JPS6178065A - Fuel cell - Google Patents

Abstract

PURPOSE:To obtain large and excellent retension force and yield force of phosphoric acid by constituting a matrix retaining phosphoric acid with only a matter rich in affinity with phosphoric acid. CONSTITUTION:In matrix, phosphate 1 is combined with each other partially to become a plate having many small holes 2. Matrix is formed by making the second, third and fourth group elements in the periodic table, salt and oxide powder into a thin plate and impregnated by phosphoric acid and reacted to be phosphate. For example, when using zirconium oxide, zirconium oxide powder is made to be a thin plate and impregnated by phosphoric acid and heated. Then, matrix plate can be obtained.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a fuel cell that uses air, oxygen, hydrogen, hydrocarbon reforming gas, etc. as an oxidizing agent and fuel, and phosphoric acid as an electrolyte. The present invention relates to a fuel cell with a matrix having superior performance in retaining certain phosphoric acids.

[Background of the invention]

In fuel cells that use phosphoric acid as an electrolyte, a method is used in which phosphoric acid is retained between a pair of gas diffusion electrodes by impregnating K, phenolic resin fiber cloth or silicon carbide powder bound with polytetrafluoroethylene. It is being The temperature of phosphoric acid for phenolic resin fiber cloth is 150C.
It can withstand long-term use in the following conditions, but as the degree of change increases,
It has the disadvantage of being soluble in phosphoric acid. In order to increase the power generation efficiency of the fuel cell, it is preferable to keep the cell temperature around 20 QC, and phenolic resin fiber cloth cannot be used at this temperature. On the other hand, a matrix made of silicon carbide bonded with polytetrafluoroethylene does not have this problem, and the fuel cell can be operated at high temperatures for a long time. This battery is Special Publication No. 58-1
It is described in Publication No. 56. By the way, in order to operate the fuel cell for a long time, K must prevent the phosphoric acid in the matrix from moving elsewhere, and must also replenish the phosphoric acid that has decreased during power generation from outside the matrix.

In order to prevent the movement of phosphoric acid, it is highly desirable that the matrix is made of a material that has a high phosphoric acid retention capacity and absorbs phosphoric acid, that is, a material that has a high affinity for phosphoric acid. Silicon carbide and phosphoric acid have a poor affinity, but polytetrafluoroethylene used as a binder is a water repellent and has the property of repelling phosphoric acid.

Therefore, using polytetrafluoroethylene,
There is a problem that the phosphoric acid retention capacity and the phosphoric acid absorption capacity become small.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the drawbacks of the prior art described above and to provide a fuel cell equipped with a matrix having excellent performance in terms of phosphoric acid retention and phosphoric acid absorption.

[Summary of the invention]

The key point of the present invention is to configure a matrix that holds phosphoric acid only with substances that have a high affinity for phosphoric acid. The matrix is made up of a substance that has a binding effect before being stabilized, and by reducing the particle size, the pore size of the voids is reduced and the capillary force is strengthened, increasing phosphoric acid retention and phosphoric acid absorption. It increases power. The present invention has discovered phosphate as a substance suitable for this purpose and clarified the structure of a KJ matrix that retains phosphoric acid. The phosphate used in the present invention belongs to Group 2 of the periodic table.

It is a compound of at least one kind of Group 3 and Group 4 elements and phosphoric acid. Among these compounds, zirconium phosphate, titanium phosphate, tin phosphate, aluminum phosphate, and silicon phosphate are particularly suitable for the present invention.

The structure of the matrix according to the present invention is as shown in the model in Fig. 1, in which phosphates 1 are partially bonded to each other, forming a plate shape with many small holes 2. Although it has a structure that is integrated with 3, it is also possible to have a plate-like structure made of only phosphate. The method of forming the matrix of the present invention is to form a thin plate of salts or oxide powders of Group 2, Group 3, and Group 4 elements of the periodic table, impregnate them with phosphoric acid, and react with them. It is something to do. The phosphates produced here have the function of partially binding each other before solidifying. For example, when using zirconium oxide, a porous matrix plate can be obtained by forming the zirconium oxide powder into a thin plate, impregnating it with phosphoric acid, and then heating it. Another method is to knead zirconium oxide and acetic acid to make a paste, form it into a plate shape, and then heat it to create a matrix made of porous zirconium phosphate. One method is to create a porous zirconium phosphate matrix. In the present invention, any method may be used, and -
Zirconium oxide was mentioned as an example, but titanium, tin,
Oxides of silicon, aluminum, etc. can be used similarly.

