KR20160027378A - Metal separator for polymer electrolyte fuel cell and method for producing the same - Google Patents

Abstract

Provided is a metal separation plate for a polymer electrolyte fuel cell, comprising a stainless steel substrate including a passive state coating layer on the surface, wherein the passive state coating layer includes 10-20 wt% of chrome oxide and 20-40 wt% of iron oxide. Provided in an embodiment of the present invention is the metal separation plate for a polymer electrolyte fuel cell simultaneously having excellent corrosion resistance and a low contact resistance.

Description

Technical Field [0001] The present invention relates to a metal separator for a polymer electrolyte fuel cell,

To a metal separator for a polymer electrolyte fuel cell and a manufacturing method thereof.

A polymer electrolyte fuel cell (FEP) is a fuel cell that uses a polymer membrane with hydrogen ion exchange properties as an electrolyte. It has a lower operating temperature, higher energy efficiency, higher current density and higher output density than other types of fuel cells, There is a fast response to change.

A bipolar plate or separator used in a polymer electrolyte fuel cell is a structure in which hydrogen and oxygen flow channels are formed. Each unit cell is separated and serves as a support for a membrane electrode assembly (MEA) And can serve as a current collector for transferring the generated energy.

The separator used in such a polymer electrolyte fuel cell is required to have high corrosion resistance and low contact resistance and is coated with a metal to meet this requirement. However, in the case of gold or platinum, the cost competitiveness is significantly lowered. In the case of nickel or copper, The resistance can not be realized at a low level, and in some cases, corrosion resistance is deteriorated.

An embodiment of the present invention provides a metal separator for a polymer electrolyte fuel cell which simultaneously realizes excellent corrosion resistance and low contact resistance.

Another embodiment of the present invention provides a method of manufacturing a metal separator for a polymer electrolyte fuel cell.

In one embodiment of the invention, the passive film comprises a stainless steel substrate having a passive coating on its surface, wherein the passive coating comprises about 10% to about 20% by weight of chromium oxide and about 20% to about 40% The present invention also provides a metal separator for a polymer electrolyte fuel cell.

The passive film may be formed by surface treatment with a mixed solution of nitric acid and hydrofluoric acid.

The surface treatment is performed by immersing a substrate made of stainless steel in a mixed solution of nitric acid and hydrofluoric acid, and the mixed solution may be stirred while the surface treatment is performed.

The mixed solution may contain about 35 wt% to about 99.999 wt% nitric acid.

The mixed solution may contain about 0.001 wt% to about 65 wt% of hydrofluoric acid.

The metal separator for a polymer electrolyte fuel cell can be applied to a fuel cell of a vehicle.

The metal separator for a polymer electrolyte fuel cell may have a contact resistance of about 12 m? · Cm ² or less.

The metal separator for a polymer electrolyte fuel cell may have a corrosion current density of about 1 μA / cm ² or less.

The thickness of the passive film may be about 0.1 nm to about 30 nm.

The thickness of the substrate may be between about 0.05 mm and about 0.2 mm.

In another embodiment of the present invention, there is provided a method of manufacturing a metal separator for a polymer electrolyte fuel cell, comprising the steps of: immersing a substrate made of stainless steel in a mixed solution of nitric acid and hydrofluoric acid;

The mixed solution may be stirred during the surface treatment of the substrate.

The mixed solution may be stirred at about 500 rpm to about 800 rpm.

The surface treatment may be carried out at about 10 캜 to about 50 캜.

The surface treatment may be performed for about 0.5 hour to about 4 hours.

The method may further include cleaning the substrate before dipping the substrate.

The metal separator for a polymer electrolyte fuel cell can achieve excellent corrosion resistance and low contact resistance at the same time.

1 is a schematic cross-sectional view of a metal separator for a polymer electrolyte fuel cell according to an embodiment of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings, which will be readily apparent to those skilled in the art to which the present invention pertains. The present invention may be embodied in many different forms and is not limited to the embodiments described herein.

In order to clearly illustrate the present invention, parts not related to the description are omitted, and the same or similar components are denoted by the same reference numerals throughout the specification.

