JPS59209278A - Fuel cell - Google Patents

Abstract

PURPOSE:To disperse electrolyte in an electrode catalyst layer or on an interface of an electrode and electrolyte, and allowing effective ionic conductivity by water penetration to increase cell performance by adding ion exchange group or placing a substance having ion exchange group between electrolyte and an electrode or in an electrode catalyst layer. CONSTITUTION:Ion exchange group is added or substance having ion exchange group is placed between an electrolyte 31 and electrodes 21 and 22 or in an electrode catalyst layer. For example, a polyelectrolyte 111, such as liquid state polystyrene sulfonic acid or poyethylene sulfonic acid is impregnated in a catalyst layer of a fuel electrode 21, or fixed by kneading in catalyst layer when the electrode is manufactured. A polyelectrolyte 112 is arranged between an ion exchange film 31 and the electrode when a unit cell is assembled, if necessary.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a fuel cell, and more particularly to a structure between an electrolyte and an electrode.

[Background of the invention]

FIG. 1 shows a diagram of the principle of a unit cell 1 of a fuel cell that facilitates electrochemical reactions. As shown in the figure, the electrode 2 is a fuel electrode 2
1 and an oxidizer electrode 22, with an electrolyte chamber 3 between the two electrodes.
It consists of A fuel chamber 4f adjacent to the fuel electrode 21 to which the fuel 6 is sent constitutes an oxidizer chamber 5 adjacent to the oxidizer electrode 22 to which the oxidizer 7 is sent. As the fuel 6, a gas such as hydrogen or a liquid such as methanol or hydrazine is used. As the oxidizing agent 7, oxygen or a gas containing oxygen (air is generally used) is used. Further, as a product 81, carbon dioxide gas is generated in the fuel electrode 21 when methanol is used as the fuel, and carbon dioxide is generated when hydrazine is used as the fuel.

On the other hand, at the oxidizer electrode 22, if the electrolyte is acidic, the product 82
Water is generated as Note that water is generated at the fuel electrode 21 when the electrolyte is basic.

In the configuration of a unit battery as shown in Figure 1, if a liquid such as sulfuric acid or potassium chloride is used as the electrolyte, the liquid leaks from the electrolyte chamber 3 and permeates into the electrodes, which is good from a performance standpoint. It is generally used because it provides certain characteristics.

However, this method has drawbacks such as the risk of the electrolyte leaking outside and the requirement for acid and base resistance for the auxiliary equipment used to operate the fuel cell, making it difficult to simplify.

To improve this, non-liquid polymer electrolytes such as sulfuric acid and potassium hydroxide, and ion exchange membranes are being considered as electrolytes. In such a case, the electrolyte tends to ooze out insufficiently, and if the electrolyte permeates into the electrode catalyst layer, there is a drawback that power and performance are insufficient.

[Purpose of the invention]

An object of the present invention is to reconsider the interface between the electrolyte 3 and the electrode 2 and to provide a method for filling this interface with the electrolyte.

[Summary of the invention]

The present invention is a method that improves the interface between an electrolyte and an electrode using the simplest method and eliminates the drawbacks of the above-mentioned known techniques.

Taking the case where an ion exchange membrane is used as an electrolyte as an example, as shown in FIG. 2, the electrolyte 3 is an ion exchange membrane,
A fuel electrode 21 and an oxidizer electrode 22 are combined. The electrode 2 consists of an electrode base coated with a catalyst. Even if this electrode 2 is overlapped with an ion exchange membrane and water permeates therein, the contact area 10 between the electrode 2 and the electrolyte 3 is small and a void layer 9 is present as shown in FIG. Therefore, even if ions are generated at one electrode, there is a large resistance due to the void layer 9 in passing through the electrolyte to the other electrode.

This is because the void layer 9 exhibits large resistance to ion conduction even in the presence of water. If we look at the finer details, the catalyst layer of the electrode 2 is also porous, and platinum or the like is usually attached to the carbon supporting material.In order to achieve effective ionic conduction, this platinum must be It is necessary that an electrolyte be dispersed around such highly active particles.

