JP2010238577A - Separator material for fuel cell and fuel cell stack using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separator material for a fuel cell which reduces contact resistance of the separator material for the fuel cell wherein an Au layer or an Au alloy layer is formed on the surface of a Ti rolled plate and secures conductivity, and a fuel cell stack using the separator material for the fuel cell. <P>SOLUTION: In the separator material for the fuel cell, the Au layer or the Au alloy layer is formed on the surface of a Ti base material, and center line average roughness on the surface of the Au layer or the Au alloy layer is 0.2 μm or less. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a fuel cell separator material in which Au or an Au alloy (a layer containing Au) is formed on the surface of a Ti substrate such as a Ti rolled plate, and a fuel cell stack using the same.

Conventionally, a solid polymer type fuel cell separator in which a gas flow passage is formed on a carbon plate has been used, but there is a problem that material costs and processing costs are high. On the other hand, when a metal plate is used instead of the carbon plate, corrosion and elution become a problem because it is exposed to an oxidizing atmosphere at a high temperature. For this reason, a technique for forming a conductive portion by sputtering a noble metal selected from Au, Ru, Rh, Pd, Os, Ir, Pt and the like and an alloy of Au on the surface of the Ti plate is known. (Patent Document 1). Further, Patent Document 1 describes that the oxide of the noble metal is formed on the Ti surface.
On the other hand, a fuel cell separator that forms an Au film on an oxide film of a Ti rolled sheet is known (Patent Document 2).

In addition, in a polymer electrolyte fuel cell, a direct methanol fuel cell (DMFC) that uses methanol that is easy to handle as a fuel gas to be supplied to an anode has been developed. Since DMFC can directly extract energy (electricity) from methanol, a reformer or the like is not necessary, and it can cope with downsizing of the fuel cell, and is also promising as a power source for portable devices.
The following two structures have been proposed as DMFC structures. First, the first structure is a single cell (stacked (active) structure in which a membrane electrode assembly (hereinafter referred to as MEA) in which a solid polymer electrolyte membrane is sandwiched between a fuel electrode and an oxygen electrode) is stacked. This structure is a planar type (passive type) structure in which a plurality of single cells are arranged in the plane direction, each of which is a structure in which a plurality of single cells are connected in series (hereinafter referred to as a stack). Of these, the passive type structure does not require an active fuel transfer means for supplying fuel gas (fuel liquid), air, or the like into the cell, and therefore further reduction in size of the fuel cell is considered promising. Yes.

By the way, the separator for a fuel cell has electrical conductivity, electrically connects each unit cell, collects energy (electricity) generated in each unit cell, and supplies fuel gas ( A flow path for fuel liquid) and air (oxygen) is formed. This separator is also called an interconnector, a bipolar plate, or a current collector.
The conditions required for a DMFC current collector are more than those for a polymer electrolyte fuel cell separator using hydrogen gas. That is, in addition to the corrosion resistance to a sulfuric acid aqueous solution required for a normal polymer electrolyte fuel cell separator, the corrosion resistance to a methanol aqueous solution and the corrosion resistance to a formic acid aqueous solution are required. Formic acid is a by-product generated when hydrogen ions are produced from methanol on the anode catalyst.
Thus, under the DMFC operating environment, the material used for the conventional polymer electrolyte fuel cell separator is not always applicable.

JP 2001-297777 A JP 2004-185998 A

The surface of the titanium material is rough compared to stainless steel, and in the case of a Ti rolled sheet, the center line average roughness of the surface often exceeds 0.2 μm. Therefore, when a separator having a surface of Ti rolled plate with a film of several nanometers to several tens of nanometers in thickness is incorporated into a fuel cell, the number of electrical contact points on the surface of the Ti rolled plate is reduced and the contact resistance is increased. Battery output may decrease. As a method of reducing the contact resistance, there is a method of increasing the electrical contact point by applying a high compression (clamping) load to the separator, but the load that can be applied to an actual fuel cell is limited to the upper limit of the structure (2 to 10 kg / cm ² ).
That is, the present invention relates to a fuel cell separator material in which an Au layer or an Au alloy layer is formed on the surface of a Ti substrate, a fuel cell separator material having reduced contact resistance and ensuring conductivity, and a fuel cell stack using the same The purpose is to provide.

  In the fuel cell separator material of the present invention, an Au layer or an Au alloy layer is formed on the surface of a Ti base material, and the center line average roughness of the surface of the Au layer or the Au alloy layer is 0.2 μm or less.

The center line average roughness of the surface of the Ti substrate is preferably 0.2 μm or less.
The Au alloy layer is made of an alloy of Au and a first component made of at least one metal selected from the group consisting of Al, Cr, Fe, Co, Ni, Cu, Mo, Sn and Bi, It is preferable that an intermediate layer containing Ti, O, and the first component and having less than 20% by mass of Au is present between the Au alloy layer and the Ti base material.
The intermediate layer preferably contains 10% by mass or more of Ti and O and 20% by mass or more of the first component.
It is preferable that the Ti base material is a strip made of a Ti rolled plate, and the Au layer or the Au alloy layer is continuously formed on the surface of the strip.
In the Au layer or the Au alloy layer, the thickness of Au 40% by mass or more is preferably 1 to 20 nm.

