JP2002025586A - Separator for solid high polymer molecule fuel cell and fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator which enable stamped out and is applicable to a low cost and highly durable solid high polymer molecule fuel cell which can be put under press processing, and a fuel cell. SOLUTION: The separator is characterized in having two or more continuous slots composed of an even peripheral part and an uneven section used as gas paths having different surfaces in their front and back in the center section. And, the separator is also characterized in having a slanted shape at an end part of the slot and having a sealing component sealing both sides of the surrounding flat sections. Further, the separator is made of stainless steel, or titanium.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polymer electrolyte fuel cell used for an automobile driven directly by electric power, a small-scale power generation system, and the like.

[0002]

2. Description of the Related Art With the increasing awareness of environmental conservation, the transition from the current internal combustion engine using fossil fuels to electric drive type automobiles using solid polymer fuel cells using hydrogen and distributed cogeneration systems is on the rise. Is being considered. In order to make these new technologies widely available to the general public, it is necessary to promote technology development related to cost reduction and high reliability, including the fuel supply system.

In recent years, the development of fuel cells for electric vehicles has begun to progress rapidly with the success of the development of solid polymer materials. Solid polymer fuel cells are different from conventional alkaline fuel cells, phosphoric acid fuel cells, molten carbonate fuel cells, solid electrolyte fuel cells, etc., in that they use a hydrogen ion selective permeation type organic membrane as the electrolyte. A fuel cell characterized by the fact that, in addition to pure hydrogen, hydrogen gas or the like obtained by reforming alcohols is used as fuel, and power is extracted by electrochemically controlling the reaction with oxygen in the air. System.

[0004] The solid polymer membrane functions satisfactorily even if it is thin, and since the electrolyte is fixed in the membrane, the solid polymer membrane functions as an electrolyte if the dew point in the battery is controlled. For example, there is no need to use a fluid medium, and the battery itself can be designed to be compact and simple.

A polymer electrolyte fuel cell includes a separator having a hydrogen flow path, a fuel electrode, a polymer electrolyte membrane, and air (oxygen).
In practice, a stack in which the single cells are stacked is used as a single cell having a sandwich structure including a pole and a separator having a flow path of air (oxygen). Therefore, both sides of the separator have independent flow paths, one side is a hydrogen path, and the other side is a flow path of air and generated water.

As a constituent material of a polymer electrolyte fuel cell that operates in a region below the boiling point of an aqueous solution for cooling, the temperature is not so high, and it is possible to sufficiently exhibit corrosion resistance and durability under the environment. In addition, carbon-based materials have been used by machining, etc. to form an arbitrary flow path shape, but stainless steel has been used to reduce cost and size, that is, to make separators thinner. Technical development on the application of steel and titanium is progressing.

Conventionally, as stainless steel for fuel cells,
JP-A-4-247852, JP-A-4-358044, JP-A-7-188870, JP-A-8-165546 and JP-A-8-2
As disclosed in Japanese Patent Publication Nos. 25892 and 8-31620, there is a stainless steel for a fuel cell which operates in a molten carbonate environment where high corrosion resistance is required. JP-A-6-264193, JP-A-6-293954, and JP-A-6-293940
As disclosed in the official gazettes of US Pat. No. 6,672,672 and the like, the invention of a solid oxide fuel cell material operating at a high temperature of several hundred degrees has been made.

Japanese Patent Application Laid-Open No. Hei 10-228914 discloses a stainless steel (SUS3 stainless steel) for the purpose of obtaining a fuel cell separator having a small contact resistance with an electrode of a unit cell.
04) is press-formed to form a bulged portion formed of a large number of irregularities on the inner peripheral portion, and a gold plating layer having a thickness of 0.01 to 0.02 μm is formed on the bulging tip side end surface of the bulged portion. A fuel cell separator characterized in that a fuel cell separator is formed, and as a method of using the fuel cell separator, a fuel cell separator is interposed between the stacked unit cells when forming the fuel cell, and the electrodes of the unit cell are bulged. There is disclosed a technique in which a gold plating layer formed on an end surface of a bulging tip side of a molding portion is disposed so as to abut, and a reaction gas passage is defined between a fuel cell separator and an electrode.

