JPS6124149A - Fuel pole substrate of liquid fuel cell - Google Patents

Abstract

PURPOSE:To reconcile the feed of fuel and the discharge of generated gas and prevent the deterioration of cell performance by providing strong and weak- water repellency portions on the fuel pole substrate. CONSTITUTION:The electrode substrate 21 of a fuel pole 2 is made of carbon fibers and is porous, conductive, and paper-like, and this electrode substrate 21 is water repellency-processed with a 10-30wet% suspension of ethylene tetrafluoride having an average grain size of 0.2-0.4mum. In this case, strong and weak- water repellency portions are provided on the electrode substrate 21. Fuel is repelled at the strong-water repellency portions (a) of the electrode substrate 21 and permeates the weak-water repellency portions (b) to reach a catalyst layer 22, and +ions and electrons are emitted by the electrochemical reaction via catalyst action. Accordingly, no fuel exists at the electrode substrate 21, thus the generated gas can permeate the electrode substrate 21 even if the gas pressure is low, and the feed of fuel and the discharge of the generated gas can be easily reconciled.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a fuel cell that generates electrical energy by directly electrochemically reacting a liquid material. It relates to preventing deterioration of characteristics by achieving both discharge and emission.

[Background of the invention]

Conventionally, in fuel cells for direct power generation using liquids such as methanol or hydrazine as fuel, carbon dioxide or nitrogen gas is generated through a chemical reaction at the fuel electrode, but this generated gas passes through the fuel chamber adjacent to the fuel electrode. Emitted outside the battery.

The fuel electrode is made by coating and firing an active catalyst on one side of a porous, electrically conductive substrate made of carbon retaining material, etc., and the catalyst layer surface faces the oxidizer electrode with an electrolyte interposed therebetween.

In the chemical reaction at the fuel electrode, the fuel that has passed through the electrode base from the fuel chamber becomes + ions, electrons, carbon dioxide gas, or nitrogen gas in the catalyst layer. + ions move to the oxidizer electrode via the electrolyte, electrons move to the oxidizer electrode via the fuel electrode base and an external circuit, and carbon dioxide or nitrogen gas passes through the fuel electrode base and moves to the fuel chamber.

Therefore, it is necessary for the fuel electrode substrate to be compatible with the supply of fuel and the discharge of generated gas, and for this reason, the fuel electrode substrate is impregnated with a suspension of polytetrafluororethylene and made water repellent by heating and baking. There is.

In this case, the entire surface of the fuel electrode base is made water repellent in consideration of the amount of fuel permeation, so the fuel is contained in the entire pores of the fuel electrode base, and the generated gas is distributed to the fuel electrode. If the gas pressure cannot be lower than the fuel liquid pressure applied to the base, the produced gas will not be discharged to the fuel chamber and will accumulate in the fuel electrode base, interfering with fuel supply to the catalyst layer. This means that, for example,
Fuel Cells and Their Applications J, published by Ohmsha in 1981, volumes 66-68.

[Purpose of the invention]

An object of the present invention is to provide a fuel cell that uses a fuel electrode base as a fuel permeation section and a generated gas permeation direct power generation system in order to achieve both fuel supply to the fuel electrode catalyst layer and discharge of gas generated in the catalyst layer. There is a particular thing.

[Summary of the Invention] “The present invention provides a means for making it easier for gas generated by an electrochemical reaction in the fuel electrode catalyst layer to be discharged into the fuel chamber and for fuel in the fuel chamber to be easily supplied to the catalyst layer. The strength of the water repellency is adjusted, and the areas with the strongest water repellency are used as the permeation area for the implanted gas, and the areas that attract are used as the permeation areas for the fuel, so that the supply of fuel to the fuel electrode catalyst layer and the discharge of the generated gas are controlled. This has been made so that both can be compatible.

[Embodiments of the invention]

The present invention will be explained using examples.

