JPH03276567A - Fuel cell - Google Patents

Abstract

PURPOSE:To stabilize the battery characteristic for a long period by inserting a reservoir plate made of a hydrophilic material functioning as an electrolyte reservoir between a ribbed electrode substrate and a separator for one electrode, and forming a hydrophilic electrolyte moving passage on the electrode substrate in contact with the reservoir plate. CONSTITUTION:A hydrophilic reservoir plate 11 made of carbon paper is inserted between a separator 2 and a ribbed electrode substrate 6 for one of anode and cathode electrodes, e.g. anode electrode 7. An electrolyte moving passage 12 communicated to a catalyst layer 5 is locally formed at the portion of a rib 6a on the face area of the anode side electrode substrate 6 in contact with the reservoir plate 11. When the electrolyte held by the reservoir 4 is scattered and decreased during an operation, the electrolyte stored in the reservoir plate 11 is moved and supplied to a matrix 4 through the electrolyte moving passage 12 of the electrode substrate 6 and the electrolyte passage hole 13 of the catalyst layer 5. The battery characteristic is stabilized for a long period.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a ribbed electrode type fuel cell, such as an Eborin # type fuel cell, and particularly to the structure of an electrolyte reservoir thereof.

[Conventional technology]

First, the conventional structure of the fuel cell to which the present invention is applied is shown in Figs. The impermeable separator 3 is a cooling plate, and these laminates constitute a cell stack. The cell 1 also includes a matrix 4 impregnated with an electrolyte and a ribbed electrode base material 5 having gas permeability (molded by adding a binder to carbon fibers).

An anode electrode 7, which is formed by carrying a catalyst layer 6 on a material (calcined and further impregnated with a fluororesin, which is a water repellent material, to make it water repellent), and disposed on both sides of the matrix. It is composed of a cathode electrode 8. Note that the reactant gases such as fuel and oxidizing secondary gas supplied from the outside diffuse inside the electrode base material 6 while flowing through the gas supply grooves 6b formed between the ribs 6a of the electrode base material 6, and become catalytic. Supplied to layer 5.

On the other hand, in the fuel cell described above, the electrolyte held in the matrix 4 is scattered outside the cell together with unreacted gas or water produced by the reaction during operation, and its amount gradually decreases over time. This may increase the internal resistance of the battery, cause reaction gases to come into contact with each other within the matrix, and cause a direct reaction, as well as moisture absorption.

Elevated temperatures may increase the volume of the electrolyte and cause leakage. As a countermeasure to this problem, as shown in the figure, a hydrophilic reservoir portion 9 for storing electrolyte is formed in one of the anode and cathode electrodes 7 and 8, for example, in a part of the electrode base material 6 of the anode electrode 7. A structure of an electrolyte reservoir in which the matrix 4 and the reservoir section 9 are communicated through the electrolyte passage 10 formed in the catalyst layer 5 is already known in Japanese Patent Application Laid-Open No. 188862/1983.

[Problem to be solved by the invention]

However, the conventional electrolyte reservoir structure in which a reservoir for storing electrolyte is formed occupying a part of the electrode as described above has the following problems.

That is, the electrolyte holding capacity of the reservoir section 9 is equal to that of the electrode base material 6.
In order to increase the capacity of the reservoir, it is necessary to enlarge the wood-loving region of the electrode base material. When the pores of the hydrophilic reservoir portion 9 are filled with electrolyte, this portion becomes gas impermeable. Therefore, if the area of the electrolyte reservoir section 9 is increased relative to the limited area of the electrode, the effective area as a gas diffusion electrode will be reduced by that amount, and the ability to supply the reaction gas to the catalyst layer 5 will be reduced. This limits the reservoir capacity to a small practical capacity in conventional electrolyte reservoir structures.

The present invention has been made in view of the above points, and provides a fuel cell which can secure a sufficient effective area as a gas diffusion electrode and also increase the storage capacity of electrolyte.
In particular, the object is to provide such an electrolyte reservoir structure.

[Means to solve the problem]

In order to solve the above problems, the fuel cell of the present invention has a small number of anode and cathode electrodes (both have a small number of anode and cathode electrodes,
A reservoir plate made of a hydrophilic material that functions as an electrolyte reservoir is inserted between the ribbed electrode base material and the separator, and a part of the electrode base material that is in contact with the reservoir plate is inserted between the matrix and the reservoir plate. The structure shall be constructed by forming a hydrophilic electrolyte movement passageway.

The electrolyte movement path in the above structure is formed as a dilute water-repellent treatment area whose water repellency is weaker than that of other electrode regions, or by locally irradiating a laser onto the water-repellent electrode base material. It can be formed by

Furthermore, in order to hold the electrolyte uniformly over the entire area of the matrix, it is preferable that the electrolyte movement paths in the above structure be distributed more in the outlet s region than in the reactant gas inlet side of the electrode.

