JP5143842B2 - Fuel cell separator material and fuel cell stack - Google Patents

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, 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 (direct methanol fuel cell)) that uses methanol, which is higher in energy density than hydrogen and easy to handle, as a fuel gas supplied to the anode is also available. 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).
Besides solid polymer fuel cells and direct methanol fuel cells, solid electrolyte fuel cells (SOFC) using ionic conductive ceramics as electrolytes, and phosphoric acid fuel cells (PAFC) using phosphoric acid as one of the electrolyte components In addition, a molten carbonate fuel cell (MCFC) using molten carbonate as one of electrolyte components has been developed.

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 may also be called an interconnector, a bipolar plate, or a current collector.
The conditions required for the DMFC current collector are more than those for the 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.
The separator material for SOFC, PAFC and MCFC must also be a material having electrical conductivity and corrosion resistance.

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.
In addition, when the titanium material described in Patent Document 2 is used in a corrosive environment, if the thickness of the conductive thin film is several tens of nanometers or less, the (semi) metal constituting the intermediate layer is corroded because it does not have corrosion resistance in the corrosive environment. Or it may elute and contact resistance may become high. On the other hand, wet gold plating has been conventionally known. In this case, if the electrodeposition shape of the gold plating is granular and the amount of gold plating is small, a portion of the titanium substrate surface has a non-plated portion. The part which becomes becomes. Therefore, in order to uniformly plate the entire surface of the titanium base material with gold, it is necessary to increase the adhesion amount of Au.
In the case of the technique described in Patent Document 3, a base material obtained by clad stainless steel on both surfaces of a copper plate is coated with a resin, and it cannot be said that the corrosion resistance is excellent.

That is, the present invention has been made to solve the above-described problems, and a fuel cell separator material capable of forming a highly corrosion-resistant conductive film containing Au on the surface of a titanium substrate with high adhesion. And to provide a fuel cell stack.
In the present invention, the fuel cell refers to a polymer electrolyte fuel cell (PEFC), a direct methanol fuel cell (DMFC), a solid electrolyte fuel cell (SOFC), a phosphoric acid fuel cell (PAFC), a molten carbonate fuel cell ( MCFC).

As a result of various studies, the inventors have formed an intermediate layer containing Ti, O and a predetermined noble metal on the surface of the Ti base material, and formed an Au alloy layer or an Au single layer on the intermediate layer. It has been found that an Au (alloy) layer can be formed firmly and uniformly on Ti, and the corrosion resistance required for a fuel cell separator can be secured.
In order to achieve the above object, the separator material for a fuel cell of the present invention has at least one or more kinds of Au selected from the group consisting of Ru, Rh, Pd, Ir, Os and Pt on the surface of a Ti base material. An alloy layer of Au and a first component made of a more easily oxidizable noble metal or an Au single layer is formed, and Ti, O, and the first layer are formed between the alloy layer or the Au single layer and the Ti base material. An intermediate layer containing one component and less than 20% by mass of Au is present, and the alloy layer has a region of 1 nm or more in thickness and 50% by mass or more of Au from the outermost surface to the lower layer, The thickness from the surface toward the lower layer is 1 nm or more .

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 20% by mass or more.
It is preferable that the proportion of Au in the alloy layer increases from the lower layer side toward the upper layer side. When an Au single layer is formed on the surface of the alloy layer, good corrosion resistance is exhibited even when a fuel cell separator is used in a severe corrosive environment.
When the layer formed on the surface of the Ti base material is the alloy layer, the alloy layer includes, in place of Au, a second component made of an element different from the first component in the noble metal and Au. It may be made of an Au alloy.

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 fuel cell.

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

  According to the present invention, by forming an intermediate layer containing Ti, O, and a predetermined noble metal on the surface of the Ti base material, and forming an Au alloy layer or an Au single layer on the intermediate layer, an Au layer or The layer containing Au can be formed firmly and uniformly on Ti, and the corrosion resistance required for the fuel cell separator can be ensured.

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 may be 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.

<First Embodiment>
Hereinafter, the fuel cell separator material according to the first embodiment of the present invention will be described. As shown in FIG. 1, the fuel cell separator material according to the first embodiment has an intermediate layer 2a formed on the surface of a Ti base 2 and an alloy layer 6 formed on the intermediate layer 2a.

