JP4496750B2 - Stainless steel for polymer electrolyte fuel cell separator and polymer electrolyte fuel cell using the stainless steel - Google Patents

Description

The present invention relates to a polymer electrolyte fuel cell using the stainless steel separators of stainless steel and its use smaller solid polymer fuel cell separator having a contact resistance value with excellent durability.

In recent years, from the viewpoint of global environmental conservation, development of fuel cells that are excellent in power generation efficiency and do not emit CO ₂ has been underway. This fuel cell generates electricity by reacting H ₂ and O _2. Depending on the type of electrolyte used, the phosphoric acid fuel cell, molten carbonate fuel cell, solid electrolyte fuel cell, alkaline type Fuel cells, polymer electrolyte fuel cells, and the like have been developed.

Among these fuel cells, the polymer electrolyte fuel cell is compared with other fuel cells,
(a) The power generation temperature is about 80 ° C, and power can be generated at a significantly lower temperature.
(b) The fuel cell body can be reduced in weight and size.
(c) Start up in a short time,
And so on. For this reason, the polymer electrolyte fuel cell is the fuel cell that is attracting the most attention today for use as a power source for mounting an electric vehicle, a stationary generator for home use, and a small portable generator.

The polymer electrolyte fuel cell takes out electricity from H ₂ and O ₂ through a polymer membrane. As shown in FIG. 1, gas diffusion layers 2 and 3 (for example, carbon paper) and separators 4 and 4 are used. The membrane-electrode assembly 1 is sandwiched by 5 to form a single component (so-called single cell), and an electromotive force is generated between the separator 4 and the separator 5.

  The membrane-electrode assembly 1 is called MEA (that is, Membrance-Electrode Assembly), and is an integration of a polymer membrane and an electrode material such as carbon black carrying a platinum-based catalyst on the front and back surfaces of the membrane. The thickness is several tens of μm to several hundreds of μm. In many cases, the gas diffusion layers 2 and 3 are integrated with the membrane-electrode assembly 1.

  When the polymer electrolyte fuel cell is applied to the above-described use, a fuel cell stack is formed by connecting several tens to several hundreds of such single cells in series.

For separators 4 and 5,
(A) In addition to serving as a partition wall that separates single cells,
(B) a conductor that carries the generated electrons,
(C) an air flow path, a hydrogen flow path through which O ₂ (ie air) and H ₂ flow,
(D) A function as a discharge path for discharging generated water and gas is required. Furthermore, in order to put the polymer electrolyte fuel cell into practical use, it is necessary to use separators 4 and 5 having excellent durability and electrical conductivity.

  In terms of durability, when used as a power source for mounting on an electric vehicle, it is assumed to be about 5000 hours. Or, if it is used as a home-use generator, it is assumed that it is about 40,000 hours. Therefore, the separators 4 and 5 are required to have characteristics such as corrosion resistance that can withstand long-time power generation.

  Regarding electrical conductivity, it is desirable that the contact resistance between the separators 4 and 5 and the gas diffusion layers 2 and 3 is as low as possible. The reason is that as the contact resistance between the separators 4 and 5 and the gas diffusion layers 2 and 3 increases, the power generation efficiency of the polymer electrolyte fuel cell decreases. That is, the smaller the contact resistance, the better the electrical conductivity.

  To date, polymer electrolyte fuel cells using graphite as separators 4 and 5 have been put into practical use. The separators 4 and 5 made of graphite have an advantage that they have a relatively low contact resistance and do not corrode. However, since it is easily damaged by an impact, it is difficult to reduce the size and the processing cost for forming the air channel 6 and the hydrogen channel 7 is high. These disadvantages of the separators 4 and 5 made of graphite are factors that hinder the spread of solid polymer fuel cells.

  Therefore, an attempt is made to apply a metal material instead of graphite as a material for the separators 4 and 5. In particular, from the viewpoint of improving durability, various studies have been made toward practical application of separators 4 and 5 made of stainless steel.

  For example, Japanese Patent Application Laid-Open No. 8-180883 discloses a technique that uses a metal that easily forms a passive film as a separator. However, the formation of a passive film causes an increase in contact resistance, leading to a decrease in power generation efficiency. For this reason, it has been pointed out that these metal materials have problems to be improved such as a contact resistance larger than that of the carbon material and inferior in corrosion resistance.

