JP2005019109A - Gasket for fuel cell and fuel cell using it, and mold for processing gasket - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve problems of a fuel cell using a proton conductive solid polymer film for an electrolyte that a gasket is not good enough in durability and stability and reduces cell performance, and the gasket made of fluororesin is not good enough in sealing performance. <P>SOLUTION: A rib both ends of which are closed is formed on the gasket, and valleys both ends of which are closed, are formed near the rib. The ribs surround the periphery of an electrode area and a manifold area singly, doubly, or more plurally. The fluororesin can be used as a material for the gasket. It is preferable that surface processing of a mold for molding the gasket is performed by photo-etching, and surface polishing is performed after the surface processing. This makes the fuel cell high in reliability at a high temperature. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a gasket for use in a fuel cell that uses a solid polymer membrane as an electrolyte, supplies a methanol aqueous solution or hydrogen gas as a fuel, and supplies oxygen or air as an oxidant gas, and a fuel cell using the gasket.
[0002]
[Prior art]
As a conventional measure for improving the airtightness of this type of fuel cell gasket, a method of providing a rib on a gasket made of an elastomer is known (for example, see Patent Document 1).
[0003]
[Patent Document 1]
JP 2002260693 A (page 2, page 4-6, FIGS. 1 to 8)
[Patent Document 2]
JP-A-11-250923 (FIG. 1)
[0004]
A fuel cell using a solid polymer membrane as an electrolyte has a relatively low operating temperature of about 100 ° C. or less and a high output, so that it can be used as a power source for mobile objects, a distributed power source, and a portable power source. Attention has been paid. In such a fuel cell using a solid polymer membrane as an electrolyte, a negative electrode and a positive electrode are arranged with the electrolyte in between, a negative electrode side gasket is arranged on the negative electrode side of the electrolyte, and fuel is supplied to each cell outside thereof. And a negative electrode side separator having a flow channel for flowing it, a positive electrode side gasket is disposed on the positive electrode side of the electrolyte, and oxygen or air is supplied to each cell as an oxidant gas outside thereof. It is a structure in which a positive electrode separator having a manifold and a flow channel for flowing it is provided. When fuel such as hydrogen gas or methanol aqueous solution is supplied to the negative electrode and oxygen or air is supplied to the positive electrode, fuel is supplied to the negative electrode. Hydrogen ions and electrons are released by an electrochemical reaction that is oxidized, and at the positive electrode, the hydrogen ions, oxygen, and electrons that have passed through the electrolyte react with each other to produce water. It is possible to supply electrical energy to.
[0005]
In fuel cells, leakage of fuel and air from the anode and cathode electrodes to the outside of the fuel cell and from each manifold to the outside of the fuel cell becomes a problem. In addition, fuel from the air side manifold inside the fuel cell Leakage of air to the flow path or fuel leakage from the fuel side manifold to the air flow path is also a serious problem. Due to leakage inside the fuel cell, deterioration of battery characteristics becomes a problem. In order to reliably prevent leakage to the outside of the fuel cell and inside the fuel cell, it is necessary to reliably seal the outer periphery of each electrode portion and the outer periphery of the manifold portion with gasket ribs.
[0006]
A fuel cell using a solid polymer membrane as an electrolyte is usually operated at a temperature of about 100 ° C., and an elastomer such as silicon rubber or an ethylene-propylene-diene monomer copolymer has been used for a gasket. However, from the viewpoint of improving characteristics and using waste heat, a high-temperature type fuel cell in which the operating temperature is raised to about 150 ° C. by improving the electrolyte material has been studied. The durability was insufficient. In addition, in direct methanol fuel cells that supply methanol aqueous solution as fuel, elastomer materials have problems in stability, and during operation, swelling or alteration occurs due to the influence of temperature, water vapor or methanol, crosslinking aids, filling There is a problem in that components are eluted from additives such as an agent and a release agent, and the eluted components affect the electrolyte and the catalyst to deteriorate the battery characteristics.
