JP7632192B2 - Fuel cell separators - Google Patents

Description

The present invention relates to a separator for a fuel cell.

A fuel cell has a stack structure in which a certain number of single cells that generate electromotive force by the reaction of fuel gas (hydrogen) and oxidant gas (oxygen) are stacked. A single cell has a membrane electrode assembly with anode and cathode electrode layers (catalyst layer and gas diffusion layer) on both sides of an electrolyte membrane, and separators arranged on both sides of the membrane electrode assembly.

Fuel cell separators function to electrically connect single cells in series and also function as partitions that isolate fuel gas, oxidant gas, and cooling water from each other.

Various research projects are being conducted on fuel cell separators and fuel cell cells that use such separators.

For example, Patent Document 1 discloses a separator for a fuel cell, which comprises a substrate made of Ti (titanium), a TiOx layer formed on the surface of the substrate, and a carbon-containing layer disposed on at least a portion of the surface of the TiOx layer, which suppresses cracking of the TiOx layer and has electrical conductivity.

Patent document 2 discloses a fuel cell having a separator, the separator having a surface that has been NC-treated, the peripheral portion of the separator having a larger amount of carbon black than the inner portion of the separator, and at least a portion of the peripheral portion being bonded to a resin having a polar group.

Patent document 3 discloses a separator made of a separator material including a stainless steel or iron substrate, a titanium layer on the substrate surface, and a mixed layer of conductive particles and titanium oxide on the titanium layer surface.

JP 2015-232937 A JP 2019-192507 A JP 2021-068539 A

In general, a reactant gas flow path for flowing reactant gas within a single cell is formed on one side of a fuel cell separator, and a cooling medium flow path for flowing a cooling medium within the single cell is formed on the other side. In addition, a reactant gas manifold opening that functions as an inlet and outlet for the reactant gas, and a cooling medium manifold opening that functions as an inlet and outlet for the cooling medium flow path are formed on the periphery of the fuel cell separator. Furthermore, sealing members are provided around the reactant gas flow path, the cooling medium flow path, the reactant gas manifold opening, and the cooling medium manifold opening as appropriate to prevent leakage of each fluid.

Fuel cell separators need to be bonded to other components, such as resin sheets or gaskets that serve as sealing members to prevent leakage of fluids, such as reactive gases _H2 and _O2 , and cooling water, which serves as a cooling medium. Therefore, the adhesion and sealing reliability between the fuel cell separator and other components, such as adhesives used to bond the separator to sealing members, are important factors in determining the characteristics of the fuel cell separator.

In addition, the power generating element clamping portion of the fuel cell separator that clamps the power generating element is required to have low contact resistance, i.e., high electrical conductivity, to conduct the electricity generated by the power generating element, and also to be corrosion resistant.

Therefore, in order to impart these characteristics to fuel cell separators, a carbon layer/titanium layer is formed by physical vapor deposition (PVD) in an area including the power generator clamping portion that clamps the power generator in the fuel cell separator, with a mask covering the rest of the area. The corrosion resistance of the fuel cell separator is ensured by the titanium layer, and the low contact resistance of the fuel cell separator is ensured by the carbon layer.

However, while conventional technology mentions the characteristics of each carbon/titanium layer, there is nothing that specifies the characteristics of each layer for each part of the separator in order to create a product with excellent productivity, and a fuel cell separator that can be manufactured at low cost while retaining excellent characteristics has not yet been revealed.

The present invention therefore aims to provide a low-cost fuel cell separator that has sufficient corrosion resistance throughout the separator, low contact resistance in the power generator clamping section, and improved adhesion to the seal member in the seal member placement section (i.e., adhesion between the seal member placement section and the adhesive used to bond the seal member).

(Corrosion resistance)
The power generator clamping portion of the fuel cell separator, which clamps the power generator, and the seal member arrangement portion, which is provided on the outer periphery of the power generator clamping portion and in which a seal member is arranged to seal the power generator clamping portion, require a titanium layer because excellent corrosion resistance is required. Therefore, by providing a titanium layer on each of the power generator clamping portion and the seal member arrangement portion, it is possible to impart just the right amount of corrosion resistance to the entire fuel cell separator.