However, when a polymer electrolyte fuel cell was actually manufactured on a trial basis based on this technique, it was found that there were the following four technical problems. a) In a polymer electrolyte fuel cell environment where long-term durability is required, SUS304, which is a general-purpose steel type, may not be sufficient as an alloy component of a stainless steel separator. Cr, Ni, Mo, etc. Need to be increased. b) In the case of stainless steel with an increased alloy composition of Cr, Ni, Mo, etc., the passive oxide film of the stainless steel is completely reduced between the gold plating layer and the stainless steel substrate by the wet gold plating method alone during the plating process. However, it may remain without being generated, causing interlayer resistance between the stainless steel and the gold plating layer, which may cause power loss. As a countermeasure, it is necessary to attach a noble metal while removing the film.

C) The separator is assumed to have a shape in which a bulge formed from a large number of irregularities is formed on the inner peripheral portion by press molding, but an attempt is made to actually process the member having flat portions on the four circumferences. Since ductile cracks occur in the bulge formed by irregularities, and the workability of stainless steel with an increased alloy composition for improving long-term reliability is lower than that of SUS304, press-forming into this shape is performed. It is difficult. d) The separator is assumed to have a shape in which a bulging portion formed of a large number of irregularities is formed on the inner peripheral portion, and the structure is such that a reaction gas freely flows between the separator and the electrode. It is difficult to flow the gas uniformly from the gas inlet to the gas outlet, reducing the reaction efficiency, and the gas flow rate is low, making it difficult to discharge water generated on the oxygen side. There's a problem. The inventors have already solved the above problems a) and b).
The solution is disclosed in Japanese Patent Application Nos. 11-62813 and 11-1.
No. 70142.

[0011]

SUMMARY OF THE INVENTION In view of the above problems c) and d), the present invention provides a press-workable separator and a fuel cell which can be applied to a low cost and high durability type polymer electrolyte fuel cell. The purpose is to provide.

[0012]

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention has been completed as a result of a detailed study of material behavior during press molding based on the operating principle of a polymer electrolyte fuel cell. The summary is as follows. (1) The peripheral portion is flat, the central portion has a plurality of continuous grooves including convex portions and concave portions serving as gas flow paths having different front and back surfaces, and the shape of the groove end is inclined. Characteristic separator for polymer electrolyte fuel cell. (2) The separator for a polymer electrolyte fuel cell according to the above (1), further comprising a sealing member for sealing both surfaces of the peripheral flat portion. (3) The separator for a polymer electrolyte fuel cell according to the above (1) or (2), wherein the separator is made of stainless steel or titanium. (4) The separator for a polymer electrolyte fuel cell according to any one of (1) to (3), wherein the inclination angle of the groove end is changed for each groove. (5) Groove pitch P (mm), shoulder radius R (mm), parallel portion length W (mm), plate thickness t (mm), material elongation EL (%), yield stress YS (kgf / mm ² ) The separator for polymer electrolyte fuel cells according to any one of the above (1) to (4), wherein the groove depth H (mm) is equal to or less than a value calculated by the following equation. H = 2 × W × (EL / YS) ^1.01 × (R / t) ^0.318 ×
(1-W / P) ^2.66 (6) Shoulder radius R (mm), parallel portion length W (mm), plate thickness t
(Mm), material elongation EL (%), yield stress YS (kgf / mm
² ) The solid polymer fuel according to any one of (1) to (4), wherein the inclination angle θ (degree) of the groove end is set to be equal to or less than a value calculated by the following equation. Battery separator. θ = 90 × (EL / YS) ^0.372 × (R / t) ^0.270 ×
(7) The solid height according to any one of (1) to (4), wherein the cross-sectional area of the groove is gradually ^{increased toward} the downstream of the flow path. Separator for molecular fuel cells. (8) A polymer electrolyte fuel cell using the polymer electrolyte fuel cell separator according to any one of (1) to (7).

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details will be described below with reference to the drawings. FIG. 1 shows an example of a plan view of the separator 1 described in the above (1) to (4), and a specific laminated structure of the separator 1, the sealing plate 10, and the carbon fiber current collector 11 as an electrode at the groove end 6. One example is shown in FIGS. Here, the fuel gas or the oxygen (air) containing hydrogen supplied from the gas inflow holes 2 and 3 is respectively supplied to the concave surface side 7 of the separator.
And flows only through the back surface 8 of the convex portion and is discharged from the outflow holes 4 or 5. Fig. 2 shows the flow of gas on the surface side at the groove end.
Shown by arrows inside.

