JPH11219712A - Phosphate type fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably operate a fuel cell for a long duration by preventing wetting of the end face of a separator inserted between neighboring fuel cell layered bodies with phosphoric acid and eliminating corrosion of the separator by phosphoric acid and possibility of leakage of the electrolytic solution between neighboring unit cells. SOLUTION: A unit cell 1 comprises a matrix 2 holding phosphoric acid and sandwiched between a fuel electrode catalytic layer 3 and an air electrode catalytic layer 4, a fuel electrode porous plate 5 holding phosphoric acid in the outer face of the layer 3, and an air electrode porous plate 6 in the outer face of the layer 4. This phosphate fuel cell layered body is so constituted by layering such unit cells 1 while inserting separators 9A into the neighboring unit cells as to give electric energy by electrochemical reaction by supplying a fuel gas to the fuel electrode catalytic layers 3 and an oxidizing gas to the air electrode catalytic layers 4. In this case, the end parts of the outer circumferential sides of the separators 9A are provided with water-repelling parts 10 formed by impregnating the end parts with polytetrafluoroethylene and sintering the resultant end parts.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phosphoric acid fuel cell which uses phosphoric acid as an electrolyte to obtain electric energy by an electrochemical reaction, and more particularly to a structure of a separator interposed in a fuel cell stack.

[0002]

2. Description of the Related Art FIG. 2 is an enlarged sectional view of a main part showing a basic structure of a fuel cell stack of a conventional phosphoric acid type fuel cell.
As shown in the figure, a unit cell 1 is composed of a square flat matrix 2 holding phosphoric acid, a fuel electrode catalyst layer 3, a fuel electrode porous plate 5 supporting the same, and an air electrode catalyst layer 4. The unit cell 1 formed in this way is sandwiched between air cathode porous plates 6 supporting
By alternately stacking the fuel cells, a fuel cell stack is formed.

[0003] Phosphoric acid is retained in the pores of the fuel electrode porous plate 5 and the air electrode porous plate 6, and during operation, the phosphoric acid of the matrix 2 is lost and the power generation performance is reduced. Is prevented. Further, the fuel electrode porous plate 5 is provided with a fuel gas passage 7 through which a fuel gas supplied from the end face of the fuel cell stack is passed, and the fuel gas flows through the fuel electrode catalyst from the fuel gas passage 7. Feed to layer 3. Similarly, the air electrode porous plate 6 is provided with an air passage 8 extending in a direction perpendicular to the fuel gas passage 7, and the reaction air supplied from the other end face of the fuel cell stack is the air The air is supplied to the air electrode catalyst layer 4 through the passage 8.

Since the separator 9 must play a role of air-tightly separating the fuel gas and air supplied to the upper and lower unit cells, the separator 9 needs to be gas-impermeable, and a large number of unit cells are required. In order to minimize the resistance loss inside the fuel cell stack in which the fuel cells are stacked, the fuel cell stack must be made of a conductive material having a small electric resistance. Further, since the separator 9 comes into contact with phosphoric acid used as an electrolyte, the separator 9 needs to be a material having excellent corrosion resistance to phosphoric acid. For this reason, usually, a carbon plate obtained by impregnating a paper made of cellulose fibers with a thermosetting resin, drying, laminating, pressing, and further firing is used for the separator 9.

[0005]

In a conventional phosphoric acid type fuel cell, a unit cell is stacked as described above to form a fuel cell stack, a desired power generation voltage is obtained, and phosphorus is added to a porous plate of both electrodes. By retaining the acid, the phosphoric acid in the matrix 2 is prevented from disappearing, and the power generation operation can be performed for a long time. However, the following problems still exist in the phosphoric acid type fuel cell configured as described above. Remaining.

That is, in the above configuration, since the separator 9 is disposed in contact with the fuel electrode porous plate 5 and the air electrode porous plate 6, the separator 9 is formed by phosphoric acid held by these porous plates. The surface of No. 9 is wet, and phosphoric acid is drawn into the fine irregularities on the surface. This phenomenon is particularly remarkable when the volume of phosphoric acid held on the porous plate expands due to a change in the operation state, etc., and the phosphoric acid drawn into the uneven portion on the surface travels along the uneven portion to the end of the separator 9. To cover the end face. When the end face of the separator 9 is covered with phosphoric acid in this manner, phosphoric acid may penetrate into the inside of the laminated carbon plate forming the separator 9 and may accelerate the corrosion of the separator 9 by phosphoric acid. Also, when the upper and lower unit cells are liquid-junctioned by phosphoric acid, ions may move through the phosphoric acid and the power generation performance may be impaired. Furthermore, there is a risk that the phosphoric acid that has flowed to the end face may cause a ground fault between the fuel cell stack and its structural members, causing serious damage to the fuel cell stack.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks of the prior art, and an object of the present invention is to prevent the end face of the separator from being wetted by phosphoric acid, thereby preventing corrosion of the separator by phosphoric acid and the unit. Eliminates the risk of liquid junction between cells,
An object of the present invention is to provide a phosphoric acid fuel cell that can be operated stably for a long period of time.

