JPH0642372B2 - Fuel cell - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel porous gas diffusion electrode, and more particularly to a fuel cell using a porous gas diffusion electrode provided with an improved sealing technique. Technical Background and Problems] In an air-metal battery or a hydrogen-air (oxygen) fuel cell, an electrode for ionizing gas is required as its electromotive mechanism. A gas diffusion electrode that continuously applies a non-conductive gas to an electromotive reaction uses a conductive and porous plate-shaped substrate, one side of which is in contact with the electrolyte, and the other side. The gas flowing in from is subjected to an electromotive reaction in the central part of the substrate. Generally, in order to supply the reaction gas, a reaction gas supply passage is provided in the substrate itself,
Alternatively, although not provided on the substrate itself, the substrate is used in contact with another element having a reaction gas supply passage.

Since the output voltage of these battery systems is only 0.5 to 1.5 V at most, it is necessary to stack a considerable number of unit cells for practical use. At this time, the reaction gas supply passages provided on one substrate itself or provided in contact with the substrate when laminated are stacked so that their directions intersect with other gas supply passages provided above or below the substrate. To be Therefore, one reaction gas, such as hydrogen gas, flowing through one reaction gas supply passage is parallel to each gas supply passage so that the other gas such as hydrogen gas flowing above or below the gas supply passage is not mixed with each other. It is necessary to treat the side edges of the substrate. At the same time, it is also necessary to treat the ends so that the electrical insulation can be maintained even if a large number of them are stacked and mechanically strongly compressed.

Thus, in order to prevent mixing of different gases at the end of the substrate parallel to the gas supply path and to treat the end so as to maintain electrical insulation, synthetic resin is applied to the end. The method of impregnating with a fluororesin coating material such as tetrafluoroethylene polymer or tetrafluoroethylene copolymer dispersion solution has also been tried, but it has not been able to obtain a sufficient function.

Furthermore, an electrode in which the end part impregnated with such a fluorocarbon resin coating was covered with a fluorocarbon resin adhesive tape and the fluorocarbon resin coating was applied to the surface of this tape again was developed, which allows the reaction gas to leak to the side surface of the electrode. A porous electrode capable of preventing the above-mentioned phenomenon and improving the wettability of the electrolyte to the edges since the outer coating does not exhibit water repellency to the electrolyte (Japanese Patent Application No. 57-176420). . However, in this case, the adhesiveness between the fluorine resin paint and the fluorine resin tape is weak, so that the paint film may peel off.

In addition, the present inventors have found that at least both ends of the substrate, which are parallel to the reaction gas supply passage, have a powdery, granular or filmy, emulsion-like tetrafluoroethylene-perfluoroalkylvinylether copolymer (hereinafter sometimes referred to as PFA). A porous gas diffusion electrode capable of reliably blocking the reaction gas and maintaining the electrical insulation even when stacked at the end of the substrate by heat fusion (Japanese Patent Application No. 58-80553). . However, in this case, since the copolymer, and hence the end portion where the copolymer is heat-sealed, has water repellency, sufficient electrolyte is not retained in the electrolyte matrix between the two electrodes, and therefore the electrolyte is There is a problem that the reaction gas easily leaks from the matrix layer.

[Object of the Invention]

Thus, the present invention solves the problems of these conventional electrode ends, improves the wettability to the electrolyte, does not cause peeling of the coating film, leakage of reaction gas, etc., and forms a reliable end seal. It is an object of the present invention to provide a fuel cell having the porous gas diffusion electrode described above.

[Outline of Invention]

Therefore, the present invention is provided with an electrolyte layer, a reaction gas path for supplying a reaction gas, one surface in contact with the reaction gas supply path, and the other surface in contact with the electrolyte layer and sandwiching the electrolyte layer. In a fuel cell formed by stacking a plurality of unit cells each having a porous gas diffusion electrode composed of a pair of conductive porous substrates arranged as described above, at least parallel to the reaction gas supply path. A heat-sealing portion formed by heat-sealing a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer so as to cover the end portion of the porous gas diffusion electrode, and at least the electrolyte layer of the heat-sealing portion is contacted. On the side, wet with the electrolyte of the electrolyte layer, and
It is intended to provide a fuel cell having a seal portion formed by thermocompression-bonding a substance that is thermally and chemically stable to an electrolyte.

