JP2011216222A - Separator material for fuel cell, separator for fuel cell using the same, fuel cell stack, and producing method of fuel cell separator material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator material for a fuel cell wherein a layer containing Au on the surface of titanium base material can be formed firmly and uniformly, and adhesiveness and corrosion property required as the separator for the fuel cell are ensured.SOLUTION: In the separator material 2 for the fuel cell, a surface layer 6 is formed to contain Au and Cr on the surface of Ti base material, a middle layer 2a of which Au atom content is less than 20% exists in which Ti, O and Cr are contained between the surface layer and the Ti base material, and a region of thickness of 1.5 nm or more exists wherein Au content is 65 atom% or more, the maximum concentration of Au is 80 atom% or more, and adhesion amount of Au is 9,000 ng/cmor more.

Description

  The present invention relates to a fuel cell separator material having a surface on which Au or an Au alloy (a layer containing Au) is formed, a fuel cell separator using the same, and a fuel cell stack.

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 is known in which an Au film is formed on an oxide film of a Ti base material through an intermediate layer made of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, or the like. (Patent Document 2). This intermediate layer has good adhesion to the base oxide film, that is, good bonding with O (oxygen atom), and good adhesion and bonding to the Au film because of the metal or metalloid. .

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. (Patent Document 3).

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 JP-A-2005-243401

However, in the case of the technique described in Patent Document 1 described above, in order to obtain an Au alloy film having good adhesion, it is necessary to remove the oxide film on the surface of the titanium base material, and the oxide film is not sufficiently removed. Has a problem that the adhesion of the noble metal film is lowered.
Patent Document 2 stipulates that a conductive thin film is formed on the surface of the oxide film on the surface of the base material. For example, Au should be formed while leaving the oxide film on the surface of the titanium base material. Then, the film is not uniformly formed. In particular, in wet gold plating, if the electrodeposition shape of the plating is granular and an oxide film remains on the surface of the titanium base material, a portion that becomes a non-plating portion is generated on a part of the surface of the titanium base material. In addition, Patent Document 2 stipulates that an intermediate layer is provided in order to improve the adhesion, but it is sufficient to simply provide the intermediate layer, and sufficient corrosion resistance and a corrosion resistance necessary for a fuel cell separator Durability cannot be obtained.
The technique described in Patent Document 3 is obtained by coating a base material with stainless steel clad on both sides of a copper plate, and cannot be said to have excellent corrosion resistance.

  That is, the present invention has been made in order to solve the above-described problems, and can form a highly corrosion-resistant conductive film containing Au on the surface of a titanium base material with high adhesion, under the fuel cell operating environment. However, an object of the present invention is to provide a fuel cell separator material having high durability, a fuel cell separator using the material, and a fuel cell stack.

As a result of various studies, the present inventors have made it possible to form a Au-containing layer firmly and uniformly on Ti by forming a surface layer containing Au and Cr on the surface of the Ti substrate. It was found that the required corrosion resistance and durability can be secured.
In order to achieve the above object, the separator material for a fuel cell of the present invention has a surface layer containing Au and Cr formed on the surface of a Ti base material, and between the surface layer and the Ti base material, An intermediate layer containing Ti, O, and Cr, with an Au concentration of less than 20 atomic%, an Au concentration of 65 atomic% or more in thickness of 1.5 nm or more, and a maximum Au concentration of 80 atomic% or more, Is 9000 ng / cm ² or more.

The ratio represented by (Au adhesion amount) / (Cr adhesion amount) is preferably 10 or more.
It is preferable that the amount of Cr deposited is 200 ng / cm ² or more, and in the intermediate layer, Ti and O are each 10 atomic% or more, and a region containing 20 atomic% or more of Cr is 1 nm or more.
The Ti base material may be formed by forming a Ti film having a thickness of 10 nm or more on the surface of a base material different from Ti.
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.

In the fuel cell separator of the present invention, the fuel cell separator material is used, and the reaction gas channel and / or the reaction liquid channel are formed in advance on the Ti base material by pressing, and then the surface layer is formed. Become.
Further, the fuel cell separator of the present invention uses the fuel cell separator material, and after forming the surface layer on the Ti base material, forms a reaction gas channel and / or a reaction liquid channel by press working. It consists of

  The fuel cell stack of the present invention uses the fuel cell separator material or the fuel cell separator.

The method for producing a fuel cell separator material according to the present invention is a method for producing the fuel cell separator material, wherein the Cr is dry-formed on the surface of the Ti base material, and then Au is dry-formed.
The dry film formation is preferably sputtering.

  According to the present invention, a layer containing Au can be formed firmly and uniformly on Ti, and adhesion and corrosion resistance required for a fuel cell separator can be secured.

