TW201804650A - Titanium alloy material, separator, cell and fuel cell - Google Patents

Abstract

A titanium alloy material which is provided with a base (1) and a first oxide layer (2) that is formed on the base (1). The base (1) is formed of a titanium alloy that contains one or more elements M selected from the group consisting of V, Ta and Nb. The first oxide layer (2) contains TiOx (wherein 1 ≤ x < 2) and MOy (wherein 1 ≤ y ≤ 2.5); and the first oxide layer (2) has a thickness of 1-100 nm. The content of the elements M in the base (1) is from 0.6% by mass to 10% by mass (inclusive). This titanium alloy material may additionally comprise a second oxide layer (3) that is formed on the first oxide layer (2). The second oxide layer (3) contains Ti1-zMzO2 (wherein 0 < z ≤ 0.2). This titanium alloy material has excellent corrosion resistance in the environment within a fuel cell, while being capable of maintaining a low contact resistance.

Description

Titanium alloy materials, spacer plates, battery cells, and fuel cells

The present invention relates to a titanium alloy material, a spacer plate provided with the titanium alloy material, a battery cell provided with the spacer plate, and a fuel cell provided with a plurality of the battery cells.

Metal materials are used in various applications as conductive materials. One of these uses is, for example, a separator for a fuel cell. Fuel cells use the energy generated during the combined reaction of hydrogen and oxygen to generate electricity. Therefore, the introduction and spread of fuel cells can be expected from two aspects of energy saving and environmental countermeasures. Fuel cells include solid electrolyte type, molten carbonate type, phosphoric acid type, and solid polymer type.

Among these, the solid polymer fuel cell has a high output density and can be miniaturized. In addition, other types of fuel cells can operate at lower temperatures and are easier to start and stop. Because of these advantages, solid polymer fuel cells are expected to be used in small-scale gas-electric coexistence for automobiles and homes.

As a fuel cell, a water-cooled fuel cell is known in which a partition plate having a cooling water flow path is arranged between two adjacent battery cells or every several battery cells. In the present invention, not only does not have cooling water A titanium alloy material for a partition plate of a flow path, and a titanium alloy material for a partition plate having a cooling water flow path can also be used.

The main functions required for the separator of the polymer electrolyte fuel cell are as follows.

(1) The function of uniformly supplying fuel gas or oxidizing gas to the "flow path" inside the cell surface

(2) The function of efficiently discharging the water generated on the cathode side with the reaction air and a carrier gas such as oxygen from the fuel cell to the "flow path" outside the system

(3) It is in contact with the electrode membrane (anode, cathode), and becomes a channel for current, and further functions as a circuit "connector" between two adjacent battery cells.

(4) The function of the "partition" between the anode chamber of one battery cell and the cathode chamber of an adjacent battery cell between adjacent battery cells

(5) In a water-cooled fuel cell, the function of the "separation wall" between the cooling water flow path and the adjacent battery cell

The base material of the spacer used in the polymer electrolyte fuel cell must be a material capable of exhibiting such a function. The base material can be roughly divided into a metal-based material and a carbon-based material.

The spacer made of carbon-based material can be calendered or injection-molded into a plate shape by impregnating the resin with a graphite substrate, hardening and firing, or kneading carbon powder with resin or coal char pitch, It is manufactured by a method such as firing to make glassy carbon. Examples of resins used in these methods include phenol resins and furan resins. If carbon-based materials are used, There is an advantage that a lightweight spacer can be obtained.

As the metal material, titanium, stainless steel, or carbon steel can be used. The intermediate separator made of these metal-based materials can be manufactured by calendering or the like. Metal-based materials have metal-specific properties that are excellent in workability, and have the advantage of reducing the thickness of the spacer, thereby achieving the weight reduction of the spacer.

Regarding metal-based materials, there have been proposals in the literature for supporting various precious metals on the surface of a spacer to suppress the increase in resistance (for example, Patent Documents 1 and 2). On the other hand, spacers that do not use precious metals have also been proposed for review. For example, Patent Document 3 proposes a method of forming a conductive contact layer made of carbon on a metal spacer having a titanium surface by vapor deposition on the surface.

Patent Document 4 proposes a Ti alloy for a spacer containing 0.005 to 0.50 mass% of elements such as V and Nb. When this alloy is heat-treated, a conductive titanium oxide layer is formed on the surface. Due to the presence of this oxide layer, the contact resistance of the spacer using this alloy is low.

[Prior technical literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 2003-105523

[Patent Document 2] Japanese Patent Laid-Open No. 2006-190643

[Patent Document 3] Japanese Patent Laid-Open No. 2004-158437

[Patent Document 4] Japanese Patent Laid-Open No. 2015-224368

[Non-patent literature]

[Non-Patent Document 1] T. Hitosugi and 6 others, "Fabrication of TiO2. Based transparent conducting oxide on glass and polyimide substrates", Thin Solid Films, 517 (2009) p. 3106-3109

[Non-Patent Document 2] Shun Suzuki and three others, "Titanium alloys containing precious metal elements have reduced contact resistance by heat treatment after pickling", Titanium, 2006, vol. 54, no. 4, p258-262

A spacer made of a carbon-based material has problems such as gas permeability and low mechanical strength.

The partition plate made of a metal-based material has a problem that the surface conductivity is reduced due to oxidation. When fluorine is supplied from a fluorine-containing electrolyte membrane in a fuel cell, the environment inside the fuel cell becomes fluorine-containing. In this case, the corrosion of the surface of the spacer may cause generation of fluoride, and the conductivity of the surface of the spacer may decrease. When the conductivity of the surface of the partition plate is reduced, the contact resistance between the partition plate and the gas diffusion layer (anode and cathode) increases, and the power generation efficiency of the fuel cell decreases.

