JP2003297379A - Manufacturing method of separator for low temperature fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To manufacture a stainless steel separator with further reduced contact resistance showing superior corrosion resistance after surface roughening by alternating electrolytic etching in a ferric chloride aqueous solution. <P>SOLUTION: The separator improved in both the corrosion resistance and contact resistance is manufactured by using a stainless steel plate raw material containing 0.5 mass% or more Cu, applying the alternating electrolytic etching of alternately carrying out anodic electrolysis at an electric potential of +0.5 VvsSCE or more and cathodic electrolysis at an electric potential in a range of -0.2 to -0.8 VvsSCE in the ferric chloride aqueous solution, roughening one face or both faces of a stainless steel plate, forming a multiplicity of pits with bristling microscopic protrusions in circumferential rims throughout the whole surface, and forming a barrier layer film mainly comprising oxide or hydroxide of Cr entrapping Cu or Cu oxide. <P>COPYRIGHT: (C)2004,JPO

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.
Of fuel cell separators that can operate at low temperatures
About. [0002] 2. Description of the Related Art Among fuel cells, polymer electrolyte fuel cells are known.
The fuel cell can operate at a temperature of 100 ° C or less,
It has the advantage of starting between. Whether each member is solid
The structure is simple, maintenance is easy, and vibration
It can also be applied to applications exposed to shocks and shocks. In addition, output density
Suitable for miniaturization due to high temperature, high fuel efficiency, low noise
It has advantages such as sai. Because of these advantages,
Applications for mounting on vehicles are being studied. Gasoline self
Equipped with a fuel cell that can provide the same mileage as a vehicle
If possible, there is almost no generation of NOx and SOx and CO2
_TwoIt is extremely clean for the environment,
Become a power source. [0003] A polymer electrolyte fuel cell has a
Solid polymer resin membrane with proton exchange group
It is based on the fact that it works as a quality
Fuel such as hydrogen on one side of the polymer electrolyte membrane
Gas, and oxidizing gas such as air to the other side.
ing. Specifically, oxidized electrodes are provided on both sides of the solid polymer film 1.
2 and the fuel electrode 3 are joined to each other with a gasket 4
The separator 5 is opposed (FIG. 1a). Oxidation pole 2
Air supply port 6 and air discharge port 7 are formed on the side separator 5
The hydrogen supply port 8 is connected to the separator 5 on the fuel electrode 3 side.
An outlet 9 is formed. The separator 5 includes hydrogen g and oxygen or
Represents hydrogen g and acid for the conduction and uniform distribution of air o.
A plurality of grooves 10 extending in the flow direction of element or air o are formed
Have been. In addition, since there is heat during power generation,
The cooling water w sent from 1 is circulated inside the separator 5
After that, the water cooling mechanism to be discharged from the drain port 12 is separated.
Data 5. From the hydrogen supply port 8 to the fuel electrode 3
The hydrogen g sent into the gap with the separator 5 converts the electrons into electrons.
The released protons pass through the solid polymer membrane 1 and
Between the oxidizing electrode 2 and the separator 5
Combustion by oxygen or air o passing through the gap. There
When a load is applied between the oxidation electrode 2 and the fuel electrode 3,
The power can be taken out. [0005] Fuel cells generate very little power per cell.
Is. Therefore, the solid height sandwiched between the separators 5,5
Stacking a plurality of cells using a molecular film as one unit (Fig. 1
The amount of power that can be taken out is increased by b). Many
In this structure, the resistance of the separator 5 is
Significantly affects efficiency. To improve power generation efficiency
Requires separators with good conductivity and low contact resistance
And a graphite separator similar to a phosphate fuel cell
Is used. [0006] Graphitic separators include graphite blocks.