In the drawings, the thickness is enlarged to clearly represent the layers and regions. In the drawings, for the convenience of explanation, the thicknesses of some layers and regions are exaggerated.

Hereinafter, the formation of any structure in the "upper (or lower)" or the "upper (or lower)" of the substrate means that any structure is formed in contact with the upper surface (or lower surface) of the substrate However, the present invention is not limited to not including other configurations between the substrate and any structure formed on (or under) the substrate.

In one embodiment of the invention, the passive film comprises a stainless steel substrate having a passive coating on its surface, wherein the passive coating comprises about 10% to about 20% by weight of chromium oxide and about 20% to about 40% The present invention also provides a metal separator for a polymer electrolyte fuel cell.

The passive film means, for example, an oxide film formed on the surface of the substrate through the oxidation reaction, reduction reaction or the like in which the surface of the substrate is in contact with an acid solution, and the oxide film is formed on the outside of the oxide film It is also referred to as an inert film because it blocks the contact of the existing metal.

Generally, a metal coating is formed on the surface of a substrate in order to enhance the corrosion resistance of a metal separator for a fuel cell and lower the contact resistance. However, in the case of gold or platinum, the cost competitiveness is remarkably decreased. In the case of nickel or copper, There is a problem that contact resistance is rather increased in some cases.

Specifically, when the metal separator for a fuel cell is applied to a fuel cell of a vehicle, for example, a hydrogen fuel cell of a vehicle, sulfuric acid and hydrofluoric acid are produced by a nafion membrane or the like included in the unit cell during use, Accordingly, the corrosion of the metal separator for fuel cells can be further promoted. Further, in the case of applying to a fuel cell of a vehicle, the space to be mounted is narrow and the number of unit cells to be used is limited, so that the electrical specification is degraded.

Thus, in one embodiment of the present invention, a stainless steel substrate is used to provide a surface of the substrate with about 10% to about 20% by weight of chromium oxide and about 20% To about 40% by weight of iron oxides, thereby providing excellent corrosion resistance and low contact resistance at the same time.

Accordingly, even when the metal separator for a polymer electrolyte fuel cell is applied to a fuel cell of a vehicle as described above, the corrosion resistance is effectively suppressed and the contact resistance is reduced, so that the durability and electrical characteristics can be further improved.

1 schematically shows a cross-sectional view of a metal separator plate 100 for a polymer electrolyte fuel cell. The metal separator plate 100 for a polymer electrolyte fuel cell includes a stainless steel substrate 110 having a passive film 120 formed on a surface thereof and the passive film 120 comprises about 10% Chromium oxide and about 20% to about 40% iron oxide by weight.

The passive film 120 may be formed by surface treatment with a mixed solution of nitric acid and hydrofluoric acid. When the substrate 110 made of stainless steel is surface-treated with a mixed solution of nitric acid and hydrofluoric acid, the content of chromium increases and the content of chromium oxide increases on the surface of the stainless steel substrate 110 , The passivation film 120 may be formed while an oxidation reaction or a reduction reaction occurs such that the content of iron oxide is decreased while the content of iron is increased.

The surface of the passive film 120 formed on the surface of the substrate 110 after the surface treatment with the mixed solution of nitric acid and hydrofluoric acid is compared with the surface composition of the substrate 110 of the stainless steel material not subjected to the surface treatment, The chromium is oxidized to increase the content of the highly corrosion resistant chromium oxide to a high level of about 10 wt% to about 20 wt% while iron is reduced so that the content of iron oxide having low electrical conductivity is about 20 wt% to about 40 wt% %, So that excellent corrosion resistance and low contact resistance can be realized at the same time.

The metal separator plate 100 for a polymer electrolyte fuel cell can be applied to a fuel cell of a vehicle. The fuel cell of the vehicle may be of various types known in the art, and may be, for example, a hydrogen fuel cell of a vehicle, but is not limited thereto.

As described above, in the case of a fuel cell of a vehicle, for example, a hydrogen fuel cell of a vehicle, the corrosion of the metal separator 100 is further promoted by sulfuric acid and hydrofluoric acid produced during use, There is a problem that the number of unit cells used must be limited.