After immersion in an aqueous solution having a sulfuric acid concentration of 0.5 g / L at 90 ° C. for 1 week, the number of titanium oxides penetrating from the Ti base material through the Au layer or the Au alloy layer is less than 5 per 1 μm in cross-sectional length. preferable.
Between the Ti base material and the Au layer or the Au alloy layer, an oxide layer containing O of 20% by mass to 50% by mass is formed with a thickness of 5 nm or less, or the oxide layer is formed. Preferably not.
It is preferable that an oxide layer containing 20% by mass or more of O is formed with a thickness of 5 to 30 nm between the Ti base material and the Au layer or the Au alloy layer.

The separator material for a fuel cell of the present invention is suitably used for a polymer electrolyte fuel cell or a direct methanol type polymer electrolyte fuel cell.
The fuel cell stack of the present invention uses the fuel cell separator material.

  According to the present invention, it is possible to reduce the contact resistance of a fuel cell separator material in which an Au layer or an Au alloy layer is formed on the surface of a Ti base material, and to ensure conductivity.

It is sectional drawing of the fuel cell stack (single cell) which concerns on embodiment of this invention. 1 is a cross-sectional view of a planar fuel cell stack according to an embodiment of the present invention. It is a figure which shows the BF-STEM image of the cross section of the separator material for fuel cells after a corrosion resistance test.

Hereinafter, a fuel cell separator material according to an embodiment of the present invention will be described. In the present invention,% means mass% (mass%) unless otherwise specified.
In the present invention, the “fuel cell separator” has electrical conductivity, electrically connects each single cell, collects energy (electricity) generated in each single cell, and collects each single cell. A fuel gas (fuel liquid) or air (oxygen) flow path is formed. The separator is also referred to as an interconnector, a bipolar plate, or a current collector.
Therefore, as a separator for a fuel cell, in addition to a separator provided with an uneven channel on the surface of a plate-like substrate, a gas or methanol channel on the plate-like substrate surface like the above-described passive DMFC separator It includes a separator having holes.

<Surface roughness of separator material for fuel cells>
In the fuel cell separator material of the present invention, an Au layer or an Au alloy layer is formed on the surface of a Ti substrate, and the center line average roughness (Ra) of the surface of the Au layer or the Au alloy layer is 0.2 μm or less. It is.
When Ra is larger than 0.2 μm, the contact resistance of the separator becomes high when the battery stack is configured within a weight range ( ^{2 to} 10 kg / cm ² ) that can be normally applied to the fuel cell, and the output of the fuel cell is increased. Decreases. In this case, if the load applied to the fuel cell is increased, the contact resistance of the separator is lowered. However, the load is excessively increased and the separator flow path may be deformed to cause a problem. Ra is preferably 0.15 μm or less, and more preferably 0.1 μm or less.

<Titanium substrate and its surface roughness>
A fuel cell separator material is required to have corrosion resistance and conductivity, and a base material is required to have corrosion resistance. For this reason, titanium having good corrosion resistance is used as the substrate, and a rolled titanium plate is preferably used.
The Ti base material is not particularly limited as long as it is titanium. In the case of a Ti rolled sheet, the thickness is preferably 10 μm or more.
The center line average roughness (Ra) of the surface of the Ti substrate is 0.2 μm or less. When an Au layer or an Au alloy layer having a thickness of several to several tens of nanometers is formed on a Ti substrate, the Au layer or the Au alloy layer is extremely thin compared to the Ra of the Ti substrate. The Ra of the surface of the steel sheet is 0.2 μm or less reflecting the Ra of the Ti rolled sheet.
In addition, Ra of a Ti rolled sheet changes with Ra of a rolling roll. When a Ti rolled sheet is continuously rolled in an actual production line, a roll of about Ra 0.06 μm is used. Titanium is softer than stainless steel, and tends to cause baking with the roll. For this reason, if the roll is not changed during rolling and the same roll is continuously used, Ra of the roll increases, and as a result, Ra of the Ti rolled sheet also increases. Therefore, by managing Ra of the rolling roll, a Ti rolled sheet having Ra of 0.2 μm or less can be continuously rolled. Specifically, it is desirable to perform rolling by exchanging with a new roll before the final pass or the final pass. Furthermore, it is also effective to perform skin pass rolling for adjusting the surface roughness after the final rolling.

In the present invention, an Au layer or an Au alloy layer may be formed on the outermost surface of the fuel cell separator material, and various layers are interposed between the titanium base material and the Au layer or the Au alloy layer. Also good.
Specifically, an Au layer or an Au alloy layer may be formed directly on the titanium substrate, and in order to ensure adhesion between the Au layer or the Au alloy layer, the substrate and the Au layer or the Au alloy layer Between these layers, an oxide layer or an intermediate layer, which will be described later, may be interposed.

