JP2002313355A - Solid polymer fuel cell and separator for it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid polymer fuel cell excellent in the initial period battery characteristics and the lifetime characteristics. SOLUTION: Materials having a Cr concentration of 20% or more are provided on the surface of a metal base board followed by formation of an electroconductive film or an electroconductive film is formed on a metal base board whose Cr concentration at the surface is over 13% and a Cr oxide layer is formed on the interface between the metal base board and electroconductive film so that a metal separator is accomplished, and using it the intended solid polymer fuel cell is embodied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polymer electrolyte fuel cell used for a distributed power source, a power source for an electric vehicle, and the like, and a separator used for the battery.

[0002]

2. Description of the Related Art A polymer electrolyte fuel cell has an operating temperature of one.
It is as low as 00 ° C. or less and can be started in a short time. Also, due to its characteristics such as no generation of NOx and SOx and low noise, its application to a small distributed power supply, a power supply mounted on an electric vehicle, and the like as a power generator with a low environmental load has attracted attention.

A polymer electrolyte fuel cell utilizes a solid polymer membrane having a proton exchange group in a molecule to function as a proton conductive electrolyte. Like other types of fuel cells, The structure is such that a fuel gas such as hydrogen flows on the fuel electrode side of the solid polymer membrane and an oxidizing gas such as air flows on the air electrode side.

Next, the basic structure of a polymer electrolyte fuel cell will be specifically described with reference to FIG. FIG. 2A is a schematic sectional view of the battery, and FIG. 2B is a schematic perspective view showing the configuration of a unit cell.

A polymer film 1 made of a polymer material has a fuel electrode 3 a and an air electrode 3 b disposed on both sides, and is sandwiched by a separator 2 via a gas diffusion layer 4. A fuel gas supply port 6 and a fuel gas discharge port 7 are formed in the separator on the fuel electrode 3a side, and an air supply port 8 and an air discharge port 9 are formed in the air electrode separator, respectively. .

[0006] The separator 2 has a gas flow path (10, 11) for introducing each gas and a gas diffusion layer 4.
And a power collection unit 12 for collecting power of the battery.
A gas seal material 5 is provided to prevent gas leakage at the end face of the unit cell. Although not shown in FIG. 2, since heat is generated during power generation, cooling means for circulating cooling water may be interposed.

Generally, a fuel cell is used in a stack configuration in which a plurality of unit cells shown in FIG. 2 are stacked according to the amount of power.

As described above, the polymer electrolyte fuel cell is expected as a power source with a low environmental load. However, since the power generation cost is high, it has not been put to practical use, and reduction of the cost is an essential issue. . In particular, the high cost of the solid polymer membrane and the separator material is one factor.

The conditions required for a separator of a polymer electrolyte fuel cell include (1) good conductivity,
(2) low contact resistance; (3) no gas permeation;
(4) Many characteristics such as high durability are required, and at present, a material obtained by cutting a densified graphite material is used.

However, the above materials require a process of densification in order to prevent gas leakage, and are difficult to process due to the brittleness of the material, which increases the processing cost and causes a rise in the price of fuel cells. I was

In recent years, several attempts have been made to reduce the cost. For example, a method using a metal plate by pressing or punching is known (Japanese Patent Application Laid-Open No. 8-
180883). However, when using a metal plate,
There has been concern that the current collection resistance of the battery increases due to corrosion of the metal, and the efficiency of the battery decreases.

In order to improve this, a separator having a conductive protective film in which carbon-based particles are dispersed on a metal surface has been proposed (JP-A-11-144744, JP-A-11-144744).
-345618, JP-A-8-222237, etc.)
Have been.

[0013] However, in the separator having the conductive protective film formed thereon, there is a danger that the metal substrate is corroded from the open pores existing in the protective film in a long-term operation (thousands of hours), and the performance of the battery is deteriorated. there were.

A method of applying a noble metal film to stainless steel is disclosed in Japanese Patent Application Laid-Open No. H11-162479. According to this method, an increase in resistance due to corrosion is suppressed, but an expensive noble metal is used. This raises the problem of high cost.

[0015]

SUMMARY OF THE INVENTION An object of the present invention is to provide a low-cost separator for a polymer electrolyte fuel cell mainly composed of a metal substrate, instead of a high-cost dense graphite separator. is there.

Another object of the present invention is to provide a polymer electrolyte fuel cell using the above separator.

