JP3330343B2 - Fuel cell separator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell separator mainly used as an electric vehicle or a small portable power supply. A gas diffusion electrode having a sandwich structure sandwiched between cathodes (cathode) is further sandwiched from both outer sides thereof, and a fuel gas flow path and an oxidizing gas flow path are formed between the anode and the cathode to constitute a fuel cell. single cell is is relates to separators for a fuel cell of solid polymer type or the like that are configured.

[0002]

2. Description of the Related Art In a fuel cell, a fuel gas containing hydrogen is supplied to an anode, and an oxidizing gas containing oxygen is supplied to a cathode, so that H2.fwdarw.2H '+ 2e'... 1) (1/2) O2 + 2H '+ 2e' → H2O (2) An electrochemical reaction of the following formula is shown. As a whole battery, the following formula is obtained: H2 + (1/2) O2 → H2O (3) The electrochemical reaction progresses, and the chemical energy of such fuel is directly converted into electric energy, thereby exhibiting a predetermined cell performance.

[0003] A separator for a polymer electrolyte fuel cell, which is a kind of fuel cell that generates the above-described energy conversion, is often applied as a power source for a moving medium such as an electric vehicle. In order to reduce the area as much as possible and reduce the weight, it is required to reduce the thickness of the separator.

On the other hand, in a polymer electrolyte fuel cell,
Since the solid polymer membrane itself is acidic, the separator sandwiching the solid polymer membrane is required to have acid resistance. In addition, hydrogen and oxygen as a fuel gas or water as a reaction product are used for the separator. It is also required that the flow path be made of a material having high corrosion resistance that can prevent the formation of an oxide film or the like because it directly contacts the gas or the generated water.

[0005] As a separator for a polymer electrolyte fuel cell of this type, the following has been proposed in the past. A sintered carbon separator obtained by subjecting a flat sintered carbon to cutting machining and forming a plurality of convex portions on the surface thereof. As shown in FIG. 8 , a flat member 30 obtained by impregnating or mixing expanded graphite alone or a strength improving material such as a phenol resin or pitch into expanded graphite is formed into a lower mold 32 and an upper mold 33 having a concave portion 31 for forming a convex portion. As shown in FIG. 9 , the thickness of the flat plate member 30 is reduced from t2 to t2 ′, and a plurality of convex portions are formed on the surface of the flat plate member 30, as shown in FIG. 34. An expanded graphite separator formed by forming No. 34.

[0006]

However, among the above-mentioned conventional separators for polymer electrolyte fuel cells, the sintered carbon separator has a flat plate portion having a thickness of 1.0 mm or less by cutting machining and has a thickness of 1.0 mm or less. 2.0 thickness
However, even if the thickness of the flat part can be reduced to about 1.0 mm, it requires a great deal of labor and skill to reduce the thickness to less than 1.0 mm. Because the mechanical strength of the thin flat plate is small,
Hundreds of separators are stacked and fastened and fixed, so that there is a problem that a fastening force at the time of assembling the fuel cell and a damage such as a crack at the time of cutting are easily generated.

The expanded graphite separator is excellent in corrosion resistance, but uses expanded graphite which inherently has poor fluidity during processing and molding, so that the flat portion has a desired thinness. When the mold is formed as described above, it is difficult to form the convex portion 34 forming the gas flow path into a predetermined shape having a right angle due to R or chipping at the corner.
As described above, the molding accuracy is poor, and as a result, when the corners of the convex portion 34 are rounded or chipped, the contact area with the electrode adjacent to the convex portion 34 is reduced, and the electrical resistivity when the separator is stacked is reduced. As the fuel gas rises, the fuel gas flows into the adjacent flow channel groove 35 formed between the convex portions, causing a short circuit in the gas flow channel (short circuit). As a result, the electromotive force of the fuel cell itself decreases. There is.