It is a schematic diagram which shows the structure of the separator material for fuel cells which concerns on embodiment of this invention. It is a figure which shows the XPS analysis result of the cross section of the separator material for fuel cells of Example 1. FIG. It is sectional drawing of the fuel cell stack (single cell) which concerns on embodiment of this invention. It is a top view which shows the structure of the separator concerning embodiment of this invention. It is a top view which shows the structure of the gasket concerning 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 top view which shows the structure of the separator for planar fuel cells.

Hereinafter, a fuel cell separator material according to an embodiment of the present invention will be described. In the present invention,% means atomic (at)% 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 will be described in detail later, as a separator for a fuel cell, in addition to a separator having an uneven flow path on a plate-like substrate surface, a plate-like substrate surface such as the above-described passive DMFC separator is used. It includes a separator with gas and methanol passage holes.

  As shown in FIG. 1, the separator material for a fuel cell according to the embodiment of the present invention has an intermediate layer 2a formed on the surface of a Ti base 2 and a surface layer 6 formed on the surface of the intermediate layer 2a.

<Ti substrate>
The fuel cell separator material is required to have corrosion resistance and conductivity, and the base material is required to have corrosion resistance. For this reason, a titanium material with good corrosion resistance is used for the base material.
The Ti substrate may be a solid titanium material, or may be a Ti substrate having a thickness of 10 nm or more formed on the surface of a substrate different from Ti. Examples of the base material different from Ti include stainless steel, aluminum, copper, and the like. By covering these surfaces with Ti, the corrosion resistance of stainless steel, aluminum, copper, etc., which has lower corrosion resistance than titanium, can be improved. it can. However, the corrosion resistance improving effect cannot be obtained unless Ti is covered by 10 nm or more.
The material of the Ti base material 2 is not particularly limited as long as it is titanium. Further, the shape of the Ti base material 2 is not particularly limited as long as it is a shape capable of sputtering Cr and gold. However, considering press forming into a separator shape, the shape of the Ti base material is preferably a plate material. The thickness of the entire Ti substrate is preferably 10 μm or more.
O (oxygen) contained in the intermediate layer 2a is naturally formed by leaving the Ti base 2 in the air, but O may be positively formed in an oxidizing atmosphere.

The Ti concentration is detected by XPS concentration detection, which will be described later, and the concentration (atomic%) of each element is analyzed with the total of designated elements as 100%. The depth of 1 nm from the outermost surface of the fuel cell separator material is a distance (distance in terms of SiO ₂ ) on the horizontal axis (thickness direction) of the chart by XPS analysis.

<Surface layer>
A surface layer 6 containing Cr and Au and having an Au concentration of 65% or more in a thickness of 1.5 nm or more is formed on the Ti substrate 2. This surface layer is for imparting Au characteristics (corrosion resistance, conductivity, etc.) and hydrogen embrittlement resistance to the Ti base material.
Cr has the properties that a) easily binds to oxygen, b) constitutes an alloy with Au, and c) hardly absorbs hydrogen. It is formed to improve the adhesion between the surface layer and the Ti substrate.
In addition, Cr is more oxidizable than Au from the potential-pH diagram, and makes use of the characteristic that it is difficult to absorb hydrogen, so Cr is used as a constituent element of the following intermediate layer.

The surface layer can be confirmed by XPS analysis which will be described later, and is a portion containing Au and Cr from the outermost surface to the lower layer by XPS analysis, and a portion located above the following intermediate layer (Au 20% or more (Part) is a surface layer. The thickness of the surface layer is preferably 5 to 100 nm. If the thickness of the surface layer is less than 5 nm, the corrosion resistance required for the fuel cell separator may not be ensured on the Ti substrate. The thickness of the surface layer is more preferably 7 nm or more, and further preferably 10 nm or more.
Further, heat treatment may be performed after forming the Cr and Au films. When heat treatment is performed, oxidation and diffusion progress, and the Au concentration in the surface layer may decrease. However, if the thickness of the region having an Au concentration of 65% or more is 1.5 nm or more, titanium does not diffuse into the surface layer and functions as a surface layer.

If the thickness of the surface layer exceeds 100 nm, money saving may not be achieved and the cost may increase.
Further, when the thickness of the region having an Au concentration of 65% or more in the surface layer is less than 1.5 nm, the corrosion resistance required for the fuel cell separator cannot be secured.

  Further, the maximum concentration of Au in the surface layer 6 needs to be 80% or more. When the maximum concentration of Au is less than 80%, the characteristics of Au (corrosion resistance, conductivity, etc.) and hydrogen embrittlement resistance are not sufficiently imparted to the Ti base material.

Note that an Au single layer may be formed on the outermost surface portion of the surface layer 6. The Au single layer is a portion where the concentration of Au is almost 100% by XPS analysis.
Moreover, the intermediate layer side of the surface layer 6 may have a composition region (precious metal region) mainly composed of Cr.