<Ti substrate>
The fuel cell separator material is required to have corrosion resistance, and the alloy layer (Au single layer) serving as the conductive film is required to have corrosion resistance and conductivity. For this reason, since a corrosion resistance is calculated | required for a base material, a titanium material is used.
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 and aluminum. By covering these surfaces with Ti, the corrosion resistance of stainless steel and aluminum having lower corrosion resistance than titanium can be improved. 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 the first component and gold, but considering the press forming into the separator shape, the shape of the Ti base material is a plate material. It is preferable that the thickness of the entire Ti base material is 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.

<Alloy layer>
An alloy layer 6 of Au and a first component made of a noble metal that is more oxidizable than at least one kind of Au selected from the group consisting of Ru, Rh, Pd, Ir, Os, and Pt is formed on the Ti substrate 2. It is formed. This Au alloy layer is for imparting Au characteristics (corrosion resistance, conductivity, decorativeness, etc.) to the Ti base material. From the potential-pH diagram, the noble metal is more oxidizable than Au, and using this property, 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 Pd is preferable because it is low in cost and easily forms an oxide.
The alloy layer can be confirmed by STEM analysis, which will be described later, and is a portion having a thickness of 1 nm or more at 50% by mass or more of Au from the outermost surface to the lower layer by STEM analysis, and a portion located above the following intermediate layer. Alloy layer. The thickness of the alloy layer is preferably 1 to 100 nm. If the thickness of the alloy layer is less than 1 nm, the corrosion resistance required for the fuel cell separator cannot be secured on the Ti base material. If the thickness of the alloy layer exceeds 100 nm, it may not be possible to save money and the cost may increase.
Further, in the 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 50% by mass, the corrosion resistance required for the fuel cell separator cannot be secured.

An Au single layer may be formed instead of the alloy layer 6. The Au single layer is a portion where the concentration of Au is almost 100% by STEM analysis, and the thickness of the Au single layer is required to be 1 nm or more.
Further, the alloy layer 6 may have a composition region (precious metal region) mainly composed of the first component on the intermediate layer side.

<Intermediate layer>
Between the alloy layer (or Au single layer) 6 and the Ti substrate 2, there is an intermediate layer 2a containing Ti, O and the first component and having less than 20% by mass of 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 noble 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.
The noble metal has higher corrosion resistance than other metals. 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, Ti, Zr, Hf, which are elements conventionally used for the intermediate layer, Compared to V, Nb, Ta, Cr, Mo, W, etc., the intermediate layer containing Ti, O and the first component has higher corrosion resistance, and an intermediate layer free from metal corrosion or elution can be formed.
On the other hand, it is preferable that the intermediate layer does not contain 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 20% by mass or more. In this case, when the cross section of the fuel cell separator material is analyzed by STEM (scanning transmission electron microscope), each of Ti and O contains 10% by mass or more and the first component contains 20% by mass or more, and Au contains 20% or more. A region containing at least mass% is 1 nm or more 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.
Here, the STEM analysis uses the EDS (Energy Dispersive X-ray Spectrometer) analyzer attached to the STEM device to specify the part (line) and element to be analyzed, and the concentration of the specified element in each part is determined by EDS. It is to detect. The elements to be specified are Au, the first component, O, and Ti. When the second component described later is used, the second component is added to the specification.

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 This is because the part less than 10% by mass is close to the alloy layer, and the part where O is less than 10% by mass does not form a sufficient oxide with the first component and Ti being O atoms. It is because it is thought that it does not function as a layer. 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.
In the STEM analysis, the distance of 1 nm in the thickness direction is the actual size of the scanning distance.

It is preferable to have a gradient composition in which the proportion of Au in the alloy layer increases from the lower layer side toward the upper layer side. Here, the ratio (mass%) of Au can be obtained by the above-described STEM analysis. The thickness of the alloy layer or the Au single layer is an actual size of the scanning distance in the STEM analysis.
When the alloy layer has a gradient composition, the ratio of the first oxidizable component is higher on the lower layer side of the alloy layer than that of Au, and the bond with the Ti substrate surface becomes stronger, while the upper layer side of the alloy layer is made of Au. Since the properties become stronger, the corrosion resistance is improved.

FIG. 2 shows an actual FE-TEM (electrolytic emission transmission electron microscope) image of a cross section of the fuel cell separator material according to the first embodiment.
It can be seen that the alloy layer 6 made of Pd and Au forms a uniform layer (black image portion in the figure). In addition, the composition at position C (outlined) of the alloy layer 6 in FIG. 2 is Pd: 43% by mass and Au: 57% by mass from EDX (energy dispersive X-ray fluorescence analysis). The composition was Pd: 32% by mass and Au: 68% by mass. That is, the Au concentration of the alloy layer increased from the lower layer side toward the upper layer side. The composition at position A indicates Ti, and the composition at position B indicates a Ti oxide film layer on the surface of the Ti substrate (detects Ti and O by EDX). However, EDX cannot determine whether this oxide film layer contains the first component (Pd).

