KR101410944B1 - Fabrication of stainless steel for PEMFC bipolar plate - Google Patents

Abstract

A stainless steel manufacturing method for a proton exchange membrane fuel cell comprises a step for preparing stainless steel and a step for forming a Ru oxide on the surface of the stainless steel by performing the cathode electrolysis deposition of the stainless steel in a mixed solution in which a solution containing ruthenium ions (Ru3+) and a nitric acid solution are mixed.

Description

Technical Field [0001] The present invention relates to a method for manufacturing a stainless steel for a polymer fuel cell separator,

The present invention relates to a method of manufacturing a stainless steel for a polymer fuel cell separator, and more particularly, to a method of manufacturing a stainless steel for a polymer fuel cell separator having a low interface contact resistance and a high corrosion resistance by coating a high- ≪ / RTI >

Solid polymer fuel cells are fuel cells that use polymer membranes with hydrogen ion exchange properties as electrolytes. They have a low operating temperature of about 80 ° C compared to other types of fuel cells and are highly efficient. Also, it has high current density and power density, simple structure, fast starting and response characteristics, and can be used as a power source for automobiles and households.

The main components of such a solid polymer fuel cell consist of a polymer electrolyte membrane, an electrode, and a separator to form a stack. In the solid polymer fuel cell, the separator plate is formed so as to block hydrogen gas and oxygen gas as reaction gases from each other, to electrically connect membrane electrode assembly (MEA), to support the membrane electrode assembly, And maintains the shape. Therefore, it should have a dense structure such that the two gases are not mixed, and should have good electrical conductivity for the role of the conductor and sufficient mechanical strength for the role of the support.

The separator is generally formed of one of graphite, carbon, Ti alloy, stainless steel and conductive plastic, and may preferably be formed of stainless steel. Stainless steel has the advantage of being able to achieve thermal conductivity, low gas permeability, and large area, and can form a good product and be made into a thin piece, thereby reducing the volume and weight of the fuel cell stack.

However, when a stainless steel separator is used, there is a problem that corrosion occurs in an acidic electrolytic solution to contaminate electrodes and electrolytes, and the interface contact resistance increases due to corrosion products on the surface.

In order to solve such a problem, Japanese Patent Application Laid-Open No. 2000-353531 proposes a method of nitriding Ti at a high temperature to form a TiN film. In addition, WO 05/124913 discloses a method of disposing a Ti thin plate in a reducing gas atmosphere by a sputtering process and forming a nitrogen diffusion layer on the surface by plasma nitriding treatment. However, since the productivity is lowered by the vacuum treatment process, There is a problem.

DISCLOSURE Technical Problem The present invention has been conceived to solve such problems, and an object of the present invention is to provide a method of manufacturing a stainless steel for a polymer fuel cell separator having a low interface contact resistance and a high corrosion resistance by coating a highly conductive Ru oxide through cathodic electrodeposition .

Method PEMFC separation panyong stainless steel according to one embodiment of the present invention to achieve the above purpose of the solution and nitric acid solution comprising the steps, and the stainless steel to prepare a stainless steel ruthenium ion (Ru ^{3 +)} And forming a Ru oxide on the surface through cathodic electrodeposition in a mixed solution.

Wherein said stainless steel comprises, by weight percent (wt%), C: not more than 0.02%, N: not more than 0.02%, Si: not more than 0.4%, Mn: not more than 0.2%, P: not more than 0.04%, S: , Cu: not more than 1%, Ni: not more than 0.2%, Ti: not more than 0.5%, Nb: not more than 0.5%, V: 0.2 to 1%, W: 4% Or the like.

The solution containing the ruthenium ion (Ru 3 +) may be a RuCl ₃ solution, the RuCl ₃ concentration is 5 to 20 mM, the nitric acid solution is 0.05 to 0.2 M, the solution temperature is 15 to 60 ° C., The applied potential is -0.45 to -0.60 V _SCE Lt; / RTI >

Interfacial contact resistance of stainless steel after the Ru oxide forming step is 140 N / in contact pressure of cm ² 4 mΩcm can be ² or less, the hydrofluoric acid of 1M sulfuric acid and 2ppm of stainless steel, a 70 ℃ corrosion current density after the Ru oxide forming step It may be 0.5μA / cm ² or less under a mixed solution.

According to the method for manufacturing a stainless steel for a polymer fuel cell separator according to the present invention, a Ru oxide is formed on the surface of a stainless steel, whereby a low interface contact resistance and a high contact angle can be ensured and corrosion resistance of the Ru oxide and the base material It is possible to produce stainless steel for a polymer fuel cell separator having excellent corrosion resistance.

