase the electric resistivity.

  The titanium alloy contains one or more of the above platinum group elements. The platinum group element content of the titanium alloy is 0.005 to 0.15%. Here, the “platinum group element content” refers to the content when the base material contains substantially only one type of platinum group element, and the base material contains two or more types of platinum group elements. When it contains, it shall mean the sum total of the content rate of each platinum group element.

  When the platinum group element content is less than 0.005%, the corrosion resistance cannot be increased and the contact resistance cannot be sufficiently reduced. On the other hand, when the platinum group element content is larger than 0.15%, the raw material cost becomes large. Considering the balance between economy and corrosion resistance, the platinum group element content is preferably 0.01 to 0.05%.

  The type of platinum group element is not particularly limited, but Pd, Ru, and Ir are preferable because they are cheaper and have a larger effect of reducing contact resistance per unit content than other platinum group elements. On the other hand, since Rh, Os and Pt are very expensive, they are not preferable from the viewpoint of economy.

1-1-2. Rare Earth Element In this specification, the rare earth element refers to Sc, Y, and Ln group (La to Lu). By including any one or more of the above rare earth elements in the titanium alloy as a base material, the platinum group element is concentrated on the surface of the base material by pickling to reduce the contact resistance of the titanium material. can do. When two or more kinds of rare earth elements are contained in the base material, such as mixed rare earth elements (Misch metal; hereinafter referred to as “Mm”) before separation and purification, and didymium alloys (alloys composed of Nd and Pr) Mixtures or alloys of rare earth elements can be used. Mm and didymium alloys can be used as materials for the titanium alloy of the present invention as long as they are commercially available. In this case, the kind of rare earth elements contained in Mm and the didymium alloy and the content ratio of each rare earth element in the Mm and didymium alloy are not limited.

Rare earth element content of the titanium alloy of the present invention, 0.0005% or more and 0.00 19% or less. Here, the “rare earth element content” refers to the rare earth element content when the titanium alloy substantially contains only one kind of rare earth element, and the titanium alloy contains two or more kinds of rare earth elements. When it contains, it shall mean the sum total of the content rate of each rare earth element.

  When the titanium alloy contains a platinum group element and a rare earth element, Ti and the rare earth element are simultaneously dissolved in an aqueous solution containing a non-oxidizing acid in the active state region of the titanium alloy, and the platinum group element on the titanium alloy surface is obtained. Precipitation can be promoted. This effect is sufficiently obtained when the rare earth element content is 0.0005% or more.

When a titanium alloy containing a rare earth element is repeatedly subjected to a load, the rare earth element becomes an oxide having poor conductivity. If the rare earth element content is too high, an increase in contact resistance due to this oxide cannot be ignored. On the other hand, if the rare earth element content is too high, this oxide deteriorates the formability such as roughening or cracking during processing. This tendency becomes remarkable when the average crystal grain size of the α phase to be described later is 2 7 [mu] m or more. When the rare earth element content is 0.0019% or less, an increase in the contact resistance of the titanium material due to a repeated load can be suppressed, and the moldability can be improved. The effect of suppressing an increase in contact resistance due to repeated load and improving the moldability is significantly obtained when the Ln group is used among the rare earth elements. Therefore, it is preferable to use the Ln group as the rare earth element.

In order to promote concentration of platinum group elements on the surface by pickling, the lower limit of the rare earth element content is preferably 0.0006%, and more preferably 0.0008%. Further, in order to suppress an increase in contact resistance due to repeated loads and to improve moldability, the upper limit of the rare earth element content is 0 . It is good preferable to 0,018 percent.

