JP2009231150A - Ferrite system roughened surface stainless steel plate for separator, and separator as well as polymer electrolyte fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stainless steel plate suitable for a separator of a polymer electrolyte fuel cell, with contact resistance reduced between the stainless steel plate and carbon paper. <P>SOLUTION: On at least a surface of a steel plate consisting of a ferrite system stainless steel type containing 16 to 40 mass% of Cr and 0.2 to 5 mass% of Mo, the roughened surface stainless steel plate for a separator of a polymer electrolyte fuel cell with a roughened surface A having a surface roughness SPa of 0.03 to 0.3 μm, is formed by immersion in nonoxidizing acid containing halogen ion such as hydrochloric acid. When the roughened surface A is made in contact with the carbon paper with a contact surface pressure of 1 MPa, the contact resistance is to be ≤15 mΩ cm<SP>2</SP>, preferably, ≤10 mΩ cm<SP>2</SP>. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a roughened ferritic stainless steel plate for constituting a metal separator of a solid polymer fuel cell, and a solid polymer fuel cell configured using the ferritic stainless steel plate as a member. The present invention relates to a separator and a polymer electrolyte fuel cell using the separator.

  Among fuel cells, a polymer electrolyte fuel cell can operate at a low temperature of 100 ° C. or less, and has an advantage of starting in a short time. In addition, since each member is made of a solid structure, maintenance is easy, and it can also be applied to applications that are exposed to vibration and impact. In addition, it has advantages such as high output, suitable for downsizing, high fuel efficiency and low noise.

  Since a polymer electrolyte fuel cell has a small power generation amount per cell, it is necessary to stack a large number of cells with one cell having a polymer electrolyte membrane sandwiched between separators in order to extract practical power. is there. The polymer electrolyte fuel cell utilizes the function of a solid polymer resin having a proton exchange group in the molecule as a proton conductive electrolyte. Like other types of fuel cells, the polymer electrolyte fuel cell The fuel gas such as hydrogen is flowed on one side and the oxidizing gas such as air is flowed on the other side.

  FIG. 1 schematically illustrates a cross-sectional structure of an in-vehicle solid polymer fuel cell using a metal separator. Separators are disposed on both sides of the solid polymer membrane with gas diffusion electrodes (a negative electrode and a positive electrode, respectively) interposed therebetween. The separator and the gas diffusion electrode are in electrical contact. The separator is in a state in which a pair of separator member 1 and separator member 2 formed by processing a metal plate into a shape having a bowl-shaped concavo-convex cross section by pressing (that is, a contact surface pressure is applied to the contact portion). It has a contact and integrated structure. The separator member 1 is in electrical contact with a negative electrode (for example, carbon paper), and a channel through which fuel gas (mainly hydrogen) passes is formed between the negative electrode and the member. On the other hand, the separator member 2 is in electrical contact with a positive electrode (for example, carbon paper) in an adjacent cell, and a flow path through which an oxidant gas (for example, mainly air) passes between the positive electrode and the member. Is formed. And a pair of separator member 1 and separator member 2 which constitute a separator have electrical contact mutually, and a channel through which cooling water passes is often provided between both members.

  FIG. 2 schematically illustrates a cross-sectional structure of a polymer electrolyte fuel cell that is assumed for stationary use in homes and the like. In this case, since it is less likely to be operated at a higher current as in-vehicle use, for example, a structure in which cooling water is passed between the separator members at a rate of about 1 cell per 3 cells is assumed. In the cell through which the cooling water passes, a separator member 3 and a separator member 4 formed by processing a metal plate into a shape having a bowl-shaped concavo-convex cross section by pressing are combined in contact with each other in a pressed state. Constitute. Also in this case, the separator and the gas diffusion electrode are in electrical contact. The pair of separator members 3 and the separator members 4 are in electrical contact with each other, and a channel through which cooling water passes is provided between the members.

  Recently, various practical applications of solid polymer fuel cells using stainless steel as a separator and carbon paper as a gas diffusion electrode have been studied. In such a type of polymer electrolyte fuel cell, reducing the contact resistance between stainless steel and carbon paper has become a major issue. Since stainless steel is covered with a passive film having low conductivity, it is difficult to ensure good conductivity even if the stainless steel surface and the carbon paper surface are simply brought into contact with each other in a pressed state. Therefore, various attempts have been made to reduce the contact resistance between different materials by, for example, a method of coating a stainless steel surface with a noble metal having no passive film or a method of roughening the surface (for example, patents). Literatures 1-3). However, the method of coating the noble metal increases the cost, and is difficult to adopt for widely spreading the polymer electrolyte fuel cell. Moreover, it is not always easy to reduce the contact resistance with the carbon paper to a satisfactory level with the conventional roughening method.

