JP2003217599A - Solid polymer type fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid polymer type fuel cell, which can achieve long life and high current supply, by controlling the concentration of a water repellency agent within an electrode layer in a thickness-wise direction of the layer and within the surface thereof to attain high efficiency and evenness of gas diffusion. <P>SOLUTION: For the solid polymer type fuel cell obtained by arranging a solid polymer electrolyte layer 1 between a pair of electrode layers 3, 3, a recessed portion 5 is formed in a surface on the side of the electrolyte layer 1 of each electrode layer 3 to control the concentration of a water repellency agent in the electrode layer 3 in a thickness-wise direction of the layer and within the surface thereof. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polymer electrolyte fuel cell in which a polymer electrolyte layer is arranged between a pair of electrode layers such as an air electrode and a fuel electrode. The present invention relates to a polymer electrolyte fuel cell in which the layer thickness direction and the surface are controlled.

[0002]

2. Description of the Related Art A polymer electrolyte fuel cell has a pair of electrode layers, a positive electrode and a negative electrode, sandwiching a solid polymer electrolyte layer such as an ion conductive resin membrane. For example, air is used for the positive electrode and hydrogen is used for the negative electrode. When supplied, electricity is generated by an electrochemical reaction.

Conventionally, the electrode layer constituting such a fuel cell is made of electrically conductive sheet-like carbon paper, and is made water-repellent by using a polytetrafluoroethylene-based dispersion as a water-repellent material. What has been processed is used. As a water-repellent treatment method, a method of impregnating the water-repellent material with carbon paper and drying it in a horizontal or vertical air stream in air or under a low pressure to vaporize or remove the solvent is generally used. is there.

Further, Japanese Laid-Open Patent Publication No. 5-25086 discloses a method for efficiently diffusing gas inside an electrode layer.
It is disclosed that the water repellent on the side of the electrolyte is strong and the water repellent on the side of the electronic conductor, which is commonly called a separator, is weakened so as to have a concentration gradient of the water repellent. In this way, by increasing the water repellency of the electrode layer, the diffusibility of gas in the electrode layer is increased, and the life of the fuel cell is increased and the current is increased.

[0005]

However, with the above-mentioned conventional structure, in a fuel cell having a power generation part composed of multiple layers, it is difficult to make the water repellency uniform among the individual electrode layers in the multilayer electrode layers, and It was difficult to control the water repellency to make the water repellency on the surface uniform.

In this way, for example, when the number of stacked electrode layers is large, for example, the larger the number of positive electrode cells exceeds 200 layers, the more the water repellency between the individual electrode layers becomes stronger. The variation of the weak one becomes large, and the power generation characteristics between the individual layers are likely to vary even in each power generation section including the pair of electrode layers and the polymer electrolyte layer, and the battery is caused by excessive water wetting of the electrode layers. There was a problem that performance was degraded. Further, even if a failure such as flooding occurs, it is difficult to identify the failure location, and the maintainability is poor.

In view of the above-mentioned conventional problems, the present invention controls the water repellent concentration in the electrode layer in the thickness direction of the layer and in the surface thereof to make gas diffusion highly efficient and uniform, thereby extending the service life. It is an object of the present invention to provide a polymer electrolyte fuel cell capable of achieving a large current.

[0008]

The solid polymer type fuel cell of the present invention is a solid polymer type fuel cell in which a solid polymer electrolyte layer is arranged between a pair of electrode layers. A concave portion is formed on the surface on the side, and the water repellent concentration in the electrode layer is controlled in the thickness direction of the layer and within the surface,
Increase the water repellent concentration near the interface of the electrode layer on the electrolyte layer side,
Since it is possible to form a concentration gradient of the water repellent agent that lowers the concentration of the water repellent agent on the opposite side of the electron conductor and to control the concentration distribution, it is possible to efficiently diffuse gas inside the electrode layer. Even in the case of stacking multiple layers, the water-repellent property between the electrode layers can be made uniform without any variation, and the reliability of the fuel cell can be improved, and the life and current can be increased.

The depth of the recess is 10 to 50% of the thickness of the electrode layer.
Therefore, it is preferable that the area ratio of the recesses be in the range of 0.2 to 40%.

The electrode layer is water repellent obtained by impregnating a sheet-like body made of carbon fiber having gas diffusion property or a flexible sheet-like body with a dispersion solution of a water repellent and evaporating and removing the solvent. Those that have been treated are preferable.

