JPH0878028A - Solid polymer electrolyte fuel cell and its manufacture - Google Patents

Abstract

PURPOSE: To satisfy both of gas seal between unit cells and reduction of current collecting resistance by filling a gap between a separator and an electrolyte film with a thermosetting resin molding in the surrounding of a gas diffusion electrode. CONSTITUTION: A groove-formed separator 10 and a gas diffusion layer 13 faced through resin paste are baked in a nitrogen atmosphere for integrally bonding them. A gas reaction layer 14 is formed on the side opposite to the separator 10 of the gas diffusion layer 13 to obtain a electrode chamber structure 15. A sealing agent molding made of phenol resin is arranged in the periphery of a gas diffusion electrode comprising the gas diffusion layer 13 and the gas reaction layer 14. A solid polymer electrolyte film 17 is interposed between the electrodes of the electrode chamber structure 15, and an optional number of unit cells are stacked and they are set in a pressing fixture. The pressing fixture is put in a heating furnace to heat and fasten the unit cell assembly. The sealing agent molding is softened in pasty state and a gap between the gas diffusion electrode and the polymer electrolyte film 17 is completely filled. The temperature of the heating furnace is lowered, and phenol resin is cured to obtain a solid polymer electrolyte fuel cell.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid polymer electrolyte fuel cell and a method for producing the same.

[0002]

2. Description of the Related Art A solid polymer electrolyte fuel cell is small in size and has a high current density, so that it is expected to be effectively used as a small power source in various fields.

A solid polymer electrolyte fuel cell is generally provided as a fuel cell stack in which single cells are stacked in series in order to obtain a high output. In designing the fuel cell stack, (1) The gap between the separator and the electrolyte membrane in the unit cell is gas-sealed, and (2) an appropriate external pressure is applied to improve the adhesion between the constituent members in each unit cell to reduce the current collecting resistance. Must be taken into account.

In the former case, when the reaction gas leaks to the outside through the gap between the separator and the electrolyte membrane, not only the efficiency of the fuel cell is lowered, but also hydrogen as a fuel gas and oxygen as an oxidizing gas are separated. It may induce an explosive reaction and is required to avoid such problems. Since the sealing material used for this purpose is required to be dense and elastic, a fluorocarbon resin has been generally used as the sealing material from the past (for example, JP-A-5-28309).
(See Japanese Patent Publication No. 3).

In order to satisfy the latter requirement, conventionally, a method has been proposed in which the upper and lower sides of the laminated body are sandwiched by fastening plates, and four tie rods penetrating the fastening plates are each fastened with nuts ( Japanese Unexamined Patent Publication No. 62-136776
See figure).

[0006]

However, the fluorine-based resin used as the conventional sealing material has the advantage that its thickness can be easily selected, but on the other hand, it is possible to completely seal a small gap with a gas. It was difficult. In order to further improve the gas sealing property, a method of compressing and deforming the sealing material by hot pressing has been proposed, but in order to deform the fluororesin, a high temperature of 300 ° C. or higher must be applied. If the polymer electrolyte membrane and the polymer electrolyte membrane are heated at the same time, the electrolyte membrane may be thermally deteriorated.

Further, the use of a jig such as a tightening plate, a tie rod, a nut or the like for applying an external pressure not only increases the total weight of the laminate, but also makes the tightening pressure of each tightening portion uniform. However, there is a problem in that the power generation efficiency is reduced due to the uneven contact between the parts of each unit cell.

[0008]

In view of the above-mentioned problems of the prior art, the present invention satisfies both reliable gas sealing in each unit cell and reduction of current collecting resistance by appropriate external pressure. It is also an object of the present invention to provide a solid polymer electrolyte fuel cell laminate having a novel structure that can eliminate the need for tightening with a jig.

In order to achieve this object, a solid polymer electrolyte fuel cell according to the present invention comprises a single cell in which a polymer electrolyte membrane is sandwiched between gas diffusion electrodes, and a fuel gas is supplied to one of the gas diffusion electrodes on the other side. In the one in which grooved separators for supplying an oxidant gas are alternately laminated, the single cell has the gas diffusion electrode bonded to the central portion of the membrane surface of the polymer electrolyte membrane, and A thermosetting resin sealant, which surrounds the gas diffusion electrode and fills a space between the separator and the polymer electrolyte membrane to seal the gas, is provided at the peripheral portion of the membrane surface of the molecular electrolyte membrane. Characterize.

The solid polymer electrolyte fuel cell of the present invention having the above structure is manufactured by the following manufacturing process.