In a spacer made of a metal-based material, by supporting a noble metal on the surface, an increase in resistance can be suppressed. However, the solid polymer fuel cell is expected to be widely used as a fuel cell for a mobile body and a fuel cell for a stationary use. The use of a large amount of precious metals is problematic from the viewpoint of economy and limited resources, and has not been widely used.

Regarding the spacer of Patent Document 3, a titanium oxide layer having no conductivity is usually formed on the surface of titanium. Therefore, even if a conductive contact layer is formed on such a titanium oxide layer, the contact resistance does not decrease. In order to reduce the contact resistance, it is necessary to form a conductive contact layer immediately after removing the titanium oxide layer. In this case, a significant increase in cost cannot be avoided.

When the spacer of Patent Document 4 is placed in a fluorine-containing environment in a fuel cell, it is difficult for the titanium oxide layer formed on the surface to maintain conductivity. As a result, there is a concern that the contact resistance of the spacer increases after power generation.

An object of the present invention is to provide a titanium alloy material that solves the aforementioned problems of the prior art, has high corrosion resistance, and can maintain low contact resistance, and a spacer for a fuel cell.

In addition, an object of the present invention is to provide a battery cell of a fuel cell and a fuel cell that can maintain high power generation efficiency.

The gist of the present invention is a titanium alloy material of the following (A), a separator between the following (B), a battery cell of the following (C), and a fuel cell of the following (D).

(A) A titanium alloy material comprising a base material and a first alloy layer formed on the base material, and the base material is composed of a material selected from the group consisting of V, Ta, and Nb. A titanium alloy composed of one or more elements M in the group, the first oxide layer contains TiO _x (1 ≦ x <2) and MO _y (1 ≦ y ≦ 2.5), and the thickness of the first oxide layer The content is 1 to 100 nm, and the content of the element M in the base material is 0.6% by mass or more and 10% by mass or less.

(B) A separator for a fuel cell, comprising the titanium alloy material as described in (A) above.

(C) A battery cell for a fuel cell, comprising a separator between the above (B).

(D) A fuel cell comprising a plurality of battery cells as described in (C) above.

The titanium alloy material and the partition plate of the present invention have high corrosion resistance and can maintain low contact resistance. The battery cell and the fuel cell of the present invention can maintain high power generation efficiency.

In addition, the titanium alloy material of the present invention does not use noble metal as an essential constituent element. In the case where the titanium alloy material does not contain noble metal, the price of the titanium alloy material, the spacer, the battery cell, and the fuel cell of the present invention can be reduced.

1‧‧‧ mother material

2‧‧‧ 1st oxide layer

3‧‧‧ 2nd oxide layer

4‧‧‧ fuel cell

8a, 8b‧‧‧ spacer

11‧‧‧Sample (titanium alloy)

FIG. 1 is a cross-sectional view of a titanium alloy related to one embodiment of the present invention.

FIG. 2A is a perspective view of the entire polymer electrolyte fuel cell according to one embodiment of the present invention.

FIG. 2B is an exploded perspective view of a battery cell (single battery cell) of a fuel cell according to an embodiment of the present invention. FIG.

FIG. 3 is a structural diagram of an apparatus for measuring the contact resistance of a titanium alloy material.

FIG. 4 shows an XPS spectrum chart of Ti2p measured on the surface of a titanium alloy material.

FIG. 5 shows an XPS spectrum of Nb3d measured on the surface of a titanium alloy material.

The present inventors reviewed the use of a titanium alloy containing one or more elements (hereinafter referred to as "M") selected from the group consisting of V, Ta, and Nb to realize the environment in a solid polymer fuel cell Underneath has a high corrosion resistance spacer. As a result, it was found that the use of a titanium alloy containing 0.6% by mass of M or more (when two or more kinds of V, Ta, and Nb are selected, and the total amount of selected elements is 0.6% by mass) can achieve such a high corrosion resistance interval board.

In the following description, unless otherwise specified, "%" in the chemical composition means "mass%".

<The titanium alloy material of the present invention>

FIG. 1 is a cross-sectional view of a titanium alloy material related to one embodiment of the present invention. The titanium alloy material of the present invention includes a base material 1 and a first oxide layer 2 formed on the base material 1. The case where this titanium alloy material is mainly used as a separator between fuel cells is described below.

In general, the oxide film formed on the surface of a titanium material is mainly composed of TiO ₂ and does not substantially exhibit conductivity. Therefore, the contact resistance of such a titanium material is high. In contrast, in the titanium alloy material of the present invention, the first oxide layer has high conductivity. Therefore, the contact resistance of the titanium alloy material of the present invention is low.

<Base material>

The total M content in the base material is 0.6% or more.

As described later, the titanium alloy material of the present invention can be used in a base material (titanium alloy) having the same composition as the base material, in an oxidizing gas environment, and in a reducing gas environment (low oxygen partial pressure gas environment). A heat treatment is performed to produce an oxide film on the surface of the substrate. In this case, if the M content of the base material is less than 0.6%, the amount of oxygen deficiency in the first oxide layer tends to decrease. Oxygen deficiency contributes to electrical conductivity. Therefore, if the amount of oxygen deficiency in the first oxide layer is small, it is difficult to obtain a low contact resistance.

