JP2005190964A - Metal separator for fuel cell, its manufacturing method, and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a metal separator capable of effectively preventing corrosion of a base body part with a thin coating of Au or the like, and having proper workability for a body part. <P>SOLUTION: This separator 10 for a fuel cell is formed of a metal material board and forms a gas passage between an electrode layer and itself, by stacking one-side plate surface on the electrode layer covering a solid polymer electrolyte membrane. The metal material board contains 30-82 mass% of Ni, 15-30 mass% of Cr, 2-4 mass% of Mo, 1-4 mass% of Cu, 0.1-3 mass% of Ti, 51.9 mass% or less (including 0 mass%) of Fe, and inevitable impurities, having a total content of 0.001-1 mass% and containing 0.0001 mass% or higher of at least either of C and S in total; and has a body alloy of not higher than an alloy remaining part wherein the total content of Ni, Cr, Mo, Cu and Ti is higher than 48.1 mass%, and a metal coating part covering the surface of the body part, formed of a metal more precious than the body alloy and having a thickness of 1-500 nm. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

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

JP 2001-68129 A JP 2000-021418 A JP-A-10-228914

  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 polymer electrolyte membrane for transporting protons between a pair of electrode layers, and a fuel gas (hydrogen) or an oxidant gas (air) is formed on the surface of the electrode layer. A separator for forming the flow path layer is laminated and disposed. On the plate surface of the separator, a recess that forms a gas flow path is formed between the separator and the electrode layer. 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 current extraction efficiency 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, various fuel cell structures in which the separator is made of metal have been proposed in order to achieve both workability, conductivity, and strength (for example, Patent Documents 1 to 3). In a fuel cell using a solid polymer electrolyte membrane, a polymer material having a functional group exhibiting strong acidity such as a sulfonic acid group is used as a solid polymer electrolyte exhibiting proton conductivity, and the polymer material is impregnated. There is a problem that an acidic component oozes out together with the moisture, and corrodes the separator. Carbon separators are very good in terms of corrosion resistance, but have problems in terms of conductivity and strength as described above.

  On the other hand, Patent Documents 1 to 3 disclose better metal separators in terms of conductivity and strength. Specifically, a stainless steel plate material such as SUS316 is used as a main body, and the main body is further plated with a noble metal such as Au. Stainless steel is an Fe-based material that imparts corrosion resistance by promoting the formation of passive state by adding Cr, Ni, and Mo. There are two reasons why noble metal plating is required. First, stainless steel has better corrosion resistance than ordinary Fe-based materials by virtue of passive formation, but the corrosion resistance in a strongly acidic environment unique to fuel cells, particularly sulfuric acid environment, is not always sufficient. If the separator is constituted alone, there is a problem that the internal resistance tends to increase with time as 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 plating film. 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, the contact resistance between the separator and the cell body can be reduced by forming a noble metal plating layer that is highly conductive and hardly oxidatively deteriorates.

  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 the contact resistance of the metal separator is to increase the thickness of the noble metal plating film formed on the separator surface. However, it is self-evident that the precious metal plating film cannot be made excessively thick if the manufacturing cost is reduced. When using an expensive material such as Au, the thickness of the precious metal plating film is rather small as much as possible. There is a request to do (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 precious metal plating film to a minimum thickness. It is.

However, stainless steel such as SUS316 used in Patent Documents 1 to 3 has the following drawbacks.
(1) When the noble metal plating layer (metal coating) is thinly formed, the plating layer becomes discontinuous (for example, in an island shape), and the main body is likely to be exposed as shown in FIG. In addition, even when the plating layer is formed to be thick to some extent, as shown in FIG. 13, pinholes are likely to be generated in the plating layer due to various factors such as etch pits and residual foreign matter, and the body portion is exposed even in the pinhole portion. Produce part. In the case where the main body is made of stainless steel, the formation of a passive state under an acidic sulfuric acid atmosphere is insufficient. Therefore, when the exposed portion is formed, it is difficult to avoid the corrosion of the main body at the exposed portion.