<Au layer or Au alloy layer>
The Au layer or the Au alloy layer is formed on the surface of the Ti base material to ensure high conductivity. From the viewpoint of ensuring conductivity, it is preferable that the thickness of the region of Au 40 mass% or more in the Au layer or the Au alloy layer is 1 to 20 nm. Here, in the present invention, since the thickness of the Au layer or the Au alloy layer is thin, the depth from the outermost surface to the underlying Ti rolled sheet is not completely 100% Au even if it is referred to as “Au layer”. . Therefore, as described above, it is necessary to define “the thickness of the region of Au 40% by mass or more” also in the Au layer or the Au alloy layer.
In the Au layer or the Au alloy layer, if the thickness of the region of Au 40 mass% or more is less than 1 nm, the obtained separator material has poor conductivity and corrosion resistance, and if it exceeds 20 nm, the cost may increase. The thickness of the Au layer or the Au alloy layer is more preferably 2 nm or more, and further preferably 4 nm or more. The thickness of the Au layer or the Au alloy layer is the actual size of the scanning distance in terms of SiO _{2 in the} XPS analysis.

In addition, in the Au layer or the Au alloy layer, even if the thickness of Au 40% by mass or more is set to 20 nm or less, as a method of reducing film defects (pinholes), the conditions for sputtering Au on the surface of the Ti substrate are appropriately set. To set.
If the argon pressure and sputtering output during sputtering are high, the collision between the sputtered particles and the argon molecules increases, so that it is difficult to obtain a uniform film structure, and film defects (pinholes) are likely to occur. Therefore, an Au layer or an Au alloy layer with few defects can be formed by adjusting the argon pressure and the sputtering output to an appropriate range. For example, it is desirable that the argon pressure is 0.2 to 0.5 Pa and the sputtering output is 50 to 75 W.

The concentration and thickness of the Au layer or the Au alloy layer can be calculated by analyzing the concentration of Au, Ti, O, C, and alloy layer components using the XPS analysis depth profile. The thickness is the actual size of the scanning distance in terms of SiO ₂ in the XPS analysis.

<Au alloy layer>
Examples of the Au alloy layer include those that form an alloy with Au, and the surface side of the Au alloy layer may be an Au layer.
The Au alloy layer can be confirmed by XPS analysis, which will be described later, and is a portion having a thickness of 1 nm or more and Au of 40% by mass or more from the outermost surface to the lower layer by XPS analysis, and is located above the following intermediate layer. The part is an Au alloy layer. The thickness of the Au alloy layer is preferably 1 to 100 nm. If the thickness of the Au alloy layer is less than 1 nm, the corrosion resistance required for the fuel cell separator may not be ensured on the Ti substrate. If the thickness of the Au alloy layer exceeds 100 nm, it may not be possible to save money and the cost may increase.
Further, in the Au alloy layer, if the Au concentration in the region of 1 nm or more in thickness from the outermost surface to the lower layer is less than 40% by mass, the corrosion resistance required for the fuel cell separator cannot be secured.

In order to further improve the durability (brittleness resistance) under the fuel cell operating environment, the Au alloy layer is made of Al, Cr, Fe, Co, Ni, Cu, Mo, Sn and Bi. It is preferable to use an alloy layer of Au and a first component made of at least one metal selected from the group. The Au alloy layer containing the first component imparts Au characteristics (corrosion resistance, conductivity, etc.) and hydrogen embrittlement resistance to the Ti base material.
The metal selected as the first component has the properties that a) easily binds to oxygen, b) constitutes an alloy with Au, and c) hardly absorbs hydrogen. While giving a function, an intermediate | middle layer is formed and the adhesiveness of an alloy layer and Ti base material is improved.
From the potential-pH diagram, the metal is more oxidizable than Au, and utilizes the property of being difficult to absorb hydrogen, and the first component is used as a constituent element of the following intermediate layer. The first component may be composed of a single element or may be composed of a plurality of elements, but Cr and Mo are preferable from the viewpoint of corrosion resistance, conductivity, and durability.

<Intermediate layer>
When the alloy layer of the first component and Au described above is used as the Au alloy layer, the intermediate layer containing Ti, O, and the first component between the alloy layer and the Ti base material and less than 20% by mass of Au. There is a layer.
Usually, a Ti substrate has an oxide layer on the surface, and it is difficult to directly form an Au (containing) layer that is difficult to be oxidized on the Ti surface. On the other hand, it is considered that the first component is more easily oxidized than Au, and forms O atoms and oxides in the Ti oxide on the surface of the Ti base material, and is firmly bonded to the Ti base material surface.
The first component is difficult to absorb hydrogen. In these respects, when the thickness of the conductive film containing Au (the alloy layer or the Au single layer) is several tens of nm or less, conventionally, as an intermediate layer, simply Ti, Zr, Hf, V, Nb, Ta, Compared to the case where Cr, Mo, W, or the like is used, a separator material with excellent durability can be provided by forming the intermediate layer from Ti, O, and the first component.
The intermediate layer preferably contains no Au, and if 20 mass% or more of Au is contained, the adhesion is lowered. In order to set the Au concentration in the intermediate layer to less than 20% by mass, it is preferable to perform sputtering on the Ti base material using the target of the first component alone or the first component-Au alloy target having a low Au concentration. .