  Japanese Patent Application Laid-Open No. 10-228914 discloses a technique for reducing contact resistance and ensuring high output by performing gold plating on the surface of a metal separator such as SUS304. However, it is difficult to prevent pinholes with thin gold plating, and conversely with thick gold plating, the problem of cost remains.

  Japanese Patent Application Laid-Open No. 2000-277133 discloses a method of obtaining a separator having improved electrical conductivity by dispersing carbon powder in a ferritic stainless steel substrate. However, even when carbon powder is used, a cost problem still remains because the surface treatment of the separator requires a corresponding cost. Further, it has been pointed out that the separator subjected to the surface treatment has a problem that the corrosion resistance is remarkably lowered when scratches or the like are generated during assembly.

  Furthermore, an attempt has been made to apply stainless steel as it is to the separator without subjecting it to surface treatment. For example, in Japanese Patent Laid-Open Nos. 2000-239806 and 2000-294255, Cu, Ni are positively added, impurity elements such as S, P, and N are reduced, and C + N ≦ 0.03 mass%. , 10.5% by mass ≦ Cr + 3 × Mo ≦ 43% by mass is disclosed. In JP 2000-265248 A and JP 2000-294256 A, Cu and Ni are limited to 0.2% by mass or less to suppress elution of metal ions, and impurity elements such as S, P, and N are added. A ferritic stainless steel for a separator that is reduced and satisfies C + N ≦ 0.03% by mass, 10.5% by mass ≦ Cr + 3 × Mo ≦ 43% by mass is disclosed.

However, all of these inventions define the components of stainless steel within a predetermined range and strengthen the passive film, so that the surface treatment is not performed and the electrode-supported catalyst based on the eluted metal ions can be used as it is. This is based on the idea of reducing the deterioration of the catalytic ability of the steel and suppressing an increase in contact resistance with the electrode due to corrosion products. Therefore, it does not attempt to reduce the contact resistance of the stainless steel itself. Further, it is not possible to ensure durability (that is, output voltage reduction) that can withstand power generation for tens of thousands of hours.
Japanese Patent Laid-Open No. 8-180883 Japanese Patent Laid-Open No. 10-228914 JP 2000-277133 A JP 2000-239806 JP JP 2000-294255 A JP 2000-265248 A JP 2000-294256 A

  In view of the above-mentioned problems of the prior art, the present invention is a stainless steel for a polymer electrolyte fuel cell separator having good corrosion resistance and low contact resistance (that is, excellent electrical conductivity). And a polymer electrolyte fuel cell using the same.

  That is, the present invention regulates not only the component of stainless steel as a raw material but also the component of the passive film existing on the surface within a predetermined range, so that the contact resistance is small and the power generation efficiency is excellent even without surface treatment. Another object of the present invention is to provide stainless steel for a polymer electrolyte fuel cell separator having high corrosion resistance of stainless steel itself, and a polymer electrolyte fuel cell using the same.

  The present inventor conducted intensive research on stainless steel separators for exhibiting high corrosion resistance while keeping contact resistance low, from the viewpoints of stainless steel components and passive film components. As a result, it has been found that contact resistance is greatly reduced by adjusting the components of the passive film formed on the surface of Mo-containing high purity ferritic stainless steel.

  First, the experimental results for conceiving the present invention will be described.

In the experiment, C: 0.004 mass%, N: 0.007 mass%, Si: 0.1 mass%, Mn: 0.1 mass%, Cr: 30.5 mass%, Mo: 1.85 mass%, P: 0.03 mass%, S: 0.005 mass% A ferritic stainless steel (thickness 0.5 mm) that contains cold rolled steel was used as a material. Some materials were annealed in the atmosphere (950 ° C., 2 minutes) and then wet-coated No. 600. The other materials were annealed (950 ° C., 2 minutes) in a 75 volume% H ₂ +25 volume% N ₂ atmosphere with a dew point of −60 ° C. to obtain a so-called BA finish. In addition, these materials were etched at various temperatures and times using an acidic aqueous solution containing 10% by mass nitric acid, 50% by mass hydrochloric acid and 1% by mass picric acid, followed by pure water cleaning and cold air drying. The contact resistance was measured.