  On the other hand, as shown in FIG. 1 and FIG. 2, a metal separator of a type in which a pair of press-formed plate members are brought into contact with each other in a pressed state (hereinafter referred to as “plate member composite separator”). Is sometimes considered to be widely adopted in the future because a cooling water flow path can be provided inside. In this type of separator, reducing the contact resistance between “stainless steel-stainless steel” generated between a pair of plate-like members is an extremely important elemental technology.

  So far, various methods for reducing the contact resistance of the stainless steel surface have been studied with the intention of a separator for a polymer electrolyte fuel cell. Patent Documents 4 to 6 disclose separator materials having improved conductivity and contact resistance while ensuring acid resistance by distributing carbon particles in an island shape on the surface of stainless steel. However, it is not always easy to stably and sufficiently secure the adhesion of the carbon particles to the stainless steel surface, and there is a concern that the carbon particles may fall off the stainless steel surface during handling or processing. In addition, a process for attaching the carbon particles with a good degree of adhesion is required, resulting in an increase in production man-hours. Patent Document 3 describes a method of reducing contact resistance by attaching a precious metal or a precious metal alloy after removing an oxide layer on the surface of stainless steel or titanium. However, this method inevitably increases costs due to the use of noble metals.

Japanese Patent Laid-Open No. 11-297338 JP 2003-223904 A JP2001-6713 Japanese Patent Laid-Open No. 11-12018 Japanese Patent Laid-Open No. 11-126621 JP-A-11-126622

  In view of such a current situation, the present invention simultaneously reduces the contact resistance between stainless steel plates, particularly inexpensive stainless steel plates for separators, which can significantly reduce the contact resistance between stainless steel separators and carbon paper. It is intended to provide a stainless steel plate suitable for a plate-shaped member composite separator. It is another object of the present invention to provide a separator composed of the stainless steel plate and a polymer electrolyte fuel cell using the separator.

As a stainless steel plate having a low contact resistance with carbon paper, in the present invention, halogen ions are formed on at least one surface of a steel plate made of a ferritic stainless steel type containing Cr: 16 to 40% by mass and Mo: 0.2 to 5% by mass. A rough surface for a separator of a polymer electrolyte fuel cell having a roughened surface A having a surface roughness SPa of more than 0.03 to 0.3 μm formed by dipping in a non-oxidizing acid such as hydrochloric acid. A stainless steel sheet is provided. The roughened surface A has a contact resistance of 15 mΩ · cm ² or less when brought into contact with carbon paper at a contact surface pressure of 1 MPa.

Further, as a stainless steel plate with reduced contact resistance between the stainless steel plates, the roughened surface A is provided on one side of the steel plate, and on the opposite side, alternating electrolysis in a ferric chloride aqueous solution or The surface roughness SPa formed by anodic electrolysis has a roughened surface B having a surface roughness of 0.3 to 2 μm. The roughened surface B is a roughened surface B of two flat plate samples cut out from the steel plate. Provided is a roughened stainless steel sheet for a separator of a polymer electrolyte fuel cell, which has a contact resistance of 10 mΩ · cm ² or less when they are brought into contact with each other at a contact surface pressure of 1 MPa.

Here, “surface roughness SPa” is obtained by measuring the arithmetic average height Pa of a cross-sectional curve defined in JIS B0601-2001 for a surface area of a certain area and taking the average value. Specifically, SPa is one of surface roughness parameters obtained by analyzing data of a three-dimensional surface profile measured by a scanning laser microscope, and the absolute value of the elevation of the cross-sectional curved surface with respect to the average surface of the cross-sectional curved surface Mean value of The surface region for measuring the three-dimensional surface profile is a rectangular surface region having a side of 50 μm or more. That is, a measurement area of 50 μm × 50 μm or more is ensured. The depth resolution of the scanning laser microscope is desirably 0.01 μm or more. “Contact surface pressure” is a stress component in a direction perpendicular to the contact surface applied between the surfaces of both plate-like materials in contact with each other. The “contact resistance” is a contact area which is a resistance value calculated from a voltage drop when a direct current (for example, a current density of 1 A / cm ^{2 on the} contact surface) is passed between both plate-like materials through the contact portion. Multiplied by.