1 is a scanning electron microscope (SEM) photograph of the surface of a stainless steel (Example 5) on which Ru oxide is formed according to an embodiment of the present invention.
2 is a photograph showing a contact angle between water and a surface of a stainless steel (Example 5) in which a Ru oxide is formed according to an embodiment of the present invention.
3 is a photograph showing the contact angle between the surface of stainless steel and water according to Comparative Example 4. Fig.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. However, it is to be understood that the present invention is not limited to the disclosed embodiments, but may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. It is intended that the disclosure of the present invention be limited only by the terms of the appended claims. Like reference numerals refer to like elements throughout the specification.

Hereinafter, a method for manufacturing a stainless steel for a polymer fuel cell separator according to a preferred embodiment of the present invention will be described.

Conventional stainless steel has a high interface contact resistance due to the nonconductive passivation film formed on the surface, and the contact angle with water is low, so that it is not easy to remove the water generated at the cathode. Therefore, there is a need for a surface modification method capable of forming a material having a high contact angle with a low interface contact resistance on a stainless steel surface.

A method of manufacturing a stainless steel for a polymer fuel cell separator according to an embodiment of the present invention includes the steps of preparing a stainless steel and a method of preparing the stainless steel by cathodic electrodeposition in a mixed solution of a solution containing ruthenium ions (Ru3 +) and a nitric acid solution And forming a Ru oxide on the surface.

First, prepare stainless steel. The content of C is 0.02% or less, the content of N is 0.02% or less, the content of Si is 0.4% or less, the content of Mn is 0.2% or less, the content of P is 0.04% or less, the content of S is 0.02% , Cu: not more than 1%, Ni: not more than 0.2%, Ti: not more than 0.5%, Nb: not more than 0.5%, V: 0.2 to 1%, W: 4% Or the like.

The reasons for limiting the components of the stainless steel of one embodiment of the present invention will be described. All percentages are percent by weight (wt%).

C: not more than 0.02%, N: not more than 0.02%

Carbon (C) and nitrogen (N) are components that form Cr carbonitride in stainless steel. Therefore, when the Cr content exceeds 0.02%, the Cr-depleted layer is formed in the steel and the corrosion resistance is lowered. Therefore, the content ratio is limited to 0.02% or less.

Si: not more than 0.4%

Silicon (Si) is an effective element for deoxidation. The content of Si is limited to 0.4% or less because the toughness and formability of the stainless steel are deteriorated when it is contained excessively.

Mn: not more than 0.2%

Manganese (Mn) is a component that increases deoxidation, but MnS, which is a generated inclusion, decreases the corrosion resistance, so that the content of Mn is limited to 0.2% or less.

P: not more than 0.04%

The phosphorus (P) reduces the corrosion resistance and toughness of the stainless steel when it is contained excessively, so the content of P is limited to 0.04% or less.

S: not more than 0.02%

Sulfur (S) forms a MnS inclusion together with Mn. Since MnS becomes a starting point of corrosion and reduces corrosion resistance, the content of S is limited to 0.02% or less.

Cr: 20 to 34%

Chromium (Cr) is a component that increases corrosion resistance in an acidic atmosphere in which a fuel cell operates. When it is contained excessively, chromium (Cr) is reduced in toughness and moldability is deteriorated, so that the content of Cr is limited to 20 to 34%.

Mo: 2.5% or less

Molybdenum (Mo) is a component favorable in improving corrosion resistance, but when it is contained excessively, toughness is weakened and the cost is low due to high cost, so that the Mo content is limited to 2.5% or less.

Cu: 1% or less

Copper (Cu) is a component that increases corrosion resistance in an acidic atmosphere in which a fuel cell is operated. If it is contained excessively, Cu may deteriorate the performance of the fuel cell due to elution, so that the content of Cu is limited to 1% or less.

Ni: not more than 0.2%

Nickel (Ni) can be eluted at the time of excessive addition, and the formability may be deteriorated. Therefore, the content of Ni is limited to 0.2% or less.

Ti: 0.5% or less, Nb: 0.5% or less

Titanium (Ti) and niobium (Nb) decrease the toughness of stainless steel when C or N in stainless steel is an effective element for forming carbonitride, or when excess amount is added, so the content is limited to 0.5% or less.

V: 0.2 to 1%

Vanadium (V) increases the corrosion resistance in the acidic atmosphere in which the fuel cell is operated, but may deteriorate the performance of the battery due to ion elution during the excessive addition, so the V content is limited to 0.2-1%.

W: 4% or less

Tungsten (W) has the effect of increasing the corrosion resistance and lowering the interface contact resistance in the acidic atmosphere in which the fuel cell is operated. However, tungsten (W) limits the tungsten content to 4% or less.