As shown in Fig. 1, a fuel electrode 2 and an oxidizer electrode 3 face each other with an alkali or acidic electrolyte 1 in between, and a fuel chamber 4 is arranged on the fuel electrode 2 side. A fuel such as hydrazine or methanol is introduced. on the other hand,
An oxidizing agent chamber 5 is arranged on the oxidizing agent electrode 3 side, and an oxidizing agent such as air is introduced into the oxidizing agent chamber 5 from the outside. Fuel electrode 2
As shown in FIG. 2, it consists of a catalyst layer 22 formed by coating or supporting a platinum-based or non-platinum-based catalyst on a porous conductive electrode base 21 made of carbon fiber or the like. The electrode base 21 of the fuel electrode is made of carbon fiber and has a conductive paper shape with pores as described above.
Water repellency treatment is performed using a suspension of 10 to 30 wt % tetrafluoroethylene having an average particle size of 0.2 to 0.4 μm. In this case, the electrode base 21 is given a name based on its water repellency, as shown in FIG. A is a portion with strong water repellency, and b is a portion with weak water repellency.

A fuel electrode 2 in which a catalyst layer 22 is coated and fired on an electrode substrate 21 with varying water repellency is arranged as shown in FIG. When a fuel such as hydraline is supplied to the fuel chamber 4, the fuel is repelled by the highly water-repellent portions a of the electrode base layer 21, passes through the weakly water-repellent portions a, and reaches the catalyst layer 22, where it reaches the catalyst layer 22. Due to the electrochemical reaction, positive ions and electrons are released, and carbon dioxide gas is produced when methanol is used as fuel, and nitrogen gas is produced when hydrazine is used as fuel. These generated gases repel fuel at the highly water-repellent portion a of the electrode base 21.
No fuel is present, and it is discharged into the fuel chamber 4 through the highly water-repellent portion a, and is further discharged from the gas discharge lower provided in the fuel chamber 4 to the outside of the cell. ``The degree of water repellency of the electrode base 21 varies depending on the material of the electrode base 21, its porosity, and the amount of electrical energy per unit area, but at least it has strong water repellency against the fuel supplied to the fuel chamber 4. Portion a needs to exhibit water repellency.

As described above, since fuel is not present in the highly water-repellent parts of the electrode base 21 of the fuel electrode 2, it is possible for the generated gas to permeate through the electrode base 21 even if the gas pressure is low.
It is possible to easily achieve both fuel supply and discharge of generated gas.

Next, an example of how to increase or decrease water repellency is shown below.

The electrode base 21 was immersed in a suspension of 20 wet'% of tetrafluoroethylene, and after being pulled up, a support as shown in FIG.
The electrode base 21' is placed horizontally on top of the electrode base 21' and dried in the air, and then heat treated at 5°C. The support base 40 is made of plastic, and is provided with slits so that there are parts that come into contact with the electrode base 2'1 and parts that do not come into contact with it. It was attached to the electrode base 21 after the heat treatment. The amount of tetrafluoroethylene is approximately 20% (by weight) greater in the portion of the receiver that is not in direct contact with the stand 40 than in the portion that is in direct contact with it.

The water repellency strength of the electrode base 21 is not limited to the example shown in FIG. 3, but may be of any shape such as circular or angular, and the material of the support 40 is not limited to plastic. It may be made of metal or the like, and the water repellency may be determined by spraying a suspension of tetrafluoroethylene.

〔Effect of the invention〕

According to the present invention, since fuel supply and generated gas discharge are compatible by processing the electrode substrate using a simple method, deterioration in battery performance is not prevented.

It has the advantage of being able to operate for long periods of time with stable performance.

[Brief explanation of the drawing]

Figure 1 is a diagram of the principle of a liquid fuel cell, Figure 2 is a sectional view of the fuel electrode, Figure 3 is a perspective view of the fuel electrode base, and Figure 4 is the support used to make the fuel electrode base water repellent. FIG. 1... Electrolyte, 2... Fuel electrode, 3... Oxidizer electrode,
4...Fuel chamber, 5...Oxidizer chamber, 6...Fuel supply port, 7...Gas $N¥] ZuNaraZ Kuchimine 3rd area

Claims (1)

[Scope of Claims] 1. A fuel electrode for a fuel cell of a direct power generation type that directly obtains electrical energy by chemically reacting liquid fuel, characterized in that the fuel electrode base has a fuel supply point and a generated gas discharge point. Fuel electrode substrate for liquid fuel cells. 2. In claim 1, the water repellency of the fuel supply point and the produced gas discharge port is varied, with the strong water repellency being the produced gas discharge point and the weak water repellency being the fuel supply point. A fuel electrode substrate for a liquid fuel cell characterized by the following. 3. A fuel electrode substrate for a liquid fuel cell according to claim 1, characterized in that tetrafluoroethylene is used as a water repellent treatment agent for the electrode substrate.