KR101410479B1 - Method for manufacturing pemfc bipolar plate - Google Patents

Abstract

The present invention relates to a polymer fuel cell separation plate having improved contact resistance and water discharge properties of the fuel cell by adjusting the roughness on the surface of high corrosion-proof ferrite-based stainless steel through a scratch, and a method for manufacturing the same. The present invention relating to a method for manufacturing the polymer fuel cell separation plate includes: (a) a step for manufacturing a stainless steel plate; (b) a step for manufacturing a separation plate by forming a flow passage comprising a channel and a land on the stainless steel plate; (c) a step for forming a scratch for changing the roughness on the surface through a mechanical friction on the land surface of the separation plate; and (d) a step for reforming the surface of the separation plate after forming the scratch.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a separator for a polymer fuel cell,

The present invention relates to a separator for a polymer fuel cell and a method of manufacturing the separator. More particularly, the present invention relates to a separator for a polymer fuel cell, And a manufacturing method thereof.

The polymer electrolyte fuel cell comprises a unit cell structure in which a gas diffusion layer and a separator are stacked on both sides of a membrane electrode assembly (MEA) composed of an electrolyte, an anode and a cathode, A fuel cell stack is composed of a plurality of cells connected in series.

The separation plate is provided with a flow path for supplying fuel (hydrogen or reforming gas) and an oxidizing agent (oxygen or air) to the fuel cell electrode and discharging water as an electrochemical reactant, and the membrane electrode assembly and the gas And functions to mechanically support the diffusion layer and to electrically connect the adjacent unit cells.

In order to withstand the corrosive environment of the fuel cell, graphite materials have been generally used. However, in recent years, a separator using stainless steel having corrosion resistance has been applied in consideration of manufacturing cost and weight.

The flow path of the fuel cell separator is composed of a channel through which the fuel or the oxidant passes and a land which acts as an electrical path by contacting the gas diffusion layer. In order to supply the reactant and discharge the product, And control of the surface state are very important.

Generally, a polymer electrolyte fuel cell is humidified by supplying a reactive gas (fuel and oxidizer) at a level higher than a certain level in order to improve the conductivity of hydrogen ions in the electrolyte membrane.

On the other hand, since water is generated by the electrochemical reaction on the cathode side, if the dew point temperature of the reaction gas is higher than the operating temperature of the fuel cell, water droplets are generated due to water vapor condensation in the channel, the gas diffusion layer or the electrode.

This phenomenon is referred to as a flooding phenomenon. The flooding phenomenon causes a non-uniform flow of the reactant gas and a deficiency of the reactant gas in the electrode, thereby deteriorating the performance of the fuel cell.

The above flooding phenomenon may occur not only at the cathode electrode but also at the anode electrode by the water passed through the electrolyte membrane. Particularly, when the clogging of the gas flow path by the condensed water occurs on the anode side, the deficiency of the fuel gas is caused, which leads to the irreversible damage of the electrode.

This is because, when the load current is forcibly applied in the state where the fuel gas is insufficient, the carbon bearing the anode catalyst reacts with water in order to make electrons and protons without fuel.

As a result of this reaction, loss of the anode-side catalyst occurs, resulting in reduction of the effective electrode area and deteriorating fuel cell performance.

In order to prevent the flooding phenomenon and to stabilize the performance of the fuel cell, it is necessary to make the angle of contact of the channel surface and the surface of the land different with respect to water, or to treat water differently in the gas diffusion layer and the flow path.

However, the conventional method of treating the surface of a separator for a fuel cell is focused on reducing the contact resistance and improving the corrosion resistance by coating a noble metal on the surface of the separator. Further coating is required to change the contact angle between the channel and the land. And the coating cost is high.

It is also difficult to treat the channel and land roughness differently in the coating step, and when the roughness is changed by post-processing of the coated surface, the cured surface is damaged and the corrosion is likely to occur.

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above problems, and it is an object of the present invention to provide a method of manufacturing a fuel cell, And to provide a separation plate for a polymer fuel cell and a method of manufacturing the same, which can improve discharge characteristics and contact resistance.

In order to achieve the above object, a separator for a polymer fuel cell according to the present invention comprises 0.02% or less of C, 0.02% or less of N, 0.4% or less of Si, , Cr: 25 to 32.0%, Cu: 0 to 2.0%, Ni: 0.8% or less, Ti: 0.5% or less, Nb: 0.5% or less, A channel made of a channel and a land is formed in the separator plate made of a ferritic stainless steel plate made of a ferrite and an inevitably contained element, and a scratch for changing the roughness of the land surface is formed And a passive film formed by modifying the surface of the separator,
The scratch has a certain directionality and is characterized in that the direction of the scratch is formed at an angle of 0 to 90 degrees with respect to the channel flow direction.