1-1-3. Optional Element The titanium alloy may contain one or more selected from the group consisting of Ni, Mo, V, Cr and W. By containing these elements, a platinum group element can be concentrated on the surface of the titanium alloy by a synergistic effect with the rare earth elements. Thereby, a titanium material having excellent crevice corrosion resistance can be obtained. When these elements are contained, the contents are Ni: 1.0% or less, Mo: 0.5% or less, V: 0.5% or less, Cr: 0.5% or less, W: 0.5 % Or less. A preferable upper limit of the Ni content is 0.7%, and a preferable lower limit of the Ni content is 0.001%. A preferable upper limit of the Mo content is 0.4%, and a preferable lower limit of the Mo content is 0.001%. A preferable upper limit of the V content is 0.4%, and a preferable lower limit of the V content is 0.001%. A preferable upper limit of the Cr content is 0.4%, and a preferable lower limit of the Cr content is 0.001%. A preferable upper limit of the W content is 0.4%, and a preferable lower limit of the W content is 0.001%.

1-1-4. Impurity elements The impurity elements of titanium alloys include raw materials, melting electrodes, and Fe, O, C, H, N, etc. introduced from the environment, and scraps as raw materials. Al, Zr, Nb, Si, Sn, Mn, Cu and the like introduced from the above. These impurity elements may be contained in the titanium alloy as long as the content does not hinder the effects of the present invention. Specifically, the contents not inhibiting the effects of the present invention include Fe: 0.3% or less, O: 0.35% or less, C: 0.18% or less, H: 0.015% or less, N : 0.03% or less, Al: 0.3% or less, Zr: 0.2% or less, Nb: 0.2% or less, Si: 0.02% or less, Sn: 0.2% or less, Mn: 0 0.01% or less, Cu: 0.1% or less, and the total content of these elements is 0.6% or less.

1-2. Average crystal grain size of the α phase The larger the crystal grain size of the α phase (parent phase) of the titanium alloy, the higher the conductivity of the titanium alloy. If the average crystal grain size of the α phase is in 2 7 [mu] m or more, conductivity can be sufficiently high. On the other hand, if the average crystal grain size of the α phase exceeds 300 μm, even if the rare earth element content is optimized, the ductility of the titanium material containing the titanium alloy is lowered, and it becomes easy to crack during press molding. Therefore, the average crystal grain size of the α-phase, 2 7 [mu] m or more, shall be 300μm or less, preferably a 2 7 ~200μm, more preferably 30 to 120 [mu] m.

  As will be described later, the average crystal grain size of the α phase can be controlled by heat treatment (annealing) conditions and the like. When the titanium alloy is annealed, the average crystal grain size of the α phase is measured by a method defined in JIS-G 0551 (2013 edition) without polishing the surface of the titanium alloy after annealing. The average crystal grain size of the α phase may be measured on the cut surface of the titanium alloy (titanium material). Even in this case, substantially the same value as that obtained when the surface of the titanium alloy after annealing is measured without polishing is obtained. When the α phase and the β phase coexist, the β phase is excluded from the measurement target and the average crystal grain size is obtained.

2. Titanium material The titanium material of the present invention includes a base material made of the titanium alloy and a film formed on the surface of the base material. The film is mainly composed of titanium oxide and a platinum group element. Here, “mainly composed of titanium oxide and platinum group element” means that the ratio of titanium oxide and platinum group element in the film is 90% by mass or more. It is considered that the platinum group element in the film exists as a metal and forms an energization path between the base material and the surface of the film.

  When the film thickness exceeds 50 nm, many corrosion products such as oxides (including oxides of platinum group elements) are formed in the environment inside the polymer electrolyte fuel cell, and the surface contact resistance is low. May decrease. For this reason, the thickness of the film is 50 nm or less, preferably 20 nm or less, more preferably 10 nm or less. On the other hand, if the film is too thin, the corrosion resistance may decrease. For this reason, the thickness of the film is set to 0.1 nm or more, preferably 0.15 nm or more, and more preferably 0.2 nm or more.

  The thickness of the film is obtained as follows. First, the titanium material is cut in the thickness direction. The cut surface is observed with an electron microscope (for example, TEM), and the thickness (the distance from the boundary between the base material and the coating to the surface of the coating) is measured at any 10 locations. The measured values are averaged to obtain the film thickness. The film can be distinguished from the base material by contrast in the electron microscope image.

