JPS59146163A - Manufacturing method of electrode for fuel cell - Google Patents

Abstract

PURPOSE:To manufacture the titled electrode that keeps the active point of a catalyst and applies effective water repellency by creating a catalytic layer on a base material, pressing, baking, and fluorinating it, and forming a graphite fluoride coat. CONSTITUTION:A cataylytic layer 4 is created by coating a base material 3 whose principal component is carbon with a mixture between conductive porous particles whose principal component is the carbon that carries noble metals catalysts and water repellent polymer and is pressed and baked. Then the base material 3 that forms the catalytic layer 4, that is, an electrode 2 is inserted by a gas separation plate 1 for a compact single cell and a flat plate 5 and proper surface pressure is applied by a press plate 8. Subsequently, F2 gas or the mixed gas between the F2 gas and inert gas is supplied from an inlet tube 7 and is made to flow into the protruded and recessed flow path of the separation plate 1 from a manifold 10. The gas enters the electrode 2 and is discharged from an outlet tube 11. At the same time, a graphite fluoride coat is formed on the surface of carbon by heating a heating device 9 and fluorinating both the base material 3 and catalytic layer 4.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing an electrode for a fuel cell, and in particular to improving its water repellency.

Electrodes used in fuel cells generally consist of a carbon-based base material supporting a precious metal catalyst, carbon-based conductive porous particles, a binder, and a water-repellent polymer added as a water-repellent agent. A catalyst layer is created by applying a mixture of the above and the like by a spraying method or a filtration method, and the base material on which this catalyst layer is created is pressure-fired. In a fuel cell, a reaction occurs at an interface where eight components, a catalyst, an electrolyte, and a reactant gas, coexist, that is, at a three-phase interface. Therefore, a paper-like gas-permeable structure of about 600 microns made of carbon fiber is used as the base material that serves as a path for the reaction gas.
For this reason, all water-repellent treatments are performed using fluororesin metal such as polytetrafluoroethylene (hereinafter abbreviated as PTFEt) to prevent the base material from getting wet with the electrolyte and inhibiting the permeation of the reaction gas. . In addition, for example, PTF added to the catalyst layer as a binder and water repellent]! Water-repellent polymers such as t play an important role in maintaining the entire three-phase interface.

This water-repellent polymer is in the form of particles until it is applied to the base material, but it melts during the pressure firing process and binds the conductive porous particles, giving water repellency to the conductive porous particles and providing three-phase This will form an interface.

Therefore, the ratio of the water-repellent polymer mixed with the conductive porous particles and the firing temperature during the pressure firing process greatly influence the formation of the three-phase interface, and greatly influence the battery characteristics and its long-term stability. For example, if the amount of water-repellent polymer is too small or the firing temperature is too low, the catalyst layer becomes easily wetted by the electrolyte, making it impossible to maintain the three-phase interface. On the other hand, if there is too much water-repellent polymer or the firing temperature is too high,
The problem arises that the active sites of the catalyst are covered with the water-repellent polymer, resulting in a low utilization rate of the catalyst and failure to obtain good battery characteristics.

In this way, how to maintain water repellency and make maximum use of the active sites of the catalyst is an important issue in order to maintain excellent battery characteristics and long-term stability, but conventional methods cannot The formation of the three-phase interface often relies on chance, making it difficult to effectively utilize the active sites of the catalyst. On the other hand, regarding the water repellent treatment performed on the base material, FT, which is a carbon fiber all-insulator,
By covering with a water-repellent polymer such as FK, the contact resistance between the base material and the #X layer or between the base material and the gas separation plate increases, resulting in disadvantages such as deterioration of battery characteristics.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above.
A process of applying a mixture of conductive porous particles mainly composed of carbon supporting a noble metal catalyst and a water-repellent polymer to form a catalyst layer on the base material, and pressurizing the base material on which this catalyst layer has been created. By performing a firing process and a process of fully fluorinating the base material on which the catalyst layer was created to form a coating of fluorinated graphite, the aim is to maintain the active sites of the catalyst and provide effective water repellency. There is.

Fluorinated graphite has better water repellency than I'TFFI, and is used in solid lubricants as a material with extremely superior chemical and thermal stability. 2 for fluorinated graphite
There are several types of stable compounds, whose chemical formulas are (CF)n and (
C, F) Represented by n, it is a substance that is structurally and physically different from PTFIC.

As a method of forming fluorinated graphite, carbon ka KF.
There is a wet method in which electrolysis is performed in a 2HF bath and a dry method in which heating is performed in a carbon-gold-fluorine atmosphere.Hereinafter, the latter dry method will be explained with reference to the drawings.