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in detail with reference to the drawings. In FIG. 1, an electrode 1 with a reaction gas supply path, an electrolyte layer 2, a thin electrode 3 and a reaction gas supply path are provided in this order from the top. Stacked element 4 is shown. Reference numeral 5 denotes a reaction gas supply passage provided in the electrode 1, and 6 denotes a reaction gas supply passage provided in the laminated element 4 in a direction intersecting with the gas supply passage 5.

An electron-conducting plate-like porous substrate having a porosity of 60 to 70% is used for both the electrodes 1 and 3. For example, a nickel sintered body or a perforated plate obtained by heat-treating a graphite fiber into a paper can be used. The latter is suitable for fuel cells and the like that use a concentrated acidic liquid such as concentrated phosphoric acid as the electrolyte.

In the present invention, first, a thermal fusion bonding part of tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) is provided at the ends of the electrodes 1 and 3, and as shown in FIG. 1 is provided at both ends 7 and 7 parallel to the reaction gas supply passage 5, and in the thin electrode 3 is provided at both ends 8 and 8 parallel to the reaction gas supply passage 6 provided in the stacking element 4 which is in contact with the thin electrode 3 at the time of lamination. . The thin electrode 3 may be provided at another portion such as an end portion intersecting with the supply passage 6, but at least the supply passage 6 is provided.
The seals are provided on both ends 8, 8 parallel to

In the present invention, PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer) is used at the heat-sealed end, and this tetrafluoroethylene has a molecular formula of CF ₂ = CF ₂ as well known, Alkyl vinyl ether has a molecular formula of CH ₂ = CHOR. Here, R usually represents a perfluoroalkyl group in which all the hydrogen atoms of the alkyl group having 3 carbon atoms are replaced with fluorine atoms. The content of tetrafluoroethylene in this copolymer is in the range of about 96-97% by weight.

This copolymer is commercially available in the form of powder, granules, film, emulsion and the like, and in the present invention, these shapes may be used alone or in combination. For example, the powdery or granular copolymer is dispersed on the end surface, and heat and pressure are applied to this to partially press-fit the copolymer into the end of the porous substrate to form a heat-sealed portion. Alternatively, the copolymer in the form of a film or a film is entirely covered with the end portion, that is, a U-shape or a U-shape, and heat and pressure are applied to the end portion to adhere the end portion to the porous substrate. The heat-sealed portion can be formed.

Alternatively, the powdery or granular copolymer is dispersed on the end surface, and the filmy copolymer is covered thereon as described above. Can be formed, or an emulsion-type copolymer is applied to the end surface and heat and pressure are applied thereto, or a film-like copolymer is further applied thereon to apply heat and pressure in the same manner. In addition, a heat fusion part can be formed.

PFA is attached to the ends of the porous gas diffusion electrodes 1 and 3 as described above.
An example of the method for forming the heat-sealed portion will be described with reference to FIG. 2. The powdery or granular copolymer (PFA) is mixed with a suitable solvent such as a fluorine-based solvent and stirred at room temperature to 40 ° C. To form a mixture for coating, and the mixture 11 is coated in a U shape or a U shape on the end surface of the porous substrate 10 forming the electrode and air-dried to obtain a powder or granules. The above copolymer (1) is uniformly dispersed throughout the end surface. The amount of heat fusion,
The amount should be about 0.1 to 0.3 mm after air drying.
Next, this is placed in the female die 12 of a metal pressure-bonding jig such as an aluminum die to which a release agent 14 made of fluorocarbon oil is applied in advance, and the male die 13 is placed on the end surface where the copolymer is dispersed.
Apply this to a temperature below 380 ° C, preferably 340-350 ° C
20 to 40 kg / cm ² while heating to a temperature range of about 15 to 30 minutes
The surface pressure is applied from both AB directions to cause heat fusion. As the fluorinated oil, commercially available fluorinated wax may be used as it is, or one obtained by further mixing this with a fluorinated solvent and stirring.