<Intermediate layer>
Between the surface layer (or Au single layer) 6 and the Ti substrate 2, there is an intermediate layer 2a containing Ti, O, and Cr and having less than 20% Au.
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 metal is more easily oxidized than Au, and forms an O atom and an oxide in the Ti oxide on the surface of the Ti base, and is firmly bonded to the surface of the Ti base.
Further, the metal is difficult to absorb hydrogen. In these respects, when the thickness of the conductive film containing Au (the surface layer or the Au single layer) is several tens of nm or less, conventionally, the intermediate layer is simply Ti, Zr, Hf, V, Nb, Ta, Compared to the case of using Cr, Mo, W or the like, a separator material with excellent durability can be provided by forming the intermediate layer from Ti, O, and Cr.
The intermediate layer preferably does not contain Au, and if 20% or more of Au is contained, the adhesion decreases. In order to reduce the Au concentration in the intermediate layer to less than 20%, it is preferable to perform sputtering using a Cr single target or a low Au concentration Cr—Au alloy target on the Ti substrate.

The adhesion amount of Cr is 200 ng / cm ² or more, and the intermediate layer is preferably present as a layer of 1 nm or more containing 10% or more of Ti and O and 20% or more of Cr. In this case, when the cross section of the fuel cell separator material is analyzed by XPS, Ti and O are each 10% or more, Cr is 20% or more, and a region containing 20% or more of Au is 1 nm or more in the thickness direction. Exists. 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 Cr.
If the adhesion amount of Cr is less than 200 ng / cm ² , the adhesion of the surface layer may deteriorate due to the small amount of Cr.

Here, a depth profile by XPS (X-ray photoelectron spectroscopy) analysis is measured, and concentration analysis of Au, Ti, O, Cr is performed to determine the layer structure of the sputtered layer. In the concentration detection by XPS, the concentration of each element is analyzed with the total of designated elements as 100%. In the XPS analysis, the distance of 1 nm in the thickness direction is the distance on the horizontal axis of the chart by XPS analysis (distance in terms of SiO ₂ ).

  The reason why the lower limit of Ti and O is 10% and the lower limit of Cr is 20% is that the part where Cr is less than 20% is close to the surface of the Ti substrate, and the part where Ti is less than 10% is the surface layer This is because the portion where O is less than 10% does not form a sufficient oxide with Cr and Ti and does not function as an intermediate layer. Ti and O decrease rapidly from 10% respectively, so 10% is the lower limit for measurement. The reason for making Au less than 20% is to improve adhesion. When the intermediate layer is less than 1 nm, Cr is thin and the portion where the Ti base material and Au are in contact with each other increases, so that the adhesion of the surface layer may deteriorate.

In the fuel cell separator material of the present invention, the amount of Au deposited needs to be 9000 ng / cm ² or more.
When the adhesion amount of Au is less than 9000 ng / cm ² , the corrosion resistance required for the fuel cell separator cannot be secured.
On the other hand, it is preferable that the adhesion amount of Au is less than 40000 ng / cm ² from the viewpoint of saving money. However, when the adhesion amount of Au is less than 40000 ng / cm ² , the ratio represented by (Au adhesion amount) / (Cr adhesion amount) is preferably 10 or more. When the adhesion amount of Au is less than 40000 ng / cm ^{2 and the} ratio represented by (Au adhesion amount) / (Cr adhesion amount) is less than 10, the portion where Cr is exposed on the surface of the sputtered film is In the corrosion resistance test with a chlorine-containing corrosive solution, there is a problem that the contact resistance after the test increases and the dissolution of Cr is relatively large.

In the present invention, it is preferable that an oxide layer containing less than 50% Ti and 20% or more of O is formed between the Ti base material and the surface layer 6 with a thickness of less than 100 nm. A part of this oxide layer may overlap with the region of the intermediate layer.
When the oxide layer is present, the titanium base material is prevented from becoming brittle when a continuous power generation test of the fuel cell is performed. The portion where Ti is less than 50% is not a portion of the titanium base material because the amount of titanium is less than half of the total amount. Since an oxide film exists on the surface of the titanium base material, an oxide layer is formed from the portion where Ti is less than 50% to the surface layer. The reason why the region containing 20% or more of O is the oxide layer is that when the O (oxygen) concentration of the oxide layer is less than 20%, the titanium base material becomes brittle when a continuous power generation test of the fuel cell is performed. This is because the durability as a fuel cell separator material deteriorates.
However, when the thickness of the oxide layer is 100 nm or more, the adhesion and conductivity of the surface layer may decrease. On the other hand, when the oxide layer is thin, the titanium base material becomes brittle when the continuous power generation test of the fuel cell is performed, and the durability as the separator material for the fuel cell may be deteriorated. Therefore, the thickness of the oxide layer is preferably 5 nm or more, more preferably 10 nm or more.