Cut out to a fixed shape and form various holes and grooves by cutting
Has formed. Therefore, material costs and processing costs are high, and overall
Raise fuel cell prices and reduce productivity
It is causing it. In addition, the material is brittle graphite
The resulting separator breaks when subjected to vibration or impact
There is a great risk of doing this. Therefore, pressing and punching
Japanese Patent Laid-Open No. Hei 8
It is proposed in -180883. [0007] The problem is that oxygen or air o
On the side of the oxidizing electrode 2 passing, an acidic atmosphere having an acidity of pH 2 to 3
It is in. Withstands such a strongly acidic atmosphere and separates
Metal materials that satisfy the characteristics required for
It has not been put to practical use. Withstands acidic atmosphere, contact
Precious metals such as Au and Pt are known as low-resistance metal materials.
Fuel cell because it is a very expensive material
It is not a practical material as a separator for use. Also,
Ni is very inexpensive and superior to Au and Pt.
It is also an electronic conductor, but in an acidic atmosphere of pH 2-3
Corrosion resistance is insufficient. On the other hand, as a metal material resistant to a strong acid,
An acid-resistant material represented by stainless steel is considered. this
These materials are formed by a strong passive film formed on the surface.
Despite acid resistance, passivation film causes surface resistance and contact
Resistance increases. If the contact resistance is high,
Amount of Joule heat is generated, resulting in large heat loss and fuel
Reduces the power generation efficiency of the pond. [0009] The effect of the passive film on the surface resistance and contact resistance
When the effect is suppressed, the excellent corrosion resistance inherent in stainless steel
Utilizes a stainless steel separator to replace graphite
Will be available. From this point of view, the applicant has
By providing many fine pits over the entire surface
And found that the surface contact resistance was reduced.
-2766893. Many fine pits
For example, a stainless steel sheet is exchanged in an aqueous ferric chloride solution.
It is formed by electro-etching. Contact resistance
Is about 10 to 20 mΩ · cm due to the formation of fine pits.^Two
However, it is expected to be used as a fuel cell separator.
Several mΩ · cm^TwoSlightly higher compared to moderate contact resistance
When stacking a large number of cell units
Heat loss is still negligible due to the generation of
Situation. [0010] The present invention is designed to solve such a problem.
It is the most suitable for stainless steel material.
, And alternate electrolytic etching in ferric chloride aqueous solution
After having been subjected to surface roughening treatment, while showing excellent corrosion resistance,
Stainless steel separator with even lower contact resistance
It is intended to manufacture. [0011] SUMMARY OF THE INVENTION A low temperature fuel cell according to the present invention.
The production method of the separator for the purpose, to achieve its purpose,
At least one side of stainless steel plate is roughened
A large number of pits with fine protrusions formed on the entire surface
0.5% by mass of Cu as stainless steel plate material
Using the one containing the above, in an aqueous solution of ferric chloride, +0.
Anodic electrolysis at a potential of 5 V vs. SCE or higher;
Cathodic electrolysis at a potential between 2 and -0.8 V vs SCE
It is characterized by applying alternating electrolytic etching to alternate between
I do. The potential display “VvsSCE” in this specification
Is the potential when a saturated calomel electrode is used as the reference electrode
(V). Anodic electrolysis and cathodic electrolysis
The potential of the solution is determined by the anodic and cathodic polarization curves.
Can be obtained from [0012] The present inventors have developed a separator for a low-temperature fuel cell.
Surface condition of stainless steel sheet used for
Investigate and study the effects of this method on various factors.
Prior application (Japanese Patent Application No. 2000-2)
No. 76893). However, the formation of fine pits
The contact resistance decreased by about 10 to 20 mΩcm^Twoso
Yes, contact resistance desired for low temperature fuel cell separators
Is still slightly higher than that of. Therefore, the present invention is effective in reducing the contact resistance.
While utilizing the effect of effective fine pits,
Exposure to corrosive atmosphere and withstands corrosive reactions
Low temperature fuel cell separators.
