JPS6029190B2 - Method for impregnating electrolyte into the matrix of matrix fuel cells - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for impregnating an electrolyte into a matrix of a matrix fuel cell.

Matrix fuel cells are constructed by impregnating a matrix interposed between a fuel electrode and an oxidizer electrode with a liquid electrolyte, and it is impossible to impregnate the liquid electrolyte into the matrix without altering its properties. This is extremely important in the production of matrix fuel cells.

Conventionally, the method of impregnating liquid electrolyte into the matrix of a matrix fuel cell was to impregnate the matrix with liquid electrolyte during battery assembly.
At this time, since the electrolyte has strong hygroscopicity, it absorbs moisture from the outside, changing the concentration of the electrolyte, and the volume of the electrolyte increases by the amount of moisture absorbed from the outside, which leaks out when the battery is assembled. There was a fear that it would.

An object of the present invention is to provide a method capable of impregnating a liquid electrolyte into a matrix without changing the concentration of the liquid electrolyte, eliminating the drawbacks of the conventional methods described above.

Next, embodiments of the present invention will be described with reference to the drawings. Figure 1 shows the structure of the battery, and Figure 2 shows the structure of the electrode.The fuel electrode 1 has a carbon fiber substrate 2, a water-repellent layer 3 made of polytetrafluoroethylene and graphite powder, and a noble metal catalyst supported. carbonaceous powder and a small amount of polytetrafluorocarbon. It consists of a catalyst layer 4 mixed with ethylene. As can be seen from FIG. 2a, a passage 30 is formed in the water repellent layer 3, and this passage 30 is filled with the same material as the hydrophilic catalyst layer 4 to bring the catalyst hydrophilic layer into contact with the carbon fiber matrix. It's forcing me. Further, the oxidizer electrode 5 is composed of a carbon fiber base material 6, a water repellent layer 7, and a catalyst layer 8. The carbon fiber substrates 2 and 6 of these electrodes are in contact with gas separation plates 9 and 10, respectively, forming gas compartments 11 and 12. The gas compartment 11 has a fuel gas supply 9 and a groove opening 13;
The gas compartment 12 is provided with an oxidizing gas supply port 14 and a drain port 16, respectively. Further, the catalyst layers 4 and 8 of both electrodes are in contact with a porous fibrous matrix 17 such as noboroid, tantalum oxide cloth, asbestos paper, etc. to form an electrolyte compartment 18. In a fuel cell having such a configuration, the matrix 17 not impregnated with liquid electrolyte is sandwiched between the fuel electrode 1 and the oxidizer electrode 5, and the carbon fiber base layers 2 and 5 sides are further sandwiched between the gas separation plates 9 and 10 to form a battery. After assembling, liquid electrolyte (Japanese 3P04, WS04,
(KOH, NaOH, etc.), and the matrix 17 is impregnated with a liquid electrolyte through the electrode from the gas side layer of the fuel electrode 1. The aforementioned passage 30 plays a major role in this impregnation. At this time, dry air, nitrogen, or an inert gas is allowed to flow through the oxidant gas section 12. Table 1 shows that the fuel gas compartment 11 is filled with 10W% phosphoric acid 3P04 at a temperature of 2500°C, and the distance traveled by the phosphoric acid reaching the matrix 17 through the passage 30 of the fuel electrode is investigated in relation to time. It is something that The results show that phosphoric acid at a high concentration (10%) permeates into the matrix at a slow rate, despite having a viscosity as high as 19 centipoise. By the way, 1.0 per single cell. 25 in the area of 60 x 60 (square) with the power of the sphere W
When impregnating with 10% phosphoric acid at a temperature of 0.00%,
In the case where the electrolyte passages are provided in the permeable water layer at 8 willow pitch,
The matrix was able to be impregnated with the specified electrolytic solution in about 2 hours. Table 1 Adequate liquid electrolyte matrix 17
After the liquid electrolyte is impregnated into the fuel gas compartment 11, the excess liquid electrolyte filled in the fuel gas compartment 11 is removed from the gas outlet 15, and the fuel gas compartment 1
Similarly to the oxidant gas compartment 12, dry air, nitrogen and inert gas are passed through the compartment 1 for drying.

If the amount of electrolyte in the matrix 17 is insufficient, repeat the same operation. This deficiency can be confirmed by detecting gas leakage from the fuel electrode side on the oxidizer electrode side using a gas chromatograph, gas detector, etc. During electrolyte impregnation, the liquid electrolyte filled in the gas compartment 11 passes through the carbon fiber base material 2 and passes through the protruding portions (passages 30 ), passes through the catalyst hydrophilic layer 4, and reaches the inside of the MATO IJ box 17. Although phosphoric acid has a high viscosity at room temperature, the viscosity decreases when it is heated to a high temperature.