Hereinafter, the present invention will be explained in detail according to examples.

[Embodiments of the invention]

Example (1) Zirconium oxide was taken up as a substance that reacts with phosphoric acid to produce phosphate. 100g of zirconium oxide with an average particle size of 1μm and 160g of phosphoric acid concentrated to a concentration of 100%
Thoroughly knead the polytetrafluoroethylene under pressure,
A paste-like substance was made. Next, this paste-like substance was applied to the catalyst layer side of the electric coffin with a lip to a thickness of 0.2 to 0.3 fl.

The size of the electrode used was 10 square. The electrode, whose surface was coated with a paste of zirconium oxide and 9-acid, was placed in an atmospheric firing furnace and heated at 150C for 2 hours while flowing nitrogen, then heated at 23QC for 20 hours to completely react the phosphoric acid and zirconium oxide and release phosphorus. Made into acid zirconium. At this time, before the zirconium phosphate crystallizes, some of it
It acted as an inder and formed a matrix layer on the electrode that was integrated with the electrode. FIG. 2 shows the components of a fuel cell using this. In FIG. 2, numeral 4 corresponds to the phosphate 1 shown in FIG. This phosphoric acid holding matrix is made integrally with an electrode consisting of a catalyst layer 5 and a lip-attached substrate 6. Note that an electrode consisting of the catalyst layer 5a and the ribbed substrate 63 is similarly pressed against the other surface. Then, the separators 7 and 7a are further pressed against each other to form a unit cell. The electrolyte, phosphoric acid, was impregnated into the phosphoric acid retention matrix before assembling the cell, using nine cells made in this way, at a current density of 220 mA/1-tl, and a temperature of 205 mA/1-tl.
Figure 3 shows the change in battery voltage over time during continuous operation at a gas pressure of 1 ata. In FIG. 3, the phosphoric acid retention matrix shown by humans is used, and the phosphoric acid retention matrix shown by B is used. As is clear from FIG. 3, when the phosphoric acid retention matrix of the present invention is used, the phosphoric acid retention capacity becomes stronger, so the decrease in phosphoric acid during power generation is suppressed, the phosphoric acid replenishment interval becomes longer, and the phosphoric acid retention matrix becomes stronger. It was found that when acid is replenished, the phosphoric acid is quickly absorbed into the phosphoric acid retention matrix, which reduces the change in battery voltage over time.

Example (2) Titanium oxide was taken up as a substance that reacts with phosphoric acid to produce phosphate. Titanium oxide 100 with an average particle size of 2 μm
g and 245 g of phosphoric acid concentrated to 100% were sufficiently kneaded in polytetrafluoroethylene to form a paste-like substance. Thereafter, a paste was applied onto the electrodes to a thickness of 0.2 to 0.3 m in the same manner as in Example (1). Next, it was placed in an atmosphere firing furnace and heated for 1 hour while flowing nitrogen.
The mixture was heated at 50C for 2 hours and then at 260C for 20 hours to complete the reaction between phosphoric acid and titanium oxide to form titanium phosphate. By this method, it was possible to obtain a phosphoric acid retention matrix made of titanium phosphate integrated with the electrode, as in Example (1). Using this, the change in battery voltage over time when a battery with the same structure as in the actual test was operated continuously under the same conditions is shown by C in FIG. FIG. 4 KB shows the results when a conventional phosphate retention matrix was used, similar to that shown in FIG. In this example, the example (
Similar to 1), excellent results were obtained.

Example (3) Tin oxide was used in place of the zirconium oxide used in Example (1). 100 g of tin oxide having an average particle diameter of 2 μm and 130 g of phosphoric acid concentrated to a concentration of 100% were kneaded in a polytetrafluoroethylene peaker to form a paste. Thereafter, a phosphoric acid retention matrix was obtained under the same conditions as in Example (2). The results obtained when a battery using this phosphoric acid retention matrix was continuously operated under the same conditions as in Example (1) are shown by D in FIG. B is when a conventional phosphate retention matrix is used. It can also be seen from FIG. 5 that the method according to the present invention is superior.

Example (4) 10c of 6g of zirconium oxide powder with an average particle size of 1μm
A pressure of about 0.3 wK was applied to the r11 corner. The pressure is 20
oKg/aA, and a polytetrafluoroethylene plate was placed underneath to keep the shape intact. This pressure-molded product was impregnated with 9.6 g of phosphoric acid concentrated to a concentration of 100%, heated in air at 150C for 2 hours, then at 230C for 20 hours,
A porous thin plate of zirconium phosphate was created by reacting phosphoric acid with zirconium oxide. This was placed between electrodes in the same manner as shown in Example (1) and used as a phosphoric acid retention matrix, and the performance measured as a battery was similar to the results shown in FIG. 3.