As a result, a specific stainless steel plate material is used
And to make the alternating electrolytic etching conditions specific
More corrosion resistance and contact resistance as a separator
The improvement was realized. Reasons why corrosion resistance and contact resistance could be further improved
Although the details are unknown, as the inventor, as follows:
thinking. Cu content of 0.5 mass% as the material plate
And use it at a potential of +0.5 V vs SCE or higher.
When pit electrolysis is performed, pits are formed, followed by -0.2 to-
Perform cathodic electrolysis at a potential between 0.8 V vs SCE
And Cu and Cr eluted from the steel sheet during anode electrolysis
Cr is reprecipitated on the plate surface and Cu is taken in.
Barrier thin film is formed on the stainless steel plate surface,
It is thought that it was possible to improve both performance and contact resistance
You. The improvement of the corrosion resistance is achieved by using an oxide of Cr or water.
The barrier thin film mainly composed of oxides
Improvement is achieved by using a buffer mainly composed of Cr oxide or hydroxide.
Cu or Cu oxide taken in the rear thin film
It is presumed to form an electric site. At this time,
0.2V vs. Cathodic electrolysis at noble potential than SCE
Is H_TwoAlmost no reduction reaction occurs.
Therefore, the starting point of pit generation during anode electrolysis does not increase.
From the surface, many pits with fine protrusions on the periphery
It becomes impossible to form it in the whole area. On the other hand, -0.8 V vs. potential lower than SCE
When performing cathodic electrolysis at
Is possible, but the re-precipitation of Fe
Occurs on the surface of the steel sheet, Fe oxide or hydroxylation
A thin film containing many substances is formed, resulting in excellent corrosion resistance.
It becomes difficult to form a barrier thin film mainly composed of Cr,
Corrosion resistance decreases. Also, the cathode electrolysis potential is
And H on the steel sheet surface_TwoThe reduction reaction of
The contact resistance is probably because the deposited Cu is removed.
No further improvement can be expected. [0017] DESCRIPTION OF THE PREFERRED EMBODIMENTS Stainless steel used as a separator substrate
Steel sheet has the corrosion resistance required in a fuel cell atmosphere.
As far as possible, there is no particular restriction on the type of steel. Fe
Light, austenitic and duplex stainless steels
Board can be used. As the stainless steel plate used,
16% by mass or more of C to ensure corrosion resistance in acidic environment
Those containing r are preferred. On the other hand, materials in acidic environment
Focusing on the passivation limit current density of
The lower the current value, the more advantageous in terms of corrosion resistance
However, focusing on the corrosion current in a high potential environment,
High potential environment is exposed to the overpassivation zone for stainless steel
The higher the Cr concentration, the higher the Cr dissolution current
Flows. Also, when the Cr content increases,
Processability is reduced and cost is increased.
You. Therefore, the upper limit of the Cr content is set to 25.0% by mass.
Preferably. In the present invention, Cu or
Incorporates Cu oxide to lower the contact resistance of the film
That is the basic idea. Cu in barrier layer
Stainless steel for high concentration and low surface contact resistance
From the results of various experiments, the Cu content in steel was at least
It was confirmed that 0.5% by mass was required. About the upper limit
Is not specified, but a large amount of Cu
Incorporation in the composition impairs manufacturability, such as lowering hot workability.
Therefore, the Cu content should be less than 5.0% by mass.
Preferably. In order to reduce contact resistance, stainless steel plate
It is preferable to roughen either the surface or the back
New Fe (OH)_ThreeAs a protective film
Since a large number of pits are formed using the action,
_Three ^-, SO_Four ^2-Ferric chloride water that does not contain a large amount of ions such as
Alternating electrolytic etching in solution is employed. NO_Three ^-,
SO_Four ^2-If a large amount of ions such as
Oxidation reaction promotes pit formation and hinders pit formation.