[0017]

In order to solve the above-mentioned problems, the present inventors have conducted various studies and found that the surface Cr
It has been found that a metal separator having excellent conductivity and durability can be obtained by applying a conductive paint to a metal substrate having a concentration of 20% or more.

The polymer electrolyte fuel cell has an operating temperature of 80
℃ and the collector of the separator is in a saturated steam environment, so even austenitic stainless steel, which is usually used as a corrosion-resistant metal, is corroded in thousands of hours of operation, increasing the contact resistance of the metal substrate. As a result, the problem of lowering the power generation efficiency of the battery occurs.

As a substrate material of the present invention which solves the above, a metal substrate having a surface with a Cr concentration of 20% or more is used, and a conductive film made of a carbon-based material or a ceramic-based material is formed on the metal substrate. It is in.

In this case, as a surface treatment method for increasing the Cr concentration on the substrate surface, a method of forming a Cr layer on the surface by CVD, PVD, or the like, or a method of applying a voltage in an electrolyte to apply a C
A method of precipitating r on a metal surface, a method of dipping in an acid solution such as HNO ₃ and chemical etching, and the like can be cited.

In this case, if the thickness of the layer having the Cr concentration of 20% or more is 2 nm or more, the effect of the present invention is further improved. However, in order to form a material with a thickness exceeding 1 μm,
Since the processing time becomes longer and the productivity is reduced, the thickness is desirably 1 μm or less.

By forming a conductive film on a metal substrate having a Cr concentration of 13% or more and forming a Cr oxide layer at the interface between the metal substrate and the conductive film, a metal separator having high conductivity and high durability is obtained. be able to.

The separator of the present invention on which the Cr oxide layer is formed can be used in a saturated steam environment at the operating temperature of the battery (about 80 ° C.), even when steam enters through open pores and the like existing in the coating layer. Corrosion of the substrate is prevented.

As a method of forming a Cr oxide layer at the interface between the metal substrate and the conductive film, a method of forming a Cr oxide layer on the substrate metal surface in advance and then coating the conductive film, A method in which a Cr oxide layer is formed after coating may be used.

In the former case, since the Cr oxide layer is formed on the entire surface of the substrate, the durability is excellent, but the conduction resistance at the interface between the metal substrate and the conductive film may increase. On the other hand, in the latter case, since the Cr oxide layer is formed after the conductive film is applied to the metal substrate, the Cr oxide layer is hardly formed at the interface between the filler in the conductive film and the substrate. As a result, although the durability is slightly inferior to the former, the conduction resistance at the interface between the metal substrate and the conductive film does not increase much.

After applying the conductive film on the latter substrate surface,
When the r-oxide layer is formed, a method of performing heat treatment in an air atmosphere, a method of forming a Cr oxide layer by applying a voltage in an electrolytic solution, and the like can be given.

When the thickness of the Cr oxide layer is 2 nm or more, the effect of the present invention is further improved. However, when forming a Cr oxide layer having a thickness exceeding 100 nm, the processing time becomes longer and the productivity is reduced.
0 nm or less is desirable.

The separator to which the present invention is applied has high conductivity and high durability without depending on the material and shape of the solid polymer film and the material and shape of the gas diffusion layer.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be specifically described based on embodiments.

[Embodiment 1] SUS430,
Using SUS304, the power generation efficiency of a metal separator battery coated with an Ag-based conductive paint was evaluated.

The substrate was subjected to chemical etching by immersing it in a 30% HNO ₃ solution for 1 hour. The Cr concentration on the substrate surface was measured using an Auger electron spectrometer (PERKIN-
ELMER PHI650), an electron gun acceleration voltage of 5.0 kV, an ion gun acceleration voltage of 2.0 kV, and an excitation current of 25 kV.
The measurement was performed under the conditions of mA and Ar gas pressures of 15 mPa.

The Cr concentration in the thickness direction from the surface of the substrate was also measured by sputtering Ar. Cr concentration on the surface after chemical etching is SUS4
The thickness of each layer having a Cr concentration of 20% or more and 20% or more and SUS304 of 20% or more was 1 nm, respectively.

As a comparative example, SS4 containing no Cr was used.
00 and a 9Cr steel in which a layer having a surface Cr concentration of 15% after chemical etching was formed with a thickness of 1 nm.
A similar study was performed.