When a film-shaped or emulsion-shaped PFA is used, the heat-sealed portion can be formed in substantially the same manner as described above. However, in the case of a film-shaped PFA, this is heat-molded in advance into a shape matched to the end portion of the substrate. The heat-sealed portion can also be formed by fitting the molded PFA to the end portion of the base body and thermocompression-bonding it using the aluminum pressure-bonding tool as described above. When used in combination with a powdery or emulsified PFA, a preformed film-like PFA can be used.

After the PFA heat-sealed portion is formed at the end of the porous substrate in this manner, the surface of the heat-sealed portion is further wetted by the electrolyte and a substance thermally and chemically stable to the electrolyte is added to the surface of the heat-sealed portion. It is thermocompression bonded. Examples of the substance used here include silicon carbide, titanium carbide, tantalum carbide, tungsten carbide, zirconium oxide, tantalum oxide, carbon powder and the like. These may be used alone or in any combination of two or more. All of these substances show wettability to electrolytes such as concentrated phosphoric acid, are chemically stable without being attacked by the electrolyte, and are stable even at a high temperature of about 200 ° C or higher at which a fuel cell using this electrolyte operates. Is.
This material is usually used in powder or granular form.

The place for thermocompression bonding of this substance may be the entire heat-sealed portion of PFA formed in a U-shape or a U-shape at the end of the substrate as described above, but at least it contacts the electrolyte layer of the heat-sealed portion. It should be thermocompression-bonded to the surface on the side to be treated.

In thermocompression bonding of such a substance, as shown in FIG. 3, the surface of the heat-sealing portion 17 formed at the end of the porous substrate 16 having the reaction gas supply passage 15 on one side, at least the reaction gas mentioned above. A material 18 that is thermally and chemically stable to an electrolyte, such as silicon carbide powder, is densely dispersed in a thickness of about 0.05 to 0.3 mm on the surface opposite to the surface having the supply path 15 Using a thermocompression-bonding jig made of metal such as aluminum as shown in FIG. 2 while heating to a temperature of 300 to 370 ° C., thermocompression bonding is performed at the same surface pressure as above.

The substance which is wet with the electrolyte as described above and thermally and chemically stable to the electrolyte may be only this substance, but it is in the form of a mixture with the PFA, or by kneading the PFA and a fluorine-based dispersion medium. It can also be used in the form of a pasty mixture. In the former case, 3 to 40 parts by weight of PFA powder is preferable to 100 parts by weight of the above substance, and in the latter case, 3 to 40 parts by weight of PFA powder and 150 to 100 parts by weight of fluorine-based dispersion medium are added to 100 parts by weight of the above substance. A proportion of 600 parts by weight is preferred. The conditions for thermocompression bonding such as temperature are almost the same as those for the above substances alone.

〔The invention's effect〕

Thus, according to the present invention, the surface of the heat-sealed portion obtained by heat-sealing PFA to both ends of the plate-like porous substrate parallel to the reaction gas supply path, at least the surface having the reaction gas supply path To the surface of the heat-sealing part on the side opposite to the surface or on the side opposite to the surface in contact with the reaction gas supply passage during lamination, thermocompression-bonding a substance that is wet with the electrolyte and is thermally and chemically stable to the electrolyte. Due to
The surface exhibits wettability to an electrolyte such as phosphoric acid, and an electrolyte layer between both electrodes can retain a sufficient amount of electrolyte to prevent leakage of reaction gas from the layer. In addition, it is possible to maintain good electrical insulation without causing peeling of the above-mentioned substance and the heat-sealed portion, and of course, to endure a strong pressure at the time of stacking without causing damage, which is reliable. A fuel cell using a porous gas diffusion electrode having an end seal can be obtained.

