JPS62165868A - Fuel cell - Google Patents

Abstract

PURPOSE:To construct a fuel cell with high reliable gas seal by providing an electrode with ribs filled with electrolyte holding matrix after filling a hydrophilic material into a groove provided on the end portion parallel to the gas flow path. CONSTITUTION:The hole portion of the edge portion 17a, 17b of a porous electrode is filled with a phosphoric acidophilic powder such as silicon carbide or carbon powder and impregnated with the phosphoric acid, so that the penetration of the gas is prevented for the sake of the surface tension of the phosphoric acid. In order to prevent the falling off of the pasty matrix filled in the groove portion when the both electrodes are assembled as an unit inserting an electrolytic layer 1, the forming of the groove 10 in the end portion of the electrode is performed from the side of the gas flow groove 5a for the upper side electrode (usually positive electrode) of the electrolytic layer and from the side of the catalyst layer coated surface 2b for the down side electrode (usually negative electrode) of the electrolytic layer respectively, and after impregnating a hydrophilic material all over the end portion the pasty matrix is filled in each groove portion, and the wet seal is performed. The silicon carbide fine powder is suitable for the hydrophilic material to be used here.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a fuel cell, and more particularly to a fuel cell which can reliably prevent gas leakage at the ends of electrodes.

[Technical background of the invention and its problems]

2. Description of the Related Art Fuel cells are conventionally known as devices that directly convert energy contained in fuel into electrical energy. This fuel cell usually has a pair of porous electrodes sandwiching an electrolyte layer between them, and a fuel gas such as hydrogen is brought into contact with the back surface of one electrode, and an oxidizing gas such as oxygen is brought into contact with the back surface of the other electrode. Electrical energy is extracted from between the electrodes by bringing them into contact and using the electrochemical reaction that occurs at this time.As long as the fuel gas and oxidant gas are supplied, electrical energy can be extracted with high conversion efficiency. It is something that can be taken out.

FIG. 3 is an exploded perspective view showing an example of the configuration of a unit cell in a ribbed electrode type fuel cell based on the above principle and using phosphoric acid as an electrolyte.

In the figure, 1 is an electrolyte layer formed by impregnating a matrix with phosphoric acid as an electrolyte, and 3a and 3b are an anode electrode and a cathode electrode made of a porous carbon material placed between the electrolyte layer 1. Catalysts 2a and 2b are respectively coated on the side in contact with the catalyst 1, and the rear side has ribs 4a and 4b and grooves 5a and 5b, respectively, through which fuel gas and oxidant gas flow. Here, the grooves 5a through which the fuel gas flows and the grooves 5b through which the oxidant gas flows are regularly formed in parallel in a direction orthogonal to each other. A unit cell is formed as described above, and a unit cell laminate is constructed by stacking a plurality of such unit cells with separators 6 made of dense carbonaceous material sandwiched therebetween.

Further, as shown in FIG. 4, the unit cell laminate is provided with a current collecting plate 7, an insulating plate 8, a clamping plate 9, and a terminal 10 on its upper and lower ends, respectively, and appropriate tightening is performed by applying pressure in the vertical direction. I try to tighten it from the beginning. Further, a pair of manifolds 12 and 13, and 14 and 15 for supplying and discharging fuel gas and oxidizing gas through pipes 16 to gasket 1 via 11 are arranged in the side walls of the unit cell stack, respectively. A fuel cell is constructed by arranging them and tightening and fixing them with an appropriate pressure.