The conductive paint was prepared according to the following procedure. Polyvinylidene fluoride was used as the binder resin, and N-methylpyrrolidone was used as the solvent.

First, a varnish was prepared by mixing a binder resin and a solvent, and a predetermined amount of Ag powder as a conductive filler was added thereto, followed by mixing for 5 hours using a ball mill. At that time, the filler content in the paint was 30 wt%. The method of applying the conductive paint to the separator will be described below.

The surface oxide of the metal substrate on which the channel processing was completed was removed by blast processing, and after the chemical etching treatment, the conductive paint was applied on the metal substrate using a spray gun. After the application, a drying process was performed to obtain a separator for a polymer electrolyte fuel cell. The conductive film was formed by keeping the substrate at a drying temperature of 120 ° C. in a vacuum for 3 hours. The filler amount in this film was 80% by volume.

In this embodiment, a conductive film having a thickness of 25 μm was used. The method for applying the coating film is not limited to the spray method shown in this embodiment, but may be a dip coating method or a printing method.

FIG. 2 shows a schematic diagram of the shape of the battery of this embodiment. The working area was 100 cm 2. The power generation conditions were a current density of 0.3 A / cm ² and an operating temperature of 80 ° C. The fuel (hydrogen) and air utilization rates at that time are
7, 0.4. For comparison of power generation efficiency, a battery using a separator machined from a carbon plate generates power under the above conditions,
The power generation efficiency when reaching the rated current density was set to 1. A relative comparison of the power generation efficiency when the rated current density of the battery using the separator of this example was reached (comparison of the relative battery efficiency with respect to the power generation time h) was performed. FIG. 1 shows the test results.

The batteries [(a) and (b)] using the separator obtained by subjecting the metal substrate of the present invention to a chemical etching treatment so as to have a surface with a Cr concentration of 20% or more and coated with a conductive paint are formed.
It was confirmed that the reduction in relative efficiency was smaller than that of the batteries [(c) and (d)] using the separator of the comparative example, and that power could be stably generated.

[Embodiment 2] SUS304,
Using SUS430 and SUS316, the power generation efficiency of a metal separator battery coated with a conductive paint was evaluated. The metal substrate was immersed in a 10% Na ₂ SO ₄ solution, and a voltage of 0.5 V was applied for an arbitrary time to change the surface Cr concentration. The Cr concentration on the substrate surface and the Cr concentration in the thickness direction were evaluated in the same manner as in Example 1.

In the SUS304 used in this example, the Cr concentration on the substrate surface was 21%, and the thickness of the layer having the Cr concentration of 20% or more was 1 nm or 3 nm.

SUS430 has a Cr concentration of 2 on the substrate surface.
2% and the thickness of the layer having a Cr concentration of 20% or more is 5n.
m. In SUS316, the Cr concentration on the substrate surface is 25%, and the thickness of the layer having the Cr concentration of 20% or more is 1%.
It was set to 0 nm.

Using TiN as the conductive filler, paints and coatings were prepared in the same manner as in Example 1. The thickness of each coating film was 25 μm, and the amount of filler in the coating film was 80% by volume.

As a comparative example, SS400 containing no Cr
A similar study was conducted for a 9Cr steel in which a layer having a surface Cr concentration of 15% after chemical etching was formed with a thickness of 1 nm.

The shape of the battery was the structure shown in FIG. 2, and the working area was 100 cm ² . Power generation conditions and fuel (hydrogen)
The air utilization was the same as in Example 1.

The power generation efficiency was also compared by a relative comparison as in Example 1. FIG. 3 shows the test results.

By using a metal substrate having a surface Cr concentration of 20% or more, it was confirmed that stable relative battery efficiency was exhibited, and the thickness of a layer having a surface Cr concentration of 20% or more was 2 nm or more. In this case, it was confirmed that the efficiency was stable for a longer period.

Example 3 13Cr steel having a surface Cr concentration of 20% or more, SUS304, SUS316, SU
Using S430 as a metal substrate, the initial power generation efficiency of a metal separator battery with a changed conductive film thickness was evaluated. The metal substrate was immersed in a solution of 10% Na ₂ SO ₄ and an arbitrary voltage was applied for 1 hour to make the surface Cr concentration 20 to 26%.

The Cr concentration on the substrate surface and the Cr in the thickness direction
The concentration was evaluated in the same manner as in Example 1. At that time, the thickness of all the layers having a Cr concentration of 20% or more was 1 nm.