First, a dense carbon grooved separator and a gas diffusion layer in contact with the separator are fired through an adhesive in a nitrogen atmosphere and carbonized to be integrated. By carbonizing, good electrical conductivity is obtained between the electrode and the separator, and these are firmly bonded. As the adhesive, a thermosetting resin (phenol resin,
A resin paste prepared by adding an alcoholic solvent to an epoxy resin, furan resin, etc.) and kneading the mixture at room temperature is preferably used.

In the uppermost and lowermost unit cells of the fuel cell stack, the gas diffusion layers are joined to one surface of the separator, and in the middle unit cells, the gas diffusion layers are joined to both surfaces of the separator.

A gas reaction layer is formed by screen-printing a dispersion of reaction layer components on the gas diffusion layer bonded to one or both sides of the separator in this way, and the separator and the gas diffusion electrode (gas diffusion electrode A polar chamber structure consisting of (layer + gas reaction layer) is obtained.

The thickness of the gas reaction layer is preferably about 40 to 50 μm. The dispersion of the gas reaction layer component can be prepared by mixing carbon with catalyst with an ion exchange resin which is a component of the solid polymer electrolyte. Platinum is suitable as a catalyst, but when introducing a hydrogen-rich reformed gas obtained by a reforming reaction from a hydrocarbon gas such as methanol to the electrode, avoid introducing a trace amount of carbon monoxide into the reformed gas. Therefore, it is preferable to use platinum and ruthenium or platinum and tin as an alloy in order to prevent the platinum from being poisoned.

By the above steps, the number of polar chamber structures corresponding to the number of solids of the single cells to be stacked in the fuel cell stack is prepared in advance.

At the same time, the resin paste is applied to a V-shaped mold having an opening in the center and heat-pressed to form a V-shaped sealing agent molding (thermosetting resin sheet).
Is created in advance. As will be described later, the central opening of the sealant molded body is for accommodating and arranging the gas diffusion electrode of the polar chamber structure, and is therefore cut out so as to have an area substantially the same as the electrode area. Also, the thickness of the sealing agent molded body is slightly thicker than the thickness of the gas diffusion electrode. This is because the sealing agent molded body is paste-like when heated again when the laminated body is pressed, as will be described later. This is to ensure that the space can be sealed and the space can be reliably sealed.

Then, the sealant molded body coated with the resin paste on both sides is arranged at the periphery of the membrane surface of the polymer electrolyte membrane, and the gas diffusion electrode of the polar chamber structure is arranged at the center of the membrane surface. Then, the unit cell is formed so that the gas diffusion electrode is housed in the central opening of the thermosetting sheet.

It should be noted that a paste prepared by adding an alcohol solvent to the thermosetting resin so as to have a predetermined viscosity without using the thermosetting resin sheet formed in the shape of a square-shape is provided around the gas diffusion electrode. It may be applied between the separator and the polymer electrolyte membrane, preferably to a thickness not less than that of the gas diffusion electrode.

As the polymer electrolyte membrane, Nafion (trade name, manufactured by DuPont, USA) is particularly suitable, but in addition to this, for example, PSSA-PVA (polystyrene sulfonate-polyvinyl alcohol copolymer) PSSA-EV.
It is also possible to use OH (polystyrene sulfonic acid-ethylene vinyl alcohol copolymer) or the like.

A fuel cell stack is obtained by stacking the single cells obtained as described above through a current collector plate.

The thermosetting resin sheet itself and the resin paste applied thereon are softened by pressing the laminated body under pressure in a furnace heated above the softening temperature (100 to 150 ° C.) of the thermosetting resin sheet. Then, the gas diffusion electrode is brought into a fluidized state, is brought into close contact with the peripheral side portion of the gas diffusion electrode, and is filled between the separator and the electrolyte membrane. After the heating is finished, the resin paste is cured as it is left to cool, and becomes a thermosetting resin molded body.

[0022]

In the laminated body of the solid polymer electrolyte fuel cell of the present invention, the side surface of the gas diffusion electrode in each unit cell is completely gas-sealed by the thermosetting resin molding. Also,
Since the separator and the gas diffusion layer are integrated, the current collecting resistance is reduced, and since the unit cells are firmly joined by the resin paste between the gas electrodes, it has been used to tighten the conventional laminate. No need for jigs such as bolts and nuts.

[0023]

EXAMPLE A solid polymer electrolyte fuel cell of the present invention was manufactured by the following manufacturing process.

Gas channel grooves 11 and 12 extending in directions orthogonal to each other are formed on both surfaces of a gas impermeable graphite plate (dense carbon sheet) to form a grooved separator 1.
Formed 0.

