JPS58163173A - Electrode for fuel cell - Google Patents

Abstract

PURPOSE:To shorten the time till performance comes out and, during working, fix a reaction interface in a catalytic layer yet longer even if the reaction interface is shifted, by providing the water repulsive performance of both electrodes sandwiching an electrolytic layer, with a gradient. CONSTITUTION:An electrode is constituted of a carbon fiber base material 1 and a catalytic layer 12 while strong repulsiveness is given to the carbon fiber base material 11 and then the catalytic layer 12 is provided with such a gradient as causing the water repulsiveness to be weakened toward the electrolytic side from the carbon fiber base material side. The fuel and oxidizer fed from each of top and bottom gas passages 7 diffuse the carbon fiber base material 11 and the catalytic layer 12 of a porous electrode 20 whereby gas is ionized by action of a catalysis at an interface (reaction interface) between the catalytic layer 12 and the electrolyte. Water repulsiveness at the side where the catalytic layer 12 makes contact with the electrolytic layer 5 becomes weak enough so that the catalytic layer 12 gets to fit well with the electrolyte and thereby the reaction interface is formed up in the catalytic 12. As the inside of the catalytic layer 12 is provided with strong water repulsiveness in regular sequence, the reaction interface will not be moved easily and therefore is steadily made up inside the catalytic layer 12.

Description

[Detailed description of the invention] This invention relates to an electrode structure for a fuel cell.

A conventional electrode of this type is shown in FIG. In the figure, (1) is a carbon fiber base material, (2) is a water-repellent layer, (3) is a catalyst layer, and (4) is a hydrophilic layer.
) to (4) constitute the t-pole (to). The electric cells 1Mon are assembled as shown in FIG. 2 to constitute the minimum unit of a fuel cell. In FIG. 2, (5) is an electrolyte layer, (6) is a pair of bipolar plates, and (7) is a gas flow path provided in the bipolar plates.

Next, the operation will be explained. The fuel and oxidizer supplied from the upper and lower gas channels (7) are fed through the porous t
Carbon fiber base material (1) and water-repellent layer (2) of Kyoku Q [)
It diffuses inside and reaches the catalyst layer (3). At the interface with the electrolyte (reaction interface) in the catalyst layer (3), the gas is ionized by the action of the catalyst. The hydrophilic layer (4) is compatible with the electrolyte of the electrolyte layer (5), which is a non-electronically conductive porous member impregnated with an electrolyte, and forms a reaction interface in the catalyst layer (3). In this way, the catalyst layers (3) are connected by the electrolyte, and a potential is generated between the pair of electrodes.

The bipolar plate (6) has an electrolyte layer (5) and a pair of electrodes 01
It is supported between the two, and functions to supply gas and collect current.

Since the conventional electrode α1 is constructed as described above, it is no longer necessary to change the ingredients for each layer and apply it to the base material by a spray method or a leakage method. In addition, in order to exhibit the characteristics, the reaction interface (the interface between the electrolyte and the gas) must reach the catalyst layer and not slip into the water repellent layer, so it takes a certain amount of time to exhibit sufficient characteristics. Another disadvantage is that if the reaction interface passes through the catalyst layer, the properties deteriorate and the life span is shortened.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above.The electrode is composed of a carbon fiber base material and a catalyst layer, and the carbon fiber base material has strong water repellency. By creating a gradient in which the water repellency decreases from the carbon fiber base material side to the electrolyte side, we provide an electrode that can shorten the time it takes to develop sufficient properties and extend its life. It is intended to.

An embodiment of the present invention will be described below with reference to the drawings. Third
In the figure, α is a carbon fiber base material treated with residual water, and (2) is a catalyst layer whose water repellency gradually weakens from the zero side of the carbon fiber base toward the electrolyte layer. (2) constitutes an electrode.

An example of a method for manufacturing the catalyst layer (6) having a gradient in water repellency will be described. The layer (2) contains a certain amount of precious metal, 1
A mixed solution of a catalyst supported on carbon powder and polytetrafluoroethylene is applied onto the carbon fiber base material (b) by a spray method or a leakage method. The thickness of the catalyst layer (6) is 150 to 200 μm, and when it is coated by the above method, it is coated several times. 300°C for each application
It is heated and fired at different temperatures. At this time, the higher the temperature and the longer the holding time, the stronger the water repellency becomes, even if the treatment is repeated at a constant temperature.