[0007]
On the other hand, the problem that the durability and stability of an elastomer are inadequate can be avoided by using fluororesins, such as tetrafluoroethylene, for a gasket. However, the gasket made of fluororesin is harder than the gasket made of elastomer material and cannot sufficiently cope with the surface roughness of the separator plate, so that the sealing performance is insufficient and the leakage of fuel and oxidant gas can be completely prevented. could not.
[0008]
High durability, stability and high resistance to leakage of polymer electrolyte fuel cells that operate at high temperatures and gaskets used in direct methanol fuel cells that use aqueous methanol as fuel. Sealability is desired. In addition, it is desirable that the processing is easy and can be manufactured at low cost. Conventional elastomeric materials have problems in durability and stability, and on the contrary, highly stable fluororesin materials have problems in sealing properties, and no gasket that satisfies all these problems is known.
[0009]
In order to improve sealing performance, for example, as disclosed in Patent Document 1, a method of providing a rib shape on a gasket is known. However, this is because ribs are provided in a portion made of rubber or elastomer, and it is not easy to perform fine rib molding on a non-thermoplastic plastomer material such as a fluororesin.
[0010]
[Problems to be solved by the invention]
The molding method of providing ribs by hot pressing is generally a method that can be carried out easily in large quantities, but when it is going to perform fine rib molding on a plastomer material that is not thermoplastic like a fluororesin and can not undergo a crosslinking reaction, Unlike the case of the elastomer material, it is difficult to ensure the shape and height accuracy of the rib because the resin does not easily turn around the rib-shaped portion of the mold. In addition, since the difficulty of molding becomes more prominent as the height of the rib is increased, it is difficult to secure a rib having a height necessary for improving the sealing performance.
[0011]
Moreover, the metal mold | die used in order to provide a rib needs a very fine process. The thickness of the positive and negative electrodes of the fuel cell attached to both sides of the proton conductive polymer membrane as an electrolyte is usually 0.5 mm or less in consideration of gas diffusivity and the like. Therefore, in order to ensure the electron conductivity for collecting current from the electrode in the central part of the separator, the thickness of the gasket sandwiching the periphery of the electrolyte membrane needs to be 0.5 mm or less. In view of the strength of the gasket and workability at the time of lamination, the rib provided on one side of the 0.5 mm thick gasket needs to have a height of about 0.2 mm. Actually, since the thickness of the electrode is often about 0.2 mm, it is necessary to make the gasket thickness 0.2 mm and the rib height 0.05 mm or less. The mold for forming such a rib shape requires extremely fine processing. Normally, the mold is manufactured by machining, but in order to perform such fine processing, it is necessary to perform processing for a long time with a precise processing apparatus. For this reason, such a mold has been expensive.
[0012]
SUMMARY OF THE INVENTION An object of the present invention is to provide a gasket for a fuel cell that is excellent in durability, stability, and sealing properties, is easy to be molded, and is low in cost. Furthermore, the mold used for molding the gasket is processed by an easy method to reduce the cost of the mold, and to provide a highly reliable fuel cell using this gasket at a low cost.
[0013]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, an invention according to claim 1 is directed to an electrode-membrane assembly in which a proton conductive polymer membrane is used as an electrolyte and a positive electrode and a negative electrode are arranged on both sides thereof, and a pair of separators arranged on both sides thereof. A gasket for a fuel cell, which is located between a plate and a gasket, wherein the gasket has a closed rib at both ends, and a closed valley at both ends in the vicinity of the rib. is there.
[0014]
The invention according to claim 2 is such that the rib shape is a triangle shape, a quadrangular shape, a trapezoidal shape, a semicircular shape, and a shape obtained by arbitrarily giving these shapes, the valley shape is a triangular shape, 2. The fuel cell gasket according to claim 1, wherein the gasket has a quadrangular shape, a trapezoidal shape, a semicircular shape, and a shape obtained by giving an arbitrary radius to these shapes.
[0015]
The invention according to claim 3 is the fuel cell gasket according to claim 1 or 2, wherein the rib has a valley on both sides or one side.
[0016]
The invention described in claim 4 has the center of the valley within a distance corresponding to twice the cross-sectional width of the rib bottom portion from the center of the rib width, according to any one of claims 1 to 3. This is a fuel cell gasket.