3. Method for Producing Titanium Material of the Present Invention A titanium material having a desired shape can be obtained by carrying out processes such as melting, casting, hot rolling, cold rolling, annealing, and pickling.

The method for forming the film is not particularly limited, but for example, the film can be formed by pickling or electrolytically treating the base material with a non-oxidizing acid and concentrating the platinum group element on the surface of the base material. The platinum group elements are concentrated by eluting from the base material and reprecipitating on the surface of the base material. As the non-oxidizing acid, for example, hydrochloric acid, sulfuric acid and the like can be employed. Although hydrofluoric acid is a non-oxidizing acid, it has a strong dissolving power in the base material, and the reprecipitation efficiency of the platinum group element is inferior to hydrochloric acid, sulfuric acid and the like. Further, when hydrofluoric acid is used, the amount of hydrogen generated during pickling is large, and hydrogen is easily absorbed by the base material. For this reason, when pickling using hydrofluoric acid, it is necessary to sufficiently control the concentration of hydrofluoric acid, the treatment time, the treatment temperature, and the like. For pickling, a plurality of types of acids such as hydrochloric acid, sulfuric acid, hydrofluoric acid, and sulfamic acid may be mixed and used. Although the conditions for the electrolytic treatment are not particularly limited, for example, the platinum group element can be uniformly concentrated on the surface of the base material by performing treatment at a current density in the range of 0.1 to 30 mA / cm ² .

  When an oxidizing acid is used for pickling, it is possible to prevent hydrogen generated by pickling from entering the base material and being absorbed. On the other hand, when an oxidizing acid is used for pickling, a thick oxide layer is formed on the surface layer of the base material, making it difficult to form a film. For this reason, even if it is a case where an oxidizing acid is used for pickling for the purpose of preventing the absorption of hydrogen into the base material, it is preferable to use the oxidizing acid at the lowest possible concentration.

  After forming the film, it is preferable to perform heat treatment in order to improve the adhesion between the base material and the film. Since the film is mainly composed of titanium oxide and a platinum group element, even when this titanium material is heat-treated in an oxidizing atmosphere, the oxidation of the surface layer hardly proceeds. Therefore, heat treatment in a vacuum (low oxygen concentration atmosphere) can be omitted when manufacturing the titanium material of the present embodiment. For the heat treatment, for example, an on-line bright annealing facility or a batch annealing furnace can be used.

By appropriately setting the heat treatment temperature, average crystal grain size of α phase 2 7 [mu] m or more, it can be made to fall within the following 300 [mu] m.

  After the heat treatment, it is possible to carry out a light pickling (for example, pickling within 10 minutes with an aqueous solution of pH 2 to 3) for the purpose of washing the surface as necessary. Light pickling does not affect the contact resistance and formability of the titanium material.

4). Separator, Cell, and Polymer Electrolyte Fuel Cell The polymer electrolyte fuel cell separator includes the titanium material described above. A cell for a polymer electrolyte fuel cell (unit battery) includes the separator described above. The polymer electrolyte fuel cell includes the above-described cell. Each cell has a solid polymer electrolyte membrane, an anode (fuel electrode membrane) superimposed on one surface of the solid polymer electrolyte membrane, and a cathode (oxidant electrode membrane) superimposed on the other surface of the solid polymer electrolyte membrane. Can be included. The polymer electrolyte fuel cell may include a plurality of cells stacked via separators. The polymer electrolyte fuel cell generates DC power by supplying a fuel gas and an oxidant gas to the anode and cathode of each cell, respectively.

  As described above, the titanium material of the present invention is suppressed from increasing in contact resistance due to repeated loads. Therefore, in the polymer electrolyte fuel cell of the present invention, an increase in contact resistance between the separator, the anode, and the cathode is suppressed.

  Furthermore, since the titanium material of the present invention has good moldability as described above, rough skin hardly occurs when it is formed into the shape of a separator. Therefore, in the polymer electrolyte fuel cell of the present invention, the adhesion between the separator and other members (for example, the anode and the cathode) can be increased.

