JP3382213B2 - Method for producing gas diffusion electrode for polymer electrolyte fuel cell - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a gas diffusion electrode used in a polymer electrolyte fuel cell, and a polymer electrolyte fuel cell including the gas diffusion electrode.

[0002]

2. Description of the Related Art Electrodes used in polymer electrolyte fuel cells are composed of a catalyst layer formed on the surface of the polymer electrolyte membrane on both sides of the polymer electrolyte membrane and a gas formed outside the catalyst layer. It has a structure including a diffusion electrode. And
As the performance required for the gas diffusion electrode, for example, gas diffusivity, conductivity for collecting electricity generated in the catalyst layer,
And water repellency for efficiently removing water generated on the surface of the catalyst layer. In order to obtain such a gas diffusion electrode, generally, a conductive porous base material having both gas diffusing ability and conductivity is used. Specifically, carbon felt made of carbon fiber, carbon paper, carbon cloth and the like are used. Further, in order to enhance the water repellency of these conductive porous substrates, a water repellent treatment of immersing in a fluororesin dispersion or the like is generally performed. More specifically, these water-repellent treated gas diffusion electrodes are prepared by immersing a conductive porous substrate in a fluororesin dispersion or the like, and then firing it to obtain moisture and a surfactant other than the fluororesin. It is made by removing the above.

On the other hand, when a polymer electrolyte fuel cell is obtained by using such a gas diffusion electrode, a catalyst layer is provided between the gas diffusion electrode and the polymer electrolyte membrane. In order to prevent falling into the electrode and to impart further water repellency, it is also common to provide a carbon layer containing carbon as a main component on the conductive porous substrate that constitutes the gas diffusion electrode. Is done in a regular manner. That is, a water-based ink containing carbon powder such as carbon black is applied onto the conductive porous substrate after the water repellent treatment by using, for example, a spray method or a printing method, and a part of the conductive porous substrate is coated. It has been practiced to form a carbon layer which is impregnated into and penetrates into. Also in this case, baking treatment is performed after coating in order to remove water and surfactant.

[0004]

However, in the prior art, the water-repellent treatment step and the carbon layer forming step are performed separately, and it is possible to efficiently and efficiently use the excellent gas by combining both steps. It was not clear whether a diffusion electrode could be obtained. For example, when the carbon layer is formed after the conductive porous substrate is subjected to water repellent treatment, the substrate has water repellency. Therefore, when a water-based carbon ink is used, the ink is repelled on the substrate, It may not be possible to apply it uniformly. Further, even if coating is possible, since the carbon layer is completely floated on the base material and becomes a state like a puddle, there is a high risk that the carbon layer will be cracked or peeled off during drying. is there. Furthermore, when a fuel cell having an electrode including the gas diffusion electrode obtained in this manner is produced, there is a problem that the water repellency in the electrode surface varies and the cell characteristics deteriorate.

When an additive such as a surfactant is mixed in the ink to improve the coating property, it is necessary to bake the composition to remove the surfactant after the coating, and further the PTFE in the carbon layer. Even when a water repellent such as dispersion is mixed, it is necessary to similarly perform baking after coating. Therefore, in consideration of the advantages and disadvantages of the water repellent treatment step and the carbon layer forming step, the present invention efficiently combines these two steps, has an excellent water repellency and a uniform carbon layer, and is excellent. An object of the present invention is to provide a method for manufacturing a gas diffusion electrode for an electrode, which can provide a polymer electrolyte fuel cell having cell characteristics.

[0006]

According to the present invention, (a) a step of immersing a conductive porous substrate in a water repellent treatment liquid containing a surfactant , and (b) the conductive porous substrate. , The conductive poly
Drying at a temperature at which the surfactant is not removed from the porous base material, (c) forming a carbon layer on the conductive porous base material, and (d) a conductive porous material having the carbon layer. The steps of firing the base material include steps (a) to
The present invention relates to a method for manufacturing a gas diffusion electrode for a polymer electrolyte fuel cell, which has the order of (d). In this case, in the step (b), it is preferable to dry in a temperature atmosphere of 50 to 120 degrees. Further, in the step (d), 250 to 400
The firing is preferably performed in a temperature atmosphere of ° C. Furthermore, in the step (a), the water repellent treatment liquid preferably contains a fluororesin. As the conductive porous substrate,
For example, it is preferable to use carbon paper, carbon cloth and carbon felt. Further, in the step (c), in order to form the carbon layer on the conductive porous substrate, it is preferable to use, for example, a screen printing method, a spray method, a curtain coating method or a roll coating method.

