JP2961806B2 - Gas seal structure of fuel cell - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode-type fuel cell with ribs, and more particularly to a gas seal structure at a side edge of each unit cell.

[Conventional technology]

A fuel cell and an oxidizing agent are formed from each pair of two pairs of manifolds which are airtightly mounted on a parallel surface of a stacked battery in which a large number of unit cells are stacked with a gas-impermeable separator plate interposed on the stacked surface. In a fuel cell in which gas is supplied in a direction orthogonal to each other to directly generate electric power, when a reaction gas leaks from a gas seal portion on a side edge of each unit cell to a gas system side facing each other, a gas partial pressure is reduced. Not only does the generated power drop, but the fuel gas and the oxidizing gas may mix with each other and generate explosive air. Therefore, it is important to obtain a gas seal structure that minimizes leakage of the reactant gas from the electrode. It is an issue.

FIG. 2 is a perspective view showing a conventional gas seal structure of a laminated fuel cell in a partially crushed section for one unit cell.
In the figure, a unit cell 1 is composed of a matrix 2 made of a porous ceramic material holding, for example, phosphoric acid as an electrolyte.
And an oxidant electrode 5 sandwiching the matrix from both sides.
And a plurality of unit cells 1 are stacked with a gas-impermeable carbon plate, for example, a separate plate 7 made of a glassy carbon plate, interposed therebetween to form a stacked fuel cell (cell stack). Is configured. The pair of electrodes 5 and 6 are provided with an electrode catalyst layer 4 on the surface on the side opposite to the ribs of the electrode substrate 3 with a rub formed of a gas-permeable carbon plate, and are combined so that the pair of grooves are orthogonal to each other. By supplying air as an oxidant to the groove on the side of the electrode 5 and supplying a hydrogen-rich fuel gas to the groove on the side of the fuel electrode 6, direct power generation based on an electrochemical reaction is performed in the electrode catalyst layer.

The gas seal portion 10 is provided with a separator plate 7 and one electrode so as to surround both sides 5S and 6S parallel to the grooves of the pair of electrodes 5 and 6 and the side edge 2S of the matrix 2 with a gap 10G therebetween. Interposed between For this reason, the width of the pair of electrodes 5 and 6 in the direction orthogonal to the groove is formed to be smaller by a size corresponding to almost twice the width of the gas seal portion 10, and the size of the matrix is reduced to a small square according to the above size. It is formed. The gas seal portion 10 includes a frame-shaped fluororesin sheet 11 in which the dimensions of the square-shaped opening are formed smaller than the size of the matrix, and fluororesin packing sheets 12A and 12B sandwiching the outer peripheral portion from both sides. Sheet 12B
Gas-impermeable sealing plate 13 made of, for example, glassy carbon material and surrounding the side edges of the electrode substrate 3 with ribs
And a packing sheet 12C interposed between the seal plate 13 and the separate plate 7. The gas seal portions 10 in the four corners of the unit cell 1 overlap in a direction orthogonal to each other to form a pair. A seal structure is formed in which two layers of gas seal portions overlap between the separate plates.

In the above-described sealing structure, the frame-like fluororesin sheet
An inner peripheral portion of the sheet 11 is sandwiched between the matrix 2 and one electrode catalyst layer 4, and an outer peripheral portion of the sheet 11 is sandwiched between a pair of separate plates via the five-layer gas seal portion 10 and the other electrode. Thus, gas leakage between the electrodes in the gap 10G is prevented by the frame-shaped fluororesin sheet 11, and gas leakage outside the unit cell 1 is prevented by the five-layer gas seal portion 10.

[Problems to be Solved by the Invention] In order to attach a manifold for supplying and discharging the reaction gas to the four side wall surfaces of the cell stack, it is necessary to assemble the unit cell and the separate plate with high precision so as not to cause irregularities on the laminated end surface. There is. However, since the gas seal portion 10 is formed of a layered body of five members, it is extremely difficult to assemble the gasket so as not to cause unevenness on the outer peripheral end face, which adversely affects the gas seal performance of the manifold. At the same time, there is a problem in that time and labor for assembly work are hindered.

In addition, when water generated by power generation is released into the reaction gas, it may be released as water vapor containing phosphoric acid mist, which adheres to the side wall surface of the cell stack, thereby causing leakage current of the fuel cell. Increase. However, the thickness t of the insulating material on the side wall surface 10S of the unit cell 1
Is determined by the thickness of the frame-shaped fluororesin sheet 11 and the packing sheets 12A and 12B on both sides thereof, and is only about 0.5 mm. For this reason, a problem arises in that the surface resistance decreases due to the phosphoric acid mist adhering to this portion, and the leakage current increases.

An object of the present invention is to provide a gas seal structure which is easy to assemble and has a high leakage current blocking performance.

[Means for solving the problem]

In order to solve the above problems, according to the present invention, a plurality of unit cells each having at least a fuel electrode and an oxidant electrode disposed on both main surfaces of a matrix holding an electrolyte are stacked via a separate plate. A frame-shaped fluororesin sheet formed in a square shape and having an inner peripheral portion sandwiched between the matrix and one of the electrodes, the frame-shaped fluorocarbon resin sheet; A resin sheet comprising: a pair of packing sheets sandwiching an outer peripheral portion of the resin sheet from both sides; and a gas-impermeable sealing plate interposed between one side of the packing sheet and the separate plate. The flexible sealing plate is composed of a core material and a fluororesin layer covering the core material. Further, the core material is made of either a glassy carbon material or a low thermal expansion metal material. Further, one in which one surface of the gas-impermeable seal plate is air-tightly fixed to the separate plate in advance is used.