<Manufacture of fuel cell separator materials>
As a method for forming an intermediate layer of a separator material for a fuel cell, a surface Ti oxide film is formed by sputtering the first component on the base material without removing the surface Ti oxide film of the Ti base material. The first component is bonded to O in the middle to form an intermediate layer. Moreover, after removing the surface Ti oxide film of the Ti base material 2, the first component may be formed by sputtering using the oxide of the first component as a target, or after removing the surface Ti oxide film of the Ti base material 2. The intermediate layer can also be formed by sputtering as a target in an oxidizing atmosphere.
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 of the intermediate layer is contained in the intermediate layer by Au atoms entering the intermediate layer by Au sputtering for forming the following alloy layer. Alternatively, an alloy target including the first component and Au may be used to form a sputter film on the surface of the Ti base material.

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

<Second Embodiment>
Next, a fuel cell separator material according to a second embodiment of the present invention will be described. As shown in FIG. 4, in the fuel cell separator material according to the second embodiment, the noble metal layer 4 is formed on the surface of the Ti base 2 via the intermediate layer 2 a, and the alloy layer 6 is formed on the surface of the noble metal layer 4. Is formed. Since the Ti base material 2 and the alloy layer 6 are the same as those in the first embodiment, description thereof is omitted.
The noble metal layer 4 is mainly composed of the above-mentioned noble metal (preferably the same as the first component of the intermediate layer), and since the first component is more easily oxidized than Au, the noble metal layer 4 has a high bondability with the intermediate layer 2a which is an oxide layer. Compared with the case where 4 is not provided, the adhesion between the alloy layer 6 and the Ti substrate 2 (intermediate layer) is improved.
The noble metal layer 4 can be appropriately formed by changing sputtering conditions (sputtering time, output) and the like.
The noble metal in the noble metal layer 4 and the first component in the alloy layer 6 may be the same element or different elements. However, when the same element is used, the manufacturing is simplified.

<Third Embodiment>
Next, a fuel cell separator material according to a third embodiment of the present invention will be described. As shown in FIG. 5, the separator material for a fuel cell according to the third embodiment has an alloy layer 6 formed on the surface of a Ti base 2 via an intermediate layer 2a, and an Au single layer on the surface of the alloy layer 6. 8 is formed. Since the Ti base material 2 and the alloy layer 6 are the same as those in the first embodiment, description thereof is omitted.
The Au single layer 8 can be appropriately formed by changing sputtering conditions (sputtering time, output) and the like.

  The layer structure of the second and third embodiments is combined to form a layer structure in which the noble metal layer 4, the alloy layer 6, and the Au single layer 8 are formed in this order on the surface of the Ti base 2 via the intermediate layer 2a. Also good.

  Instead of Au, an Au alloy of Au and a second component made of an element different from the first component of the noble metal may be used. In this case, the intermediate layer is composed of Ti, O and the first component, while the alloy layer is composed of the first component, the second component and Au.

  According to the separator material for a fuel cell according to the embodiment of the present invention, an Au (alloy) layer can be formed firmly and uniformly on Ti, and this layer has conductivity and corrosion resistance. Suitable as a separator material. In addition, according to the embodiment of the present invention, if an Au (alloy) layer is formed by sputtering, this layer becomes a uniform layer, so that the surface becomes smoother than wet gold plating, and Au is wasted. There is an advantage that it is not necessary.

<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. 6 is a cross-sectional view of a single cell of a stacked (active) fuel cell. In FIG. 6, current collector plates 140A and 140B are 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. 6, an anode electrode 40 and a cathode electrode 60 are laminated on both sides of the solid polymer electrolyte membrane 20 to constitute 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

  Next, the structure of the separator 10 will be described with reference to the plan view 7. 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 with the direction from the upper side to the lower side of the separator 10 (up and down direction in FIG. 7) 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 8.
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. 8 along the linear 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 path groove 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. 8) 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. Similarly, the gas flow is folded back in the vicinity of the partition member 12e4, and after being along the straight flow path groove 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. 6 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. 9 shows an example of a cross-sectional view of a single cell of a planar (passive type) fuel cell. In FIG. 6, current collector plates 140A and 140B are 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. 9, since the configuration of the MEA 80 is the same as that of the fuel cell of FIG. 6, the same reference numerals are given and description thereof is omitted (in FIG. 9, the description of the gas diffusion films 90A and 90B is omitted. Gas diffusion films 90A and 90B may be included).