Example of Invention

Example 1 Tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) (Mitsui Fluorochemical Co., Ltd., trade name Teflon MP-20) 192 g was used as a fluorine-based solvent (Sumitomo 3M Co., Ltd., trade name Florard FC721). 128
Mix with g and stir at room temperature for 30 minutes to make a mixture for coating.

Next, both ends of a plate-like porous substrate (Kureha Chemical Industry Co., Ltd., trade name E-715) made of thin graphite fiber, which is made of carbon paper having a size of 700 mm × 700 mm and a thickness of 0.5 mm,
The mixture was applied to a width of 20 mm and left to air dry to disperse the copolymer at the ends.

On the other hand, Futsumoto Wax (Osaka Metal Industry Co., Ltd., trade name DAIFLOYL # 100) was applied in advance to the required parts of the mold as shown in the drawing, and obtained in the mold as described above. 340-37 under a load of 20kgf / mm ^{2 with} a porous substrate
Heat to a temperature of 0 ° C for about 15 minutes, then at 80-90 ° C for about 1
Annealed for hours. When the mold is removed, left to stand and air dried, the copolymer is pressed into the inside of the substrate and the amount of the copolymer is about 0.
The PFA heat-bonded portion was formed by adhering so as to rise about 1 mm.

After forming the PFA heat-sealed portion at the end of the porous substrate in this way, at the end of the surface opposite to the gas supply path, silicon carbide (SiC) powder (manufactured by Showa Denko KK, average (Particle size 0.5 micron) is densely dispersed to a thickness of 0.1 mm, and this is heated to 330 ° C with an aluminum thermocompression bonding jig, and the surface pressure is 20 kg / cm.
^It was crimped at ² for 5 minutes.

When taken out from the jig and observed the surface, the PFA of SiC is fused and fixed to the end surface, and the surface subjected to such treatment shows wettability to an electrolyte such as phosphoric acid and is reliable. The end seal could be formed.

Example 2 The PF formed on the edge of the porous substrate in the same manner as in Example 1.
At the end of the surface opposite to the reaction gas supply path of the heat fusion portion of A,
0.2 mm of a mixture of 100 parts by weight of SiC and 20 parts by weight of PFA powder (Teflon MP10 manufactured by Mitsui Fluorochemical Co., Ltd.)
And was thermocompression bonded in the same manner as in Example 1. The surface thus obtained showed wettability to the electrolyte.

Example 3 The PF formed on the edge of the porous substrate in the same manner as in Example 1.
100 parts by weight of SiC, 15 parts by weight of PFA powder, and Daiflon S3, which is a fluorine-based dispersion medium (Osaka Metal Industry Co., Ltd.), at the end of the surface opposite to the surface having the reaction gas supply passage of the heat fusion portion of A.
500 parts by weight and 4 parts by weight of Daifloyl # 100 (produced by Osaka Metal Industry Co., Ltd.) were kneaded, and a paste-like mixture was applied to a thickness of 0.2 mm, followed by thermocompression bonding as in Example 1. did.

The thermocompression-bonded surface of the substrate end thus obtained also showed wettability to the electrolyte.

Example 4 Size as a plate-like porous substrate made of thin graphite fiber
700mm x 700mm, 0.5mm thick carbon paper (Kureha Chemical Industry Co., Ltd., trade name E-715), 20mm wide, 0.13mm thick tetrafluoroethylene-perfluoroalkyl vinyl ether Polymer (Mitsui Fluorochemical Co., Ltd., trade name Teflon PFA 500LP) is softened by a molding die heated to 220 to 230 ° C. and is molded into a U-shape or a U-shape that is almost matched to the end shape, Insert this at the end.

Then, the die surface of the thermocompression-bonding jig is covered with aluminum foil, and the porous substrate is placed in a die in which the required area of this surface is coated with fluorine wax (Osaka Metal Industry Co., Ltd., Daifloyl # 100). After crimping at 20 kgf / cm ² , heating at 350 to 370 ° C. for 30 minutes, annealing at 80 to 90 ° C. for 1 hour, thermocompression bonding, and then removing from the mold to complete the end seal.