Accordingly, in one embodiment, the surface of the substrate 110 made of stainless steel is surface-treated with a mixed solution of nitric acid and hydrofluoric acid to form a passive film 120 having excellent corrosion resistance and low contact resistance, Even when applied to a fuel cell of the present invention, excellent durability and excellent electrical characteristics can be realized for a long period of time.

The surface treatment is performed by immersing the substrate 110 made of stainless steel in a mixed solution of nitric acid and hydrofluoric acid, and the mixed solution may be stirred while the surface treatment is performed.

The surface of the substrate 110 can be uniformly surface-treated by stirring so that the passive film 120 can be uniformly formed on the surface of the substrate 110 as a whole, High corrosion resistance and low contact resistance can be achieved at a relatively constant level. In other words, since the surface of the substrate 110 is not subjected to the surface treatment, portions where the passive film 120 is not formed are prevented from being generated, thereby effectively solving the problem of partial defects.

The mixed solution may comprise, for example, from about 35 wt% to about 99.999 wt%, and specifically from about 35 wt% to about 65 wt% nitric acid. By including nitric acid in the content within the above range, the surface of the substrate 110 can be sufficiently passivated, whereby excellent corrosion resistance and low contact resistance can be realized.

The mixed solution may contain, for example, from about 0.001 wt% to about 65 wt% of hydrofluoric acid. By including hydrofluoric acid in the content within the above range, the surface of the substrate 110 can be stably passivated while surface damage can be prevented.

In addition, the mixed solution may not contain distilled water, or may further include distilled water. When the distilled water is further included, the content may vary depending on the purpose and function of the invention, and is not particularly limited.

In addition, the mixed solution may further include a transition metal-based catalyst. The transition metal catalyst may be of any kind known in the art and is not particularly limited.

In one embodiment, the metal separator 100 for a polymer electrolyte fuel cell may have a contact resistance of, for example, less than or equal to about 12 m OMEGA .cm ² , and more specifically from about 1 m OMEGA -cm ² to about 10 m OMEGA -cm ² . By having the contact resistance within the above range, it is possible to realize excellent electrical characteristics, so that electrons can smoothly move in the fuel cell to improve energy efficiency.

The polymer electrolyte fuel cell, the metal bipolar plate 100 include, for example, the corrosion current density, can be up to about ² 1μA / cm, can be specifically from about 0.001μA / cm ² to about 0.8μA / cm ^2. By having the corrosion current density within the above range, the metal is prevented from being eluted from the metal separator 100, and long-term durability can be realized.

The thickness of the passive film 120 may be about 0.1 nm to about 30 nm. By having the thickness within the above range, the surface of the substrate 110 can be sufficiently and stably passivated, and excellent corrosion resistance and low contact resistance can be realized, and surface damage can be prevented. Further, The thickness of the portion where the passive film 120 is not formed is sufficiently secured, and the impact resistance and gas tightness can be maintained at a high level.

The thickness d _t of the substrate 110 may be about 0.05 mm to about 0.2 mm. By having a thickness within the above range, sufficient impact resistance and gas tightness can be realized without excessively increasing the thickness of the metal separator 100. The thickness d _t of the substrate 110 means the total thickness d _t of the substrate 110 on which the passive film 120 is formed.

In another embodiment of the present invention, there is provided a method of manufacturing a metal separator for a polymer electrolyte fuel cell, comprising the step of immersing a substrate made of stainless steel in a mixed solution of nitric acid and hydrofluoric acid to perform a surface treatment. According to the above production method, the metal separator for a polymer electrolyte described above can be produced in one embodiment.

In the above manufacturing method, a substrate made of stainless steel can be surface-treated by immersing it in a mixed solution of nitric acid and hydrofluoric acid, so that a surface of the substrate is coated with about 10% by weight to about 20% by weight of chromium oxide and about 20% To about 40% by weight of iron oxide.

The metal separator for a polymer electrolyte manufactured by the above-described method uses a stainless steel substrate to maintain a high level of impact resistance and gas tightness, while applying a chromium (Cr) content of about 10 wt% to about 20 wt% Oxide and about 20 wt.% To about 40 wt.% Of iron oxide, thereby providing excellent corrosion resistance and low contact resistance at the same time.

