JP2003086191A - Solid polymer fuel cell and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid polymer fuel cell and its manufacturing method stabilizing a polymer electrolyte in catalyst layers and facilitating preparation of catalyst ink. SOLUTION: The solid polymer fuel cell has the catalyst layers on both sides of a solid electrolyte membrane. At least one of the catalyst layers uses carbon powders with at least catalyst particles supported thereon, and also uses no less than two kinds of polymer electrolytes of different characteristics.

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 and a method for producing the same, and particularly to a catalyst layer thereof.

[0002]

2. Description of the Related Art As an electrode of a polymer electrolyte fuel cell, a catalyst layer formed on a porous conductive electrode base material is used.
Usually, these catalyst layers are formed by using a fine carbon powder carrying a noble metal and a solution of a polymer electrolyte having hydrogen ion conductivity, and using a solvent such as water or isopropyl alcohol to prepare a catalyst ink. In general, the catalyst ink is also formed by coating the carbon ink or carbon cloth as an electrode base material with a screen printing method or a spray method after adjusting the viscosity, and then drying or firing.
The electrodes produced in this manner are joined together by hot pressing through the electrolyte membrane to produce a polymer electrolyte fuel cell.

As another method, a catalyst ink is coated on a polymer film by gravure printing or a coater method, dried to form a catalyst layer, and then transferred and bonded to an electrolyte membrane to form a solid polymer type. Methods of making fuel cells have also been proposed. Also in this case, it is general to prepare ink before coating.

As described above, the polymer electrolyte in these catalyst layers is generally added in the state of the polymer electrolyte solution at the stage of preparing the catalyst ink. Therefore, it is often the case that only heat treatment is applied after forming the catalyst layer.

Further, the viscosity and solid content ratio of the catalyst ink are often influenced by the viscosity and solid content ratio of the polymer electrolyte solution, and during the final preparation of the catalyst ink before coating, the solvent component is removed from the catalyst ink. Are taken and measures such as adding a viscosity adjusting agent are taken.

Further, unlike the polymer electrolyte membrane, the polymer electrolyte in the catalyst layer is formed by using the polymer electrolyte solution as described above, so that it is less stable and deteriorates than the polymer electrolyte membrane. Therefore, as proposed in Japanese Patent No. 2881630, heat treatment is added after formation of the catalyst layer,
In many cases, measures such as stabilization are taken.

[0007]

The optimization of the catalyst ink before coating is essential for forming a smooth and uniform catalyst layer. However, in many cases
Optimization of the catalyst ink is often performed because it depends on the viscosity and solid content ratio of the polymer electrolyte solution to be mixed. Usually, the solid content ratio of commercially available polymer electrolyte solutions is 5
It is as low as about 10%. The viscosity of such a polymer electrolyte solution is 0.01 to 0.1 Pa · s (0.1 to 1.
0P), which is very low. For this reason, in the process of optimizing the catalyst ink, measures are taken to evaporate the solvent component to increase the solid content ratio, but it is very difficult to remove the solvent in a predetermined amount, and the reproducibility is reproducible. It is not preferable from the viewpoint. In addition, it is not preferable to increase the viscosity of the catalyst ink by adding a thickener, because impurities are added to the catalyst layer from the viewpoint of battery performance. These methods have a problem that the steps for forming the catalyst layer are complicated.

Further, as described in Japanese Patent No. 2881630, heat treatment after forming the catalyst layer for stabilizing the polymer electrolyte in the catalyst layer is useful from the viewpoint of the durability of the battery. However, after forming the catalyst layer, there is a problem that sufficient heat treatment cannot be performed in consideration of the shape and dimensional change of the catalyst layer.

From the above, there is a demand for a polymer electrolyte fuel cell which stabilizes the polymer electrolyte in the catalyst layer and allows the catalyst ink to be easily prepared, and a method for producing the same.

[0010]

The polymer fuel cell of the present invention is a solid polymer fuel cell in which a catalyst layer is provided on both sides of a polymer electrolyte membrane, and at least one of the catalyst layers has a catalyst. The layer is characterized by having at least carbon powder carrying catalyst particles and two or more kinds of polymer electrolytes having different properties. Two or more polymer electrolytes having different properties can be realized by changing the heat treatment temperature.

Further, it is effective that the catalyst layer has polymer electrolytes having different ion exchange capacities.

Further, the method for producing the catalyst layer comprises a first step of mixing carbon particles carrying catalyst particles and a polymer electrolyte and heat-treating the mixture to prepare a catalyst-supporting carbon powder with the polymer electrolyte. In the catalyst-supporting carbon powder with the polymer electrolyte,
A manufacturing method characterized by having a second step of applying a solution containing a polymer electrolyte and applying a catalyst layer and a third step of heat-treating the applied catalyst layer is effective.