Stainless steels having the above composition ranges can be produced from cast steel in a vacuum induction furnace, and can be made of cold rolled steel sheets by repeated annealing, pickling, cold rolling and annealing through hot rolling. The thickness of the cold-rolled sheet may be 2 mm.

The prepared stainless steel is subjected to cathodic electrodeposition in a mixed solution of a solution containing ruthenium ions (Ru ^{3 +} ) and a nitric acid solution to form Ru oxide on the surface.

Preferably, surface coating can be performed by cathodic electrodeposition in a mixed solution of RuCl ₃ solution of 5 to 20 mM concentration and nitric acid solution of 0.05 to 0.2 M concentration for a certain period of time.

If the concentration of the RuCl ₃ solution is less than 5 mM, a uniform Ru oxide may not be generated, and corrosion resistance of the stainless steel may be deteriorated. When the concentration exceeds 20 mM, the effect of formation of Ru oxide is insignificant, Of Ru can be used to increase the production cost. Therefore, the concentration of the RuCl ₃ solution is limited to the above range.

If the concentration of the nitric acid solution is less than 0.05M, a uniform Ru oxide may not be generated and the surface may be damaged, so that the corrosion resistance of the stainless steel may be deteriorated. If the concentration is more than 0.2M, Nitric acid solution can be used and the production cost can be increased. Therefore, the concentration of the nitric acid solution is limited to the above range.

The applied electric potential in the surface coating is -0.45 to -0.60 V _SCE . When the applied potential is higher than -0.45 V _SCE , since the driving force for formation of Ru oxide is insufficient, it is difficult to obtain a uniform Ru oxide, which may cause problems in corrosion resistance. When the applied potential is lower than -0.60, This is because energy consumption can occur.

Hereinafter, the present invention will be described in more detail with reference to Examples.

A stainless steel having the composition shown in the following Table 1 was produced as a slab by a vacuum induction furnace, subjected to hot rolling, annealed, pickled, cold rolled and annealed repeatedly to produce a cold rolled plate having a thickness of 2 mm.

Steel grade C Si Mn P S Al Cr Ni Cu Ti Nb Mo Etc N Example 1 0.006 0.141 0.23 <0.003 <0.003 0.051 30.25 0.11 0.80 0.05 0.26 0 0.3V 0.009 Example 2 0.008 0.130 0.154 <0.003 <0.003 0.083 28.19 0.11 0.20 0.056 0.26 0.5 0.37 W 0.009

The contents of each component in Table 1 are weight percent (wt%). The ruthenium oxide was formed on the surface of stainless steel by varying the solution composition, solution temperature, coating time, and applied electric potential of each of the cold-rolled sheet materials corresponding to Example 2 of the cold-rolled sheet material, Respectively.

The criteria for evaluation of corrosion resistance are as follows: when the corrosion current density in a solution of 1 M sulfuric acid and 2 ppm hydrofluoric acid at 70 ° C, which is the atmosphere of the polymer fuel cell after surface modification, is X and 0.5 ㎂ / cm 2 or less when the corrosion current density is 0.5 ㎂ / Respectively.

division Surface modification solution composition Solution temperature
(° C) Coating time
(minute) Applied potential
(V _SCE ) Interface contact resistance
(m? cm ² )
at 140 N / cm ² Corrosion resistance RuCl ₃
(Unit: mM) nitric acid
Unit: M) Comparative Example 1 5 - Room temperature 30 -0.45 5.2 X Comparative Example 2 5 - 60 30 -0.45 4.7 X Comparative Example 3 10 - 60 30 -0.60 4.1 X Comparative Example 4 10 0.01 60 30 -0.60 3.6 X Inventory 1 5 0.1 60 60 -0.60 3.1 ○ Inventory 2 5 0.2 60 30 -0.45 3.5 ○ Comparative Example 5 5 0.1 60 30 -0.30 4.9 X Inventory 3 5 0.2 Room temperature 60 -0.60 3.3 ○ Honorable 4 10 0.05 60 30 -0.60 2.7 ○ Inventory 5 10 0.1 60 10 -0.60 3.2 ○ Inventory 6 10 0.1 60 60 -0.45 2.9 ○ Honorable 7 10 0.1 60 30 -0.60 2.5 ○ Honors 8 10 0.1 40 30 -0.60 2.8 ○ Proposition 9 10 0.2 60 30 -0.60 2.6 ○ Inventory 10 20 0.2 60 30 -0.60 2.5 ○ Comparative Example 6 - - - - - 30.8 ○

As shown in Table 2, in Comparative Examples 1 to 3, only RuCl ₃ without nitric acid can provide a low interface contact resistance. However, in this case, due to the fact that the Ru oxide is not uniformly formed, local formulations are generated, It can be harmful.

