JPH03101059A - Sealing structure of phosphoric acid fuel cell - Google Patents

Abstract

PURPOSE:To steadily seal a cell over a long period of time without electrolyte leakage by bonding an electrode to a gasket with an adhesive whose elastic modulus is larger than that of the gasket. CONSTITUTION:Spaces between a gasket 18 and electrodes 14, 16 are filled with adhesive layers 20 to prevent electrolyte leakage from a matrix 12. The adhesive 20 whose elastic modulus is larger than that of the gasket is used and commercially available gaskets can be used. Since the elastic modulus of the adhesive 20 is larger than that of the gasket 18, stress applied to a cell 10 is mainly applied to the gasket 18, and stress applied to the adhesion layer 20 is decreased. Since the opening between the gasket 18 and the matrix 12 can be decreased, the contact area of the adhesive with a phosphoric acid electrolyte is decreased. Deterioration of the adhesive layer 20 is prevented and the cell 10 is steadily sealed over a long period of time without electrolyte leakage.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a seal structure for a phosphoric acid fuel cell.

(Background of the Invention) A phosphoric acid fuel cell consists of an electrolyte matrix impregnated with a phosphoric acid electrolyte sandwiched between an air electrode and a hydrogen electrode, and further sandwiched between separate electrodes on the top and bottom to form a cell (single cell). These are stacked to form a stack, and the outer periphery of each cell is covered with a gasket to prevent leakage of electrolyte.

To prevent leakage of the phosphoric acid solution, it is best to tighten the gasket strongly, but there is a limit to how tightly it can be tightened since it may destroy other parts. One possible solution to this problem is to glue the gasket to the electrode for sealing, or to form the gasket from very soft rubber.

However, when sealing with an adhesive, there is a problem that the adhesive itself has a low molecular weight and has a reactive functional group, which is disadvantageous in terms of chemical resistance and heat resistance, and that it is susceptible to deterioration. Particularly during high-temperature operation, the bonded area with the gasket and electrodes expands due to the difference in thermal expansion between them, and extremely large stress is applied to the adhesive layer. Therefore, the adhesive layer is directly exposed to hot phosphoric acid under this high stress, and the adhesive is likely to deteriorate in a very short period of time.

On the other hand, even if it is attempted to form the gasket itself from a material with a high modulus of elasticity, the normally used fluororubber cannot have a rubber hardness H8 of 50 or less due to its characteristics, and sufficient elasticity cannot be obtained. If the gasket is made of sponge, the gasket will be sufficiently soft to form a complete sill, but the sponge itself will easily weaken under high temperatures, and leakage of the electrolyte will be inevitable after long-term operation. In particular, regular sponges have open cells (
Since the sponge is an open cell, there is a problem that the electrolyte permeates inside the sponge and leaks.

(Objective of the Invention) The present invention was made in view of the above circumstances, and an object thereof is to provide a sealing structure for a phosphoric acid fuel cell that can be stably sealed without electrolyte leaking over a long period of time. shall be.

(Structure of the Invention) This object of the present invention is to provide a seal structure for a phosphoric acid fuel cell in which an electrolyte matrix and electrodes stacked above and below are sealed with a gasket, in which the elastic modulus between the electrode and the gasket is higher than the elastic modulus of the gasket. This is achieved by a seal structure for a phosphoric acid fuel cell, which is characterized by being bonded with an adhesive having a high elastic modulus.

In other words, the present invention reduces the stress applied to the adhesive layer by making the elastic modulus of the adhesive larger than that of the gasket, and also reduces the gap between the gasket and the electrode, so that the adhesive layer is made of phosphoric acid electrolyte. This reduces the contact area with the gasket, thereby preventing deterioration of the adhesive layer and perfecting the seal of the gasket.

Another object of the present invention is to provide a sealing structure for a phosphoric acid fuel cell in which an electrolyte matrix and electrodes stacked above and below the electrolyte matrix are sealed with a gasket, wherein the gasket is formed of a closed-cell sponge. This can also be achieved by the seal structure of acid fuel cells.

In this second invention, by using a closed-cell sponge, the sponge is prevented from becoming stale during long-term use, and leakage of the electrolyte is prevented over a long period of time.

(First Embodiment) FIG. 1 is a partially sectional perspective view of a first embodiment of the present invention, and FIG. 2 is a sectional view of a main part thereof.

In these figures, the cell (single cell) indicated by the reference numeral 10 has an electrolyte matrix 12 and each electrode 1 sandwiching it above and below.
4.16, and a gasket 18 covers the outer periphery of these. The gap between the gasket 18 and the electrodes 14 and 16 is sealed with an adhesive layer 20 to prevent leakage of the electrolyte from the matrix 12. It is sufficient for the adhesive 20 to have a higher elastic modulus than that of the gasket 18, and commercially available adhesives can be used.

However, since the material needs to be resistant to hot phosphoric acid, fluororubber adhesives are generally preferred. When a fluorine-based sponge is used for the gasket, Eight Seal (manufactured by Taihei Kasei Corporation) can be used as the adhesive 20, for example.

Since the elastic modulus of the adhesive layer 20 is made larger than that of the gasket 18 in this way, the stress related to the cell 10 is mainly applied to the gasket 18, and the stress applied to the adhesive layer 20 is reduced. Furthermore, since the opening between the gas scaler 1-18 and the electrode 12 can be made small, the area where the adhesive comes into contact with the phosphoric acid electrolyte is small. Therefore, the adhesive becomes less susceptible to deterioration, and the electrode can be used stably for a long period of time without leaking electrolyte.