Next, the present invention provides a polymer electrolyte membrane, an anode and a cathode sandwiching the polymer electrolyte membrane, an anode-side conductive separator plate having a gas flow path for supplying a fuel gas to the anode, and the cathode. A polymer electrolyte fuel cell comprising a cathode-side conductive separator plate having a gas flow path for supplying an oxidant gas,
The present invention relates to a polymer electrolyte fuel cell in which the anode and the cathode are gas diffusion electrodes obtained by the method for producing a gas diffusion electrode for a polymer electrolyte fuel cell. In this case, it is preferable that the gas diffusion electrode of the anode and the gas diffusion electrode of the cathode have different fluororesin contents.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION A method for manufacturing a gas diffusion electrode for a polymer electrolyte fuel cell according to the present invention will be described in the order of steps. First, in step (a), the conductive porous substrate is immersed in the water repellent treatment liquid. As the conductive porous substrate,
In the polymer electrolyte fuel cell, a conventional sheet-like material that constitutes an electrode (anode and cathode) together with a catalyst layer can be used, and examples thereof include a metal porous base material and a carbon porous base material. . Among them, it is preferable to use, for example, carbon paper, carbon cloth and carbon felt made of carbon fiber because they have excellent electric conductivity and high gas diffusion ability.

Next, the water repellent treatment liquid may be a conventional one used for imparting water repellency to the conductive porous substrate, for example, an aqueous dispersion of fluororesin or fluorine. Examples include alcohol dispersion of resin. Among them, an aqueous dispersion of a fluororesin is preferable from the viewpoint of easy exhaust gas treatment during drying. Examples of the fluororesin include tetrafluoroethylene-hexafluoropropylene copolymer, polytetrafluoroethylene (PTFE), tetrafluoroethylene-ethylene copolymer and the like. The dipping method and conditions are not particularly limited as long as the water-repellent treatment liquid is sufficiently impregnated in the conductive porous substrate,
Those skilled in the art can appropriately select.

Next, in the step (b), the step (a)
The conductive porous substrate immersed in the water repellent treatment liquid is taken out and dried. The drying temperature is 50 to 12 because the solvent or dispersion medium other than the surfactant in the dispersion is quickly dried (for example, water or alcohol).
It may be 0 ° C, and preferably 80 to 100 ° C. The drying time varies depending on the drying temperature, but is 20 to 9 for the reason of shortening the process control time.
It may be about 0 minutes.

In step (c), the carbon ink is applied onto the dried conductive porous substrate to form a carbon layer. The carbon ink used here is water-based, and examples of carbon include acetylene black (for example, Denka Black manufactured by Denki Kagaku Kogyo Co., Ltd.) and Ketjen Black (for example, Ketj manufactured by Lion Co., Ltd.).
en Black EC), furnace black (for example, Vulcan XC72 manufactured by CABOT Co., Ltd.) and the like can be used. In order to obtain the water-based carbon ink, water is mixed with carbon black. At this time, it is preferable to add a surfactant in order to improve the wettability of carbon black and improve the dispersibility. As such a surfactant, for example, octylphenoxypolyethoxyethanol (for example, Tr manufactured by ACROS ORGANICS
Iton X-100), alkyl ether, alkyl phenyl ether and the like. The primary particle size of carbon black may be in the range that does not impair the effects of the present invention, but is preferably 30 to 40 nm.

Additives such as a water repellent and a polymer electrolyte may be mixed with the carbon ink as long as the effects of the present invention are not impaired. As a method for forming the carbon layer on the conductive porous substrate, a conventionally known method can be used, and examples thereof include a screen printing method, a spray method, a curtain coating method and a roll coating method. After coating, the coating is dried, for example, at 60 ° C. for 30 minutes, although it depends on the coating method.

Next, in step (d), the conductive porous substrate having the carbon layer is fired to obtain a gas diffusion electrode for a polymer electrolyte fuel cell. The firing at this time is
250 to 250 because of the complete removal of the surfactant.
In a temperature atmosphere of 400 ° C, further 300 to 380 ° C
It is preferable to perform the firing in an atmosphere of temperature. Although the firing time varies depending on the firing temperature, it may be about 30 to 120 minutes from the point of time to remove all the surfactant.