Now, in the fuel cell having such a configuration, the anode electrode 3a
The cathode electrode 3b is made of a carbonaceous porous material because it requires air permeability. Therefore, the fuel gas flowing through the groove 5a may freely pass through the inside of the edge 17a of the anode electrode 3a and leak into the manifolds 14 and 15 on the oxidizing gas side, or the oxidizing gas flowing through the groove 5b may leak. The gas may freely pass through the edge 17b of the cathode electrode 3b and leak into the manifolds 12 and 13 on the fuel gas side, resulting in mixing of both gases, which is extremely dangerous. Therefore, it is necessary to seal the edges 17a and 17b of the anode electrode 3a or the cathode electrode 3b as a measure to prevent gas leakage.
a and 17b are impregnated with a resin or rubber material, or a heat-resistant and acid-resistant resin film is wrapped in a U-shape, or silicon carbide powder is applied to make them hydrophilic, and phosphoric acid, which is the same as the electrolytic solution, is applied. Edge sealing, such as the so-called wet sealing method, is applied.

(Japanese Unexamined Patent Publication No. 60-95863) The last wet seal is a simple method, but the sealing performance is incomplete and the reliability is low.

The process of impregnating the end of an electrode with a hydrophilic material is usually done by immersing the end of the electrode in an aqueous solution of hydrophilic powder, reducing the pressure in the system to impregnate the powder, and then drying it to retain the phosphoric acid. However, in this case, even if a hydrophilic material with a fairly small particle size is used, it is difficult to fill the inside of the porous electrode end because they aggregate in the flowing liquid and form secondary particles. It is impregnated only to the very vicinity of the surface layer.

Therefore, when phosphoric acid was retained here, sufficient sealing performance could not be ensured. Considering these circumstances, R.D.
, Breaalt et al. proposed a method in which the end of the electrode is first impregnated with a hydrophilic material, and then the groove of the gas flow path at the edge is filled with the hydrophilic material, and then phosphoric acid is retained and sealed. (U.S.P. 4,279,970) With this method, the hydrophilic material is filled only in a relatively thin portion (t = 0.5 mm) of the remaining wall of the gas flow groove by the reduced pressure impregnation treatment. The material was sufficiently impregnated, and the groove above it was filled with a hydrophilic material, so when phosphoric acid was retained there, the sealing performance was improved and gas leakage from the electrode end was sufficiently prevented.

Although this method sufficiently prevented gas leakage, it had the disadvantage that gas leakage from the stacked surface of the unit cell would increase if the laminated surface of the hydrophilic material filled in the grooved portion was not sufficiently leveled.

[Object of the Invention] The present invention was made to solve the above-mentioned problems, and it is possible to easily and reliably wet-seal the end of a porous electrode, and also to prevent gas leakage from the cell stack surface. It is an object of the present invention to provide a fuel cell having a highly reliable gas seal that can also prevent

[Summary of the invention]

It is filled with phosphoric acid powder such as silicon carbide or carbon powder, and is impregnated with phosphoric acid to prevent gas from passing through due to the surface tension of the phosphoric acid.

In the present invention, as shown in FIGS. 1 and 2, grooves are formed on the edge of the electrode, and after the remaining thickness of the groove is impregnated with a hydrophilic material, a highly viscous paste is applied to the groove. The reactant gas is sealed by filling the matrix itself.

In this case, when integrating the two electrodes through the electrolyte layer 1, in order to prevent the paste matrix filled in the groove from falling off, the groove 10 at the end of the electrode is formed on the electrolyte layer as shown in FIGS. 1 and 2. At the upper electrode (usually the cathode), the gas flow groove 5a is formed, and at the lower electrode (usually the cathode), from the side where the catalyst layer is coated 2b. After the entire surface is impregnated with the hydrophilic material, each groove is filled with a pasty matrix and wet-sealed. As the hydrophilic material used for this removal, silicon carbide fine powder is suitable.

As mentioned above, the end of the porous electrode with grooves processed in each direction is immersed in an impregnating liquid having the following composition, and this system is connected to a vacuum pump and the cycle of reduced pressure and normal pressure is repeated several times. Fill the entire end of the electrode, especially the remaining thickness of the groove, with parent wood.

After drying in air at 200° C. for 30 minutes, a paste-like matrix containing silicon carbide as a main component was filled.