  Examples of the ferritic stainless steel types include those corresponding to the ferritic steel types defined in JIS G4305: 2005, and having Cr and Mo contents in the above ranges. Based on these standard steel types, it is also possible to adopt steel types whose characteristics are improved by adding various elements as necessary. In particular, P is allowed to contain up to 0.08% by mass. The component composition range is exemplified by C: 0.12% or less, Si: 1% or less, Mn: 2% or less, P: 0.08% or less, S: 0.03% or less, Cr: 16 -40%, Mo: 0.2-5%, N: 0.025% or less, Ni: 0-0.6%, Cu: 0-1%, Al: 0-1%, Ti: 0 0.8%, Nb: 0 to 0.8%, V: 0 to 1%, Ca: 0 to 0.1%, REM (rare earth element): 0 to 0.1%, B: 0 to 0.1 %, The balance Fe, and a steel type having a composition that is an inevitable impurity. Here, the element whose lower limit is 0% is an optional component, and 0% means that the element is not added and is below the measurement limit in the analysis method in the normal steelmaking process.

  The present invention also provides a polymer electrolyte fuel cell separator obtained by press-forming the roughened stainless steel plate having the roughened surface A. This separator has a reduced contact resistance with the carbon paper of the gas diffusion electrode. As the polymer electrolyte fuel cell in which this separator is incorporated, in the example of FIG. 1 and FIG. Has a roughened surface A.

  Furthermore, in the present invention, a pair of separator members formed by press-forming the above-mentioned roughened stainless steel plate having roughened surfaces A and B as plate-shaped member composite type separators are provided between the roughened surfaces B. A solid polymer fuel cell separator integrated so that a contact point is formed between the two is provided. What has the cooling water flow path partitioned off by the said contact location between said pair of separator members becomes a suitable object. This separator simultaneously reduces the contact resistance of the gas diffusion electrode with carbon paper and the contact resistance between stainless steel plates. In the example of FIGS. 1 and 2, the separator in which the separator member 1 and the separator member 2 are overlapped corresponds to this, and the roughened surface A is provided in the portion of the thick line in the drawing, and the separator member 1 and the separator member 2 has a roughened surface B on the contact surface.

  According to the present invention, a roughened stainless steel sheet in which the contact resistance when contacting a ferritic stainless steel sheet and carbon paper or the contact resistance when contacting the surfaces of a ferritic stainless steel sheet is significantly reduced. Was provided. Therefore, the roughened stainless steel sheet of the present invention is extremely useful for a polymer electrolyte fuel cell using carbon paper as a gas diffusion electrode. In particular, it is suitable for a member constituting a solid polymer fuel cell separator having a rational structure having a cooling water flow path. Moreover, the plate-shaped member composite type separator composed of the roughened stainless steel plate of the present invention is made of a relatively inexpensive ferritic stainless steel, and is low in cost because it uses no precious metal and has a cooling function. However, since it is possible to maintain high conductivity, it contributes to the spread of practical solid polymer fuel cells for in-vehicle use and stationary use.

[Ferrite stainless steel grade]
In the present invention, as a stainless steel exhibiting high durability in an acidic environment to which a separator of a polymer electrolyte fuel cell is exposed, a ferritic stainless steel species containing Mo: 0.2 to 5% by mass is targeted. As such a steel type, an existing known steel type can be adopted. For example, a ferritic steel type specified in JIS G4305: 2005, which contains Mo in the above range can be exemplified.

  Specific component composition ranges are shown, for example, in mass%, C: 0.12% or less, preferably 0.025% or less, Si: 1% or less, preferably 0.5% or less, and Mn: 2% or less, preferably 1% or less, P: 0.08% or less, S: 0.03% or less, Cr: 16-40%, preferably 16-35%, more preferably 16-32%, Mo: 0.2-5%, preferably 1 to 3%, N: 0.025% or less, Ni: 0 to 0.6%, Cu: 0 to 1%, preferably 0 to 0.5%, Al: 0 to 1%, preferably 0 to 0 .3%, Ti: 0 to 0.8%, preferably 0 to 0.3%, Nb: 0 to 0.8%, preferably 0 to 0.3%, V: 0 to 1%, Ca: 0 to 0 0.1%, preferably 0-0.01%, REM (rare earth element): 0-0.1%, preferably 0-0.01%, B: 0-0.1%, preferably 0-0.01%, Balance Fe and Compositions consisting avoidable impurities like.