(Low contact resistance, adhesion and sealing reliability)
In fuel cell separators, the power generator sandwiching portion that sandwiches the power generator requires low contact resistance, and therefore a carbon layer is necessary. On the other hand, in the seal member disposition portion that is provided on the outer periphery of the power generator sandwiching portion and that disposes a seal member that seals the power generator sandwiching portion, if a carbon layer is present in the same manner as in the power generator sandwiching portion, adhesion to the seal member and sealing reliability will decrease. Therefore, in fuel cell separators, by providing a carbon layer in the power generator sandwiching portion but not providing a carbon layer in the seal member disposition portion, it is possible to provide the right amount of low contact resistance, adhesion, and sealing reliability according to the requirements of each portion.

The inventors have investigated various means for solving the above problems, and have found that a fuel cell separator having a power generator clamping portion that clamps a power generator and a seal member arrangement portion that is provided on the outer periphery of the power generator clamping portion and that has a seal member that seals the power generator clamping portion can be manufactured by forming a titanium layer in the area that will become the power generator clamping portion and the seal member arrangement portion, and then forming a carbon layer in the area that will become the power generator clamping portion where the titanium layer is formed, thereby making it possible to manufacture at low cost a fuel cell separator that has sufficient corrosion resistance throughout the separator, low contact resistance, i.e., high conductivity, in the power generator clamping portion, and improved adhesion to the seal member in the seal member arrangement portion, and thus completed the present invention.

That is, the gist of the present invention is as follows.
(1) A fuel cell separator having a power generating unit clamping portion that clamps a power generating unit, and a seal member disposition portion that is provided on an outer periphery of the power generating unit clamping portion and that disposes a seal member that seals the power generating unit clamping portion,
the power generating body holding portion includes a metal substrate, a titanium layer formed on a surface of the metal substrate, and a carbon layer formed on the titanium layer;
the seal member disposition portion includes a metal substrate and a titanium layer formed on a surface of the metal substrate;
A fuel cell separator, in which a titanium layer is exposed on the surface at a portion where a seal member is to be disposed.

The present invention provides a low-cost fuel cell separator that has sufficient corrosion resistance throughout the separator, low contact resistance in the power generator clamping area, and improved adhesion to the seal member in the seal member placement area.

1A and 1B are schematic diagrams showing A) suitable examples and B) unsuitable examples of a method for measuring the surface of a separator having a flow path shape by X-ray diffraction analysis. 1 is a schematic diagram of Miller index planes of the (100) plane, (002) plane, and (101) plane originating from titanium, and the shape and cross-sectional shape formed. 1 is a diagram showing a schematic diagram of an embodiment of a fuel cell separator according to the present invention; 1 is a scheme showing a method for producing a fuel cell separator in an embodiment. FIG. 1 is a diagram showing an outline of a test method for hot water peel strength (maximum peel strength in hot water at 95° C.). 1 is a graph showing the relationship between the surface titanium ratio and hot water peel strength in a seal member-disposed portion of a fuel cell separator.

Preferred embodiments of the present invention will now be described in detail.
In this specification, the features of the present invention will be described with reference to the drawings as appropriate. In the drawings, the dimensions and shapes of each part are exaggerated for clarity, and the actual dimensions and shapes are not accurately depicted. Therefore, the technical scope of the present invention is not limited to the dimensions and shapes of each part shown in these drawings. Note that the fuel cell separator of the present invention is not limited to the following embodiments, and can be embodied in various forms with modifications and improvements that can be made by those skilled in the art, without departing from the gist of the present invention.

The present invention relates to a fuel cell separator having a power generator clamping section that clamps a power generator and a seal member arrangement section that is provided on the outer periphery of the power generator clamping section and that arranges a seal member that seals the power generator clamping section, in which the power generator clamping section includes a metal substrate, a titanium layer formed on the surface of the metal substrate, and a carbon layer formed on the titanium layer, and the seal member arrangement section includes a metal substrate and a titanium layer formed on the surface of the metal substrate, and in the seal member arrangement section, the titanium layer is exposed on the surface.

In the present invention, the metal substrate is a metal substrate known in the art, such as, but not limited to, a metal (including an alloy), for example, stainless steel (SUS: an alloy of iron, chromium, and nickel). The metal substrate is preferably stainless steel, for example, SUS304.

By choosing stainless steel as the metal substrate for fuel cell separators, raw material costs can be reduced.

The thickness of the metal substrate is not limited, but is usually 0.05 mm to 0.2 mm, preferably 0.08 mm to 0.12 mm.

By keeping the thickness of the metal substrate within the above range, raw material costs can be reduced.