The drawing is a side view showing the inside of a fluorination apparatus according to an embodiment of the present invention with a part removed, and the electrode area I
The case of fluorinating a small single cell test electrode of about Q Oct 1 will be explained. In the figure, (1) is a gas separation plate for small single cell testing, (2) is an electrode made of a base material (3) and a catalyst layer (4), (5) is a flat plate made of carbon, for example, and (6) is an electrode made of a base material (3) and a catalyst layer (4). is a fitting made of fluororesin, (7) is an inlet pipe made of fluororesin, (8) is a holding plate, (9) is a heater, (1 (1 is a manifold, +19 is an outlet connected to the manifold at the opposite end) It's a tube.

A method of manufacturing a fuel cell electrode using this apparatus will be described below. First, a mixture of conductive porous particles mainly composed of carbon supporting a noble metal catalyst and a water-repellent polymer is applied to a base material (3) mainly composed of carbon to form a catalyst layer (3).
4) is prepared and baked under pressure. Note that since the water-repellent polymer such as PTFEI added at this time is intended to bind the conductive porous particles, the amount is extremely small compared to the conventional example.

Next, the base material (3) on which this catalyst layer (4) was formed, that is, the electrode (2), the gas separation plate (1) for all small single cells, and the flat plate (5).
) and apply surface pressure of about 8 to 5 kg/- with the presser plate (8). Place the manifold 00′+: on the uneven reaction gas flow path provided on the gas separation plate (1), connect the fitting (61$”) and the pipe (7) made of fluororesin to this,
Place it in the heater (9). introduction? +7) 'i Connect to a nitrogen gas cylinder (not shown), flow nitrogen gas, and extract it'! +Il+ to keep the channel clean. Next, connect the inlet g (7) to a fluorine gas cylinder (not shown).
reading, fluorine gas or fluorine gas and e.g. argon,
Supply a gas mixture with an inert gas such as helium or nitrogen.

The fluorine gas flows from the manifold flow path O to the concavo-convex channel of the gas plate (1), enters the porous electric pupil from there, and is discharged from the outlet pipe (11). At the same time, heat with a heater (9>'1200 to 8500 for several minutes to several tens of minutes. Through the above steps, the base material (3) and the contact km
(4) is fluorinated and a broken film of fluorinated graphite is formed on the carbon surface, but the base material 13) in contact with the convex part of the reaction gas flow path of the gas separation plate (1) is not fluorinated. do not have.

Therefore, the electronic conductivity between the gas separation plate (1) and the base material 13) is maintained. In addition, since fluorine gas only reacts with carbon and does not react with precious metal catalysts, it is possible to provide water-repellent gold near the active sites without covering the active sites of the catalyst with a broken film of fluoride. .

In addition, the ruptured membrane of fluorinated graphite of which VA degree and 1f is in the form IN.
, the sample is 1 part of the fluorine gas supplied during fluorination.
The optimum conditions can be selected depending on the type of conductive porous particles and the water-repellent polymer to be added, although this depends on the type of inert gas to be mixed and the heating temperature and time.

In addition, in Example 2, the base material (3) and the catalyst layer (4) were fluorinated by a dry method, but they may also be fluorinated by a wet method, resulting in the same effect as in Example 2. Have a meeting.

In the above example, the electrode for a small single-cell V battery (2
) has been described, but it may also be an electrode for a large laminated battery, with the same effect as in the above example. play.

Further, the order of the step of fully pressurizing the base material (3) on which the catalyst layer (4) is formed and the step of fluorinating it to form a ruptured film of fluorinated graphite may be reversed, as in the above example. It has the effect of

As shown above, this invention allows a noble metal catalyst to be added to a base material mainly composed of carbon and gold. Step 1 of applying a mixture of conductive porous particles containing supported carbon as a main component and a water-repellent polymer to create a catalyst coating on the substrate and firing the substrate under pressure, and forming the catalyst layer. Since the prepared base material was subjected to a step of completely fluorinating and completely removing the fluorinated graphite, it is possible to maintain all the active points of the melting medium while imparting effective water repellency.

[Brief explanation of drawings]

The drawing is a side view showing the inside of a fluorination apparatus according to an embodiment of the present invention, with some parts removed. In the figure, (1) is a gas separation plate, (2) is an electrode, and (3) is a gas separation plate.
) is the base material, (4) is the contact W, layer, (5) is the flat plate, (6) is the joint, (7) is the tube, (8) is the holding plate, and (9) is the heater. Agent Makoto Kuzuno

Claims (1)

[Claims] A step of applying a mixture of conductive porous particles mainly composed of carbon supporting a noble metal catalyst and a water-repellent polymer to a base material mainly composed of carbon to form a complete catalyst layer on the base material. A method for producing an electrode for a fuel cell, which includes the steps of pressurizing and firing a base material on which a catalyst layer has been entirely formed, and fluorinating the base material on which a catalyst layer has been formed to form a coating of fluorinated graphite.