At the end of the groove, the inclination angle of the projections and the depressions is made to have a steep or steep difference every other line so that short-circuiting of the gas to the downstream side is suppressed. It is possible to flow the gas uniformly in a substantially one-stroke shape. Further, since the flow rate of the gas can be increased, the water generated on the oxygen side can be easily discharged. The seal plate 10 is slightly thicker than the groove height of the separator 1 and the angle of the end face of the central hollow portion of the seal plate is made slightly larger than the above-mentioned maximum inclination angle of the groove end portion, so that the gas toward the downstream side of the gas flows toward the downstream side. Short circuits are further suppressed.

FIGS. 4 and 5 show examples of groove arrangements in which the inclination angles of the convex portions and the concave portions are gradually and steeply changed every four lines at the groove end. The flow of gas on the surface side at the end of the groove is indicated by an arrow in FIG. In this example, the gas flows in parallel through the two grooves, and the gas is mixed at the folded portion at the end to form a flow path structure that branches and flows again into two. Compared with the arrangement of FIG. 1 described above, the flow velocity in the parallel portion of the groove is slightly reduced, but the effect of reducing the pressure loss is obtained. Needless to say, the arrangement of the grooves providing the steepness difference is not limited to the two examples shown here, and should be arbitrarily selected from the capacity of the gas supply device, the power generation efficiency, and the like.
Thus, by providing a gentle and sharp difference at the end of the groove, various flow path patterns can be formed.

The material of the separator may be a graphite plate, a metal plate, or the like from the viewpoints of electron conductivity, corrosion resistance, and airtightness, but is preferably made of stainless steel or titanium, which can be made thin and can be pressed. .

FIG. 6 shows the structure of the fuel cell stack according to the above (6) using the separator and the sealing plate according to the above (1) to (4). Separator 1, seal plate 1
0, a single cell is formed by sandwiching the solid polymer film 12 having an electrode catalyst coated on both sides in the laminated structure of the carbon fiber current collector 11 as an electrode. The fuel cell stack is formed by repeatedly stacking the cycle A in the figure. Further, in the polymer electrolyte fuel cell, there is heat generated by the reaction, and it is necessary to cool the stack in order to keep the solid polymer membrane at an appropriate temperature. It is also possible to cool the stack by inserting a B cycle including a cooling water channel at an appropriate interval of the stack cycle.

The material of the seal plate may be a material having a suitable elasticity and not decomposing or plastically deforming below the boiling point of the cooling water. Silicon resin, butadiene rubber resin, fluorine resin and the like can be used. Thus, the gas is sealed by tightening the seal plate slightly thicker than the groove height, and it has a suitable elasticity, so that it is possible to follow a minute deformation of the separator or the like. In the figure, the hydrogen-side and oxygen-side flow paths are opposed to each other with a solid polymer film interposed therebetween. However, the present invention is not limited to this.

FIG. 7 shows a cross-sectional shape of the groove described in the above (5). The groove period of the separator is desirably smaller from the viewpoint of gas supply uniformity and current collection efficiency, and from the viewpoint of reducing contact resistance, the contact area with the electrode is desirably large, but compared with the plate thickness. As the groove period decreases, bending strain increases, and the distortion also increases by reducing the radius of curvature of the corner to increase the contact area or increasing the length of the parallel part, causing breakage during processing. Molding becomes difficult. Generally, a groove having a groove cycle of 2 to 3 mm and a groove depth of about 1 mm at the maximum is used as a flow path of a fuel cell separator. However, when a metal plate having a plate thickness of about 0.1 to 0.3 mm is formed, The groove shape was fine compared to the plate thickness, the bending distortion at the corners was large, and the corners were often broken during molding.

Therefore, as a result of trial production of molds of various shapes and pressing using various materials, groove period, groove depth, shoulder curvature with respect to the material thickness, elongation and yield stress were determined. It has been found that the mold can be formed if the mold is designed so that the radius and the length of the parallel portion maintain an appropriate relationship. Specifically, groove pitch P (mm), shoulder radius R (mm), parallel portion length W (mm), plate thickness t (mm), material elongation EL (%), yield stress YS (kgf / mm) ² ) As long as the groove depth H (mm) is less than the value calculated by the following equation, it will not break. I found what I could do. H = 2 × W × (EL / YS) ^1.01 × (R / t) ^0.318 ×
(1-W / P) ^2.66