As described above, even in a fuel cell separator made of expanded graphite having excellent corrosion resistance, when the flat plate portion is formed to have a desired thinness, the grooves and convex portions forming the gas flow path are not formed. There is a demand for precision molding of them to prevent a decrease in electric conductivity such as an increase in electric resistivity when a large number of separators are stacked. By the way, about the thinness of this kind of separator,
Specifically, the thickness of the separator is preferably 2 mm or less, and the thickness of the flat plate portion other than the convex portion is preferably 1.0 mm or less,
As for the electrical characteristics of the separator, it is required that the electrical conductivity (electrical contact resistance) be as low as possible.

The present invention has been made in view of the above circumstances, and a gas flow path is formed even if the fuel cell itself is made thinner enough to reduce the installation area and reduce the weight. and its object is to provide a separators for a fuel cell can exhibit excellent electrical properties to ensure a very high forming accuracy to the shape and dimensions of the grooves and protrusions.

[0010]

In order to achieve the above object, a fuel cell separator according to the first aspect of the present invention is a fuel cell separator mainly comprising a sheet-shaped member and a projection-forming member. A plurality of protrusions are formed on the surface of the sheet-like member, and a protrusion-forming member is embedded in a concave portion on the back surface corresponding to the protrusion of the sheet-like member. The forming member spirally winds the expanded graphite material a plurality of times so as to be arranged in a direction perpendicular to the plane of the sheet-like member, and shapes it into a predetermined convex shape, or a band-like expansion. It is characterized by being made by laminating a plurality of graphite sheet materials in parallel to a plane.

According to the first aspect of the present invention, the sheet-like member and the protrusion-forming member dedicated to forming the protrusion are separately formed and formed on the sheet-like member. By embedding both members having different characteristics, such as embedding a protrusion forming member in a concave portion corresponding to the formed convex portion, cutting work requiring labor and skill is not required, thereby reducing manufacturing costs. At the same time as reducing the thickness, the flat plate portion is made thinner to satisfy the requirements for the reduction of the installation area of the entire fuel cell and the weight reduction, but the corner portion of the convex portion forming the gas flow path does not have R or chip, and the like. It is possible to form a convex portion having a predetermined shape and a predetermined dimension with a right angle at a high precision so as to have excellent electric characteristics. In particular,
It is possible to flatten the top end surface of the separator convex part that is in contact with the electrode, and it is also excellent in conformity with the electrode, to reduce the electrical resistivity of the contact part and improve the electrical characteristics, and ultimately to improve the fuel cell performance. Can be.

[0012] Further, as the above-mentioned convex portion forming member, an expanded graphite sheet material formed by spirally winding a plurality of times and shaping it into a predetermined convex shape, or a belt-like expanded graphite sheet material is used. By using one formed by laminating a plurality of sheets in parallel with the plane, the volume resistivity of the projection-forming member itself becomes extremely low, and the electrical characteristics of the entire separator can be further improved.

Here, when the sheet-like member is made of expanded graphite as described in claim 2, it is not necessary to preform the sheet-like member with a convex portion, and the convex portion is formed on the back side thereof. It is possible to form a convex portion on the surface of the sheet-like member and press-fit the convex-portion forming member into the corresponding concave portion on the rear surface side only by arranging the forming member and performing mold molding. In addition to reducing the number of production steps, the production cost can be further reduced, and a separator excellent in corrosion resistance required for this type of separator can be obtained.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. First, the configuration and operation of a polymer electrolyte fuel cell as an embodiment of a fuel cell separator will be briefly described with reference to FIGS.
The polymer electrolyte fuel cell 20 is formed of, for example, a solid polymer membrane 1 which is an ion exchange membrane formed of a fluorine-based resin, and a carbon cloth, carbon paper or carbon felt woven with carbon fiber yarns. A plurality of sets of single cells 5 each comprising an anode 2 and a cathode 3 serving as a gas diffusion electrode forming a sandwich structure sandwiching the molecular film 1 from both sides and separators 4 and 4 further sandwiching the sandwich structure from both sides are laminated. It has a stack structure in which current collector plates (not shown) are arranged at both ends.