  In addition, since the above-described film is provided on the surface of the titanium material, the separator using this titanium material has low initial contact resistance and excellent corrosion resistance in the environment inside the polymer electrolyte fuel cell. Therefore, the low contact resistance of this separator is maintained in the polymer electrolyte fuel cell. Therefore, the polymer electrolyte fuel cell using this separator has a high initial voltage and a small voltage drop with time.

In order to confirm the effect of the present invention, a titanium material sample was prepared and evaluated by the following method.
1. Production of Titanium Material A titanium ingot was prepared as a titanium material. Table 1 shows the chemical composition of the titanium ingot (material). These titanium ingots were obtained by melting and solidifying the raw material at the laboratory level. Material 1 contained substantially no platinum group elements and rare earth elements. The rare earth element content of the material 2 was lower than the range defined as the base material of the present invention. The rare earth element contents of the materials 3, 5, 8, 10, 11, 15, and 52 were higher than the range defined as the base material of the present invention. The platinum group element content of the material 51 was lower than the range defined as the base material of the present invention. In these respects, the materials 1 to 3, 5, 8, 10, 11, 15, 51, and 52 did not satisfy the chemical composition requirements of the base material of the present invention. The raw materials 4, 6, 7, 9, 12-14, and 53-60 satisfied the chemical composition requirements of the base material of the present invention.

  These ingots were subjected to hot rolling, cold rolling, and heat treatment (annealing) in a temperature range of 700 to 850 ° C. to finish a titanium plate having a thickness of 0.2 mm. For these titanium plates, the average crystal grain size was measured by the method defined in JIS-G 0551 (2013 edition) without polishing the surface after annealing.

Next, pickling was performed by immersing the titanium plate in an aqueous solution of any of the following (a) to (d) as an acid solution.
(A) An aqueous solution having a hydrochloric acid concentration of 7.5% by mass (b) An aqueous solution having a sulfuric acid concentration of 25% by mass (c) An aqueous solution having a nitric acid concentration of 4% by mass and a hydrofluoric acid concentration of 1.5% by mass ( d) An aqueous solution having a sulfuric acid concentration of 25% by mass and a hydrofluoric acid concentration of 0.1% by mass.

  During pickling, the temperature of the acid solution was 45 to 70 ° C., and the immersion time of the titanium plate in the acid solution was 0.3 to 20 minutes. As a result, an oxide film was formed on the surface of the titanium plate. It was confirmed by analyzing with TEM-EDX that this oxide film was mainly composed of titanium oxide and a platinum group element (film in the titanium material of the present invention). Hereinafter, the term “film” simply refers to this oxide film. Moreover, the thickness of this oxide film was calculated | required from the TEM image.

  A groove-like gas flow path having a width of 2 mm and a depth of 1 mm is formed on both surfaces of the titanium plate (corresponding to the anode side and the cathode side of the separators 5a and 5b in FIG. 1B) and used as a separator. In a form that can be.

2. Measurement of Contact Resistance (1) Initial Contact Resistance FIG. 2 is a diagram for explaining a contact resistance measurement method. A titanium material (hereinafter referred to as “separator”) 21 processed into a separator shape is sandwiched between a pair of carbon papers (TGP-H-90 manufactured by Toray Industries, Inc.) 22 and this is plated with a pair of gold. It was sandwiched between electrodes 23. The carbon paper 22 was used for the gas diffusion layer (the anode 3 and the cathode 4 in FIG. 1B), and the area thereof was 1 cm ² .

Next, a load is applied between the pair of gold-plated electrodes 23, and in this state, a constant current is passed between the pair of gold-plated electrodes 23. The voltage drop was measured and the resistance value was determined based on this result. The load was 20 kgf / cm ² (1.96 × 10 ⁶ Pa). Since the obtained resistance value is a sum of the contact resistances on both sides of the separator 21, this is divided by 2 to obtain a contact resistance value (initial contact resistance) per one side of the separator 21.