As the conductive filler, WC, graphite, TiC,
A coating material was prepared using FeSi, FeSi ₂ , and amorphous carbon by the method of Example 1 to form a coating film. The thickness of the coating film was varied from 25 to 150 μm, but the filler amount in the coating film was all 80% by volume.

As a comparative example, SS400 containing no Cr
A similar study was also conducted on a 9Cr steel having a layer with a surface Cr concentration of 15% after chemical etching and having a thickness of 1 nm.

The shape of the battery was the structure shown in FIG. 2, and the operating area was 100 cm ² . The power generation conditions and the utilization rates of fuel (hydrogen) and air were the same as in Example 1.

The comparison of the power generation efficiency is as follows. A battery using a separator obtained by machining a carbon plate is generated under the above conditions, and the power generation efficiency when the rated current density is reached is set to 100. Relative comparison was made with the power generation efficiency when the rated current density was reached. Table 1 shows the test results.

It was confirmed that when the conductive film applied to a metal substrate having a surface Cr concentration of 20% or more was 30 to 100 μm, the initial battery characteristics were excellent.

[0055]

[Table 1] [Embodiment 4] SUS304, SUS4 as metal substrates
05, SUS430, SUS316, 13Cr steel, immersed in a solution of 10% Na ₂ SO ₄ and applying a voltage of 0.5 V for an arbitrary time to make the thickness of the layer having a Cr concentration of 20% 2 nm. . The Cr concentration on the substrate surface and the Cr concentration in the thickness direction were evaluated in the same manner as in Example 1.

SUS304 having a surface Cr concentration of 21%
25 μm and 50 μm of conductive film are applied to
For SUS405, SUS430 having an r concentration of 25%, SUS316 having a surface Cr concentration of 23%, and 13Cr steel having a surface Cr concentration of 20%, a metal separator battery coated with a 30 μm conductive film was used. Power generation efficiency was evaluated.

Example 1 was made using WC as the conductive filler.
A paint was prepared by the method shown in (1) to form a coating film.

The shape of the battery was the structure shown in FIG. 2, and the working area was 100 cm ² . Power generation conditions and fuel (hydrogen)
The air utilization was the same as in Example 1.

The power generation efficiency was also compared by a relative comparison as in Example 1. FIG. 4 shows the test results.

The thickness of the layer having a Cr concentration of 20% is 2 nm.
It was confirmed that when a conductive film was formed on the above metal substrate with a thickness of 30 to 100 μm, power generation could be performed with higher relative efficiency for a longer time.

Example 5 13Cr steel (surface Cr concentration 13%) in which a carbon-based conductive film was coated on a metal substrate, SUS3
04 (surface Cr concentration 18%), SUS430 (surface Cr concentration)
(Concentration: 17%), the power generation efficiency of a metal separator battery having a Cr oxide layer formed at the metal substrate / conductive film interface was evaluated.

As a comparative example, SS400 containing no Cr was used.
The same evaluation was carried out for a 9Cr steel having a surface Cr concentration of 9%.

The Cr oxide layer was formed by applying a carbon-based conductive paint prepared in the same manner as in Example 1 and then applying the coating at 250 ° C.
The heat treatment was performed in the air for 5 hours.

The presence or absence of the formation of the Cr oxide layer is determined by removing the conductive film of the sample prepared under the same conditions with acetone, and then performing X-ray diffraction (RU-200, manufactured by Rigaku Denki) on the substrate surface.
Using a Cu-kα ray having a tube voltage of 50 kV and a tube current of 150 mA, 20 to 120 deg. It confirmed by measuring in the range of. The thicknesses of the conductive films shown in this example were all 25 μm.

The thickness of the Cr oxide layer was determined by measuring the oxygen concentration in the thickness direction of the substrate by Auger electron spectroscopy under the conditions shown in Example 1. As a result, the thickness of the Cr oxide layer on the metal side surface at the metal substrate / conductive film interface was 1 nm.

The shape of the battery was the structure shown in FIG. 2, and the operating area was 100 cm ² . Power generation conditions and fuel (hydrogen)
The air utilization was the same as in Example 1.

The power generation efficiency was also compared by a relative comparison as in Example 1. FIG. 5 shows the test results.

When a metal substrate having a surface Cr concentration of 13% or more is used and a separator having a Cr oxide layer formed on the metal surface side at the metal substrate / conductive film interface is used, the relative efficiency of the battery is stable. Was confirmed.