[0017]
The invention according to claim 5 is characterized in that the thickness is within 0.5 mm, and the height of the rib is within 0.2 mm. It is a battery gasket.
[0018]
A sixth aspect of the present invention is the fuel cell gasket according to any one of the first to fifth aspects, wherein the rib surrounds the outer periphery of the electrode portion and the manifold portion.
[0019]
The invention according to claim 7 is the fuel cell gasket according to claim 6, characterized in that the rib surrounds at least one of the outer periphery of the electrode portion or the manifold portion more than double.
[0020]
The invention according to claim 8 is the fuel cell gasket according to any one of claims 1 to 7, wherein the gasket material is a fluororesin.
[0021]
The invention according to claim 9 is characterized in that the material is any one of polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, and tetrafluoroethylene-hexafluoropropylene copolymer. 8. The fuel cell gasket according to 8.
[0022]
A tenth aspect of the present invention is a mold for use in molding a fuel cell gasket according to any one of the first to ninth aspects, wherein the surface processing is performed by photoetching. It is a type.
[0023]
An eleventh aspect of the present invention is the gasket molding die according to the tenth aspect, in which mechanical processing such as surface polishing is performed after photoetching.
[0024]
A twelfth aspect of the invention is a fuel cell using a proton conductive polymer membrane as an electrolyte, wherein the gasket according to any one of the first to ninth aspects is used.
[0025]
In a fuel cell in which a large number of unit cells are stacked, leakage of fuel and air from the electrode part to the outside of the fuel cell and from the manifold to the outside of the fuel cell becomes a problem, but in addition to this, the air side inside the fuel cell Leakage of air from the manifold to the fuel flow path, or leakage of fuel from the fuel side manifold to the air flow path is also a major problem. In particular, in a fuel cell using a proton conductive polymer membrane as an electrolyte, an electrode thickness of 0.5 mm or less is usually used in consideration of gas diffusibility and the like. Therefore, in order to ensure the electron conductivity between the electrode and the separator plate, the thickness of the gasket directly sandwiching the electrolyte membrane needs to be 0.5 mm or less. Further, in order to improve the discharge characteristics of the battery, the battery is required to operate at a high temperature, and naturally, long-term reliability is required. The above-described configuration of the present invention provides a gasket that can meet these requirements, a mold for efficient production of the gasket, and the use of the gasket provides a means for obtaining an excellent fuel cell.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a gasket as a component of a direct methanol fuel cell according to an embodiment of the present invention, a fuel cell using the gasket, and a mold for processing the gasket will be described with reference to the drawings. In each figure, the same code | symbol is attached | subjected to the part which has the same function.
[0027]
FIG. 1 is an exploded perspective view of a main part of a unit cell of a direct methanol fuel cell according to the present invention. The electrolyte 1 made of a solid polymer film is joined with a negative electrode 2 on one central surface and a positive electrode 3 on the other surface, except for four rounds. On the negative electrode side of the electrolyte 1, a negative electrode side separator 4 having manifolds 41 and 41 ′ for supplying fuel to each cell via a negative electrode side gasket 6 and a flow channel groove 42 for flowing the fuel is provided. Yes. The fuel appears from the manifold 41 through a passage (not shown) penetrating the inside of the separator 4 at the upper left end of the flow channel groove 42, and reaches the manifold 41 ′ through the flow channel groove 42. On the positive electrode side of the electrolyte 1, a positive electrode side having manifolds 51, 51 ′ for supplying oxygen or air as an oxidant gas to each cell via a positive electrode side gasket 7, and a flow channel 52 for flowing it. A separator 5 is provided. The oxidant gas passes through the inside of the separator 5 from the manifold 51 and appears at the lower left end of the flow channel groove 52, and reaches the upper right manifold 51 ′ through the flow channel groove 52.
[0028]
FIG. 2 is a cross-sectional view of the negative side gasket 6 of FIG. 1 taken along the line A-A, and is provided with an uneven portion 8 including a rib 81 and a trough 82 arranged in the vicinity thereof, and the uneven portion 8 is shown in FIG. Thus, it arrange | positions so that an electrode part outer periphery and a manifold part outer periphery may be enclosed. The positive-side gasket 7 is also provided with the same uneven portion.
