JP2011038166A - Energizing member for fuel cell and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an energizing member made of stainless steel for a fuel cell which has excellent reduction effect of contact resistance and also excellent elution suppression effect of metal ions in an acidic environment. <P>SOLUTION: The energizing member for a fuel cell of a low temperature working type is composed of a steel sheet having a composition comprising, by mass, ≤0.1% C, ≤1% Si, ≤2% Mn, 15 to 35% Cr and 0.5 to 3% Mo, if required, further comprising one or more kinds selected from ≤2% Ni, ≤1% Cu, ≤3% Al, ≤0.8% Nb and ≤0.8% Ti, and the balance Fe with inevitable impurities, and has a roughened surface with the average surface roughness SPa of 0.1 to 2.0 μm, and in which the surface layer part of the roughened surface is composed of a modified layer in which the concentration of Fe is reduced in such a manner that atomic ratio of Fe/(Cr+Fe) reaches ≤0.25 by the contact with an organic acid. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention is an energization member used for a low temperature operation type fuel cell having an operation temperature of 250 ° C. or less, such as a solid polymer fuel cell and a phosphoric acid fuel cell, and particularly as a current collector such as a separator. The present invention relates to a suitable energizing member and a manufacturing method thereof.

  Among the low-temperature operating fuel cells, solid polymer fuel cells can operate at low temperatures below 100 ° C, start up in a short time, and each member is made of a solid structure, making maintenance easy. It has many advantages such as being strong against vibrations and shocks, high fuel efficiency and low noise, and some have already been put into practical use.

  In general, a fuel cell has a structure in which practical power is taken out by connecting cells in series. For example, in the case of a polymer electrolyte fuel cell, electrodes made of carbon paper or the like are arranged on both sides of an ion exchange membrane (solid polymer membrane), one electrode is used for fuel such as hydrogen, and the other electrode is used for oxidation such as air. One cell is formed by sandwiching both electrodes between separators so as to be exposed to the respective gases, and one fuel cell is constructed by stacking such cells. Recently, a “direct methanol fuel cell” of a type in which fuel methanol directly reacts on an electrode has been developed.

  The separator is a member that separates the cells and is in contact with the electrodes to carry electricity between the cells. Recently, a solid polymer fuel cell of the type using stainless steel as a separator and carbon paper as an electrode has been actively 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 electrical conductivity, it is difficult to ensure good electrical 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 a technique of coating the surface of stainless steel with a noble metal having no passive film or a technique of roughening (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 a general roughening method.

  In addition, in the case of a general polymer electrolyte fuel cell using a fluororesin as an ion exchange membrane, depending on operating conditions, the ion exchange membrane may be decomposed to generate an acidic substance, and the separator is exposed to an acidic environment. Is assumed. In that case, metal ions are likely to elute from the stainless steel surface of the separator. When the eluted metal ions enter the ion exchange membrane, it leads to a decrease in ionic conductivity, and further promotes the decomposition of the ion exchange membrane. Therefore, it is desirable to apply stainless steel having the property of preventing the elution of metal ions as much as possible when exposed to an acidic environment as a current-carrying member for a fuel cell.

Japanese Patent Laid-Open No. 11-297338 JP 2003-223904 A JP2001-6713 JP 2008-91225 A JP 2000-345363 A

  As a technique for reducing the contact resistance between stainless steel and carbon paper, the present applicant discloses, in Patent Document 4, a technique that combines a roughening process for forming micropits and a passivation process for increasing the Cr concentration. did. This technique has the effect of improving the familiarity of stainless steel and carbon paper by forming a fine rough surface on the stainless steel surface that matches the surface irregularities of the carbon fibers that make up the carbon paper (patented) This is the use of the effect of suppressing the increase in contact resistance by increasing the Cr concentration in the passive film (see paragraph 0017 in reference 4 and FIG. 1 (C)). A method of immersing in a non-oxidizing acid such as hydrochloric acid is employed for the roughening treatment, and a method of immersing in nitric acid is employed for the passivation treatment.

  However, since the technique of Patent Document 4 uses “surface unevenness matching” as a method of reducing contact resistance, a good effect of reducing contact resistance can be obtained for specific carbon paper. For electrode materials other than those, sufficient effects may not be expected, and the versatility is poor. Further, in the roughening treatment, it is necessary to immerse in an aqueous solution of non-oxidizing acid such as hydrochloric acid for 3 minutes (180 seconds) or longer (see Table 1 of Patent Document 4), and the productivity is always good. I can't say that. Passivation requires nitric acid, which is heavy on the work, environment, and costs. Furthermore, no particular consideration has been given to suppressing the elution of metal ions in the acidic environment of the polymer electrolyte fuel cell. Therefore, further improvement is desired in the technique of Patent Document 4.