  The intermediate layer preferably exists as a layer of 1 nm or more in which Ti and O are each 10% by mass or more and the first component is contained by 20% by mass or more. In this case, when the cross section of the separator material for a fuel cell is analyzed by XPS, there are regions in which Ti and O are each 10% by mass or more and the first component is 20% by mass or more and Au is 20% by mass or more. 1 nm or more exists in the thickness direction. The upper limit of the thickness of the intermediate layer having such a composition is not limited, but is preferably 100 nm or less from the viewpoint of the cost of the first component.

The reason why the lower limit of Ti and O is 10% by mass and the lower limit of the first component is 20% by mass is that the portion where the first component is less than 20% by mass is close to the surface of the Ti substrate, and Ti is 10% by mass. This is because the portion less than 10% is close to the alloy layer, and the portion where O is less than 10% by mass does not form a sufficient oxide with the first component and Ti atoms as O atoms. This is because it is considered not to function. Moreover, since Ti and O each decrease rapidly from 10% by mass, 10% by mass is set as the lower limit from the measurement. The reason for making Au less than 20% by mass is to improve adhesion.
The thickness is the actual size of the scanning distance in terms of SiO ₂ in the XPS analysis.

<Corrosion resistance test>
When the fuel cell separator material obtained as described above was immersed in an aqueous solution having a sulfuric acid concentration of 0.5 g / L for 1 week at 90 ° C., a cross-sectional sample in the thickness direction was prepared, and when this cross section was observed, Ti The number of titanium oxides penetrating from the substrate through the Au layer or the Au alloy layer is preferably less than 5 per 1 μm in cross-sectional length. Titanium oxide penetrating the Au layer or Au alloy layer is considered to indicate the presence of coating defects in the Au layer or Au alloy layer, the aqueous solution penetrates from the coating defects, grows an oxide film on the surface of the Ti substrate, It breaks through the above-mentioned film defect and appears.
It has been found that there is a correlation between the number of titanium oxides penetrating the Au layer or the Au alloy layer and the failure of the fuel cell separator material (increase in contact resistance). When the number of titanium oxides penetrating the Au layer or Au alloy layer exceeds 5, the contact resistance of the fuel cell separator material increases, and when the fuel cell separator material is assembled into a battery, the output after the continuous power generation test The voltage tends to decrease.
The film defect of the Au layer or the Au alloy layer cannot be discriminated with a TEM (Transmission Electron Microscope) level analyzer, but can be easily discriminated by using the accelerated test in the aqueous solution. When the number of titanium oxides penetrating the Au layer or the Au alloy layer is less than 5 per 1 μm in cross-sectional length, a fuel cell separator material with good power generation characteristics can be determined in a short time.
FIG. 3 shows a BF-STEM image of a cross section of the fuel cell separator material (Example 6) after the corrosion resistance test in the aqueous solution. The composition found by mapping this cross section with EDX is shown in FIG. It can be seen that titanium oxide penetrates the Au layer.

<Oxide layer>
In order to ensure the adhesion and conductivity of the Au layer, it is desirable that the oxide layer formed on the surface of the Ti substrate is thin.
(1) The first case is a case where a region containing 20% by mass to 50% by mass of O is an oxide layer, and the oxide layer is formed with a thickness of 5 nm or less. The first case corresponds to a case where an Au layer or an Au alloy layer is directly provided on the surface of the Ti base material without using the above-described intermediate layer or the like.
The reason why the region containing 20% by mass or more of O is an oxide layer is that when the O (oxygen) concentration of the oxide layer is less than 20% by mass, the titanium base material is brittle when a fuel cell continuous power generation test is performed. This is because the durability as a fuel cell separator material deteriorates.
On the other hand, when the O (oxygen) concentration in the oxide layer is 50% by mass or more, even if the Au layer appears to be uniformly formed on the Ti substrate, the adhesion is inferior, and as a fuel cell actually The Au layer or the Au alloy layer may be peeled off during operation.
When the thickness of the oxide layer exceeds 5 nm, the adhesiveness of the Au layer or Au alloy layer formed on the Ti base material surface decreases.

(2) The second case is a case where a region containing 20% by mass or more of O is an oxide layer, and the oxide layer is formed with a thickness of 5 to 30 nm. As the second case, there is a case where it is desired to improve the durability of the fuel cell separator material than in the first case.
That is, as described above, if the Au layer is directly formed in a state where the oxide layer on the surface of the Ti substrate exceeds 5 nm, the adhesion of the Au layer is deteriorated. However, in order to improve the durability (brittleness resistance) of the separator in the fuel cell operating environment, an oxide layer (hereinafter defined by the present invention described above) with a thickness of about 10 nm is previously formed on the surface of the Ti substrate. In order to distinguish it from the oxide layer, it is necessary to form a “primary oxide layer”). However, since the primitive oxide layer formed on the Ti base has an O concentration of more than 50% by mass on the surface side, the adhesion of the Au layer or the Au alloy layer may be lowered as described above. Therefore, when a Ti film having a thickness of 1 nm or more is formed on the surface of the Ti base material on which the primitive oxide layer is formed, the O concentration on the surface side of the primitive oxide layer is reduced, and O is contained by 20 mass% or more. The oxide layer can be formed with a thickness of 5 to 30 nm.
Here, when the Ti substrate is left in the air, a primitive oxide layer (TiO ₂ ) is naturally formed on the surface, but this alone is insufficient to form the above-described oxide layer with a thickness of 5 nm or more. Sometimes. Therefore, the Ti base material may be actively oxidized, and the primitive oxide layer may be formed until the thickness reaches about 10 → 6 nm. Examples of the oxidizing method include anodizing treatment and atmosphere annealing. Note that the oxide layer formed on the surface of the Ti base also usually contains 20% by mass or more of O.