It is preferable to have a gradient composition in which the proportion of Au in the surface layer increases from the lower layer side toward the upper layer side. Here, the Au ratio (at%) can be obtained by the XPS analysis described above. The thickness of the surface layer is the actual size of the scanning distance in XPS analysis.
When the surface layer has a gradient composition, the proportion of Cr that is more oxidizable than Au increases on the lower layer side of the surface layer, and the bond with the Ti substrate surface becomes stronger, while the upper layer side of the surface layer has the characteristics of Au. Since it becomes stronger, corrosion resistance and durability are improved.

<Manufacture of fuel cell separator materials>
As a method for forming the intermediate layer of the separator material for the fuel cell, the surface Ti oxide film of the Ti base material is not removed, and sputtering is performed on this base material using Cr as a target, thereby forming the O in the surface Ti oxide film. Cr can be bonded to each other to form an intermediate layer. In addition, after removing the surface Ti oxide film of the Ti base material 2, sputtering film formation is performed using Cr oxide as a target, or after removing the surface Ti oxide film of the Ti base material 2, sputtering is performed using Cr as a target in an oxidizing atmosphere. The intermediate layer can also be formed by forming a film.
During sputtering, the surface Ti oxide film on 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.
The Au in the intermediate layer is included in the intermediate layer by Au atoms entering the intermediate layer by Au sputtering for forming the following surface layer. Alternatively, sputter deposition may be performed on the surface of the Ti substrate using an alloy target containing Cr and Au.

As a method for forming the surface layer, for example, Cr can be deposited on a Ti base material by sputtering as described above, and then Au can be deposited by sputtering on the Cr film. In this case, since the sputtered particles have high energy, even if only the Cr film is formed on the surface of the Ti base, by sputtering Au there, Au enters the Cr film and becomes a surface layer. Further, in this case, the composition is a gradient composition in which the proportion of Au in the surface layer increases from the lower layer side toward the upper layer side.
Sputter film formation may be first performed on the Ti base material surface using an alloy target having a low Au concentration of Cr and Au, and then using an alloy target having a high Au concentration of Cr and Au.

  According to the fuel cell separator material according to the embodiment of the present invention, a layer containing Au can be formed firmly and uniformly on Ti, and since this layer has conductivity, corrosion resistance and durability, fuel It is suitable as a battery separator material. Further, according to the embodiment of the present invention, if a layer containing Au is sputter-deposited, this layer becomes a uniform layer. Therefore, the surface becomes smoother than wet gold plating, and Au is not wasted. There is an advantage that it can be done.

<Separator for fuel cell>
Next, an example of 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. 3 is a cross-sectional view of a single cell of a stacked (active) fuel cell. In FIG. 3, 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. 3, a membrane electrode assembly (MEA) 80 is configured by laminating an anode electrode 40 and a cathode electrode 60 on both sides of the solid polymer electrolyte membrane 20. 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

  Next, the structure of the separator 10 will be described with reference to the plan view 4. The separator 10 is formed into a rectangular shape by press working from the fuel cell separator material of the present invention, and a fuel gas introduction hole 10x is opened on the left side at the upper edge (upper side) of the separator 10. Further, a fuel gas discharge hole 10y is opened on the right side at the lower end edge (lower side) of the separator 10.

Furthermore, a plurality of linear flow channel grooves 10 </ b> L extending in parallel to the direction from the upper side to the lower side of the separator 10 (up and down direction in FIG. 4) are formed by pressing or the like. The straight flow path groove 10L generates a parallel flow in the gas flow.
Further, in this embodiment, the start and end of the linear flow channel 10L do not reach the outer edge of the separator 10, and a flat portion where the linear flow channel 10L is not formed exists on the outer peripheral edge of the separator 10. Further, in this embodiment, the adjacent linear flow path grooves 10L are positioned at equal intervals, but may be at unequal intervals.
In addition, positioning holes 10f are opened at opposing side edges (side edges) of the separator 10, respectively.

In addition, a flow path groove | channel may be not only a straight line but a curve, and each flow path groove does not necessarily need to be mutually parallel. Further, as a curve, for example, an S-shape may be used in addition to a curved line.
From the viewpoint of facilitating the formation of the flow channel, straight lines parallel to each other are preferable.
The thickness of the separator 10 is preferably 10 μm or more in terms of press formability, but is preferably 200 μm or less from the viewpoint of cost.