Further, if a solid or water-repellent resin-coated fiber made of a water-repellent resin is mixed in the vicinity of the surface of the electrode layer on the side of the electrolyte layer, the water-repellent agent concentration distribution in the electrode layer can be further improved. It is desirable because it can be surely controlled.

Further, in a solid polymer electrolyte fuel cell in which a solid polymer electrolyte layer is arranged between a pair of electrode layers, a solid or hydrophobic resin made of a water-repellent resin is provided in the vicinity of the surface of the electrode layer on the electrolyte layer side. By mixing fibers coated with an aqueous resin and controlling the concentration of the water repellent in the electrode layer in the thickness direction of the layer and within the surface, a concentration gradient of the water repellent and its concentration distribution can be controlled. Similar to the above, the reliability of the fuel cell can be improved, the life can be extended, and the current can be increased.

As the water-repellent resin material, those containing a simple substance or a mixture of tetrafluoroethylene, a copolymer of ethylene tetrafluoride and propylene hexafluoride, a copolymer of ethylene tetrafluoride and a perfluorovinyl ether. It is preferably used.

In addition, a power generating section constituted by arranging a pair of electrode layers facing each other with a catalyst layer sandwiched between both sides of the solid polymer electrolyte layer, a gas supply channel for supplying gas to the electrode layer and an electrode layer. In a polymer electrolyte fuel cell in which conductive electron conductors having gas discharge channels for discharging gas are alternately stacked and which has two or more layers of power generation sections, the effect is particularly exerted when the above configuration is applied. To be done.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the polymer electrolyte fuel cell of the present invention will be described below with reference to FIGS.

In FIG. 1 showing the basic structure of the fuel cell of this embodiment, 1 is a solid polymer electrolyte layer, which is made of a solid polymer material having hydrogen ion conductivity. A pair of electrode layers 3 are arranged with the electrolyte layer 1 sandwiched between them, and a gas supply channel for supplying gas to the electrode layer 3 and a gas discharge channel for discharging gas from the electrode layer 3 are provided outside the electroconductive layer 3. The electronic conductor 4 of is arranged. At the interface between the electrolyte layer 1 and the electrode layer 3, a catalyst layer 2 in which carbon powder carries a catalyst composed of a noble metal component or the like is interposed, and the electrolyte layer 1 and the electrode layer 3 are bonded via this catalyst layer 2. , A power generation unit is configured.

The electrode layer 3 is made of carbon paper having a thickness of about 400 μm and a porosity of 38%, and a large number of minute recesses 5 are evenly distributed over substantially the entire surface of the electrolyte layer 1 side. Has been formed. Then, on the surface of the carbon paper on which the recess 5 is formed, there is a water-repellent effect 4
Apply a solution or suspension of fluorinated ethylene as the main component, which is diluted 12 times with distilled water, and place the opposite side on a hygroscopic cotton cloth or polyethylene felt sheet and let it stand in the air for about 6 hours. After leaving it in the oven, it is dried in a drying oven at 60 ° C in air for 30 minutes and then in a baking oven at 350 ° C for 3 minutes.
The electrode layer 3 made of water-repellent carbon paper having a predetermined porosity and gas permeability is formed by heat-treating for a period of time and heat-melting the water-repellent agent into the fibrous material of carbon paper. As a method of applying the water repellent, carbon paper may be dipped in a solution of the water repellent.

The recess 5 on the surface of the electrode layer 3 can be formed by a carbon dioxide gas laser, a YAG laser, or the like, or can be mechanically pressed by a roller or the like. Further, the shape of the recess 5 has a diameter Dd of 0.00, as shown in FIG.
A circular shape of 5 to 0.5 mm is preferable, but needless to say, a triangular shape, a quadrangular shape, an elliptical shape, or the like may be used as shown in FIG. Further, in some cases, it may be formed in a linear concave portion which is intermittent or continuous.

By forming the recesses 5 evenly over the entire surface of the electrode layer 3 on the side of the electrolyte layer 1 as described above,
A water repellent concentration distribution A as shown in FIG. 1 was obtained in the thickness direction of the electrode layer 3. FIG. 2 shows the concentration distribution of the water repellent agent in the thickness direction of the electrode layer 3 by the recess 5 when Td / Ts is changed, where Td is the depth of the recess 5 and Ts is the thickness of the electrode layer 3. The depth Td of the recess 5 is set to be 10 to 5 of the thickness Ts of the electrode layer 3.
As a result of the experiment with 0%, the maximum current density was more desirably obtained in the range of 15 to 25%. Td / Ts
Is 10% or less, the current density is 300 mA.
/ Cm ² and the contact resistance with the electrode was increased, tending to deteriorate the battery characteristics.