  The present invention is a stainless steel current-carrying member for a fuel cell that has an excellent effect of reducing contact resistance and an excellent metal ion elution suppressing effect in an acidic environment, and is provided for the uneven form of a contact partner material (for example, electrode material). It aims at providing the thing which improved the versatility, and providing the technique which manufactures such an electricity supply member by a comparatively simple method.

  The purpose is mass%, C: 0.1% or less, Si: 1% or less, Mn: 2% or less, Cr: 15 to 35%, Mo: 0.5 to 3%, and if necessary, Ni : 2% or less, Cu: 1% or less, Al: 3% or less, Nb: 0.8% or less, Ti: 0.8% or less, containing Fe and unavoidable impurities It is made of a steel plate and has a roughened surface with an average surface roughness SPa of 0.1 to 2.0 μm. The surface layer portion of the roughened surface has an Fe concentration of Fe / (Cr + Fe) by contact with an organic acid. This is achieved by a low temperature operation type fuel cell energization member composed of a reforming layer reduced so that the atomic ratio is 0.25 or less.

  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 the surface roughness parameters obtained by analyzing the data of the three-dimensional surface profile measured by the scanning confocal laser microscope, and the elevation of the cross-sectional curved surface relative to the average surface of the cross-sectional curved surface. Means the average of absolute values. The surface region for measuring the three-dimensional surface profile may be a rectangular surface region having a side of 20 to 120 μm. It is desirable that the resolution in the depth direction of the scanning confocal laser microscope is 0.01 μm or less.

  The Fe / (Cr + Fe) atomic ratio of the modified layer formed on the surface portion of the roughened surface is the atomic% of Fe and Cr in the compound state determined by analysis from the outermost surface by XPS (X-ray photoelectron spectroscopy) Can be calculated based on

  It is extremely effective that the roughened surface has an edge-like boundary at a portion where adjacent concave portions are in contact with each other. Such a roughened surface can be formed by etching in a mixed aqueous solution of a non-oxidizing inorganic acid and ferric chloride.

As a specific method for producing the current-carrying member for a fuel cell of the present invention, a steel plate having the above chemical composition is prepared by using FeCl ₃ (ferric chloride) concentration: 5 to 30% by mass, HCl concentration: 2 to 20% by mass, HCl. / FeCl ₃ molar ratio: 0.3-20, temperature: 35-70 ° C. Hydrochloric acid + ferric chloride aqueous solution soaked in conditions within the range of 3-120 seconds, the average surface roughness SPa is 0 Forming a roughened surface that is .1 to 2.0 μm;
The surface of the roughened surface is contacted with an aqueous solution of an organic acid to preferentially dissolve Fe in the surface layer, and the surface layer of the roughened surface has a Fe / (Cr + Fe) atomic ratio of 0.25 or less. Forming a layer;
The manufacturing method which has can be mentioned.
As the organic acid, for example, one or more of citric acid, maleic acid, tartaric acid, lactic acid, malic acid, and succinic acid are preferably used.

  According to the present invention, as will be described later, the stainless steel for a fuel cell, in which the contact resistance with the contact partner material is reduced by utilizing plastic deformation of the roughened surface and the metal ion suppression effect in an acidic environment is excellent. A steel energizing member can be realized. Since this material is highly versatile with respect to the uneven form of the counterpart material (for example, electrode material), it is suitable as a current collecting material for various polymer electrolyte fuel cells such as direct methanol fuel cells.

The figure which showed typically the cross-sectional form of the surface vicinity in the conventional stainless steel plate for fuel cell separators which formed the micropit. The figure which showed typically the cross-sectional form of the surface vicinity in the electricity supply member of this invention.

