JP2005340163A - Metallic separator for fuel cell and its manufacturing method, metallic material for fuel cell and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a metallic separator for a fuel cell in which corrosion resistance to sulfuric acid atmosphere is sufficiently secured, and which is sufficiently superior in corrosion resistance for the pitting even if a pin hole or the like occurs at the metal coated part. <P>SOLUTION: The fuel cell separator 10 has a main part 13 consisting of a main part alloy which contains Ni of 9 wt% or more and 30 wt% or less, Cr of 15 wt% or more and 30 wt% or less, Mo of 1.5 wt% or more and 6 wt% or less, N of 0.04 wt% or more and 0.8 wt% or less, and Fe so that the total content adding Fe may be 90 wt% or more and 100 wt% or less, and furthermore, has a composition in which by making the content of Cr as WCr (wt%), mass content of Mo as WMo (wt%), and the content of N as WN (wt%), the value of pitting index PI as expressed by PI=WCr+3.3 WMo+16 WN, 30 or more and 44 or less, and a metallic coated part 12 which covers the surface of the main part 13 and is composed of a metal more precious than the main part alloy. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel cell metal separator and a method for manufacturing the same, a fuel cell metal material, and a fuel cell.

JP 2002-348640 A

  Conventionally, various fuel cells such as a polymer electrolyte fuel cell, a phosphoric acid fuel cell, a solid electrolyte fuel cell, and a molten carbonate fuel cell have been proposed. Among these, solid polymer fuel cells use solid polymer electrolyte membranes, can be operated at low temperatures, and can be easily reduced in size and weight. Yes. Specifically, a unit cell is formed by sandwiching a solid polymer electrolyte membrane for transporting protons between a pair of electrode layers, and fuel gas (hydrogen) or oxidant gas (air) is applied to the surface of the electrode layers. A separator in which a flow path layer for flowing is formed is laminated. On the plate surface of the separator, a flow path (concave portion) for flowing gas between the electrode layer and the electrode layer is formed. Further, since the separator also serves as a conductive path for taking out the output from the electrode layer of the unit cell, the separator needs to be entirely made of a conductive material.

  Conventionally, as the material of the separator, a material mainly composed of carbon has been used. As described above, it is necessary for the separator for a fuel cell to form complex irregularities on the plate surface for forming a gas flow path. Therefore, it is not practical to perform the shape processing by cutting out from the solid carbon material in consideration of manufacturing efficiency. Therefore, conventionally, a binder made of a polymer material such as a thermoplastic resin is blended with carbon powder to obtain a desired shape by injection molding or the like. However, since the carbon separator obtained in this way contains a considerable amount of an insulating binder, it has poor conductivity and the internal resistance tends to increase, so a large number (for example, 100 or more) unit cells are laminated. The output current is significantly reduced. Further, when the fuel cell is reduced in size and thickness, it is desirable to reduce the thickness of the separator as much as possible. However, the carbon separator described above has poor strength, and the thickness reduction is about 1 to 2 mm.

  Therefore, Patent Document 1 discloses a metal separator that is better in terms of conductivity, strength, and workability. Specifically, a stainless steel plate material is used as a main body, and the main body is further coated with a noble metal coating (for example, plating) such as Au. Stainless steel is an Fe-based material that promotes passive formation by adding Cr, Ni, and Mo to impart corrosion resistance, but there are two reasons why noble metal coating (for example, plating) is required. First, stainless steel has a better corrosion resistance than ordinary Fe-based materials due to the formation of a passive film. However, the corrosion resistance in a strongly acidic environment unique to fuel cells, particularly in a sulfuric acid environment, is not always sufficient. If the separator is made of steel alone, there is a problem that the internal resistance tends to increase with time as the corrosion progresses. In this case, in addition to an increase in contact resistance between the separator and the cell body, deterioration of the solid polymer electrolyte membrane due to diffusion of the eluted metal also causes an increase in internal resistance. Therefore, the corrosion resistance is compensated by forming a noble metal coating. On the other hand, the passive film formed on the surface of stainless steel is an insulating film mainly composed of oxide, which improves the corrosion resistance of the separator, while increasing the contact resistance with the cell body and thus the internal resistance of the battery. It also becomes. However, if a noble metal layer that is highly conductive and hardly oxidatively deteriorates is formed, the contact resistance between the separator and the cell body can be reduced, and high reliability can be obtained.