Cannot be obtained. From this perspective,
For a ferritic stainless steel sheet, use Fe³⁺Is 1 to 5
0 g / l ferric chloride aqueous solution and austenitic
Fe stainless steel ³⁺Is 30 to 120 g / l
It is preferable to use an aqueous solution of ferric chloride. Anode electrolytic cell in alternating electrolytic etching
And the appropriate range of the cathode electrolysis potential are as described above.
It is. A table with many fine protrusions on the periphery of the pit
Anode energization time is 0.05 to 1 second to make surface state
And the cathode energization time is set to 0.01 seconds or more.
It is preferable to specify Suitable for one cycle of alternating electrolysis
Positive energization time is 0.05 to 1 second for anodic electrolysis, cathode
It is 0.01 seconds or longer in electrolysis. It should be noted that Cu or Cu oxide as described above is used.
The formation of a roughened film incorporating
Constant potential assuming production or continuous processing to the coil
Since the operation is very difficult, measure the potential-current curve in advance.
To determine the current density corresponding to the potential range of the present invention.
In this case, the constant current density operation can be performed according to the value.
For example, FIG.³⁺Is 50 g / l and the liquid temperature is 50 ° C.
In a ferric chloride aqueous solution, stir the solution with a stirrer.
While measuring the sweep speed at 100 mV / sec.
3 shows an anode-cathode polarization curve of US304. Figure
In this case, the appropriate anode and cathode current density range
Are +1.3 kA / m, respectively.^TwoAbove and -0.2 ~-
1.3kA / m^TwoBecomes [0022] [Examples] Table 1 shows the chemical components of the test materials used in this study.
The example and the concentration and the temperature of the electrolytic solution applied to each test material are shown. each
The test material used was a 2D finished material. Anode, catho
The energization time is 0.1 sec and the alternation cycle is 5
Hz and the processing time was unified to 60 sec. [0023] [0024]Example 1 Each stainless steel sheet shown in Table 1 was alternately rotated under the conditions shown in Table 2.
A surface roughening treatment was performed by electrolytic etching. Roughening
In each of the samples, the surface of the steel plate had fine protrusions on the periphery.
Many pits formed across the entire surface
did it. Samples subjected to each surface roughening treatment were adjusted to pH 2 and bath temperature.
Immerse in a sulfuric acid aqueous solution at 90 ° C for 168 hours,
The corrosion weight loss was calculated from the weight measurement. In addition, each surface roughening process
The test piece cut from the applied stainless steel plate has a load of 0.
Contact with carbon electrode at 98MPa, stainless steel plate
/ Contact resistance between carbon electrodes was measured. Those results
Are also shown in Table 2. In the table, contact resistance: 7 mΩ · cm^Two
Below, corrosion weight loss: 0.5 g / cm^TwoThe following are examples of the present invention.
Minutes. In addition, roughening treatment by alternating electrolytic etching
The sample is prepared in the electrolyte solution to be used in advance.
Equivalent to the target electrolytic potential by measuring the sword polarization curve
The current density was determined, and this was performed by constant current density electrolysis. Also,
Stainless steel after surface roughening by Auger electron spectrometer
Measure the surface of the board and, based on the obtained profile,
Read the strength of Cr, Fe and Cu, and
The power ratio was calculated. [0025]From the above results, it was found that Cu was contained in an amount of 0.5% by mass or more.
Use stainless steel plates that are within the range specified in the claims.
When alternating electrolytic etching is performed under the conditions, Cu
It can be seen that the concentration increases and the contact resistance decreases.
On the other hand, if the Cu content in the stainless steel sheet is low,
Even if alternating electrolytic etching under predetermined conditions is performed (test N
o. 7) There is no concentration of Cu in the film, and the contact resistance is reduced
I haven't. In addition, a predetermined amount of Cu
Even if a material containing
When electrolysis is performed under even lower conditions (Test Nos. 9, 10, 1)
1) The film may have been deposited once again because it was eluted.