As shown in FIG. 2, the two separators 4 have fuel gas holes 6 and 7 containing hydrogen at their peripheral portions.
And oxidizing gas holes 8 and 9 containing oxygen and cooling water holes 10 are formed. When a plurality of sets of the single cells 5 are stacked,
Each hole 6, 7, 8, 9, 10 of each separator 4 penetrates through the inside of the fuel cell 20 in the longitudinal direction, and the fuel gas supply manifold, fuel gas discharge manifold, oxidizing gas supply manifold, oxidizing gas discharge manifold, cooling It is designed to form a channel.

Further, by forming a large number of projections on the surface of the separators 4, a groove 11 is formed between the projections.
The groove 1 is formed as shown in FIG.
A fuel gas flow path 12 is formed between the surface of the anode 1 and the anode 2, and an oxidizing gas flow path 13 is formed between the groove 11 and the surface of the cathode 3.

In the polymer electrolyte fuel cell 20 having the above-described structure, the fuel gas containing hydrogen supplied to the fuel cell 20 from the externally provided fuel gas supply device passes through the fuel gas supply manifold. The fuel gas is supplied to the fuel gas flow channel 12 of each unit cell 5 and undergoes an electrochemical reaction on the anode 2 side of each unit cell 5 on the anode 2 side as described in the above formula (1). The fuel gas is discharged from the fuel gas passage 12 of the cell 5 to the outside via the fuel gas discharge manifold. At the same time, an oxidizing gas (air) containing oxygen supplied to the fuel cell 20 from an oxidizing gas supply device provided outside is supplied to the oxidizing gas passage 13 of each unit cell 5 via the oxidizing gas supply manifold. Is supplied to the cathode 3 side of each unit cell 5 to cause an electrochemical reaction as shown in the above-mentioned equation (2), and the oxidized gas after the reaction flows from the oxidized gas flow path 13 of each unit cell 5 to the oxidized gas. The gas is discharged to the outside via the gas discharge manifold.

With the electrochemical reactions of the above formulas (1) and (2), the electrochemical reaction of the fuel cell 20 as a whole proceeds as shown in the above formula (3), and the chemical energy of the fuel is directly converted to the electric energy. By converting to energy, predetermined battery performance is exhibited. In addition, the fuel cell 20 generates heat because it is operated in a temperature range of about 80 to 100 ° C. due to the properties of the solid polymer membrane 1. Therefore, during operation of the fuel cell 20, the fuel cell 2 is supplied from a cooling water supply device provided outside.
By supplying cooling water to the cooling water channel 0 and circulating the cooling water in the cooling water channel, a rise in the temperature inside the fuel cell 20 is suppressed.

Next, the structure of the separator 4 in the polymer electrolyte fuel cell 20 having the above-described structure and operation and a method of manufacturing the separator 4 will be described. FIG. 4 is a partially cutaway perspective view showing a first embodiment of the fuel cell separator 4 according to the present invention. The fuel cell separator 4 includes a sheet-like member 14 and a projection-forming member 15. The sheet member 14 is made of expanded graphite, and the thickness of the flat plate portion is formed at t1. On the other hand, the convex part forming member 15 has a long strip shape.
Of the expanded graphite sheet material 15a
Many times so that they are arranged in a direction perpendicular to
And shaped into a predetermined convex shape.
As hereinbefore, it is formed in a small convex shape than in similar shape with the convex portion 19 of the size and predetermined shape necessary (described below) in the separators 4.

As shown in FIG. 5, the expanded graphite sheet-like member 14 having a thickness of t0 is placed on the upper surface of a lower mold 17 having a concave portion 17a at a position corresponding to the convex portion forming portion, as shown in FIG. Is set to face upward, and an upper die 18 having a movable press die 18a is disposed above the set sheet-like member 14 at a position corresponding to the projection forming portion. Movable die 1
The protrusion forming member 15 is arranged on the back surface of the sheet-like member 14 below 8a.