At this time, the heat treatment temperature in the first step and the heat treatment temperature in the third step are different temperatures.

The viscosity of the solution obtained by mixing the catalyst-supporting carbon powder and the polymer electrolyte solution in the first step is the solution containing the polymer electrolyte in the catalyst-supporting carbon powder with polymer electrolyte in the second step. Is lower than the viscosity of the mixed solution.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Since the polymer electrolyte fuel cell of the present invention uses, for example, two kinds of polymer electrolytes having different heat treatment temperatures in the catalyst layer, the conventional polymer electrolyte can be treated with one heat treatment temperature. In contrast, when a battery is constructed, the durability is improved while maintaining the initial characteristics of the battery. Also, by using polymer electrolytes with different ion exchange capacities,
The effect can be further increased.

Further, since the catalyst-supporting carbon powder with the polymer electrolyte is once formed and then added again to the polymer electrolyte solution to prepare the catalyst ink, the solid content ratio must be increased to prepare the catalyst ink. It becomes possible to produce a catalyst ink having a high viscosity. Further, the catalyst-supported carbon powder with a polymer electrolyte prepared in advance can be heat-treated in a wide temperature range within a range where the polymer electrolyte is not thermally deteriorated because the catalyst layer is not formed.

As a result, heat treatment at a higher temperature becomes possible as compared with heat treatment after forming the catalyst layer, and the stability of the polymer electrolyte is improved. Further, since the catalyst layer is formed using the catalyst-supported carbon powder with polymer electrolyte that has been preheated, the heat treatment temperature after the catalyst layer is formed is set low, and the shape and dimensional stability of the catalyst layer are maintained at a high level. The stability of the molecular electrolyte can be ensured.

[0018]

EXAMPLES Examples will be described below.

Example 1 First, the specific surface area is 800 m ^2.
/ G, carbon particles having a DBP oil absorption of 360 ml / 100 g (Ketjen Black International, Furnace Black, product name Ketjen Black EC),
Platinum particles having an average particle size of about 30Å were supported at a weight ratio of 50% to obtain catalyst particles. This was mixed with a 5 wt% hydrogen ion conductive polymer electrolyte solution (SE-5012 manufactured by Aldrich, ion exchange capacity 1.0 meq / g) to prepare a catalyst ink. At this time, the weight ratio of the catalyst particles to the hydrogen ion conductive polymer electrolyte was set to 1: 1.

The catalyst ink is dried under reduced pressure and dry-pulverized to obtain a catalyst-supporting carbon powder A with a polymer electrolyte.
(Hereinafter, referred to as powder A) was produced. This powder A is divided into two and heat-treated at 80 ° C and 160 ° C for 3 hours,
Powder A80 and powder A160 were obtained. These powders were mixed in equal amounts in isopropyl alcohol to prepare a catalyst ink A.
Was produced. For comparison, Powder A80 and Powder A1
Catalyst ink A80 using only 60 and catalyst ink A1
60 was also produced.

The catalyst ink prepared in this manner was used as a carbon paper (TGP-H-90, which became a gas diffusion layer).
(Manufactured by Toray) to form a catalyst layer. These are joined together with a gasket via a polymer electrolyte membrane (Nafion 112, made by DuPont) to form a single cell A, a single cell A80,
A unit cell A160 was produced.

These were set in a unit cell test device and the characteristics of each cell were examined. Hydrogen gas was supplied to the fuel electrode and air was supplied to the air electrode of the prepared unit cell, the cell temperature was 80 ° C, the fuel utilization rate was 80%, the air utilization rate was 40%, and the humidification was hydrogen gas at 75 ° C. The air was adjusted to have a dew point of 60 ° C.

FIG. 1 shows the current-voltage characteristics, and FIG. 2 shows the life characteristics of these batteries at 0.2 A / cm 2 for comparison. From this, it was found that the performance of the unit cell A was excellent in both battery characteristics and life characteristics.

In the unit cell A80, the battery characteristics were high, but the life characteristics were poor. This is probably because the initial battery characteristics were good because the heat treatment temperature of the polymer electrolyte in the catalyst layer was low, but the life characteristics were low because the polymer was not sufficiently activated and stabilized. Was given. On the other hand, in the unit cell A160, the heat treatment temperature is high, so that the adhesion with the catalyst-supporting carbon powder is improved and the durability and life characteristics of the battery are improved, but the gas diffusibility in the catalyst layer is lowered,
The initial characteristics were considered to have deteriorated.

On the other hand, in the unit cell A, since the powders A80 and A120 are mixed, the activated polymer electrolyte exists while maintaining the gas diffusibility in the catalyst layer. As a result, it was considered that the durability was improved while maintaining the initial characteristics.