The metal substrate usually has an uneven shape for delivering fluids such as reaction gases _H2 and _O2 and cooling water as a cooling medium. The difference between the unevenness of the uneven shape of the metal substrate is usually 10 μm to 500 μm, excluding the thickness of the metal substrate. In the fuel cell separator of the present invention, the thicknesses of the titanium layer and the carbon layer formed on the metal substrate are thinner than the thickness of the metal substrate, so the shape of the fuel cell separator depends on the uneven shape of the metal substrate.

The thickness of the titanium layer formed on the surface of the metal substrate in the power generator clamping portion and the sealing member arrangement portion is not limited, but is usually 50 nm to 1000 nm, preferably 50 nm to 500 nm, in average thickness. The average thickness of the titanium layer can be measured, for example, by cross-sectional TEM observation.

By setting the upper limit of the thickness of the titanium layer as described above, it is possible to reduce the amount of titanium used, and it is also possible to prevent the film stress caused by the deposition of the titanium layer from becoming too large, thereby suppressing the occurrence of cracks in the titanium layer and deformation of the substrate on which the titanium layer is laminated, such as a stainless steel substrate on which a titanium layer is laminated.

By setting the lower limit of the thickness of the titanium layer as described above, sufficient corrosion resistance can be ensured.

In the titanium layer of the present invention, the ratio (orientation ratio) of the (100) plane to the sum of the peak intensities of the (100) plane, (002) plane, and (101) plane derived from titanium in an X-ray diffraction analysis of the separator surface, divided by their relative intensities, is usually 16.9% or more, and preferably 20.0% or more.

Here, conventional measurement methods can be used as the measurement method for the X-ray diffraction analysis of the separator surface. Therefore, in the measurement method for the X-ray diffraction analysis of the separator surface, the separator surface to be measured is a portion suitable for measurement by X-ray diffraction analysis (a portion without curvature, for example a flat portion, or a direction without curvature).

For example, when the separator to be measured has a flow path shape, the incident X-rays are incident on the separator so that the diffracted X-rays do not contain information about the curvature of the separator flow path. As an example, FIG. 1 shows A) an appropriate example and B) an inappropriate example of a measurement method for X-ray diffraction analysis of a separator surface having a flow path shape. In FIG. 1, S indicates a separator flow path shape cross section. In FIG. 1A, the X-rays are incident on the convex portion (top portion) of the separator in the y-axis direction (direction perpendicular to the flow path direction), and the incident X-rays are diffracted in the y-axis direction at the separator. In the case of FIG. 1A, the incident X-rays are incident on the convex portion of the separator in a direction perpendicular to the flow path direction, so the obtained diffracted X-rays do not include the influence of the curvature based on the separator flow path shape. On the other hand, in FIG. 1B, the X-rays are incident on the convex portion (top portion) of the separator in the x-axis direction (direction parallel to the flow path direction), and the incident X-rays are diffracted in the x-axis direction at the separator. In the case of B) in FIG. 1, the incident X-rays are incident on the convex part of the separator in a direction parallel to the flow path direction, so the obtained diffracted X-rays may include the influence of the curvature based on the separator's flow path shape. Therefore, in the measurement method of X-ray diffraction analysis of the separator surface in this invention, when the separator has a flow path shape, the measurement method shown in A) in FIG. 1 is used.

The relative intensity of each lattice plane derived from titanium means the theoretical diffraction intensity (theoretical value of diffraction intensity), and is a general theoretical value that can be calculated from the crystal structure of titanium. In other words, the relative intensity of the (100) plane derived from titanium is the diffraction intensity theoretically obtained when X-rays are irradiated to the (100) plane, the relative intensity of the (002) plane derived from titanium is the diffraction intensity theoretically obtained when X-rays are irradiated to the (002) plane, and the relative intensity of the (101) plane derived from titanium is the diffraction intensity theoretically obtained when X-rays are irradiated to the (101) plane. Here, the X-rays irradiated to each lattice plane are the same X-rays. Therefore, the relative intensity of each lattice plane derived from titanium can also be expressed as the ratio of the theoretical diffraction intensity of each lattice plane obtained when the same X-rays are irradiated to each lattice plane (i.e., the theoretical diffraction intensity of the (100) plane: the theoretical diffraction intensity of the (002) plane: the theoretical diffraction intensity of the (101) plane). The relative intensity of each lattice plane originating from titanium is the theoretical diffraction intensity when the same X-ray is irradiated, and is therefore a characteristic value that is basically independent of the XRD device or type of X-ray used, as long as the XRD measurements are performed using the same X-ray.