  By the way, fuel cells are expected to have great potential demand for fuel cell vehicles that will replace gasoline vehicles in the future. However, in addition to improving the performance and durability of each component, production costs will also be fully reduced. Is the key to a widespread use. The simplest method for improving both the corrosion resistance and contact resistance of the metal separator is to increase the thickness of the noble metal film formed on the separator surface. However, it is self-evident that the precious metal film cannot be made thicker if the manufacturing cost is to be reduced. If expensive materials such as Au are used, the thickness of the precious metal film should be made as small as possible. (For example, up to 500 nm). Therefore, it is essential to use a material with a certain level of corrosion resistance for the main body because the corrosion resistance necessary for the separator must be sufficiently secured while keeping the noble metal film to a minimum thickness. is there.

  However, when stainless steel is applied to a fuel cell separator, there are the following problems. That is, when the noble metal coating layer is formed thin, as shown in FIG. 10, the plating layer becomes discontinuous (for example, an island shape), and exposure of the main body portion is likely to occur. Further, even when the coating layer is formed to be thick to some extent, as shown in FIG. 11, pinholes are likely to occur in the coating layer due to various factors such as etch pits and residual foreign matter, and the main body portion is also exposed in the pinhole portion. Produce part. When such an exposed portion occurs, so-called pitting corrosion may easily proceed, apart from corrosion in a sulfuric acid atmosphere. The pitting corrosion is particularly easy to proceed when a chlorine component is present in the corrosive atmosphere. When the atmosphere is used as the oxygen source of the fuel cell as the chlorine contamination source, salt contained in the atmosphere (for example, seawater) Or chlorine in tap water used for cooling water or the like can be considered.

  Pitting corrosion is a corrosion form that progresses while destroying the passivation film layer of stainless steel, and the heterogeneous interface between the noble metal coating and the underlying stainless steel is exposed at the exposed part of the main body such as a pinhole. If so, there is a problem that the progress is further accelerated by the formation of the local battery. In other words, the noble metal coating portion that has been actively formed to prevent corrosion under a sulfuric acid atmosphere leads to the result of promoting corrosion rather than pitting corrosion due to the formation of local batteries. However, it goes without saying that if the noble metal coating is omitted to prevent local battery formation, the corrosion resistance against the sulfuric acid atmosphere cannot be secured.

  The object of the present invention is to provide a metal coating portion such as a noble metal, thereby ensuring sufficient corrosion resistance to a sulfuric acid atmosphere, and in spite of inevitable pinholes in the metal coating portion. An object of the present invention is to provide a metal separator for a fuel cell and a manufacturing method that are sufficiently excellent in corrosion resistance against the above, a metal material for a fuel cell used therein, and a fuel cell using the metal separator for a fuel cell.

Means for Solving the Problems and Effects of the Invention

In order to solve the above problems, the metal separator for a fuel cell of the present invention comprises:
By laminating a plate surface on one side on an electrode layer formed of a metal material plate and covering the solid polymer electrolyte membrane of the fuel cell, a gas flow path is formed between the electrode layer,
Metal material plate
9 mass% or more and 30 mass% or less of Ni;
15 mass% or more and 30 mass% or less of Cr,
1.5% by mass or more and 6% by mass or less of Mo,
0.04 mass% or more and 0.8 mass% or less N,
Fe, which forms the balance composition with respect to the total of Ni, Cr, Mo and N so that the total content of Fe, Ni, Cr, Mo and N is 90% by mass or more and 100% by mass or less,
Further, a Pitting Index represented by PI = WCr + 3.3WMo + 16WN, where Cr content is WCr (mass%), Mo mass content is WMo (mass%), and N content is WN (mass%). A main body portion made of a main body alloy having a composition in which a PI value is adjusted to a value of 30 or more and 44 or less; a metal coating portion covering the surface of the main body portion and made of a metal that is electrochemically more noble than the main body alloy; It is characterized by having.

The metal material for a fuel cell of the present invention is used as a main alloy of the metal separator for a fuel cell of the present invention,
9 mass% or more and 30 mass% or less of Ni;
15 mass% or more and 30 mass% or less of Cr,
1.5% by mass or more and 6% by mass or less of Mo,
0.04 mass% or more and 0.8 mass% or less N,
Fe, which forms the balance composition with respect to the total of Ni, Cr, Mo and N so that the total content of Fe, Ni, Cr, Mo and N is 90% by mass or more and 100% by mass or less,
Further, a Pitting Index represented by PI = WCr + 3.3WMo + 16WN, where Cr content is WCr (mass%), Mo mass content is WMo (mass%), and N content is WN (mass%). It has a composition in which the value of PI is adjusted to a value between 30 and 44.