In addition, if the M content of the base material is less than 0.6%, if the titanium alloy material is exposed to the corrosive environment in the fuel cell, TiO _{2 with} high resistance is easily generated. Therefore, in a fuel cell, the contact resistance between an electrode and a spacer (titanium alloy material) is gradually increased, and power generation efficiency is reduced.

In order to generate the first oxide layer having high conductivity and to obtain high corrosion resistance in the environment in the fuel cell, the M content of the base material is set to 0.6% or more. The M content is preferably set to 0.7% or more, and more preferably 1.0% or more.

On the other hand, even if M is contained in the base material more than 10%, It does not help to improve the conductivity of the first oxide layer and reduce the contact resistance of the titanium alloy material, but may cause adverse effects. In addition, if the M content exceeds 10%, the economy is deteriorated, and the workability of the titanium alloy material is deteriorated. Therefore, the M content of the base material is set to 10% or less. The M content is preferably set to 8% or less, and more preferably 6% or less.

The base material may contain, for example, M: 0.6 to 10%, and the remaining portion may be composed of Ti and impurities. Examples of impurities that can be contained in the base material include Fe, Cu, C, N, O, and H. The total content of these impurities should be below 1%. In this case, the conductivity and workability of the titanium alloy material are good.

<First oxide layer>

The first oxide layer contains TiO _x (1 ≦ x <2) and MO _y (1 ≦ y ≦ 2.5).

The titanium oxide represented by the chemical formula of TiO _x may include low-order oxides such as TiO, Ti ₂ O ₃ , and Ti ₄ O ₇ , and titanium oxides having a crystalline structure of TiO ₂ and a part of which is deficient in oxygen. Two or more of these titanium oxides may be present in the first oxide layer. In the average chemical composition of titanium oxide, x is the atomic ratio of O to Ti.

The M oxide represented by the MO _y formula includes not only the most stable oxides M ₂ O ₅ (Nb ₂ O ₅ , Ta ₂ O ₅ , V ₂ O ₅ ), but also MO ₂ (NbO ₂ , TaO ₂ , VO ₂ ), MO (NbO, TaO, VO) and the like. Two or more of these M oxides may be present in the first oxide layer. In the average chemical composition of M oxide, y represents the atomic ratio of O to M.

The presence or absence of TiO _x (1 ≦ x <2) and MO _y (1 ≦ y ≦ 2.5) can be confirmed by, for example, XPS (X-ray Photoelectron Spectroscopy; X-ray photoelectron spectroscopy). In the XPS spectrum, regarding the binding energy of Ti and O, if a peak of Ti ⁴⁺ plus a peak of at least one of Ti ³⁺ and Ti ²⁺ is present, it can be determined that 1 ≦ x <2. In addition, regarding the binding energy of M and O, if there is only a peak of Nb ⁵⁺ , it can be determined that y = 2.5. If a peak of M ⁵⁺ plus a peak of at least one of M ⁴⁺ and M ²⁺ is present, it can be determined that 1 ≦ y <2.5.

The reason why the first oxide layer has high conductivity is presumed as follows.

(i) Oxygen deficiency in TiO _x , and the case where y does not reach 2.5, because of the oxygen deficiency in MO _y , the electron carrier increases.

(ii) With the presence of MO _y , the amount of oxygen deficiency in TiO _x is stabilized, for example, the phenomenon of oxidation to TiO ₂ is suppressed.

In the first oxide layer, the ratio of the amount of M to the amount of Ti (atomic ratio; hereinafter referred to as "M / Ti ratio") is preferably 0.1 to 15 atomic%. When the number of Ti atoms in the first oxide layer is [Ti] and the number of M atoms in the first oxide layer is [M], the M / Ti ratio is [M] / [Ti] × 100. The M / Ti ratio can be obtained from the ratio of the peak area derived from M to the peak area derived from Ti in the XPS spectrum.

If the M / Ti ratio is less than 0.1 atomic%, the resistance of the first oxide layer will significantly increase during the power generation of the fuel cell, that is, under a corrosive environment. On the other hand, if the M / Ti ratio exceeds 15 atomic%, the cost is increased, and the workability and manufacturability are lowered, which is not preferable. The preferable range of the M / Ti ratio is 0.3 to 10 atomic%.

When the first oxide layer is obtained by thermally oxidizing the surface of the base material, the ratio of the amount of M to the amount of Ti in the first oxide layer is different from that in the base material. The ratio of the amount of M to the amount of Ti is approximately equal.

<Second oxide layer>

Referring to FIG. 1, the titanium alloy material of the present invention may include a second oxide layer 3 on the first oxide layer 2. The second oxide layer contains Ti _1-z M _z O ₂ (0 <z ≦ 0.2). Ti _1-z M _z O ₂ is a substance in which a part of Ti forming a TiO ₂ lattice is replaced with M. The presence of Ti _1-z M _z O ₂ (0 <z ≦ 0.2) in the second oxide layer can be confirmed by XAFS (X-ray Absorption Fine Structure) analysis or X-ray diffraction. In the analysis using XAFS, the average coordination number of oxygen atoms around the M atom is evaluated. If it is an M-06 structure (6 coordination structure), it can be judged as Ti _1-z M _z O ₂ (0 <z ≦ 0.2).

Since Ti _1-z M _z O ₂ (0 <z ≦ 0.2) has conductivity, the second oxide layer has conductivity. Even if the value of z is small, Ti _1-z M _z O ₂ has conductivity. In order to make Ti _1-z M _z O ₂ sufficiently conductive, z should be set to 0.0001 or more. On the other hand, when z exceeds 0.2, the conductivity of Ti _1-z M _z O ₂ is reduced. Therefore, z is set to 0.2 or less.