Therefore, for example, when the relative intensity of the (101) plane originating from titanium is taken as 100, the relative intensity of the (100) plane originating from titanium can be calculated as 25, and the relative intensity of the (002) plane originating from titanium can be calculated as 30 (i.e., theoretical diffraction intensity of the (100) plane: theoretical diffraction intensity of the (002) plane: theoretical diffraction intensity of the (101) plane = 25:30:100).

From the above, the ratio (orientation ratio) of the (100) plane to the sum of the peak intensities of the (100), (002), and (101) planes derived from titanium divided by their relative intensities is expressed by the following formula.
Proportion of (100) plane (orientation ratio) (%)
= {(Peak intensity of (100) plane/relative intensity of (100) plane)/[(Peak intensity of (100) plane/relative intensity of (100) plane)+(Peak intensity of (002) plane/relative intensity of (002) plane)+(Peak intensity of (101) plane/relative intensity of (101) plane)]} × 100

Furthermore, in a titanium layer containing titanium formed on the surface of a metal substrate, the ratio (orientation ratio) of the titanium-derived (002) plane to the total value obtained by dividing the peak intensities of the titanium-derived (100) plane, (002) plane, and (101) plane by their relative intensities in an X-ray diffraction analysis of the separator surface is usually 61.0% or less, and preferably 40.0% or less.

The ratio (orientation ratio) of the (002) plane originating from titanium to the sum of the peak intensities of the (100), (002), and (101) planes originating from titanium divided by their relative intensities is expressed by the following formula, as described above.
Proportion of (002) plane (orientation ratio) (%)
= {(Peak intensity of (002) plane/relative intensity of (002) plane)/[(Peak intensity of (100) plane/relative intensity of (100) plane)+(Peak intensity of (002) plane/relative intensity of (002) plane)+(Peak intensity of (101) plane/relative intensity of (101) plane)]}×100

In the titanium layer formed on the surface of the metal substrate, the ratio (orientation ratio) of the (100) and/or (002) planes to the sum of the peak intensities of the (100), (002), and (101) planes derived from titanium in an X-ray diffraction analysis of the separator surface divided by their relative intensities is within the above range, resulting in a fuel cell separator with high corrosion resistance. The corrosion resistance can be confirmed by the amount of iron (Fe) eluted in a elution test of the fuel cell separator.

Figure 2 shows the Miller index planes of the (100), (002), and (101) planes derived from titanium, as well as a schematic diagram of the shape and cross-sectional shape formed. From Figure 2, an increase in the proportion of the (100) plane derived from titanium means that the proportion of titanium having a flat structure in the titanium layer increases, and a decrease in the proportion of the (002) plane derived from titanium means that the proportion of titanium having a columnar structure in the titanium layer decreases.

The titanium-containing titanium layer formed on the surface of the metal substrate may contain other components, such as C, N, H, O, Ar, Ag, Mo, Rh, Pd, Pt, Pb, Ru, Al, Ni, and Co. It is preferable that the titanium-containing titanium layer is a titanium layer made of titanium.

Corrosion resistance is ensured by the titanium-containing layer formed on the surface of the metal substrate.

In the power generating body sandwiching portion of the fuel cell separator of the present invention, the thickness of the carbon layer formed on the titanium layer surface is not limited, but the average thickness is usually 10 nm to 300 nm, preferably 10 nm to 150 nm. The average thickness of the carbon layer can be measured, for example, by cross-sectional TEM observation.

By setting the thickness of the carbon layer formed on the surface of the titanium layer in the power generator clamping portion within the above range, it is possible to ensure low contact resistance in the power generator clamping portion, i.e., high conductivity.

In the fuel cell separator of the present invention, the titanium layer is exposed on the surface in the area where the seal member is disposed.

The surface titanium ratio in the area where the seal member is disposed is usually 0.5 atomic percent or more, preferably 1.0 atomic percent or more, and more preferably 1.5 atomic percent or more.

The surface titanium ratio in the area where the seal member is located can be measured using X-ray photoelectron spectroscopy (XPS).

By exposing the titanium layer to the surface in the sealing member placement area, it is possible to ensure adhesion and sealing reliability with other components in the sealing member placement area, such as adhesives used to bond the sealing member.