For example, as shown in Figure 6, with 10 skin t% phosphoric acid, 30
A substance with a viscosity of 15 specific p at °C has a viscosity of 16 p at 100 qC.
Therefore, the viscosity can be reduced to about 1/10. Therefore, by supplying the phosphoric acid electrolyte to the fuel gas compartment in a state in which the temperature of the phosphoric acid electrolyte is raised to lower its viscosity, the matrix can be impregnated with the electrolyte relatively easily. In this case, if only the phosphoric acid is heated, the temperature of the phosphoric acid will drop inside the battery, so it is desirable to heat the battery by placing it in a furnace or the like. Furthermore, the viscosity of phosphoric acid decreases when its concentration is lowered. For example, as shown in Table 2, in the case of 2500 phosphoric acid, it has a viscosity of about 19 ratio p at 10 t%, but 27. The position becomes p. Therefore, an electrolytic solution with a predetermined concentration can also be obtained by repeatedly impregnating a matrix with a phosphoric acid electrolytic solution of a low concentration and then heating the battery to near the operating temperature. Table 2 How to make the passage 30 in this fuel electrode 1 will be explained based on FIGS. 3 to 5.

First, lattice-shaped molds 20 to 22 are thinly formed on the surface of the carbon fiber base material 2 surrounded by the film forming frame 19. The mold 20 has a lattice shape, and the mold thickness corresponds to the thickness of the twill water layer 3. After placing the mold 20, a mixture of polytetrafluoroethylene and graphite is applied onto the carbon fiber substrate 2 to a thickness of 0.3 to 0.5 ribs by screen printing, spraying, or the like. After application, the mold is removed to form the passageway 30 of FIG. 2a. Furthermore, a mixture of carbonaceous powder supporting a noble metal catalyst and polytetrafluoroethylene is applied thereon by screen printing, spraying, or the like to form the catalyst hydrophilic layer 4.
Since the catalyst hydrophilic layer 4 enters the portion excluding the mold, the catalyst hydrophilic layer 4 comes into contact with the carbon fiber base material 2 . After drying, this is heated and fired to produce a fuel electrode consisting of three layers: a carbon fiber base material, a filtrated water layer, and a catalyst hydrophilic layer. In this case, the amount of polytetrafluoroethylene used as a binder is 30 to 80% by weight in the water-repellent layer to prevent leakage of the liquid electrolyte.On the contrary, the amount of polytetrafluoroethylene used as a binder in the hydrophilic layer is 0.1% to a maximum of 1%. up to % by weight. FIGS. 4 and 5 show an example in which a mold having a shape different from that in FIG. 3 is used. The mold 21 in FIG. 4 is an elongated rectangle, and a plurality of molds are arranged at intervals.

In FIG. 5, a mesh mold 22 is placed on the carbon fiber base material 2. In FIG. Like the mold 20, the molds 21 and 22 are both molds for forming the protruding portions of the catalyst hydrophilic layer. The oxidizer electrode 5 has a three-layer structure similar to the fuel electrode 1, as shown in FIG. are sequentially coated and heated and fired.

The degree of polarization of the oxidant electrode 5 is much greater than that of the fuel electrode 1, and it is not preferable to reduce the reaction area by providing the passage 30 in FIG. As described above, according to the present invention, the liquid electrolyte can be injected from the fuel electrode side after the fuel electrode and the oxidizer electrode are roughly combined by inserting a matrix, so that the electrolyte does not change in quality due to moisture absorption. This makes it possible to impregnate the required amount of electrolyte at the desired concentration without increasing the volume, and has the added effect of making it easy to replenish electrolyte during operation, making it suitable for practical use. This provides many advantages.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of a matrix fuel cell according to the present invention, FIG. 2 a is a longitudinal sectional view of a fuel electrode, and FIG. 2 b is a longitudinal sectional view of an oxidizer electrode. FIGS. FIG. 6 is a graph showing the relationship between temperature and viscosity of phosphoric acid with different concentrations. 1...Fuel electrode, 2,6...Carbon fiber base material, 3,7...
... Water repellent layer, 4,8... Catalyst hydrophilic layer, 5.
... Oxidizer electrode, 9, 10 ... Gas separation plate, 11, 12 ... Gas compartment, 13, 14 ... Gas supply port, 15, 16 ... Gas exhaust Exit, 17...
... Matrix, 18 ... Electrolyte compartment, 19
...Filming frame, 20, 21, 22...Model. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] 1. In a matrix type fuel cell in which a fuel electrode and an oxidizer electrode are disposed with a matrix sandwiched between them, and a fuel gas and an oxidant gas are supplied from the opposite side of the fuel electrode and the oxidizer electrode, respectively, the carbon fiber A fuel cell is assembled by providing a passage through the water-repellent layer of a fuel electrode, which is formed by sequentially laminating a base material, a water-repellent layer, and a catalyst hydrophilic layer, and bringing the carbon fiber base material into contact with the catalyst hydrophilic layer. 1. A method for impregnating a matrix of a matrix fuel cell with an electrolyte, which comprises subsequently impregnating a liquid electrolyte from the fuel gas compartment side through a fuel electrode.