(2) Although related to (1), the separator is usually formed with a recess for forming a gas flow path by plastic working such as a die press. In this case, as shown in FIG. 14, a method of forming a plating layer after performing plastic forming for forming a recess in the main body, and a plating layer after forming a plating layer on the main body as shown in FIG. 15. At the same time, two methods are conceivable: a method of forming recesses. In the process of FIG. 15, since a plating layer has already been formed at the time of processing, a strong tensile bending stress acts on the plating layer at the corner (or edge) portion outside the recess, causing cracks in the plating layer and the main body portion Easy to be exposed. On the other hand, in the process of FIG. 14, since the recess is formed before plating, foreign matter and dirt are likely to remain on the surface of the main body at the corner (or edge) inside the recess, and the contact of the plating layer deteriorates. Exposure of the main body is likely to occur. In either case, when the main body is made of stainless steel, it is difficult to avoid the progress of corrosion of the main body at the exposed portion, as shown in FIG.
(3) In addition, stainless steel with a general composition has difficulty in workability, and when strong processing is performed to form deep recesses in a thin plate, cracks are formed at the corners (or edges) of the recesses as shown in FIG. Is likely to occur, and exposure of the main body based on the cracks is likely to be a problem.
(4) The corrosion resistance of the stainless steel is improved by increasing the amount of Cr and Mo, for example. However, if these elements are excessively increased, the groove workability becomes more difficult and the processing cost also increases. To do. In addition, the passive film becomes excessively strong, leading to a decrease in the adhesion of the plating film.

  An object of the present invention is to provide a metal separator for a fuel cell that can effectively prevent corrosion of the main body portion as a base even if the coating thickness of Au or the like is reduced, and has good workability of the main body portion and is easy to manufacture. An object of the present invention is to provide a manufacturing method thereof and a fuel cell using the same.

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
30 mass% or more and 82 mass% or less of Ni;
15 mass% or more and 30 mass% or less of Cr,
2 to 4% by mass of Mo,
1 mass% or more and 4 mass% or less of Cu,
0.1 mass% or more and 3 mass% or less of Ti,
Fe of 51.9% by mass or less (including zero% by mass);
A total content of 0.001% by mass or more and 1% by mass or less, and unavoidable impurities including at least one of C and S in total of 0.0001% or more, and Ni, Cr, A main body made of a main alloy having a total content of Mo, Cu and Ti of 48.1% by mass or more;
It has a metal coating portion that covers the surface of the main body and has a thickness of 1 nm to 500 nm made of a metal that is electrochemically more noble than the main alloy.

The fuel cell of the present invention is
A solid polymer electrolyte membrane, a first electrode layer covering the first main surface, a second electrode layer also covering the second main surface, and the metal separator for a fuel cell according to the present invention laminated on the first electrode layer In addition, the first separator for forming the gas flow path layer for the fuel gas by the recess and the metal separator for the fuel cell of the present invention are stacked on the second electrode layer, and the recess for the oxidant gas. A second separator forming a gas flow path layer;
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.

  The metal separator for a fuel cell according to the present invention includes, as the composition of the main body, in addition to Cr and Mo in the above composition range, the Ni content is increased to 30% by mass or more, and further contains Cu and Ti in the above composition range. To do. Thereby, the corrosion resistance of the main body is greatly enhanced, and the exposed portion as shown in FIGS. 12, 14 and 15 is formed, for example, by keeping the thickness of the metal coating to 500 nm or less, or FIG. Even when pinholes such as these are formed, elution of the main body alloy due to corrosion from the exposed surface is less likely to occur, and as a result, the battery internal resistance over time due to the progress of separator corrosion when incorporated in a fuel cell Increase can be effectively suppressed. Moreover, the said main body alloy has favorable corrosion resistance, and contact resistance with a cell main body can fully be reduced by formation of a thin metal coating.

  Moreover, by adding Cu in the above composition range as an essential component of the main alloy, not only the corrosion resistance of the main body but also the workability (particularly cold workability) when processing into the required separator shape is greatly improved. . As a result, cracks are unlikely to occur in the main body during processing, and as a result, problems such as the progress of corrosion of the main body exposed by the cracks and the outflow of gas due to the cracks communicating with the gas flow path are unlikely to occur.