When the fuel cell is operating, the spacer (titanium alloy) is exposed to a corrosive environment. Ti _1-z M _z O ₂ contained in the second oxide layer has corrosion resistance and high oxidation resistance, and there is little concern about changes in the structure and composition of the fuel cell during operation. That is, it is difficult to reduce the conductivity during the operation of the fuel cell. Depending on the conditions of the fuel cell environment, the TiO _x and MO _{y of the} first oxide layer may be oxidized to impair the conductivity. Since both the second oxide layer and the first oxide layer are based on titanium oxide, the interface between these layers will be sufficiently tight at the heat treatment stage. Therefore, when the titanium alloy material includes the second oxide layer, the first oxide layer is protected, and oxidation in the fuel cell environment is more suppressed. Therefore, the use of a titanium alloy spacer having a second oxide layer makes it difficult to reduce the electrical conductivity in a fuel cell environment.

It is assumed that a conductive material layer (for example, indium-doped tin oxide (ITO), indium zinc oxide, tungsten carbide, etc.) other than the titanium oxide-based oxide is formed on the first oxide layer instead of the second oxide layer. In this case, the first oxide layer cannot be sufficiently protected. This is because these conductive material layers have insufficient corrosion resistance and oxidation resistance, and the interface between the first oxide layers becomes a heterogeneous interface.

<Thickness of oxide layer>

The thickness of the oxide layer is 1 to 100 nm. The "oxide layer" refers to the first oxide layer when the second oxide layer is not provided, and refers to the first and second oxide layers when the second oxide layer is provided. The "thickness of the oxide layer" when the second oxide layer is not provided means the thickness of the first oxide layer. The “thickness of the oxide layer” when the second oxide layer is provided refers to the total of the thickness of the first oxide layer and the thickness of the second oxide layer.

In the SEM (Scanning Electron Microscope) image or the TEM (Transmission Electron Microscope) image of the cross section of the titanium alloy material, the base material and the oxide layer can be identified by the difference in contrast. As a result, the boundary between the base material and the oxide layer can be discriminated. Therefore, the thickness of the oxide layer can be determined based on the boundary. The thickness of the second oxide layer can be obtained, for example, by using It was measured by composition analysis in the depth (thickness) direction of XPS. This is because the concentration of M changes abruptly near the boundary between the first oxide layer and the second oxide layer.

If the thickness of the oxide layer is less than 1 nm, in a battery cell of a fuel cell (such as a polymer electrolyte fuel cell), if the oxide layer is damaged due to contact with an electrode (such as an electrode made of carbon fiber), The base material is easily exposed. In this case, undesired TiO ₂ is formed in the exposed portion due to corrosion or oxidation. TiO _{2 has} a high electrical resistance, so this also increases the contact resistance of a titanium alloy material (spacer). On the other hand, if the thickness of the oxide layer exceeds 100 nm, the resistance of the oxide layer itself becomes high, and the oxide layer is easily peeled from the base material during the rolling process. The thickness of the second oxide layer is preferably 50 nm or less. The thickness of the second oxide layer is preferably 5 nm or more, and more preferably 10 to 30 nm.

A preferable range of the thickness of the oxide layer is 3 to 50 nm. When the thickness of the oxide layer is within this range, the high corrosion resistance and the resistance of the oxide layer itself are well balanced.

<Precious metal>

One or both of the first and second oxide layers may contain a noble metal. In addition, a noble metal may be supported on the outermost surface portion of the titanium alloy material. `` Precious metals '' means gold (Au), silver (Ag), and platinum group elements (ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), and platinum (Pt) ) 1 or more. The amount of the noble metal can be appropriately set within a range allowed by the cost. For example, the ratio of the amount of precious metal to the amount of Ti in the first or second oxide layer It is preferably 10 atomic% or less, and more preferably 5 atomic% or less.

<Thickness of titanium alloy material>

The thickness of the titanium alloy material is not limited. However, in order to satisfy the lightness, strength, processability, economy, etc. required for the spacer, the thickness of the titanium alloy material is preferably 0.05 to 1.0 mm, and more preferably 0.05 to 0.5 mm.

<Method for manufacturing titanium alloy material of the present invention>

The titanium alloy material of the present invention can be heat-treated in, for example, a base material (titanium alloy material) having the same composition as the base material in an oxidizing gas environment and a reducing gas environment (low oxygen partial pressure gas environment). It is manufactured by forming an oxide film on the surface of this substrate. In this case, the surface oxide film is the first oxide layer, and the remainder of the substrate is the base material.

Hereinafter, a case where the titanium alloy material of the present invention is manufactured by such a method will be described in detail. However, the titanium alloy material of the present invention is not limited to this method, and may be produced by other methods.

The manufacturing method of the titanium alloy material as a base material is not limited. For example, a general titanium alloy manufacturing method may be adopted, that is, a method prepared by dissolving and casting a material having a predetermined composition, hot rolling, and then cold rolling to a predetermined thickness. The obtained substrate becomes an object having an oxide film formed on its surface.

This substrate is pickled. Pickling is performed to remove oxides and carbides on the surface of the substrate. When these oxides and carbides are present, the contact resistance becomes high. Pickling can be performed using a hydrochloric acid aqueous solution or a fluorinated nitric acid aqueous solution used for general pickling. However, when the acid cleaning is performed using an aqueous solution containing fluoride ions, the resistance of the oxide film can be reduced. The fluoride ion-containing aqueous solution may be, for example, an aqueous solution obtained by dissolving HF 0.5% by mass, NaF 0.5% by mass, NaCl 0.5% by mass, or HNO ₃ 0.5% by mass.

