JPH0578145B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention is a novel method for producing a porous gas diffusion electrode, and more specifically, it is used in air-metal batteries, fuel cells, etc., and is easy to stack and is easy to stack. The present invention relates to a method for manufacturing a porous gas diffusion electrode equipped with an end seal that constitutes a power generation element that can be used with high reliability.

[Technical background of the invention and its problems] Air-metal battery or hydrogen-air (oxygen)
Fuel cells require electrodes to ionize gas as a starting mechanism. A gas diffusion electrode that allows a non-conductive gas to continuously participate in an electromotive reaction uses a conductive porous plate-shaped base, with one side of the base in contact with an electrolyte and the other side of the base in contact with an electrolyte. The structure is such that the gas introduced from the base body undergoes an electromotive reaction in the middle of the base body. Generally, in order to supply a reactive gas, a reactive gas supply channel is provided on the base itself, or the base itself is not provided with a reactive gas supply channel, but the base is brought into contact with another element having a reactive gas supply channel. use

In these battery systems, the output voltage of a single cell is at most 0.5
Since the voltage is only ~1.5V, it is necessary to stack a considerable number of single cells in order to put it into practical use. In this case, the reaction gas supply channel provided on one substrate itself or in contact with the substrate in case of laminated use is arranged such that the directions thereof intersect with other gas supply channels provided above or below it. Can be stacked. Therefore, one reaction gas, such as hydrogen gas, flowing through one reaction gas supply channel, and another gas, such as air, flowing in the gas supply channels above and below it, are arranged in the respective gas supply channels so that they do not mix with each other. It is necessary to process the side edges of the substrate parallel to. It is also necessary to treat the edges so that electrical insulation can be maintained even if a large number of them are stacked at the same time and are mechanically compressed strongly.

In order to prevent different gases from mixing at the ends of the base parallel to the gas supply channel and to maintain electrical insulation, it is necessary to coat the ends with a synthetic resin. Attempts have also been made to impregnate the material with a dispersion liquid of a tetrafluoroethylene polymer or a tetrafluoroethylene copolymer, but these methods have not achieved sufficient functionality.

[Purpose of the invention]

Thus, the present invention provides an air-metallic battery or a hydrogen-based battery composed of an electrically conductive plate-like porous substrate, which itself has a reactive gas supply channel or is used in contact with a reactive gas supply channel during use. In a method for manufacturing a porous gas diffusion electrode for an air (oxygen) fuel cell, the gas flow is reliably interrupted even when stacked at the base end parallel to the reaction gas supply channel, and electrical insulation is maintained. It is an object of the present invention to provide a method for manufacturing a porous gas diffusion electrode that can improve the yield in the process.

[Summary of the invention]

Therefore, the present invention has a reactive gas supply channel or is used in contact with a reactive gas supply channel,
A gas made of a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer is applied to at least both ends of the porous gas diffusion electrode made of a conductive plate-like porous substrate parallel to the reaction gas supply channel. A method of manufacturing an impermeable, electrically insulating seal is provided, the method comprising: applying a tetrafluoroethylene-perfluoroalkyl vinyl ether to at least the end of the substrate parallel to the reactant gas supply channel; The copolymer is pre-formed into a shape that matches the shape of the end, and the copolymer is fitted onto metals that are difficult to weld, such as aluminum, which has a smooth surface, and which the copolymer is coated with fluorine oil in advance.
Alternatively, a gas-impermeable, electrically insulating seal made of the copolymer is formed by thermal compression bonding using an aluminum alloy crimping jig.

[Specific description of the invention]

The present invention will be described in detail with reference to the drawings showing an embodiment thereof. In FIG. An additional layered element 4 is shown. Reference numeral 5 indicates several reaction gas supply channels provided in the electrode 1, and reference numeral 6 indicates a reaction gas supply channel provided in the laminated element 4 in a direction intersecting with the gas flow channel 5.

Both electrodes 1 and 3 have a porosity of 60 to 70%.
An electronically conductive plate-shaped porous substrate is used.
For example, a perforated plate obtained by paper-making and heat-treating nickel sintered body or graphite fiber can be used. The latter is suitable for fuel cells that use a concentrated acidic liquid such as concentrated phosphoric acid as an electrolyte.