Figure 3 shows a schematic diagram of an example of a fuel cell separator according to the present invention. As shown in Figure 3, the fuel cell separator according to the present invention has a power generator clamping section 1 that clamps a power generator, and a seal member arrangement section 2 that is provided on the outer periphery of the power generator clamping section 1 and that arranges a seal member that seals the power generator clamping section 1. Here, the power generator clamping section 1 includes a metal substrate 3, a titanium layer 4 formed on the surface of the metal substrate 3, and a carbon layer 5 formed on the titanium layer 4. The seal member arrangement section 2 includes a metal substrate 3 and a titanium layer 4 formed on the surface of the metal substrate 3, and the titanium layer 4 is exposed on the surface of the seal member arrangement section 2.

The fuel cell separator in this invention is a component of a fuel cell (single cell) and is arranged on both sides of a membrane electrode assembly (electrolyte membrane, anode and cathode electrode layers arranged on both sides of the electrolyte membrane).

The fuel cell separator of the present invention is bonded, for example with an adhesive, to components of a fuel cell known in the art, such as a membrane electrode assembly and a sealing member, to produce a fuel cell.

Fuel cells manufactured using the fuel cell separator of the present invention can be used in various electrochemical devices such as solid polymer fuel cells.

The fuel cell separator of the present invention can be manufactured by a method including the steps of (i) preparing a metal substrate, (ii) depositing titanium on the surface of the metal substrate to form a titanium layer, and (iii) depositing carbon in the region of the metal substrate on which the titanium layer is deposited that will become the power generator clamping portion to form a carbon layer.

(i) Step of Preparing Metal Substrate First, a metal substrate that will be the material of the fuel cell separator is prepared.

As the metal substrate, any metal substrate known in the art can be used, for example, but not limited to, a roughly rectangular plate made of metal (including alloys). As the metal substrate that is the material of the separator, a roughly rectangular plate made of stainless steel (SUS: alloy of iron, chromium, and nickel), for example SUS304, is preferred.

By selecting a metal substrate as the material for the fuel cell separator, a titanium layer and a carbon layer can be formed on the metal substrate by PVD, as described below, and by selecting stainless steel as the metal substrate, the cost of manufacturing the separator can be reduced.

It is preferable to use a metal substrate that has already been pressed into the shape of the final fuel cell separator.

By using a pre-pressed metal substrate as the metal substrate, a fuel cell separator can be obtained without further pressing after the titanium layer and carbon layer are formed.

(ii) Step of forming a titanium layer by depositing titanium on the surface of the metal substrate The titanium layer can be produced by depositing a titanium film on the metal substrate using a sputtering method under conditions in which (a) the UBM coil current value or (b) the bias voltage value applied to the metal substrate is controlled within a certain range.

The sputtering method is a type of physical vapor deposition method, and an example of the sputtering method is the unbalanced magnetron sputtering method (UBMS).

The unbalanced magnetron sputtering (UBMS) method is a sputtering method that enhances plasma exposure to the substrate by intentionally making the magnetic field of the sputtering cathode unbalanced, making it possible to form dense thin films.

In the sputtering method, (a) the UBM coil current value that controls the plasma intensity is typically 6.5 A to 10 A, and preferably 7.0 A to 9.0 A.

By setting the UBM coil current value in the sputtering method within the above range, the titanium particles, which are the film-forming particles, can reach the metal substrate in a high-energy state. Therefore, even if a metal substrate having an uneven shape is used as the metal substrate, a highly corrosion-resistant fuel cell separator having a densified titanium layer in all of the convex (top) and concave (bottom) parts of the metal substrate, and the diagonal parts between the convex and concave parts, can be obtained stably. In particular, a highly corrosion-resistant fuel cell separator having a ratio (orientation ratio) of the (100) and/or (002) planes to the total value obtained by dividing the peak intensities of the (100) plane, (002) plane, and (101) planes derived from titanium by their relative intensities in the X-ray diffraction analysis of the separator surface described above, in which the ratio is within the above range.

In addition/alternatively, in the sputtering method, (b) the bias voltage applied to the metal substrate is greater than -700V and less than -150V. In the unbalanced magnetron sputtering method, a glow discharge is generated between the target (i.e., titanium) as the cathode and the metal substrate as the anode to form an inert gas plasma, for example, Ar plasma, and positively ionized Ar ions in the Ar plasma repel the target atoms, accelerating the target atoms to form a film on the surface of the metal substrate, so that a negative voltage is applied to the metal substrate as a bias voltage. In addition, in this specification, when expressing the level of a negative bias voltage, the bias voltage closer to 0V is expressed as "high bias voltage."