Accordingly, even when the metal separator for a polymer electrolyte fuel cell is applied to a fuel cell of a vehicle, the corrosion resistance is effectively suppressed, and the contact resistance is reduced, so that the durability and electrical characteristics can be further improved.

The mixed solution of nitric acid and hydrofluoric acid may be prepared by mixing and stirring nitric acid and hydrofluoric acid, and further, a transition metal catalyst, distilled water, and the like may be further mixed and stirred. The distilled water and the transition metal-based catalyst are as described above in one embodiment.

The mixed solution may be prepared, for example, by mixing about 35 wt% to about 99.999 wt% of nitric acid, specifically, about 35 wt% to about 65 wt% of nitric acid. By mixing the nitric acid with the content within the above range, the surface of the substrate is sufficiently passivated, whereby excellent corrosion resistance and low contact resistance can be realized.

The mixed solution may, for example, be mixed with about 0.001 wt% to about 65 wt% of hydrofluoric acid. By mixing hydrofluoric acid with the content within the above range, the surface of the substrate can be stably passivated while preventing surface damage.

Further, the mixed solution may be stirred during the surface treatment of the substrate.

As described above, by stirring, the surface of the substrate can be uniformly surface-treated to uniformly form the passive film on the surface of the substrate as a whole, so that the corrosion resistance and the low contact resistance of the entire surface of the substrate are relatively constant Level. That is, since the surface of the substrate is not subjected to the surface treatment, a portion where no passive film is formed is prevented from being generated, thereby effectively solving the problem of generating partial defects.

The mixed solution may be stirred at about 500 rpm to about 800 rpm. By stirring at a stirring speed within the above range, a passive film can be formed uniformly on the entire surface of the substrate, and a superior surface appearance can be realized. If the temperature is less than about 500 rpm, agitation may not proceed properly and the agitation time may become longer to reduce the productivity. If the temperature exceeds about 800 rpm, traces of a whirl-like pattern may remain on the surface of the substrate.

In the above manufacturing method, the surface treatment may be performed at about 10 캜 to about 50 캜. By performing the reaction at a temperature within the above-mentioned range, the oxidation, reduction reaction, and the like proceed appropriately on the surface of the substrate, the passive film can be smoothly formed, and the occurrence of strong acid vapor can be prevented. The surface treatment may be performed for about 0.5 hour to about 4 hours. By performing the process for the time within the above range, the passive film can be formed uniformly on the entire surface of the substrate, while being formed to an appropriate thickness, thereby realizing excellent electrical characteristics and not damaging the surface of the substrate.

Generally, the surface of the stainless steel is covered with grease, coolant or other chemicals, which may interfere with the surface treatment. For example, grease reacts with nitric acid to form bubbles on the surface, Etc., and the corrosion of stainless steel, and the grease, cooling oil, and other chemicals contaminate the passivation reaction by increasing the concentration of chlorine ions in the acid solution, etc., thereby deteriorating the properties of the passivated coating.

The method may further include cleaning the substrate before immersing the substrate so that a more uniform passivation reaction occurs on the surface of the substrate immersed in the mixed solution of nitric acid and hydrofluoric acid It is possible to more uniformly form the passive film as a whole.

Further, the composition of the mixed solution may be prevented from changing due to a concentration of chlorine ions or other impurities in the mixed solution of nitric acid and hydrofluoric acid due to grease, cooling oil, or other chemicals on the surface of the substrate The passive film can be formed more effectively and excellent corrosion resistance and excellent electrical characteristics can be realized.

The cleaning step may be performed using a dry or wet cleaning method known in the art.

The cleaning step may be performed by a degreasing step. For example, a solvent degreasing method, an emulsion degreasing method, an alkali degreasing method, a transfer pretreatment method, an ultrasonic degreasing method, or the like may be used, no.

The metal separator for a polymer electrolyte fuel cell produced by the above-described method may have a contact resistance of, for example, about 12 m? · Cm ² or less, specifically about ¹ m? · Cm ² to about 10 m? · Cm ² . By having the contact resistance within the above range, it is possible to realize excellent electrical characteristics, so that electrons can smoothly move in the fuel cell to improve energy efficiency.