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In the scratch, the roughness of the surface of the separator is in the range of 0.1 to 1 μm in Ra value.

According to another aspect of the present invention, there is provided a method of manufacturing a separator for a polymer fuel cell, comprising the steps of: (a) preparing a stainless steel sheet; (b) forming a separator by forming a channel made of a channel and a land on the stainless steel plate; (c) forming a scratch on the land surface of the separator plate by mechanical friction to change the surface roughness; (d) modifying the surface of the separator after formation of the scratch,
The scratch has a certain directionality, and the direction of the scratch has an angle of 0 to 90 degrees with respect to the channel flow direction.

In the step (a), the stainless steel sheet may contain 0.02% or less of C, 0.02% or less of N, 0.4% or less of Si, 0.2% or less of Mn, 0.04% or less of P , S: not more than 0.02%, Cr: 25.0 to 32.0%, Cu: 0 to 2.0%, Ni: not more than 0.8%, Ti: not more than 0.5%, Nb: not more than 0.5% .

The separating plate is formed through a metal sheet forming process using upper and lower molds having a reversed phase pattern of the separating plate.

The separating plate may be formed by pressing a metal plate toward a mold with a strong water pressure on the first surface side by using a lower mold having a reversed phase pattern of a second surface of the separating plate to form a desired shape by hydroforming ) Process.

The scratching of the separating plate is performed through a process of physically removing a part of the surface of the separating plate using a tool having a higher hardness than the surface of the separating plate.

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And the roughness of the surface of the separator is controlled in the range of 0.1 to 1 mu m in Ra value.

Further, the surface modification of the separator may include: (A) removing the first passivation film by acid pickling at a temperature of 50 to 75 ° C in an aqueous 10-20 wt% sulfuric acid solution; Washing the stainless steel plate with water; Passivating the stainless steel sheet at a temperature of 40 to 60 ° C. in a mixed acid of 10 to 20 wt% nitric acid and 1 to 10 wt% hydrofluoric acid to form a second passivation film.

According to the embodiment of the present invention, accumulated water between the gas diffusion layer and the land can be easily discharged to the channel through the surface roughness control through the scratch.

And the surface roughness formed on the separator land can reduce the contact resistance between the separator and the gas diffusion layer.

In addition, the surface roughness control of the separator plate is made by a simple scratch process on the surface of the ferritic stainless steel of high corrosion resistance, and the corrosion resistance of the surface can be secured through surface modification. Therefore, A battery separator can be manufactured.

1 is a front view of a separator plate to which a separator plate manufacturing method for a polymer fuel cell according to the present invention is applied.
2 is a cross-sectional view of a unit cell of the fuel cell of the essential part of FIG.
3 is a saturation degree contour line of water between the cathode separator and the gas diffusion layer.
4 is an exploded perspective view of a unit cell having scratches formed on a surface of a separator plate according to the present invention.
5 is a view showing movement of water through scratching of the land surface.
6 is a flowchart sequentially illustrating a method of manufacturing a separator for a polymer fuel cell according to the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The separator for a fuel cell according to the present invention is a stainless steel (steel plate) containing high Cr in order to ensure adequate corrosion resistance under an operating environment in a polymer fuel cell.

More preferably 0.02% or less of C, not more than 0.02% of N, not more than 0.4% of Si, not more than 0.2% of Mn, not more than 0.04% of P, not more than 0.02% of S, not more than 0.02% of Cr, not more than 0.02% To 32.0%, Cu: 0 to 2.0%, Ni: not more than 0.8%, Ti: not more than 0.5%, Nb: not more than 0.5%, and the balance Fe and inevitably contained elements.

The composition range of the present invention and the reason for its limitation will be described in more detail. In addition, all the percentages described below are% by weight.

C and N form Cr carbonitride in the steel, and as a result, the corrosion resistance of the layer lacking Cr is lowered, so that the lower both elements are, the better. Therefore, in the present invention, the composition ratio is limited to 0.02% or less of C and 0.02% or less of N.

Since Si inhibits elements effective in deoxidation, toughness and formability, the composition ratio of Si is limited to 0.4% or less in the present invention.