Next, using the polymer electrolyte solutions having different ion exchange capacities, the same catalyst ink as above was prepared. Nafion solution (S with an ion exchange capacity of 0.9 meq / g)
E-5112, manufactured by DuPont) was used to prepare a catalyst ink in the same manner as above, and these were dried under reduced pressure to prepare a catalyst-supporting carbon powder with a polymer electrolyte (powder B). This was heat-treated at 80 ° C. to prepare powder B80. This powder B80 and the previously prepared powder A160 were mixed in isopropyl alcohol in the same amount in the same manner as above to prepare a catalyst ink,
A unit cell B was produced through the same process.

FIG. 3 shows the current-voltage characteristics of the unit cell B in comparison with the unit cell A. From this, it is understood that the performance of the unit cell B is superior to that of the unit cell A. Also, the result of examining the life characteristics was found to be superior to the unit cell A. This is because a polymer electrolyte with a small ion exchange capacity has a higher stability of the polymer itself than a polymer electrolyte with a large ion exchange capacity, and the stability of the polymer electrolyte becomes higher even if heat-treated at the same temperature. It was considered.

As described above, by using two kinds of polymer electrolytes having different heat treatment temperatures, it is possible to construct a polymer electrolyte fuel cell which is more durable than conventional ones.

Example 2 In this example as well, the catalyst ink prepared in Example 1 was used. However, the polymer electrolyte and the catalyst particles were mixed so that the weight ratio was 0.3: 1, and this was used as catalyst ink C. For comparison, a catalyst ink D was also prepared in which the polymer electrolyte and the catalyst particles were mixed at a ratio of 0.5: 1. This catalyst ink C is dried under reduced pressure,
By dry grinding, a catalyst-supporting carbon powder C with a polymer electrolyte (hereinafter referred to as powder C) was produced. This powder C was heat-treated at 160 ° C. for 3 hours. The powder C after the heat treatment was mixed again in the 5% Nafion solution to prepare the catalyst ink C2. The ratio of the polymer electrolyte to the catalyst-supporting carbon powder in this catalyst ink was set to 0.5.

Here, the viscosities of the catalyst ink C and the catalyst ink C2, and the comparative catalyst ink D were measured using a viscoelasticity measuring device (Rheostress RS150, manufactured by HAAKE, Germany). The viscosity of the catalyst layer ink C at a shear rate of 0.1 (1 / s) is 1 Pa · s, the viscosity of the catalyst layer ink C2 is 100 Pa · s, and the viscosity of the catalyst ink D is 5 Pa · s at the same shear rate. there were.

Next, catalyst ink C2 and catalyst ink D were coated on carbon paper in the same manner as in Example 1. At this time, when the catalyst ink D was used, since the viscosity of the ink was low, the coating could not be performed with good reproducibility, and the coating variation was larger than that of the catalyst layer ink C2. On the other hand, when the catalyst layer ink C2 was used, the catalyst layer could be stably formed without the ink viscosity being too low. After heat treating these catalyst layers at 80 ° C., a polymer electrolyte membrane (Nafion 112, manufactured by DuPont)
It joined together with the gasket and the single cell C2 and the single cell D were produced.

These were set in a unit cell tester and the characteristics of each cell were examined under the same conditions as in Example 1. FIG. 4 shows the current-voltage characteristics of these batteries. As a result, it was found that the unit cell C2 had better characteristics than the unit cell D. This is because when the ink viscosity D when the catalyst ink was applied was lower, the formation state of the catalyst layer was worse and the catalyst layer was non-uniform, and the heat treatment temperature of the polymer electrolyte in the catalyst layer was as low as 80 ° C. It was considered that the activation of the molecular electrolyte was not sufficient.

Although it is possible to raise the heat treatment temperature after forming the catalyst layer, it is difficult to perform heat treatment at a temperature higher than this because the catalyst layer may be cracked or fall off from the carbon paper. On the other hand, in the unit cell C, the carbon powder with the polymer electrolyte was prepared in advance and the heat treatment was performed, so it was considered that the battery characteristics did not deteriorate even if the heat treatment temperature after the catalyst layer formation was low. . Further, since the produced powder C is mixed again with the polymer electrolyte solution, the viscosity of the catalyst ink C2 is higher than that of the catalyst ink D.
As described above, it was considered to be high because the catalyst layer could be stably formed on the carbon paper.

As described above, since the heat treatment can be performed in the state of the catalyst-supporting carbon powder with the polymer electrolyte, even if the heat treatment at high temperature cannot be performed after the formation of the catalyst layer, the polymer electrolyte fuel having high characteristics can be obtained. A battery can be constructed. Further, since the catalyst-supporting carbon powder with the polymer electrolyte is again mixed with the polymer electrolyte solution to form the catalyst ink, the ink viscosity is higher than that of directly preparing the catalyst ink with only the polymer electrolyte solution and the catalyst-supporting carbon powder. Is easy to control, and the catalyst ink in a wide viscosity range can be freely adjusted by the ratio of the initial polymer electrolyte to the catalyst-supporting carbon powder and the addition of a solvent and the like.