[Embodiment 6] SUS304 is applied to a metal substrate.
(Surface Cr concentration 18%), SUS316 (Surface Cr concentration 17%), SUS430 (Surface Cr concentration 17%), and a TiN-based conductive paint is applied, and a Cr oxide layer is formed on the metal surface side at the metal substrate / conductive film interface. The power generation efficiency of the metal separator battery formed with was evaluated.

After a TiN-based conductive paint prepared in the same manner as in Example 1 was applied to the substrate,
_It was immersed in a solution of ₂ SO ₄ and formed by applying a voltage of 0.2 V for an arbitrary time. In the case of a SUS304 substrate, the thickness of the Cr oxide layer was 1 nm and 2 nm.

The thickness of the Cr oxide layer was 5 nm in the case of the SUS316 substrate, and 3 nm in the case of SUS430.
The presence or absence and the thickness of the Cr oxide layer were evaluated in the same manner as in Example 5. The thickness of each conductive film was 25 μm, and the amount of filler in the conductive film was 80% by volume.
And

The shape of the battery was the structure shown in FIG. 2, and the operating area was 100 cm ² . Power generation conditions and fuel (hydrogen)
The air utilization was the same as in Example 1.

The power generation efficiency was also compared by a relative comparison as in the first embodiment. FIG. 6 shows the test results.

It was confirmed that when the thickness of the Cr oxide layer formed on the metal surface side at the metal substrate / conductive film interface was 2 nm or more, the power generation efficiency was stable for a longer time.

[Embodiment 7] 13Cr steel (surface Cr concentration 13%), SUS304 (surface Cr concentration 18)
%), SUS316 (surface Cr concentration 17%), SUS4
Using 30 (17% surface Cr concentration), the initial battery efficiency of a metal separator battery with a changed conductive film thickness was evaluated.

As the conductive filler, WC, graphite, TiC,
Using FeSi, FeSi ₂ , and amorphous carbon, a paint is prepared by the method shown in Example 1 to form a coating film, and is heat-treated at 250 ° C. for 5 hours to thereby oxidize Cr on the metal substrate side of the metal substrate / conductive film interface. An object layer was formed to a thickness of 1 nm.

The presence / absence and thickness of the Cr oxide layer were evaluated in the same manner as in Example 5. The thickness of the conductive film is 20 to
Although the thickness was changed at 150 μm, the amount of filler in the coating film was all 8
0% by volume.

As a comparative example, SS400 containing no Cr was used.
The same examination was performed on 9Cr steel (surface Cr concentration 9%) in which a 1 nm Cr oxide layer was formed on the metal substrate side of the metal substrate / conductive film interface by performing a heat treatment at 250 ° C. for 5 hours.

The shape of the battery was the structure shown in FIG. 2, and the working area was 100 cm ² . Power generation conditions and fuel (hydrogen)
The air utilization was the same as in Example 1.

A comparison of the power generation efficiency was made by generating a battery using a separator obtained by machining a carbon plate under the above conditions, setting the power generation efficiency at the time of reaching the rated current density to 100, and comparing the battery using the separator of the example with the battery. Relative comparison was made with the initial power generation efficiency when the rated current density was reached. Table 2 shows the test results.

When a metal substrate having a surface Cr concentration of 13% or more is used and a Cr oxide layer is formed on the metal substrate at the metal substrate / conductive film interface, when the conductive film is 30 to 100 μm, the initial battery characteristics are poor. It was confirmed that it was excellent.

[0082]

[Table 2] [Embodiment 8] 13Cr steel (surface Cr concentration 1
3%), SUS304 (Surface Cr concentration 18%), SUS
316 (surface Cr concentration 17%), SUS430 (surface C
(r concentration 18%), and the power generation efficiency of a metal separator battery in which the thickness of the conductive film was changed was evaluated.

Example 1 was made using WC as the conductive filler.
A coating material was prepared by the method shown in (1), and after forming a coating film, heat treatment was performed at 250 ° C. for an arbitrary time to form a Cr oxide layer on the metal substrate side at the interface between the metal substrate and the conductive film. The presence / absence and thickness of the Cr oxide layer were evaluated in the same manner as in Example 5.