[0029]
In the above-described embodiment, the negative electrode side separator 4 having the flow channel 42 and the positive electrode side separator 5 having the flow channel 52 are separated from each other, but are composed of a cell stack in which a plurality of unit cells are connected in series. In practical batteries, in each intermediate unit cell, the negative separator 4 contacts the positive separator of another battery, and the positive separator 5 contacts the negative separator of another battery. Thus, it is preferable to form the fuel flow dew groove 42 and the oxidant gas flow channel 52 on both sides of one separator.
[0030]
Further, the pattern of the concavo-convex portion provided on the gasket may be a pattern surrounding the outer periphery of the electrode portion or the manifold portion without crossing all the ribs as shown in FIG. 3, and the electrode portion as shown in FIG. A pattern in which a part of the concavo-convex portion surrounding the outer periphery touches the concavo-convex portion surrounding the manifold outer periphery may be used. In any case, the both ends of the concavo-convex part must be closed patterns by contacting one concavo-convex part or other concavo-convex part without ending with both ends open.
[0031]
For example, in Patent Document 2, the passage between each manifold and each channel groove is formed by a groove carved on the separator surface. In this case, the uneven portion of the present invention has a manifold that controls a pair of inflow and outflow. It is necessary to enclose it including the channel groove between them. When the passage within the thickness of the separator is provided in the separator, the manifold and the channel groove can be separately surrounded by the concavo-convex portion, and fuel and oxidant gas leakage can be completely prevented. .
[0032]
【Example】
(Example 1)
5A and 5B, with reference to the flat surface 61 of the gasket 6, a rib 81 having a height a = 0.05 mm and a bottom width b = 0.15 mm, and a distance from the center of the rib on both sides of the rib. A mold for heating and press-molding a frame-type gasket having an outer dimension of 10 cm square having a valley 82 with a depth d = 0.1 mm centered at a position c = 0.15 mm away from each other by machining. A set was made. Using this mold, a 0.25 mm thick tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer sheet is used as a material, and the uneven portion 8 is molded by hot pressing at 200 ° C. and 15 MPa. 1 was obtained.
[0033]
(Comparative example)
As shown in FIG. 6A and FIG. 6B, a rib 81 ′ having a = 0.05 mm and b = 0.15 mm, and on both sides thereof, c ′ = 0.4 mm away from the center, and d = 0.1 mm. A set of molds for heating and press-molding a frame-type gasket having a trough 82 'and having an outer dimension of 10 cm square was produced by machining. Using this mold, a 0.25 mm-thick tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer sheet was used as a material, and hot pressing was performed at 200 ° C. and 15 MPa to mold the uneven portion 8 ′. Such a gasket was obtained.
[0034]
When Example 1 after molding and a comparative example were compared, in both cases, the trough was able to be molded into the shape of the mold, but there was a difference in the ribs. The rib of the comparative example was found to be defective because the resin did not rotate around in some places, but the rib of Example 1 was able to be molded into the shape of the mold. From this result, it can be seen that the interval between the rib and the valley needs to be close. The required degree of proximity depends on the heating temperature and the applied pressure, but if the center of the valley is selected within a distance corresponding to twice the cross-sectional width of the rib bottom from the center of the rib width, there is no practical problem. The rib shape can be molded.
[0035]
(Example 2)
A catalyst containing platinum and ruthenium, a polytetrafluoroethylene fine particle, a negative electrode coated with an ion exchange resin on carbon paper, and a catalyst containing platinum, a polytetrafluoroethylene fine particle, and a positive electrode coated with carbon ion paper on Nafion It pressed on both surfaces of the solid polymer film which consists of 117, and produced the electrode-membrane assembly (MEA).
[0036]
Photo-etching processing was performed by drawing a pattern of irregularities as shown in FIG. 4 on the surface of the base material of the gasket molding die. The relationship between the ribs and the valley set was the position shown in FIGS. 5A and 5B, and then the surface was polished to the shape and dimensions shown in FIG. 5B. By using the photo-etching process, the mold cost can be reduced to 1/3 compared with the case where a gasket processing mold is manufactured by conventional machining. Using this gasket processing mold, a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer sheet was molded as a material to obtain a gasket of Example 2.