In FIGS. 3 and 4, Ad is the total area of the recesses 5 formed on the surface of the electrode layer 3, and As is the total area of the surface of the carbon paper forming the electrode layer 3 on the electrolyte layer 1 side. . As shown in FIG. 3, the value of Ad / As is 0.2 to
By setting the range to 40%, the concentration distribution of the water repellent agent in the length direction of the electrode layer 3 was uniform and stable in the length direction as shown by the curve B. In this way, a constant water repellent concentration is obtained over most of the area of the electrode layer 3, so that when the fuel cell is in operation for a long period of time,
Even when a large current is output, it is possible to effectively prevent the electrode layer 3 from getting wet with water excessively, prevent deterioration of cell performance due to water getting wet, and achieve a long life of the fuel cell and a large current. be able to.

Also in the experiment, the value of Ad / As was 0.2 to 40.
%, The limiting current density is 300 mA / cm
^{With the value of 2} kept, it operated with a stable output for a long period of 1000 hours or more.

On the other hand, when the value of Ad / As is less than 0.2 or exceeds 40%, there is a tendency that the life time of maintaining a constant current density of 300 mA / cm ² is rapidly reduced. It was

FIG. 3 shows a conventional method, that is, a case where a flat carbon paper whose surface is not processed is dipped in a water repellent and then the carbon paper is placed vertically and dried. As shown by the water repellent concentration curve C, the water repellent concentration is high on one side and low on the other side, resulting in a non-uniform concentration distribution.

In the above description, the porosity of 3 is used as the electrode layer 3.
Although an example in which 8% carbon paper is used is shown, even in the case of carbon cloth having a porosity of 55% as the electrode layer 3, by providing the concave portion 5 similar to the above, it is possible to improve the battery performance due to excessive water wetting. It was possible to prevent the deterioration, and it was possible to achieve a long life of the fuel cell and a large current. In addition, the electrode layer 3
As other materials, porous graphite and carbon-based sintered body,
The sheet-like conductive fiber body and the conductive carbon fiber material may be used.

Further, an example in which an aqueous solution of tetrafluoroethylene was used as a water repellent was shown, but a copolymer of ethylene tetrafluoride and propylene hexafluoride was prepared and a copolymer of ethylene tetrafluoride and perfluorovinyl ether was used. The same concentration distribution of the water repellent as described above was obtained also in the simple substance or the mixture, and the same effect was obtained.

In the above description, in order to explain the basic structure of the fuel cell, as shown in FIG. 1, one electrolyte layer 1, a pair of electrode layers 3 on both sides of the electrolyte layer 1, and a catalyst provided at the interface between them. Although an example in which a single-layer power generation section composed of the layer 2 and the electron conductor 4 are arranged outside the single-layer power generation section has been described, in an actual fuel cell, as shown in FIG.
(A), 1 (b) .. 1 (n) .., and electrode layers 3 (a), 3 (b) .. 3 (n) ... on both sides of each electrolyte layer 1,
Catalyst layers 2 (a), 2 provided at the interface between them
(B) .. 3 (n) ..
(B) .. 4 (n), 4 (n + 1) .. By configuring the electrode layer 3 as described above, for example, in a fuel cell in which the electrolyte layer 1 is composed of 50 layers, the current density is 250 mA / cm ^{2 in} a long continuous operation of about 1500 hours or more. It was possible to stably perform high current output operation.

Next, a polymer electrolyte fuel cell according to another embodiment of the present invention will be described with reference to FIG. In addition,
The same components as those of the above-described embodiment are designated by the same reference numerals, description thereof will be omitted, and only different points will be described.

In the above embodiment, the electrolyte layer 1 of the electrode layer 3 is used.
Although an example in which the concave portion 5 is formed on the side surface to control the water repellent concentration distribution has been described, in the present embodiment, the concave portion 5 is formed, and the portion near the surface of the electrode layer 3 on the electrolyte layer 1 side is formed. A fiber coated with a solid or water-repellent resin such as a fiber 6 made of a water-repellent resin is mixed.

The water-repellent resin is composed of a copolymer of ethylene tetrafluoride and hexafluoropropylene, or a mixture of the copolymer of ethylene tetrafluoride and perfluorovinyl ether.