(2) Contact resistance after applying repeated load After measuring the initial contact resistance, the load was removed, and then the above load (20 kgf / cm ² ) was added and removed for 4 cycles. When the load of the fourth cycle was applied, the contact resistance was measured in the same manner as the measurement of the initial contact resistance, and the contact resistance after repeatedly applying the load was obtained.

(3) Contact resistance after operation of fuel cell Next, a single-cell solid polymer fuel cell was prepared using a separator whose initial contact resistance had been measured. The cell uses FC50-MEA, which is a standard MEA for PFEC manufactured by Toyo Corporation, as a membrane electrode assembly (MEA) including a solid polymer electrolyte membrane (Nafion (registered trademark) -1135 as an ion exchange membrane) ) Was used. A load was applied as a clamping pressure between the separator and the anode and the cathode. The contact resistance after operation of this fuel cell was measured.

  A fuel cell operated by incorporating a separator was not a multi-cell fuel cell in which single cells were stacked. The reason is that in the state where the single cells are stacked, the difference in the stacked state is reflected in the evaluation result, and the reproducibility of the measured value is lowered.

To this fuel cell, hydrogen gas having a purity of 99.9999% was flowed as the anode side fuel gas, and air was flowed as the cathode side gas. The gas pressure for introducing hydrogen gas and air into the fuel cell was 0.04 to 0.20 bar (4000 to 20000 Pa). The temperature of the fuel cell main body was kept at 70 ± 2 ° C., and the humidity control inside the fuel cell was adjusted by setting the inlet dew point to 70 ° C. The pressure inside the battery was about 1 atmosphere (about 1.01 × 10 ⁵ Pa).

This fuel cell was operated at a constant current density of 0.5 A / cm ² . The output voltage was highest in 20 to 50 hours from the start of operation. After reaching this highest voltage, the operation was continued for 250 hours, and then the operation of the fuel cell was temporarily stopped. Thereafter, the load, that is, the tightening pressure was removed and the load was applied again to restart the operation of the fuel cell. Then, after reaching the highest voltage, the operation was continued for 250 hours. Thereafter, the cell was disassembled, the separator was taken out, and the contact resistance was measured by the method described above to obtain the contact resistance after the power generation operation.

  A digital multimeter (KEITLEY 2001 manufactured by Toyo Technica Co., Ltd.) was used for measurement of contact resistance and measurement of current and voltage during operation of the fuel cell.

3. Formability Evaluation Hereinafter, the titanium plate to be evaluated (a titanium plate that has been pickled and a titanium plate that has not been intentionally pickled) is referred to as a “titanium material”. Separately from the above pressing, the Eriksen test specified in JIS Z 2247 (2006 edition) is performed on the titanium material, and the side surface of the titanium material is magnified 50 times to confirm the presence or absence of wrinkles (unevenness). did. This was evaluated as rough skin by processing. For rough skin, “no” was given when no wrinkles were observed in the observed visual field, and “yes” was given when at least one wrinkle was found.

4). Evaluation Results Table 2A and Table 2B show the above evaluation results together with the average crystal grain size of the base material, pickling conditions, and the thickness of the oxide film (film). The titanium alloys (base materials) used for the titanium materials 6 and 7 satisfied the requirements of the titanium alloy of the present invention, but the titanium materials 6 and 7 did not satisfy the requirements of the titanium material of the present invention. For this reason, in the column of Table 2A and Table 2B, the titanium materials 6 and 7 are described as “reference examples”.

The contact resistance of the titanium material of the present invention (titanium materials 4, 9-11, 14, 18-20, 51, 53, 56 and 58-65) is initially, after repeatedly applying a load, and after operation of the fuel cell. All of these were sufficiently low at 10 mΩ · cm ² or less.

  Furthermore, none of the titanium materials according to the examples of the present invention produced rough skin in the Eriksen test.

  In the titanium materials 1 and 2 which are comparative examples, the contact resistance was large at the initial stage, after repeatedly applying a load, and after the power generation operation. The contact resistance of the titanium material 1 was large because the base material contained substantially neither a platinum group element nor a rare earth element. This is thought to be due to the formation of The reason why the contact resistance of the titanium material 2 was large is considered to be that a film in which the platinum group element was sufficiently concentrated on the surface was not formed by pickling because the rare earth element content of the base material was low.