  By the way, the main body alloy contains a relatively large amount of Ni of 30% by mass or more and 82% by mass or less as a basic element for imparting corrosion resistance and workability as described above. In this case, in addition to a single Ni metal obtained directly by refining, ferronickel and scraps mainly composed of Ni are used as Ni-based raw materials. These Ni-based raw materials always contain impurities such as S and C, and the main body alloy manufactured using these Ni-based raw materials also contains at least one of S and C as an inevitable impurity. There are various factors in which S and C are contained as impurities in the Ni-based raw material. One of them is that the mat electrolysis method, which is a typical Ni refining method, uses Ni sulfide ore as a raw material. In addition, ferronickel produced by the carbon reduction method and mondo nickel using a nickel carbonyl compound as a raw material mainly contain a relatively large amount of C. In addition, since nickel is a relatively expensive metal, scrap reuse is almost without exception. However, the origin of Ni-based raw materials in the scrap is miscellaneous, and C and S are mixed and C There is also a tendency for the absolute content of to increase.

  When melting the main body alloy using such a Ni-based raw material, decarburization or desulfurization by oxygen blowing or the like is performed in parallel with melting, but C and S are completely removed by the treatment. Of course, this is impossible, and at least one of C and S remains as an inevitable impurity in a total of 0.0001% by mass or more. The amount of residual C as an inevitable impurity varies depending on various factors, but generally 0.001% to 0.05% by mass (in many cases, 0.005% to 0.02% by mass) Similarly, the residual amount of S as an inevitable impurity is 0.0001% by mass or more and 0.015% by mass or less (in many cases, 0.0005% by mass or more and 0.005% by mass or less). It will be within the range.

  In the main body alloy employed in the present invention, the following adverse effects are caused by the residual C. That is, the main body alloy contains 15% by mass or more and 30% by mass or less of Cr for imparting corrosion resistance, but in a specific temperature range (for example, 500 ° C. or more and 900 ° C. or less) during hot rolling or annealing. If this is maintained, or if the temperature range is gradually cooled, Cr carbide may precipitate at the grain boundaries. When such Cr carbide precipitates at the grain boundary, Cr near the grain boundary is depleted and the intergranular corrosion resistance is significantly lowered. On the other hand, S is easily segregated at the grain boundaries of the main alloy, causing a problem of reducing hot workability and corrosion resistance.

  Therefore, in the present invention, in order to suppress the above-described adverse effects due to C or S remaining in the main alloy, 0.1 mass% or more and 3 mass% or less of Ti is contained. Ti tends to form carbides more easily than Cr, and tends to form carbides dispersed in the crystal grains of the alloy. As a result, the addition of an appropriate amount of Ti can effectively suppress the precipitation of Cr carbide at the grain boundaries and thus the depletion of Cr at the grain boundary portions, and can greatly enhance the intergranular corrosion resistance. Moreover, the addition of Ti also reduces S grain boundary segregation, thereby improving hot workability and corrosion resistance. In addition, Cr carbide may precipitate at grain boundaries during hot working, which may promote grain boundary cracking during hot working. However, the addition of Ti suppresses such grain boundary precipitation of Cr carbide, thereby further improving the hot workability of the main body alloy. The above-described effects are particularly prominent when the main alloy plate is manufactured by hot rolling.

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: 30% by mass or more and 82% by mass or less If the Ni content is less than 30% by mass, the corrosion resistance of the main body, particularly corrosion resistance in a strongly acidic atmosphere cannot be secured sufficiently. On the other hand, if the Ni content exceeds 82% by mass, the necessary addition amount of other essential elements cannot be secured, and sufficient corrosion resistance and workability cannot be imparted to the main body. The Ni content is more preferably 30% by mass or more and 60% by mass or less.
(2) Cr: 15% by mass or more and 30% by mass or less If the Cr content is less than 15% by mass, the corrosion resistance of the main body, particularly corrosion resistance in a strongly acidic atmosphere cannot be secured sufficiently. On the other hand, when the Cr content exceeds 30% by mass, the groove processing performance deteriorates. The Cr content is more preferably 15% by mass or more and 25% by mass or less.