For the measurement of contact resistance, four test pieces (50 mm × 50 mm) etched under the same conditions were prepared, and two test pieces 8 as shown in FIG. Carbon paper (Toray TGP-H-120) 9 is alternately sandwiched, and the copper plate is contacted with gold-plated electrodes 10, and a pressure of 137.2 N / cm ² (ie, 14 kgf / cm ² ) is applied per unit area. The resistance between the test pieces 8 was measured. The value obtained by multiplying the measured value by the area of the contact surface and further dividing by the number of contact surfaces (= 2) was taken as the contact resistance value.

  The contact resistance values were calculated based on the measurement values measured six times while exchanging a set of two test pieces 8, and the average values are shown in Table 1.

  As a reference example, the same measurement was performed on a stainless steel plate (thickness 0.3 mm, equivalent to SUS304) and a graphite plate (thickness 5 mm) with gold plating (thickness approx. 0.1 μm) on the surface, and the contact resistance value was calculated. Calculated. The results are also shown in Table 1.

  In addition, the passive film after etching is measured by photoelectron spectroscopy, and the spectral intensity of Fe, Cr, and Al in the passive film (that is, the oxidized state) is calculated by the peak separation method. Content, Fe content, and Al content were determined. Furthermore, the Cr / Fe ratio was calculated from the Cr content and the Fe content to calculate the Cr / Fe ratio. The number of Cr, Fe, and Al atoms was calculated from the Cr content, Fe content, and Al content, and the Al / (Cr + Fe) ratio was calculated as the ratio of the number of atoms. The results are shown in Table 1.

  Of the O (oxygen) contained in the passive film, oxygen present in the metal oxide state (hereinafter referred to as O (M)) and oxygen present in the metal hydroxide state (hereinafter referred to as O (H) ))) And the respective spectrum intensities were calculated, the number of O (M) and O (H) atoms was calculated, and the O (M) / O (H) ratio was calculated as the number of atoms. . The results are shown in Table 1.

As is apparent from Table 1, the contact resistance value is lowered by etching the stainless steel plate. In particular, when the Cr / Fe ratio of the passive film is 1 or more in terms of the number of atoms, the contact resistance value of the stainless steel plate is 10 mΩ · cm ² or less. If the O (M) / O (H) ratio is 0.9 or less in terms of the number of atoms, the contact resistance value is further reduced to 8 mΩ · cm ² or less.

Further, in the stainless steel with BA finish, Al is contained in the passive film, but when the Al content is reduced by the etching treatment, the contact resistance value also decreases. At this time, if the Al / (Cr + Fe) ratio calculated from the respective contents of Cr, Fe, and Al, which are the main metal elements constituting the passive film, is less than 0.05 in terms of the atomic ratio, the BA finish is used. The contact resistance value of stainless steel sheet is 10 mΩ · cm ² or less.

If the contact resistance value is 10 mΩ · cm ² or less, the fuel cell characteristics are hardly adversely affected.

  There has been an example in which the influence of the Cr / Fe ratio of the passive film has been investigated from the viewpoint of corrosion resistance, but it has never been possible to significantly reduce the contact resistance value by adjusting the components of the passive film by this experiment. Obtained knowledge. The present invention completed based on this finding is as follows.

1. C is 0.03% by mass or less, N is 0.03% by mass or less, Cr is 20 to 45% by mass, Mo is 0.1 to 5.0% by mass , Si is 1.0% by mass or less, Mn is 1.0% by mass or less, and Al is 0.001 to 0.2% by mass. %, And the total of C content and N content satisfies 0.03% by mass or less, and further contains 0.01 to 0.5% by mass of Ti or Nb, or 0.01 to 0.5% by mass of Ti and Nb , The balance is stainless steel having a composition composed of Fe and inevitable impurities, and the Cr / Fe ratio calculated from the Fe content and the Cr content in the passive film on the surface of the stainless steel is the number of atoms. The Al / (Cr + Fe) ratio calculated from the Al content, the Cr content and the Fe content contained in the passive film is less than 0.05 in atomic ratio, Of the oxygen contained in the passive film, the content of oxygen: O (M) present in the form of a metal oxide and metal water Solid polymer fuel characterized in that the O (M) / O (H) ratio calculated from the content of oxygen: O (H) present in the oxide state is 0.9 or less in terms of the number of atoms Stainless steel for battery separator.