A commercially available porous carbon sheet (thickness: 0.
8 to 1 mm, size 100 mm x 100 mm) 7.5
After immersing in a PTFE aqueous solution of about wt% for about 2 minutes, it was made water-repellent by drying in an inert gas atmosphere to form a gas diffusion layer 13.

Next, a commercially available phenol resin (trade name:
20 per 2g of powder of Bell Pearl (manufactured by Kanebo Ltd.)
After adding cc of methanol or ethanol at room temperature to prepare a uniform paste, the resin paste is applied to the separator bonding surface of the gas diffusion layer 13 and the separator 10 is attached, and then the temperature is set to 600 ° C. or higher in a nitrogen atmosphere. It was fired under the conditions. As a result, the phenol resin forming the resin paste was carbonized, and the separator 10 and the gas diffusion layer 13 were firmly bonded and integrated (FIG. 1). The thickness of the gas diffusion layer after joining was 500 to 800 μm.

Further, a mixture obtained by mixing carbon with catalyst with an ion exchange resin which is a component of the solid polymer electrolyte is screen-printed on the surface of the gas diffusion layer 13 opposite to the separator 10 to obtain a thick film. A gas reaction layer 14 having a thickness of 40 to 50 μm was formed. Thereby, the separator 10
A polar chamber structure 15 including a gas diffusion electrode (gas diffusion layer 13 + gas reaction layer 14) was obtained (FIG. 2).

On the other hand, the phenol resin paste is applied to an outer frame of 120 mm × 120 mm and an inner frame of 100 mm × 100 m.
It is applied to a m-shaped die and dried at about 150 ° C to form a sheet with a thickness of about 1.0 mm,
A sealant molding 16 made of phenol resin was prepared.

The above-mentioned phenol resin paste is applied as an adhesive on both sides of this sealant molded body 16, preliminarily dried by leaving it at room temperature, and then placed on the periphery of the gas diffusion electrode, and the polar chamber structure thus obtained is obtained. The solid polymer electrolyte membrane 17 was sandwiched between the electrodes of the body 15, and an arbitrary number of single cells were laminated and set on a pressing jig (FIGS. 3 and 4). As the polymer electrolyte membrane, Nafion having a thickness of 0.1 to 0.2 mm and a size of 120 mm × 120 mm was used.

The pressure jig having the laminated body set therein was placed in a heating furnace, and heated and pressed for 1 hour under an applied load pressure of about 150 ° C. and 2.5 kg / cm ² . Since the softening temperature of the phenol resin forming the sealant molded body is about 150 ° C., the sealant molded body softens into a paste in this heating and pressing step, and the paste between the gas diffusion electrode and the polymer electrolyte membrane is formed. The gap could be completely filled.

After the temperature of the heating furnace is lowered and the paste-like phenol resin filled between the gas diffusion electrode and the polymer electrolyte membrane is cured to form a molded body, gas leak of each single cell in the laminated body. After checking, the pressure jig was removed.

The structure of the fuel cell stack manufactured as described above is shown in FIG. That is, this fuel cell stack 2
In No. 0, a single cell 18 in which a polymer electrolyte membrane 17 is sandwiched between gas diffusion electrodes 15 composed of a gas diffusion layer 13 and a gas reaction layer 14, and grooved separators 17 are alternately laminated. In each unit cell, the gas diffusion electrode 15 is joined to the central portion of the membrane surface of the polymer electrolyte membrane 17, and the periphery of the membrane surface of the polymer electrolyte membrane 17 surrounds the gas diffusion electrode 15 and forms the separator 10. A resin sealant 19 is provided to fill the space between the polymer electrolyte membrane 17 and seal the gas.

In this embodiment, the applied load pressure at the time of heating and pressing the laminate was set to 2.5 kg / cm ² , but even under such a low pressurizing condition, the contact between the separator and the gas diffusion electrode was made. The resistance was 0.1 to 0.2 Ω · cm ² . On the other hand, in the case of the prior art in which the separator and the gas diffusion electrode are simply joined only by pressing, 10 kg / cm
^{Even if} the pressure of ² is applied, the contact resistance can be reduced only to about 0.3 Ω · cm ² (FIG. 6). This allows
In the present invention in which the separator and the gas diffusion layer are integrated through carbonization of the adhesive, it has been proved that the current collecting resistance can be sufficiently reduced even with a small applied pressure.

[0034]

In the solid polymer electrolyte fuel cell according to the present invention, the gas diffusion electrode is completely gas-sealed by the thermosetting resin molding which is disposed between the separator and the polymer electrolyte membrane around the gas diffusion electrode. Therefore, the power generation efficiency is not reduced due to the gas leak, and the explosive reaction between hydrogen and oxygen can be avoided.