In this state, as shown in FIG.
Is brought close to the lower mold 17, the sheet-shaped member 14 is pinched and fixed to reduce the flat plate portion from the thickness t0 to t1, and then the movable pressing die 1
Pressing and moving the mold 8a to the lower mold 17 side, that is, pressing the convex forming member 15 from the back surface 14a side of the sheet-like member 14 toward the front surface side via the movable press die 18a. As a result, the sheet-like member 14
Of the lower mold 17 corresponding to the concave portion 17a is
While deforming along the inner surface of 7a to form protrusions 16 at a plurality of locations on the surface of the sheet-like member 14,
By fitting (embedding) the protrusion forming member 15 into the recess 16 a on the back surface side of the sheet member 14 corresponding to the protrusion 16, and integrating the two members 14, 15, the sheet member 14 is formed. A plurality of protrusions 19 formed of the protrusions 16 of the sheet-like member 14 and the protrusion formation members 15 are formed on the surface, and the fuel gas flow path 12 is formed between adjacent protrusions 19.
And a groove 11 that becomes the oxidizing gas flow path 13 .

FIG. 7 is a partially cutaway perspective view showing a second embodiment of a fuel cell separator 4 according to the present invention.
This is a belt-shaped expanded graphite sheet material 15b which is prepared by laminating a plurality of sheets in parallel with a plane, and other configurations and manufacturing methods are the same as those described in the first embodiment. Therefore, detailed description is omitted.

The fuel cell separator 4 having the structure shown in each of the above embodiments is a sheet-like member 14 composed of only a flat plate portion.
And a protrusion forming member 15 dedicated to forming the protrusion 19 are separately formed, and the protrusion forming member 15 is formed in the concave portion 16 a corresponding to the protrusion 16 formed on the sheet-like member 14 or the preformed portion 16. By combining the two members 14 and 15 having different characteristics, such as embedding, a cutting machine is not required to reduce the manufacturing cost, and at the same time, the flat plate portion is thinned to reduce the entire fuel cell 20. While satisfying the requirements for the reduction of the installation area and the weight reduction, the convex portion 19 having a right angle in a predetermined shape and a predetermined size is formed without generating a radius or a chip at the corner portion of the convex portion 19 forming the gas flow path. Can be molded with high precision to have excellent electrical characteristics. In particular, it is possible to flatten the top end surface of the separator convex portion 19 in contact with the electrodes (anode 3 and cathode 4), to have excellent conformability with the electrodes 3 and 4, to reduce the electrical resistivity of the contact portion, It is possible to improve the characteristics and eventually the fuel cell performance.

In particular, as shown in the first and second embodiments, it is preferable to use expanded graphite as a constituent material of the projection- forming member 15 in terms of corrosion resistance. In particular, the expanded graphite sheet material 15a is wound. In the case of using a material formed by laminating a plurality of sheets of the expanded graphite sheet material 15b or a material formed by laminating a plurality of sheets of the expanded graphite sheet material 15b, the volume resistivity of the convex portion forming member 15 becomes extremely low, and the electrical characteristics of the entire separator 4 are reduced. It can be further improved.

[0025]

EXPERIMENTAL EXAMPLES Hereinafter, the present invention will be described in more detail with reference to experimental examples. Below the electrical contact resistance and molding accuracy of the separator for a conventional fuel cell corresponding to Comparative Example 1 and the fuel cell separator of the present invention corresponding to Example 1 was manufactured with the specifications shown in Table 1 As a result, the results shown in Table 2 were obtained.

Electric contact resistance: measured by measuring the current and voltage of the electrodes by a four-terminal method after two separators were placed between the copper plate electrodes and pressurized. Molding accuracy: Ｒ indicates that no R was generated at the corner of the convex portion forming the gas flow path, and × indicates that R was generated.