  FIG. 1 schematically shows a cross-sectional form in the vicinity of the surface of a conventional stainless steel plate for a fuel cell separator in which micropits as disclosed in, for example, Patent Document 4 are formed. A large number of recesses 2 are formed on the surface of the stainless steel substrate 1 by etching with a non-oxidizing acid (hydrochloric acid, sulfuric acid, etc.) and a passivation treatment with an oxidizing acid (nitric acid). A boundary portion between adjacent recesses 2 is also subjected to an etching action, and a recess boundary 3 having a relatively gentle cross-sectional shape is formed. According to the method of Patent Document 4, such uneven pitch exhibits good matching with the uneven shape of the carbon paper fiber surface (see FIG. 1 (c) of Patent Document 4), thereby making contact resistance effective. It is said that it is reduced. However, in this case, the passivation treatment also plays an important role in reducing the contact resistance. That is, it is not sufficient to simply obtain an uneven pitch with good matching, and the contact resistance with the carbon paper is not significantly reduced only after the passivation treatment (Comparative Example and Implementation in Table 5 of Reference 4). See example contrast).

  In FIG. 2, the cross-sectional form of the surface vicinity in the electricity supply member by which average surface roughness SPa of this invention was adjusted to 0.1-2.0 micrometers is typically shown. On the surface of the stainless steel substrate 1, there are a large number of recesses 2 formed by etching with an aqueous solution of an inorganic acid to which ferric chloride is added, for example. When such an aqueous solution is used, the inner wall of the pit generated on the surface of the steel sheet is etched, and a deep recess 2 is formed instead of the opening diameter. As the pits grow, the wall surfaces of the adjacent pits collide with each other, and as a result, the recess boundary 3 has an edge shape. Further, in the surface modification with an organic acid, etching that greatly changes the concavo-convex shape does not occur, so that an edge boundary exists even after the step of forming the modified layer.

When a fuel cell stack is constructed with a surface pressure applied between a current-carrying member made of such a roughened stainless steel plate and a contact partner material, the edge boundary of the roughened stainless steel plate is separated from the contact partner material. The plastic deformation is caused by the received stress, and the contact area with the contact partner increases. Moreover, defects such as cracks are introduced into the passive film of the stainless steel substrate due to plastic deformation. Together, these actions bring about a significant contact resistance reduction effect. The contact resistance reduction effect is not dependent on matching with the microstructure of the contact partner material, and is therefore highly versatile.
Hereinafter, the matter which specifies this invention is demonstrated.

[Chemical composition of stainless steel sheet]
In the present invention, a ferritic stainless steel type having a smaller thermal expansion coefficient than that of the austenitic steel type is employed. Hereinafter, “%” in the steel composition means “% by mass” unless otherwise specified.
When C is contained in a large amount, it may adversely affect the workability and low temperature brittleness of stainless steel, but in the present invention, C content up to 0.1% is allowed. More preferably, it is 0.05% or less.

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

  When Mn is contained in a large amount, workability, corrosion resistance, and contact resistance are increased. Therefore, Mn is limited to 2% or less, and more preferably 1.5% or less.

  Cr is an important element for ensuring the corrosion resistance of stainless steel. Considering the in-cell environment of the polymer electrolyte fuel cell, it is necessary to ensure a Cr content of 15% or more. However, since a large amount of Cr causes a decrease in workability, the Cr content is limited to 35% or less, and more preferably 30% or less. You may manage to 25% or less.

  Mo is an element that improves the corrosion resistance of stainless steel by coexistence with Cr. In the present invention, a steel type having a Mo content of 0.5% or more is employed so as to exhibit excellent durability when exposed to the in-cell environment. However, since a large amount of Mo content hardens stainless steel and causes deterioration of workability, and is also disadvantageous in terms of cost, the upper limit of the Mo content is limited to 3%. You may manage to 2% or less.

  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 action, it is more effective to secure a content of 0.15% or more in the case of Ni and 0.2% or more in the case of Cu. However, elution of these elements during use of the fuel cell may lead to a decrease in cell performance. As a result of various studies, when one or more of Ni and Cu are added, Ni is 2% or less, and Cu is 1% 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% or more. However, in the case of adding Al, it is preferably 3% or less, and more preferably 1.5% or less.

  Ti and Nb have the effect of fixing C and N and improving workability, and are added as necessary. For that purpose, it is more effective to add one or more of Ti: 0.03% or more and Nb: 0.03% or more. However, when adding 1 or more types of Ti and Nb, it is necessary to make content of both Ti and Nb into 0.8% or less, and 0.5% or less is more preferable.