Further, it is not necessary to use a tightening jig as in the prior art for joining the single cell and the separator to obtain the laminated body, and the laminated body can be made smaller and lighter in weight.
Uneven battery performance due to imbalance of tightening pressure is eliminated.

Further, since the gas diffusion layer and the separator are integrated by carbonizing the resin paste serving as the adhesive, the contact resistance between them is significantly reduced, and the applied pressure at the time of stacking is reduced. Can be lowered,
The porosity of the gas diffusion layer is not impaired and the reaction gas transport efficiency is not reduced.

[Brief description of drawings]

FIG. 1 is a perspective view schematically showing one step in the production of a solid polymer electrolyte fuel cell of the present invention.

FIG. 2 is a perspective view schematically showing a manufacturing process performed subsequent to the process of FIG.

3 is a perspective view schematically showing a manufacturing process performed subsequent to the process of FIG.

FIG. 4 is a perspective view schematically showing a manufacturing step subsequent to the step of FIG. 3, which is a step of obtaining a fuel cell stack.

FIG. 5 is a cross-sectional view showing the structure of a fuel cell stack manufactured through the steps of FIGS. 1 to 4.

FIG. 6 is a graph showing a comparison of the relationship between the applied pressure and the contact resistance between the separator and the electrode when the single cells are stacked in the fuel cell stack according to the present invention and the prior art.

[Explanation of symbols]

 10 Grooved Separator 13 Gas Diffusion Layer 14 Gas Reaction Layer 15 Polar Chamber Structure 16 Sealant Molded Body 17 Solid Polymer Electrolyte Membrane 18 Single Cell 19 Thermosetting Resin Sealant 20 Fuel Cell Laminate

Claims (5)

[Claims] 1. A single cell in which a polymer electrolyte membrane is sandwiched between gas diffusion electrodes and a grooved separator for supplying a fuel gas to one of the gas diffusion electrodes and an oxidant gas to the other are alternately laminated. In the solid polymer electrolyte fuel cell consisting of the single cell, the gas diffusion electrode is joined to the central portion of the membrane surface of the polymer electrolyte membrane, and the periphery of the membrane surface of the polymer electrolyte membrane is A solid polymer electrolyte fuel cell, comprising: a thermosetting resin sealant that surrounds the gas diffusion electrode and fills a space between the separator and the polymer electrolyte membrane to seal the gas. 2. The gas diffusion electrode, wherein the gas diffusion electrode is made of a porous base material having pores for diffusing the fuel gas and the oxidant gas, and the fuel gas and the gas diffusion layer adjacent to the gas diffusion layer. A polar chamber structure comprising a gas reaction layer provided in contact with the polymer electrolyte membrane to cause a cell reaction of an oxidant gas, and the gas diffusion layer is bonded and integrated to the grooved separator by carbonization of an adhesive. 2. The solid polymer electrolyte fuel cell according to claim 1, wherein 3. The grooved separator and the gas diffusion layer are bonded and integrated with each other by firing the separator with a groove and the gas diffusion layer in an atmosphere of nitrogen through an adhesive to carbonize the adhesive. A gas reaction layer is formed on the diffusion layer to form a gas diffusion electrode, and a plurality of polar chamber structures composed of the separator and the gas diffusion electrode are thus created, and the gas is provided at the center of the membrane surface of the polymer electrolyte membrane. A thermosetting resin is arranged so as to surround the gas diffusion electrode at the periphery of the membrane surface of the polymer electrolyte membrane together with the diffusion electrode.
The polymer electrolyte membrane is laminated by sandwiching it between the two polar chamber structures, and the resulting laminate is pressure-welded in a furnace heated to a temperature not lower than the softening temperature of the thermosetting resin, thereby thermosetting the thermosetting resin. The resin close to the peripheral side of the gas diffusion electrode,
Moreover, the method for producing a solid polymer electrolyte fuel cell is characterized in that the thermosetting resin is cured by filling it between the separator and the polymer electrolyte membrane and then allowing it to cool. 4. A mouth-shaped sealant molded body is prepared from the thermosetting resin, and the sealant molded body is arranged at the peripheral edge of the membrane surface of the polymer electrolyte membrane. Of the method for producing a solid polymer electrolyte fuel cell. 5. The thermosetting resin having a thickness equal to or larger than that of the gas diffusion electrode is arranged at a peripheral portion of a membrane surface of the polymer electrolyte membrane, and is softened to form a paste when the laminate is heated and pressed. The method for producing a solid polymer electrolyte fuel cell according to claim 3 or 4, wherein a thermosetting resin is caused to flow and fill between the separator and the polymer electrolyte membrane.