The polymer electrolyte fuel cell, the metal bipolar plate is, for example, the corrosion current density, can be up to about ² 1μA / cm, can be specifically from about 0.001μA / cm ² to about 0.8μA / cm ^2. By having a corrosion current density within the above range, the metal can be prevented from being eluted from the metal separator, thereby achieving excellent durability for a long period of time.

Hereinafter, examples and comparative examples of the present invention will be described. The following embodiments are only examples of the present invention, and the present invention is not limited to the following embodiments.

( Example )

Example  One

A stainless steel substrate having a size of 10 cm X 20 cm was prepared, and a mixed solution of nitric acid and hydrofluoric acid was prepared by mixing and stirring 50 wt% of nitric acid and 0.001 wt% of hydrofluoric acid.

The mixed solution was immersed in the substrate for 2 hours while stirring at a stirring speed of 800 rpm at room temperature to prepare a metal separator for a polymer electrolyte fuel cell.

Example 2 (addition of cleaning step)

The substrate was immersed in a degreasing solution before the stainless steel substrate was immersed in a mixed solution of nitric acid and hydrofluoric acid, and the substrate was cleaned at a temperature of 55 ° C for 5 minutes. Subsequently, the substrate was washed with distilled water, A metal separator for a polymer electrolyte fuel cell was prepared by the same conditions and procedures as those in Example 1,

Example 3 (no agitation during surface treatment)

A metal separator for a polymer electrolyte fuel cell was prepared in the same manner as in Example 1, except that the substrate was immersed in the mixed solution without stirring to perform the surface treatment.

Comparative Example 1 (surface treatment not performed)

A metal separator for a polymer electrolyte fuel cell was fabricated on a stainless steel substrate with a size of 10 cm × 20 cm without surface treatment.

Comparative Example 2 (Surface treatment with an acid solution containing nitric acid, not including hydrofluoric acid)

Except that the stainless steel substrate was immersed in a mixed solution of nitric acid and hydrofluoric acid and immersed in an acid solution containing 90 wt% of nitric acid and 10 wt% of distilled water to perform surface treatment, A metal separator for polymer electrolyte fuel cell was fabricated.

evaluation

The contact resistance and the corrosion current density of the metal separator for the polymer electrolyte fuel cell of Examples 1-3 and Comparative Examples 1 and 2 were measured. Specifically, the contact resistance is measured based on a unit area of 25 cm ² , and the corrosion current density is measured based on a unit area of 1 cm ^2. For the metal separator for polymer electrolyte fuel cells of Examples 1 and 3, The contact resistance and the corrosion current density were measured for two different portions of the substrate to evaluate whether or not the passivation film was uniformly formed.

1. Contact Resistance

Measurement method: The modified Davids method was used to obtain optimized constants for unit cell clamping, and when the pressure was applied to the copper plate, a metal separator and carbon paper (SGL, 10BA GDL The current was supplied to the metal separator using a current supply device (KIKUSUI), and an electrode having an amplitude of 0.5 A and an electrode of 25 cm < 2 > 5A was applied as a DC current having an area, and the voltage was measured using a multimeter.

Further, in the contact resistance measuring instrument, measurement was carried out by providing a pressure of 100 N / cm ² using a compression holding tester (Instron, 5566).

2. Corrosion current density

Measurement method: A current density was measured using a current density meter (Princeton) under the conditions of sulfuric acid 0.05M, hydrofluoric acid 2ppm, and temperature 80 占 폚.

Contact resistance
mΩ · cm ² Corrosion current density
μA / cm ² Example 1 9.0, 9.0 0.09, 0.09 Example 2 7.3 0.06 Example 3 9.5, 11.3 0.1, 0.2 Comparative Example 1 54.3 1.4 Comparative Example 2 33 0.2

The metal separator for a polymer electrolyte of Example 1-3 exhibits low contact resistance and low corrosion current density and can be expected to realize excellent electrical characteristics and corrosion resistance. Particularly, in the case of Example 1, It is expected that the contact resistance and the corrosion current density measured are the same and the passive film is formed more uniformly so that the electrical characteristic and the corrosion resistance are uniformly realized.