[Average surface roughness SPa]
As a result of detailed studies, the inventors have formed a roughened surface having an average surface roughness SPa of 0.1 μm or more by a roughening method described later, and plastic deformation is caused in a portion where adjacent concave portions are in contact with each other. It is possible to realize a roughened form having an edge boundary that is easy to achieve, and to obtain a significant contact resistance reduction effect due to plastic deformation when pressed against a contact partner material. When SPa is less than 0.1 μm, the growth of pits is insufficient, and an edge boundary with a sharp angle is difficult to be formed, so that it becomes difficult to stably obtain a remarkable contact resistance reduction effect. On the other hand, on the roughened surface where SPa exceeds 2.0 μm, the pits grow excessively, and the amount of edge-like boundaries with sharp angles is reduced due to the “biting” between the pits. There are many cases. If it becomes so, the reduction effect of contact resistance will become small. Therefore, the present invention is directed to a stainless steel plate whose average surface roughness SPa is adjusted to 0.1 to 2.0 μm. A particularly preferable range of SPa is 0.1 to 1.0 μm.

[Modified layer]
In the present invention, as a means for suppressing elution of metal ions in the in-cell environment of a low temperature operation type fuel cell, Fe that exists as a compound on the surface layer of the roughened surface by contact with an organic acid. Then, a modified layer is formed in which the Fe concentration is reduced so that the Fe / (Cr + Fe) atomic ratio is 0.25 or less. According to the study by the inventors, the metal element with the largest amount of elution from stainless steel in the cell environment is Fe that is contained most as a constituent element of the stainless steel substrate. It was found that the amount of Fe elution in the acidic environment in the cell can be greatly reduced by reducing the Fe concentration in the surface layer portion in advance. On the other hand, in order to ensure corrosion resistance and reduce the total amount of elution of metal elements including steel component elements other than Fe (especially Mo which tends to be concentrated in the passive film), the passive film exists on the surface layer. It is extremely effective to increase the Cr concentration in the medium. As a result of detailed examination, metal ions were eluted in an acidic environment when a modified layer was formed such that the Fe / (Cr + Fe) atomic ratio in the compound state was 0.25 or less by analysis from the outermost surface by XPS. The amount was found to be significantly reduced. Although the basic corrosion resistance level differs depending on the steel type, when compared with the same steel type, any ferritic stainless steel having the composition range defined in the present invention can be obtained by combining Fe / (Cr + Fe) atoms in a compound state in any steel type. By setting the ratio to 0.25 or less, a remarkable reduction effect of the elution amount of metal ions is recognized. It is particularly preferable that the Fe / (Cr + Fe) atomic ratio is adjusted to 0.20 or less.

(Roughening treatment)
As a method for forming the roughened surface, a method of etching a stainless steel plate in a mixed aqueous solution of “non-oxidizing inorganic acid (for example, hydrochloric acid)” and “ferric chloride” is extremely effective. Specifically, FeCl ₃ (ferric chloride) concentration: 5-30% by mass, HCl concentration: 2-20% by mass, HCl / FeCl ₃ molar ratio: 0.3-20, temperature: 35-70 ° C., Immersion time: Within the condition range of 3 to 120 seconds, it is possible to find a condition for obtaining a roughened surface having an average surface roughness SPa of 0.1 to 2.0 μm. At this time, the roughening form (refer FIG. 2) which has an edge-like boundary in the part which adjacent recessed parts contact | connect is obtained. Depending on the steel type, the optimum conditions within the above condition range will vary somewhat.

  Ferric chloride has the action of generating pitting corrosion on the stainless steel surface, and hydrochloric acid has the action of completely dissolving the stainless steel surface. The technique of immersing ferritic stainless steel in an aqueous solution in which these two types of substances are mixed is particularly suitable for obtaining a roughened form having an edge-like boundary.

[Organic acid treatment]
After performing the roughening treatment, a modified layer having an Fe / (Cr + Fe) atomic ratio of 0.25 or less can be formed by bringing the roughened surface into contact with an organic acid. As the organic acid, for example, one or more of citric acid, maleic acid, tartaric acid, lactic acid, malic acid, and succinic acid are preferably used. For example, Patent Document 5 discloses a technique for modifying a stainless steel surface using an organic acid. The organic acid is considered to have an action of chelating and removing Fe from the surface layer portion of the stainless steel. Since Cr, which is one of the main constituent elements of the passive film, is not chelated, Fe in the surface layer is preferentially removed by contact with an organic acid. As a result, when exposed to the in-cell environment, Fe that easily elutes has already decreased in the vicinity of the surface layer, so that new elution of Fe is remarkably reduced. Further, since Cr is concentrated in the surface layer portion, the effect of preventing the elution of metal ions other than Fe is improved by improving the corrosion resistance. Furthermore, it has been found that the treatment with an organic acid can maintain the roughened form already formed, unlike the treatment using an inorganic acid (hydrochloric acid, sulfuric acid, nitric acid, etc.). Therefore, it becomes possible to form a modified layer in which the Fe concentration is reduced on the roughened surface having an edge boundary by combination with the roughening treatment using ferric chloride.