The main component elements will be briefly described.
C can be tolerated up to 0.12% by mass, but it is preferably 0.12% by mass or less because it lowers the workability and low temperature toughness of ferritic stainless steel. When emphasizing those characteristics, it is more desirable to set it as 0.05 mass% or less, and it is still more preferable that it is 0.025 mass% or less.

  When Si is contained in a large amount, it hardens the steel and impairs workability, so it is preferably 1% by mass or less, and more preferably 0.5% by mass or less.

  When Mn is contained in a large amount, workability, corrosion resistance, and contact resistance are increased. Therefore, Mn is preferably 2% by mass or less, and more preferably 1% by mass or less.

  P is an element effective for improving the corrosion resistance in the internal environment of the fuel cell to which the separator is exposed. However, since the workability decreases as the P content increases, it is preferably 0.08% by mass or less.

  S is an element harmful to corrosion resistance, and is preferably 0.03 mass% or less.

  Cr is an important element for ensuring the corrosion resistance of stainless steel, and generally the corrosion resistance improves as the Cr content increases. In view of the in-cell environment of the polymer electrolyte fuel cell, it is desirable to ensure a Cr content of 16% by mass or more. However, since a large amount of Cr causes a decrease in workability, the Cr content must be suppressed to 40% by mass or less. It is desirable to set it as 35 mass% or less, and 30 mass% or less is more preferable.

  Mo is an element that improves the corrosion resistance of stainless steel by coexistence with Cr. In the present invention, an austenitic stainless steel having a Mo content of 0.2% by mass or more is targeted so as to exhibit excellent durability when exposed to the in-cell environment. The Mo content is more preferably 1% by mass or more. However, a large amount of Mo hardens stainless steel and causes deterioration of workability, and is also disadvantageous in terms of cost, so the upper limit of the Mo content is limited to 5% by mass. More preferably, the content is 3% by mass or less.

  N is preferably 0.025% by mass or less because it lowers workability and low temperature toughness.

  Since Ni and Cu have the effect of improving the general corrosion resistance in an acidic atmosphere and improving the low temperature toughness of the ferritic stainless steel, one or more of these can be added as necessary. In order to sufficiently exhibit the above-described action, it is desirable to secure a content of 0.15% by mass or more in the case of Ni and 0.2% by mass or more in the case of Cu. However, these elements have a property of easily eluting, and battery performance is likely to deteriorate when the eluted Ni ions reach the catalyst layer. Therefore, when adding 1 or more types of Ni and Cu, it is desirable to carry out Ni in the range of 0.6 mass% or less and Cu in the range of 0.8 mass% or less.

  Al functions as a deoxidizer for steel and is also useful for fixing N. Therefore, Al can be added as necessary. In this case, it is more effective to secure a content of 0.04% by mass or more. However, when adding Al, it is desirable to set it as 1 mass% or less, and 0.3 mass% or less is more preferable.

  Ti and Nb have the effect of fixing C and N and improving workability, and are added as necessary. For that purpose, it is effective to add one or more of Ti: 0.03 mass% or more and Nb: 0.03 mass% or more. However, when adding 1 or more types of Ti and Nb, it is desirable to make content of both Ti and Nb into 0.8 mass% or less, and 0.3 mass% or less is more preferable.

  V has an effect of improving the corrosion resistance in the internal environment of the fuel cell, and is added as necessary. In order to obtain the effect sufficiently, it is desirable to secure a V content of 0.2% by mass or more. However, when adding V, it is desirable to make it content of 1 mass% or less.

  In addition, various elements can be added as long as the effects of the present invention are not impaired. For example, Ca: 0.1 mass% or less, preferably 0.01 mass% or less, REM (rare earth element): 0.1 mass% or less, preferably 0.01 mass% or less, B: 0.1 mass% or less, preferably Addition of one or more of 0.01 mass% or less is permitted.