When a Ti film is further formed on the surface of Ti on which the primitive oxide layer is formed to be about 6 nm, if the thickness of the Ti film is less than 1 nm, the O concentration on the surface side may not be sufficiently lowered. Therefore, the thickness of the Ti coating is more preferably 2 nm or more. In order not to lower the conductivity of the obtained fuel cell separator material (the oxide layer is made to be 30 nm or less), the thickness of the Ti coating is preferably less than 10 nm.
In addition, when the primitive oxide layer formed in advance on the surface of the Ti base is too thick (generally over 10 nm), if the above-described Ti coating is formed thick (over 10 nm), the O concentration on the surface side is reduced, but it is obtained. Since the oxidized layer becomes too thick (greater than 30 nm), the conductivity is lowered. In addition, the primitive oxide layer that is too thick cannot be thinned even if reverse sputtering, which is a pretreatment before the Au layer formation described later, is performed for a long time.
Here, the concentration and thickness of O in the final oxide layer can be controlled by further forming a primitive oxide layer formed on the Ti base material or a Ti film.

In both the first case and the second case, the concentration of O in the oxide layer and the thickness of the oxide layer depend on the depth (Depth) profile of XPS (X-ray photoelectron spectroscopy) analysis. , C concentration analysis. The thickness is the actual size of the scanning distance in terms of SiO ₂ in the XPS analysis.

<Manufacture of a separator material for a fuel cell having an oxide layer of 5 nm or less>
A fuel cell separator material having an oxide layer of 5 nm or less can be produced, for example, as follows. First, it is confirmed whether the primitive oxide layer on the Ti substrate surface (the oxide layer formed on the Ti substrate from the beginning) has a thickness of about 3 nm. Prior to sputtering, the film is treated with a fluoride-containing pretreatment liquid to make the thickness of the primitive oxide layer 3 nm or less.
Next, reverse sputtering (ion etching) is performed as necessary for the purpose of cleaning the surface of the Ti base material and adjusting the primitive oxide layer. Reverse sputtering can be performed, for example, by irradiating the Ti base with argon gas at an output of about RF 100 W and an argon pressure of about 0.2 Pa.
Then, an Au layer or an Au alloy layer is formed on the Ti substrate by sputtering using an Au target for forming the Au layer.

<Manufacture of a separator material for a fuel cell having an oxide layer of 5 to 30 nm>
A fuel cell separator material having an oxide layer of 5 to 30 nm can be produced, for example, as follows. First, it is confirmed whether the primitive oxide layer on the surface of the Ti substrate has a thickness of about 6 to 10 nm. If the thickness of the primitive oxide layer is thin, the Ti substrate is actively oxidized to reduce the thickness to about 10 nm. To do.
Next, reverse sputtering (ion etching) is performed as necessary for the purpose of cleaning the surface of the Ti base material and adjusting the primitive oxide layer. Reverse sputtering can be performed, for example, by irradiating the Ti base with argon gas at an output of about RF 100 W and an argon pressure of about 0.2 Pa.
Next, a Ti film having a thickness of 1 nm or more is formed on the surface of the primitive oxide layer of the Ti base material, and the O concentration on the surface side of the primitive oxide layer is lowered to form an oxide layer having the above composition and thickness.
Then, an Au layer or an Au alloy layer is formed on the oxide layer by sputtering using an Au target for forming the Au layer.

<Manufacture of fuel cell separator material having intermediate layer>
As a method for forming a separator material for a fuel cell having an intermediate layer, the surface Ti oxide film on the Ti base material is sputter-deposited on the Ti base material as a target without removing the surface Ti oxide film on the Ti base material. The first component can be bonded to O in the oxide film to form an intermediate oxide layer. Also, after removing the surface Ti oxide film of the Ti base material, sputtering is performed using the first component oxide as a target, or after removing the surface Ti oxide film of the Ti base material 2, the first component is targeted. The intermediate oxide layer can also be formed by sputter deposition in an oxidizing atmosphere.
During sputtering, the surface Ti oxide film of the Ti base material may be appropriately removed, and reverse sputtering (ion etching) may be performed for the purpose of cleaning the base material surface. Reverse sputtering can be performed, for example, by irradiating the substrate with argon gas at an output of about RF 100 W and an argon pressure of about 0.2 Pa.
An Au alloy layer is formed by Au atoms entering the intermediate layer by sputtering of Au. Alternatively, an alloy target containing the first component and Au may be used to form a sputter film on the surface of the Ti substrate.

<Separator for fuel cell>
Next, a fuel cell separator using the fuel cell separator material of the present invention will be described. The fuel cell separator is formed by processing the above-described fuel cell separator material into a predetermined shape, and a reaction gas flow path for flowing fuel gas (hydrogen) or fuel liquid (methanol), air (oxygen), cooling water, and the like. Alternatively, a reaction liquid channel (a groove or an opening) is formed.