Then, the substrate is subjected to a heat treatment to form a predetermined oxide layer. The heat treatment includes: a first heat treatment step of forming a predetermined oxide layer on the surface of the substrate; and a second heat treatment step of reducing a predetermined amount of the oxide layer.

The first heat treatment step is performed in an oxidizing gas environment containing an oxidizing gas. As a result, Ti and M (V, Ta, Nb) in the substrate are oxidized. Examples of the oxidizing gas include oxygen (O ₂ ), water vapor (H ₂ O), and carbon dioxide (CO ₂ ). The oxidizing gas environment is preferably a gas environment in which one or two or more of these oxidizing gases are mixed with an inert gas. Specific gas components include, for example, a gas obtained by mixing oxygen or water vapor with argon (Ar) or nitrogen (N ₂ ). The concentration of the oxidizing gas in the oxidizing gas environment can be appropriately selected depending on the processing temperature so as to oxidize Ti and M. The partial pressure of the oxidizing gas in the oxidizing gas environment is preferably 0.1 Pa or more, and more preferably 1.0 Pa or more.

The first heat treatment step is preferably performed in a temperature range of 200 to 400 ° C. When the first heat treatment step is performed at a temperature of less than 200 ° C, the oxidation rate is slow, and therefore the treatment takes time. In particular, M is not easily oxidized, and it is difficult to form MO _y (1 ≦ y ≦ 2.5). In this case, the resistance of the first oxide layer becomes high.

On the other hand, if the first heat treatment step is performed at a temperature higher than 400 ° C, the oxidation of the surface of the substrate will proceed excessively. In this case, reduction of the oxide film is not easily performed in the next second heat treatment step, and ultimately, the resistance of the first oxide layer cannot be reduced. The first heat treatment step is preferably performed in a temperature range of 250 ° C or higher and less than 350 ° C. The heat treatment time may be set in a range of, for example, 10 to 3600 seconds. The heat treatment time can be appropriately determined in consideration of the balance between the performance and the economy of the obtained titanium alloy material.

Next, the substrate subjected to the first heat treatment step is subjected to a second heat treatment step. The second heat treatment step is performed in a reducing gas environment (low oxygen partial pressure gas environment). As a result, the oxide film generated in the first heat treatment step is reduced, and the conductivity is increased. The low oxygen partial pressure gas environment may be a vacuum (decompression) gas environment or a gas environment mainly composed of an inert gas such as argon or nitrogen. If the oxygen partial pressure in the low-oxygen partial pressure gas environment is 0.1 Pa or more, the oxide film will not be sufficiently reduced. Therefore, the oxygen partial pressure is preferably less than 0.1 Pa, and more preferably 0.01 Pa or less.

The thickness of the first oxide layer can be controlled by the temperature, time, and oxygen concentration of the gas environment in the first heat treatment step. When the second oxide layer is not formed, by appropriately setting these parameters, the thickness of the first oxide layer can be 1 to 100 nm.

The second heat treatment step is preferably performed in a temperature range of 300 to 900 ° C. In this case, the oxide film generated in the first heat treatment step can be sufficiently reduced. By performing the second heat treatment step at a temperature higher than that of the first heat treatment step, the crystal growth in the oxide film and the substrate can be promoted, and the resulting The density of the grain boundaries with increased electrical resistance significantly reduces the electrical resistance of the obtained titanium alloy material. When the second heat treatment step is performed at a temperature of less than 300 ° C, the oxide film is hardly reduced, so the resistance of the first oxide layer cannot be reduced. On the other hand, when the second heat treatment step is performed at a temperature exceeding 900 ° C., the titanium alloy material is phase-transformed into a β-type. This makes it easy to increase the hardness of the material, makes it difficult to use it as a spacer, and reduces the economy. The second heat treatment step is preferably performed in a temperature range of 350 to 600 ° C.

For a substrate that does not substantially contain M such as pure Ti, the first heat treatment step and the second heat treatment step are sequentially performed. The oxide film (titanium oxide) generated in the first heat treatment step is hardly covered in the second heat treatment step. reduction. It is formed in an oxide film having a base material (titanium alloy material) having the same composition as the base material of the titanium alloy material of the present invention. In the second heat treatment step, Ti and M in titanium oxide affect each other. And M oxide will be reduced.

The second oxide layer need not be formed. When the second oxide layer is formed, the layer can be formed by, for example, a vapor deposition method. The vapor deposition method can be performed in accordance with, for example, the sputtering method described in Non-Patent Document 1. The target used at this time may be, for example, a target mainly composed of TiO ₂ and M ₂ O ₅ (M = V, Nb, Ta), a target mainly composed of a composite oxide of Ti and M, or Ti And metal Nb as a target.

When the evaporation is performed, the substrate may be at room temperature or may be heated. By heating the substrate, crystallization can be promoted during vapor deposition. Examples of the vapor deposition method include vacuum deposition, ion plating using plasma, and sputtering. The value of z of Ti _1-z M _z O ₂ contained in the second oxide layer can be controlled to 0.2 or less by appropriately selecting the ratio of M ₂ O ₅ to TiO ₂ in the target. In addition, when using a target mainly composed of an oxide of Ti and a target mainly composed of an oxide of M, the value of z can be controlled to 0.2 or less by appropriately setting the output to each target. .

The second oxide layer may be formed after the first heat treatment step is performed, or may be formed after the second heat treatment step is performed. In either case, there are many cases where carbon-containing dirt adheres to the surface of the base layer (oxide layer) where the second oxide layer should be formed. Therefore, it is preferable to clean the surface of the base layer by Ar sputtering or the like before vapor deposition .