The contact resistance has increased due to the low Cu concentration in the
Was. [0027]Example 2 In the case of No. 1 subjected to the surface roughening treatment in the same manner as in Example 1, 3,5 and 7
For the sample of
Built into the fuel cell. Humidified water for each fuel cell
While supplying element and oxygen, the current density was set to a constant value of 0.5.
A / m^TwoAfter 100 hours of continuous operation of the fuel cell,
Remove the separator from the fuel cell and place it on the separator table.
Investigate the corrosion state by observing the surface and reduce the contact resistance.
It was measured. Table 3 shows the measurement results of the contact resistance. [0028] For the corrosion products, any sample
Was not observed. Sample No. 3 and 5
The fuel cell is used for the separator using stainless steel plate.
A sufficiently low contact resistance is maintained even after continuous operation for 100 hours.
Sample no. 7 stainless steel
For separators using steel plates, contact after use on the oxygen electrode side.
Tactile resistance was slightly higher. When the contact resistance increases,
The loss due to Joule heat increases, and as a fuel cell
This means that the power generation efficiency becomes worse. [0030] As described above, according to the present invention,
Roughening at least one side of the stainless steel sheet
A large number of pits with fine protrusions were formed on the entire surface
When using Cu as a stainless steel sheet material, 0.5% by mass or less
Use the above-mentioned components in a ferric chloride aqueous solution
Alternating current that performs anodic electrolysis and cathodic electrolysis alternately
By performing de-etching, it is excellent even after roughening
Excellent corrosion resistance and further reduced contact resistance
A stainless steel plate was obtained. Separate this steel plate
The Joule heat at the contact area
A fuel cell with low power generation and high power generation efficiency
it can.

BRIEF DESCRIPTION OF THE DRAWINGS [Figure 1] a polymer membrane cross-sectional view illustrating the internal structure of a fuel cell using as the electrolyte (a) and exploded perspective view (b) [2] Fe ³⁺ is 50 g / 1. Anode-cathode polarization curve of SUS304 measured in aqueous ferric chloride solution at 50 ° C

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Tsutomu Miyano             5 Ishizu Nishimachi, Sakai-shi, Osaka Nisshin Steel Co., Ltd.             Inside the company technology laboratory (72) Inventor Shinichi Kamoshida             5 Ishizu Nishimachi, Sakai-shi, Osaka Nisshin Steel Co., Ltd.             Inside the company technology laboratory (72) Inventor Yoshikazu Morita             5 Ishizu Nishimachi, Sakai-shi, Osaka Nisshin Steel Co., Ltd.             Inside the company technology laboratory (72) Inventor Keiji Izumi             5 Ishizu Nishimachi, Sakai-shi, Osaka Nisshin Steel Co., Ltd.             Inside the company technology laboratory (72) Inventor Yuichi Yagami             1 Toyota Town, Toyota City, Aichi Prefecture Toyota Auto             Inside the car company (72) Inventor Takeshi Takahashi             1 Toyota Town, Toyota City, Aichi Prefecture Toyota Auto             Inside the car company (72) Inventor Yoshiaki Kajikawa             1 Toyota Town, Toyota City, Aichi Prefecture Toyota Auto             Inside the car company (72) Inventor Kota Kodama             1 Toyota Town, Toyota City, Aichi Prefecture Toyota Auto             Inside the car company F term (reference) 5H026 AA06 BB00 BB10 EE08 HH05                       HH06

Claims (1)

Claims 1. When forming a large number of pits having fine protrusions on the periphery by forming a rough surface on at least one surface of a stainless steel plate over the entire surface, the stainless steel plate material may be made of Cu.
Is used in an aqueous ferric chloride solution at an electric potential of +0.5 V vs. SCE and a cathodic electrolysis at a potential of -0.2 to -0.8 V vs. SCE in an aqueous ferric chloride solution. A method for producing a separator for a low-temperature fuel cell, wherein alternating electrolytic etching is performed alternately.