<Laminated (active) fuel cell separator>
FIG. 1 shows a cross-sectional view of a single cell of a stacked (active) fuel cell. In FIG. 1, current collector plates 140A and 140B are respectively arranged outside the separator 10 described later. Usually, when a stack is formed by stacking single cells, a pair of current collectors is provided only at both ends of the stack. A board is placed.
The separator 10 has electrical conductivity, has a current collecting action in contact with an MEA described later, and has a function of electrically connecting each single cell. Further, as will be described later, the separator 10 is formed with a groove serving as a flow path for fuel gas and air (oxygen).

  In FIG. 1, an anode electrode 40 and a cathode electrode 60 are laminated on both sides of a solid polymer electrolyte membrane 20 to form a membrane electrode assembly (MEA) 80. An anode side gas diffusion film 90A and a cathode side gas diffusion film 90B are laminated on the surfaces of the anode electrode 40 and the cathode electrode 60, respectively. In the present invention, the membrane electrode assembly may be a laminate including the gas diffusion films 90A and 90B. For example, when a gas diffusion layer is formed on the surface of the anode electrode 40 or the cathode electrode 60, the laminated body of the solid polymer electrolyte membrane 20, the anode electrode 40, and the cathode electrode 60 is referred to as a membrane electrode assembly. May be.

On both sides of the MEA 80, the separator 10 is disposed so as to face the gas diffusion films 90A and 90B, respectively, and the separator 10 holds the MEA 80 therebetween. A flow path 10L is formed on the surface of the separator 10 on the MEA 80 side, and gas can enter and leave the interior space 20 surrounded by a gasket 12, a flow path 10L, and a gas diffusion film 90A (or 90B) described later. .
A fuel gas (hydrogen or the like) flows in the internal space 20 on the anode electrode 40 side, and an oxidizing gas (oxygen, air or the like) flows in the internal space 20 on the cathode electrode 60 side, so that an electrochemical reaction occurs. It has become.

The outer periphery of the periphery of the anode electrode 40 and the gas diffusion film 90 </ b> A is surrounded by a frame-shaped seal member 31 having substantially the same thickness as the laminated thickness. A substantially frame-shaped gasket 12 is interposed between the seal member 31 and the peripheral edge of the separator 10 so as to contact the separator, and the gasket 12 surrounds the flow path 10L. Furthermore, a current collector plate 140A (or 140B) is laminated on the outer surface of the separator 10 (the surface opposite to the MEA 80 side) in contact with the separator 10, and between the current collector plate 140A (or 140B) and the periphery of the separator 10 is stacked. A substantially frame-shaped sealing member 32 is interposed between the two.
The seal member 31 and the gasket 12 form a seal that prevents fuel gas or oxidizing gas from leaking out of the cell. When a plurality of single cells are stacked to form a stack, a gas different from the space 20 (when an oxidizing gas flows into the space 20) is formed in the space 21 between the outer surface of the separator 10 and the current collector plate 140A (or 140B). , Hydrogen flows in the space 21). Therefore, the seal member 32 is also used as a member for preventing gas from leaking outside the cell.

  The fuel cell is configured to include the MEA 80 (and the gas diffusion films 90A and 90B), the separator 10, the gasket 12, and the current collector plates 140A and 140B, and a fuel cell stack is configured by stacking a plurality of fuel cells. The

  The stacked (active) fuel cell shown in FIG. 1 can be applied to a DMFC using methanol as a fuel in addition to the fuel cell using hydrogen as a fuel.

<Flat type (passive type) fuel cell separator>
FIG. 2 shows a cross-sectional view of a single cell of a planar (passive type) fuel cell. In FIG. 2, current collector plates 140A and 140B are arranged outside the separator 10, which will be described later. Usually, when a stack is formed by stacking single cells, a pair of current collectors is provided only at both ends of the stack. A board is placed.
2, the configuration of the MEA 80 is the same as that of the fuel cell of FIG. 1, and thus the same reference numerals are given and description thereof is omitted (in FIG. 2, the description of the gas diffusion films 90 </ b> A and 90 </ b> B is omitted, Gas diffusion films 90A and 90B may be included).

In FIG. 2, the separator 100 has electrical conductivity, has a current collecting action in contact with the MEA, and has a function of electrically connecting each single cell. In addition, as will be described later, the separator 100 is formed with holes serving as fuel liquid and air (oxygen) flow paths.
The separator 100 is formed with a step portion 100s in the vicinity of the center of the long flat plate-like base material so that the cross section has a crank shape, an upper piece 100b positioned above the step portion 100s, and a step portion 100s. And a lower piece 100a located below. The step portion 100 s extends in a direction perpendicular to the longitudinal direction of the separator 100.
A plurality of separators 100 are arranged in the longitudinal direction, and a space is formed between the lower piece 100a and the upper piece 100b of the adjacent separators 100, and the MEA 80 is interposed in this space. A structure in which the MEA 80 is sandwiched between the two separators 100 is a single cell 300. In this way, a stack in which a plurality of MEAs 80 are connected in series via the separator 100 is configured.

