JPS6288277A - Electrode-end section sealing process for fuel cell - Google Patents

Abstract

PURPOSE:To improve the sealing performance with strong fusing force by performing preliminary processing for dispersion adhering fluororesin onto the sealing face of an electrode member then applying fluororesin film onto the sealing face and thermally pressing. CONSTITUTION:In a preliminary process, fluororesin dispersion is applied onto a sealing face at the end of a gas dispersion electrode member 4 then dried and burnt under the temperature near 350 deg.C to remove surfactant contained in the dispersion thus to adhere the fluororesin onto the surface of the electrode member 4 while dispersing. Then an electrode catalyst layer 5 is bonded onto the surface of the electrode member 4 at the matrix side and a fluororesin film 8 is applied onto the sealing face thereafter proper surface pressure and heating temperature are applied to thermally fuse the film 8 to the electrode member thus to complete the sealing process.

Description

[Detailed description of the invention] [Technical field to which the invention pertains]

The present invention relates to a fuel cell electrode end sealing method for a phosphoric acid fuel cell.

[Prior art and its problems]

First, Fig. 4 shows the structure of a unit cell of a phosphoric acid fuel cell using a lip-equipped electrode system, which is the subject of the present invention. And on both sides there is fuel'wi
The electrode 2 and the oxidizer electrode i3 are provided and constitute a unit cell. Here, each of the electrodes 2 and 3 has a porous gas diffusion electrode base material 4 having gas permeability, and the 'gL8i
Matrix ji of base material 4! Reactant gas supply/discharge passages 6 in the form of multiple grooves are formed on the surface of the electrode base material 4 opposite to the electro-stirring catalyst N5, and on the surface opposite to the electro-stirring catalyst N5. . Note that the reactant gas supply and discharge passages 6 of the fuel electrode 2 and the oxidizer electrode 3 are set to be orthogonal to each other. Further, a cell stack is constructed by stacking a large number of such unit batteries with separate plates 7 interposed therebetween. With this configuration, the fuel electrode 2. Fuel gas and oxidant gas (air) are supplied to the oxidizer electrode 3 through the reaction gas supply and exhaust passages 6, respectively.
It is well known that by supplying from the outside, each reaction gas is diffused in the electrode base material 4 and supplied to the electrode catalyst layer 5, and power is generated by the electrochemical reaction carried out here. By the way, in a fuel cell with such a configuration, if gas leaks outward from the fuel it electrode and the electrode end of the oxidizer 't8ii3, especially from both ends parallel to the reaction gas supply/discharge path 5, the fuel gas and the oxidizer gas are separated. Since there is a possibility of a direct reaction between the two electrodes, it is necessary to perform gas leakage prevention treatment at the end of each electrode to prevent this gas leakage. On the other hand, as a means to prevent leakage of reaction gas from the ends of each electrode, as shown in FIG. After covering with a fluororesin film 8 of either one or both of (hereinafter referred to as PFA) or a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (hereinafter referred to as PFA), the film 8 is thermocompression bonded to the electrode base material 4. Methods of sealing the core have been known for some time. However, in the conventional sealing method using thermocompression bonding of a fluororesin film as described above, the results of fuel cell operation tests show that the film peels off from the surface of the Ti base material and reactant gas leaks even though the film itself is sound. It became clear that a phenomenon that occurs frequently occurs. The inventor of the present invention investigated this point and found that the cause lies in the following points. That is, the PTFE or PFA of the fluororesin film is thermally fused to the electrode base material by a thermocompression bonding operation. Many of the PTFE and PFA heated and melted during the process are absorbed into the porous electrode base material, and because the electrode base material has a rough surface, it does not look like a film microscopically. The surface of the electrode base material is not sufficiently bonded to the surface of the electrode base material, and sufficient fusing force cannot be obtained between the two.Additionally, the heat cycle that accompanies the operation and shutdown of the fuel cell is added to the fluororesin film. It easily peels off from the surface of the base material, leading to gas leakage.

[Purpose of the invention]

This invention has been made in consideration of the above points, and is aimed at the above-mentioned sealing method of fluororesin film by thermocompression bonding, which provides strong thermal fusion properties and high sealing between the fluororesin film and the electrode base material. An object of the present invention is to provide a method for sealing the end of an electrode in such a manner that the properties of the electrode end can be improved.

[Key points of the invention]

In order to achieve the above object, this invention disperses and adheres a fluororesin to the sealing surface of an electrode base material as a preliminary treatment step, and in a subsequent step coats the sealing surface with a fluororesin film and bonds it by thermocompression. By doing so, the fluororesin added in the previous step flattens and densifies the surface of the electrode base material and prevents the resin of the film from being absorbed into the electrode base material during thermocompression bonding of the fluororesin film. This ensures sufficient surface adhesion between the material surfaces and, as a result, secure heat fusion bonding between the fluororesin film and the electrode base material, resulting in a seal structure with high airtightness and long life. It is.