In SUS304, a conductive film having a thickness of 25 μm has a Cr oxide layer of 1 nm, and a conductive film having a conductive film of 50 μm has a thickness of Cr.
The oxide layer was 2 nm. SUS316 has a conductive film of 50 μm
And the SUS430 has a conductive film of 30 μm.
m, Cr oxide layer 3nm, 13Cr steel conductive film 70μm
To make the Cr oxide layer 3 nm. The amount of filler in the conductive film was all 80% by volume. Using WC as the conductive filler,
A coating material was prepared by the method shown in Example 1 to form a coating film.

The shape of the battery was the structure shown in FIG. 2, and the operating area was 100 cm ² . The power generation conditions and the utilization rates of fuel (hydrogen) and air were the same as in Example 1.

The power generation efficiency was also compared by a relative comparison as in Example 1. FIG. 7 shows the test results.

On the metal substrate side of the metal substrate / conductive film interface,
It was confirmed that when the oxide layer was formed to have a thickness of 2 nm or more and the conductive film was formed to have a thickness of 30 to 100 μm on the metal substrate, power generation could be performed with higher relative efficiency for a longer time.

[Embodiment 9] 13Cr steel, S
Using US304, SUS430, and SUS316, a polarization test was performed on a metal coated with a carbon-based conductive paint in a sulfuric acid solution. The substrate was immersed in a 30% HNO3 solution for 1 hour and subjected to a chemical etching treatment. The Cr concentration on the surface was measured by the method shown in Example 1, and the content of 13Cr steel was 20%, SUS3
04 and SUS430 22%, SUS316 23
%Met. The thickness of each layer having a Cr concentration of 20% or more was 1 nm.

The carbon-based conductive paint was prepared in the same procedure as in Example 1. The method of applying the conductive paint to the substrate will be described below.

[0090]

(Equation 1) The substrate surface oxide represented by the above formula (1) is removed by polishing. After the chemical etching treatment, a conductive paint was applied to the surface by a printing method. After the application, the film was held in a vacuum at 140 ° C. for 3 hours to form a conductive film.

The thickness of the conductive film shown in this embodiment is 30 μm
Was used. The polarization test was performed according to JIS G0597.
The concentration of sulfuric acid was 0.05 M according to the method described in
And

As a comparative example, SS400 containing no Cr was used.
And that the surface Cr concentration after chemical etching is 15% 9
A similar test was conducted for Cr steel.

Table 3 shows the evaluation results. In the table, ○ indicates that the weight loss before and after the polarization test was less than 1%, and ×
Indicates that a weight reduction of 1% or more was observed.

As a result of the evaluation, the Cr concentration on the substrate surface was 20%.
As described above, it was confirmed that when the carbon-based conductive film was formed, it was excellent in corrosion resistance.

[0095]

[Table 3] [Embodiment 10] 13Cr steel (surface Cr concentration 13%), SUS304 (surface Cr concentration 18%), SU
S316 (Surface Cr concentration 17%), SUS430 (Surface Cr concentration 17%), SUS405 (Surface Cr concentration 18%)
%), A polarization test was performed in a sulfuric acid solution of a material having a Cr oxide layer formed on the metal substrate side of the metal substrate / conductive film interface after applying the WC-based conductive paint.

As a comparative example, SS400 containing no Cr
And a similar test using a 9Cr steel having a Cr concentration of 9%. The WC-based conductive paint was prepared in the same procedure as in Example 1. The method of applying the conductive paint to the substrate will be described below.

The substrate surface oxide represented by the above formula (1) is removed by polishing. Thereafter, a conductive paint was applied to the surface by a printing method. After the coating, a heat treatment was performed in the air at 250 ° C. for 5 hours to form a Cr oxide layer with a thickness of 2 nm on the interface between the substrate and the conductive film.

The presence / absence and thickness of the Cr oxide layer were determined in the same manner as in Example 5. The thickness of the conductive film shown in this example was 60 μm. The polarization test is based on JIS
According to the method described in G0597, the concentration of sulfuric acid was 0.05M. Table 4 shows the evaluation results.

In the table, ○ indicates that the weight loss before and after the polarization test was less than 1%, and X indicates that the weight loss was 1% or more.

As a result, it was confirmed that those having a Cr concentration of 13% or more on the substrate side surface at the substrate / conductive film interface had excellent corrosion resistance.

[0101]

[Table 4]

When the separator of the present invention is used, a large amount of Cr having high corrosion resistance is scattered on the surface of the metal substrate under the coating film, so that a decrease in efficiency when power is generated for a long time is suppressed.