Also, as shown in Comparative Example 4, even when nitric acid is added at a concentration of 0.05 M or less, a uniform Ru oxide can not be formed, which may cause corrosion resistance. Therefore, uniform Ru oxide should be formed to obtain excellent corrosion resistance. To this end, it should be a mixed solution of RuCl ₃ and nitric acid, and the concentration of nitric acid should be 0.05 M or more.

As shown in Examples 1 and 2 and Comparative Example 5, Ru oxide can be formed if the applied potential is the negative electrode potential, but it is preferably -0.45 V _SCE or less in the present invention. When the applied potential is higher than -0.45 V _SCE , it is difficult to obtain a uniform Ru oxide because the driving force of the Ru oxide formation is insufficient, which may cause corrosion resistance.

As shown in Examples 1 to 10, due to the uniform formation of Ru oxide, a low interface contact resistance of 4 m? Cm ² or less and excellent corrosion resistance can be obtained.

1 is a scanning electron microscope (SEM) photograph of the surface of a stainless steel (Example 5) on which Ru oxide is formed according to an embodiment of the present invention. Referring to FIG. 1, Ru oxide is uniformly formed on the stainless steel surface.

2 is a photograph showing a contact angle between water and a surface of a stainless steel (Example 5) in which a Ru oxide is formed according to an embodiment of the present invention. 3 is a photograph showing the contact angle between the surface of stainless steel and water according to Comparative Example 4. Fig.

As shown in FIGS. 2 and 3, the contact angle between Ru oxide formed according to Inventive Example 5 and water on the surface of Comparative Example 6 was measured. As a result, Inventive Example 5 showed a high contact angle of 111.4 degrees, Which indicates a low contact angle. This is because it is easy to remove the water generated in the cathode of the fuel cell because the contact angle is increased as Ru oxide is generated on the surface.

In the above experiments, conditions for forming Ru oxide on the surface of stainless steels having a composition range according to one embodiment of the present invention are important factors for reducing the interface contact resistance, decreasing the contact angle with water, and improving the corrosion resistance And it was found.

According to an embodiment of the present invention, a highly conductive Ru oxide is formed on the surface of a stainless steel through cathodic electrolytic deposition to secure a low interface contact resistance and a high contact angle, and to produce a stainless steel for a polymer fuel cell separator having corrosion resistance .

Although the polymer electrolyte fuel cell separator has been described in the above embodiments, the present invention can be applied to other fuel cell separators.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the exemplary embodiments or constructions. It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. will be.

It is therefore to be understood that the above-described embodiments are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the appended claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be interpreted as being included in the scope of the present invention .

Claims (7)

Preparing a stainless steel; And
Forming a Ru oxide on the surface of the stainless steel by cathodic electrodeposition in a mixed solution of a solution containing ruthenium ions (Ru ^{3 +} ) and a nitric acid solution;
For producing a stainless steel for a polymer fuel cell separator The method of claim 1,
Wherein said stainless steel comprises, by weight percent (wt%), C: not more than 0.02% (excluding 0%), N: not more than 0.02% (not including 0%), Si: not more than 0.4% (Not including 0%), P: not more than 0.04% (not including 0%), S: not more than 0.02% (not including 0%), Cr: (Not including 0%), not more than 0% (not including 0%), Ti: not more than 0% (Not including 0%), Nb: not more than 0.5% (excluding 0%),
V: 0.2 to 1%, W: 4% or less (not including 0%),
And a composition which inevitably contains impurities such as iron and the remainder is inevitably contained in the stainless steel. 3. The method of claim 2,
Wherein the solution containing the ruthenium ions (Ru &lt; 3 + &gt;) is a RuCl ₃ solution. 4. The method of claim 3,
Wherein the concentration of the RuCl ₃ is 5 to 20 mM, the concentration of the nitric acid solution is 0.05 to 0.2 M, the temperature of the solution is 15 to 60 ° C., the applied potential is -0.45 to -0.60 V _SCE Of producing a stainless steel for a polymer fuel cell separator. 5. The method of claim 4,
Wherein the interface contact resistance of the stainless steel after the Ru oxide formation step is 4 m? Cm ² or less at a contact pressure of 140 N / cm ² . 5. The method of claim 4,
The Ru oxide forming step, after the stainless steel corrosion under the current density of the mixture of hydrofluoric acid of 1M sulfuric acid and 2ppm of 70 ℃ solution 0.5μA / cm ² or less PEMFC separation panyong stainless steel manufacturing method. A stainless steel for a polymer fuel cell separator produced by any one of claims 1 to 6.

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