Furthermore, the fuel cell of the present invention includes a solid polymer electrolyte membrane, a first electrode layer covering the first main surface, a second electrode layer covering the second main surface, and the metal for a fuel cell of the present invention. A first separator that is laminated as a separator on the first electrode layer, and a gas flow path layer for fuel gas is formed by a recess, and a second separator as a metal separator for a fuel cell according to the present invention. And a second separator that forms a gas flow path layer for the oxidant gas by the recess,
It is characterized by having.

Furthermore, the method for producing a metal separator for a fuel cell of the present invention is a method for producing the metal separator for a fuel cell of the present invention,
A body part forming step of forming a body part from a body alloy plate made of a body alloy;
And a coating step of forming a metal coating portion on the surface of the main body alloy sheet.

  In the metal separator for a fuel cell and the metal material for a fuel cell of the present invention, the composition of the main body alloy forming the main body contains 9 mass% or more and 30 mass% or less of Ni in addition to Cr and Mo in the above composition range. . With this composition, even if inevitable pinholes are formed in the metal coating, corrosion resistance under a sulfuric acid atmosphere can be sufficiently ensured, and elution of the main alloy due to sulfuric acid corrosion is less likely to occur. An increase in battery internal resistance over time due to the progress of corrosion of the separator when incorporated in the battery can be effectively suppressed. Further, the contact resistance with the cell main body can be sufficiently reduced by forming the metal coating portion. Furthermore, since it has a composition of austenitic stainless steel, the workability is good, and cracks are hardly generated by pressing into a grooved shape peculiar to metal separators for fuel cells.

  And, in addition to Cr and Mo in the above composition range as essential components of the main alloy, 0.04 mass% or more and 0.8 mass% or less of N is added, and the value of the pitting index PI based on the above-described definition formula is By adjusting the composition to 30 or more, not only corrosion resistance in a sulfuric acid atmosphere but also pitting corrosion in a pinhole portion in a state where a metal coating portion is formed, particularly pitting corrosion in an atmosphere containing chlorine Generation | occurrence | production can be suppressed very effectively. In this respect, it is desirable that the pitting corrosion potential (VC) of the surface of the metal material plate provided with the metal coating portion is 400 mV vs SCE or more.

  The value of PI is an index that quantitatively represents the degree of pitting corrosion resistance of the main alloy. Cr and Mo, which are responsible for the formation of the passive film, also increase PI, and in particular, Mo contributes to an increase in PI of 3 times or more of Cr even with the same addition amount, as in Patent Document 1 (Table 1: Number 2). Furthermore, if the total content of Cr and Mo is increased to a certain level or more while increasing the Mo content, the PI value can be secured to 30 or more. However, if the total content of Cr and Mo is excessively increased, the workability of the material deteriorates, and there is a problem that cracks and cracks are likely to occur when a plate material is pressed into a grooved shape, for example. The material employed in Patent Document 1 has a composition of ferritic stainless steel with a low Ni content and cannot sufficiently secure corrosion resistance under sulfuric acid acidity. Further, if an attempt is made to adjust the PI to be 30 or more only by the total content of Cr and Mo, the solid solution hardening of the ferrite matrix becomes remarkable, and deterioration of workability is unavoidable.

  However, according to the metal material for a fuel cell of the present invention, the corrosion resistance under sulfuric acid acidity can be improved without problems by increasing the Ni content as described above. In addition, by adding a certain range of N, the pitting corrosion resistance is greatly improved without significantly increasing the total content of Cr and Mo, coupled with the addition of Ni to the austenite phase, Workability is also very good. N itself also contributes to stabilization of the austenite phase.

In the present invention, “a metal coating portion having an unavoidable pinhole” means that a corrosion evaluation region having an area of 2000 mm ² is defined on the surface of the metal material plate covered with the metal coating portion, and a composite for pinhole identification. As a cycle test, the salt spray-drying-wetting cycle shown in FIG. 12 was carried out for 30 cycles, which is a condition in which pitting corrosion is much more likely to occur than usual, and five pitting corrosions with an equivalent circle diameter of 5 μm or more were performed. It means a metal coating part generated at a density of / mm ² or more and 500 pieces / mm ² or less.