In this embodiment, the concentration of the water repellent agent can be controlled so that the water repellency on the side of the electrolyte layer 1 is higher and the water repellency on the side of the electronic conductor 4 is weaker. It is possible to exert an effect.

In the present embodiment, an example in which the formation of the recessed portion 5 and the mixing of the solid or the coated fiber made of the water-repellent resin is used together is shown. Even if it does, the same effect can be produced.

[0032]

According to the polymer electrolyte fuel cell of the present invention, as is apparent from the above description, the surface of the electrode layer is provided with a recess or is coated with a solid or water-repellent resin made of a water-repellent resin. Since the water repellent concentration in the electrode layer was controlled in the film thickness direction and in the surface by mixing the fibers, the water repellency on the electrolyte layer side was high and the water repellency on the electronic conductor side was weakened to reduce the water repellent inside the electrode layer. Gas can be diffused with high efficiency,
Even in the case of stacking multiple layers, the water repellency of each electrode layer can be made uniform without any variation, and the reliability of the fuel cell can be improved and the life and current can be increased.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the basic configuration of an embodiment of a polymer electrolyte fuel cell of the present invention.

FIG. 2 is a distribution diagram of the water repellent concentration in the thickness direction of the electrode layer in the same embodiment.

FIG. 3 is a distribution diagram of the water repellent concentration in the surface direction of the electrode layer in the same embodiment.

FIG. 4 is an explanatory diagram of a recess shape formed on the surface of the electrode layer in the same embodiment.

FIG. 5 is a cross-sectional view showing a schematic configuration of a fuel cell according to the same embodiment.

FIG. 6 is a cross-sectional view showing the basic configuration of another embodiment of the polymer electrolyte fuel cell of the present invention.

[Explanation of symbols]

1 Solid polymer electrolyte layer 3 electrode layers 5 recess 6 Fibers made of water-repellent resin

Continued front page    F-term (reference) 5H018 AA06 AS01 BB05 BB06 BB08                       BB12 CC06 DD05 DD06 DD08                       EE05 EE19 HH00 HH02                 5H026 AA06 BB03 BB04 BB08 CC03                       CX02 CX03 CX04 CX05 EE05                       EE19 HH00 HH02 HH03

Claims (7)

[Claims] 1. A solid polymer electrolyte fuel cell comprising a solid polymer electrolyte layer disposed between a pair of electrode layers, wherein a recess is formed on the surface of the electrode layer on the electrolyte layer side, and a water repellent agent in the electrode layer is formed. A polymer electrolyte fuel cell, characterized in that the concentration is controlled in the thickness direction of the layer and in the surface. 2. The depth of the recess is set to be 10 to 50 of the thickness of the electrode layer.
%, And the area ratio of the recesses is in the range of 0.2 to 40%. 3. The polymer electrolyte fuel cell according to claim 1, wherein 3. The electrode layer is water-repellent obtained by impregnating a sheet-like body made of carbon fiber having gas diffusion property or a sheet-like molded body having flexibility with a dispersion solution of a water repellent to evaporate and remove the solvent. The polymer electrolyte fuel cell according to claim 1, wherein the polymer electrolyte fuel cell is treated. 4. A portion near the surface of the electrode layer on the electrolyte layer side,
The polymer electrolyte fuel cell according to any one of claims 1 to 3, wherein solid or water-repellent resin-coated fibers are mixed. 5. A solid polymer electrolyte fuel cell having a solid polymer electrolyte layer disposed between a pair of electrode layers. A polymer electrolyte fuel cell, characterized in that fibers coated with an aqueous resin are mixed and the concentration of the water repellent agent in the electrode layer is controlled in the layer thickness direction and in the surface. 6. The water-repellent resin material is tetrafluoroethylene,
Copolymer of tetrafluoroethylene and propylene hexafluoride, 4
The polymer electrolyte fuel cell according to claim 4 or 5, comprising a simple substance or a mixture of a copolymer of fluorinated ethylene and perfluorovinyl ether. 7. A power generation section comprising a pair of electrode layers facing each other with a catalyst layer sandwiched between both sides of a solid polymer electrolyte layer, a gas supply channel for supplying gas to the electrode layer, and an electrode layer. 7. The solid polymer according to claim 1, wherein electrically conductive electronic conductors having gas discharge channels for discharging gas are alternately laminated and have two or more power generation sections. Type fuel cell.