(3) Mo: 2% by mass or more and 4% by mass or less If the Mo content is less than 2% by mass, the corrosion resistance of the main body, particularly corrosion resistance in a strongly acidic atmosphere cannot be secured sufficiently. On the other hand, even if Mo exceeding 4 mass% is added, the effect of improving the corrosion resistance is saturated and the manufacturing cost is increased due to the expensive elements. Further, the groove workability is also deteriorated. The Mo content is more preferably 2% by mass or more and 3% by mass or less.

(4) Cu: 1% by mass or more and 4% by mass or less When the Cu content is less than 1% by mass, the workability of the material deteriorates, and for example, cracks are likely to occur in the main body during processing. Addition of Cu is also effective for improving corrosion resistance, but a significant effect cannot be expected when the content is less than 1% by mass. On the other hand, the addition of Cu exceeding 4% by mass saturates the effect of improving workability and conversely reduces the corrosion resistance. The Cu content is more preferably 1% by mass or more and 3% by mass or less. When Cu is added together with Mo, the corrosion resistance can be further improved by the synergistic effect of these components.

(5) Ti: 0.1% by mass or more and 3% by mass or less When the Ti content is less than 0.1% by mass, the effect of suppressing adverse effects due to C or S is weakened, and the intergranular corrosion resistance and hot of the material This leads to deterioration of workability. On the other hand, addition of Ti exceeding 3% by mass results in the formation of a large amount of TiNi-based intermetallic compounds, leading to a decrease in cold workability. For example, as described later, the recesses serving as gas channels are cooled. This leads to the occurrence of cracks and the like when formed by hot pressing. The Ti content is more preferably 0.6% by mass or more and 1.2% by mass or less.

(6) Fe: 51.9 mass% or less (including zero mass%)
When Fe is adopted as the element constituting the balance of the above five elements (hereinafter referred to as essential five elements), as long as the content of the essential five elements is ensured within the above range, both corrosion resistance and workability are achieved. It is possible to dilute the material composition with cheap Fe without significantly impairing it, which contributes to the reduction of the material cost. However, it is also possible to exclude the inclusion of Fe from the composition of the main alloy, for example, when the material is composed of only the five essential elements described above, or when a composition in which subelements as described below are blended is adopted. .

(7) Mn: 10 mass% or less (including zero mass%)
It is possible to add up to about 10% by mass of Mn as an alloy dilution component similar to Fe. More preferably, the amount of Mn added is 2% by mass or less. However, if the amount of Mn added exceeds 10% by mass, it leads to problems such as deterioration of the corrosion resistance of the main body alloy or deterioration of workability.

  The total content of the five essential elements is 48.1% by mass, which is the sum of the lower limit values, and the lower limit value. On the other hand, the upper limit value can be extended to the entire remaining alloy part excluding inevitable impurities. The upper limit of the total content of inevitable impurities is set to 1% by mass in order to ensure the performance of the main alloy. From the economical viewpoint, the lower limit of the total content of inevitable impurities is 0.001% by mass, and the total content of the five essential elements is 100% by mass minus the lower limit of the total content of inevitable impurities. Up to 99.999 mass% is possible.

  Moreover, if the total content of Ni, Cr, Mo, Cu, Ti, Fe and Mn is less than 95% by mass, the corrosion resistance of the main alloy may be deteriorated or the workability may be deteriorated. In addition, Nb thru | or Ta can also be added to a main body alloy as an auxiliary component other than five essential elements in order to further improve corrosion resistance. However, in order to saturate the effect, it is desirable to set the upper limit of the amount added to 2 mass%. Further, when the addition amount is less than 0.1% by mass, the remarkable effect of adding Nb or Ta is lost.

On the other hand, there is no problem even if the following inevitable impurities are contained in the alloy as long as it is up to a certain amount in addition to the above-mentioned components that are positively added (excluding already explained C and S). . Hereinafter, the allowable upper limit values of main impurity elements are as follows.
(A) P: 0.05 mass% or less When P exceeds the allowable upper limit, the workability of the main body alloy is likely to deteriorate.
(B) O: 0.08 mass% or less When O is contained exceeding the allowable upper limit, the workability of the main body alloy is likely to deteriorate.
(C) Al: 0.2% by mass or less, Si: 0.5% by mass or less If Al or Si is contained in excess of the allowable upper limit, the workability of the main body alloy is likely to be deteriorated. The formation of the dynamic film becomes non-uniform and the corrosion resistance may be adversely affected.