After the PFA heat-sealed portion was formed at the end of the porous substrate in this manner, silicon carbide powder (Showa Denko K.K. )
(The average particle size was 0.5 micron) was densely dispersed to a thickness of 0.1 mm, and this was heated to 330 ° C. with an aluminum thermocompression bonding jig and pressure-bonded for 5 minutes at a surface pressure of 20 kg / cm ² .

In this case as well, the treated end surface was wettable by the electrolyte and formed a reliable end seal.

A brief description of the commercially available fluorine-containing oils and fluorine-containing solvents used in these examples is as follows. First, the product name Daifloyl of Osaka Metal Industry Co., Ltd. is generally trifluoroethylene chloride. It is an oily or wax-like substance depending on the degree of polymerization. Daifloyl # 100 has an average molecular weight of about 130
A wax with a degree of polymerization of 0. Fluorard of Sumitomo 3M Limited is a fluorocarbon-based surfactant.
Daiflon S3 is a die-foil type wax.

In the above Examples 1 to 4, especially silicon carbide (SiC)
The case of thermocompression bonding is shown, but in addition to the above-mentioned other substances, that is, titanium carbide, tantalum carbide, tantasten carbide, zirconium oxide, tantalum oxide, carbon powder and the case of silicon carbide. A similar good effect was obtained.

Thus, according to the present invention, when a seal is formed at the end of the porous electrode substrate, it exhibits wettability to the electrolyte, retains the electrolyte, does not cause leakage of the reaction gas, and does not cause damage or the like. Therefore, it is possible to obtain a fuel cell using a very effective porous gas diffusion electrode.

[Brief description of drawings]

FIG. 1 is an explanatory view showing the general structure of a power generating element including a porous gas diffusion electrode having a seal formed at an end thereof according to the present invention,
FIG. 2 is an explanatory view showing an example of a state in which a PFA heat-sealed portion is first formed at an end portion of an electrode substrate according to the present invention, and FIG. 3 is an electrolyte wetted with an electrolyte in the PFA heat-sealed portion according to the present invention. It is explanatory drawing which shows an example of the state at the time of thermocompression-bonding the thermally and chemically stable substance to. 1 ... Electrode with reaction gas supply channel, 2 ... Electrolyte layer, 3 ... Thin electrode, 5, 6, 15 ... Reactant gas supply channel, 14 ... Release agent, 17 ... Heat fusion part, 18 …… Wet with electrolyte A substance that is thermally and chemically stable to the electrolyte.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-58-164153 (JP, A) JP-A-58-161261 (JP, A) JP-A 58-157063 (JP, A)

Claims (4)

[Claims] 1. An electrolyte layer, a reaction gas path for supplying a reaction gas, one surface of which is in contact with the reaction gas supply path and the other surface of which is in contact with the electrolyte layer. In a fuel cell formed by stacking a plurality of unit cells each having a porous gas diffusion electrode composed of a pair of conductive porous substrates arranged so as to be sandwiched, at least parallel to the reaction gas supply path. And a heat-sealing portion formed by heat-sealing a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer so as to cover the end portion of the porous gas diffusion electrode, and contacting at least the electrolyte layer of the heat-sealing portion. A fuel cell characterized by having a seal portion formed on the side where the electrolyte layer is wetted with an electrolyte of the electrolyte layer and thermocompression-bonded with a material that is thermally and chemically stable to the electrolyte. 2. The substance which is wet with the electrolyte and is thermally and chemically stable to the electrolyte is any one of silicon carbide, titanium carbide, tantalum carbide, tungsten carbide, zirconium oxide, tantalum oxide and carbon powder. One kind or a combination of two or more kinds,
The fuel cell according to claim 1. 3. The substance which is wet with the electrolyte and is thermally and chemically stable to the electrolyte is used as a mixture with a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer powder. The fuel cell according to item 1. 4. The substance which is wet with the electrolyte and is thermally and chemically stable to the electrolyte is a paste-like mixture of tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer powder and a fluorine-based dispersion medium. Used,
The fuel cell according to claim 1.