In FIG. 9, 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. 10 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. 9, oxygen comes into contact with the cathode electrode 60 side of the MEA 80 through the hole 100 h of the separator 100 and a reaction occurs. On the other hand, when methanol is allowed to flow from the lower side of FIG. 9, the methanol comes into contact with the anode electrode 40 side of the MEA 80 through the hole 100h of the separator 100, and a reaction occurs. Methanol is supplied from a tank (methanol cartridge) 200 in the lower part of FIG.
The planar (passive) fuel cell shown in FIG. 9 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 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 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 already described with reference to FIGS. 6 and 9, but is not limited thereto.

<Sample preparation>
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 6 nm was formed on the surface of the Ti substrate in advance. did.
Further, in some examples, an industrial pure stainless steel material (SUS316L) having a thickness of 100 μm was coated with Ti having a predetermined thickness shown in Tables 1 and 2 (Ti coating material). The Ti coating was performed by vacuum vapor deposition using an electron beam vapor deposition apparatus (manufactured by ULVAC, MB05-1006).

Next, Pd (noble metal film) was formed on the surface of the titanium oxide layer of the Ti base material using a sputtering method so as to have a target thickness of 1 nm. Pure Pd was used for the target. Next, Au was deposited using a sputtering method so as to have a target thickness of 1 nm. Pure Au was used for the target.
The target thickness was determined as follows. First, an object (for example, Pd) is formed in advance on a titanium substrate by sputtering, and the actual thickness is measured by a fluorescent X-ray film thickness meter (SEA5100 manufactured by Seiko Instruments, collimator 0.1 mmΦ), and the sputtering rate under this sputtering condition (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 Pd 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>
By observing an actual FE-TEM (electrolytic emission transmission electron microscope) image of the cross section of the obtained sample, designating the position where EDX analysis is desired in the image, and performing EDX analysis of that portion, The composition of each layer was analyzed.
As an FE-TEM apparatus, an HF-2000 FE-TEM manufactured by Hitachi, Ltd. was used, and observation was performed at an acceleration voltage of 200 kV, a magnification of 100,000 times, and a magnification of 700,000 times. Moreover, the EDX apparatus analyzed using the EDAX Genesis series attached to the said FE-TEM apparatus in the analysis area of 1 nm.
FIG. 2 shows a cross-sectional FE-TEM of the sample. It can be seen that the alloy layer 6 made of Pd and Au forms a uniform layer. Further, the composition at position C of the alloy layer 6 in FIG. 2 is EDX to Pd: 43 mass%, Au: 57 mass%, and the composition at position D of the alloy layer 6 is Pd: 32 mass%, Au: 68 mass%. Met. That is, the Au concentration of the alloy layer increased from the lower layer side toward the upper layer side. In addition, the composition of the position A showed Ti, and the composition of the position B showed the Ti oxide film layer (or intermediate layer) on the Ti base material surface.
11 shows an EDX analysis chart at position A, and FIG. 12 shows an EDX analysis chart and composition analysis results at position C.

Moreover, the cross section near the Ti base material surface of the sample was analyzed by STEM (scanning transmission electron microscope), and the concentrations of Ti, O, and Pd were detected. As the STEM, an HD-2000 STEM manufactured by Hitachi, Ltd. was used, and measurement was performed with an acceleration voltage of 200 kV, a magnification of 900,000 times, and an n number of 3 fields of view.
In addition, the concentration detection by STEM analyzed the density | concentration (mass%) of each element by excluding carbon from a detection element and making the designated element total 100 mass%. In the STEM analysis, the distance of 1 nm in the thickness direction is the distance on the horizontal axis of the chart (FIG. 3) by the STEM analysis.
Similarly, the cross section on the outermost surface side of the sample was analyzed by STEM.