The gas diffusion electrode made of the conductive porous substrate obtained as described above has excellent water repellency, and a carbon layer is uniformly and surely formed on the conductive porous substrate. To be done. By forming a catalyst layer on such a gas diffusion electrode and using it as an anode and a cathode, a polymer electrolyte fuel cell having good cell characteristics can be obtained. Therefore, the present invention provides a polymer electrolyte membrane, an anode and a cathode sandwiching the polymer electrolyte membrane, an anode-side conductive separator plate having a gas flow path for supplying a fuel gas to the anode, and an oxidant gas to the cathode. A polymer electrolyte fuel cell comprising a cathode-side conductive separator plate having a gas flow path to be supplied, wherein the anode and cathode are obtained by the method for producing a gas diffusion electrode for a polymer electrolyte fuel cell. It also relates to a polymer electrolyte fuel cell including a diffusion electrode.

In this case, it is preferable that the content of the fluororesin in the gas diffusion electrode of the anode and the content of the fluorocarbon resin in the gas diffusion electrode of the cathode after firing are different from the viewpoint of keeping a good water balance inside the battery. However, since the water balance varies depending on the operating conditions and environment of the fuel cell, the balance of the fluororesin content of the gas diffusion electrodes of the anode and the cathode can be appropriately changed within a range that does not impair the effects of the present invention. . Specifically, from the viewpoint of efficiently removing water generated in the cathode, for example, the content of the fluororesin in the gas diffusion electrode of the anode is set to 5 to 30% by weight, and the content of the fluororesin in the gas diffusion electrode of the cathode is set to 30 to 30% by weight.
It is preferably 50% by weight. In this way, in order to adjust the fluororesin content of the electrode, the amount of fluororesin contained in the water repellent treatment liquid may be appropriately adjusted in step (a) of the method for producing a gas diffusion electrode.

Besides, a polymer electrolyte membrane, an anode side conductive separator plate having a gas flow path for supplying a fuel gas to the anode, and a cathode side conductive separator plate having a gas flow path for supplying an oxidant gas to the cathode. For the above, a conventionally known one may be used. Further, the polymer electrolyte fuel cell of the present invention can also be manufactured by a conventionally known method except for the method for manufacturing the gas diffusion electrode. Furthermore, when manufacturing the gas diffusion electrode of the present invention and when manufacturing a fuel cell, each step can be performed separately, but all steps are performed on one line to produce continuously. You can also Besides, various design changes can be made within a range that does not impair the effects of the present invention.

[0017]

EXAMPLES The present invention will be described below in detail with reference to the drawings using examples, but the present invention is not limited thereto. << Example 1 and Comparative Example 1 >> First, an aqueous dispersion of tetrafluoroethylene and a hexafluoropropylene copolymer (ND-1 manufactured by Daikin Industries, Ltd.) and water, and a volume ratio of the copolymer and water. Was mixed to give a water repellent treatment liquid A. Next, carbon paper (TGP-H-120 manufactured by Toray Industries, Inc.) cut into a predetermined size as a conductive porous substrate was placed in a closed container, and the inside of the container was depressurized. After that, the water-repellent treatment liquid A is introduced into the depressurized container, and the carbon paper is treated with water-repellent treatment liquid A
It was immersed in it for 10 minutes. After 10 minutes, the immersed carbon paper was taken out and placed in a dryer to evaporate water sufficiently. The temperature of this dryer is 90 ° C and the drying time is 90
Minutes.

The dried carbon paper was taken out and coated with a water-based carbon ink. Acetylene black, water and surfactant (Triton X-100) 15:
Aqueous carbon ink A was prepared by mixing in a weight ratio of 1:84, and was applied onto dried carbon paper using a spray application device. Here, for comparison, the water-based carbon ink A was applied to a carbon paper which was dried and then baked at 360 ° C. for 1 hour. At this time, when the water-based carbon ink A is applied to the carbon paper which is dried only after the water repellent treatment, the surface condition is uniform,
Even after being placed in a dryer at 50 ° C. and dried, a uniform carbon layer could be formed without cracks or the like. On the other hand, in the case where the water-based carbon ink A is applied to the carbon paper that has been subjected to the firing treatment, the carbon ink is not impregnated into the carbon paper at all, and the carbon layer is in a state of floating on the surface of the carbon paper. There was also a part where I was playing. When this was dried in a dryer at 50 ° C. as before, cracks were generated in the carbon layer.

