JPS6155225B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fuel cell using phosphoric acid as an electrolyte, and more particularly to a fuel cell having a structure in which a fuel cell matrix for holding phosphoric acid is arranged between a pair of gas diffusion electrodes. be.

Conventionally, in fuel cells using phosphoric acid as an electrolyte, a matrix for holding phosphoric acid has been used that is a mixture of phenolic resin fiber cloth or silicon carbide powder with polytetrafluoroethylene as a binder. However, these matrices have the following drawbacks. That is, in the case of using a phenolic resin fiber cloth as a matrix, when the operating temperature of the fuel cell reaches 130° C. or higher, the phenolic resin gradually carbonizes, and as a result, long-term operation becomes impossible. In order to eliminate these drawbacks, it is conceivable to lower the operating temperature of the fuel cell, but in this case a serious problem arises in that the output of the fuel cell is significantly reduced. Another difficulty is that sufficient care must be taken to control the temperature of the fuel cell to prevent it from becoming partially high temperature. On the other hand, in those that use silicon carbide as a matrix, the operating temperature of the fuel cell is
Silicon carbide has the advantage of being able to be heated to temperatures as high as 190 to 200°C, but on the other hand, silicon carbide is not a perfect insulator, has a specific resistance value of 10 ³ to ^{10 7} Ω・cm, and has electronic conductivity. There is a drawback. That is, there is a problem in that a short circuit occurs inside the fuel cell, resulting in poor performance. Furthermore, in the case of silicon carbide, since carbon and silicon carbide are reacted at high temperatures during manufacture, unreacted carbon remains, which causes problems in electronic conductivity. In addition, the negative effects of iron present as an impurity, such as deterioration of catalyst activation, are also a major problem.

The object of the present invention was made in view of the above-mentioned drawbacks, and it is an object of the present invention to provide a fuel cell with significantly improved cell performance.

To achieve such an object, the present invention provides a fuel cell comprising a pair of gas diffusion electrodes and a matrix holding phosphoric acid as an electrolyte interposed between the gas diffusion electrodes, wherein the matrix is made of titanium oxide. This is a fuel cell characterized in that it is configured by bonding the following with a binding material.

The present invention will be explained below.

In general, the important properties of a fuel cell matrix are (1) stability against phosphoric acid at high temperatures (190°C to 200°C) (not soluble in high-temperature phosphoric acid); (3) It has no electronic conductivity (being an insulator), and (4) It has a high affinity for phosphoric acid. However, after various studies were conducted on materials that satisfy these properties, it became clear that titanium oxide satisfies these conditions. That is,
The matrix is made of fine powder of titanium oxide mixed with 1 to 15% by weight of polytetrafluoroethylene as a binder. The matrix made in this way is stable against high-temperature phosphoric acid, has no electronic conductivity, and has a high affinity for phosphoric acid, and its retention of phosphoric acid is better than that of conventional matrices. It has the characteristic that it is nearly twice as large as the

Hereinafter, the present invention will be explained in detail with reference to Examples.

98g of titanium oxide fine powder obtained by thermally decomposing metatitanic acid at 900℃ (passed through a 200 mesh wire mesh)
A solution of polytetrafluoroethylene fine powder suspended in water with a surfactant as a binder.
Add 30ml to make a paste. The amount of polytetrafluoroethylene fine powder is about 2 g. Next, this mixture was heated at 200°C for about 8 hours to remove water, and then 98% concentrated phosphoric acid was added.
A matrix retaining the phosphoric acid was obtained. The amount of phosphoric acid is approximately 70% by weight. The matrix made in this way is placed on one gas diffusion electrode to a certain thickness.
After coating to a thickness of 0.3 mm, the other gas diffusion electrode was stacked and integrated to assemble the fuel cell.
FIG. 1 shows the structure of a fuel cell according to the present invention. The gas diffusion electrode is made by applying platinum-supported carbon powder onto carbon paper. In FIG. 1, 1 is a matrix impregnated with phosphoric acid, 2 is a matrix impregnated with phosphoric acid;
is the anode (fuel electrode), 3 is the cathode (air electrode)
, hydrogen is present at the anode 2, and hydrogen is present at the cathode 3.
The air is in contact with each other. Figure 2 shows the current density-voltage characteristics of a battery using the matrix obtained in the present invention, and Figure 3 shows the change in battery voltage over time when the battery was continuously discharged at a current density of 200 mA/ ^cm2 . It shows. 2 and 3, for comparison, the characteristics of a fuel cell using a conventional silicon carbide matrix is indicated by the symbol B.

As is clear from FIGS. 2 and 3, when the matrix of the present invention is used, superior performance can be obtained compared to the conventional one. This is because the matrix of the present invention has no electronic conductivity, has a high phosphoric acid retention ability, has a high affinity for phosphoric acid, and is stable to phosphoric acid. it is conceivable that.

As described above, according to the present invention, since the matrix is made of titanium oxide and a binder, it is possible to obtain an excellent matrix that eliminates the drawbacks of the conventional matrix.
The performance of batteries can be greatly improved, and its practical value is extremely large.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of a fuel cell using the matrix of the present invention, and Fig. 2 shows the relationship between current density and voltage in a fuel cell using the matrix of the present invention and a fuel cell using a conventional matrix. 3 are diagrams showing the relationship between discharge time and voltage in a fuel cell using the matrix of the present invention and a fuel cell using a conventional matrix. 1...matrix, 2...anode, 3...
cathode.

Claims (1)

[Claims] 1. A fuel cell comprising a pair of gas diffusion electrodes and a matrix holding phosphoric acid as an electrolyte interposed between the gas diffusion electrodes, wherein the matrix binds titanium oxide with a binder. A fuel cell characterized by comprising: 2. The fuel cell according to claim 1, wherein the binder is polytetrafluoroethylene.