Embodiments of the Invention FIG. 1 is a process diagram of a method for sealing an electrode end according to an embodiment of the present invention, and FIG. 2 shows a sealing structure of an electrode formed by the treatment method shown in FIG. The seal processing method according to the present invention will be explained step by step with reference to FIG. 1, in which the same members as in FIG. 5 are given the same reference numerals. That is, first, the porous gas diffusion electrode base material 4 is coated with a fluororesin disverdicin on the sealing surface of the end of the electrode base material 4 in the preliminary step of the previous stage, and after drying, this is applied in a heating furnace. The dispersion is baked at around 350° C., which is higher than the melting temperature of the fluororesin, to remove surfactants and the like contained in the dispersion, and the fluororesin is dispersed and adhered to the surface of the electrode base material 4. Reference numeral 9 indicates a heater of the heating furnace. By melting and adhering this fluororesin, the sealing surface of the porous electrode base material 4 is flat and tightly filled with the fluororesin indicated by 10 on the porous uneven surface. Next, after layering and bonding the electrode catalyst layer 5 on the matrix-side surface of the electrode base material 4, a fluororesin film 8 is coated on the sealing surface in the same manner as in the conventional method. The film 8 is sandwiched from above and below using the pressure bonding jig shown, and then an appropriate surface pressure and heating temperature are applied to thermally fuse the film 8 to the electrode base material 4 for sealing treatment. Regarding the weight of the fluororesin deposited in the pretreatment process mentioned above, the results of experiments conducted by varying the weight of the deposit show that if the amount of fluororesin deposited is too small, a flat and dense sealing surface will form on the surface of the electrode base material. It has become clear that if the amount of resin is too large, the fluororesin adhering to the surface of the electrode base material will cause unevenness, which will cause pinholes to occur in the film during the film crimping operation. Resin adhesion amount is 10mg/d ~ 100mg/c
It has been found that good results can be obtained within a range of ri. That is, the present inventor conducted the following test in order to investigate the relationship between the amount of fluororesin deposited in the pretreatment step and the fusion strength of the fluororesin film thermocompression bonded to the sealing surface. First, dispersion with various weight percentages of fluororesin was applied to a porous plate of a predetermined size made from the same material as the electrode base material, and after drying and baking, a fluororesin film was bonded by thermocompression. Next, each sample was subjected to a peel test in which heat cycles were repeated 10 times between room temperature and 200° C. to examine the state of fusion and peeling. The results of this peel test are shown in FIG. The horizontal axis in the figure is the adhesion of fluororesin added to the electrode base material in the pretreatment process! (mg/cd), and the vertical axis indicates the fusion rate of the fluororesin film. Here, the fusion rate was determined by the following formula. Fusion rate - (1 - number of peeled sheets/number of sample sheets) x 100% As is clear from Figure 3, 1
The film and @
, the fusion force between the electrode substrates. It was confirmed that a long-life seal structure with high sole properties and unaffected by heat cycles could be obtained.

【Effect of the invention】

As described above, according to the present invention, a fluororesin is dispersed and adhered to the sealing surface of the electrode base material as a preliminary treatment step, and a fluororesin film is coated on the sealing surface in the subsequent step and bonded by thermocompression. As a result, it was possible to obtain a sealing structure at the end of the electrode that has strong fusion force and high sealing performance between the fluororesin film and the electrode base material, as well as excellent durability and reliability.

[Brief explanation of drawings]

FIG. 1 is a process diagram of the sealing method according to the present invention, and FIG.
The figure is a diagram of the seal structure of the electrode obtained by the treatment method shown in Figure 1, and Figure 3 shows the results of a peel test conducted to determine the appropriate amount of fluororesin deposited when implementing the treatment method shown in Figure 1. FIG. 4 is a perspective view of the structure of a unit cell of a phosphoric acid fuel cell, which is the subject of the present invention, and FIG. 5 is a diagram of the sealing structure of the electrode by thermocompression bonding of a conventional fluororesin film. In the question, 1: matrix layer, 2: fuel electrode, 3: oxidizer electrode,
4: Electrode base material, 5: Electrode catalyst layer, 6: Reaction gas supply/discharge path, 8: Fluororesin film, 10: Fluororesin attached in the pretreatment process. Figure 1 Figure 3 Figure 5! ! I

Claims (1)

[Claims] 1) For a fuel electrode and an oxidizer electrode, which serve as gas-permeable porous gas diffusion electrodes, facing on both sides with a matrix layer holding an electrolyte in between, at the edge of each electrode, In an electrode end sealing method in which a fluororesin film is coated and the film is thermocompression bonded to an electrode base material for sealing, the fluororesin is dispersed and adhered to the sealing surface of the electrode base material as a preliminary treatment step, and the subsequent A method for sealing an electrode end of a fuel cell, characterized in that, in the step, a fluororesin film is coated on the sealing surface and bonded by thermocompression. 2) In the seal treatment method according to claim 1, the pretreatment step is to apply a fluororesin dispersion to the sealing surface of the electrode base material, and then to bake the fluororesin at a temperature higher than the melting temperature of the fluororesin. 1. A method for sealing an electrode end of a fuel cell, characterized in that the electrode end sealing method comprises dispersing and adhering to an electrode base material. 3) In the seal treatment method according to claim 1, the weight of the fluororesin deposited on the electrode base material in the pretreatment step is selected to be 10 to 100 mg/cm^2. Electrode end seal processing method.