Next, the structure of the gasket 12 will be described with reference to the plan view 5.
The gasket 12 is in the form of a sheet made of, for example, Teflon (registered trademark), and the outer edge is a rectangular frame having the same size as the separator 10, and the inner edge is a fuel gas introduction hole 10 x, a discharge hole 10 y, and a linear flow. The fuel gas introduction hole 10x, the discharge hole 10y, and the linear flow path groove 10L are communicated with each other in the internal space of the gasket 12 so as to surround the road groove 10L.
In addition, positioning holes 12f are opened at opposite side edges (sides) of the gasket 12, and the gaskets 12 are stacked so as to overlap the positioning holes 10f of the separator 10, thereby making the relative relationship between the separator 10 and the gasket 12 different. Define the location.

  The material of the gasket 12 includes corrosion resistance, Teflon (registered trademark) having heat resistance at 80 to 90 ° C. which is the operating temperature of the fuel cell, and a metal plate (titanium, stainless steel, A sheet of aluminum) or a carbon material can be used. Although the thickness of the gasket 12 varies depending on the uneven shape of the separator 10, it is necessary to make the thickness equal to or greater than the groove height of the separator (the height difference between the frame portion and the concave or convex). For example, when the groove height of the separator is 0.5 mm, the thickness of the gasket is 0.5 mm.

Next, the shape of the gasket 12 will be described in more detail. The upper inner edge 12c of the gasket 12 is positioned slightly above the upper end 10L1 of the linear flow channel, and a space is formed for the gas flowing along the linear flow channel 10L to turn back and turn 180 degrees. Further, the left end portion of the upper inner edge 12c extends outward so that the fuel gas introduction hole 10x of the separator 10 is exposed in the gasket 12.
Similarly, the lower inner edge 12d of the gasket 12 is positioned slightly below the lower end 10L2 of the linear flow channel, and there is a space for the gas flowing along the linear flow channel 10L to turn back and turn 180 degrees. Is formed. Further, the right end portion of the lower inner edge 12d extends outward, and the fuel gas discharge hole 10y of the separator 10 is exposed in the gasket 12.

Further, a piece-like partition member 12e1 extends inward at a position adjacent to a portion extending toward the fuel gas introduction hole 10x in the upper inner edge 12c. Further, another piece of partition member 12e2 extends inward at a position on the right side of the upper inner edge 12c by a predetermined distance from the partition member 12e1. And the front-end | tip of the partition members 12e1 and 12e2 is contacting the upper end (equivalent to a start end or a termination | terminus) 10L1 of a linear flow path groove.
Similarly, a piece-like partition member 12e3 extends inward at a position on the right side by a predetermined distance from the position facing the partition member 12e1 in the lower inner edge 12d. In addition, a piece of partition member inward toward the inside at a position on the lower inner edge 12d that is a predetermined distance to the right from the position facing the partition member 12e2 and adjacent to the portion extending toward the fuel gas discharge hole 10y. 12e4 extends. And the front-end | tip of the partition members 12e3 and 12e4 is contacting the lower end (equivalent to a start end or a termination | terminus) 10L2 of a linear flow path groove.

Further, the partition members 12e1 to 12e4 extending from the opposing inner edges 12c and 12d of the gasket 12 are the partition members 12e1 (upper inner edge 12c), 12e3 (lower inner edge 12d) and 12e2 (upper inner edge 12c) from the left side of FIG. , 12e4 (lower inner edge 12d).
Thus, since the partition members extending from the opposing inner edges of the gasket 12 are arranged in a staggered manner, the gas flow path flowing along the linear flow path groove 10L is folded back in the vicinity of the partition member, and the meandering flow path Will be configured.

  Specifically, the gas introduced into the separator 10 from the fuel gas introduction hole 10x flows downward in FIG. 5 along the straight flow path groove 10L, but the partition member 12e3 has one flow path groove 10L. Since it is in contact with the lower end, the flow along the flow path groove 10L is suppressed. Further, the flow crossing the flow channel 10L is originally suppressed. Therefore, the flow channel 10L with which the partition member 12e3 is in contact functions as a dike that prevents both the flow in which the gas is short-cut in the horizontal direction (right direction in FIG. 5) and the flow in the vertical direction. The gas flow is folded back in the vicinity of the partition member 12e3, changes its direction by 180 degrees, and flows upward along the linear flow channel 10L. Next, since the partition members 12e1 and e2 similarly prevent the shortcut flow in the lateral direction, the gas flow is folded back in the vicinity of the partition member 12e2 and flows downward along the linear flow channel groove 10L. In the same manner, the gas flow is folded in the vicinity of the partition member 12e4, and after passing along the straight flow channel 10L, the right inner edge (side edge) of the gasket 12 is folded at this portion in order to prevent a shortcut flow. The fuel gas is discharged to the fuel gas discharge hole 10y along the straight flow channel 10L.