In the case of Example 3, a passivation film is formed by performing a passivation reaction more uniformly on the surface of the substrate by performing cleaning before performing the surface treatment, so that the contact resistance and the corrosion current density can be further improved to realize more excellent electrical characteristics and corrosion resistance Can be clearly predicted.

On the other hand, in Comparative Example 1, it is clear that the contact resistance and the corrosion current density are so high that both electrical characteristics and corrosion resistance are significantly inferior. In Comparative Example 2, the corrosion current density is good but the contact resistance is very high, Inferiority can be clearly predicted.

100: Metal separator plate for polymer electrolyte fuel cell
110: substrate made of stainless steel
120: passive film
d _t : Thickness of the substrate made of stainless steel

Claims (16)

And a substrate made of stainless steel on which a passive film is formed,
Wherein the passive film comprises 10% to 20% by weight of chromium oxide and 20% to 40% by weight of iron oxide
Metal Separation Plates for Polymer Electrolyte Fuel Cells.
The method according to claim 1,
The passive film is formed by surface treatment with a mixed solution of nitric acid and hydrofluoric acid
Metal Separation Plates for Polymer Electrolyte Fuel Cells.
3. The method of claim 2,
Wherein the surface treatment is performed by immersing a substrate made of stainless steel in a mixed solution of nitric acid and hydrofluoric acid,
While the surface treatment is being carried out,
Metal Separation Plates for Polymer Electrolyte Fuel Cells.
3. The method of claim 2,
Wherein the mixed solution comprises 35 wt% to 99.999 wt% nitric acid
Metal Separation Plates for Polymer Electrolyte Fuel Cells.
3. The method of claim 2,
Wherein the mixed solution comprises 0.001 wt.% To 65 wt.% Of hydrofluoric acid
Metal Separation Plates for Polymer Electrolyte Fuel Cells.
The method according to claim 1,
Wherein the metal separator for a polymer electrolyte fuel cell is applied to a fuel cell of a vehicle
Metal Separation Plates for Polymer Electrolyte Fuel Cells.
The method according to claim 1,
When the contact resistance is 12 mΩ · m ² or less
Metal Separation Plates for Polymer Electrolyte Fuel Cells.
The method according to claim 1,
A corrosion current density of 1 μA / cm ² or less
Metal Separation Plates for Polymer Electrolyte Fuel Cells.
The method according to claim 1,
Wherein the thickness of the passive film is from 0.1 nm to 30 nm
Metal Separation Plates for Polymer Electrolyte Fuel Cells.
The method according to claim 1,
Wherein the thickness of the substrate is 0.05 mm to 0.2 mm
Metal Separation Plates for Polymer Electrolyte Fuel Cells.
Immersing a substrate made of stainless steel in a mixed solution of nitric acid and hydrofluoric acid to perform a surface treatment;
Wherein the metal separator comprises a polymer electrolyte membrane.
12. The method of claim 11,
And stirring the mixed solution during the surface treatment of the substrate
(METHOD FOR MANUFACTURING METAL BINDING PLATE FOR POLYMER ELECTROLYTE FUEL CELL.
13. The method of claim 12,
The mixed solution is stirred at 500 rpm to 800 rpm
Manufacturing method of metal separator for polymer electrolyte fuel cell
12. The method of claim 11,
The surface treatment is carried out at a temperature of < RTI ID = 0.0 > 10 C &
(METHOD FOR MANUFACTURING METAL BINDING PLATE FOR POLYMER ELECTROLYTE FUEL CELL.
12. The method of claim 11,
The surface treatment is carried out for 0.5 to 4 hours
(METHOD FOR MANUFACTURING METAL BINDING PLATE FOR POLYMER ELECTROLYTE FUEL CELL.
12. The method of claim 11,
Further comprising cleaning the substrate prior to immersing the substrate
(METHOD FOR MANUFACTURING METAL BINDING PLATE FOR POLYMER ELECTROLYTE FUEL CELL.

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