JPS5991671A - Fuel cell - Google Patents

Abstract

PURPOSE:To continue normal reaction of a fuel cell by making hydrophilic the circumference of an electrode, facing an electrolyte reservoir installed in the circumference of a gas separating plate and by setting a water repellent part compared with the hydrophilic part, between the central reaction part and the hydrophilic part to suppress transfer of electrolyte. CONSTITUTION:An electrolyte reservoir 8 is installed in the circumference of a gas separating plate 1 having a fuel flow path 2 and an oxidizing agent flow path 3 on its both sides. The circumference 4b of a fuel electrode 4, facing the reservoir 8 is made hydrophilic to make electrolyte penetration easy. A boundary layer 9 which is more water repellent than a central reaction part 4a is arranged between the circumference 4b and the central reaction part 4a carrying a catalyst. The boundary layer 9 suppresses transfer of the electrolyte contained in the circumference 4b to the reaction part 4a. Thereby, decrease of gas transmission to the reaction part 4a is prevented and the normal reaction of a fuel cell is continued.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fuel cell, and particularly to the structure of an electrode portion thereof.

A conventional fuel cell of this type is shown in FIG. In the figure, (1) is a gas separation plate with a fuel flow path (2) and an oxidant flow path (2) provided on both sides. (4) is a fuel electrode, which is in contact with an electrolyte matrix (5). ), on which is the oxidizer electrode (6). (7) is the backing for sealing, and (8) is the gas separation plate (1).
This is an electrolyte reservoir that is provided around the periphery of the electrolyte and holds electrolyte. The part with each number (a) is the part where the battery reaction occurs, and the part (6) is the sealed part and is treated to be air-impermeable.

Next, the operation will be explained. The fuel supplied from the fuel flow path (2) is oxidized at the fuel electrode (4), hydrogen becomes cations and electrons, and the cations move through the reaction part (5a) of the electrolyte matrix (5) to the oxidation side. reaching the electrode (6);
It reacts with the oxidizing agent supplied from the oxidizing agent channel (3) to generate water. Electrons generated at the fuel electrode (4) pass through an external load (not shown) and reach the oxidizer electrode (6), where they contribute to a reduction reaction and become electrical energy in the external load. During the reaction, the electrolyte matrix (5) must always hold an electrolyte, and for this purpose an electrolyte reservoir (8) is provided as an electrolyte reservoir. In order to supply electrolyte from the electrolyte reservoir (8) to the electrolyte matrix (5) and seal the gas, the surrounding area of the electrode (4) (
4b) is treated to be hydrophilic in order to allow the electrolyte to permeate1. Conventional fuel cells are constructed as described above, so the hydrophilic peripheral portion (4b) of the electrode (4) is ) and into the central reaction portion (4a) of the electrode (4). The central reaction part (4a) of the electrode (4) is PT
Water contact treatment using FE (polytetrafluoroethylene) is performed, but if water contact treatment is performed too strongly, the pores of the electrode base material will be filled, resulting in poor gas permeability and gas diffusion [! The function as i is impaired. In this way, the electrode (
4) When the electrolyte permeates from the peripheral portion (4b) into the central reaction portion (4a), gas permeability deteriorates, resulting in a disadvantage that the function as a gas diffusion electrode is impaired.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above.
By making the peripheral part of wS hydrophilic and providing a part that is more water-contacting than the central reaction part between the hydrophilic peripheral part of the electrode and the central reaction part, the hydrophilic peripheral part of the electrode can be made hydrophilic. The purpose is to suppress the movement of electrolyte to the reaction part and maintain normal reactions in the fuel cell.

An embodiment of the present invention will be described below with reference to the drawings. Second
The figure is a sectional view of a fuel cell according to the present invention. In the figure, (4) and (6) are a fuel electrode and an oxidizer electrode, respectively, which are carbon paper with a thickness of 400 to 500 μm coated with a catalyst layer.

(4b) has an average particle size of 1 to 5 in the peripheral part of the fuel electrode (4).
It is filled with silicon carbide particles as fine as micrometers. (9)
is a central reaction part (4a) provided between this electrode peripheral part (4b) and a catalyst-coated central reaction part (4a).
It is a part that is more water-contactable than the central reaction part, and has a width of 6 to 151 nnl, and is obtained by mixing a larger amount of PTFE than the central reaction part.

Electrolyte must be sufficiently retained in the electrode peripheral area (4b) for gas sealing, but when the electrolyte moves to the adjacent central reaction area (4a), the central reaction area (4a)
The gas diffusivity of 4a) deteriorates and the electrode function deteriorates. Therefore, by providing a boundary layer (9) with strong water contact between the electrode peripheral part (4b) and the central reaction part (4a), which acts as a gas seal, the electrolyte contained in the electrode peripheral part (4b) can be removed. can be suppressed from migrating to the central reaction portion (4a). In general, carbon paper, which is the electrode base material of the electrode reaction part (4a), has been appropriately water-wetted, but this is because the electrolyte from the electrolyte matrix (5) has a catalyst layer that also has some water-wettability. This is done in order to reduce the amount of water that enters the electrode (4).
It is not carried out because it inhibits the reactivity of a). In this sense, the conventional structure can sufficiently deal with the intrusion of electrolyte from the electrode peripheral part (4b) into the central reaction part (4a), compared to the central reaction part (4a) of the electrode according to the present invention. A boundary layer (9) with strong water contact is important.

In addition, in the above embodiment, the oxidant electrode (6) uses a backing (7) as a gas seal, but
In the same way as the fuel electrode (4), a gas seal filled with an electrolyte may be used, and in that case, the part (9) that is more in contact with water than the central reaction part (6a) of the oxidizer electrode (6) is used as the central reaction part. It may be provided between the part (6a) and the gas seal part. Further, in this case, the fuel electrode (4) may be sealed with gas using a backing.

As described above, according to the present invention, the peripheral part of the electrode facing the electrolyte reservoir is made hydrophilic, and the area between the hydrophilic peripheral part of the electrode and the central reaction part is more water-contacted than the central reaction part. This section suppresses the movement of electrolyte from the hydrophilic peripheral area of the electrode to the central reaction area,
It has the effect of sustaining the normal reaction of the fuel cell.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing the main parts of a conventional fuel cell, and FIG. 2 is a cross-sectional view showing the main parts of a fuel cell according to the present invention. In the figure, (1) is a gas separation plate, (4) is a fuel electrode,
(4a) is the central reaction part, (4b) is the peripheral part, (5)
is an electrolyte matrix, (6) is an oxidizer electrode, (8) is an electrolyte reservoir, and (9) is a part that is more in contact with water than the central reaction part (4a). Note that the same reference numerals in the figures indicate the same or corresponding parts. Figure 1 σ J Figure 2

Claims (1)

[Claims] In a fuel cell configured by sequentially stacking a gas separation plate, a fuel electrode, an electrolyte matrix, and an oxidizer electrode with an electrolyte reservoir in the peripheral part, the peripheral part of the electrode facing the electrolyte reservoir is made hydrophilic, and A fuel cell characterized in that a portion more in contact with water than the central reaction portion is provided between the hydrophilic peripheral portion of the electrode and the central reaction portion.