  The planar (passive) fuel cell shown in FIG. 2 can be applied to a fuel cell using hydrogen as a fuel in addition to the above-described DMFC using methanol as a fuel. Further, the shape and number of openings of the planar (passive type) fuel cell separator are not limited, and the openings may be slits in addition to the holes described above, or the entire separator may be net-like.

<Fuel cell stack>
The fuel cell stack of the present invention uses the fuel cell separator material of the present invention.
The fuel cell stack is formed by connecting a plurality of cells in which an electrolyte is sandwiched between a pair of electrodes, and a fuel cell separator is interposed between the cells to block fuel gas and air. The electrode in contact with the fuel gas (H ₂ ) is the fuel electrode (anode), and the electrode in contact with the air (O ₂ ) is the air electrode (cathode).
The configuration example of the fuel cell stack is as described with reference to FIGS. 1 and 2, but is not limited thereto.

<Preparation of sample>
A strip of industrial pure titanium material (JIS type 1) having a thickness of 100 μm was cold-rolled while changing the use conditions of the rolling roll as follows to prepare Ti rolled plates having different surface centerline average surfaces Ra.
Rolling condition A: Rolling roll roughness (Ra) is 0.06, the final pass is replaced with a new roll, rolling, and after the final pass rolling, further skin pass rolling is performed. Rolling condition B: Rolling roll roughness (Ra) is 0.06. Rolling with the final pass replaced with a new roll Rolling condition C: Roll roll roughness (Ra) is 0.1, rolling with final roll replaced with a new roll Rolling condition D: Rolling roll roughness (Ra) is 0.06, final pass Rolling condition E: Rolling condition E: Rolling roll roughness (Ra) is 0.1 and rolling is not performed even in the final pass. Next, the surface of each Ti rolled plate has a predetermined target thickness by sputtering. Thus, Cr, Mo, or Ti (metal film) was formed. Next, Au was deposited to a predetermined target thickness using a sputtering method (In Example 6, the original oxide layer on the surface of the Ti base was adjusted to 3 nm with acid, and then Au was directly deposited. A film was formed.)
In addition, before sputtering of Ti, reverse sputtering (ion etching) was performed under the condition of an output RF of 100 W and an argon pressure of 0.2 Pa for the purpose of cleaning the substrate surface.

The target thickness was determined as follows. First, a target object (for example, Ti) is formed on a copper foil material by sputtering in advance, and the actual thickness is measured with a fluorescent X-ray film thickness meter (SEA5100 manufactured by Seiko Instruments, collimator 0.1 mmΦ). The rate (nm / min) was grasped. Then, sputtering was performed under each condition based on the grasped sputtering rate.
Sputtering of Cr, Mo, Ti, and Au was performed using a sputtering apparatus manufactured by ULVAC, Inc. under the conditions of an output of DC 50 W and an argon pressure of 0.2 Pa.
Table 1 shows the rolling conditions and sputtering conditions of each sample. In the sample of Comparative Example 8, a roll after continuously rolling a Ti rolled sheet of 10 tons or more without maintenance was used as a rolling roll for cold rolling the Ti rolled sheet.

<Measurement of layer structure>
The obtained sample was subjected to concentration analysis of Au, Ti, O, C, and the first component (Cr, Mo) by a depth profile of XPS (X-ray photoelectron spectroscopy) analysis, and the layer structure was measured. . The XPS apparatus, using a ULVAC-PHI Co. 5600MC, ultimate vacuum: 6.5 × ¹⁰ -8 Pa, excitation source: monochromatic AlK, output: 300 W, detection area: 800Myuemufai, incident angle: 45 °, The take-off angle was 45 degrees, no neutralization gun was used, and the measurement was performed under the following sputtering conditions.
Ion species: Ar +
Accelerating voltage: 3kV
Sweep area: 3mm x 3mm
Rate: 3.7nm / min (SiO ₂ conversion)
In addition, the concentration detection by XPS analyzed the density | concentration (mass%) of each element as a total of 100 mass% of a designated element. In XPS analysis, the distance of 1 nm in the thickness direction is the distance on the horizontal axis (distance in terms of SiO ₂ ) of the chart (FIG. 3) by XPS analysis.

<Measurement of the number of titanium oxides penetrating the Au layer>
Titanium oxide penetrating the Au layer was measured by observing a cross section of the sample with BF-STEM and mapping the portion by EDX mapping (analytical elements: Au, Ti, O, C). FIG. 3 is a BF-STEM image of the cross section of the fuel cell separator material (Example 6) after the corrosion resistance test. When this portion is analyzed by EDX mapping, it can be confirmed that the composition shown in FIG. 3 is obtained. It was. According to FIG. 3, it can be seen that titanium oxide was formed to penetrate the Au layer.
The STEM used for the measurement was an HD-2000 STEM manufactured by Hitachi, Ltd., and an arbitrary place of 10 visual fields was measured for one separator material.

The following evaluation was performed for each sample.
A. Measurement of surface roughness Measurement of surface roughness was performed using a non-contact type three-dimensional measuring device (model NH-3, manufactured by Mitaka Kogyo Co., Ltd.) in accordance with JISB0601. The cut-off was 0.25 mm, the measurement length was 1.50 mm, and measurement was performed 5 times per sample.