  A stainless steel plate (No. 2D finishing material) having a thickness of 0.2 mm having the composition shown in Table 1 was prepared.

  A test piece was cut out from each stainless steel plate, subjected to a roughening treatment, and then subjected to an organic acid treatment to obtain a test material. A part of the test material that was not subjected to one or both of roughening treatment and organic acid treatment was also prepared.

The roughening treatment was performed by using a hydrochloric acid + ferric chloride aqueous solution having the following concentration as a treatment solution and immersing each stainless steel plate in this solution. The treatment temperature and the immersion time were the conditions described in Table 2-1 and Table 2-2.
(Roughening solution)
FeCl ₃ (ferric chloride) concentration: 19% by mass, HCl concentration: 5% by mass, HCl / FeCl ₃ molar ratio: 1.17

  In the organic acid treatment, a 200 ppm citric acid aqueous solution was used as a treatment solution, and the treatment conditions were 60 ° C. and the immersion conditions were 1 h.

The following test was done about the surface of each test material after the said process. In addition, each test material was prepared so that it might become the same surface state on both surfaces.
[Measurement of average surface roughness SPa]
The roughened surface was observed at a magnification of 5000 times with a scanning confocal laser microscope (Olympus; OLS1200), and the surface profile of a rectangular region of 50 μm × 50 μm was captured with a resolution of 0.01 μm in the depth direction. After performing isolated point removal once and image luminance averaging once, the average surface roughness SPa was calculated.

[Measurement of Fe / (Cr + Fe) atomic ratio of surface layer]
The surface analysis of the test material was conducted using XPS (AXIS-NOVA). The measurement area was set to 0.3 mm × 0.7 mm, the excitation line of AlKα (single color) was used, the photoelectron extraction angle was set to 90 °, and the surface of the test material was analyzed without sputtering. This analysis provides information from the surface to a depth of about 5 nm. The Fe / (Cr + Fe) atomic ratio in the compound state was calculated from the quantitative values of Fe and Cr.

[Measurement of contact resistance]
A carbon paper having a diameter of 15 mm (manufactured by Toray Industries Inc .; TGP-H-120) is brought into contact with both surfaces of the sample collected from the test material at an equal pressure of 1 MPa, and the current density I at the contact surface is 1 A / cm. ^{2 A} DC voltage E is applied between the carbon papers on both sides so that the current value is 1.77 A, the voltage E is measured by the four-terminal method, and contact resistance R (mΩ · cm ² ) = E / I Asked.

[Measurement of metal ion elution amount]
A test piece of 80 mm × 40 mm cut out from a test material was immersed in 300 mL of dilute sulfuric acid aqueous solution adjusted to pH = 2.0, and held at 168 h at 80 ° C., then the test piece was taken out and eluted into the test solution. The amount of metal ions was measured using ICP-AES. Metal ions were quantified with Fe, Cr, and Mo, and the sum of these was used as the elution amount.
The test results are shown in Tables 2-1 and 2-2. In addition, it was confirmed by the surface observation separately that the edge-like boundary was formed in the part where the adjacent recessed parts contact | abutted on the roughening surface of the example of this invention.

  As can be seen in Tables 2-1 and 2-2, the contact resistance of each steel type is significantly reduced when the average surface roughness SPa is adjusted to 1.0 μm or more as compared with the steel having a smaller SPa. You can see that Moreover, it is possible to significantly reduce the Fe / (Cr + Fe) atomic ratio of the surface layer portion by performing the organic acid treatment. In each steel type, the examples of the present invention subjected to the organic acid treatment were not subjected to the roughening treatment and the organic acid treatment even though the surface area was increased by the roughening treatment (original stainless steel). It can be seen that the elution amount of metal ions is remarkably reduced as compared with (steel plate). Since steel type G does not contain Mo, basic corrosion resistance is insufficient, and the amount of metal ions eluted is very large.

  Some of the test materials shown in Table 2-1 and Table 2-2 were used as separator materials, and the following two types of battery tests were performed.