FIG. 8 shows the shape of the groove end described in the above (6). The shape of the groove end, that is, the inclination angle, is desirably a right angle from the viewpoint of suppressing the gas from short-circuiting to the downstream side, but as described above, increasing the inclination angle increases bending distortion at the corner. In many cases, breakage occurred at corners during molding. Therefore, prototypes of molds of various shapes were produced and pressed using various materials.As a result, the thickness of the material, the elongation, and the yield stress, the shoulder radius of curvature and the length of the parallel portion were appropriately determined. If a mold is designed so that it can be maintained, it can be molded. Specifically, shoulder radius R (mm), parallel portion length W (mm), plate thickness t (mm),
If the inclination angle θ (degree) of the groove end is not more than the value calculated by the following equation as the material elongation EL (%) and the yield stress YS (kgf / mm ² ), there is no breakage and the following equation It was found that by setting the value to about the value calculated in the above, the short circuit of the gas to the downstream side can be suppressed low. θ = 90 × (EL / YS) ^0.372 × (R / t) ^0.270 ×
(W / t) ^-0.265

FIG. 9 shows an example of a groove arrangement in which the cross-sectional area of the groove described in (7) is gradually increased toward the downstream of the flow path. Generally, the pressure of the gas decreases due to pressure loss as it goes downstream along the flow path. On the other hand, it is desirable that the pressure be higher from the viewpoint of catalytic reaction efficiency, and that the pressure difference between the hydrogen side and the oxygen side be small from the viewpoint of the strength of the solid polymer membrane. Therefore, by gradually increasing the cross-sectional area of the flow passage toward the downstream of the flow passage, it is possible to reduce the pressure drop, without increasing the capacity of the pump for gas supply, and on both sides of the solid polymer membrane. Can be reduced. Although the figure shows a form in which the width of the flow path is gradually widened, the depth of the flow path may be gradually increased, or both may be changed simultaneously. In addition, when the width and depth of the flow path are gradually increased / decreased, the flow of material from the surroundings is promoted in the press forming, and there is also an effect that the forming is facilitated.

[0023]

EXAMPLE A polymer electrolyte fuel cell was prototyped based on the above-mentioned invention, and gas sealing performance and power generation performance were confirmed. FIG.
Are fuel cell stacks stacked by the configuration shown in FIG. 6, and the vertical direction in FIG. 6 is indicated by an arrow in FIG. Bolt holes were placed on the four circumferences of each member for the purpose of positioning and applying full pressure, and the stack was tightened using high-tensile bolts and rigid end plates, but this state is omitted in this figure. is there. The stack cycle was configured such that the A cycle shown in FIG. 6 was repeated every four times and the B cycle was repeated once, and a total of 200 single cells were stacked.
The size of the fuel cell is 250 mm long x 250 mm wide x 15 height
0 mm.

The size of the flow path portion of one separator is 1
00 mm x 200 mm, and the separator has a plate thickness of 0.2 mm
Using 20Cr-15Ni-3Mo-based austenitic stainless steel, the solid polymer membrane, the electrode catalyst and the carbon fiber current collector are commercially available perfluorosulfonic acid-based ion-exchange membranes, carbon black carrying platinum, A prototype of a polymer electrolyte fuel cell was fabricated using porous carbon paper. The groove shape of the separator was as follows, and two types of grooves having a constant groove pitch and a pitch increasing toward the downstream side were prototyped and processed by press molding.

In the groove arrangement, in the first embodiment, one groove shown in FIGS. 1, 2 and 3 flows in a one-stroke shape,
The smaller one of the end inclination angles θ is 5.7 degrees (= 0.5 / 5.
0). Further, in Example 2, as in the case shown in FIG. 9, it is assumed that one groove flows in a one-stroke shape, and the smaller one of the end inclination angles θ is 5.7 degrees. A 0.6 mm thick silicone resin was used for the seal plate.

A cooling water inlet 17 and a cooling water outlet 18 shown in FIG. 10 are provided with side caps for supplying and discharging cooling water from the side surfaces of the stack. Sealed not to. Reference numerals 13 and 15 denote fuel gas inlet / outlet ports, respectively, and reference numerals 14 and 16 denote air gas inlet / outlet ports.

