JP2005019057A - Sealing structure of solid polymer fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sealing structure of a solid polymer fuel cell capable of preventing breakage during the packing, storage and transportation of a formed gasket, and having high reliability and easily obtaining a flat sealing surface particularly in the use of a liquid sealing agent in the sealing structure between separators of the fuel cell. <P>SOLUTION: In the fuel cell formed by layering a separator and an MEA formed of an electrode and a solid polymer membrane, the sealing structure of the fuel cell is so structured that projected parts are disposed at the peripheral edge of the MEA, recessed parts are disposed at the peripheral part edge of the separator, the projected parts are disposed so as to be engaged with the recessed parts at layering the separator and the MEA, the gasket is filled in the recessed part of the separator, the gasket does not protrude from the recessed part, and the projected parts compress the gasket. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a seal structure between a separator and an MEA in a polymer electrolyte fuel cell.
[0002]
[Prior art]
A fuel cell is known as a device that directly converts energy of fuel into electric energy. 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, and an electromotive force is obtained by a chemical reaction by an electric reaction occurring at both electrodes.
[0003]
A typical structure of a fuel cell can be shown in FIG. A fuel cell MEA (Mebrane Electrode Assembly) 2 is composed of a solid electrolyte membrane M and electrodes Eo and Eh, and gaskets Go and Gh are disposed between a pair of separators (also referred to as collector electrodes) 1o and 1h sandwiching the membrane, respectively. This is achieved by laminating a plurality of cells, each of which is a laminated cell. The MEA is sometimes called a power generation element or an electrode film structure.
[0004]
This will be described in more detail with reference to a cross-sectional view of one cell. The fuel cell is composed of a single cell C composed of separators 1o, 1h and MEA 2, and a plurality of such single cells C are laminated. The separators 1o and 1h divide the fuel gas, the oxidizing gas, and the refrigerant, and the flow paths for guiding the fuel gas and the oxidizing gas to the inside of the MEA and the cooling water to the MEA and cooling it. It has a path (not shown). On the other hand, the MEA is provided with an oxygen electrode Eo (cathode electrode) and a hydrogen electrode Eh (anode electrode) with the solid electrolyte membrane M interposed therebetween.
[0005]
The separators 1o and 1h are made of a material such as carbon, and have a function of separating fuel gas, oxidizing gas, and refrigerant, have the flow paths Ph and Po, and have an electron transfer function. . In this fuel cell, when supply air is passed through the oxygen electrode side gas flow path Po and supply hydrogen is supplied to the hydrogen electrode side gas flow path Ph, hydrogen is ionized by the catalytic action to generate protons at the hydrogen electrode Eh. The generated protons move through the electrolyte membrane M and reach the oxygen electrode Eo. And the proton which reached | attained the oxygen electrode Eo reacts with the oxygen ion produced | generated from the oxygen of supply air in presence of a catalyst, and produces | generates water. The generated water and supply air containing unused oxygen are exhausted from the outlet on the oxygen electrode side of the fuel cell as exhaust air (exhaust air contains a large amount of water). In addition, when hydrogen is ionized at the hydrogen electrode Eh, electrons e− are generated. The generated electrons e− reach the oxygen electrode Eo via an external load such as a motor.
[0006]
The fuel cell having such a configuration supplies fuel gas, oxidant gas, and refrigerant to each single cell C through independent flow paths Ph and Po, but seals are provided to seal these systems in an airtight manner. Will be needed. In particular, when the outer periphery of the MEA leaks, hydrogen and oxygen react with each other, resulting in a significant decrease in power generation efficiency. Therefore, as shown in FIG. 9 and FIG. 10, the portion was sealed by sandwiching a gasket such as a rubber sheet or a solid gasket such as an O-ring. However, the method of sandwiching the solid gasket is problematic in that it is difficult to automate in the assembling process or is thin and large in size, so that the handling is bad and it is easily damaged. In addition to being disadvantageous in terms of cost, the sealing performance is not good, so it is not an optimal method.
[0007]
In order to eliminate the above inconvenience, a method of integrating the sealing material into the separator in advance or integrating it into the MEA has been considered. Specific examples of the method include a method in which a solid packing such as a rubber packing is bonded to an MEA or a separator in advance, a FIPG (Formed-In-Place-Gasket) using a liquid gasket, and a CIPG (Cured-In-Place-Gasket). MIPG (Molded-In-Place-Gasket) has been devised.