Hereinafter, the critical meaning of the composition and numerical limitation requirements other than the composition in the present invention will be described. The reason for limiting the composition of the main alloy is as follows.
(1) Ni: 9% by mass or more and 30% by mass or less Ni is an austenite phase stabilizing element and also has a function of strengthening the passive film. It is necessary to add to Cr and Mo which are ferrite phase forming elements in balance with N which is an austenite phase forming element. If the Ni content is less than 9% by mass, the austenite phase cannot be stabilized, and the corrosion resistance in a sulfuric acid atmosphere cannot be secured sufficiently. However, since Ni is expensive and the effect is saturated even if it is added excessively, the upper limit is set to 30% by mass in consideration of cost. Ni is more preferably added in the range of 10% by mass to 20% by mass.

(2) Cr: 15% by mass or more and 30% by mass or less Cr is a passivating element and functions to improve PI and increase pitting corrosion resistance along with improving corrosion resistance under sulfuric acid acidity. When the Cr content is less than 15% by mass, it is not possible to sufficiently ensure the pitting corrosion resistance as well as the corrosion resistance of the main body under sulfuric acid acidity. On the other hand, if the Cr content exceeds 30% by mass, since Cr is a ferrite-forming element, the content of Ni, which is an austenite stabilizing element, must be further increased, resulting in an increase in cost. Moreover, the workability of the material also deteriorates. In addition, from the viewpoint of improving workability, the Cr content is preferably 15% by mass or more and 25% by mass or less. Further, the Cr content is more preferably added in the range of 20% by mass to 25% by mass.

(3) Mo: 1.5% by mass or more and 6% by mass or less Mo is added in an amount smaller than Cr and serves to further strengthen the effect of Cr addition, and is particularly prominent in increasing PI and thus improving pitting corrosion resistance. Contribute to. If the content is less than 1.5% by mass, the corrosion resistance of the main body, particularly corrosion resistance and sulfuric acid corrosion resistance in a sulfuric acid atmosphere cannot be sufficiently secured. On the other hand, even if Mo exceeding 6 mass% is added, the effect of improving the corrosion resistance is saturated and the manufacturing cost increases due to the expensive elements. In addition, workability is also deteriorated. The Mo content is more preferably 2% by mass or more and 4% by mass or less.

  From the viewpoint of improving workability, the total content of Cr and Mo is preferably 29% by mass or less, more preferably 26% by mass or less.

(4) N: 0.04% by mass or more and 0.8% by mass or less N contributes most significantly to the increase of PI and hence to the improvement of pitting corrosion resistance. It is also an austenite phase stabilizing element. When the content is less than 0.04% by mass, the effect of improving pitting corrosion resistance is poor, and when the content exceeds 0.8% by mass, the hardness of the material increases excessively, leading to deterioration of workability. Further, when the N content exceeds 0.8% by mass, special melting equipment such as a pressure melting furnace is required, leading to an increase in cost. In order to make the pitting corrosion resistance improving effect more prominent, the N content is preferably 0.1% by mass, and the more desirable N content considering the balance with securing workability is 0.2. It is not less than 0.5% by mass. On the other hand, when it is desired to prioritize the securing of workability over the effect of improving pitting corrosion resistance, it is desirable that the N content is 0.04 mass% or more and less than 0.1 mass%.

(5) PI: 30 or more and 44 or less When PI is less than 30, pitting corrosion is sufficiently prevented under the situation where the local battery effect is superimposed due to the formation of a metal cover portion in which inevitable pinholes are formed. I can't do that. When all three components (Cr, Mo, N) contributing to PI are increased to the allowable upper limit value, PI becomes the maximum value 44. The value of PI is more preferably 33 or more, and more preferably 35 or more.

(6) The balance composition with respect to the total of Ni, Cr, Mo, and N is formed so that the total content of Fe: Fe, Ni, Cr, Mo, and N is 90% by mass or more and 100% by mass or less.
Fe is a main element of the matrix. Fe, together with unavoidable impurities, can constitute the remainder of the total content of Ni, Cr, Mo and N. On the other hand, a part of the remaining composition relative to the total content of Ni, Cr, Mo and N may be occupied by other subcomponents, but Fe, Ni, Cr so as not to impair the effects of the present invention. The total content of Mo and N is 90% by mass or more (100% by mass or less). When the total content of Fe, Ni, Cr, Mo, and N is less than 90% by mass, the corrosion resistance of the main alloy is deteriorated and the workability is deteriorated.