  The number of flow channel grooves in contact with one partition member is not particularly limited because it depends on the size of the separator and the size (width) of the flow channel grooves. Since the contributing groove is reduced, it is preferably 1 to 3 grooves.

  As described above, since the gas flow path in the separator becomes a meandering flow path due to the shape of the gasket that can be easily processed, it is not necessary to form a complicated flow path in the separator, and the flow path of the separator itself The power generation characteristics of the fuel cell can be improved by simplifying the shape and improving the gas flow without impairing productivity. That is, the parallel flow through the separator flow path can be changed to a serpentine flow (serpentine) depending on the shape of the gasket.

However, as a flow channel groove of the separator, a serpentine (meandering) shape may be used, and the shape of the flow channel is not limited.
The stacked (active) fuel cell shown in FIG. 3 can be applied not only to the above-described fuel cell using hydrogen as a fuel, but also to a DMFC using methanol as a fuel.

<Flat type (passive type) fuel cell separator>
FIG. 6 shows a cross-sectional view of a single cell of a planar (passive) fuel cell. In FIG. 3, 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.
In FIG. 6, since the configuration of the MEA 80 is the same as that of the fuel cell of FIG. 5, the same reference numerals are given and description thereof is omitted (in FIG. 6, the description of the gas diffusion films 90A and 90B is omitted, Gas diffusion films 90A and 90B may be included).

In FIG. 6, 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.

FIG. 7 shows a top view of the separator 100. The lower piece 100a and the upper piece 100b each have a plurality of holes 100h, which serve as oxygen (air) reaction gas flow paths and methanol reaction liquid flow paths.
In this stack, when air (oxygen) is flowed from above in FIG. 6, oxygen comes into contact with the cathode electrode 60 side of the MEA 80 through the holes 100 h of the separator 100, thereby causing a reaction. On the other hand, when methanol is flowed from the lower side of FIG. 6, the methanol comes into contact with the anode electrode 40 side of the MEA 80 through the hole 100 h of the separator 100 to cause a reaction. Note that methanol is supplied from a lower tank (methanol cartridge) 200 in FIG.
The planar (passive) fuel cell shown in FIG. 6 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.

In the fuel cell separator of the present invention, it is preferable that the reaction gas flow path and / or the reaction liquid flow path by press working are formed in advance on the Ti base material. In this way, there is no need to form a reaction gas channel (reaction liquid channel) in the subsequent process, and the reaction gas can be easily processed by pressing the Ti substrate before forming the intermediate layer, surface layer, etc. Since a flow path (reaction liquid flow path) can be formed, productivity is improved.
Further, in the fuel cell separator of the present invention, the reaction gas flow path and / or the reaction liquid flow path are formed by pressing later on the fuel cell separator material in which the surface layer or the Au single layer is formed on the surface of the Ti substrate. It may be formed. In the fuel cell separator material of the present invention, the surface layer or the Au single layer is firmly adhered to the surface of the Ti base material. Road) and productivity is improved.

  In addition, in order to perform the press work for forming the reaction gas flow path (reaction liquid flow path), it is preferable that the Ti base material has a thickness of 10 μm or more as the fuel cell separator material. The upper limit of the thickness of the Ti base material is not limited, but is preferably 200 μm or less from the viewpoint of cost.

<Fuel cell stack>
The fuel cell stack of the present invention comprises the fuel cell separator material of the present invention or the fuel cell separator 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 has already been described with reference to FIGS. 3 and 6, but is not limited thereto.

<Preparation of sample>
As a Ti base material, an industrial pure titanium material (JIS type 1) having a thickness of 100 μm was used, and pretreatment was performed by FIB (focused ion beam processing). When observed by energy dispersive X-ray fluorescence (EDX) analysis using FE-TEM (electrolytic emission transmission electron microscope), it was confirmed that a titanium oxide layer of about 10 nm was formed on the surface of the Ti substrate in advance. did.
In some examples, a 100 μm thick industrial pure stainless steel material (SUS316L) or a 100 μm thick pure copper (C1100) coated with Ti having a predetermined thickness shown in Table 1 (Ti coating material) was used. The Ti coating was performed by vacuum vapor deposition using an electron beam vapor deposition apparatus (manufactured by ULVAC, MB05-1006).
Next, Cr was formed on the surface of the titanium oxide layer of the Ti base so as to have a predetermined target thickness by sputtering. Pure Cr was used for the target. Next, Au was deposited using a sputtering method so as to have a predetermined target thickness. Pure Au was used for the target.
The target thickness was determined as follows. First, an object (Cr, Au) is formed in advance on a titanium substrate by sputtering, and the actual thickness is measured with a fluorescent X-ray film thickness meter (SEA Instruments 100A, collimator 0.1 mmΦ) manufactured by Seiko Instruments. The sputter rate (nm / min) was grasped. Based on the sputtering rate, the sputtering time for a thickness of 1 nm was calculated, and sputtering was performed under these conditions.
Sputtering of Cr and Au was performed using a sputtering apparatus manufactured by ULVAC, Inc. under the conditions of an output DC of 50 W and an argon pressure of 0.2 Pa.