B. Contact resistance The contact resistance was measured by applying a load to the entire surface of the sample. First, carbon paper was laminated on one side of a 40 × 50 mm plate-like sample, and Cu / Ni / Au plates were further laminated on both sides thereof. The Cu / Ni / Au plate is a material in which a 10 μm thick copper plate is plated with a 1.0 μm thick Ni base, and the Ni layer is plated with a 0.5 μm Au plate. They were placed in contact with the sample and carbon paper.
Further, a Teflon (registered trademark) plate was arranged outside the Cu / Ni / Au plate, and a load of 10 kg / cm ² was applied in the compression direction from the outside of each Teflon (registered trademark) plate with a load cell. In this state, when a constant current with a current density of 100 mA / cm ² was passed between the ^two Cu / Ni / Au plates, the electrical resistance between the Cu / Ni / Au plates was measured by a four-terminal method.

^Two typical properties required for fuel cell separators are low contact resistance (10 mΩ · cm ² or less) and corrosion resistance in the environment of use (low contact resistance after corrosion test and no leaching of harmful ions). It is.
The obtained results are shown in Table 1.

As is clear from Table 1, in Examples 1 to 6 in which the center line average roughness of the Au layer surface and the Ti rolled plate surface was 0.2 μm or less, the contact resistance was low and the conductivity was excellent. .
In addition, when the cross section of the sample of Examples 1-3 was analyzed by XPS, Ti and O were each 10 mass% or more, Cr was contained 20 mass% or more, and Au was contained 20 mass% or more (intermediate) Layer) was 1 nm or more in the thickness direction. Furthermore, Au (alloy) layer of Au 40 mass% or more existed in thickness of 1 nm or more from the outermost surface to the lower layer. The intermediate layer was present between the Au alloy layer and the Ti rolled sheet.
Further, when the cross section of the sample of Example 4 was analyzed by XPS, a region containing 10% by mass or more of Ti and O and 20% by mass or more of Mo and 20% by mass or more of Au (intermediate layer) 1 nm or more existed in the thickness direction. Furthermore, Au (alloy) layer of Au 40 mass% or more existed in thickness of 1 nm or more from the outermost surface to the lower layer. The intermediate layer was present between the Au alloy layer and the Ti rolled sheet.
Further, when the XPS image of the cross section of the sample of Example 5 was measured, an oxide layer having O of 20% by mass or more and less than 50% by mass was present in an amount of 5 to 30 nm, and further Au 40% by mass or more from the outermost surface toward the lower layer. The Au layer was present with a thickness of 1 nm or more.
As a result of the corrosion resistance test of the sample of Example 6, the number of titanium oxides penetrating the Au layer was 5 or less / μm.

  On the other hand, in the case of Comparative Examples 7 and 8 in which the center line average roughness of the surface of the Ti rolled plate exceeded 0.2 μm, the contact resistance before the corrosion resistance test was higher than the target value and the conductivity was inferior.

Claims (12)

A separator material for a fuel cell, wherein an Au layer or an Au alloy layer is formed on a surface of a Ti base material, and a center line average roughness of the surface of the Au layer or the Au alloy layer is 0.2 μm or less. 2. The fuel cell separator material according to claim 1, wherein the center line average roughness of the surface of the Ti base material is 0.2 μm or less. The Au alloy layer is made of an alloy of Au and a first component made of at least one metal selected from the group consisting of Al, Cr, Fe, Co, Ni, Cu, Mo, Sn, and Bi,
3. The fuel cell separator material according to claim 1, wherein an intermediate layer containing Ti, O, and the first component and having an Au content of less than 20% by mass exists between the Au alloy layer and the Ti base material. 4. The fuel cell separator material according to claim 3, wherein the intermediate layer is present as a layer of 1 nm or more in which Ti and O are each 10% by mass or more and the first component is 20% by mass or more. The fuel cell according to any one of claims 1 to 4, wherein the Ti base material is a strip made of a Ti rolled plate, and the Au layer or the Au alloy layer is continuously formed on a surface of the strip. Separator material. 6. The fuel cell separator material according to claim 1, wherein the Au layer or the Au alloy layer has a thickness of 1 to 20 nm in a region of Au 40 mass% or more. The titanium oxide penetrating the Au layer or the Au alloy layer from the Ti base material after being immersed in an aqueous solution having a sulfuric acid concentration of 0.5 g / L at 90 ° C. for less than 5 weeks is less than 5 per 1 μm in cross-sectional length. The fuel cell separator material according to any one of 1 to 6. Between the Ti base material and the Au layer or the Au alloy layer, an oxide layer containing O of 20% by mass to 50% by mass is formed with a thickness of 5 nm or less, or the oxide layer is formed. The fuel cell separator material according to any one of claims 1 to 7. The oxide layer containing 20 mass% or more of O is formed between the Ti base material and the Au layer or the Au alloy layer with a thickness of 5 to 30 nm. Fuel cell separator material. The separator material for fuel cells according to any one of claims 1 to 9, which is used for a polymer electrolyte fuel cell. The separator material for fuel cells according to any one of claims 1 to 9, which is used for a direct methanol type polymer electrolyte fuel cell. A fuel cell stack using the fuel cell separator material according to claim 1.