[0037]
Three single cells sandwiching the MEA are stacked between the negative electrode side separator 4 via the negative electrode side gasket 6 thus produced and the positive electrode side separator 5 via the positive electrode side gasket 7 produced in the same manner. Thus, the cell stack according to the example was obtained.
[0038]
(Experiment 1)
Using the cell stack according to the example described above, the presence or absence of leakage to the outside of the cell stack was inspected at a temperature of 90 ° C. First, distilled water was supplied to the negative electrode side and air was supplied to the positive electrode side at a flow rate of 12 cm 3 / min and 3 dm 3 / min, respectively, and leakage of distilled water or air to the outside of the cell stack was investigated. Next, air was supplied to the negative electrode side and distilled water was supplied to the positive electrode side at the same flow rate as above, and leakage of distilled water or air to the outside of the cell stack was investigated. As a result, no leakage was observed in any case.
[0039]
(Experiment 2)
Using the cell stack according to the above-described embodiment, the presence or absence of leakage inside the cell stack was inspected at a temperature of 90 ° C. First, distilled water was supplied to the negative electrode side and air was supplied to the positive electrode side at a flow rate of 12 cm 3 / min and 3 dm 3 / min, respectively, and the amount of air mixed in the waste liquid discharged from the negative electrode side was investigated. Next, air was supplied to the negative electrode side and distilled water was supplied to the positive electrode side at the same flow rate as before, and the amount of air mixed in the waste liquid discharged from the positive electrode side was investigated. As a result, no leakage of air into the fuel waste liquid was observed in any case.
[0040]
In order to reliably perform the rib molding by hot pressing, it is necessary that a valley for feeding the resin into the rib portion is in the vicinity of the rib. Therefore, it is necessary to have the center of the valley within a range corresponding to twice the width of the rib cross section from the center of the rib shape. The volume formed by the valley should be designed to exceed that of the rib.
[0041]
In order to reliably perform the shape molding of the ribs by hot pressing, it is desirable to provide valleys on both sides of the ribs, but it is also possible to make the valleys only on one side of the ribs. Further, by providing a common valley between the two ribs, it is possible to narrow the interval between the ribs and provide many ribs. Seal performance can be improved by making the ribs more than double. [0042]
Among fluororesins, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer and tetrafluoroethylene-hexafluoropropylene copolymer are particularly suitable for the gasket of the present invention because they are excellent in heat resistance and easy to hot melt molding. is there. Of course, other fluororesins can also be used effectively depending on the operating temperature of the battery.
[0043]
Photo-etching is a surface processing method used for manufacturing electronic parts and the like, and can be easily manufactured even with complicated and fine patterns. The invention according to claim 10 has found that such a photo-etching process is suitable for producing a mold for a gasket for a fuel cell. The gasket mold must have a narrow and accurate depth cavity to mold sharp and uniform height ribs, and a projection to create a valley in the immediate vicinity. It can be used suitably.
[0044]
Considering the flow during molding of the resin constituting the gasket, it is desirable to make the corners somewhat gentle after photoetching. Further, considering the releasability at the time of gasket molding, it is desirable to perform polishing after photoetching on the mold surface that tends to be textured.
[0045]
【The invention's effect】
According to the first aspect of the present invention, since a gasket that can reliably prevent leakage of fuel and oxidant and mutual mixing in a fuel cell using a proton conductive polymer membrane as an electrolyte, the performance and reliability of the cell can be obtained. Helps improve.
[0046]
According to the second to seventh aspects, the effect of the first aspect can be further enhanced by the shape, arrangement, and size.
[0047]
According to the eighth aspect, in addition to the effects of the first to seventh aspects, it is possible to prevent the decomposition of the elastomer material and the elution of the additive which have been often used as the conventional gasket material. However, there is no elution of impurities from the gasket material, deformation and aging are unlikely to proceed, and a gasket having a high sealing effect can be obtained. A battery using this can be operated at a high temperature, which can contribute to improvement and stabilization of the characteristics of the fuel cell. Battery durability can also be extended significantly.