The thickness of the second oxide layer can be controlled by the conditions under which the second oxide layer is formed, such as a vapor deposition time, a supply amount of a raw material substance per unit time, and the like. By appropriately selecting the formation conditions of the first and second oxide layers, the total thickness of the first and second oxide layers can be adjusted to 1 to 100 nm.

When a noble metal is supported on the outermost surface portion of the titanium alloy material, the noble metal can be supplied to the oxide layer or the like as a base layer by a method such as plating or vapor deposition. In the case of using any method, it is desirable to control the basis weight by, for example, processing time so that the coverage ratio of the layer formed of the supported precious metal to the base layer does not reach 98%. This can reduce costs.

In the manufacturing steps of the titanium alloy material, the timing of supporting the precious metal is not limited. For example, the first heat treatment step, the second heat treatment step, or the formation of the second oxide layer may be performed simultaneously with the first heat treatment step, Do it before, or after it. For example, support of a noble metal may be performed before the second heat treatment step is performed, and when a second oxide layer is formed by vapor deposition, it may be performed after vapor deposition. In the second oxidation When the physical layer contains a noble metal, the noble metal can be supplied at the same time as vapor deposition.

<Fuel Cell Spacer>

The intermediate separator according to the present invention includes the above-mentioned titanium alloy material. As this partition plate, a partition plate formed into a desired shape by calendering can be used. When the fuel cell is, for example, a polymer electrolyte fuel cell, as described later, a partition plate that is formed as a groove for fuel gas and oxidizing gas flow paths by calendering may be used. In this case, a titanium oxide layer may be formed after the base material is rolled into a desired shape, or a titanium alloy material having a titanium oxide layer formed on a base material may be obtained, and then the titanium alloy material may be rolled and formed.

<Battery Cells for Fuel Cells and Fuel Cells>

A battery cell for a fuel cell according to the present invention includes the above-mentioned spacer.

FIG. 2A is a perspective view of a whole fuel cell according to an embodiment of the present invention, and FIG. 2B is an exploded perspective view of a battery cell (a single cell) of the fuel cell. 2A and 2B show an example in which the fuel cell is a polymer electrolyte fuel cell.

As shown in FIGS. 2A and 2B, the fuel cell 4 is an assembly of single cells. As shown in FIG. 2B, in the single cell, a fuel electrode film (anode) 6 and an oxidant electrode film (cathode) 7 are laminated on one surface and the other surface of the solid polymer electrolyte membrane 5, respectively. Next, the spacers 8a and 8b are laminated on both surfaces of this laminated body. The fuel cell 4 may be a battery having a well-known structure. Pool. The solid polymer electrolyte membrane 5, the fuel electrode membrane 6, and the oxidant electrode membrane 7 may be MEA (Membrane Electrode Assembly) which is a structural member that is bonded to each other to be integrated.

The partition plates 8a and 8b are provided with the titanium alloy material of the present invention. The solid polymer electrolyte membrane 5, the fuel electrode membrane 6, and the oxidant electrode membrane 7 may be made of a known material.

The groove formed in the partition plate 8a is a flow path 9a, and a fuel gas (hydrogen or a hydrogen-containing gas) A flows therethrough. Thereby, the fuel gas A can be supplied to the fuel electrode membrane 6. In the fuel electrode membrane 6, the fuel gas A contacts the catalyst layer through the diffusion layer. In addition, the groove formed in the partition plate 8b is a flow path 9b, and an oxidizing gas B such as air flows therethrough. Thereby, the oxidizing gas B can be supplied to the oxidant electrode film 7. In the oxidant electrode film 7, the oxidizing gas B comes into contact with the catalyst layer through the diffusion layer. By supplying these gases, an electrochemical reaction occurs, and a DC voltage is generated between the fuel electrode film 6 and the oxidant electrode film 7.

The fuel cell of the present invention includes a plurality of the above-mentioned battery cells. A plurality of battery cells can be stacked on each other to form a battery connected in series on a circuit.

[Example]

In order to confirm the effect of the present invention, a sample of a titanium alloy material or the like was produced by the following method and evaluated.

1. Preparation of sample

A raw material having a predetermined mass ratio is dissolved and cast to obtain a cast. sheet. This cast piece was rolled to a thickness of 0.1 mm, and then annealed to obtain a base material in the form of a foil. A sample of a titanium alloy material for a spacer was produced by subjecting this substrate to the processing described below. Table 1 shows the composition of the substrate and the manufacturing conditions of the samples.

[Table 1]

As shown in Table 1, each of the substrates is a titanium alloy material containing Nb, Ta, or V. After surface treatment of these substrates using an aqueous fluoric nitric acid solution, firing was performed in the atmospheric environment as the first heat treatment step, and then heat treatment was performed in a vacuum (a reduced pressure air gas environment of 0.01 to 0.001 Pa) as the second A heat treatment step to form a first oxide layer on the substrate.

In the case of test numbers 15, 16, 19, and 20, after the first heat treatment step is performed, before the second heat treatment step is performed, the substrate (on the oxide film formed in the first heat treatment step) is subjected to vapor deposition. A layer containing Ti _1-z Nb _z O ₂ as a main component is provided as a second oxide layer. The vapor deposition was performed by magnetron sputtering using a target having a composition of Ti _1-z Nb _z O ₂ , without heating the substrate, and with an output of 500 W in an Ar gas environment containing 5% O ₂ . The value of z in the target composition is set to be the same as the value of z in the target composition of the second oxide layer.