[Form of roughened surface A]
The roughened surface A has a significantly reduced contact resistance with the carbon paper. The carbon paper applied to the gas diffusion layer of the polymer electrolyte fuel cell is made by weaving carbon fibers having a diameter of about 10 μm. When a cross section perpendicular to the longitudinal direction of the carbon fiber is viewed, the surface has irregularities like a gear. The uneven pitch is on the order of submicrons. Therefore, it is considered that if the surface of the stainless steel plate that is the contact partner is formed with unevenness having a size close to the surface unevenness of the carbon fiber, the contact resistance can be reduced due to a significant increase in the contact area. However, according to the study by the inventors, it has been found that the presence of irregularities on the order of submicrons does not necessarily lead to an increase in contact resistance. The reason for this is that even if the unevenness of the submicron order is not formed on the stainless steel plate side, the effect of reducing the contact resistance cannot be sufficiently obtained unless the unevenness of the carbon fiber is well matched with that of the carbon fiber. It is done.

As a result of various investigations, in a polymer electrolyte fuel cell using a stainless steel separator and a carbon paper electrode, in order to ensure sufficient conduction between the separator and the carbon paper, contact with the carbon paper at a contact surface pressure of 1 MPa. It was found that a stainless steel plate having a roughened surface A such that the contact resistance when it was made to be 15 mΩ · cm ² or less must be used for the separator. It is difficult to ensure stable and good energization on a roughened surface that does not satisfy such characteristics. In particular, a steel sheet having a roughened surface A that makes a contact resistance of 10 mΩ · cm ² or less when contacted at a contact surface pressure of 1 MPa is more preferable.

  As a result of repeated detailed studies by the inventors, as such a roughened surface A, fine pits formed when a ferritic stainless steel sheet is immersed in a non-oxidizing acid containing halogen ions such as hydrochloric acid are used. It has been found that it is extremely effective to exhibit a roughened form comprising a roughened form having a surface roughness SPa in the range of more than 0.03 to 0.3 μm. The SPa is more preferably in the range of more than 0.03 to 0.1 μm.

[Roughening surface A forming method]
First, it is preferable to perform normal electrolytic degreasing as a preliminary treatment. As the electrolytic degreasing, for example, anode electrolysis in a sodium orthosilicate aqueous solution having a concentration of 1 to 10% by mass can be suitably employed. The liquid temperature and anode current density of electrolytic degreasing can be set to, for example, 60 ° C. ± 5 ° C., ² to 10 A / dm ^2, and the treatment time may be adjusted in the range of, for example, 5 to 30 seconds.

  The degreased ferritic stainless steel sheet is roughened by immersing it in a non-oxidizing acid containing halogen ions such as hydrochloric acid. An acid having an oxidizing power such as nitric acid, hydrofluoric acid, or aqua regia cannot be appropriately roughened. In roughening using these acids, etching proceeds along the grain boundaries on the surface of the stainless steel, and the roughening form tends to be large unevenness depending on the form of the crystal grains. Even if it is a non-oxidizing acid, appropriate roughening is impossible with sulfuric acid containing no halogen ions. On the other hand, roughening with a non-oxidizing acid containing halogen ions such as hydrochloric acid can cause pitting corrosion without depending on the grain boundaries, and fine pits can be formed on the entire surface of the steel sheet. It becomes. The uneven size (pit size) can be controlled by the acid concentration, temperature, and immersion time of the etching solution according to the steel type.

[Form of roughened surface B]
The roughened surface B is obtained by remarkably reducing the contact resistance between stainless steel plates, and is effective when a plate-shaped member composite separator is constructed.
In FIG. 3, the SEM photograph in the cross section parallel to the plate | board thickness direction about the contact part which the roughening surfaces of the roughening steel plate of this invention are contacting with the contact pressure of 1 Mpa is illustrated. The edge of the pit boundary observed as a sharp protrusion shape undergoes plastic deformation under a large load due to pressing, and the passive film on the surface breaks along with the plastic deformation, and the fresh surfaces come into contact with each other and have a good energized state. It is considered to be.

  In FIG. 4, the SEM photograph in the cross section parallel to the plate | board thickness direction about the contact part which the surfaces of the steel plate which is not roughened is contacting with the contact pressure of 1 Mpa is illustrated. In this case, even when subjected to a contact pressure of 1 MPa, it can be seen that when viewed microscopically, there are few portions where both the steel plates are in contact and there are many portions where gaps are formed. Further, the surface passive film is not easily destroyed. In such a state, contact resistance is high and a good energized state cannot be expected.

