JPS6113572A - Phosphoric acid type fuel cell - Google Patents

Abstract

PURPOSE:To improve a sealing property of the peripheral part of an electrode base material by filling the peripheral part of the electrode base material with gel of a phosphate compound. CONSTITUTION:Zirconium phosphate gelatinized by adding phosphoric acid fills the peripheral part of a fuel electrode base material 8, or the wet sealing part 9, for instance, by press fitting. Zirconium phosphate is gelatinized while being dissolved in phosphoric acid when a sufficient amount of phosphoric acid is existing while otherwise being solidified. In either case, zirconium phosphate snows a fully excellent gas sealing property as compared with the case where former SiC is used for filling.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a phosphoric acid fuel cell, and more particularly to a wet seal at the peripheral edge of an electrode base material.

[Conventional technology]

A phosphoric acid fuel cell is a well-known device that generates electricity through an electrochemical reaction between an externally supplied fuel and an oxidizing agent, and basically consists of two electrodes separated by an electrolyte of phosphoric acid. It is operated at an operating temperature of 150 to 220°C and an operating pressure of normal pressure to 10 atmospheres. In phosphoric acid fuel cells, it is absolutely necessary and important to prevent leakage of reactive gases inside and outside the cell, and if leakage occurs and mixture of reactive gases occurs, there is a risk of a major disaster. be.

In particular, the electrode periphery is important as a region where the reaction gas must be effectively and reliably sealed.

One of the sealing methods that has conventionally been performed at the periphery of an electrode is a wet seal that uses the wetting effect of the electrolyte itself. This method is a technique as disclosed in Japanese Patent Publication No. 58-152, and utilizes the fact that the electrode base material of a phosphoric acid fuel cell is composed of a gas-permeable porous carbon sheet. The method involves filling the periphery of the material with electrolyte through capillary action, and involves filling techniques with materials such as tantalum, graphite, and polyallylsulfone to make the periphery of the electrode base material hydrophilic. These fillers are intended to make it easier for t-solites to be retained around the periphery of the electrode base material, and they do not dissolve in the electrolyte.

Note that recently, silicon carbide (SiC) has been widely used as a filler.

Another gas sealing method conventionally used at the peripheral edge of an electrode is a gas seal.

A sheet made of polytetrafluoroethylene or fluorine rubber is used as the packing, and a method of filling the periphery of the electrode base material with fluorine rubber has also been used.

Among these conventional gas sealing technologies, the packing seal made of fluorocarbon rubber has the best performance as a seal. However, one of the important techniques in phosphoric acid fuel cells is the replenishment of phosphoric acid, and this replenishment is often performed using the wet seal portion at the peripheral edge of the electrode base material. Phosphoric acid replenishment is an essential technique because phosphoric acid shortages occur during operation due to evaporation and scattering of phosphoric acid. Therefore, a wet seal is necessary as long as the wet seal portion is used to replenish phosphoric acid.

However, in conventional wet seals, no matter how easily the phosphoric acid is retained by the filling, the phosphoric acid becomes very fluid at the operating temperature and moves easily, creating a pressure difference at the operating pressure side. It is easy to leak outside in case of
There were drawbacks to the gas sealing properties, such as when the phosphoric acid was insufficient, the gas sealing properties at the wet seal portion were most significantly reduced.

[Summary of the invention]

This invention was made in order to eliminate the above-mentioned drawbacks of the conventional electrode base material, and the sealing performance of the electrode base material periphery is improved by filling the electrode base material periphery with a gel of a phosphate compound. The purpose is to improve.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings.

The drawing is an enlarged cross-sectional view of the main parts of a conventional phosphoric acid fuel cell and an embodiment of the present invention. In the figure, (1) and 'QI are gas separation plates, (2) are oxidant gas flow passages, (3) are oxidant electrode base materials, and (4) are catalysts fixed to oxidant electrode base materials. (5) is a fluorine-based rubber gasket placed on the periphery of the oxidizer electrode base material (3) and catalyst layer (4), (6) is an electrolyte holding matrix made of SiC, and (7) is a fuel electrode catalyst layer. , (8) is the fuel electrode base material, (9) is the wet seal part provided at the circumference Ii & part of the fuel electrode base material (8), 0υ is the fuel gas flow path part, and (2) is the external rear part. It's a bar. This figure shows an example in which the packing seal technique is used at the oxidizer electrode and the wet seal technique is used at the fuel electrode. The external reservoir 09 serves to supply phosphoric acid to the electrolyte holding matrix (6) through the wet seal part (9), and when the phosphoric acid in the external reservoir is insufficient, this phosphoric acid is supplied from the outside. Refill the external reservoir (6).