Therefore, in order to bring this electrolyte into sufficient contact with the electrode catalyst layer, the ion exchange membrane alone is not sufficient as an electrolyte, and it is necessary to combine it with another electrolyte.

Until now, only liquids such as sulfuric acid and potassium have been used.

By using a polymer electrolyte instead of the above-mentioned liquid, it can fill the inside of the catalyst layer of the electrode or between the electrode and the ion exchange membrane, and can perform the role of good ion conduction.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. The catalyst layer of the electrode 2 is impregnated with a liquid polymer electrolyte 111 (for example, polystyrene sulfonic acid and polyethylene sulfonic acid have large molecules, so they do not easily leak outside), or the catalyst layer is formed in advance during electrode fabrication. It can be fixed by a method such as kneading. Further, if necessary, it is also easy to interpose the polymer electrolyte 112 between the ion exchange membrane 31 and the electrodes when assembling the unit battery. In this case, apply a paste of polymeric acid to the surface of the catalyst layer, or
It may be kneaded in advance when forming the catalyst layer. This method is similar even when the electrolyte is a base.

Further, the electrolyte 3 is a solid or sol-like semi-solid consisting of an ion exchange membrane or a polymer electrolyte, and examples of acidic electrolytes include polystyrene sulfonic acid, polyethylene sulfonic acid, and polystyrene divinylbenzene. These materials can be controlled relatively arbitrarily by appropriately selecting the degree of crosslinking.

In other embodiments, it can be used by applying it to the fine particulate solid or semi-solid catalyst layer used in the electrolyte 3, or by kneading it in advance when forming the decomposition medium. When it comes to solid materials, submicron particles exhibit better water absorption and ion conductivity than particles of several micrometers, and those with less strong crosslinking exhibit better results.

Naturally, it is preferable to increase the ion concentration of this polymer electrolyte.

Next, as mentioned above, depending on the battery structure, liquid polymer electrolytes may easily escape to the outside, so in that case, it is possible to use the solid or semi-solid electrolytes mentioned above, but other As a method, a method may be used in which a liquid polymer electrolyte is kneaded at the time of catalyst formation or impregnated into the catalyst layer afterwards, and then crosslinked by heating to prevent leakage to the outside.

Furthermore, by kneading organic monomers (such as styrene and polyethylene) in a catalyst-forming manner or impregnating them into a catalyst layer, crosslinking and sulfonation are performed in concentrated sulfuric acid or fuming sulfuric acid to form polymeric polystyrene sulfonic acid or A similar effect can be obtained by using polyethylene sulfonic acid.

〔Effect of the invention〕

According to the present invention, when a polymer electrolyte is used as an electrolyte in a fuel cell without using a conventional liquid such as sulfuric acid or potassium hydroxide, it does not leak to the outside, and moreover, the electrolyte does not leak into the electrode catalyst layer or between the electrodes. The electrolyte is dispersed, including at the interface.
Since effective ionic conduction is enabled by the infiltration of water, a battery with good performance can be obtained.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the principle of a fuel cell, FIG. 2 is a diagram showing the principle configuration of a conventional embodiment, and FIG. 31 is a diagram showing the configuration of an embodiment of the present invention. 111... Polymer electrolyte applied to the catalyst layer, 112
...polymer electrolyte filled in the electrode and electrolyte, 9.
...Contact point between the electrode catalyst layer and the electrolyte, 10...Gap between the electrode and the electrolyte. Agent Patent Attorney Akio Takahashi (7) 2nd m

Claims (1)

[Claims] 1. In a fuel cell that is suitable for electrochemical reactions. A fuel cell characterized by adding an ion exchange group or interposing a substance having an ion exchange group between the electrolyte and the electrodes interposed between the electrodes or in the electrode catalyst layer.