[0027]

[Table 1]

[0028]

[Table 2]

As is clear from Table 1 above,
The fuel cell separator of the present invention corresponding to one, while it is possible to thin the thickness t of the flat portion of the sheet-like member to 1.0mm or less, as is clear from Table 2,
It is possible to maintain high molding accuracy and, consequently, the electrical contact resistance when stacking separators is small.
On the other hand, the conventional fuel cell separator corresponding to Comparative Example 1 has a flat plate thickness of 1.3 mm, which does not reach the thinness required as a separator, and is extremely inferior in terms of molding accuracy. Thus, it was found that the effective electromotive force of the fuel cell was adversely affected.

[0030]

As described above, according to the first aspect of the present invention, it is possible to reduce the thickness of the flat plate portion of the separator to reduce the installation area and the weight of the entire fuel cell.
A convex portion having a predetermined shape and a predetermined dimension can be formed with very high precision without causing an R or a chip at a corner portion of the convex portion forming the gas flow path, and excellent electric characteristics can be provided.
In particular, it is possible to improve the conformability with the electrode by flattening the top end surface of the separator convex portion in contact with the electrode, to reduce the electrical resistivity of the contact portion, to improve the electrical characteristics, and thereby to remarkably improve the fuel cell performance. It has the effect of being able to.

According to the second aspect of the present invention, in addition to the above effects, the volume resistivity of the projection-forming member can be made extremely low, and the electrical characteristics of the entire separator can be further improved.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view showing a configuration of a stack structure constituting a polymer electrolyte fuel cell provided with a separator of the present invention.

FIG. 2 is an external front view of a separator in the polymer electrolyte fuel cell.

FIG. 3 is an enlarged cross-sectional view of a main part showing a configuration of a single cell which is a structural unit of the polymer electrolyte fuel cell.

FIG. 4 is a partially cutaway perspective view showing a first embodiment of a fuel cell separator according to the present invention.

FIG. 5 is a sectional view illustrating a first step of the method for manufacturing a fuel cell separator.

FIG. 6 is a sectional view illustrating a second step of the method for manufacturing a fuel cell separator.

FIG. 7 is a partially broken perspective view showing a second embodiment of the fuel cell separator according to the present invention.

FIG. 8 is a cross-sectional view illustrating a method for manufacturing a conventional fuel cell separator.

FIG. 9 is a partially cutaway perspective view showing an example of a conventional fuel cell separator manufactured by the above manufacturing method.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 solid polymer membrane 4 separator for fuel cell 14 sheet member 15 protrusion forming member 15 a, 15 b expanded graphite sheet material 16 protrusion of sheet member 16 a recess corresponding to protrusion of sheet member 19 protrusion of separator 20 Fuel cell

Continued on the front page. (72) Inventor Shoji Kato 541-1, Shimouchi jinji bat, Mita city, Hyogo prefecture. Inside the Mita plant of Nippon Pillar Industry Co., Ltd. (72) Inventor Kiyoshi Shimoyama. No. 541, No. 1, Japan Pillar Industry Co., Ltd. Mita Factory Examiner Kenichi Hara (56) References JP-A-2000-12048 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 8 / 02 H01M 8/10

Claims (2)

(57) [Claims] 1. A fuel cell separator mainly comprising a sheet-shaped member and a projection-forming member, wherein a plurality of projections are formed on a surface of the sheet-shaped member. A convex portion forming member is embedded in a concave portion on the back surface side corresponding to the portion, and a plurality of the convex portion forming members are arranged so that the expanded graphite sheet material is arranged in a direction orthogonal to the plane of the sheet-like member. It is formed by winding in a spiral shape and shaping it into a predetermined convex shape, or laminating a plurality of strip-shaped expanded graphite sheet materials in parallel to a plane. Fuel cell separator. 2. The fuel cell separator according to claim 1, wherein the sheet-like member is made of expanded graphite.