[0008]
A method for pre-bonding rubber packing or the like is described in JP-A-8-148169. However, just because the bonding process is separate from the stack assembly process, the number of processes itself is not reduced, and packing is prepared according to the shape of the sealed portion, which is not preferable.
[0009]
FIPG is described in Japanese Patent Application Laid-Open No. 2003-3239. A curable liquid resin such as a moisture curable silicone resin or a heat curable fluororesin is applied to a portion to be sealed along its shape, In this method, the liquid resin is cured after being assembled in a liquid state. Since this method can form a sealing material on the spot, it can be applied even when the sealed portion has a complicated shape or a wide variety of parts, and can be applied to the surface of the sealed portion. Since the contact is made in an uncured state and then cured, the sealing property can be secured even if the surface state of the sealed portion is not smooth.
[0010]
CIPG uses the same resin and equipment as FIPG to form a sealant in-situ, but the difference from FIPG is that FIPG assembles parts when uncured, while CIPG assembles parts after curing after application. Is. Further, MIPG is described in Japanese Patent Application Laid-Open No. 2002-86482, etc., and a sealed part is put in a mold, or a mold is placed on a part to be sealed to form a cavity between the member and the mold. The sealing material is molded by injecting the sealing material.
[0011]
[Problems to be solved by the invention]
However, FIPG has to be applied and repeated as many times as the number of cells, and the stack assembly process takes time, and the sealing material will protrude when combined unless the coating amount of the sealing agent is controlled accurately. There is a problem. Since CIPG is cured in the form of the applied shape, in the case of dispense application, a seam of beads is generated, and the bead height is difficult to be uniform, so that extremely high application accuracy is required and management becomes very difficult. Since MIPG uses a mold, the initial cost is high, and there is a disadvantage in designing changes.
[0012]
Also, in the sealing method except FIPG, a sealing material is interposed between the member to be sealed and the sealing performance is exhibited by maintaining a sufficient surface pressure. It is difficult to reduce the sealing performance, maintain the surface pressure under high temperature and high pressure, and stabilize the dimensions.
[0013]
Moreover, the method of forming the sealing material on the separator or MEA as described above results in a shape in which the sealing material protrudes from the separator or MEA having a planar shape. Since the sealing material is a soft material, when these parts are packed, transported, or stored, the sealing part may come into contact with other members or be damaged by its own weight, which may cause a problem in sealing performance. . Further, when the sealing material has tacking, a blocking problem occurs.
[0014]
In addition, in recent years, in order to achieve a reduction in the thickness of the fuel cell, the sealing member usually needs to be covered with the thickness of the electrode of the MEA and the current collecting layer or the diffusion layer, and this thickness ensures a sufficient seal. There is also a problem that it is difficult.
[0015]
Therefore, as a result of intensive studies to solve the above problems, the present invention has a sealing structure in which the assembly process of the polymer electrolyte fuel cell is simple and the sealing material is not damaged during packaging, transportation and storage of the member. It is to provide.
[Means for Solving the Problems]
The present invention provides a polymer electrolyte fuel cell in which a separator, an electrode, and an MEA made of a solid polymer membrane are laminated. In the polymer electrolyte fuel cell, a protrusion is provided at the peripheral edge of the MEA, and a recess is provided at the peripheral edge of the separator. When the MEA is laminated, the convex portion is provided so as to engage with the concave portion, the separator concave portion is filled with a gasket, and the gasket does not protrude from the concave portion, and the convex portion compresses the gasket. It is a sealing structure of a polymer electrolyte fuel cell.
[0016]
The MEA as used in the present invention is one in which a cathode electrode and an anode electrode are formed on both surfaces of a solid polymer film, respectively, as described in the prior art. The MEA is sandwiched between two separators. Air, oxygen, or hydrogen is supplied from between the separator and the MEA to the cathode side and the anode side, respectively.
[0017]
In the present invention, convex portions are formed on the peripheral edge of the MEA. It is preferable that the convex part formed in a peripheral part is connected 1 round along the outer periphery of MEA. Moreover, the convex part of a peripheral part is formed in both surfaces of MEA. The convex part is formed on the peripheral edge of the MEA. However, when the solid polymer film is provided so as to protrude from the two electrodes toward the outer peripheral direction, the convex part is formed on the solid polymer film. It is preferable. However, it does not necessarily have to be formed on the solid polymer film, and a convex portion may be formed on the electrode in accordance with the shape of the MEA.