Mn is an element that increases deoxidation, but MnS, which is an inclusion, decreases the corrosion resistance. Therefore, the composition ratio of Mn is limited to 0.2% or less in the present invention.

P reduces not only the corrosion resistance but also the toughness, so that the composition ratio of P is limited to 0.04% or less in the present invention.

S forms MnS. Since MnS is a starting point of corrosion and reduces corrosion resistance, in the present invention, the composition ratio of S is limited to 0.02% or less.

Cr increases the corrosion resistance in the acidic atmosphere in which the fuel cell operates, but decreases the toughness. Therefore, in the present invention, the composition ratio of Cr is limited to 25% to 32%.

Cu increases corrosion resistance in an acidic atmosphere in which a fuel cell operates, but when it is added in an excessive amount, the performance of the fuel cell may deteriorate due to elution of Cu. Therefore, in the present invention, the composition ratio of Cu is limited to a range of 0% to 2% or less.

Ni plays a role to reduce some contact resistance, but Ni addition and formability may be deteriorated when added excessively. Therefore, in the present invention, the composition ratio of Ni is limited to 0.8% or less.

Ti and Nb are effective elements for forming C and N in the steel as carbonitrides, and toughness is lowered. Therefore, in the present invention, the respective composition ratios are limited to 0.5% or less.

The stainless steel material according to the present invention may be produced by subjecting a material produced through an ingot casting or a continuous casting process to a thin plate shape of 0.05 to 0.3 mm suitable for the use of the fuel cell separator through the ordinary hot rolling and cold rolling processes do.

1 is a front view of a separator plate to which the above-described stainless steel plate is applied.

Referring to FIG. 1, the fuel cell separator 100 is provided with a channel in which the channels 20 repeatedly projected from the protruded land 10 are formed. The fuel inlet manifold 41, And the oxidant inlet manifold 51 are formed through the separator plate 100 and the fuel outlet manifold 42 and the oxidant outlet manifold 52 through which the unreacted fuel and the oxidant are discharged are separated from the separator plate 100, As shown in FIG.

A cooling medium is required to discharge the heat generated by the fuel cell reaction. The separator plate 100 is provided with a cooling medium inlet manifold 61 required for cooling medium inlet and a cooling medium outlet manifold 62 are formed through the separator plate 100.

The method of forming the above-described flow path in the fuel cell separator 100 is a method of forming the above-described flow path in a shape opposite to the cooling surface (not shown) of the upper mold and the flow path formed in a shape opposite to the anode electrode surface 70 of the flow path Stamping can be used in which a metal sheet is placed between the processed lower molds, and the sheet is stamped with strong force and at a high speed.

Further, it is also possible to use a multi-stage progressive stamping method in which after the primary molding is performed, additional molding is repeated using a mold having another shape to finally shape a desired shape.

Further, a metal plate material is placed between the upper mold and the lower mold which are formed in a shape opposite to the cooling surface (not shown) of the oil flow path and the flow path formed in the opposite shape to the anode electrode surface 70 of the flow path, And a servo-pressing method in which a desired shape is continuously formed while precisely controlling the stroke and the stroke can be used.

Further, a hydroforming process is used in which only the lower mold processed to have a shape opposite to the cooling surface of the flow path described above is used and the metal plate is pressed into the metal mold with a strong water pressure on the anode electrode surface 70 side to mold a desired shape. It can also be used.

2 is a cross-sectional view of a fuel cell unit cell comprising an MEA, a gas diffusion layer, an anode separation plate, and a cathode separation plate.

2, the MEA 90 includes an electrolyte membrane 91, anode electrodes 92 and cathode electrodes 93 on both sides thereof, and a gas diffusion layer 94 is formed on both sides of the MEA 90, do. The gas diffusion layer 94 is made of carbon paper or carbon nonwoven fabric having permeability and electron conductivity to transfer the reaction gas from the separation plate flow path to the electrode while transmitting the generated water from the electrode to the separation plate flow path .

An anode separation plate 110 and a cathode separation plate 120 are located outside the gas diffusion layer 94.

The anode separation plate 110 includes a flow path in which a surface protruding from the anode electrode surface 70 and a surface protruding from the cooling surface 80 are alternately repeated and the flow path from the flow path to the anode electrode surface 70 A portion where the projected surface and the gas diffusion layer 94 are in contact with each other is referred to as a land 10 and a space between the land 10 and the land 10 is referred to as a channel 20.

The channel 20 serves as a passage through which fuel (hydrogen or reformed gas) necessary for the fuel cell reaction flows.