The present invention is a manufacturing method in which a gas-impermeable, electrically insulating seal is provided at the ends of the electrodes 1 and 3 with a high yield.As shown in FIG. They are provided at both ends 7, 7 parallel to the flow path 5, and at both ends 8, 8 of the thin electrode 3 parallel to the reactive gas supply flow path 6 provided in the laminated element 4 which is in contact with the thin electrode 3 during lamination. Note that in the thin electrode 3, for example, the flow path 6
Although it can be provided at other parts such as the ends crossing the flow path 6, at least both ends 8, 8 parallel to the flow path 6 are provided.
shall be provided with the seal.

In order to form the seal, the pores at the end are sealed to prevent the reaction gas from passing through or leaking therethrough, and to maintain electrical insulation despite the mechanical pressure during stacking. It has excellent chemical resistance to withstand high-temperature operation using concentrated acidic electrolytes, is thermally stable at temperatures exceeding 250℃, can withstand temperatures of 350℃ for short periods of time, and has excellent heat sealability. It is necessary to use materials that have
As such a material, a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer is used in the present invention. As is well known, tetrafluoroethylene has a molecular formula of CF ₂ =CF ₂ , and perfluoroalkyl vinyl ether has a molecular formula of CH ₂ =CHOR. Here, R usually represents a perfluoroalkyl group in which all hydrogen atoms of an alkyl group having 3 carbon atoms are substituted with fluorine atoms. The tetrafluoroethylene content of this copolymer ranges from about 96 to 97% by weight.

This copolymer is commercially available in the form of powder, granules, film, emulsion, etc. In the present invention, in particular, the film-like copolymer is prepared in advance into a U-shape or a U-shape according to the shape of the end. It is formed into a U-shape, and the end is completely covered with it, and heat and pressure are applied to it to bring it into close contact with the end of the porous substrate to form a seal.

Alternatively, the copolymer in the form of powder, granules, or emulsion is dispersed or applied on the surface of the end portion, and the copolymer in the form of a film is covered thereon as described above, and heat and pressure are applied thereto. Additionally, a seal can be formed.

Furthermore, to explain in detail the method for forming the end seals of the porous gas diffusion electrodes 1 and 3, the film-like copolymer is relatively hard at room temperature, so it is not easy to cover the ends. 200~ in advance
It is heated to a temperature of 230°C and formed into a U-shaped or U-shaped cross section to match the edge using a jig, and then the end of the porous substrate is covered with a mold release agent made of fluorine oil. Place it inside the female mold of a metal crimping jig, such as a metal mold made of aluminum or aluminum alloy with a smooth surface coated with the agent, and release it in the same way as the female mold onto the end surface covered with the copolymer. Apply the male mold coated with the agent and heat at a temperature of 380℃ or less, preferably in the range of 340 to 350℃ for 15 to 30 minutes.
Heat for 30 minutes and pressurize to bond with heat. As the fluorine oil, a commercially available fluorine wax may be used as it is, or one obtained by further mixing this with a fluorine solvent and stirring the mixture can be used. What is important here is that experiments have shown that the above-mentioned copolymer has good heat-sealing properties even for ordinary metals when used as a metal crimping jig, but it is difficult to weld to the smooth surfaces of aluminum or aluminum alloys. Focusing on this, a jig with a smooth surface made of aluminum or aluminum alloy is used, and a release agent is applied in advance to the required part of the surface of this crimping jig, that is, at least the part that will come into contact with the part coated with the copolymer. It is also important to apply fluorine oil as a preventative measure, and to not let the heating temperature exceed 380°C.

Figure 2 is for explaining this method, and numeral 10 indicates a porous substrate on which the electrodes are to be formed, and a membrane-like copolymer with a thickness of about 0.1 to 0.2 mm formed in a U-shape in advance is attached to the end of the porous substrate. The polymer 15 is covered and put into the female die 12 of the mold, which has been coated with the fluorine oil mold release agent 14 in advance, and then the male mold, which has also been coated with the mold release agent 14, is used to move the polymer 15 in the upper and lower A and B directions. From about 20 to 40
Applying a surface pressure of Kg/cm ² and a temperature of 340 to 380℃ for 15 to 30
The material is heated for 1 minute and then annealed for about 1 hour at a temperature of 80 to 90 DEG C. for thermocompression bonding.