According to the study by the inventors, in a plate-shaped member composite type separator, in order to ensure sufficient energization between the plate-shaped members constituting the separator, the contact resistance when contacting at a contact surface pressure of 1 MPa is It has been found that it is necessary to use a plate-like member in which a contact state such as 10 mΩ · cm ² or less is formed. When plate-like members that do not satisfy such characteristics are combined, it is difficult to ensure stable and good energization. In particular, the steel sheet is preferably a roughened steel sheet having a contact resistance of 3 mΩ · cm ² or less when contacted at a contact surface pressure of 1 MPa, and more preferably 1 mΩ · cm ² or less.

As a result of detailed examination, in order to realize a contact state with a contact resistance of 10 mΩ · cm ² or less by contact between fresh surfaces as shown in FIG. A unique roughening form obtained by roughening (roughness formed with a high density of about 80% or more in terms of the ratio of spherical pits with deep openings to the projected area of the steel sheet surface, although the openings are small. It has been found that a roughened surface having a surface roughness SPa of 0.3 μm or more is extremely effective. If SPa is less than 0.3 μm, the ratio of the pit non-occurrence area to the projected area of the steel sheet surface is too large, or the pit is too shallow and the pit boundary is not sharp enough. It is difficult to achieve stable reduction of contact resistance stably.

[Method of forming roughened surface B]
The roughened surface B is obtained by subjecting only one surface of the ferritic stainless steel plate formed with the roughened surface A by the acid dipping treatment to electrolytic roughening treatment in an aqueous ferric chloride solution. Can be made. Even if the roughened surface A has already been formed, the unevenness is sufficiently fine compared to the unevenness required for the roughened surface B, so that there is no problem in forming an appropriate roughened surface B. . Therefore, according to the procedure of “immersion with a non-oxidizing acid containing a halogen ion → electrolytic surface roughening treatment in a ferric chloride aqueous solution on only one side”, a roughened surface A is provided on one side and the opposite side thereof. A ferritic stainless steel sheet having a roughened surface B on the surface can be obtained.

As electrolytic conditions, alternating electrolytic treatment or anodic electrolytic treatment in a ferric chloride aqueous solution containing Fe ³⁺ ions can be suitably applied. The fact that the electrolyte does not contain ions such as NO ³⁻ and SO ₄ ²⁻ that promote the oxidation action of stainless steel also facilitates pitting, that is, the formation of pits, and roughens the surface for a short time. Is important to finish with. In the case of ferritic stainless steel containing Mo, alternating electrolysis is relatively suitable for steel types having a Cr content of approximately 25% by mass or less, and anode for high corrosion resistance steel types having a higher Cr content. Electrolysis is relatively suitable.

It is necessary to set the concentration of the electrolytic solution and the electrolysis conditions in an appropriate range in which the above roughened form can be obtained according to the stainless steel type. For example, in the case of alternating electrolysis, in a ferric chloride aqueous solution having an Fe ³⁺ concentration of 5 to 100 g / L, the current density during anode electrolysis is 1 to 10 kA / m ² , and the current density during cathode electrolysis 0.03 to ² kA / Optimum conditions may be determined in a condition range in which alternating electrolysis of 1 to 20 Hz with m ² is performed for 10 to 300 seconds. In the case of anodic electrolysis, when optimum conditions are determined in a condition range in which anodic electrolysis with a current density of 1 to 10 kA / m ² is performed for 10 to 300 seconds in an aqueous ferric chloride solution with an Fe ³⁺ concentration of 50 to 100 g / L, Good.

[Separator]
The roughened stainless steel plate of the present invention as described above can be a separator member having predetermined bowl-shaped irregularities formed by pressing. It has been experimentally confirmed that the contact resistance reduction effect of the roughened surface A and the roughened surface B is comparable to that when the sample before press working is used even after the press work. When constructing a plate-shaped member composite type separator, a pair of separator members are combined so that the roughened surfaces B are in contact with each other, and usually the contact portions of both members are brazed or caulked. Are integrated so as to be pressed.