  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.

  By adopting the composition specific to the present invention as the main body alloy, the corrosion resistance itself of the main body part that forms the base of the coating is greatly improved. Even if it is small, the corrosion resistance required as a fuel cell metal separator can be sufficiently secured, and the contact resistance with the cell body can be sufficiently reduced. In this case, as shown in FIG. 12, the metal coating portion may be coated 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.

  When the recess is formed by sheet metal pressing, as shown in FIG. 14, the body alloy sheet can be subjected to a coating process after being subjected to sheet metal pressing for forming the recess. In this process, since the recess is formed before plating, foreign matter and dirt are likely to remain on the surface of the main body at the corner (or edge) inside the recess, and the contact of the plating layer deteriorates, exposing the main body. However, in the present invention, by using the main body alloy having a specific composition as described above, the progress of the corrosion of the main body is sufficiently suppressed even if such exposure occurs.

  On the other hand, as shown in FIG. 15, after the main alloy plate material is subjected to the coating process, the main alloy plate material can be subjected to sheet metal pressing for forming the recess. When this process is adopted, since the plating layer is already formed at the time of processing, a strong tensile bending stress acts on the plating layer at the corner (or edge) outside the recess, causing cracks in the plating layer and the main body portion. However, in the present invention, by using the main body alloy having a specific composition as described above, the progress of corrosion of the main body can be sufficiently suppressed even if such exposure due to cracks occurs.

  In addition, when the main body part is formed of the main body alloy having the above composition, the corrosion of the non-formed part may proceed excessively even if the metal coating part forming part and the non-forming part are mixed on the surface of the main body part. There is no. However, if the formation of the metal covering portion is completely omitted, the contact resistance between the metal separator and the cell body is likely to increase, and a certain portion of the surface of the main body portion (for example, 90% or more in area ratio) The formation of the metal coating portion can improve the corrosion resistance itself of the non-formed portion. The cause is that the local battery electromotive force formed between the metal cover and the main body exposed surface changes the electrode potential of the main body exposed surface to the passive region side, so that the metal cover does not coexist. It is considered that passivation of the exposed body surface is promoted. In this case, on the contrary, it means that the corrosion resistance can be ensured without any problem even if about 50% of the surface of the main body is an exposed surface.

  The fact that the passivation of the exposed portion is promoted by the partial metal coating means that, for example, the following simple separator manufacturing method and configuration can be rationally adopted. That is, a plurality of separators are formed on a single main body alloy plate, a metal coating covering the plurality of separators is formed by plating, and then cut and separated into individual separators. In this case, since the side surface of the separator becomes a cut surface, the metal coating is at least partially lost, and the exposed surface of the main body is formed. However, if the metal coating is formed on the main surface of the separator, the passivation of the exposed surface of the side surface is promoted, and the corrosion resistance is hardly reduced. In this case, it is not necessary to individually plate the main body portion of the separator after separation, and it is only necessary to collectively plate the large body alloy plate before separation, which contributes to a significant simplification of the process. However, in order to sufficiently secure the corrosion resistance of the exposed side surface, it is desirable to keep the width of the exposed side surface to 1 mm or less.

    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 first electrode layer 2 that covers the first main surface 3a of the solid polymer electrolyte membrane 3, the second electrode layer 4 that also covers the second main surface 3b, and the metal separator for a fuel cell of the present invention. And a first separator 10a that is stacked on the first electrode layer 2 and forms a gas flow path for the fuel gas by the recess 21; and a metal separator for a fuel cell of the present invention, and the second electrode layer 4, and a second separator 10 b that 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 material constituting the separator 10 is Ni of 30% by mass to 82% by mass, Cr of 15% by mass to 30% by mass, Mo of 2% by mass to 4% by mass, and 1% by mass or more. 4% by mass or less of Cu, 0.1% by mass or more and 3% by mass or less of Ti, 51.9% by mass or less (including zero% by mass) of Fe, and a total content of 0.001% by mass or more and 1% by mass And an inevitable impurity containing at least one of C and S in total of 0.0001% by mass or more, and the total content of Ni, Cr, Mo, Cu and Ti is 48.1 A main body portion 13 made of a main body alloy having a mass% or more, and a thickness of 1 nm to 500 nm (preferably 5 nm to 50 nm, more preferably 5 nm to 20 nm) made of a metal that covers the surface of the main body portion 13 and is noble than the main body alloy. And the metal coating portion 12 of the following). In the present embodiment, the metal coating portion is an Au plating layer. Moreover, the thickness of the main-body part 13 is 0.01 mm or more and 1 mm or less.