When a metal substrate having an uneven shape is used as the metal substrate, the lower the bias voltage applied to the metal substrate in the sputtering method, the thinner the titanium layer formed in the diagonal portion between the convex portion and the concave portion tends to be. Therefore, by setting the bias voltage applied to the metal substrate in the sputtering method within the above range, the titanium particles, which are the film-forming particles, can be made to reach the metal substrate in a high-energy state. Therefore, even if a metal substrate having an uneven shape is used as the metal substrate, a highly corrosion-resistant fuel cell separator having a densified titanium layer in all of the convex portions (top portions), concave portions (bottom portions), and diagonal portions between the convex portions and the concave portions of the metal substrate, in particular, a highly corrosion-resistant fuel cell separator having a ratio (orientation ratio) of the (100) plane and/or the (002) plane to the total value obtained by dividing the peak intensities of the (100) plane, (002) plane, and (101) plane derived from titanium by their relative intensities in the X-ray diffraction analysis of the separator surface described above, can be stably obtained.

In the sputtering method, the distance between the titanium target, which is the titanium raw material, and the metal substrate, particularly the convex portion (top portion) of the metal substrate, is usually 10 cm ± 1 cm.

Regarding the sputtering method, conditions other than those described above, such as the initial vacuum in the device chamber, cleaning conditions for the metal substrate surface (e.g., argon bombardment treatment conditions), plasma generation gas conditions, film formation time, film formation temperature, etc., can be conditions known in the art (e.g., see International Publication No. WO 2015/068776). Note that the longer the film formation time, the thicker the film will be, so the desired film thickness can be obtained by adjusting the film formation time.

(iii) Step of forming a carbon layer by depositing carbon in an area of the metal base material on which the titanium layer is formed that will become the power generator clamping portion In step (iii), carbon is deposited in an area of the metal base material on which the titanium layer is formed that will become the power generator clamping portion to form a carbon layer.

The power generator clamping portion is a generally rectangular portion of the fuel cell separator that clamps the power generator located in the center, and the sealing member placement portion is a portion of the fuel cell separator that is provided on the outer periphery of the power generator clamping portion and that places a sealing member that seals the power generator clamping portion.

The region that becomes the power generator clamping portion is a region of the approximately rectangular plate-shaped metal substrate for clamping an approximately rectangular power generator that is smaller than the metal substrate located in the center, and the region other than the region that becomes the power generator clamping portion is the region on the periphery of the region that becomes the power generator clamping portion, i.e., the region that becomes the seal member arrangement portion.

In step (iii), the area of the metal substrate other than the area that will become the power generator clamping portion, i.e., the area that will become the seal member arrangement portion, is masked, for example, by arranging a masking member, so that a carbon film can be formed in the area that will become the power generator clamping portion to form a carbon layer, and the titanium layer is exposed on the surface in the seal member arrangement portion. The masking member can be arranged with a space between it and the metal substrate (the area of the metal substrate that will become the seal member arrangement portion), and in this case, the plate-shaped masking member is arranged with a space parallel to the plate-shaped metal substrate. The degree of exposure of the titanium layer to the surface in the seal member arrangement portion, i.e., the surface titanium ratio in the seal member arrangement portion, can be adjusted by the distance between the masking member and the metal substrate (the area of the metal substrate that will become the seal member arrangement portion).

The process for depositing the carbon layer can be a process known in the art, such as the filterless arc ion plating (AIP) method.

The filterless arc ion plating method is a method in which an ionized substance (the target is evaporated and ionized, hereafter referred to as ionized evaporated substance) generated by an arc discharge generated between an anode and a target constituting a cathode is accelerated by applying a bias voltage to a metal substrate, forming a film of the ionized evaporated substance on the metal substrate.

The bias voltage in the filterless arc ion plating method is usually -450V to -250V, preferably -350V to -250V. In the filterless arc ion plating method, a negative voltage is applied to the metal substrate in order to accelerate the positively ionized evaporating material to form a film on the surface of the metal substrate on which the titanium layer has been formed, similar to the principle of applying a negative voltage as a bias voltage in the unbalanced magnetron sputtering method.