2 . A solid polymer type fuel cell comprising a solid polymer membrane, an electrode and a separator, wherein the separator is the stainless steel for a solid polymer type fuel cell separator as described in 1 above. Fuel cell.

  As described above, according to the present invention, a stainless steel for a polymer electrolyte fuel cell separator having a low contact resistance value and excellent corrosion resistance can be obtained. Accordingly, it has become possible to provide an inexpensive stainless steel separator for a polymer electrolyte fuel cell that has conventionally used an expensive graphite separator due to durability problems.

  The present invention is not limited to the polymer electrolyte fuel cell separator, but can be widely used as an electrical component made of stainless steel having electrical conductivity.

  First, the reasons for limiting the components of the separator stainless steel according to the present invention will be described.

C: 0.03% by mass or less, N: 0.03% by mass or less, C + N: 0.03% by mass or less C and N both react with Cr in stainless steel and precipitate as Cr carbonitrides at grain boundaries, resulting in reduced corrosion resistance Bring. Therefore, the smaller the content of C and N, the better. If C: 0.03% by mass or less and N: 0.03% by mass or less, the corrosion resistance will not be significantly reduced. On the other hand, if the total of the C content and the N content (hereinafter referred to as C + N) exceeds 0.03% by mass, cracks generated when the separator is pressed are remarkably increased. Therefore, C + N is 0.03% by mass or less. Preferably, C: 0.015 mass% or less, N: 0.015 mass% or less, and C + N: 0.02 mass% or less.

Cr: 20 to 45 mass%
Cr is an element necessary for ensuring the corrosion resistance of the stainless steel plate. If the Cr content is less than 20% by mass, it cannot be used for a long time as a separator. On the other hand, if the Cr content is less than 20% by mass, it is difficult to adjust the Cr / Fe ratio of the passive film to 1 or more and make the contact resistance value 10 mΩ · cm ² or less. On the other hand, if the Cr content exceeds 45% by mass, the toughness decreases due to the precipitation of the σ phase. Therefore, the Cr content is set to 20 to 45% by mass. Preferably it is 22-35 mass%.

Mo: 0.1-5.0 mass%
Mo is an element effective for improving the crevice corrosion resistance of the stainless steel plate. In order to exert this effect, it is necessary to contain 0.1% by mass or more. On the other hand, if added over 5.0% by mass, the stainless steel becomes extremely brittle and production becomes difficult. Therefore, the Mo content is set to 0.1 to 5.0 mass%. Preferably it is 0.5-3.0 mass%.

Sebareta stainless steel according to the present invention, in addition to the above-described composition, containing the following Ingredients.

Si: 1.0 mass% or less
Si is an effective element for deoxidation, and is added at the melting stage of stainless steel. However, if it is contained excessively, the stainless steel plate becomes hard and the ductility decreases. Thus the upper limit of the Si content shall be the 1.0 wt%. More preferably, it is 0.01-0.6 mass%.

Mn: 1.0 mass% or less
Mn combines with S and has the effect of reducing S dissolved in the stainless steel, so it is an effective element for suppressing grain boundary segregation of S and preventing cracking during hot rolling. If the Mn content is 1.0% by mass or less, this effect is sufficiently exhibited. Preferably it is 0.001-0.8 mass%.

Al: 0.001 to 0.2 mass%
Al is an element effective for deoxidation in the steelmaking process, and 0.001% by mass or more is necessary to obtain the effect. On the other hand, even if added over 0.2% by mass, the effect is saturated and the cost increases. Therefore the Al content shall be the 0.001 wt%.

0.01 to 0.5% by mass of Ti or 0.01 to 0.5% by mass of Nb or 0.01 to 0.5% by mass of Ti and Nb
Ti and Nb are effective elements for fixing C and N in stainless steel as carbonitrides and improving press formability. When the C content and the N content satisfy the above range and Ti or Nb is added, the effect is exhibited when the Ti content is 0.01% by mass or more or the Nb content is 0.01% by mass or more. Moreover, when adding Ti and Nb, the effect will be exhibited, if Ti and Nb are contained 0.01 mass% or more in total. On the other hand, when Ti or Nb is added, if the Ti content exceeds 0.5% by mass or the Nb: content exceeds 0.5% by mass, the effect is saturated. In addition, when Ti and Nb are added, if Ti and Nb exceed 0.5 mass% in total, the effect is saturated. Therefore, when adding Ti or Nb is Ti was contained 0.01 to 0.5 wt% or Nb 0.01 to 0.5 wt%, when adding Ti and Nb are Ti and Nb Ru is total 0.01 to 0.5 wt%.