In the press working of the separator, the polymer electrolyte fuel cell fabricated without breaking is operated at 80 ° C., and hydrogen and air as fuel gas are humidified and supplied at 90 ° C. To generate power. In any polymer electrolyte fuel cell,
No gas leakage or water leakage occurs, and about 9 at open voltage
It was confirmed that about 100 A of power was generated at 0 V and a short-circuit current. Thus, it was confirmed that the separator of the present invention functions well as a fuel cell.

[0028]

Industrial Applicability The present invention enables press forming of high corrosion resistant stainless steel or titanium as a separator for a polymer electrolyte fuel cell, and is extremely useful as a technology for realizing a low cost polymer electrolyte fuel cell. It is valid.

[Brief description of the drawings]

FIG. 1 is an example of a plan view of a separator of the present invention.

FIG. 2 is a schematic diagram showing an example of a laminated structure using the separator of the present invention.

FIG. 3 is an enlarged plan view of a groove end of the separator of the present invention, and a cross-sectional view of a laminated structure using the separator of the present invention.

FIG. 4 is an example of a plan view of another separator of the present invention.

FIG. 5 is an enlarged view of a groove end of another separator of the present invention.

FIG. 6 is a schematic view showing an example of constructing a polymer electrolyte fuel cell stack using the separator of the present invention.

FIG. 7 is a schematic diagram showing a cross-sectional shape of the separator of the present invention.

FIG. 8 is a schematic view showing a groove end shape of the separator of the present invention.

FIG. 9 is a plan view showing another example of the separator of the present invention.

FIG. 10 is a schematic external view showing an example of a polymer electrolyte fuel cell experimentally produced by applying the present invention.

[Explanation of symbols]

1: separator 2: fuel gas inflow hole 3: oxygen (air) inflow hole 4: fuel gas outflow hole 5: oxygen (air) outflow hole 6: groove end 7: concave portion (fuel gas flow path) 8: convex portion (oxygen (Air channel) 9: Four-round flat portion of separator 10: Seal plate 11: Electrode (carbon fiber current collector) 12: Solid polymer film 13: Fuel gas inlet 14: Oxygen (air) inlet 15: Fuel gas Outlet 16: Oxygen (air) and generated water outlet 17: Cooling water inlet 18: Cooling water outlet 19: Gas flow

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Tsutomu Hatano 20-1 Shintomi, Futtsu-shi Nippon Steel Corporation Technology Development Division (72) Inventor Hiroshi Kihira 20-1 Shintomi, Futtsu-shi Nippon Steel Corporation F-term in the Company Technology Development Division (reference) 5H026 AA06 CC03 EE02 EE08 HH02 HH03

Claims (8)

[Claims] 1. A peripheral portion is flat, a central portion has a plurality of continuous grooves formed of a convex portion and a concave portion having different gas flow paths on the front and back surfaces, and the shape of the groove end is inclined. A separator for a polymer electrolyte fuel cell, comprising: 2. The separator for a polymer electrolyte fuel cell according to claim 1, further comprising a sealing member for sealing both surfaces of the peripheral flat portion. 3. The separator for a polymer electrolyte fuel cell according to claim 1, wherein the separator is made of stainless steel or titanium. 4. The polymer electrolyte fuel cell separator according to claim 1, wherein the inclination angle of the groove end is changed for each groove. 5. A groove pitch P (mm), a shoulder radius R (mm),
Parallel part length W (mm), plate thickness t (mm), material elongation EL
(%), Yield stress YS (kgf / mm ² ), groove depth H
The separator for a polymer electrolyte fuel cell according to any one of claims 1 to 4, wherein (mm) is equal to or less than a value calculated by the following equation. H = 2 × W × (EL / YS) ^1.01 × (R / t) ^0.318 ×
(1-W / P) ^2.66 6. A shoulder radius R (mm) and a parallel portion length W (m
m), the thickness t (mm), the material elongation EL (%), and the yield stress YS (kgf / mm ² ). Claim 1 characterized by the following:
The separator for a polymer electrolyte fuel cell according to any one of claims 4 to 4. θ = 90 × (EL / YS) ^0.372 × (R / t) ^0.270 ×
(W / t) ^-0.265 7. The polymer electrolyte fuel cell separator according to claim 1, wherein the cross-sectional area of the groove is gradually increased as it goes downstream of the flow path. 8. A polymer electrolyte fuel cell using the polymer electrolyte fuel cell separator according to any one of claims 1 to 7.