  For example, the main alloy is 9 mass% to 30 mass% Ni, 15 mass% to 30 mass% Cr, 1.5 mass% to 6 mass% Mo, 0.04 mass% or more. When it is configured to contain 0.8 mass% or less of N, the Fe content is 33.2 mass% or more and 74.4 mass% or less. When the Fe content exceeds 74.4% by mass, it is impossible to ensure the necessary addition amount of the additive element while satisfying the PI30 or higher condition. In addition, when the addition amount is less than 33.2% by mass, a part or all of the above-described additive element becomes excessive, which leads to an increase in cost and the above-described problems at the time of excessive addition. The content of Fe is more desirably 50% by mass or more and 70% by mass or less.

The main alloy can contain other additive elements and inevitable impurities as long as they do not cause excessive deterioration of workability and corrosion resistance.
(7) C: 0.005 mass% or more and 0.05 mass% or less C can be added for the purpose of improving the strength of the material. If the C content is less than 0.005% by mass, the strength improvement effect is not remarkable. On the other hand, if the C content exceeds 0.05% by mass, the hardness of the material increases excessively, leading to a decrease in workability. The C content is more preferably 0.01% by mass or more and 0.03% by mass or less.
(8) Mn: 10% by mass or less Mn is useful as a deoxidizing element during refining and is often unavoidably contained. If the Mn content is excessive, the hardness of the material increases too much and the workability is hindered, so the upper limit is 10% by mass. The Mn content is more preferably 0.1% by mass or more and 7% by mass or less.
(9) Cu: 5% by mass or less Cu is effective for improving the corrosion resistance. Further, the composition to which N is added has an effect of improving the cold workability. However, since hot workability will fall when it adds excessively, when making it contain, it adjusts in 3 mass% or less. The Cu content is more preferably 0.1% by mass or more and 3% by mass or less.
(10) One or more selected from Nb, V, Ta and Hf: 0.01 to 0.5% by mass
Since Nb, V, Ta, and Hf have the effect of forming carbonitrides to refine the crystal grains of the steel and increasing the toughness, each can be added in a range of up to 0.5% by mass. In order to clarify the effect of increasing toughness, it is desirable to contain 0.01% by mass or more.

On the other hand, there is no problem even if the following inevitable impurities are contained as long as they are up to a certain amount in addition to the above-mentioned components that are positively added. Hereinafter, the allowable upper limit values of main impurity elements are as follows.
Si: 1.0% by mass or less Si is useful as a deoxidizing element. If the content exceeds 1.0% by mass, the moldability decreases, so the upper limit is made 1.0% by mass. In order to obtain a sufficient effect as a deoxidizer, addition of 0.05% by mass or more is preferable.
P: 0.030 mass% or less Hot workability will worsen when an upper limit is exceeded. The lower the better.
S ≦ 0.010 mass% or less When the upper limit is exceeded, harmful sulfides that adversely affect hot workability and the like are produced. The lower the better.

  The metal coating part can be composed of, for example, any one of Au, Ag, Pt, Ru, and Pd as a main component (50% by mass or more). Au, Ag, Pt, Ru and Pd are all excellent in conductivity and corrosion resistance, and are plated (especially chemical plating methods such as electrolytic plating or electroless plating), vapor deposition, sputtering or ion plating (especially Further, it is easy to form a coating by a vapor phase film forming method such as a physical method using plasma. When the thickness of the metal coating portion is less than 1 nm, the contact resistance reduction effect or the corrosion resistance improvement effect by the metal coating portion becomes insufficient. On the other hand, forming the metal cover to a thickness exceeding 500 nm leads to a rise in material cost. The thickness of the metal cover is desirably 5 nm or more and 50 nm or less. In this case, as shown in FIG. 10, the metal covering portion may be covered in a form in which the main surface of the main body portion is partially exposed. Naturally, the thickness of the metal cover can be reduced in this way, so that the manufacturing cost can be greatly reduced.

  Moreover, the recessed part for forming a gas flow path can be formed in the main surface by the side of laminating | stacking on the solid polymer electrolyte membrane of a metal material board | plate material. When the recess is formed by processing, the use of the main body alloy having the above composition makes it difficult to cause cracks or the like in the corner or edge portion of the recess bottom, which is particularly bent. This effect is remarkable when the concave portion is formed by sheet metal pressing.

    Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 schematically illustrates an example of a fuel cell in a stacked form. The fuel cell 1 is a solid polymer fuel cell employing a solid polymer electrolyte membrane 3. Specifically, the solid polymer electrolyte membrane 3 is formed of a fluororesin containing a sulfonic acid group, and has a pair of electrode layers 2 and 4 sandwiching this, and the solid polymer electrolyte membrane 3 and the electrodes 2, 4 has a unit battery body 5. Specifically, the unit battery main body 5 includes a first electrode layer 2 covering the first main surface 3a of the solid polymer electrolyte membrane 3, a second electrode layer 4 covering the second main surface 3b, and the present invention. 1st separator 10a which is comprised as a metal separator for fuel cells, is laminated | stacked on the 1st electrode layer 2, and forms the gas flow path for fuel gas by the recessed part 21, and is comprised as a metal separator for fuel cells of this invention The second separator 10b is stacked on the second electrode layer 4 and forms a gas flow path for the oxidant gas by the recess 21. A gasket is disposed between the unit cell main body 5 and the separator 10 in order to prevent leakage of fuel gas and oxidant gas, but is omitted in FIG.

  2 and 3 are a plan view and an enlarged side sectional view showing an outline of separators 10a and 10b (hereinafter, collectively referred to as "separator 10"). As shown in FIG. 2, the separator 10 is formed of a metal plate material, and as shown in FIG. 3, irregularities are formed on the main surface thereof. As shown in FIG. 1, the tip of the convex portion 20 contacts the electrodes 2 and 4. On the other hand, the recess 21 forms a gas flow path between the electrode layers 2 and 4. In the present embodiment, as shown in FIG. 2, the concave portion 21 is formed in a meandering groove shape sandwiched between the convex portions 20, and both ends thereof serve as a gas inlet 22 and a gas outlet 23.

  Returning to FIG. 1, a unit cell body 5 and a separator 10 are used as a unit cell U, and a plurality of unit cells U are stacked via a cooling water circulation substrate 11 made of a conductor such as carbon. Is done. About 20 to 400 unit cells U are stacked, for example, and conductive sheets 9, current collector plates 8, insulating sheets 7 and clamping plates 6 are arranged on both ends of the stacked body from the side in contact with the unit cells U, respectively. Thus, the fuel cell stack 1 is obtained. The current collector plate 8 and the plurality of separators 10 are connected in series, and currents from the plurality of unit battery bodies 5 are collected.

  The metal material plate constituting the separator 10 includes 9% by mass to 30% by mass Ni, 15% by mass to 30% by mass Cr, 1.5% by mass to 6% by mass Mo, The total of Ni, Cr, Mo and N so that the total content of N in the range of 04% to 0.8% by mass and Fe, Ni, Cr, Mo and N is 90% to 100% by mass. Fe, which forms the balance composition with respect to the above, further, the Cr content is WCr (mass%), the Mo mass content is WMo (mass%), and the N content is WN (mass%). = Br + 3.3WMo + 16WN The value of the pitting index PI represented by a body alloy having a composition adjusted to a value of 30 or more and 44 or less, and the body part 13 covering the surface of the body part 13 and from the body alloy Also made of precious metal 1 to 500 nm or less (preferably 5 nm to 50 nm or less). In the present embodiment, the metal coating portion is an Au plating layer.

  Furthermore, the value of the pitting index PI represented by PI = WCr + 3.3WMo + 16WN is adjusted to a value of 30 to 44 while containing N of 0.04% by mass to 0.8% by mass. In particular, it is possible to effectively suppress the progress of pitting corrosion in the pinhole formed in the metal coating portion 12 in an atmosphere containing chlorine.

  Hereinafter, an example of the manufacturing method of the separator 10 will be described. First, the main body alloy is melted so as to have the desired composition, and is subjected to hot forging, hot rolling, cold rolling, and heat treatment to obtain a plate material (main body portion) 13. Next, Au plating is applied to the main surface of the plate material 13 to form the metal coating portion 12. FIG. 5 shows an outline of an apparatus for performing electrolytic Au plating on the plate material 13. In the plating tank B, for example, a plating bath SL containing potassium cyanide cyanide is erected. In the plating bath SL, the cathode electrodes 55, 55 are opposed to both surfaces of the plate material 13, and the metal coating portion 12 made of an Au plating layer can be formed by energizing the plating power source 120 so that the plate material 13 side becomes the anode. .

  Next, die pressing for forming irregularities is performed on the plate 13 after plating by cold working. First, as shown in step 1 of FIG. 6, the plate 13 is placed between the press dies 51, 51 having the uneven pattern 51a to be transferred. Then, as shown in step 2, the concavo-convex pattern is transferred by relatively bringing the molds 51, 51 closer together and pressurizing the plate 13 between both the molds 51, 51. Thereafter, as shown in step 3, the press dies 51 are separated. In addition, you may reverse the order of the metal mold | die press work for uneven | corrugated transfer, and the coating | coated process for forming the metal coating | coated part 12. FIG.