  In the present invention, in order to improve the hot workability of the stainless steel plate as the material of the separator, in addition to the above elements, Ca, Mg, REM (ie, rare earth element) and B are each 0.1% by mass or less, or the stainless steel plate For the purpose of improving toughness, Ni: 1% by mass or less may be added. In order to reduce the contact resistance value, Ag: 1 mass% or less, Cu: 5 mass% or less may be added, and V: 0.5 mass% or less may be added for the purpose of finely dispersing Ag.

  Other elements are the balance Fe and inevitable impurities.

  Next, the characteristics that the stainless steel for separators according to the present invention should have will be described.

The Cr / Fe ratio of the passive film on the stainless steel plate surface is 1 or more in terms of atomic ratio. The components of the passive film are an important factor in reducing the contact resistance value. It is necessary to increase the Cr / Fe ratio calculated from the Cr content and the Fe content of the active film. As explained in the above experimental results, in order to obtain a contact resistance value of 10 mΩ · cm ² or less, the Cr / Fe ratio needs to be 1 or more in terms of the number of atoms.

O (M) / O (H) ratio of passive film on stainless steel sheet surface: 0.9 or less in atomic ratio The bonding state of O (oxygen) contained in the passive film is also important in reducing the contact resistance value. It is a serious factor. In order to reduce the contact resistance value, oxygen (that is, O (M)) present in the metal oxide state and oxygen (that is, O (H)) present in the metal hydroxide state is calculated from O ( It is effective to lower the M) / O (H) ratio. As explained in the above experimental results, when the O (M) / O (H) ratio is 0.9 or less in terms of the number of atoms, a contact resistance value of 8 mΩ · cm ² or less can be obtained.

Al / (Cr + Fe) ratio of passive film on stainless steel plate surface: atomic ratio is less than 0.05. If Al oxide is contained in the passive film, the contact resistance value increases. Compared to pickled and polished stainless steel plates, BA-finished stainless steel plates contain more Al in the passive film. Therefore, in order to reduce the contact resistance value of the BA-finished stainless steel plate, it is necessary to reduce the amount of Al in the passive film. As explained in the above experimental results, if the Al / (Cr + Fe) ratio calculated from the Cr content, the Fe content, and the Al content of the passive film is less than 0.05 in terms of the atomic ratio, the BA-finished stainless steel plate Also, a contact resistance value of 10 mΩ · cm ² or less is obtained.

  Thus, in order to adjust the Cr content, Fe content, Al content and O (oxygen) bonding state of the passive film, etching using acid, immersion in acidic aqueous solution, electrolytic etching, etc. Can be used.

  Such adjustment of the composition of the passive film may be performed before the stainless steel plate is processed into a separator, or may be performed after the stainless steel plate is processed into a separator. However, in order to stably maintain the Cr / Fe ratio, O (M) / O (H) ratio, and Al / (Cr + Fe) ratio within the predetermined ranges, the pickling process is performed after the separator is processed. Is preferred.

  When a polymer electrolyte fuel cell is produced using the stainless steel separator thus produced, a polymer electrolyte fuel cell having a low contact resistance value, excellent power generation efficiency, and high corrosion resistance can be produced.

[Example 1]
Stainless steel having the components shown in Table 2 was melted by a converter and a strong stirring vacuum oxygen decarburization treatment method (SS-VOD), and further a 200 mm thick slab was formed by a continuous casting method. This slab was heated to 1250 ° C., and then hot rolled into a hot-rolled stainless steel plate having a thickness of 4 mm, and further subjected to annealing (850 to 1100 ° C.) and pickling treatment. Next, the thickness was reduced to 0.3 mm by cold rolling, and after annealing (850 to 1100 ° C.) and pickling treatment, temper rolling was performed to obtain a cold rolled stainless steel sheet having a so-called 2B finish.