2B finish of 18Cr-2Mo steel (SUS444 equivalent steel) with 0.15 mm thickness, 2D finish of 22Cr-1.2Mo steel (SUS445J1 equivalent steel) with 0.2 mm thickness, and 30Cr-2Mo with 0.25 mm thickness A 2B-finished ferritic stainless steel plate of steel (SUS447J1 equivalent steel) was prepared.
About the steel plate cut out from these, after performing electrolytic degreasing as follows, the roughening surface A was formed by the acid immersion process.

First, the steel sheet was immersed in a sodium orthosilicate solution having a concentration of 5% by mass and a liquid temperature of 60 ° C., and electrolytic degreasing was performed by applying anode electrolytic degreasing at a current density of 5 A / dm ² for 10 seconds.
Next, a roughened surface A was formed by subjecting the degreased steel sheet to a hydrochloric acid immersion treatment by dipping in a hydrochloric acid aqueous solution having a concentration of 10% by mass and 50 ° C. The surface roughness SPa was controlled by adjusting the immersion time. As some comparative examples, those not subjected to acid immersion treatment and those subjected to immersion treatment with aqua regia instead of hydrochloric acid aqueous solution were prepared. Here, the surface of these comparative examples is also referred to as roughened surface A.
For the roughened surface A, the surface roughness SPa and the contact resistance with the carbon paper were examined as follows.

[Surface roughness SPa]
For the roughened surface A, the surface roughness SPa was measured at a resolution of 0.01 μm with respect to a 51 μm × 51 μm surface region using a scanning confocal laser microscope (OLS1200, manufactured by Olympus Corporation). Specifically, the objective lens is set to 100 × (depth resolution: 0.01 μm) and the zoom is set to 2.5 × magnification, and after removing the rough surface of the 51 μm × 51 μm field of view, peak noise is removed. Then, a three-dimensional surface profile was obtained by performing image processing for image luminance averaging, and a surface roughness SPa calculated based on the data was obtained.

[Contact resistance]
The sample steel plate was left in the room for about 72 hours, and then a circular sample having a diameter of 15 mm was punched from the steel plate. This circular sample having the roughened surface A was overlapped with carbon paper, Cu blocks were placed on the top and bottom, and a load that gave a contact pressure of 1 MPa was applied by an autograph. A current of 1.77 A (1 A / cm ² ) is passed from a DC power source between the upper and lower Cu blocks, and the voltage drop E (mV) generated between the overlapped circular sample (stainless steel plate) and carbon paper is digitally converted. It measured with the multimeter and calculated | required contact resistance R (mohm * cm < ² >) = E / I.
The results are shown in Table 1. A processing time of 0 min means no processing.

The roughened ferritic stainless steel sheet of the present invention having a roughened surface A having a surface roughness SPa of more than 0.03 to 0.3 μm has a contact resistance between the roughened surface A and carbon paper. However, it became 15 mΩ · cm ² or less at a contact surface pressure of 1 MPa, and a significant reduction in contact resistance was observed.

Using some of the steel plates (including those not subjected to acid immersion treatment) on which the roughened surface A was formed in Example 1, the one side of the roughened surface A was further added in a ferric chloride aqueous solution. The roughened surface B was formed by performing the electrolytic treatment. The electrolysis conditions are as follows. In any case, the surface roughness SPa was controlled by adjusting the treatment time.
[18Cr-2Mo steel]
Fe ³⁺ : 20 g / L, liquid temperature 50 ° C., anode current density: 3.0 kA / m ² , cathode current density: 0.5 kA / m ² , alternating electrolytic treatment with alternating cycle 5 Hz [22Cr-1.2Mo steel]
Fe ³⁺ : 30 g / L, liquid temperature 50 ° C., anode current density: 3.5 kA / m ² , cathode current density: 0.8 kA / m ² , alternating electrolytic treatment with alternating cycle 10 Hz [30Cr-2Mo steel]
Anode electrolytic treatment of Fe ³⁺ : 70 g / L, liquid temperature 50 ° C., anode current density: 3.0 kA / m ² Note that some comparative examples were not subjected to electrolytic treatment, and shot instead of electrolytic treatment A blasted product was prepared. Here, the surface of these comparative examples is also referred to as roughened surface B.