[Effect]

As in the above configuration, by interposing a reservoir plate made of a hydrophilic material 1 such as carbon paper between the ribbed electrode base material and the separator, a sufficient gas diffusion area is secured in the electrode base material. , an electrolyte reservoir with a large storage capacity can be constructed within a single cell.

In addition, the dilute water-repellent treatment part formed on a part of the electrode base material maintains gas diffusivity that allows the reactive gas supplied from the outside to the inside of the cell to be diffused and supplied toward the catalyst layer, while at the same time protecting the matrix and reservoir. It functions as an electrolyte transfer path spanning between the plates.

Furthermore, by locally irradiating a laser beam from the catalyst layer side to the electrode base material, which has been treated to be water repellent over the entire area, the electrode base material is exposed to the laser beam in the area that has been irradiated with the laser.

A water repellent material such as a fluororesin contained in the catalyst layer is thermally decomposed and removed, and a hydrophilic electrolyte transfer path is formed in this portion.

On the other hand, the temperature distribution of the battery is higher on the outlet side than on the inlet side with respect to the flow direction of the reaction gas, so the amount of electrolyte scattered from the matrix and the amount of expansion of the electrolyte are also higher than on the inlet side of the reaction gas. Therefore, by distributing more electrolyte transfer passages that communicate between the matrix and the reservoir plate on the reaction gas outlet side of the electrode, the distribution of the amount of electrolyte retained over the entire matrix area is made uniform. can.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

In each embodiment, the same members corresponding to FIG. 7 are given the same reference numerals.

Example 1: In FIG. 1, for one of the anode and cathode electrodes, for example, the anode electrode 7, there is a hydrophilic material made of carbon vapor or the like between the separator 2 and the ribbed electrode base material 6. A reservoir play) 12 is inserted. Further, in the surface area of the anode side electrode base material 6 in contact with the reservoir plate 12, an electrolyte transfer passage 12 communicating with the catalyst layer 5 is locally formed in the rib 6a portion.

The electrolyte transfer passage 12 is formed by subjecting it to a dilute water repellent treatment so that its water repellency is weaker than that of other base material regions, and is made, for example, by the following method. That is,
First, the portion of the porous electrode base material 6 that has gas diffusivity that will become the electrolyte transfer passage 12 is masked, and a fluororesin (suspension of fluororesin), which is a water repellent material, is applied to the electrode base material 6.
and then, after removing the mask, the area is impregnated with a diluted suspension of fluorine. As a result, the portion that will become the electrolyte transfer path 12 is subjected to a dilute water repellent treatment. The diluted water-repellent treated portion thus formed has both wood-philicity and gas diffusivity.

Furthermore, an electrolytic through hole 13 communicating with the matrix 4 is bored in the catalyst layer 5 in series with the electrolyte transfer path 12 .

Note that this electrolytic through-hole 13 is made of S, which is the same as the matrix material.
Fill it with iC powder.

With this configuration, the reservoir plate 12 is impregnated and held with an electrolyte prior to the start of operation of the fuel cell.
Here, when the electrolyte held in the reservoir 4 scatters and decreases during operation of the fuel cell, the electrolyte stored in the reservoir plate 12 is transferred to the electrolyte transfer passage 1 of the electrode base material 6.
2. The matrix 4 passes through the electrolyte passage holes 13 of the catalyst layer 5.
will be moved to and resupplied. In this case, since the movement of the electrolyte is controlled by capillary force, the pore diameter is set in advance as the reservoir plate 12 in the matrix 4. The solute base material 6
By using a material larger than the pore diameter of the electrolyte, the electrolyte moves smoothly toward the matrix 4 by capillary force.

On the other hand, when the volume of the electrolyte increases due to moisture absorption by the electrolyte or an increase in battery temperature, excess electrolyte moves from the matrix 4 toward the reservoir plate 12, contrary to the above.

Note that the electrolyte movement passage 12 of the electrode base material 6 formed by dilute water repellent treatment is locally formed in an extremely narrow area, and the road itself has gas diffusivity.
The overall reaction gas supply capacity of the anode electrode 7 hardly decreases.

Embodiment 2: FIGS. 4 and 4 show an embodiment different from Embodiment 1 described above. In this embodiment, the basic structure of the electrolyte reservoir is the same as that of the first embodiment described above, and in particular, an electrolyte transfer path extending between the reservoir plate 11 and the matrix 4 is formed by laser irradiation.