<Measurement of layer structure>
About the obtained sample, the depth (Depth) profile by XPS (X-ray photoelectron spectroscopy) analysis was measured, the density | concentration analysis of Au, Ti, O, and Cr was performed, and the layer structure of the sputter | spatter layer was determined. As an XPS device, ULVAC-PHI Co., Ltd. 5600MC was used, ultimate vacuum: 6.5 × 10 ⁻⁸ Pa, excitation source: monochromatic AlK, output: 300 W, detection area: 800 μmΦ, incident angle: 45 degrees, 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 +
Acceleration voltage: 3 kV
Sweep area: 3mm x 3mm
Rate: 2 nm / min. (SiO ₂ equivalent)
The concentration detection by XPS was performed by analyzing the concentration (at%) of each element with the total of designated elements as 100%. In the XPS analysis, the distance of 1 nm in the thickness direction is the distance on the horizontal axis of the chart by XPS analysis (distance in terms of SiO ₂ ).

FIG. 2 shows an actual XPS image of the cross section of the sample of Example 1.
A surface layer 6 made of Cr and Au is formed on the surface of the Ti base 2. Further, it can be seen that an intermediate layer 2a containing Ti, O, Cr and Au of less than 20% is present at 1 nm or more between the Ti base 2 and the surface layer 6.
Furthermore, it can be seen that an oxide layer containing less than 50% Ti and 20% or more of O is formed with a thickness of less than 100 nm on the Ti base material 2 side from the surface layer 6.
In the present invention, the concentration of Ti, O, etc. is defined in order to define the intermediate layer. Therefore, since the boundary of the intermediate layer is determined by the Ti and O concentrations for convenience, a layer different from both the intermediate layer and the Ti substrate may be interposed between the intermediate layer and the upper and lower layers (for example, the Ti substrate 2). is there.

<Preparation of each sample>
Samples of Examples 1 to 8 were prepared by variously changing the target thicknesses of the Cr film and Au film at the time of sputtering for titanium substrates (pure Ti and Ti coating materials) having different thicknesses of the initial surface Ti oxide layer. did.
As Comparative Example 9, a sample was prepared by reducing the sputtering thickness of the Au film to 4 nm.
As Comparative Example 10, a sample was prepared with an Au adhesion amount / Cr adhesion amount of less than 10.
As Comparative Example 11, a sample was prepared by reducing the sputtering thickness of the Cr film to 0.25 nm.
As Comparative Example 12, a sample was prepared by performing atmospheric heat treatment (120 ° C. × 12 hours) after sputtering.
As Comparative Example 13, a substrate was heated (300 ° C.) during sputtering to produce a sample.

<Evaluation>
The following evaluation was performed for each sample.
A. Adhesion of coating After marking the grids on the outermost surface (surface layer) of each sample at intervals of 1 mm, stick adhesive tape, and bend each specimen 180 ° to return it to its original state. A peel test was performed to quickly and strongly peel the tape.
The case where there was no peeling at all was marked as ◯, and the case where some peeling was visually observed was marked as x.

B. Contact resistance The contact resistance was measured by applying a load to the entire surface of the sample. First, carbon papers were laminated on the front and back sides of a 40 × 50 mm plate-like sample, and Cu / Ni / Au plates were further laminated on the outer sides of the front and back carbon papers. 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. The carbon paper was placed in contact with it.
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.

The contact resistance was measured before and after the sample was tested under the following two conditions.
Condition 1: immersion test of sample in sulfuric acid aqueous solution (bath temperature 90 ° C., sulfuric acid concentration 0.5 g / L, immersion time 240 hours, liquid volume 1000 cc)
Condition 2: immersion test of sample in aqueous solution of sulfuric acid (0.5 g / L) + sodium chloride (Cl: 10 ppm) (bath temperature 90 ° C., immersion time 240 hours, liquid volume 1000 cc)

C. Metal Elution Amount The metal elution amount was evaluated by ICP (inductively coupled plasma) emission spectroscopic analysis of all metal concentrations (mg / L) in the test solution after the test under the above conditions 1-2.
Typical characteristics required for fuel cell separators are low contact resistance (10 mΩ · cm ² or less), corrosion resistance in the environment of use (low contact resistance after corrosion test, no leaching of harmful ions) There are two.
The obtained results are shown in Tables 1 and 2. The presence of the intermediate layer and the oxide layer was confirmed by determining the ratio of each component from the actual XPS image of the sample cross section.