[0018]
The material of the formed convex part is preferably one that does not easily deform due to external pressure. In the conventional fuel cell sealing structure, an elastic sealing material is provided in this portion. However, in the present invention, it is preferable that the sealing structure is not elastic and does not easily deform.
[0019]
On the other hand, the MEA is generally a thin film of 200 μm or less, and since a flexible film is used as a base, the film may be damaged due to a local load when a surface pressure is applied. In order to solve this problem, it is known to provide a frame with a rigid member such as plastic on the peripheral edge of the MEA. In this invention, it is preferable to provide a convex part by making the cross-sectional shape of this frame into a protrusion shape. The material of the frame is selected in consideration of compressive strength, creep resistance, heat resistance, acid resistance, hydrolysis resistance, electrical insulation, absence of eluting components harmful to the catalyst on MEA, and the like. The material of the frame is not limited in the present invention, but PEEK (polyetheretherketone), PBT (polybutylene terephthalate), PPS (polyphenylene sulfide), POM (polyacetal), PES (polyethersulfone), LCP A plastic called super engineering plastic such as (liquid crystal polyester) is desirable.
[0020]
In the present invention, examples of the method for forming the convex frame include outsert molding performed using a mold on the MEA, and a method of bonding the molded frame component to the MEA. Alternatively, the MEA may be formed by applying and curing a liquid curable resin in a protruding shape. In this case, a hard resin such as an epoxy resin is desirable. In addition, it has been described that the material forming the convex portion is preferably one that does not easily deform due to external pressure, but if the surface pressure may be low, it may be a soft material similar to a conventional gasket material. In this case, the convex portion may be deformed during storage and transportation of the MEA. However, in the present invention, the sealing portion formed in the MEA is sealed in combination with a sealing material existing inside the concave portion described later. Even if it is deformed to some extent, sealing properties can be exhibited. Therefore, even if a soft sealing material is used as the convex portion in the present invention, the conventional problems can be solved.
[0021]
The shape of the convex portion of the present invention is preferably such that the tip of the convex portion is configured with a gentle curve in accordance with the curvature of the liquid surface (meniscus) that occurs when a gasket material is prevented from being damaged or a liquid gasket is injected.
[0022]
In the present invention, a recess is formed in the peripheral edge of the separator. The recess is a groove and is preferably connected one turn along the outer periphery of the separator. If the thickness and rigidity of the separator are sufficient, the recess can be formed by cutting or molding, and is selected according to the manufacturing process of the separator. In the case of a thin separator, a groove (depression) that becomes the concave portion can be provided when a gas or cooling water flow path is formed by press molding. The width dimension, depth, and cross-sectional shape of the groove are not particularly limited, and are desirably determined by the balance with the shape and dimensions of the protrusions provided on the MEA, and the hardness and compression force of the gasket material (described later) to be used. However, when the liquid gasket is injected, it is preferable that the groove is formed in a horizontal plane and that there is no hole or scraping or the like from which the injected liquid gasket flows out. In addition, the highest surface of the recess formed in the separator may be horizontal with respect to the mating surface of the gas flow path, but may be chamfered in a step or taper shape to prevent MEA damage.
[0023]
A gasket is formed in the separator recess. It is preferable that the gasket be easily deformed by compression and return to its original shape when the compressive force is removed. The gasket material can be used for both solid gaskets and liquid gaskets. The solid gasket can be obtained by preparing a solid packing substantially the same shape as the groove shape of the recess and fitting it into the recess. The liquid gasket can be obtained by pouring a curable liquid resin into the concave groove and curing it. The material of the gasket is not particularly limited in the present invention, but considering the required characteristics of the fuel cell, EPDM, IIR, fluorine-based rubber, etc. are desirable for solid gaskets, and polyolefin-based and fluorine-based materials are desirable for liquid gaskets. Particularly desirable.
[0024]
In the present invention, it is desirable that the liquid gasket has excellent fluidity in consideration of making the seal portion smooth. When the fluidity is low, sufficient self-leveling cannot be obtained, and the liquid level after injection does not become smooth. Moreover, the thing with a high viscosity needs time for self-leveling, and since workability | operativity falls, a thing with a low viscosity is desirable. The injection amount is determined in consideration of a predetermined surface pressure and design dimensions, the volume of the convex and concave portions, the deformation characteristics of the gasket material, and the like.
[0025]
Even when the separators are manufactured by mass production, the separators can be stacked and transported and stored even when the separators are manufactured by mass production. There is no collision with this part, and even if they are stacked as they are, there is no occurrence of bead breakage or blocking.