By setting the bias voltage in the filterless arc ion plating method within the above range, a denser carbon layer with lower contact resistance can be formed, ensuring lower contact resistance in the power generator clamping portion. The crystallinity of the carbon layer can be measured, for example, by Raman spectroscopy or X-ray diffraction.

For the filterless arc ion plating method, for example, the initial vacuum in the device chamber, cleaning conditions for the metal substrate surface (for example, argon bombardment treatment conditions), plasma generation gas conditions, film formation time, film formation temperature, etc. can be conditions known in the relevant technical field (for example, see JP 2008-204876 A). Note that the longer the film formation time, the thicker the film will be, so the desired film thickness can be obtained by adjusting the film formation time.

Several examples of the present invention are described below, but it is not intended that the present invention be limited to those examples.

I. Production of Fuel Cell Separators According to the procedure shown in FIG.

(i) Step of Preparing Metal Substrate As a metal substrate, stainless steel (SUS304) having an uneven shape that had been pressed in advance into the shape of a fuel cell separator was prepared.

(ii) A step of forming a titanium layer by depositing titanium on the surface of the metal substrate (surface treatment 1: deposition)
After removing the passivation on the surface of SUS304 as the metal substrate by Ar etching, a titanium layer was formed on the SUS using a sputtering method under the conditions of a UBM coil current value of 6.5 A and a bias voltage to the metal substrate of −250 V.

(iii) A step of forming a carbon layer by forming a carbon film on the region of the metal base material on which the titanium layer is formed, which will become the power generator clamping portion (surface treatment 2: film formation)
Areas of the metal substrate other than the area that would become the power generator clamping portion were masked by arranging a masking material, and a carbon layer was formed on the titanium layer in the area that would become the power generator clamping portion using the AIP method, thereby producing a fuel cell separator.
The fuel cell separators No. 1 to 3 were manufactured by changing the distance between the masking member and the metal base material (the area of the metal base material where the seal member was to be disposed) in the step (iii).

II. Measurement of surface titanium ratio in seal member disposition portion of fuel cell separator produced in I The surface titanium ratio in the seal member disposition portion of fuel cell separators No. 1 to 3 produced in I was measured by X-ray photoelectron spectroscopy (XPS).

III. Measurement of hot water peel strength (adhesion) of fuel cell separators manufactured in I.

The hot water peel strength of each separator at the seal member placement portion was measured according to the outline of the hot water peel strength test method shown in Figure 5. In Figure 5, a maleic acid-modified olefin-based adhesive sheet was first sandwiched between two L-shaped separators (seal member placement portions) and heat-pressed for 4 seconds at 180°C to prepare a T-shaped peel test specimen. The resulting peel test specimen was then placed in hot water at 95°C, and a weight was attached to one of the separators as shown in Figure 5. The hot water peel strength was determined by measuring the weight of the weight at which the adhesive sheet and separator peeled off.

Table 1 shows the results of the surface carbon ratio, surface titanium ratio, surface oxygen ratio, and hot water peel strength in the seal member arrangement part of the fuel cell separator, and Figure 6 shows the relationship between the surface titanium ratio and hot water peel strength in the seal member arrangement part measured in II.

From Table 1 and Figure 6, it can be seen that the hot water peel strength increases as the surface titanium ratio increases.

The hot water peel strength test results in Table 1 and Figure 6 are for maleic acid-modified olefin-based adhesive sheets, but they can also be applied to epoxy-based, acrylic-based, vinyl acetate-based, polyamide-based, polyester-based, and polyvinyl alcohol-based adhesive sheets other than maleic acid-modified olefin-based adhesive sheets.

S: Separator flow path shape cross section 1: Power generating body sandwiching portion 2: Seal member arrangement portion 3: Metal substrate 4: Titanium layer 5: Carbon layer

Claims (1)

A fuel cell separator having a power generating unit sandwiching portion that sandwiches a power generating unit, and a seal member disposition portion that is provided on an outer periphery of the power generating unit sandwiching portion and that disposes a seal member that seals the power generating unit sandwiching portion,
the power generating body holding portion includes a metal substrate, a titanium layer formed on a surface of the metal substrate, and a carbon layer formed on the titanium layer;
the seal member disposition portion includes a metal substrate and a titanium layer formed on a surface of the metal substrate;
A fuel cell separator, in which a titanium layer is exposed on the surface at a portion where a seal member is to be disposed.

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