Composition of impregnating liquid: 5iC (manufactured by Showa Denko) Average particle size 1 μm 120 g Pure water 75n+9 Tricon X-100 (nonionic surfactant)
8g (manufactured by Rohm & Hass) Taflon 3O-J (PTFE dispersion)
1.9 g (manufactured by Mitsui Fluorochemical Co., Ltd.) This is less than the composition of the electrolyte retention matrix used.

The porous electrode wet-sealed as described above is sandwiched between the flat interconnectors, tightened with a surface pressure of 2 kg/d, and then the manifold is attached, and air at a constant pressure is sealed inside the manifold. The rate of air leakage from one end of the was measured at 200°C and was 1 at a sealing pressure of 10 cm A g per 10 cm of seal length.
．． 3 x 10-'cc/sec-cmAg.

Furthermore, the rate of leakage hardly changed even when the air sealing pressure was increased to 20 cmHg. A catalyst layer was applied to the pair of wet-sealed porous electrodes by a known method, and then integrated via the electrolyte retention matrix layer described above to produce a unit cell, and the battery performance was investigated. Equivalent I-V characteristics of the electrode with a legal seal were obtained.

Furthermore, when this battery was operated for a long time under a constant load, it was able to exhibit stable battery characteristics for approximately 5,000 hours without causing crossover of the reactant gas.

〔Effect of the invention〕

As mentioned above, leakage of reactive gas from the electrode end of a single cell produced using a wet-sealed electrode is sufficiently prevented by the filled paste-type matrix and the electrolyte-retaining parent wood impregnated into the remaining flesh. It was done. It was confirmed that this sealing performance was sufficiently ensured even when an abnormal pressure difference (20 cmHg) was applied between the electrodes.

In addition, since the matrix filled in the groove of the lower electrode was in direct contact with the electrolytically retained matrix layer 1, a sufficient liquid junction with the matrix layer 1 was established, and a long-term sealing property of the reactant gases was ensured. Furthermore, the paste-type matrix filled into the processed groove at the upper electrode end via the matrix layer 5 had improved adhesion with the separator S, so that leakage of reaction gas from the stacked surface of the cell was prevented.

According to the present invention, wet sealing of the ends of porous electrodes that ensures high sealing performance over a long period of time can be performed relatively easily compared to conventional methods even when the size of the battery is increased. became.

Batteries manufactured by this method have the advantage that leakage of reaction gas from the stacked surfaces of the single cells is prevented, so it is also advantageous when the batteries are stacked to increase capacity.

[Brief explanation of drawings]

Fig. 1 is a perspective view of a unit cell using a wet-sealed porous electrode of the present invention, Fig. 2 is a side view of the unit cell of Fig. 1, and Fig. 3 is a ribbed electrode (gas flow channel). Fig. 4 is a structural diagram of a unit cell of a fuel cell using a grooved porous electrode). 1... Electrolyte layer 2... Catalyst 3... Electrode
4...Rib 5...Groove +"CF-i Patent Attorney Noriyuki Hirofumi MitsumataFigure 2; Figure 3Figure 4

Claims (2)

[Claims] (1) A conductive porous substrate sandwiching a matrix holding an electrolyte, with flow paths for fuel gas and oxidant gas formed on one side, and fine carbon powder supporting a noble metal catalyst and fluorine on the other side. It consists of a pair of ribbed electrodes coated with a catalyst layer made of a system binder, and outputs electrical energy under the condition that fuel gas and oxidant gas are flowing through each of the gas flow paths. In a fuel cell configured by stacking a plurality of unit cells, a groove is formed at the end of the surface of the ribbed electrode on which the gas flow passage is formed in parallel with the gas flow passage; A fuel cell comprising a ribbed electrode filled with an electrolyte retention matrix after being filled with a material. (2) The fuel cell according to claim 1, wherein the hydrophilic material is silicon carbide, and the electrolyte retention matrix is a mixture of phosphoric acid and silicon carbide.