Next, referring to Fig. 3, first, the powdered or granular copolymer is mixed with an appropriate solvent such as a fluorine-based solvent, and stirred at room temperature to 40°C to prepare a mixture for coating. is applied to the end surface of the porous substrate 10 constituting the electrode and air-dried to uniformly disperse the powder or granular copolymer 11 over the end surface. The amount should be such that it will rise by about 0.1 to 0.3 mm after subsequent thermocompression bonding and air drying.
Next, a film-like copolymer 15 formed into the thickness and shape as described above is placed on top of the copolymer 15, and then a metal film made of aluminum or an aluminum alloy having a smooth surface and coated with fluorine oil 14 in required places is placed on top of the copolymer film 15. It is placed in a female mold, and then heat-compressed using a male mold under the same pressure and temperature conditions as described above. Incidentally, a powder or granular copolymer may be first dispersed and thermocompression bonded, then press-fitted into the porous substrate, and then a film-like copolymer may be further covered and thermocompression bonding may be performed again.

Alternatively, the copolymer in the form of an emulsion may be applied onto the surface of a porous substrate, dried, and then covered with a copolymer in the form of a film, followed by thermocompression bonding using the mold as described above. The emulsion-like copolymer can be prepared, for example, by adding 100 parts by weight of water and 1 to 5 parts by weight of a nonionic surfactant to 20 to 60 parts by weight of a powdered or granular copolymer and stirring vigorously. can.

〔Effect of the invention〕

As described above, according to the present invention, a gas-impermeable, electrically insulating seal made of a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer is provided at least at both ends of the porous substrate parallel to the reaction gas supply channel. If a flat film-like copolymer that does not follow the shape of the end is used for the end, the shape of the end will not fit into a U-shaped cross section, for example, and the yield after thermocompression bonding will be 50%. If the film-like copolymer does not reach ~60%, it can be reduced to 80~90% by molding the membrane copolymer into a U-shaped cross section, for example, roughly matching the shape of the end, and covering the end with heat compression bonding. %, but by making the jig surface for thermocompression bonding smooth with aluminum or aluminum alloy, welding of the copolymer to the mold is eliminated and the yield can be almost 100%. This allows the porous gas diffusion electrode to not only completely prevent leakage of reactant gas from the end, but also to be mechanically reinforced and able to withstand strong pressure when stacking these electrodes and other power generation elements. It does not cause damage even when subjected to damage, has good electrical insulation properties, and can completely prevent semi-shortage at the ends, which often occurs in the past. Furthermore, the power generation elements can be easily stacked, the time required for stacking and assembly can be significantly shortened, and the high reliability of the stack can be maintained.

[Embodiments of the invention]

Example 1 As a plate-shaped porous substrate made of thin graphite fibers, the ends of carbon paper (manufactured by Kureha Chemical Industry Co., Ltd., trade name: E-715) with a size of 700 mm x 700 mm and a thickness of 0.5 mm were prepared in advance to a width of 20 mm. A film-like tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (Mitsui Fluorochemical Co., Ltd., trade name Teflon PFA500LP) with a thickness of 0.13 mm is softened in a mold heated to 220 to 230°C and shaped into an end shape. Form into a U-shape or U-shape that almost fits together, and insert this into the end.

Next, the surface of the mold of the thermocompression jig was covered with aluminum foil, and the above porous substrate was placed in a mold whose surface was coated with fluorine wax (Dyfroil #100, Osaka Metal Industry Co., Ltd.), and surface pressure was applied. It was crimped at 20 Kgf/cm ² , heated at 350 to 370°C for 30 minutes, annealed at 80 to 90°C for 1 hour to perform thermocompression bonding, and then removed from the mold to complete the end seal. The end seal thus obtained had a uniform end face, and no gas leaked therefrom.