(Second Example) In this example, instead of using an adhesive as in the first example, a gas kerat was formed using a foamed sponge. That is, as shown in the cross-sectional view of FIG. 3, a lower gasket 22 having a cross-sectional shape covers the outer periphery of the electrode 16 and supports the electrolyte matrix 12. Further, an upper gasket 24 placed on the lower gasket 22 covers the outer periphery of the electrode 14. Surfaces 22a, 24a of each gasket 22.24 in contact with electrode 14.16 and surfaces 22b in contact with gaskets 22.24.

24b is formed to be smooth and dense, and prevents the electrolyte from leaking along these interfaces.

Both gaskets 22 and 24 are made of closed foam.
ll), the electrolyte will not seep into the gaskets 22, 24 and leak out.

In addition, since it is a closed cell foam, even if stress is applied to the gaskets 22 and 24 when incorporated into the cell 10, the gas within each cell will not escape. Therefore, the gaskets 22 and 24 are resistant to deterioration and can be used stably for a long period of time without leaking electrolyte.

In this example, the surfaces of the gaskets that contact the electrodes and the surfaces that the gaskets contact with each other are made smoother and denser than the inside, thereby preventing bubbles appearing on the sponge surface from leaking out. However, in the present invention, when assembling the gasket, a certain amount of force may be applied to make the sponge surface dense. However, if the surface is smooth and dense as in the second embodiment, assembly is easy.

In particular, it is not easy to tighten the gasket from the periphery to the inside than from the top and bottom of the gasket, so at least each electrode
It is preferable that the surfaces 22a and 24a in contact with 4.16 are smooth.

The sponge used as a gasket needs to be resistant to hot phosphoric acid, and a fluororubber sponge is preferable. In particular, a fluororubber sponge substantially free of metal oxides and metal hydroxides is preferred. This is because ordinary fluororubber contains metal oxides and metal hydroxides in order to promote the crosslinking reaction, and when these are present, a slight amount of penetrating phosphoric acid and phosphates are formed, and this phosphoric acid This is because salt has a strong affinity for phosphoric acid, which promotes phosphoric acid penetration, which tends to cause swelling of the sponge and consequent sagging. In consideration of such a deterioration mechanism, the fluororubber sponge used in the present invention is one that does not require the presence of metal oxides or metal hydroxides during crosslinking. As such fluororubber, there is a fluororubber in which iodine is introduced as a crosslinking site, and this can be crosslinked with peroxide.

Examples of the main polymer of such a fluororubber sponge include 0902 commercially available from Daikin Industries. As a peroxide as a crosslinking agent, Perhexa 25
B (NOF ■), and as the crosslinking aid, triallyl isocyanurate, triallyl cyanurate, etc. are preferred.

A gasket can be obtained by mixing these materials with additives such as carbon black as necessary and molding the mixture. During this molding, the surface in contact with the mold is normally formed to be smooth and dense, so it can be used as it is as the gasket of the present invention. When the gasket of the present invention is formed by cutting out the sponge base material, the cut surface has a cut surface of bubbles, but if it is heat-processed with a hot iron or iron, the surface can be made smooth and dense. I can do it. It goes without saying that the upper and lower gaskets may not be separate, but may be integrated as in the first embodiment.

(Effect of the invention) As described above, the invention of claim 1 prevents deterioration of the adhesive layer by making the elastic modulus of the adhesive larger than that of the gasket, so that the electrolyte can be stably prevented from leaking. Can be closed for a long time.

In the second aspect of the invention, since a closed-cell sponge is used for the gasket, the sponge does not deteriorate during long-term use, and leakage of the electrolyte can be prevented for a long period of time.

Further, in the third aspect of the present invention, at least the surface of the sponge in contact with the electrode is formed to be smooth and dense, so that the electrolyte will not leak out from the gap between the sponge and the electrode.

Furthermore, in claim 4, the sponge is a fluororubber sponge that does not substantially contain metal oxides and metal hydroxides, so it does not deteriorate even after long-term use.

[Brief explanation of drawings]

FIG. 1 is a partially sectional perspective view of the first embodiment of the present invention, FIG. 2 is a sectional view of the main part thereof, FIG. 3 is a sectional view of the second embodiment, and FIG.
The figure is a cross-sectional perspective view of the main part. 12... Electrolyte matrix, 14.16... Electrode, 1B, 22.24... Gasket, 20... Adhesive.

Claims (4)

[Claims] (1) In the seal structure of a phosphoric acid fuel cell, in which the electrolyte matrix and the electrodes stacked above and below are sealed with a gasket, the electrodes and the gasket are bonded using an adhesive that has a higher elastic modulus than that of the gasket. A seal structure for a phosphoric acid fuel cell characterized by: (2) A sealing structure for a phosphoric acid fuel cell in which an electrolyte matrix and electrodes stacked above and below the electrolyte matrix are sealed with a gasket, wherein the gasket is formed of a closed-cell sponge. Seal structure. (3) The seal structure for a phosphoric acid fuel cell according to claim (2), wherein the gasket has at least a smooth and dense contact surface with the electrode. (4) The seal structure for a phosphoric acid fuel cell according to claim (2) or (3), wherein the gasket is made of a fluororubber sponge substantially free of metal oxides and metal hydroxides. .