  For example, as shown in FIG. 7, the uneven pattern of the plurality of separators can be transferred to the plate 13 and the uneven pattern of the plurality of separators can be collectively covered with the metal covering portion 12. In this case, the individual fuel cell separator 10 ′ can be obtained by cutting the plated plate member 17 along the planned cutting line CL. As shown in FIG. 8, the plated plate material 17 is cut by placing the plated plate material 17 on a pedestal 20 and bringing the cutting blade 19 into contact with the surface of the plated plate material 17. Can be cut while being pressed against the plated plate member 17. In the plated plate member 17, the metal covering portion 12 extends along the side surface 16 serving as a cut surface, and an extended covering portion 12 e that covers a part of the side surface 16 is formed. Thereby, the exposed surface of the main-body part 13 can be reduced among the side surfaces 16, and the width | variety of this exposed surface can be 1 mm or less by extension.

In order to confirm the effect of the present invention, the following experiment was conducted. First, alloy ingots having various compositions shown in Table 1 are melted using a high-frequency induction melting furnace, then, after hot forging, hot rolling, cold rolling and heat treatment are repeated to form a main body portion. The plate was 0.11 mm thick. Next, an Au plating layer (metal coating part) was formed on both surfaces of the plate by a known electrolytic Au plating with a thickness of 40 nm. The generation density of pitting corrosion (namely, pinhole) having a size of 5 μm or more specified by the pinhole specifying test described above was 10 / mm ^{2 to} 100 / mm ² . After the Au plating, the groove-shaped recesses shown in FIG. 2 were formed by die pressing. In addition, the width | variety of the recessed part was 1.0 mm and the depth was 0.6 mm. Thereafter, the plate material after plating was cut and separated into individual separators with a shearing cutter (planar shape: rectangular shape of 50 mm × 40 mm).

Each separator sample after cutting was visually checked with a magnifying glass for cracks at the bottom of the recess, etc., and no cracks were observed. Good moldability (◯), cracks were observed. The product was determined as a formability defect (x). Moreover, the following test was done with respect to each separator sample.
(1) Measurement of pitting potential (VC):
A test piece having a size of 15 mm × 15 mm was taken from the plate material before grooving, and the pitting potential (VC) was measured by a method defined in JIS: G0577. The VC is measured as V ′ _C10 of the standard.

(2) Combined cycle test:
A test piece having a size of 40 mm × 50 mm is taken from the plate material before grooving, and a total of 6 cycle tests are performed with the salt spray-drying-wetting shown in FIG. 12 as one cycle. did. The judgment conditions are as follows:
“○ (good)”: pitting corrosion is not recognized “△ (possible)”: only thin rust is generated (pitting corrosion is relatively small and small)
“× (impossible)”: Dark rust on the entire surface (pitting corrosion is large and deep)

(3) Corrosion test in sulfuric acid solution A test piece having a size of 40 mm x 50 mm was taken from the plate material before grooving and immersed in a sulfuric acid solution to measure the corrosion consumption rate before and after the test. The sulfuric acid solution had a pH of 1 and a temperature of 100 ° C., and the elution amount of metal ions after corrosion was measured and evaluated at an immersion time of 168 hours. Those having an eluted ion amount of 0.1 mg or less were judged as good (◯), and those exceeding 0.1 mg were judged as bad (x).
(4) Evaluation of workability After grooving, visually check with the magnifying glass for cracks at the edges of the recesses, etc., and if no cracks were observed, good (○), very few cracks Those that remained were judged as acceptable (Δ), and those with cracks were judged as bad (x). The results are shown in Table 1.

  As described above, it can be seen that the separator of the inventive example prepared using the fuel cell metal material of the present invention is excellent in both sulfuric acid corrosion resistance and pitting corrosion resistance, and has good workability.