Example 2 192 kg of tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer powder (Mitsui Fluorochemical Co., Ltd., trade name HP-20) was added to a fluorinated solvent (Sumitomo 3M Co., Ltd., trade name Fluorato FC721).
A mixture for coating was prepared by mixing with 128 g of the mixture and stirring at room temperature for 30 minutes.

As a plate-like porous substrate obtained by paper-making graphite fibers, the above-mentioned bond was placed at a 20 mm end point of carbon paper (Kureha Chemical Co., Ltd., trade name E-750) with a size of 700 mm x 700 mm and a thickness of 2 mm. After applying the agent and letting it air, apply a 0.13 mm thick film of tetrafluoroethylene perfluoroalkyl vinyl ether copolymer (Mitsui Fluorochemical Co., Ltd., trade name: Teflon).
PFA500LP) was previously formed into a U-shape or U-shape as in the previous example, and this was inserted into the end.

Separately, mix 120 g of fluorine wax (Osaka Metal Industry Co., Ltd., Daifloyl #100) with 180 g of fluorine solvent (Mitsui Fluorochemical Co., Ltd., Freon 113) at 45-50℃.
The oil was stirred for 30 minutes to obtain a fluorine oil, and this was applied to the required portions of an aluminum mold, which had been finished with a smooth surface, to coat the mold. A porous substrate having a copolymer dispersed or coated thereon was placed therein and thermocompression bonded under the same conditions as in Example 1 to form an end seal.

There is no gas leakage from the end seal obtained in this way, and the end surface is flat, and in particular, a battery obtained by stacking power generation elements including electrodes obtained using this seal can be used at high temperatures. No deterioration could be detected even after long hours of operation. The same was true for electrical insulation.

Example 3 40 parts by weight of tetrafluoroethylene-perfluoroalkylvinyl copolymer (Mitsui Fluorochemical Co., Ltd., each product Teflon MP-20), 100 parts by weight of water and a nonionic surfactant (Rohm & Haas Japan Co., Ltd.) ), trade name Tritonx-100) was added and stirred vigorously to disperse the copolymer to form an emulsion.

Next, a plate-like porous substrate made of thin graphite fibers made of carbon paper having a size of 700 mm x 700 mm and a thickness of 0.5 mm (Kureha Chemical Industry Co., Ltd., trade name E-) was prepared.
The above emulsion was applied to both ends of 715) with a width of 20 mm and dried. Then add an additional thickness of 0.13mm on top of this.
A film-like tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (manufactured by Mitsui Fluorochemical Co., Ltd., trade name PFA500LP) was prepared in Example 1 as described above.
Similarly, it was formed into a U-shape or U-shape, and this was inserted into the end.

After this, thermocompression bonding was carried out under the same conditions in a mold made of Silumin, an aluminum alloy coated with fluorine oil, in the same manner as in the previous example. was formed.

[Brief explanation of the drawing]

Drawings FIG. 1 is an explanatory diagram showing the general structure of a power generation element including a porous gas diffusion electrode with a seal formed at the end according to the present invention, and FIGS. FIG. 2 is an explanatory diagram showing the state of thermocompression bonding using a mold; FIG. 2 shows a case in which a film-like copolymer is used, and FIG. 3 shows a case in which a powder or granular copolymer and a film-like copolymer are used. FIG. 1... Electrode with gas flow path, 2... Electrolyte layer, 3...
...Thin electrode, 4...Laminated element with gas flow path, 5,
6... Gas flow path, 14... Mold release agent.

Claims (1)

[Claims] 1. A method for producing a porous gas diffusion electrode comprising a conductive plate-like porous substrate having a reactive gas supply channel or used in contact with a reactive gas supply channel, at least the reactive gas in the substrate. A film-like tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer is heat-molded in advance into a shape that matches the ends on both ends parallel to the supply channel, and the formed copolymer is placed on the ends. A porous material, characterized in that it is fitted together and thermocompressed using a crimping jig having a smooth surface coated with heat-resistant oil in advance to form a gas-impermeable, electrically insulating seal made of the polymer. A method of manufacturing a gas diffusion electrode.