[Operation] In the present invention, since the seal plate is insulated and covered and the creepage insulation distance on the side wall surface is increased by the thickness of the seal plate, that is, about four times that of the related art, by adopting the above configuration,
The leakage current caused by the contamination with the phosphoric acid mist can be greatly reduced, and the packing sheet on the separate plate side of the gas seal portion, which has conventionally been composed of five layers, can be omitted to have four layers.

Also, with the above configuration, even if the cell stack rises to the operating temperature, the dimensions of the gas seal portion will change following the unit cell or the separate plate,
It is possible to prevent the deterioration and deterioration of the sealing performance due to the generation of thermal stress.

Further, by adopting the above configuration, the number of assembling steps of the gas seal portion can be greatly reduced, and the positioning accuracy of the seal plate is improved, so that the unevenness of the cell stack side wall surface is reduced.

〔Example〕

 Hereinafter, the present invention will be described based on examples.

FIG. 1 is a perspective view showing a sealing structure of a fuel cell according to the present invention in a partially crushed section with respect to a unit cell. The same parts as those in the prior art are denoted by the same reference numerals, and detailed description thereof will be omitted. In the figure, a gas-impermeable seal plate 21 in a gas seal portion 20 is made of, for example, a glassy carbon material of the same quality as the separate plate 7 or a core material 22 made of a low thermal expansion metal such as an invar material having a body thermal expansion coefficient substantially equal to this. The core material is composed of, for example, a fluororesin layer 23 formed as a coating layer, which covers the surface of the core material. The one surface 23S of the fluororesin layer 23 is hermetically bonded to a predetermined position of the separate plate 7 in advance as a fusion surface.

The gas seal structure configured as described above has a seal plate 21.
Is sealed airtight to the separate plate 7 in advance, so that the packing sheet 12C in the prior art becomes unnecessary and the positioning accuracy of the seal plate 12 is improved. However, it is possible to save labor and time, and it is also possible to easily reduce irregularities on the side wall surface 20S of the cell stack, and to improve the gas sealing performance between the side wall surface and the manifold.

Further, since the sealing plate 21 is coated with a fluororesin and functions to extend the creeping insulation distance T on the side wall surface 20S to about four times the insulation distance t in the prior art, the phosphoric acid mist adheres to the side wall surface 20S. The resulting leakage current can be reduced to less than a quarter of that of the prior art. Further, the core material of the seal plate 21 is made of a low thermal expansion material having a thermal expansion coefficient substantially equal to that of the carbon material which is a main constituent material of the unit cell, so that the cell stack becomes 200 ° C during power generation.
Even if the temperature rises to a near operating temperature, the dimensions of the gas seal double 20 will change following the unit cell 1 and the separate plate 7, and the deterioration of the sealing performance and the long-term deterioration due to the generation of thermal stress will be prevented. Can be prevented.

〔The invention's effect〕

In the present invention, as described above, the gas-impermeable seal plate of the gas seal portion is made of a low-thermal-expansion conductive material coated with a fluororesin, and the seal plate is air-tightly fixed to a predetermined position of the separate plate in advance. It was configured as follows. As a result, the number of gas seal portions conventionally formed of five layers is reduced to four layers, and since the seal plate is integrated with the separate plate in advance, the work of assembling the gas seal plate during the stacking operation of the cell stack can be saved. And the time can be saved, and the side wall surface of the cell stack can be smoothed.
A fuel cell equipped with a gas seal structure that can obtain a fuel cell with a small loss of reactant gas as well as low detonation gas as well as economical advantage with a small number of man-hours due to a marked improvement in the sealing performance of the reaction gas. can do.

In addition, since the seal plate is covered with a fluororesin layer and functions to extend the creepage insulation distance on the side wall of the cell stack several times, the leakage current that was a problem due to the short creepage insulation distance in the conventional technology is suppressed. Therefore, it is possible to provide a fuel cell with low leakage loss of generated power and high insulation reliability.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a gas seal structure of a fuel cell according to an embodiment of the present invention in a partially crushed section for one unit cell, and FIG. 2 is a perspective view showing a conventional gas seal structure. DESCRIPTION OF SYMBOLS 1 ... Unit cell, 2 ... Matrix, 3 ... Electrode base material with ribs, 4 ... Electrocatalyst layer, 5 ... Oxidant electrode, 6 ...
Fuel electrode, 7: Separate plate, 10, 20 ... Gas seal part, 11: Frame-shaped fluororesin sheet, 12A, 12B, 12C ... Packing sheet, 13, 21 ... Seal plate, 22 ... Core material, twenty three
...... Fluororesin layer, 23S ... fusion surface, 10S, 20S ... side wall surface, 2S, 5S, 6S ... edge, 10G ... gap.

Claims (3)

(57) [Claims] 1. A unit for forming a fuel cell stack by laminating a plurality of unit cells each having at least a fuel electrode and an oxidant electrode on both main surfaces of a matrix holding an electrolyte via a separate plate. A cell sealing structure, a frame-shaped fluororesin sheet formed in a square shape and having an inner peripheral portion sandwiched between the matrix and one electrode,
A pair of packing sheets sandwiching the outer peripheral portion of the frame-shaped fluororesin sheet from both sides, and a gas-impermeable seal plate interposed between one side of the packing sheet and the separate plate, A gas seal structure for a fuel cell, wherein the gas-impermeable seal plate comprises a core material and a fluororesin layer covering the core material. 2. The gas seal structure for a fuel cell according to claim 1, wherein the core material is made of one of a glassy carbon material and a low thermal expansion metal material. 3. The gas seal structure of a fuel cell according to claim 1, wherein one surface of the gas-impermeable seal plate is air-tightly fixed to the separate plate in advance.