FIG. 3 shows an actual STEM image of the sample cross section.
It can be seen that the surface of the Ti substrate 2 contains 10% by mass or more of Ti and O, 20% by mass or more of Pd, and 1 nm or more of the intermediate layer 2a having less than 20% by mass of Au. .
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 16 were produced by changing the target thicknesses of the Pd film and Au film at the time of sputtering to a titanium base material (pure Ti, Ti coating material).
As Comparative Example 17, a 50 nm Au layer was formed on the surface of the Ti base material by wet plating instead of sputtering. In wet plating, the substrate was dipped and degreased, washed with water, pickled, washed with water, activated, and washed with water, followed by gold plating, followed by washing with water and heat treatment.
As Comparative Examples 18 and 19, only an Au film and a Pd film were formed during sputtering, respectively.
As Comparative Example 20, a Pd—Au alloy (Pd 70 mass%, Au 30 mass%) was used instead of sputtering the Pd film and Au film separately. As Comparative Example 21, a Pd—Au alloy (Pd 50 mass%, Au 50 mass%) was used instead of sputtering the Pd film and Au film separately. As Comparative Example 22, a Pd—Au alloy (Pd 30 mass%, Au 70 mass%) was used instead of sputtering the Pd film and Au film separately.
As Comparative Example 23, the target thickness of the Pd film during sputtering was reduced to 0.5 nm. As Comparative Example 24, the target thickness of the Au film during sputtering was reduced to 0.5 nm.
As Comparative Example 25, sputtering was performed on a Ti coating material (Ti thickness: 1 nm) with a target thickness of Pd of 5 nm and a target thickness of Au of 10 nm.

<Evaluation>
The following evaluation was performed for each sample.
A. Adhesion After marking the grid of the grid at 1 mm intervals on the outermost alloy layer of each sample, apply adhesive tape, and then bend each specimen 180 ° to return it to its original state. A peeling test was conducted to peel off rapidly and strongly.
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. Film formation shape FE-TEM image of the cross section of each sample is taken, and when the uneven structure where particles of several to several hundred nm are gathered is observed on the surface, it is granular, and the surface is smoother than granular Layered.

C. 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 Au plated surface of the Cu / Ni / Au plate is carbon paper. It arranged so that it might touch.
Further, a Teflon (registered trademark) plate was disposed 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 plate with a load cell. In this state, when a constant current having 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 corrosion resistance test in which the sample was immersed in an aqueous solution under the following four conditions.
Condition 1: sulfuric acid aqueous solution (bath temperature 80 ° C., concentration 0.5 g / L, immersion time 240 hours)
Condition 2: Aqueous methanol solution A (bath temperature 80 ° C., concentration 400 cc / L, immersion time 240 hours)
Condition 3: methanol aqueous solution B (bath temperature 60 ° C., concentration 100%, immersion time 240 hours)
Condition 4: Formic acid aqueous solution A (bath temperature 80 ° C., concentration 1 g / L, immersion time 240 hours)
Condition 5: Formic acid aqueous solution B (bath temperature 80 ° C., concentration 9 g / L, immersion time 240 hours)
In the case of DMFC, conditions 2 to 5 are added to condition 1 (normal solid polymer fuel cell corrosion resistance test conditions), and there are more corrosion resistance test environments to be evaluated than normal solid polymer fuel cells. .
Typical characteristics required for fuel cell separators are low contact resistance (10 mΩ · cm ^{2 or more} ), corrosion resistance in the environment of use (low contact resistance after corrosion test, no harmful ion elution) There are two.

  Tables 1 to 3 show the results. In Tables 1 to 3, the thickness of the intermediate layer and the thickness of the outermost layer are both average values obtained by performing STEM analysis at three locations. Further, the thickness of the intermediate layer and the thickness of the outermost layer each have a width of ± 0.25 nm. For example, when the intermediate layer is 1.0 nm, the average value is 0.75 nm or more and less than 1.25 nm. . However, when the thickness is 10 nm or more, the width is ± 0.5 nm.

As is apparent from Tables 1 to 3, Ti and O are each contained in an amount of 10% by mass or more, Pd is contained in an amount of 20% by mass or more, and Au is 20% by mass between the alloy layer and the Ti base material. In Examples 1 to 13 in which an intermediate layer of less than 1 nm was present, the adhesion of each layer was excellent, and the alloy layer or Au layer (outermost layer) formed by sputtering became a smooth layer. Furthermore, the contact resistance of the sample did not change before and after the corrosion resistance test, and the corrosion resistance and conductivity were excellent. In addition, in Examples 14 to 16 using a Ti coating material having a thickness of 10 nm or more instead of a pure Ti base material, corrosion resistance and conductivity equivalent to those of other examples were obtained.
In each of Examples 1 to 16, the thickness of the region of 50% by mass or more of Au from the outermost surface toward the lower layer was 1 nm or more.