The cathode separation plate 120 includes a flow path in which a surface protruding from the cathode electrode surface 71 and a surface protruding from the cooling surface 81 are alternately repeated and the flow path from the flow path to the cathode electrode surface 71 A portion where the protruding surface and the gas diffusion layer 94 are in contact with each other is referred to as a land 11 and a space between the land 11 and the land 11 is referred to as a channel 21. [

The channel 21 serves as a passage through which the oxidant (oxygen or air) necessary for the fuel cell reaction flows.

The opposite side of the anode separation plate channel 20 and the opposite side of the cathode separation plate channel 21 are in contact with each other to serve as mechanical support and electrical passage, The space formed by the opposite surface of the face and cathode separator land 11 is the cooling medium channel 30 through which the cooling medium flows.

The fuel 130 in the anode separator channel 10 is diffused through the gas diffusion layer to the anode electrode 92 and the oxidant 131 in the cathode separator plate channel 21 And moves to the cathode electrode 93 via the gas diffusion layer 94 through diffusion.

At this time, the water 132 generated in the electrode through the reaction moves to the anode channel 20 or the cathode channel 21 through the gas diffusion layer 94 and is discharged to the outside of the fuel cell.

The gas diffusion layer 94 is subjected to hydrophobic treatment using PTFE or the like to facilitate the discharge of the generated water.

On the other hand, the metal surface used as the fuel cell separator has high surface energy and is hydrophilic. In the portion where the hydrophobic gas diffusion layer and the hydrophilic land are in contact with each other, water can not be discharged into the channel, It becomes an accumulative condition.

FIG. 3 is a graph showing the liquid saturation contour of water at a region where a land on a hydrophilic surface and a cathode gas diffusion layer on a minority surface meet.

Here, the degree of saturation of water is the ratio of the volume of water to the volume of the pores of the gas diffusion layer.

As shown in FIG. 3, a large amount of water is accumulated in the portion where the land 11 and the gas diffusion layer 94 meet, compared with the region of the channel 21, and water droplets grow greatly with time, and the pores of the gas diffusion layer 94 Flooding will occur that will block all.

The flooding occurring in the vicinity of the land 11 gradually expands to the vicinity of the channel 21, and consequently, the fuel or the oxidant flow necessary for the reaction is blocked to greatly deteriorate the performance of the fuel cell and irreversibly damage the electrode.

4, a minute scratch is formed on the surface of the land 11, and water accumulated between the land 11 and the gas diffusion layer 94 is supplied to the channel 21 as shown in FIG. So as to perform the function of discharging quickly.

It is effective that the scratch 140 on the surface of the land 11 has a certain direction rather than an arbitrary direction. Preferably, as shown in Fig. 4, the flow direction 141 of the channel 21 and the angle it is preferable to form the scratch 140 so as to have the angle?

The water 132 accumulated between the land 21 and the gas diffusion layer 94 is quickly moved to the channels 21 on both sides through the capillary phenomenon by the scratch 140 on the surface of the land 11, And may be discharged to the outside of the fuel cell through evaporation of the fluid in the channel 21 and movement by the flow of the fluid.

The scratches on the surface of the lands 11 increase the contact area between the separator and the gas diffusion layer 94, thereby reducing the contact resistance of the interface.

A method of manufacturing a separation plate for a fuel cell is shown in Fig.

6, 0.02% or less of C, 0.02% or less of N, 0.4% or less of Si, 0.2% or less of Mn, 0.04% or less of P, 0.02% or less of S, A ferritic stainless steel sheet composed of 25.0 to 32.0% of Cr, 0 to 2.0% of Cu, 0.8% or less of Ni, 0.01 to 0.5% of Ti, 0.01 to 0.5% of Nb and the balance Fe and inevitably contained elements (Step 210).

Then, the stainless steel plate is formed to process the channel 21, the land 11, and the manifolds 41, 42, 51, 52, 61, and 62 (step 220)

Next, a scratch is formed on the surface of the land 11 perpendicular to the flow direction of the channel 21 (step 130)

And reforming the separator surface (step 240).

This will be described in more detail.

The scratch on the surface of the land 11 in the above step 130 can be formed by using suitable means such as rotational motion of the roller or rectilinear motion of the rectangular tool after forming the flow path of the separator, Is an Ra value that does not affect the surface modification for reducing the contact resistance and improving the corrosion resistance, and is preferably within the range of 0.1 to 1 mu m.