  If 50% or more, desirably 90% or more, of the main surface 10a of the separator is covered with the metal coating part 12, for example, the oxidant gas or the solid content is increased even in the recess in which the fuel gas or oxidant gas flows. Corrosion based on sulfate ions eluted from the molecular film 3 can be suppressed. Further, as shown in FIG. 4, the separator 10 has an end face 16 (side face) following the main surface 10 a as a cut face 16, and the metal covering portion 12 is not formed on a part of the cut face 16. Although there is a region where the portion 13 is exposed, the progress of corrosion on the exposed surface can be significantly suppressed by setting the width of the exposed surface to 1 mm or less. In addition, when the anodic polarization curve is measured under the pH 1 condition, the main body alloy constituting the main body portion 13 can distinguish between the active potential region and the passive potential region in the anodic polarization curve.

  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. When cutting the plated plate material 17, as shown in FIG. 9, the cutting blades 19 are brought into contact with both main surfaces of the plated plate material 17, and the opposed cutting blades 19 are brought close to each other. You may make it cut. According to this method, the extension covering portions 12e and 12e extend from both sides of the main body portion 13 in the thickness direction, and the side surface coverage can be further increased.

  As shown in FIG. 10, a thin portion 13t (which can be formed by, for example, pressing the plate member 13 with a compression member 25) along the planned cutting line is formed in the plate member 13, and the thin blade portion 13t is cut by the cutting blade 19. You can also. In addition, the fuel cell separator is formed with an opening such as a gas distribution port 23 (FIG. 2) and an alignment hole used during the lamination assembly. In such an opening, as shown in FIG. 11, a thin portion 13t can be formed in a region including the planned opening portion region, and the opening 27 can be punched out by the punch 26 in the thin portion 13t. By forming the thin portion 13t, the exposed portion width of the side surface or the inner peripheral surface of the opening can be further reduced. In addition, by covering the inner peripheral surface of the opening 27 after punching in the plate material thickness direction by the squeezing member 29, the covering state of the opening inner peripheral surface by the extended covering portion 12e can be further improved.

  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 0.10 mm thick. Next, Au plating layers (metal coating portions) were formed on the both surfaces of the plate at various thicknesses by well-known electrolytic Au plating. The plate material was then formed with a groove-shaped recess shown in FIG. 2 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). In the cut surface, the width of the exposed surface of the metal substrate was 1 mm or less.

  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). Each separator sample was subjected to a corrosion test in a sulfuric acid solution. The sulfuric acid solution had a pH of 1, a temperature of 100 ° C., an immersion time of 168 hours, a change in weight before and after corrosion was measured, and the degree of corrosion was evaluated in terms of a weight consumption rate per unit area. The results are shown in Table 1. According to this, it turns out that the sample which has a main-body part of the composition of No. 1-No. 5 applicable to the Example of this invention has both favorable workability and corrosion resistance. On the other hand, numbers 6 to 15 are comparative examples in which at least one of the five essential elements is outside the range of the composition already described in detail. The composition of No. 6 is inferior in formability (workability) and corrosion resistance because Cu is not added. Furthermore, the corrosion resistance of No. 7 with no addition of Mo is further deteriorated. On the other hand, No. 11 in which Cu is not added and only Mo is added has insufficient corrosion resistance. Similarly, Nos. 8 to 10 are not added with molybdenum and are inferior in corrosion resistance. On the other hand, regarding the effect of addition of Ti, when the reference number 4 is used as the reference composition, it can be seen that the corrosion resistance is greatly deteriorated in the number 13 composition in which Ti is excluded from the reference composition. On the other hand, in No. 12 where Ti was excessively added exceeding the upper limit value, it was found that the corrosion resistance was good but the workability was deteriorated.