Next, a sample of the titanium alloy material obtained in accordance with the above steps is calendered to form a partition plate shape in which a groove (gas flow path) is formed.

With respect to the obtained sample, the M / Ti ratio of the first oxide layer and the _{z 1} of Ti _1-z M _z O ₂ in the second oxide layer were obtained from the peak area ratio of XPS. The thickness of the oxide layer was determined from the SEM image of the sample cross section. For the samples (test numbers 15, 16, 19, and 20) on which the second oxide layer was formed, the composition in the depth direction was analyzed by XPS to determine the thickness of the second oxide layer. The thickness of each of the second oxide layers is about 15 nm. Table 1 shows the M / Ti ratio of the first oxide layer, the value of z in the composition of the second oxide layer, and the thickness of the oxide layer.

2. Evaluation of contact resistance

FIG. 3 is a block diagram of a device for measuring the contact resistance of a sample. Using this device, the contact resistance of each sample was measured according to the method described in Non-Patent Document 2. Referring to FIG. 3, first, the produced sample 11 is sandwiched between a pair of carbon papers 12 (TGP-H-90 manufactured by Toray Industries, Ltd.) for use as a gas diffusion layer for a fuel cell, and the gold plating A pair of electrodes 13 are sandwiched. The area of each carbon paper 12 was 1 cm ² .

Next, a load was applied between the pair of gold-plated electrodes 13 to generate a pressure of 10 kgf / cm ² (9.81 × 105 Pa). In this state, a certain current flows between the pair of gold-plated electrodes 13, and the voltage drop between the carbon paper 12 and the sample 11 that occurred at this time is measured. Based on this result, the resistance value was obtained. The obtained resistance value is a value obtained by totaling the contact resistances on both sides of the sample 11. Therefore, it was divided by 2 to determine the contact resistance value (initial contact resistance) on each side of the sample 11.

Next, using the sample after the initial contact resistance measurement as a spacer, a solid polymer fuel cell was produced. The reason for designing a single battery cell is that when the single battery cells are stacked to form a multi-battery cell, the state of the stack greatly affects the evaluation result. In the battery cell, a solid polymer electrolyte membrane made of Toyo Technica's PFEC standard product MEA (for Nafion (registered trademark) -1135) FC50-MEA (membrane electrode assembly (MEA)) was used.

In this fuel cell, hydrogen having a purity of 99.9999% is circulated as a gas for the fuel on the anode side, and air is circulated as a gas on the cathode side. The gas pressure when hydrogen and air are introduced into the fuel cell is set to 0.04 to 0.20 bar (4000 to 20,000 Pa). The main body of the fuel cell is maintained at 70 ± 2 ° C, and the humidity inside the fuel cell is controlled by setting the dew point of the gas introduction part to 70 ° C. The pressure inside the battery is about 1 atmosphere (1.01 × 10 ⁵ Pa).

This fuel cell is operated with a constant current density of 0.5 A / cm ² . Next, after 500 hours of operation, the spacer (titanium alloy material) was taken out. The contact resistance of this spacer was measured by the method described above, and was determined as the contact resistance after power generation. Then, the corrosion resistance of the titanium spacer was evaluated from the initial contact resistance and the contact resistance after power generation.

The measurement of contact resistance and the measurement of current and voltage during fuel cell operation were performed using a digital multimeter (KEITHLEY 2001, manufactured by Toyo Technica Co., Ltd.).

3. Evaluation results

Table 1 also discloses the values of the initial contact resistance of each sample, the contact resistance after power generation, and the results of the total evaluation. The judgment criteria for the aggregate evaluation are as follows.

Particularly good: Initial and after power generation, the contact resistance is 10mΩ. cm ² or less.

Good: The contact resistance is 35mΩ after power generation. cm ² or less (except when the "extra good" criterion is satisfied).

Bad: The contact resistance exceeds 35mΩ after power generation. cm ² .

The initial contact resistance of the titanium alloy material (example of the present invention) that satisfies the requirements of the present invention is 20 mΩ. cm ² or less. These titanium alloy materials generally have a lower heat treatment temperature in the first heat treatment step, and a shorter heat treatment time in the first heat treatment step results in lower initial contact resistance. It is presumed that under these conditions, the thickness of the first oxide layer to be formed is small, whereby the initial contact resistance is reduced.

Test No. 7, as shown in Table 1, in the first heat treatment step, the heat treatment temperature was the highest and the heat treatment time was the longest. In response to this, the thickness of the oxide layer is large, and the initial contact resistance value is high. The samples of test numbers 2 and 13 had the same thickness of the oxide layer as compared to the sample of test number 10, but the initial contact resistance was low. From this result, it is understood that the larger the content ratio of M in the first oxide layer, the more the contact resistance can be reduced.

The production conditions of the samples of test numbers 4, 8 to 10, 17, and 18 were substantially the same except for the M content of the substrate. In the test sample No. 10, the M (Nb) content of the base material was 0.2%, which was lower than the lower limit of the range specified in the present invention by 0.6%. The test samples No. 4, 8, 9, 17 and 18 had an M content of more than 0.6%, which was within the range specified by the present invention. All of the initial contact resistances of the samples of test numbers 4, 8, 9, 17, and 18 were lower than the initial contact resistance of the samples of test number 10. When the M content is in the range of 0.2 to 6%, the higher the M content, the lower the initial contact resistance.

Test No. 4, 8, 9, 17, and 18 contact resistance after power generation, any one is 35Ω. cm ² or less. On the other hand, the contact resistance of the sample No. 10 after power generation exceeded 35Ω. cm ² . When the M content is in the range of 0.2 to 6%, it is observed that the higher the M content of the base material, the lower the contact resistance after power generation. From this result, it is understood that it is necessary to make the M content of the base material higher than 0.6%.