These carbon papers with carbon layers were baked at 360 ° C. for 90 minutes to remove anything other than fluororesin. Here, the fluororesin content of the gas diffusion electrode A was 33% by weight. The gas diffusion electrodes A and B produced in this manner sandwich a polymer electrolyte membrane (Nafion membrane manufactured by DuPont, USA) having a catalyst layer (a layer composed of 50% Pt-carrying carbon and a polymer electrolyte) on both sides. A single cell was constructed and set in a single cell test device to examine the battery performance. In the unit cell, the gas diffusion electrode and the catalyst layer form an electrode. In this test, hydrogen gas was passed through the anode and air was passed through the cathode of the prepared unit cell at a cell temperature of 80 ° C. and a fuel utilization rate of 80%.
%, And the air utilization rate was 40%. The humidification was adjusted so that the hydrogen gas had a dew point of 75 ° C. and the air had a dew point of 60 ° C. Here, FIG. 1 shows the relationship between the battery voltage and the current density, which is the battery characteristic of the unit cell using the gas diffusion electrode A or the gas diffusion electrode B. As is clear from FIG. 1, the battery characteristics are improved when the gas diffusion electrode A is used. This is considered to be because when the gas diffusion electrode B was used, the uniformity of the carbon layer was insufficient and the contact between the catalyst layer and the carbon layer was reduced.

Examples 2 and 3 Instead of carbon paper, carbon cloth (GF manufactured by Nippon Carbon Co., Ltd.)
-20-P7) or using carbon felt,
A battery was manufactured using the gas diffusion electrode manufactured in the same manner as in Example 1, and the battery characteristics were examined. The results were almost the same as when carbon paper was used, and the battery characteristics of Comparative Example 1 in which the carbon layer was formed by performing the water repellent treatment and the firing treatment were inferior.

Examples 4 to 10 Next, when the carbon paper is dipped in the water repellent treatment liquid A and then dried, the drying temperature is in the range of 20 to 150 ° C., 20, 40, 60, and
The case where the temperature was changed to 80, 100, 120 or 140 ° C. was examined. When the drying temperature was 50 ° C. or lower, the time required for drying was at least 10 hours or longer. Further, when dried at a temperature higher than 120 ° C., the phenomenon that the carbon paper was destroyed was observed. It is considered that this is because the water that has entered the carbon paper is exposed to a high temperature of not less than the boiling point and the volume thereof is largely changed. In consideration of shortening the drying time and avoiding damage to the carbon paper, it is considered that the optimum drying temperature is in the range of 50 to 120 ° C.

<< Examples 11 to 16 >> Next, the carbon ink is applied and dried in the same manner as in Example 1, and then the firing temperature of the conductive porous substrate is set to the obtained fuel having a gas diffusion electrode. The effect of the battery on the battery characteristics was investigated. In the range of 200 to 450 ° C., the temperature (20
0, 250, 300, 350, 400 or 450 ° C)
A unit cell was prepared in the same manner as in Example 1, using the carbon paper with a carbon layer, which was the gas diffusion electrode obtained by firing at. Table 1 shows the firing temperature and the current density of 0.7 A / c.
The relationship with the battery voltage at m ² is shown.

[0023]

[Table 1]

From the results shown in Table 1, it can be seen that the fuel cell provided with the gas diffusion electrode obtained by using the firing temperature of 250 to 400 ° C. has excellent cell characteristics. 250
It is considered that at a firing temperature lower than ° C, the surfactant in the carbon paper or the carbon layer, which is the conductive porous substrate, cannot be completely removed, and the water repellency is reduced, so that the battery characteristics are reduced. Further, it is considered that at a high baking temperature of 400 ° C. or higher, the structure of the carbon paper itself becomes brittle, so that the battery characteristics deteriorate. As described above, by using the present invention, it is possible to realize a gas diffusion electrode having a uniform carbon layer and an electrode without cracks, and by using the gas diffusion electrode, it is possible to produce a polymer electrolyte fuel cell having higher characteristics. it can.

Example 17 Tetrafluoroethylene-hexafluoropropylene copolymer aqueous dispersion (ND-1 manufactured by Daikin Industries, Ltd.) and water, and the copolymer-water volume ratio of 2: Mixing so as to be 1 to prepare a water repellent treatment liquid B for water repellent treatment of the conductive porous substrate. A gas diffusion electrode C was obtained in the same manner as in Example 1 except that this treatment liquid was used. The amount of fluororesin of the gas diffusion electrode A produced in Example 1 was 30% by weight, whereas the amount of fluororesin of the gas diffusion electrode C was 42% by weight. Using these gas diffusion electrodes, a single cell was produced in the same manner as in Example 1. In this case, the gas diffusion electrode A
On the anode side and the gas diffusion electrode C on the cathode side. The prepared unit cell was set in a unit cell test apparatus, and the cell performance was examined under the same measurement conditions as in Example 1.