[0008]

In order to achieve the above-mentioned object, in the present invention, a matrix holding phosphoric acid is sandwiched between a fuel electrode catalyst layer and an air electrode catalyst layer, and phosphoric acid is further coated on the outer surfaces thereof. A fuel cell stack is formed by stacking a plurality of flat unit cells formed by arranging a porous plate holding a fuel cell with a conductive and gas-impermeable separator interposed therebetween, and forming an anode catalyst. In a phosphoric acid fuel cell that obtains electric energy by an electrochemical reaction by supplying a fuel gas to a layer and an oxidizing gas to an air electrode catalyst layer, a carbon separator having a water-repellent treatment portion at an outer peripheral end is used. For example, the water-repellent portion is formed by impregnating a carbon plate with polytetrafluoroethylene and firing it.

By providing a water-repellent treatment portion at the outer peripheral end of the separator interposed between the unit cells to be stacked, the phosphoric acid held on the porous plate can be applied to the uneven portion on the surface of the separator. Even if the phosphoric acid is drawn, the movement of the phosphoric acid to the end face is prevented by the water-repellent treatment section. Accordingly, there is no danger of liquid junction due to leakage of phosphoric acid to the end face of the separator, and the various risks associated with the liquid junction seen in the conventional phosphoric acid type fuel cell are eliminated.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an enlarged sectional view of a main part showing a basic structure of a fuel cell stack according to an embodiment of the phosphoric acid type fuel cell of the present invention. In the figure, components having the same functions as the components of the conventional example shown in FIG. 2 are denoted by the same reference numerals, and redundant description will be omitted. The difference of this embodiment from the conventional example is that the water-repellent treatment section 10 is provided on the outer peripheral end of the separator 9A.
Is provided. This water-repellent processing section 10
A portion of about 10 mm at the outer peripheral end of the separator 9A was dipped in a polytetrafluoroethylene dispersion (trade name: Teflon 30J, manufactured by Mitsui Fluorochemicals Co., Ltd.), pulled up, and baked at 340 to 360 ° C. for 10 minutes. Things.

In the configuration of this embodiment, since the water repellent portion 10 is provided at the outer peripheral end of the separator 9A, the separator 9A is held by the porous fuel electrode plate 5 and the porous air electrode plate 6. Even if the phosphoric acid is drawn into the surface of the separator 9A, the movement of the phosphoric acid to the end face is prevented. According to the test operation, no liquid junction as in the prior art was observed, and there was no corrosion of the separator 9, and stable operation was possible for a long time.

[0012]

As described above, according to the present invention, a matrix holding phosphoric acid is sandwiched between a fuel electrode catalyst layer and an air electrode catalyst layer, and a porous plate holding phosphoric acid on the outer surface thereof. A flat unit cell formed by arranging
A fuel cell stack is formed by stacking a plurality of conductive and gas-impermeable separators, and a fuel gas is supplied to the anode catalyst layer and an oxidant gas is supplied to the air electrode catalyst layer to generate electricity. In a phosphoric acid type fuel cell that obtains electric energy by a chemical reaction, the separator is formed from a carbon plate provided with a water-repellent portion on the outer peripheral side end. Impregnated with fluoroethylene,
Since it is formed by firing, wetting of the end face of the separator with phosphoric acid is prevented, and the risk of corrosion of the separator due to phosphoric acid and the risk of liquid junction between unit cells is eliminated, and stable operation for a long time Thus, a phosphoric acid type fuel cell that can be obtained is obtained.

[Brief description of the drawings]

FIG. 1 is an enlarged sectional view of a main part of a fuel cell stack according to an embodiment of the phosphoric acid fuel cell of the present invention.

FIG. 2 is an enlarged sectional view of a main part of a fuel cell stack of a conventional phosphoric acid type fuel cell.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Unit cell 2 Matrix 3 Fuel electrode catalyst layer 4 Air electrode catalyst layer 5 Fuel electrode porous plate 6 Air electrode porous plate 7 Fuel gas passage 8 Air passage 9A Separator 10 Water repellent treatment part

Claims (2)

[Claims] 1. A flat unit cell formed by sandwiching a matrix holding phosphoric acid between a fuel electrode catalyst layer and an air electrode catalyst layer, and further arranging a porous plate holding phosphoric acid on the outer surface thereof. A fuel cell laminate is formed by laminating a plurality of conductive and gas-impermeable separators therebetween,
In a phosphoric acid fuel cell in which a fuel gas is supplied to a fuel electrode catalyst layer and an oxidizing gas is supplied to an air electrode catalyst layer to obtain electric energy by an electrochemical reaction, the separator has a water-repellent treatment on an outer peripheral end. A phosphoric acid type fuel cell comprising a carbon plate having a portion. 2. The phosphoric acid fuel cell according to claim 1, wherein the water-repellent portion of the separator is formed by impregnating a carbon plate with polytetrafluoroethylene and firing the carbon plate. Phosphoric acid fuel cell.