  In the titanium material 3 as a comparative example, the initial contact resistance was small, but the contact resistance after repeated load application and after power generation operation was large. This is presumably because the rare earth element content in the base material was high, so that the rare earth element was oxidized by repeated loading and fuel cell operation. Further, the titanium material 3 was roughened by processing. This is probably because the rare earth element promoted non-uniform deformation due to the high rare earth element content of the base material.

  In the titanium materials 5 and 57 which are comparative examples, the initial contact resistance was small, but the contact resistance after applying the load repeatedly and after the power generation operation was large. Further, the initial contact resistance of these titanium materials was larger than the average initial contact resistance of the titanium materials of the present invention examples. This is considered to be related to the fact that in the titanium materials 5 and 57, the average crystal grain size of the α phase of the base material was as small as 25 μm or less.

  In the titanium material 6 as a reference example, the contact resistance was high at the initial stage, after repeatedly applying a load, and after the power generation operation. This is probably because the titanium material 6 was not subjected to the pickling treatment, and therefore no film was formed.

  In the titanium material 7 as a reference example, the contact resistance was large at the initial stage, after repeatedly applying a load, and after the power generation operation. This is probably because the titanium material 7 has an increased contact resistance as a result of the film thickness obtained by the pickling treatment being too thick.

In the titanium materials 8, 12, 15-17, 21, and 55, which are comparative examples, the contact resistance was sufficiently low at 10 mΩ · cm ² or less at the initial stage, after applying the repeated load and after the power generation operation. However, the titanium materials 8, 12, 15-17, 21, and 55 were roughened by processing. This is probably because the rare earth element promoted non-uniform deformation due to the high rare earth element content of the base material.

  In the titanium material 13 as a comparative example, the initial contact resistance was small, but the contact resistance after repeatedly applying a load and after the power generation operation was large. Moreover, the initial contact resistance of the titanium material 13 was larger than the average initial contact resistance of the titanium material of the present invention example. This is considered to be related to the fact that in the titanium material 13, the average crystal grain size of the α phase of the base material was as small as 25 μm or less. Further, the titanium material 13 was roughened by processing. This is probably because the rare earth element promoted non-uniform deformation due to the high rare earth element content of the base material.

In the titanium material 52 as a comparative example, the contact resistance at the initial stage, after repeatedly applying a load, and after the power generation operation, was sufficiently low at 10 mΩ · cm ² or less. However, rough skin was caused by processing. This is presumably because, in the titanium material 52, the ductility was remarkably reduced because the average crystal grain size of the α phase of the base material exceeded 300 μm.

  In the titanium material 54 as a comparative example, the contact resistance was large both initially, after repeatedly applying a load, and after the power generation operation. This is presumably because, in the titanium material 54, the platinum group element content of the base material was low, so that a film in which the platinum group element was sufficiently concentrated on the surface was not formed by pickling.

    1: Solid polymer fuel cell, 5a, 5b, 21: Separator

Claims (5)

% By mass
Platinum group elements: 0.005% to 0.15%,
Rare earth elements: 0.0005% or more, 0.0019% or less,
Ni: 0 to 1.0%,
Mo: 0 to 0.5%,
V: 0 to 0.5%
Cr: 0 to 0.5%, and W: 0 to 0.5%
And the balance consists of Ti and impurities,
The average crystal grain size of the α phase, 2 7 [mu] m or more and 300μm or less, a titanium alloy. A base material comprising the titanium alloy according to claim 1;
A titanium material formed on the surface of the base material and comprising a titanium oxide and a film mainly composed of a platinum group element and having a thickness of 50 nm or less.   A separator for a polymer electrolyte fuel cell, comprising the titanium material according to claim 2.   A polymer electrolyte fuel cell, comprising the separator according to claim 3.   A polymer electrolyte fuel cell comprising the cell according to claim 4.

Images