FIG. 2 shows a fuel cell in which the gas diffusion electrode A of Example 1 is used as both an anode and a cathode, and a fuel cell in which the gas diffusion electrode A is used as an anode and the gas diffusion electrode C is used as a cathode. Characteristics (relationship between current density and battery voltage)
Are shown in comparison. From FIG. 2, it can be seen that the fuel cell manufactured in this example has further improved cell characteristics than the fuel cell manufactured in Example 1. It is considered that this is because the gas diffusion electrode C having strong water repellency is used on the cathode side, so that water generated on the cathode side during power generation is more easily repelled. In this embodiment, the amount of fluororesin on the cathode side is set to be larger than that on the anode side. However, since the water balance varies depending on the operating conditions and environment of the battery, the amount of fluororesin that is the water repellent material is adjusted accordingly. The balance also needs to be changed and can be set freely within the applicable range of the present invention.

[0027]

As described above, according to the present invention, according to the method for producing the gas diffusion electrode constituting the electrode used in the polymer electrolyte fuel cell, the conductive porous substrate is used as the water repellent treatment liquid. Since the carbon layer is formed on the surface after the immersion and drying, cissing and uneven coating of the water-based carbon ink when forming the carbon layer can be reduced as much as possible. Moreover, since it is not necessary to perform baking after the water repellent treatment, the number of manufacturing steps can be reduced. Furthermore, by configuring the fuel cell using the gas diffusion electrode manufactured by such a method, it is possible to reduce the in-plane variation in water repellency as compared with the related art and to obtain a fuel cell having stable cell characteristics. Further, by changing the fluorine resin content of the gas diffusion electrodes on the anode side and the cathode side, the water retention state inside the cell can be improved, and it can be expected to obtain a fuel cell having improved cell characteristics.

[Brief description of drawings]

FIG. 1 is a diagram showing cell characteristics of fuel cells manufactured in Example 1 and Comparative Example 1 of the present invention.

FIG. 2 is a diagram showing cell characteristics of the fuel cells produced in Example 1 and Example 17 of the present invention.

Front page continuation (72) Inventor Osamu Sakai 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor, Yasushi Sugawara 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. (56 ) References JP-A-9-245801 (JP, A) JP-A-8-78020 (JP, A) JP-A-9-259893 (JP, A) JP-A-7-130374 (JP, A) JP-A-7-130374 (JP, A) 6-330367 (JP, A) JP 7-296818 (JP, A) JP 9-245800 (JP, A) JP 2000-67874 (JP, A) (58) Fields investigated (Int.Cl) . ^7, DB name) H01M 4/86 H01M 4/88 H01M 8/02 H01M 8/10

Claims (6)

(57) [Claims] 1. A conductive porous substrate comprising (a) a surfactant.
A step of immersing in a water repellent treatment liquid containing (b) the conductive porous substrate from the conductive porous substrate to the surface active agent.
A step of drying at a temperature at which the agent is not removed , (c) a step of forming a carbon layer on the conductive porous substrate, and (d) a step of firing the conductive porous substrate having the carbon layer, A method for producing a gas diffusion electrode for a polymer electrolyte fuel cell, which comprises steps (a) to (d) in this order. 2. The method for producing a gas diffusion electrode for a polymer electrolyte fuel cell according to claim 1, wherein, in the step (b), drying is performed in a temperature atmosphere of 50 to 120 ° C. 3. In step (d), 250 to 400 ° C.
The method for producing a gas diffusion electrode for a polymer electrolyte fuel cell according to claim 1 or 2, wherein the firing is performed under the temperature atmosphere. 4. The method for producing a gas diffusion electrode for a polymer electrolyte fuel cell according to claim 1, wherein in the step (a), the water repellent treatment liquid contains a fluororesin. 5. A polymer electrolyte membrane, an anode and a cathode sandwiching the polymer electrolyte membrane, an anode-side conductive separator plate having a gas flow path for supplying a fuel gas to the anode, and an oxidant gas supplied to the cathode. A polymer electrolyte fuel cell comprising a cathode-side conductive separator plate having a gas flow path, wherein the anode and the cathode are formed by the method for producing a gas diffusion electrode for a polymer electrolyte fuel cell according to claim 1. A polymer electrolyte fuel cell comprising the obtained gas diffusion electrode. 6. The fluororesin content of the gas diffusion electrode of the anode and the gas diffusion electrode of the cathode are different.
The polymer electrolyte fuel cell described.