[0026]
The convex portion formed on the peripheral edge portion of the MEA and the concave portion formed on the peripheral edge portion of the separator are required to have a positional relationship, shape, and size such that the convex portion engages in the concave portion. The convex portion compresses the gasket in the concave portion, the gasket is elastically deformed, and a sealing property is developed by the surface pressure of the gasket in the concave portion and the convex portion, and hydrogen gas and oxygen gas (air) in the fuel cell are mixed inside. Without leaking outside. Here, the peripheral portion does not mean the outermost peripheral end of the MEA or the separator, but means the outer periphery from the power generation portion of the MEA where fuel is supplied and power is generated in the MEA. Therefore, depending on the configuration of the fuel cell, a concave portion or a convex portion may be formed on the inner side about 2 to 3 cm from the outermost periphery of the MEA.
[0027]
Further, when the entire convex portion is tapered and the maximum width of the bottom portion is larger than the groove width of the concave portion formed in the separator, the bottom portion of the convex portion and the top portion of the concave portion are in contact with each other, and the deformation space of the gasket material is limited. Therefore, excessive deformation and damage to the gasket material can be prevented.
[0028]
[Action]
The conventional seal structure has a structure in which a gasket and seal material are interposed between a smooth MEA or MEA frame in the same manner as a smooth separator surface. And deformation is free. For this reason, creeping is likely to occur due to a long-term compressive stress, and the reduction in surface pressure becomes significant. For the same reason, in the case of CIPG, the cross-sectional shape of the applied liquid gasket depends on the flow characteristics of the liquid gasket and the accuracy of the coating machine. If the fluidity is high, a sufficient bead height cannot be obtained. If the property is suppressed, the leveling property is lowered and the height of the bead apex tends to become unstable. Also, bead seams may remain in dispensing. Further, when the positional accuracy is poor, the sealing performance is deteriorated because the contact is not made uniformly. On the other hand, in the present invention, the above-described problem can be avoided or alleviated by a structure in which the gasket is formed as a smooth surface that does not protrude and the cross section of the frame that matches the seal portion is pressed against the gasket. Moreover, if the convex part formed in MEA enters the concave part formed in the separator, stable sealing performance can be obtained even if the height and positional accuracy are somewhat poor.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
【Example】
Examples of the seal structure of the present invention will be described below.
Example 1
The MEA shown in the cross-sectional view of FIG. A convex portion 3 having a semi-elliptical cross section was formed on the peripheral edge of the MEA. The convex part 3 was formed by outsert molding. Moreover, the separator shown by sectional drawing of FIG. The groove cross section of the recess 4 was U-shaped, and a liquid sealant was injected into the recess and cured to form a gasket 5. Injection into the recess was easy, and a smooth gasket material surface could be formed by self-leveling. The separator and MEA were combined. The convex portion 3 formed on the MEA engages with the concave portion 4 of the separator and compresses the gasket 5 inside, so that the convex portion 3 can be in close contact with the gasket uniformly, so that poor sealing due to poor adhesion can be avoided. It was. This situation is represented in FIG.
[0030]
Example 2
The same MEA 2 as in Example 1 was used. (FIG. 2a) Moreover, the separator shown by sectional drawing of FIG. The groove section of the recess 4 is U-shaped, and a liquid sealant is injected into the recess 4 and cured to form a gasket 5. Injection into the recess 4 was easy, and a smooth gasket material surface could be formed by self-leveling. Furthermore, compared with the case of Example 1, bubbles were less likely to be mixed when the liquid sealing agent was injected. The convex portion 3 formed on the MEA 2 engages with the concave portion 4 of the separator and compresses the gasket 5 inside, so that the convex portion 3 can be in close contact with the gasket uniformly, so that poor sealing due to poor adhesion can be avoided. It was. This situation is represented in FIG. Furthermore, since the distortion generated when the gasket 5 is compressed is less likely to be localized than in the first embodiment, it is easy to alleviate the damage and creeping of the gasket. This situation is represented in FIG.
[0031]
Example 3
The MEA shown in the cross-sectional view of FIG. A convex molded body having a semi-elliptical cross section was prepared in advance, and the double-sided convex molded body 3 was bonded to the peripheral edge of the MEA 2 with an epoxy resin adhesive 6. The same separator 1 as in Example 1 was used. (FIG. 3b) The separator 1 and MEA 2 were combined. The convex portion 3 formed on the MEA 2 engages with the concave portion 4 of the separator and compresses the gasket 5 inside, so that the convex portion 3 can be in close contact with the gasket uniformly, so that poor sealing due to poor adhesion can be avoided. It was. This situation is represented in FIG.