In the case of Comparative Example 17 in which the Au layer was formed by wet plating, the outermost layer became granular, and the amount of Au used increased.
In the case of Comparative Example 18 in which only Au was sputtered, the adhesion was deteriorated without forming the intermediate layer. On the other hand, in the case of Comparative Example 19 in which only Pd was sputtered, the outermost layer did not contain Au, and the contact resistance significantly increased after the corrosion resistance test. This is considered because corrosion resistance deteriorated because the outermost layer did not contain Au.
In the case of Comparative Example 20 in which sputtering was performed using a Pd—Au alloy (Pd 70% by mass) as a target, the contact resistance was significantly increased after the corrosion resistance test. This is presumably because the layer containing 50 mass% or more of Au in the outermost layer was not formed because the proportion of Au in the Pd—Au alloy was small, and the corrosion resistance was deteriorated.

In the case of Comparative Example 21 in which sputtering was performed using a Pd—Au alloy (Pd 50 mass%) as a target and Comparative Example 22 in which sputtering was performed using a Pd—Au alloy (Pd 30 mass%) as a target, the thickness of the intermediate layer was less than 1 nm. Some of them did not have sufficient adhesion.
This is presumably because the intermediate layer was not sufficiently formed because of the small proportion of Pd in the Pd—Au alloy.
In the case of Comparative Example 23 in which the target thickness of the Pd film was reduced and sputtered, the thickness of the intermediate layer was less than 1 nm, and the adhesion was not sufficient.

In the case of Comparative Example 24 in which the target thickness of the Au film was reduced and sputtered, the thickness of Au 50 mass% or more from the outermost surface to the lower layer was as thin as less than 1 nm, and the contact resistance was significantly increased after the corrosion resistance test.
In addition, in the case of Comparative Example 25 using a Ti coating material having a thickness of 1 nm instead of a pure Ti base material, the stainless steel base material was corroded because the Ti film thickness was thin, and the contact resistance was greatly increased after the corrosion resistance test.

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 cross-sectional FE-TEM image of the separator material for fuel cells which concerns on embodiment of this invention. It is a figure which shows the STEM analysis result of the cross section of the separator material for fuel cells which concerns on embodiment of this invention. It is a schematic diagram which shows the structure of the separator material for fuel cells which concerns on another embodiment of this invention. It is a schematic diagram which shows the structure of the separator material for fuel cells which concerns on another embodiment of this invention. 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. It is a figure which shows the EDX analysis chart in the position A of the alloy layer of FIG. It is a figure which shows the EDX analysis chart in the position C of the alloy layer of FIG.

Explanation of symbols

2 Ti substrate 2a Intermediate layer 4 Noble metal layer 6 Alloy layer 8 Au single layer 2 Solid polymer electrolyte membrane 4, 6 Electrode 8 Membrane electrode assembly 10, 100 Separator 10L, 10LB (Gas) flow channel 10L1, 10LB1 Flow channel 10L2, 10LB2 End of channel groove 12, 12B Gasket 12c, 12d Gasket inner edge 12e1-12e4 Partition member 12eb1-12eb4 Gasket channel 20 Solid polymer electrolyte membrane 40 Anode electrode 60 Cathode electrode 80 Membrane electrode assembly (MEA) )
100h hole (for separator)

Claims (9)

An alloy layer of Au and a first component made of a noble metal more easily oxidized than Au selected from the group consisting of Ru, Rh, Pd, Ir, Os and Pt on the surface of the Ti substrate, or Au single layer is formed,
Between the alloy layer or the Au single layer and the Ti substrate, there is an intermediate layer containing Ti, O and the first component, and less than 20% by mass of Au,
In the alloy layer , there is a region having a thickness of 1 nm or more and Au of 50% by mass or more from the outermost surface to the lower layer, or in the Au single layer, the thickness from the outermost surface to the lower layer is 1 nm or more. . 2. The fuel cell separator material according to claim 1, 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 separator material according to claim 1 or 2, wherein a ratio of Au in the alloy layer increases from a lower layer side toward an upper layer side. The fuel cell separator material according to claim 1, wherein an Au single layer is formed on a surface of the alloy layer. When the layer formed on the surface of the Ti base material is the alloy layer, the alloy layer includes, in place of Au, a second component made of an element different from the first component in the noble metal and Au. the fuel cell separator material according to any one of Ru Au alloy Tona claims 1-4. The fuel cell separator material according to any one of claims 1 to 5, 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 fuel cell separator material according to any one of claims 1 to 6, which is used in a polymer electrolyte fuel cell. The fuel cell separator material according to claim 7, which is used in a direct methanol fuel cell. A fuel cell stack using the fuel cell separator material according to claim 1.