  Four test pieces each having a size of 200 mm × 200 mm were cut out from the central portion in the plate width direction and the central portion in the longitudinal direction of the obtained cold-rolled stainless steel plate. Four test pieces cut out from each of the cold-rolled stainless steel plates of steel numbers 1 to 9 were subjected to press working to obtain a separator having a predetermined shape. Then, the composition adjustment process of the passive film was performed to some separators for every steel number, and Cr / Fe ratio was adjusted. Here, when performing the composition adjustment treatment of the passive film, A: a solution containing 10% by mass of nitric acid, 50% by mass of hydrochloric acid and 1% by mass of picric acid (50 ° C., 120 seconds) or B: 5% nitric acid A solution containing 50% by mass and 20% by mass of hydrofluoric acid (50 ° C., 300 seconds) was used.

  In addition, in the case where the composition adjustment treatment of the passive film was not performed, the Cr content, the Fe content, the Al content, the O content existing as a metal oxide, and the metal hydroxide after the press working After measuring the O content present and calculating the number of atoms of each element, the Cr / Fe ratio, O (M) / O (H) ratio, and Al / (Cr + Fe) ratio were calculated. Passive coating composition adjustment treatment is performed after pressing, and after passivation coating composition adjustment treatment, the passive coating Cr content, Fe content, Al content, and metal oxide are present. After measuring the O content present as a metal hydroxide and calculating the number of atoms of each element, the Cr / Fe ratio, O (M) / O (H) ratio, Al / ( Cr + Fe) ratio was calculated. In addition, content of each element was calculated | required by carrying out peak separation of the spectral intensity using photoelectron spectroscopy.

Thus, the power generation characteristics were investigated using the separator that had been subjected to the composition adjustment treatment of the passive film and the separator that had not been subjected to the treatment. For evaluation of power generation characteristics, a membrane-electrode assembly 1 (FC50-MEA manufactured by Electrochem Co., Ltd.) having an effective area of 50 cm ² in which a polymer membrane and an electrode and gas diffusion layers 2 and 3 are integrated is used. A single cell having the shape shown in FIG. 1 was prepared. The single cell air flow path 6 and hydrogen flow path 7 were both rectangular with a height of 1 mm and a width of 2 mm, and were arranged in 17 rows in total. Air is allowed to flow on the cathode side, and ultrahigh purity hydrogen (purity 99.9999 vol%) is supplied to the anode side after being humidified by a bubbler maintained at 80 ± 1 ° C and supplied with a current density of 0.4 A / cm ² (Condition 1) And an output voltage of 0.7 A / cm ² (condition 2) was measured.

Moreover, after operating continuously for 2000 hours on the conditions of 0.4 A / cm < ² > current density, the output voltage of the conditions 1 and 2 was measured. During the period of the power generation experiment of this single cell, the temperature of the single cell main body was maintained at 80 ± 1 ° C. The membrane-electrode assembly 1, carbon paper 9 and the like were replaced with new ones every time the test piece was changed.

As a reference example, a stainless steel plate (equivalent to SUS304) was processed into the same shape as steel numbers 1 to 9 above, and then a gold plated (thickness of about 0.1 μm) surface was applied to the separator, and a graphite plate with a thickness of 3 mm. Using a separator in which 17 rows of grooves having a width of 2 mm and a height of 1 mm were arranged on one side of the substrate at 2 mm intervals, output voltages of current densities of 0.4 A / cm ² and 0.7 A / cm ² were measured. The method for measuring the output voltage is the same as the steel numbers 1 to 9 described above.

  The results are shown in Table 3.

  As is apparent from Table 3, stainless steel (ie, steel numbers 3 to 6 and 9) satisfying the component range of the present invention is treated with the A or B solution to adjust the passive film components and Cr. A single cell using a separator with a / Fe ratio of 1 or more can obtain an output voltage equivalent to that of a gold plated separator or a graphite plate separator, both of the initial output voltage and the output voltage after 2000 hours. It was a level that could sufficiently withstand practical use.

  Furthermore, the single cell using the separator having an O (M) / O (H) ratio of 0.9 or less has further improved performance, and both the initial output voltage and the output voltage after 2000 hours have been subjected to gold plating. And an output voltage equivalent to that of a graphite plate separator.