In order to clarify the gas sealing problem in the phosphoric acid fuel cell shown in this drawing, the inventor used various methods to separate the leakage rate of the reactant gas in the path shown by a = c in the drawing. I succeeded in measuring it. route a”
-c is the part where the reaction gas is expected to leak, path a is the leak between the fluoro rubber gasket (5) and the gas separation plate (1), and path is the leak through the wet seal part (9). , path C is a leak that passes between the wet seal part (9) and the gas separation plate a. Regarding route a, when fluorine-based grease was applied between the fluorine-based rubber gasket (5) and the gas separation plate (1), a highly satisfactory gas sealing property was obtained. However, regarding route C, , fuel electrode base material (
8) In the conventional case in which the peripheral edge, that is, the wet seal part (9), was filled with fine particles of silicon carbide to retain phosphoric acid, gas leaked at a considerable rate. It became clear that if phosphoric acid was not retained, a considerable amount of gas would leak from the path.

Next, zirconium phosphate, which has been gelled by adding phosphoric acid, is applied to the periphery of the fuel electrode base material (8), that is, the wet seal part (9).
), for example, by press-fitting, and measuring the leakage rate of the reaction gas in the valley path, it was found that the leakage of the reaction gas from paths 3 and 4 was several times lower than in the conventional case where SiC was filled and phosphoric acid was retained. It was demonstrated that the gas sealing performance was improved by 20%. In addition, the leakage rate of the reaction gas was measured by simulating a case where phosphoric acid was insufficient by reducing the amount of phosphoric acid added to zirconium phosphate, and the leakage rate of the reaction gas was measured, and it showed better cassealing performance than the conventional case filled with SiC. Zirconium phosphate dissolves in phosphoric acid and gels when there is sufficient phosphoric acid present, and solidifies when it does not, but the above measurement values show that zirconium phosphate is superior to conventional SiC in all cases. *J states that it exhibits sufficiently superior cassealing properties compared to when it is filled.

The case where zirconium phosphate is filled in the peripheral part of the electrode base material (8), that is, the wet seal part (9) has been described above, but the materials that gel in the presence of phosphoric acid are not limited to zirconium phosphate, but include Ag, St, There are many Ta-based phosphate compounds, and it is clear that these phosphate compounds will exhibit excellent gas sealing properties similar to zirconium/acid.

In addition, even when the wet seal part (9) is formed with a gel of a phosphate compound as in the above example, the role of the electrolyte passage between the external reservoir σ and the electrolyte holding matrix is somewhat inhibited. On the contrary, this role becomes more effective than in the conventional example.

In the above embodiment, the present invention was applied to a phosphoric acid fuel cell equipped with a gas separation plate (1), a QO reactive gas flow path section (2), and an αυ.
It goes without saying that the present invention can also be applied to those having a reaction gas flow path section in (8) and (8).

In addition, in the above embodiment, the periphery of the oxidizer electrode is sealed with a fluorine rubber gasket (5), and the fuel electrode base material (8) is sealed.
In the above description, we have explained the case where the periphery of the electrode base material (3) and (8) is a wet seal filled with zirconium phosphate gel, but the opposite may also be used. Even when filled, the same effect as in the above embodiment can be obtained.

〔Effect of the invention〕

As described above, according to the present invention, since the periphery of the electrode base material is filled with gel of a phosphate compound, the sealing performance of the periphery of the electrode base material is improved.

BRIEF DESCRIPTION OF THE DRAWINGS The drawing is an enlarged sectional view showing the main parts of a conventional phosphoric acid fuel cell and an embodiment of the present invention. In the figure, (1), (11 are gas separation plates, (2), (
lυ is the reaction gas flow path, (3) and (8) are the electrode base materials, (4) and (7) are the catalyst layers, (5) is the fluorine rubber packing, (6) is the electrolyte retention matrix, and (9) is the wet seal part. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (3)

[Claims] (1) A unit cell, a gas separation plate, and the above, in which a fuel and oxidizer electrode having an electrode base material and a catalyst layer fixed thereto are disposed with an electrolyte holding matrix interposed therebetween, with the catalyst layers facing each other; A phosphoric acid fuel comprising an uneven gas flow path formed by a plurality of grooves on either side of an electrode and a gas separation plate, and in which the above-mentioned unit cells and gas separation plates are alternately stacked. A phosphoric acid fuel cell, characterized in that a periphery of the electrode base material is filled with a gel of a phosphate compound. (2) The phosphoric acid fuel cell according to claim 1, wherein the gel of the phosphate compound is formed from a mixture of the phosphate compound and phosphoric acid. (3) The phosphoric acid fuel cell according to claim 2, wherein the phosphate compound is zirconium phosphate.