FIG. 4 shows the XPS spectra of Ti2p on the surfaces of the test samples 2 and 10. FIG. 5 shows the XPS spectra of Nb3d on the surfaces of the test samples 2 and 10.

In test sample No. 2, large peaks of Ti ⁴⁺ derived from TiO ₂ and small peaks of Ti ³⁺ and Ti ²⁺ derived from lower-order Ti oxides (Ti ₂ O ₃ , TiO) were observed (reference Figure 4). Therefore, when the entire oxide layer in the average chemical composition of titanium oxide TiO _x to be represented, compared with 1 <x <2. In addition, in the sample No. 2 test, in addition to the peaks derived from Nb ⁵⁺ derived from stable Nb ₂ O ₅ , there were Nb ⁴⁺ and Nb ²⁺ derived from lower-order Nb oxides. (Refer to Figure 5). Therefore, when the average chemical composition of M oxide in the entire first oxide layer is expressed as MO _y , it is 1 <y <2.5.

In the samples of the present invention examples, peaks of Ti ³⁺ and Ti ²⁺ derived from TiO _x (1 <x <2) and Nb ⁴ derived from NbO _y (1 <y <2.5) were all observed. ⁺ , Nb ²⁺ peaks. It is known that low-order TiO _x has conductivity, and the initial contact resistance of the sample of the example of the present invention is low, which is considered to be because the presence ratio of TiO _x (1 ≦ x <2) is high. It is speculated that because the substrate contains M, the generation of TiO _x (1 ≦ x <2) is promoted during the oxidation-reduction process. The detailed reasons for this promotion are unknown. In addition, it is also estimated that low-order M oxide (MO _y (1 ≦ y <2.5)) itself has conductivity. In the sample according to the present invention, TiO _x and NbO _y may possibly contribute to the reduction of resistance.

In the test sample No. 10, the M content of the base material was outside the range specified in the present invention (M = 0.2%). In the XPS spectrum of this sample, almost no peaks of Ti ³⁺ and Ti ²⁺ derived from low-order Ti oxides (Ti ₂ O ₃ , TiO) were observed (see FIG. 4). In addition, the base material of the test sample No. 10 contained Nb, but in the XPS light spectrum, no peak of a low-order Nb oxide was observed (refer to FIG. 5). Therefore, the initial contact resistance of the sample of test number 10 is high, and it is presumed that the first oxide layer does not substantially contain low-order Ti oxide and low-order Nb oxide.

Regarding the contact resistance after power generation, as in the initial contact resistance, a sample with a M content of the base material within the range specified in the present invention and a sample with the M content of the base material lower than the range specified in the present invention (test number 10) In comparison, it shows rather low values.

In the sample in which the second oxide layer was not formed, the contact resistance after power generation was increased compared to the initial contact resistance. This is considered to be because the lower-order oxide contained in the first oxide layer is oxidized in a corrosive environment in the fuel cell. On the other hand, in the samples (15, 16, 19, and 20) in which the second oxide layer was formed, the increase in contact resistance with respect to the initial contact resistance after power generation was small. Among these samples, Ti _1-z Nb _z O ₂ (z = 0.01, 0.06, 0.19) contained in the second oxide layer has high conductivity, and Nb mainly contributes to conductivity as a carrier, so Less deterioration due to oxidation. Therefore, even in a sample in which the second oxide layer is formed, the contact resistance does not increase much. It is considered that by forming the second oxide layer on the first oxide layer, the first oxide layer is protected, and an increase in contact resistance due to corrosion is suppressed for the entire oxide layer.

The M (Nb) content in the base material is higher than the range specified in the present invention. In the case of the sample (Test No. 11), the amount of Nb (M / Ti ratio) contained in the first oxide layer was high, and not only the initial contact resistance, but also the contact resistance after power generation was high. It can be seen that even if the base material contains more than 10% of M, the effect of reducing the contact resistance by containing M cannot be obtained.

[Industrial availability]

The titanium alloy material of the present invention can be used in, for example, a separator for a fuel cell, an electrode for electrolysis (for example, an electrode for electrolysis of water), and the like.

1‧‧‧ mother material

2‧‧‧ 1st oxide layer

3‧‧‧ 2nd oxide layer

Claims (6)

A titanium alloy material comprising a base material and a titanium alloy material having a first oxide layer formed on the base material, and the base material contains 1 selected from the group consisting of V, Ta, and Nb. The first oxide layer contains TiO _x (1 ≦ x <2) and MO _y (1 ≦ y ≦ 2.5), and the thickness of the first oxide layer is 1 to 100 nm. The content of the element M in the base material is 0.6% by mass or more and 10% by mass or less. For example, the titanium alloy material according to item 1 of the patent application range, wherein the proportion of the content of element M with respect to the amount of Ti in the first oxide layer is 0.1 to 15 atomic%. For example, the titanium alloy material according to item 1 of the patent application scope further includes a second oxide layer formed on the first oxide layer, and the second oxide layer contains Ti _1-z M _z O ₂ (0 <z ≦ 0.2), and the total of the thickness of the first oxide layer and the thickness of the second oxide layer is 1 to 100 nm. A separator for a fuel cell, which is provided with a titanium alloy material according to any one of claims 1 to 3 of the scope of patent application. A battery cell for a fuel cell is provided with a partition as described in the fourth item of the patent application. A fuel cell is provided with a plurality of battery cells such as the fifth item in the patent application scope.