[Battery test 1]
After coating carbon black carrying platinum fine particles on both sides of the fluorine-based solid polymer membrane, carbon paper (Toray Industries, Inc .; TGP-H-120) is thermocompression bonded to produce a membrane-electrode assembly (MEA). did. On the other hand, the separators (current collectors) on the anode side and the cathode side were produced by press-molding the stainless steel plates of the test materials shown in Tables 2-1 and 2-2. A fuel cell composed of a single cell was fabricated by combining the MEA and the separator. In each fuel cell, the same type of test material was applied to the separators on both sides. Purified hydrogen was flowed on the anode side of the single cell, air was flowed on the cathode side, the current density of the current passing through the MEA was maintained at 0.3 A / cm ² , and the temperature was maintained at 70 ° C., and a continuous 100 h discharge test was conducted. It was. And the cell voltage at the time of 100-hour progress was measured. The results are shown in Tables 2-1 and 2-2.

[Battery test 2]
A fuel cell composed of a single cell was produced in the same manner as in battery test 1. Here, a direct methanol fuel cell was operated by injecting 3M methanol on the anode side of the single cell and flowing air on the cathode side. A discharge test was conducted continuously for 100 hours with the current density of the current passing through the MEA maintained at 0.1 A / cm ² and the temperature maintained at 30 ° C. And the cell voltage at the time of 100-hour progress was measured. The results are shown in Tables 2-1 and 2-2.

  In both the battery tests 1 and 2, in the fuel cell to which the sample material of the present invention which was subjected to roughening treatment and organic acid treatment was applied, a comparative example in which at least one of roughening treatment and organic acid treatment was not performed The cell voltage after 100 hours showed a higher value than that using the test material.

1 Stainless steel substrate 2 Recess 3 Recess boundary

Claims (7)

  In mass%, C: 0.1% or less, Si: 1% or less, Mn: 2% or less, Cr: 15 to 35%, Mo: 0.5 to 3%, balance Fe and inevitable impurities It is made of a steel plate and has a roughened surface with an average surface roughness SPa of 0.1 to 2.0 μm. The surface layer portion of the roughened surface has an Fe concentration of Fe / (Cr + Fe) by contact with an organic acid. A current-carrying member for a low-temperature operation type fuel cell, which is composed of a reformed layer that is reduced so that the atomic ratio is 0.25 or less.   The composition of the steel sheet is% by mass: C: 0.1% or less, Si: 1% or less, Mn: 2% or less, Cr: 15 to 35%, Mo: 0.5 to 3%, and Ni: 2. One or more of 2% or less, Cu: 1% or less, Al: 3% or less, Nb: 0.8% or less, Ti: 0.8% or less, and the balance is Fe and inevitable impurities. The current-carrying member described in 1.   The current-carrying member according to claim 1, wherein the roughened surface has an edge boundary at a portion where adjacent concave portions are in contact with each other.   The current-carrying member according to claim 1, wherein the roughened surface is formed by etching in a mixed aqueous solution of a non-oxidizing inorganic acid and ferric chloride. In mass%, C: 0.1% or less, Si: 1% or less, Mn: 2% or less, Cr: 15 to 35%, Mo: 0.5 to 3%, balance Fe and inevitable impurities The steel sheet is made of hydrochloric acid with FeCl ₃ (ferric chloride) concentration: 5-30% by mass, HCl concentration: 2-20% by mass, HCl / FeCl ₃ molar ratio: 0.3-20, temperature: 35-70 ° C. + A step of forming a roughened surface having an average surface roughness SPa of 0.1 to 2.0 μm by immersing in a ferric chloride aqueous solution under conditions within a range of 3 to 120 seconds;
Forming a modified layer having an Fe / (Cr + Fe) atomic ratio of 0.25 or less on a surface layer portion of the roughened surface by contacting the roughened surface with an aqueous solution of an organic acid;
The manufacturing method of the electricity supply member for fuel cells of a low-temperature operation type which has this.   The composition of the steel sheet is% by mass: C: 0.1% or less, Si: 1% or less, Mn: 2% or less, Cr: 15 to 35%, Mo: 0.5 to 3%, and Ni: 6. One or more of 2% or less, Cu: 1% or less, Al: 3% or less, Nb: 0.8% or less, Ti: 0.8% or less, and the balance is Fe and inevitable impurities. The manufacturing method of the electricity supply member as described in any one of.   The method for producing a current-carrying member according to claim 5 or 6, wherein one or more of citric acid, maleic acid, tartaric acid, lactic acid, malic acid, and succinic acid is used as the organic acid.

Images