JPH01122565A - Composite electrode for fuel cell - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to the structure of a composite electrode for a fuel cell, and particularly to the structure of a water repellent in a composite electrode electrode catalyst layer.

[Conventional technology]

A fuel cell converts the chemical energy of fuel directly into electrical energy, and its configuration is as shown in Figure 3, in which an anode 98 and a cathode 9B are arranged with a matrix 8 containing phosphoric acid sandwiched between them. The electrode catalyst layers 5 of each electrode are stacked together with a separate plate 10 in between, and fuel gas and oxidant gas are supplied to each electrode from an external gas supply system.
Fuel gas and oxidant gas are electrochemically reacted on A and 5B, and as a result, electrical energy is taken out of the system.

Each of the anodes 9A and cathodes 9B is constructed by depositing an electrode catalyst layer 5 on a ribbed electrode base material 4, as shown in FIG. The electrode catalyst layer 5 is constituted by fine catalyst particles 7 having noble metal fine particles 1 supported on the surface of a catalyst carrier 2 bound by fine particles 3 of fluororesin. Inside this electrode catalyst layer 5, the gas from the ribbed electrode base material 4 side and the electrolytic solution from the matrix 8 side come into contact, a three-phase interface is formed, and an electrochemical reaction progresses.

In order to carry out this electrochemical reaction efficiently and stably, it is necessary to increase the number of three-phase interfaces where the catalyst particles 7 in the electrode catalyst layer, the electrolytic solution, and the gas are in contact with each other, and to improve the diffusion of the supplied gas and generated gas. is necessary. For example, the electrode reaction at the anode on the fuel gas supply side is H, -= 2 H" + 2 e
−−−−−−−−−−−−−−−(1), the electrode reaction of the cathode, which is the oxidant gas supply side, is 1/20z +2 H” +2 e”Hz O・−−
--------(21. As shown in the above reaction, water vapor is generated inside the cathode electrode due to the electrode reaction, but the diffusion ability of this water vapor is equal to the hydrogen diffusion ability required in the anode reaction. Since the electrode is relatively small, it is necessary to make the amount of electrolyte within the electrode relatively smaller at the cathode than at the anode to increase the amount of water vapor diffusion.

To this end, conventionally, the firing temperature of each electrode containing a fluororesin as a water repellent was changed to change the water repellency of the electrode catalyst layer, thereby adjusting the amounts of electrolyte at the anode and cathode.

[Problems to be Solved by the Invention] Recently, however, a composite electrode has been proposed in which the anode and cathode are integrally formed instead of forming the anode 9A and cathode 9B of a fuel cell separately. This composite electrode has a structure in which an anode 9A and a cathode 9B are joined via a separate plate 10, as shown in FIG. Such a composite electrode is formed by joining electrode base materials with lips through a separate plate 10 to form a composite electrode substrate, and then simultaneously depositing electrode catalyst layers 5A and 5B on each electrode side.

The composite electrode has the effect of reducing the electrical resistance and thermal resistance between the separate plate 0 and the anode 98 and cathode 9B, making the electrode easier to handle. However, in such a composite electrode, since the electrode catalyst layer 5 is fired at the same temperature, a problem arises in that the water repellency of each electrode cannot be adjusted by changing the firing temperature.

The present invention has been made in view of the above points, and its object is to provide a composite electrode in which the anode and cathode can have different water repellency even when fired at the same temperature.

[Means for solving problems]

According to the present invention, the above-mentioned object is to heat and press an electrode catalyst layer containing a water repellent onto both sides of a composite electrode substrate in which electrode base materials with lips are bonded via a separate plate, thereby integrating the anode and cathode electrodes. In the composite electrode for fuel cells formed, the content of the water repellent agent 3 contained in the electrode catalyst layer 5A on the anode side is higher than the content of the water repellent agent 3 contained in the electrode catalyst layer 5B on the cathode side. This is achieved by having fewer electrocatalyst layers. As the water repellent, a fluororesin dispersion or the like is used. The amount of water repellent in the electrode catalyst layer on the anode side is 3 times the amount of water repellent in the electrode catalyst layer on the cathode side.
It is adjusted to be between 0 and 80%.