  In addition, as a reference experiment, Table 2 shows the results of a corrosion test performed on the samples having the alloy compositions of Nos. 1 to 9 shown in Table 2 without forming recesses (formability is not evaluated).

  First, when comparing corrosion resistance with no Au plating layer formed (Au thickness: 0 nm), numbers 1 to 3 corresponding to the present invention are general stainless steel (SUS316: numbers 4 to 6), Ni—Cr alloy. Compared with (Nos. 7 to 9), the corrosion degree is smaller by one digit or more, and it can be seen that the main body alloy has inherently good corrosion resistance. In comparison with a 50 nm Au plated layer, the corrosion resistance of the stainless steel No. 5 has been improved to some extent by the formation of the Au plated layer. Not too much. In addition, the number 6 stainless steel and the number 8 Ni—Cr alloy are obtained by increasing the Au plating layer to 100 nm, but in the alloy of the present invention, the results of numbers 1 to 5 in Table 1 are compared. As is apparent, corrosion resistance that surpasses these is achieved with an Au plating layer of about 50 nm.

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 schematic diagram which similarly shows a 3rd example. The schematic diagram which similarly shows a 4th 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 figure explaining the conventional problem when a metal coating | coated part is formed after recessed part formation. The figure explaining the conventional problem when a metal coating | coated part is formed before recessed part formation. The figure explaining the concept that corrosion of a main-body part advances from an exposed part.

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 an 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
30 mass% or more and 82 mass% or less of Ni;
15 mass% or more and 30 mass% or less of Cr,
2 to 4% by mass of Mo,
1 mass% or more and 4 mass% or less of Cu,
0.1 mass% or more and 3 mass% or less of Ti,
Fe of 51.9% by mass or less (including zero% by mass);
A total content of 0.001% by mass or more and 1% by mass or less, an inevitable impurity containing at least one of C and S in total of 0.0001% by mass or more, and Ni, Cr, Mo , A main body portion made of a main body alloy having a total content of Cu and Ti of 48.1% by mass or more;
A metal separator for a fuel cell, characterized by having a metal coating portion that covers the surface of the main body and has a thickness of 1 nm or more and 500 nm or less made of a metal that is electrochemically more noble than the main body alloy.   The metal separator for a fuel cell according to claim 1, wherein C as the inevitable impurity is contained in a range of 0.001% by mass to 0.05% by mass.   The metal separator for a fuel cell according to claim 1 or 2, wherein S as the inevitable impurity is contained in a range of 0.0001 mass% to 0.015 mass%.   The metal separator for a fuel cell according to any one of claims 1 to 3, 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 claim 4, wherein the thickness of the metal coating portion is 5 nm or more and 50 nm or less.   The metal separator for a fuel cell according to claim 4, wherein the thickness of the metal coating portion is 5 nm or more and 20 nm or less.   The metal separator for a fuel cell according to any one of claims 1 to 6, wherein the metal coating portion covers the main surface of the main body portion so as to be partially exposed.   The concave part for forming the said gas flow path is formed in the main surface of the side laminated | stacked on the said solid polymer electrolyte membrane of the said metal material board | plate material, The any one of Claim 1 thru | or 7 formed. Metal separator for fuel cells.   The metal separator for a fuel cell according to claim 8, wherein the concave portion 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 9,
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.   11. The fuel cell according to claim 10, wherein the recess is formed by sheet metal pressing, and the covering process is performed on the main body alloy sheet after the main body alloy sheet is subjected to sheet metal pressing for forming the recess. Of manufacturing metal separators for use.   11. The fuel cell according to claim 10, wherein the recess is formed by sheet metal pressing, and the body alloy sheet is subjected to sheet metal pressing to form the recess after the covering step is performed on the body alloy sheet. A method for producing a metal separator. 10. 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. 10. A fuel cell metal according to claim 1, 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, and the metal for a fuel cell according to claim 1. A second separator that is laminated on the second electrode layer as a separator and forms a gas flow path for an oxidant gas;
A fuel cell comprising:

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