Even if the treatment is carried out by gradually lowering the temperature, the desired gradient of the water-repellent car can be obtained.

Next, the operation will be explained. The fuel and oxidizer supplied from the upper and lower gas channels (7) diffuse through the carbon fiber base material of the porous electrode and the catalyst layer (6), and the electrolyte in the catalyst N1I (2). interface with (reaction interface)
The gas is ionized by the action of a catalyst.

Since the water repellency of the side of the catalyst layer (2) in contact with the electrolyte J@ (5) is sufficiently weak, it blends well with the electrolyte and quickly forms a reaction interface in the catalyst layer (2). Since the inside of the catalyst layer (2) has strong water repellency, it does not move easily and forms a stable reaction interface in the catalyst layer (2).

The electrode gradient is connected by an electrolyte as described above, and a potential is generated between the pair of electrodes.

In this way, according to the above embodiment, one type of catalyst layer component can achieve tW
Since the degree of water repellency of i is changed, there is no need to take the trouble of applying a new water layer or water repellent layer.Therefore, only one type of coating material with different ingredients is needed, and coating equipment compatible with the material can be used. In the above example, the carbon fiber base material (b) was made to have residual aqueous properties, but this is not always necessary. Also, touch Kl-(
2) has a gradient so that the water repellency is weak on the side in contact with the electrolyte (5) and strong on the carbon fiber base side, but the strongest water repellency may be given to the intermediate layer. In the above examples, the strength of water repellency was adjusted by heat treatment, but it may also be done by changing the concentration of tritetrafluoroethylene.

As described above, according to the present invention, by creating a gradient in the water repellency of both electrodes sandwiching the electrolyte layer, the time required for properties to appear is shortened, and even if the reaction interface moves during use, Since the reaction interface is fixed in the catalyst layer for a longer period of time, it is possible to provide a more stable and long-life electrode.

Furthermore, since a hydrophilic layer or a water-repellent layer is not specially created, the thickness can be reduced by that amount, and the electrical resistance of unnecessary layers is eliminated, making it possible to reduce output loss.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of a conventional electrode structure, FIG. 2 is a sectional view showing the structure of a fuel cell incorporating the electrode in FIG. 1, and FIG. 3 is a sectional view showing an example of a conventional electrode structure. FIG. 4 is a cross-sectional view showing the structure of a fuel cell to which the electrode in FIG. 3 is applied. In the figure, (5) is an electrolyte layer, and (6) is a gas separation plate. αQ is an electrode. Note that the same reference numerals in each figure indicate the same or corresponding parts. Agent Makoto Kuzuno - Figure 1 Figure 2/Figure 3 Procedural Amendment (Ha Moxibustion) 57715 Showa Year, Month, Day 2, Name of the invention Fuel cell electrode 3, Relationship with the person making the amendment Patent amount 1 territory Address: 2-3, Marunouchi-chome, 1-ku, Tokyo Name (601,) Mitsubishi Electric Corporation Representative: Katayuni Hachibe 4, Agent Address: 2-2, Sanno-chome, Marunouchi-chome, Chiyo, 1-ku, Tokyo Number 3
-g=5, Specification subject to amendment Detailed explanation column 6 of the weir invention, Contents of amendment (1) In the second line of page 5 of the specification, "Shinsui" is corrected to "Shinui" . (2) On page 5, lines 4 and 5 of the same article, there is a statement that says, “Ingredients...
. . . with just one machine" should be corrected to "The coating material only requires one type of component, and the desired electrode can be made with one coating device compatible with the material." (3) On page 5, line 6 of the same document, the phrase "on the base material (b)" is corrected to "also on the base material (11)." (4) "Tritetrafluoro" on page 5, line 12 of the same
Correct that to "polytetrafluoro".

Claims (1)

[Claims] An electrolyte layer made of a non-conductive porous member impregnated with an electrolyte, two water-repellent electrodes sandwiching the electrolyte layer, and a gas separation plate that supplies fuel and an oxidizer to the electrolyte layer. A fuel cell electrode characterized in that both of the electrodes have a gradient in water repellency.