[Effect]

Fluororesin is water repellent. Since the amount of fluororesin in the electrode catalyst layer on the anode side is smaller than the amount of fluororesin in the electrode catalyst layer on the cathode side, the water repellency of the anode electrode catalyst layer is lower than that of the cathode even if fired at the same temperature. water repellency.

〔Example〕

Water containing a surfactant is added to the carbon catalyst carrier 2 on which platinum fine particles 1 are supported, and the catalyst carrier is well dispersed by ultrasonic waves, and then 40 to 60% by weight of fluororesin dispersion is added as a fluororesin. Mix well to prepare a dispersion of catalyst carrier and fluororesin. A water-soluble organic solvent is added to this dispersion and mixed to coagulate the fluororesin and the catalyst carrier to perform solid-liquid separation. The obtained solid content is thoroughly kneaded to prepare an electrode paste. This paste is rolled with a calender roll, formed into a sheet, and then dried to prepare an electrode film to be used as an electrode catalyst layer on the cathode side. The electrode film used for the electrode catalyst layer on the anode side is the same as above, except that the amount of fluororesin is 3 to 8 in the case of the cathode electrode film.
The amount will be adjusted accordingly. Both electrode films are simultaneously bonded to both sides of an integrated composite electrode substrate having porous lipped electrode base materials on both sides of the separate plate at a fluororesin melting temperature of 320 to 380°C. A fuel cell was constructed using the obtained composite electrode, and the current-voltage characteristics and durability performance of the cell were tested.

[Comparative example]

Electrode films used for the electrode catalyst layer on the cathode side were deposited on both sides of a composite electrode substrate to form a composite electrode, and the characteristics of a fuel cell using this composite electrode were measured.

Figure 1 shows the current-voltage characteristics of the fuel cell, Figure 2 shows the current density 2
The durability of the relationship between time and voltage at 00 mA/- is shown. In FIGS. 1 and 2, 21A and 21B are the conventional method in which the anode and cathode are formed separately without using a composite electrode method, 22A and 22B are the comparative example, and 23
A and 23B are cases related to the embodiment of the present invention. The characteristics according to this example are good.

〔Effect of the invention〕

According to this invention, an anode and a cathode electrode are integrally formed by heat-pressing an electrode catalyst layer containing a water repellent agent on both sides of a composite electrode substrate in which a ribbed electrode base material is bonded via a separate plate. The composite electrode for fuel cells includes an electrode catalyst layer in which the content of water repellent contained in the electrode catalyst layer on the anode side is smaller than the content of water repellent contained in the electrode catalyst layer on the cathode side. The water repellency of the electrocatalyst layer on the side is less than the water repellency of the electrocatalyst layer on the cathode side, and the anode contains relatively more electrolyte than the cathode, and the cathode contains less electrolyte, so The diffusion of water molecules becomes better, and the characteristics and durability of the fuel cell are improved.

[Brief explanation of the drawing]

FIG. 1 is a current-voltage characteristic diagram of a fuel cell using a composite electrode according to an embodiment of the present invention, FIG. 2 is a time-voltage characteristic diagram of a fuel cell using a composite electrode according to an embodiment of this invention, and FIG. FIG. 4 is a perspective view showing the structure of a conventional fuel cell, FIG. 4 is a sectional view showing the structure of an electrode, and FIG. 5 is a perspective view showing the structure of a composite electrode. 3: water repellent, 58 near-node side electrode catalyst layer, 5B: cathode side electrode catalyst layer. ＜＜＜ （△）Technical Senq乎CD co c. (△) T7 exclusive t1.乎

Claims (1)

[Claims] 1) For fuel cells, in which both electrodes, an anode and a cathode, are integrally formed by heat-pressing an electrode catalyst layer containing a water repellent agent on both sides of a composite electrode substrate in which a ribbed electrode base material is bonded via a separate plate. The composite electrode is characterized by comprising an electrode catalyst layer in which the content of the water repellent agent contained in the electrode catalyst layer on the anode side is smaller than the content of the water repellent agent contained in the electrode catalyst layer on the cathode side. Composite electrode for fuel cells.