D. Amount of adhesion The amount of adhesion was evaluated by acid decomposition / ICP (inductively coupled plasma) emission spectroscopic analysis. Specifically, the entire amount of one 50 mm × 50 mm sample was dissolved in a hydrofluoric acid solution, and the adhesion amount of Au and Cr was analyzed. The number of samples per condition was five, and the average values of the five measurement results are shown in Table 1, respectively.

  As apparent from Tables 1 and 2, the surface layer and the intermediate layer are present, the thickness of the region where Au is 65 atomic% or more is 1.5 nm or more, and the maximum concentration of Au is 80 atomic% or more. In each Example, the contact resistance of the sample did not change before and after the corrosion resistance test, and the coating adhesion and corrosion resistance were excellent.

In the case of Comparative Example 9 in which the Au adhesion amount was less than 9000 ng / cm ² , the contact resistance after the test increased in the corrosion resistance test of Condition 2, the amount of Cr eluted under Condition 2 was large, and the corrosion resistance of the film was inferior.
In the case of Comparative Example 10 in which the ratio represented by (Au adhesion amount) / (Cr adhesion amount) is less than 10, the contact resistance after the test increased in the corrosion resistance test of Condition 2, and the Cr The amount of elution was large, and the corrosion resistance of the film was inferior.
In the case of Comparative Example 11 in which the Cr adhesion amount was less than 200 ng / cm ² , the adhesion of the sputtered film deteriorated, and the corrosion resistance could not be evaluated.

In the case of Comparative Example 12 where the maximum concentration of Au was less than 80 atomic% due to the atmospheric heat treatment after sputtering, the contact resistance after the test increased in the corrosion resistance test of Condition 2, and the dissolution of Cr under Condition 2 The amount was large and the corrosion resistance of the film was poor.
In the case of Comparative Example 13 in which the thickness of the region having an Au concentration of 65% or more is less than 1.5 nm, the contact resistance after the test increased in the corrosion resistance test of Condition 2, the amount of Cr eluted under Condition 2 was large, Corrosion resistance was inferior.

2 Ti substrate 2a Intermediate layer 6 Surface layer 10, 100 Separator 10L, 10LB (Gas) flow channel 10L1, 10LB1 Flow channel groove start 10L2, 10LB2 Flow channel groove end 12, 12B Gasket 12c, 12d Gasket inner edge 12e1- 12e4 Partition member 12eb1 to 12eb4 Gasket channel 20 Solid polymer electrolyte membrane 40 Anode electrode 60 Cathode electrode 80 Membrane electrode assembly (MEA)
100h hole (for separator)

Claims (11)

A surface layer containing Au and Cr is formed on the surface of the Ti substrate,
Between the surface layer and the Ti base material, there is an intermediate layer containing Ti, O and Cr, and less than 20 atomic% Au,
The thickness of the region having an Au concentration of 65 atomic% or more is 1.5 nm or more, and the maximum concentration of Au is 80 atomic% or more,
A fuel cell separator material having an adhesion amount of Au of 9000 ng / cm ² or more. 2. The fuel cell separator material according to claim 1, wherein a ratio expressed by (Au adhesion amount) / (Cr adhesion amount) is 10 or more. The amount of Cr deposited is 200 ng / cm ² or more,
3. The fuel cell separator material according to claim 1, wherein in the intermediate layer, a region containing 10 atomic% or more of Ti and O and 20 nm% or more of Cr is present at 1 nm or more.   The separator material for a fuel cell according to any one of claims 1 to 3, wherein the Ti substrate is formed by forming a Ti film having a thickness of 10 nm or more on a substrate surface different from Ti. The separator material for fuel cells according to any one of claims 1 to 4, which is used for a polymer electrolyte fuel cell. The separator material for fuel cells according to any one of claims 1 to 4, which is used for a direct methanol type polymer electrolyte fuel cell. A fuel cell separator using the fuel cell separator material according to any one of claims 1 to 6, wherein a reaction gas channel and / or a reaction liquid channel are formed in advance on the Ti base material by pressing. And a fuel cell separator formed by forming the surface layer. A fuel cell separator using the fuel cell separator material according to any one of claims 1 to 6, wherein after forming the surface layer on the Ti base material, a reaction gas flow path and / or by press working A fuel cell separator formed by forming a reaction liquid channel. A fuel cell stack using the fuel cell separator material according to claim 1 or the fuel cell separator according to claim 7 or 8. It is a manufacturing method of the separator material for fuel cells in any one of Claims 1-6,
A manufacturing method of a separator material for a fuel cell, in which the Cr is dry-formed on the surface of the Ti substrate, and then Au is dry-formed.   The method for producing a fuel cell separator material according to claim 10, wherein the dry film formation is sputtering.

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