[0032]
Example 4
As shown in the cross-sectional view of FIG. 4 a as MEA 2, a curable liquid sealing material was applied in a bead shape to the peripheral edge of MEA 2 and cured to form convex portions 3. The bead (convex portion) of the sealing material was approximately uniform in height, but not very accurate. The same separator 1 as in Example 1 was used. (FIG. 4b) The separator 1 and MEA 2 were combined. The bead which is the convex portion 3 formed on the MEA 2 compresses the gasket 5 according to the height thereof, and the convex portion 3 can be adhered to the gasket 5 uniformly, so that the bead (convex portion) has a uniform height. Even without this, it was possible to avoid a sealing failure due to poor adhesion. This situation is represented in FIG. 4c.
[0033]
Example 5 and Example 6
As in the case of Example 1, the recess of the separator was provided with a step 7 in Example 5 and a tapered chamfer 8 in Example 6. (FIGS. 5 and 6) Even if the MEA was excessively compressed by creeping the gasket material or the like, the corners of the separator groove could be mitigated from biting into the MEA.
[0034]
Example 7 and Example 8
Although it is the same as the case of Example 1, the example in case the convex part 3 of MEA is a taper shape, and the width | variety of the bottom-most part 3a of a taper is larger than the opening width of the recessed part of a separator is shown. (FIG. 7) The separator and MEA2 were combined. The tip of the convex part 2 formed on the MEA 2 compresses the gasket inside the concave part of the separator, and the bottom part 3a of the convex part contacts the separator concave part and acts as a spacer, thereby limiting the amount of compression of the gasket. Therefore, it is easy to maintain the surface pressure. Furthermore, in Example 8, the concave portion of the separator was tapered chamfered 8. (FIG. 8) In this case, since the contact area between the convex part and the concave part was larger than that in Example 7, the contact pressure was alleviated and the separator and MEA could be prevented from being damaged.
[0035]
【The invention's effect】
According to the seal structure of the present invention, excellent sealing performance can be exhibited even when the molding accuracy of the seal portion to be formed is not so high. For example, in CIPG using a liquid gasket, application management can be facilitated and highly reliable sealing performance can be exhibited. In addition, it is possible to suppress a decrease in sealing performance and a MEA damage due to a decrease in surface pressure. Further, it is possible to prevent damage and blocking during packing and transportation of the fuel cell parts, and to obtain a highly reliable sealing property.
[0036]
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing the configuration of Embodiment 1 of the present invention. FIG. 2 is a cross-sectional view showing the configuration of Embodiment 2 of the present invention. 4 is a cross-sectional view showing the configuration of Example 4 of the present invention. FIG. 5 is a cross-sectional view showing the configuration of Example 5 of the present invention. FIG. 6 is a cross-sectional view showing the configuration of Example 6 of the present invention. FIG. 8 is a cross-sectional view illustrating the configuration of Example 8 of the present invention. FIG. 8 is a cross-sectional view illustrating the configuration of Example 8 of the present invention. FIG. 9 is a perspective view illustrating the stack structure of a conventional fuel cell. Sectional view showing one cell of battery [Explanation of symbols]
1 Separator 2 MEA
3 Convex 4 Concave 5 Gasket 6 Adhesive 7 Step 8 Chamfer M Solid Polymer Film E Electrode P Channel

Claims (4)

In a polymer electrolyte fuel cell formed by laminating a separator, an electrode, and an MEA made of a solid polymer membrane, a convex portion is provided at the peripheral portion of the MEA, a concave portion is provided at the peripheral portion of the separator, and the separator and the MEA are laminated. The convex portion is provided so as to be engaged with the concave portion, the separator concave portion is filled with a gasket, and the gasket does not protrude from the concave portion, and the convex portion compresses the gasket. A solid polymer fuel cell seal structure. 2. The polymer electrolyte fuel cell sealing structure according to claim 1, wherein the gasket in the recess is formed by pouring a curable liquid sealant into the recess and curing. 2. The polymer electrolyte fuel cell sealing structure according to claim 1, wherein the convex portion of the MEA is integrally molded with the MEA, or a convex molded body is bonded to the MEA. Solid polymer fuel cell seal having a convex shape with a cross-section of the convex portion, the maximum width of which is larger than the groove width of the concave portion formed in the separator, and the height of the protrusion is smaller than the maximum depth of the groove. Construction.

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