The side view which shows an example of the lamination | stacking form of the fuel cell of this invention. The top view which shows an example of the metal separator for fuel cells of this invention used for the fuel cell of FIG. The figure which expands and shows the partial cross section of the separator of FIG. The schematic diagram which expands and shows the state of the cut surface. The schematic diagram of the apparatus for plating and forming a metal coating | coated part. Process explanatory drawing of the die press processing of a recessed part formation. The conceptual explanatory drawing of the process of manufacturing in the form which cuts and isolate | separates a some separator from one board | plate material. The schematic diagram which shows the 1st example of a cutting process. The schematic diagram which similarly shows a 2nd example. The figure which shows the concept of the exposed part formed when a metal coating | coated part is formed thinly. The figure which shows the concept of the pinhole formed in a metal coating | coated part. The condition explanation flow diagram of the combined cycle test for pinhole identification.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell 2, 4 Electrode layer 3 Solid polymer electrolyte membrane 10a, 10b Metal separator for fuel cells 12 Metal coating | cover part 13 Main-body part 21 Recessed part

Claims (13)

Forming a gas flow path between the electrode layer by laminating a plate surface on one side on the electrode layer that is formed of a metal material plate and covers the solid polymer electrolyte membrane of the fuel cell,
The metal material plate is
9 mass% or more and 30 mass% or less of Ni;
15 mass% or more and 30 mass% or less of Cr,
1.5% by mass or more and 6% by mass or less of Mo,
0.04 mass% or more and 0.8 mass% or less N,
Fe, which forms the balance composition with respect to the total of Ni, Cr, Mo, and N, so that the total content of Fe, Ni, Cr, Mo, and N is 90% by mass or more and 100% by mass or less,
Further, a Pitting Index represented by PI = WCr + 3.3WMo + 16WN, where Cr content is WCr (mass%), Mo mass content is WMo (mass%), and N content is WN (mass%). A main body portion made of a main body alloy having a composition in which a PI value is adjusted to a value of 30 or more and 44 or less, and a metal covering portion that covers the surface of the main body portion and is made of an electrochemically noble metal than the main body alloy And a metal separator for a fuel cell. 2. The metal separator for a fuel cell according to claim 1, wherein the main alloy contains 0.1 mass% or more and 0.8 mass% or less of N. 3. The metal separator for a fuel cell according to claim 1, wherein the main alloy contains 0.04% by mass or more and less than 0.1% by mass of N. The metal separator for a fuel cell according to any one of claims 1 to 3, wherein the main body alloy contains 15 mass% or more and 25 mass% or less of Cr. The metal separator for a fuel cell according to any one of claims 1 to 4, wherein a pitting corrosion potential (VC) of a surface of the metal material plate provided with the metal coating portion is 400 mV vs SCE or more. The metal separator for a fuel cell according to any one of claims 1 to 5, wherein the metal coating portion is composed mainly of any one of Au, Ag, Pt, Ru, and Pd. The metal separator for a fuel cell according to any one of claims 1 to 6, wherein a thickness of the metal coating portion is 1 nm or more and 500 nm or less. The metal separator for a fuel cell according to claim 7, wherein the thickness of the metal coating portion is 5 nm or more and 50 nm or less. 9. The recess according to claim 1, wherein a recess for forming the gas flow path is formed on a main surface of the metal material plate that is laminated on the solid polymer electrolyte membrane. Metal separator for fuel cells. The metal separator for a fuel cell according to claim 9, wherein the recess is formed by sheet metal pressing. A method for producing a metal separator for a fuel cell according to any one of claims 1 to 10,
A body part forming step of forming the body part from a body alloy plate made of the body alloy;
And a coating step of forming the metal coating portion on the surface of the main body alloy plate material. It is used as the main body alloy of the metal separator for a fuel cell according to any one of claims 1 to 10,
9 mass% or more and 30 mass% or less of Ni;
15 mass% or more and 30 mass% or less of Cr,
1.5% by mass or more and 6% by mass or less of Mo,
0.04 mass% or more and 0.8 mass% or less N,
Fe, which forms the balance composition with respect to the total of Ni, Cr, Mo and N so that the total content of Fe, Ni, Cr, Mo and N is 90% by mass or more and 100% by mass or less,
Further, a Pitting Index represented by PI = WCr + 3.3WMo + 16WN, where Cr content is WCr (mass%), Mo mass content is WMo (mass%), and N content is WN (mass%). A metal material for a fuel cell having a composition in which a PI value is adjusted to a value of 30 or more and 44 or less. 11. The fuel cell according to claim 1, a solid polymer electrolyte membrane, a first electrode layer covering the first main surface, a second electrode layer covering the second main surface, and the fuel cell according to claim 1. The fuel according to any one of claims 1 to 10, wherein the first separator is laminated on the first electrode layer as a metal separator for a gas and forms a gas flow path for fuel gas by the recess. A second separator which is laminated on the second electrode layer as a metal separator for a battery and forms a gas flow path for an oxidant gas by the recess;
A fuel cell comprising:

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