For the roughened surface B, the surface roughness SPa and the contact resistance between the roughened surfaces B collected from the same steel plate were examined.
The surface roughness SPa was measured by the same method as in Example 1.
For contact resistance, after leaving the sample steel plate in the room for about 72 hours, a circular sample having a diameter of 15 mm was punched out from the steel plate and overlapped so that the roughened surfaces B of the two circular samples faced each other. It measured by the same method.
The results are shown in Table 2. A processing time of 0 min means no processing.

The roughened ferritic stainless steel sheet of the present invention having a roughened surface B having a surface roughness SPa of 0.3 to 2 μm has a contact resistance between the roughened surfaces B of 1 MPa. With a margin of 10 mΩ · cm ² or less, a significant reduction in contact resistance was observed. Although the contact resistance of Comparative Example No. g subjected to the shot blast treatment was 10 mΩ · cm ² or less, the shot blast treatment is likely to warp the plate, and there is a problem of dust, etc. Not very suitable. The value of the contact resistance itself was higher than that of the example of the present invention, and a contact resistance of ³ mΩ · cm ² or less could not be realized.

The figure which illustrated typically the cross-sectional structure of the polymer electrolyte fuel cell for vehicles using a metal separator. The figure which illustrated typically the cross-sectional structure of the polymer electrolyte fuel cell for stationary use using metal separators. The SEM photograph in the cross section parallel to the plate | board thickness direction about the contact part which is contacting in the state by which the roughening surfaces B of the roughening steel plate of this invention were pressed. The SEM photograph in the cross section parallel to the plate | board thickness direction about the contact part which is contacting in the state where the surfaces of the steel plate which is not roughened are pressed.

Claims (10)

  Surface roughness formed by dipping in a non-oxidizing acid containing halogen ions on at least one surface of a steel plate made of a ferritic stainless steel type containing Cr: 16 to 40% by mass and Mo: 0.2 to 5% by mass. A roughened stainless steel plate for a separator of a polymer electrolyte fuel cell having a roughened surface A having a thickness SPa of more than 0.03 to 0.3 μm.   The roughened stainless steel sheet for a separator of a polymer electrolyte fuel cell according to claim 1, wherein the non-oxidizing acid is hydrochloric acid. The roughened surface A is a roughened stainless steel sheet for a separator of a polymer electrolyte fuel cell, which has a contact resistance of 15 mΩ · cm ² or less when brought into contact with carbon paper at a contact pressure of 1 MPa.   The roughened stainless steel sheet for a separator according to any one of claims 1 to 3, wherein the ferritic stainless steel type corresponds to a ferritic steel type specified in JIS G4305: 2005.   The ferritic stainless steel type is, by mass, C: 0.12% or less, Si: 1% or less, Mn: 2% or less, P: 0.08% or less, S: 0.03% or less, Cr: 16 -40%, Mo: 0.2-5%, N: 0.025% or less, Ni: 0-0.6%, Cu: 0-1%, Al: 0-1%, Ti: 0 0.8%, Nb: 0 to 0.8%, V: 0 to 1%, Ca: 0 to 0.1%, REM (rare earth element): 0 to 0.1%, B: 0 to 0.1 The roughened stainless steel sheet for a separator according to any one of claims 1 to 3, which is a steel type having a composition of%, balance Fe and inevitable impurities. While having a roughened surface A on one surface of the steel sheet, the surface roughness SPa formed by alternating electrolysis or anodic electrolysis in a ferric chloride aqueous solution is 0.3 to 2 μm on the opposite surface. The roughened surface B has a roughened surface B. When the roughened surfaces B of two flat plate samples cut out from the steel plate are brought into contact with each other at a contact pressure of 1 MPa, the contact resistance is 10 mΩ · polymer electrolyte fuel cell roughened stainless steel plate for a separator according to claim 1 in which exhibits cm ² or less.   A separator for a polymer electrolyte fuel cell obtained by press-forming the roughened stainless steel plate according to any one of claims 1 to 5.   A solid polymer mold in which a pair of separator members formed by press-forming the roughened stainless steel plate according to claim 6 are integrated so that contact points are formed between the respective roughened surfaces B. Fuel cell separator.   The separator according to claim 8, further comprising a cooling water flow path partitioned by the contact location between the pair of separator members.   A polymer electrolyte fuel cell comprising a gas diffusion electrode using the separator and carbon paper according to claim 7, wherein the roughened surface A of the separator and the carbon paper surface are in contact with each other.