In addition, the surface modification of the separator of step 140 may include: removing the first passivation film on the surface formed by the light annealing or the annealing and pickling by acid pickling at a temperature of 50 to 75 ° C in an aqueous sulfuric acid solution of 10 to 20% Washing the stainless steel with water, and subjecting the stainless steel to passivation treatment at a temperature of 40 to 60 ° C. in a mixed acid of 10 to 20 wt% nitric acid and 1 to 10 wt% hydrofluoric acid to form a second passive film .

Wherein the stainless steel has a thickness of 2 to 4.5 nm and a Cr / Fe oxide ratio of 1.5 or more in a region of 1.5 nm or less and a Cr (OH) 3 / Cr oxide distribution of 1 nm or less In the range of 0 to 0.7.

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 disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. . Therefore, the true scope of protection of the present invention should be defined only by the appended claims.

10: anode land 11: cathode land
20: anode channel 21: cathode channel
30: coolant channel 41: fuel inlet manifold
42: fuel outlet manifold 51: oxidant inlet manifold
52: oxidant outlet manifold 61: cooling medium inlet manifold
62: cooling medium outlet manifold 70: anode electrode face
71: cathode electrode surface 80: anode cooling surface
81: cathode cooling surface 90: MEA
91: electrolyte membrane 92: anode electrode
93: cathode electrode 94: gas diffusion layer
100: separator plate 110: anode separator plate
120: cathode separation plate 130: fuel
131: oxidizer 132: water
140: Scratch 141: Channel flow direction
142: Channel flow direction and angle of scratch

Claims (11)

A method of manufacturing a separator plate for a polymer fuel cell,
(a) preparing a stainless steel sheet;
(b) forming a separator by forming a channel made of a channel and a land on the stainless steel plate;
(c) forming a scratch on the land surface of the separator plate by mechanical friction to change the surface roughness;
(d) modifying the surface of the separator after formation of the scratch,
The scratches have a certain directionality,
Wherein the direction of the scratch has an angle of 0 to 90 degrees with respect to the direction of the channel flow. The method according to claim 1,
In the step (a), preferably,
At most 0.02% of C, at most 0.02% of N, at most 0.4% of Si, at most 0.2% of Mn, at most 0.04% of P, at most 0.02% of S, , Cu: 0 to 2.0%, Ni: 0.8% or less, Ti: 0.5% or less, Nb: 0.5%
And the balance Fe and inevitably contained elements. The method according to claim 1,
The separator plate
Wherein the separating plate is formed by a metal sheet forming process using upper and lower molds having a reversed phase pattern of the separator. The method according to claim 1,
The separator plate
A hydroforming process in which a metal plate is pressed into a metal mold at a high water pressure on the first surface side using a lower metal mold having a reversed phase pattern of the second surface of the separator to form a desired shape Wherein the polymer electrolyte membrane is a polymer electrolyte membrane. The method according to claim 1,
The scratch of the separator plate
And a step of physically removing a part of the surface of the separator using a tool having a hardness higher than that of the surface of the separator. delete The method according to claim 1,
Wherein the surface roughness of the separator is controlled in the range of 0.1 to 1 占 퐉 in terms of Ra value. The method according to claim 1,
The surface modification of the separator plate,
(A) removing the first passivation film by acid pickling at a temperature of 50 to 75 ° C in an aqueous 10-20 wt% sulfuric acid solution;
Washing the stainless steel plate with water;
And a step of passively treating the stainless steel sheet at a temperature of 40 to 60 DEG C in a mixed acid of 10 to 20 wt% nitric acid and 1 to 10 wt% hydrofluoric acid to form a second passive film A method for manufacturing a separator for a battery. In a separator for a polymer fuel cell,
At most 0.02% of C, at most 0.02% of N, at most 0.4% of Si, at most 0.2% of Mn, at most 0.04% of P, at most 0.02% of S, Of the separator is made of a ferritic stainless steel sheet composed of 0 to 2.0% of Cu, not more than 0.8% of Ni, not more than 0.5% of Ti, not more than 0.5% of Nb, A channel made of lands is formed,
A scratch is formed to change the illuminance of the land surface,
And a passive film formed by modifying the surface of the separator,
The scratches have a certain directionality,
Wherein the direction of the scratch is formed at an angle of 0 to 90 degrees with respect to the channel flow direction. delete 10. The method of claim 9,
The scratch may be,
Wherein the roughness of the surface of the separator is in the range of 0.1 to 1 占 퐉 in Ra value.

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