  On the other hand, in the case of stainless steel (ie, steel numbers 1, 2, 7, and 8) that falls outside the component range of the present invention, the initial output voltage and the output voltage after 2000 hours are passed regardless of the composition adjustment treatment of the passive film. Were lower than those of gold-plated separators or graphite plate separators.

  Further, even when stainless steel (ie, steel numbers 3 to 6 and 9) satisfying the component range of the present invention is not subjected to the composition adjustment treatment of the passive film, the Cr / Fe ratio of the passive film is low, The initial output voltage was lower than that of gold plated separators or graphite plate separators.

[Example 2]
The hot-rolled stainless steel plate used in Example 1 was made into a thickness of 0.2 mm by cold rolling and further annealed (850 to 1050 ° C.) in ammonia decomposition gas having a dew point of −60 ° C. A steel plate was used.

  A test piece was collected from the obtained cold-rolled stainless steel plate by the same method as in Example 1 to obtain a separator having a predetermined shape. Further, the Cr / Fe ratio, O (M) / O (H) ratio, and Al / (Cr + Fe) ratio of the passive film of this separator were calculated. In addition, since the shape of a separator, a shaping | molding method, the composition adjustment process of a passive film, and the measuring method of content of each element are the same as Example 1, description is abbreviate | omitted.

  Furthermore, as in Example 1, the power generation characteristics of the separator were investigated. The results are shown in Table 4.

  As is apparent from Table 4, even in the stainless steel plate finished with BA, the stainless steel (that is, steel numbers 3 to 6 and 9) satisfying the component range of the present invention is processed using the liquid A or B. Single cells using separators with a passive film component adjusted to a Cr / Fe ratio of 1 or more are gold plated separators and graphite plate separators for both the initial output voltage and the output voltage after 2000 hours. An output voltage equivalent to the above was obtained, and it was at a level that could sufficiently withstand practical use.

  A single cell using a separator with an O (M) / O (H) ratio of 0.9 or less, or a separator with an Al / (Cr + Fe) ratio of less than 0.05, has further improved performance, initial output voltage and 2000 hours. Both the output voltage after the lapse of time and the output voltage equivalent to the gold plated separator and the graphite plate separator were obtained.

  On the other hand, in the case of stainless steel (ie, steel numbers 1, 2, 7, and 8) that falls outside the component range of the present invention, the initial output voltage and the output voltage after 2000 hours are passed regardless of the composition adjustment treatment of the passive film. Were lower than those of gold-plated separators or graphite plate separators.

It is a perspective view which shows the example of a solid polymer type fuel cell typically. It is sectional drawing which shows typically the sample used for the measurement of contact resistance.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Membrane-electrode assembly 2 Gas diffusion layer 3 Gas diffusion layer 4 Separator 5 Separator 6 Air flow path 7 Hydrogen flow path 8 Test piece 9 Carbon paper
10 electrodes

Claims (2)

C is 0.03% by mass or less, N is 0.03% by mass or less, Cr is 20 to 45% by mass, Mo is 0.1 to 5.0% by mass , Si is 1.0% by mass or less, Mn is 1.0% by mass or less, and Al is 0.001 to 0.2% by mass. %, And the total of C content and N content satisfies 0.03% by mass or less, and further contains 0.01 to 0.5% by mass of Ti or Nb, or 0.01 to 0.5% by mass of Ti and Nb , The balance is stainless steel having a composition consisting of Fe and inevitable impurities, and the Cr / Fe ratio calculated from the Fe content and the Cr content contained in the passive film on the surface of the stainless steel is the number of atoms. The Al / (Cr + Fe) ratio calculated from the Al content, the Cr content and the Fe content contained in the passive film is less than 0.05 in atomic ratio, Of the oxygen contained in the passive film, the oxygen: O (M) content present in the form of a metal oxide and the metal Solid polymer fuel characterized in that the O (M) / O (H) ratio calculated from the content of oxygen: O (H) present in the oxide state is 0.9 or less in terms of the number of atoms Stainless steel for battery separator . A solid polymer fuel cell comprising a solid polymer membrane, an electrode and a separator, wherein the stainless polymer for a polymer electrolyte fuel cell separator according to claim 1 is used as the separator. Type fuel cell .

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