[0048]
According to the ninth aspect, even when the temperature is 100 ° C. or higher, the more accurate rib shape of the gasket is maintained, and the effect of the eighth aspect can be enhanced.
[0049]
According to the tenth aspect, the mold for producing the gasket according to any one of the first to ninth aspects can be processed with finer and more accurate dimensions than conventional machining, and the mold The cost required for production can be greatly reduced.
[0050]
According to the eleventh aspect, in addition to the effect of the tenth aspect, it is possible to obtain a mold capable of producing a precise gasket having a rib shape, particularly a rib head shape, which has good mold flow and mold separation during molding.
[0051]
According to the twelfth aspect, the gasket having the effect of any one of the first to ninth aspects is free from leakage and mutual mixing of fuel and oxidizing gas, is compact, has high proton conductivity and is highly reliable even at high temperatures. A molecular membrane fuel cell can be obtained.
[Brief description of the drawings]
FIG. 1 is an exploded perspective view of a fuel cell unit cell according to the present invention.
FIG. 2 is a cross-sectional view taken along line AA of the gasket for a fuel cell according to the present invention.
FIG. 3 is a plan view of one embodiment of the gasket.
FIG. 4 is a plan view of another embodiment of the gasket.
5A is an AA cross-sectional view of a gasket according to Embodiment 1, and FIG. 5B is an enlarged view of a portion B in FIG.
6A is an AA cross-sectional view of a gasket according to a comparative example, and FIG. 6B is an enlarged view of a portion B in FIG.
[Explanation of symbols]
4 Negative electrode side separator 5 Positive electrode side separator 6 Negative electrode side gasket 7 Positive electrode side gasket 8, 8 'Uneven portion 41, 41', 51, 51 'Manifold 42, 52 Channel groove 61 Flat surface 81, 81' rib of negative electrode side gasket 82, 82 'valley a height of the rib from the flat surface,
b Same as above, bottom width,
c, c ′ The distance between each center of the rib and the valley,
d Depth of valley from flat surface

Claims (12)

A fuel cell gasket positioned between an electrode-membrane assembly in which a proton conductive polymer membrane is used as an electrolyte and a positive electrode and a negative electrode are arranged on both sides thereof, and a pair of separator plates arranged on both sides of the membrane. A gasket for a fuel cell, wherein the gasket has closed ribs at both ends, and closed valleys at both ends in the vicinity of the ribs. The rib shape is triangular, quadrangular, trapezoidal, semicircular, and these shapes are given an arbitrary radius, and the valley is triangular, quadrangular, trapezoidal, semicircular 2. The gasket for a fuel cell according to claim 1, wherein the gasket has a shape and an arbitrary round shape in these shapes. The gasket for a fuel cell according to claim 1 or 2, wherein the gasket has a valley on both sides or one side in contact with the rib. The gasket for a fuel cell according to any one of claims 1 to 3, wherein the gasket has a valley center within a distance corresponding to twice the cross-sectional width of the rib bottom from the center of the rib width. 5. The fuel cell gasket according to claim 1, wherein the thickness is within 0.5 mm and the height of the rib is within 0.2 mm. 6. The gasket for a fuel cell according to any one of claims 1 to 5, wherein the rib has a structure surrounding the outer periphery of each of the electrode part and the manifold part. 7. The fuel cell gasket according to claim 6, wherein the rib has a structure surrounding at least one of the outer periphery of the electrode part or the manifold part more than double. The fuel cell gasket according to any one of claims 1 to 7, wherein the material is a fluororesin. 9. The fuel cell gasket according to claim 8, wherein the material is any one of polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, and tetrafluoroethylene-hexafluoropropylene copolymer. A gasket molding die used for molding a gasket according to claim 1, wherein the surface processing is performed by photoetching. 11. The gasket molding die according to claim 10, wherein mechanical processing such as surface polishing is performed after photoetching. A fuel cell using the proton conductive polymer membrane as an electrolyte, wherein the gasket according to any one of claims 1 to 9 is used.

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