Even if a pinhole is present in the conductive film applied to the substrate, the separator for a polymer electrolyte fuel cell has a long life because the Cr oxide layer is formed at the metal substrate / conductive film interface. And a polymer electrolyte fuel cell.

In particular, when the Cr concentration on the surface of the separator is 20
%, Or a conductive film is formed on a metal substrate having a Cr concentration of 13% or more on the surface of the metal substrate, and a Cr oxide layer is provided at the metal substrate / conductive film interface. By using, a polymer electrolyte fuel cell having excellent initial characteristics and life characteristics can be provided.

[Brief description of the drawings]

FIG. 1 is a graph showing a relative efficiency evaluation of a metal separator battery of Example 1.

FIG. 2 is a schematic cross-sectional view (A) and a schematic configuration diagram (B) of a polymer electrolyte fuel cell.

FIG. 3 is a graph showing a relative efficiency evaluation of the metal separator battery of Example 2.

FIG. 4 is a graph showing a relative efficiency evaluation of the metal separator battery of Example 4.

FIG. 5 is a graph showing a relative efficiency evaluation of the metal separator battery of Example 5.

FIG. 6 is a graph showing a relative efficiency evaluation of the metal separator battery of Example 6.

FIG. 7 is a graph showing a relative efficiency evaluation of the metal separator battery of Example 8.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Solid polymer electrolyte membrane, 2 ... Separator, 3a ... Fuel electrode, 3b ... Air electrode, 4 ... Gas diffusion layer, 5 ... Gas seal material, 6 ... Fuel gas inlet, 7 ... Fuel gas outlet, 8 ... Air inlet , 9 air outlet, 10 fuel gas channel, 11 air channel, 12 current collector.

Continued on the front page (72) Inventor Hiroshi Yamauchi 7-1-1, Omika-cho, Hitachi-shi, Ibaraki F-term in Hitachi Research Laboratory, Hitachi Ltd. 5H026 AA06 CC03 CX05 EE02 EE12 HH03 HH05

Claims (8)

[Claims] An electrode and a gas diffusion layer are provided between a solid polymer electrolyte membrane and a separator, wherein the separator comprises a metal substrate having a gas flow path and a current collector in contact with the gas diffusion layer, In a polymer electrolyte fuel cell in which a conductive film is formed on a surface of the metal substrate, the separator uses a metal substrate having a surface with a Cr concentration of 20% or more. battery. 2. The polymer electrolyte fuel cell according to claim 1, wherein the metal substrate has a surface layer having a Cr concentration of 20% or more and a thickness of 2 nm or more. 3. The polymer electrolyte fuel cell according to claim 1, wherein the conductive film has a thickness of 30 to 100 μm. 4. An electrode and a gas diffusion layer are provided between the solid polymer electrolyte membrane and a separator, wherein the separator is formed of a metal substrate having a gas flow path and a current collector in contact with the gas diffusion layer, In a solid polymer electrolyte fuel cell in which a conductive film is formed on the surface of the metal substrate, the metal substrate has a surface Cr concentration of 13% or more and has a surface side of the metal substrate at the interface between the metal substrate and the conductive film. A polymer electrolyte fuel cell comprising a Cr oxide layer. 5. The polymer electrolyte fuel cell according to claim 4, wherein the thickness of the Cr oxide layer formed on the surface of the metal substrate at the interface between the metal substrate and the conductive film is 2 nm or more. 6. The polymer electrolyte fuel cell according to claim 4, wherein said conductive film has a thickness of 30 to 100 μm. 7. A polymer electrolyte fuel cell separator in which a conductive film is formed on the surface of a metal substrate having a gas flow path and a current collector, wherein the surface has a Cr concentration of 20% or more and a surface Cr concentration of 20% or more. The thickness of the layer having a concentration of 20% or more is 1 nm.
A separator for a polymer electrolyte fuel cell, using the metal substrate described above. 8. A polymer electrolyte fuel cell separator in which a conductive film is formed on a surface of a metal substrate having a gas flow path and a current collector, wherein the metal substrate has a surface Cr concentration of 1%.
A separator for a polymer electrolyte fuel cell, wherein a Cr oxide layer is formed with a thickness of 1 nm or more on the surface side of the metal substrate at an interface between the metal substrate and the conductive film of 3% or more.