Further, according to this method, since the catalyst-supporting carbon powder with the polymer electrolyte is once formed, it is added again to the polymer electrolyte solution to prepare the catalyst ink.
It is possible to increase the solid content ratio for producing the catalyst ink and to produce the catalyst ink having high viscosity. Further, the catalyst-supported carbon powder with a polymer electrolyte prepared in advance can be heat-treated in a wide temperature range within a range where the polymer electrolyte is not thermally deteriorated because the catalyst layer is not formed.

This makes it possible to perform heat treatment at a higher temperature as compared with heat treatment after formation of the catalyst layer, and the stability of the polymer electrolyte is improved. Further, since the catalyst layer is formed using the catalyst-supported carbon powder with polymer electrolyte that has been preheated, the heat treatment temperature after the catalyst layer is formed is set low, and the shape and dimensional stability of the catalyst layer are maintained at a high level. The stability of the molecular electrolyte can be ensured.

[0037]

As described above, since the solid polymer electrolyte fuel cell of the present invention uses two kinds of polymer electrolytes having different heat treatment temperatures in the catalyst layer, the conventional heat treatment temperature is higher by one. When a battery is constructed, durability is improved in comparison with a molecular electrolyte while maintaining the initial characteristics of the battery.

The effect can be further enhanced by using polymer electrolytes having different ion exchange capacities. Further, once the catalyst-supporting carbon powder with the polymer electrolyte is formed, it is added to the polymer electrolyte solution again to prepare the catalyst ink.
The solid content ratio can be increased, and a catalyst ink having a high viscosity can be manufactured.

Further, the catalyst-supported carbon powder with polymer electrolyte prepared in advance can be heat-treated in a wide temperature range within the range where the polymer electrolyte is not thermally deteriorated because the catalyst layer is not formed. . This enables heat treatment at a higher temperature than heat treatment after forming the catalyst layer, and improves the stability of the polymer electrolyte. Further, since the catalyst layer is formed using the catalyst-supported carbon powder with polymer electrolyte that has been preheated, the heat treatment temperature after the catalyst layer is formed is set low, and the shape and dimensional stability of the catalyst layer are maintained at a high level. The stability of the molecular electrolyte can be ensured.

[Brief description of drawings]

FIG. 1 is a diagram showing a first characteristic of the polymer electrolyte fuel cell according to the first embodiment of the present invention.

FIG. 2 is a diagram showing a second characteristic of the polymer electrolyte fuel cell according to the first embodiment of the present invention.

FIG. 3 is a diagram showing a third characteristic of the polymer electrolyte fuel cell according to the first embodiment of the present invention.

FIG. 4 is a diagram showing characteristics of a polymer electrolyte fuel cell according to a second embodiment of the present invention.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Akihiko Yoshida             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Yoshihiro Hori             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. F-term (reference) 5H018 AA06 BB01 BB06 BB08 BB12                       DD06 EE03 EE08 EE17 EE18                       HH00 HH08                 5H026 AA06 BB04 BB08 CX05 EE18                       HH00 HH08

Claims (5)

[Claims] 1. A polymer electrolyte fuel cell having a catalyst layer on both sides of a polymer electrolyte membrane, wherein at least one catalyst layer of the catalyst layer comprises carbon powder carrying at least catalyst particles, and characteristics. A polymer electrolyte fuel cell comprising two or more kinds of polymer electrolytes different from each other. 2. The polymer electrolyte fuel cell according to claim 1, wherein the catalyst layer has polymer electrolytes having different ion exchange capacities. 3. A method for producing a catalyst layer comprises a first step of mixing carbon particles carrying catalyst particles and a polymer electrolyte and heat-treating the mixture to prepare a catalyst-supporting carbon powder with the polymer electrolyte. A second step of applying a solution containing a polymer electrolyte to the catalyst-supported carbon powder with a polymer electrolyte to apply a catalyst layer, and a third step of heat-treating the applied catalyst layer, The method for producing a polymer electrolyte fuel cell according to claim 1 or 2. 4. The method for producing a polymer electrolyte fuel cell according to claim 3, wherein the heat treatment temperature in the first step and the heat treatment temperature in the third step are different temperatures. 5. A solution containing a polymer electrolyte in the second step, wherein the viscosity of a solution obtained by mixing the carbon powder carrying the catalyst in the first step and the polymer electrolyte solution is added to the carbon powder carrying the catalyst with the polymer electrolyte in the second step. 5. The method for producing a polymer electrolyte fuel cell according to claim 3, wherein the viscosity is lower than the viscosity of the mixed solution.