Example (5) Fine titanium oxide powder 7gt-10z square with a thickness of about 0.3
The pressurization method for applying pressure to m is the same as in Example (4). After impregnating this pressure-molded product with 17 g of phosphoric acid concentrated to a concentration of 100%, it was heated to 2B at 150C in air, then 2Q at 260C.
h to react with phosphoric acid and titanium oxide to obtain a phosphoric acid-retaining matrix plate made of porous titanium phosphate.

Example (6) Fine tin oxide powder Log with a thickness of about 0.3 m at a 10α angle
Pressure was applied. The pressurization method was the same as in Example (4). This press-molded product was impregnated with 13 g of phosphoric acid concentrated to a concentration of 100 m, and heated under the same conditions as in Example (5) to obtain a phosphoric acid retention matrix plate made of porous tin phosphate.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to produce a fuel cell with a longer life and less change over time in cell voltage than a fuel cell using a conventional phosphoric acid retention matrix. The reason for this improvement is thought to be that the phosphate salt has a high affinity with phosphoric acid and has a large retention force.

In the examples of the present invention, a single substance was used, but a mixture of these substances may be used, and aluminum or silicon may also be used.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram modeling the phosphoric acid retention matrix of the present invention, FIG. 2 is a perspective view of a fuel cell using the phosphoric acid retention matrix of the present invention, and FIGS. 3, 4, and 5.
The figure is a characteristic diagram showing the continuous operation performance of a fuel cell using a phosphoric acid retention matrix according to the present invention in comparison with a conventional one. 1... Phosphate, 2... Small pore, 3... Electrode, 4...
... Phosphoric acid retention matrix, 5.5a... Catalyst layer,
6.6a unit room voltage (V diode)

Claims (1)

[Claims] 1. In a fuel cell having a matrix holding phosphoric acid between a pair of gas diffusion electrodes, the matrix is composed of a porous thin plate-shaped phosphate, and the voids in the matrix are A fuel cell characterized in that phosphoric acid is retained in a portion of the fuel cell. 2. The fuel according to claim 1, wherein the phosphate is a compound of phosphoric acid and at least one of Group 2, Group 3, and Group 4 elements of the periodic table. battery. 3. The fuel cell according to claim 1, wherein the phosphate is made of zirconium phosphate. 4. The fuel cell according to claim 1, wherein the phosphate is made of titanium phosphate. 5. The fuel cell according to claim 1, wherein the phosphate is made of tin phosphate. 6. In a fuel cell having a matrix that holds phosphoric acid between a pair of gas diffusion electrodes, phosphoric acid is held in the voids of the matrix made of phosphate that is integrated with the electrodes. A fuel cell featuring: 7. In claim 6, the phosphate is a reaction product of a salt or oxide of at least one of Group 2, Group 3, and Group 4 elements of the periodic table and phosphoric acid. A fuel cell characterized by: 8. Claim 6, characterized in that the means for integrating the electrode and the phosphate is by applying a kneaded mixture of zirconium oxide and phosphoric acid onto the electrode, and then heating and reacting the mixture. fuel cell. 9. Claim 6, characterized in that the means for integrating the electrode and the phosphate is by applying a kneaded mixture of titanium oxide and phosphoric acid onto the electrode, and then heating and reacting the mixture. fuel cell. 10. Claim 6, characterized in that the means for integrating the electrode and the phosphate includes applying a kneaded mixture of tin oxide and phosphoric acid onto the electrode, and then heating and reacting the mixture. fuel cell. 11. In a fuel cell that holds phosphoric acid as an electrolyte between a pair of gas diffusion electrodes, some of the phosphates are bonded to each other in a porous plate-like matrix. A fuel cell characterized in that phosphoric acid is retained in the fuel cell. 12. In a fuel cell of a type in which phosphoric acid as an electrolyte is held between a pair of gas diffusion electrodes, a salt or oxidation of at least one of Group 2, Group 3, and Group 4 elements of the periodic table is used. 1. A fuel cell characterized in that phosphoric acid is held in a matrix made of a phosphate formed by forming a powder into a plate shape and then reacting with phosphoric acid to form a plate shape. 13. The fuel cell according to claim 12, wherein the oxide is zirconium oxide. 14. The fuel cell according to claim 12, wherein the oxide is titanium oxide. 15. The fuel cell according to claim 12, wherein the oxide is tin oxide.