That is, for the anode electrode 7 that comes into contact with the reservoir plate ll incorporated inside the unit cell 1, first, the entire area of the electrode base material 6 is impregnated with fluororesin to make it water repellent, and then it is treated as shown in FIG. A laser beam 16 emitted from a laser oscillator 15 is irradiated from the catalyst layer 5 supported on the electrode base material 6 toward the rib 6a portion of the electrode base material 6. This causes the area irradiated by the laser to be locally heated,
The fluororesin resin coated in the water-repellent treatment step in the internal pores of this portion thermally decomposes and scatters, returning to the tree-friendly state before the water-repellent treatment. In addition, the thickness of the electrode base material 6 is extremely thin, about 1 to 2 mm, and by adjusting the laser output,
A hydrophilic electrolyte transfer passage 14 extending in the thickness direction of the electrode 6
can be easily formed. Additionally, in this case, the spot diameter of the laser beam irradiated onto the electrode 6 is made as small as possible to minimize the cross-sectional area of the electrolyte transfer passage 14, thereby ensuring a sufficient effective area that functions as a gas diffusion electrode. Good.

FIGS. 3 and 4 show examples of patterns of electrolyte transfer passages 14 formed in this manner.

Here, in FIG. 3, the electrolyte movement passage 14 is connected to the anode electrode 7.
On the other hand, in Fig. 4, the area on the outlet side (right side Il) is smaller than the inlet side (left side in the figure) with respect to the reaction gas supply direction to the electrode. Concentrate more on electrolyte movement passages! 4 is formed.

In other words, the concentration of the electrode during operation is higher on the outlet side than on the inlet side of the reaction gas, and matrix 4
Therefore, as shown in FIG. 4, by forming more electrolyte transfer passages 14 in one region on the reaction gas outlet side and increasing the number of electrolyte supply points to the matrix 4, The in-plane distribution of the retained electrolyte is always uniform. Note that even if such a distribution pattern of electrolyte movement paths is applied to the first embodiment, the same effect can be obtained.

〔Effect of the invention〕

Since the fuel cell of the present invention is configured as described above, it achieves the following effects.

(1) For at least one of the anode and cathode electrodes, a reservoir plate made of a hydrophilic material that functions as an electrolyte reservoir is inserted between the ribbed electrode base material and the separator, and the electrode base is in contact with the reservoir plate. However, by forming a hydrophilic electrolyte transfer path between the matrix and the reservoir plate in a part of the electrode, gas diffusion in the electrode is improved compared to the conventional structure in which the electrode reservoir part is formed in a part of the electrode. It is possible to achieve long-term stabilization of battery characteristics by increasing the electrolyte storage capacity while ensuring sufficient performance.

(2) By forming the electrolyte movement passage inside the electrode as a dilute water-repellent treatment area whose water repellency is weaker than that of other electrode regions, the matrix The electrolyte can be smoothly moved between the reservoir plate and the reservoir plate.

(3) By forming the electrolyte movement path inside the electrode by irradiating the fingernail-treated electrode base material with a laser, the electrolyte movement path can be formed at any location on the electrode surface with a simple work process.

(4) By forming more electrolyte transfer passages on the outlet side of the reactant gas than on the inlet side of the electrode, the in-plane distribution of the electrolyte held in the matrix can be made uniform.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of the structure of a unit cell corresponding to Example 1 of the present invention, Fig. 2 is a cross-sectional view of the structure of a unit cell corresponding to Example 2 of the present invention, and Fig. 3 is the electrolyte movement in Fig. 2. A work process diagram for forming passages by laser irradiation, Figures 4 and 5 are pattern diagrams of electrolyte transfer passages distributed on the electrode surface, and Figures 6 and 7 are cell diagrams showing the conventional structure of a fuel cell, respectively. FIG. 2 is a perspective view of a stack and a cross-sectional view of a cell. In the figure, l: unit cell, 2: separator, 4: matrix, 5: catalyst layer, 6: electrode base material, 6a: rib 1.7: anode/electrode, 8: cathode electrode, 11: reservoir plate, 13
, 14: Electrolyte movement path, 16: Laser beam Figure 2, Figure 4, Figure 4

Claims (1)

[Scope of Claims] 1) A unit cell is constituted by a matrix impregnated with an electrolyte, and an anode and a cathode electrode arranged on both sides of the matrix with a catalyst layer supported on a ribbed electrode base material having gas permeability. In a fuel cell formed by stacking a large number of single cells with separators in between, a hydrophilic material that functions as an electrolyte reservoir between a ribbed electrode base material and the separator for at least one of the anode and cathode electrodes. What is claimed is: 1. A fuel cell comprising: a reservoir plate inserted therein; and a hydrophilic electrolyte transfer passageway communicating between the matrix and the reservoir plate formed in a part of the electrode base material in contact with the reservoir plate. 2) The fuel cell according to claim 1, wherein the electrolyte transfer passage is formed as a dilute water-repellent treatment section whose water repellency is weaker than that of other electrode regions. 3) The fuel cell according to claim 1, wherein the electrolyte movement passage is formed by locally irradiating a water-repellent electrode base material with a laser. 4) The fuel cell according to claim 1, characterized in that the electrolyte transfer passages are more distributed on the outlet side of the reactant gas than on the inlet side of the electrode.