JPS6046515B2 - Method for manufacturing electrolyte retention matrix for fuel cells - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing an electrolyte retention matrix for a fuel cell formed of an inorganic compound and polytetrafluoroethylene.

As is well known, a fuel cell (for example, a phosphoric acid electrolyte fuel cell) has a matrix holding liquid phosphoric acid as an electrolyte between gas diffusion electrodes placed opposite each other, and each gas diffusion electrode contains hydrogen. It is used by passing a gas containing oxygen as a fuel gas and air, for example, containing oxygen, as an oxidizing agent.

Here, in order to operate the fuel cell in an optimal state, the electrolyte retention matrix must have the following characteristics. That is, (1) it is stable under fuel cell operating conditions; (2) Hydrophilic and has liquid retention properties. (3) Prevent cross-crossing and mixing of gases within the fuel cell. (4) It should be thin and have sufficient mechanical strength to ensure sufficient contact with the electrode and minimize internal resistance. Various limitations arise in manufacturing electrolyte retention matrices having the above characteristics using conventional manufacturing methods.

When selecting matrix materials from the viewpoint of chemical stability, inorganic compounds such as silicon carbide, zirconium oxide,
Tantalum pentoxide can be selected, and a fluorine-based polymer can be used as a binder. Conventionally, a suspension of a fluorine-based polymer is added to and mixed with the matrix material selected in this way, and the moisture is removed by heating. Forms an electrolyte-retaining matrix. In order to obtain mechanical strength, the amount of binder added may be increased to strengthen the bond between the matrix materials. However, since the fluorine-based polymer used as a binder is water-repellent, simply increasing the amount of binder added to increase mechanical strength will deteriorate its hydrophilicity as an electrolyte retention matrix and its ability to retain electrolyte. . On the other hand, if the amount of fluorine-based polymer used as a binder is reduced, hydrophilicity will be improved, but the mechanical strength will be reduced and the matrix material will not be bonded, resulting in cross-crossing and mixing of gases within the fuel cell. It becomes easier.

One way to solve these problems is to use a fibrous matrix material from the beginning and bind this material with a binder, but fibrous inorganic compounds are expensive and require large quantities. There are naturally limits to its use in fuel cells, and it is not common.

The present invention was made to solve the above problems.
The binder is made into fibers, and the matrix material is bonded with the binder to form a mesh-like electrolyte retention matrix, which enables fuel cells to operate in optimal conditions and can be realized at a low cost. The purpose is to provide a manufacturing method for.

That is, the manufacturing method according to the present invention uses a suspension of a fluorine-based polymer as a binder, mixes this with a matrix material made of an inorganic compound, and after heating the mixture, adds an additive such as methanol. In addition, there is a method of further heating and then molding it into a predetermined shape. Hereinafter, the manufacturing method according to the present invention will be explained in detail.

Before describing the examples, two main steps of the present invention will be described. The first step takes advantage of the generally known fact that micelles in suspensions are destroyed and separated into a solid phase and a liquid phase when heat is applied, and a suspension of a fluorine-based polymer and an inorganic compound are The mixture with the matrix material is heated to precipitate the solid phase fluorine-based polymer, thereby adhering the fluorine-based polymer to the matrix material. In the second step, an additive such as methanol is added to the mixture heated in the first step to destroy micelles remaining in the mixture. At this time, methanol acts as a micelle-destroying agent, and the surfactant covering the fluorine-containing polymer particles is destroyed, exposing the fluorine-containing polymer particles, causing bonding between the particles and promoting fiberization. Excess methanol added is removed by further heating. Through the above two steps, the fluorine-based polymer serving as the binder is sufficiently fiberized, and the inorganic compound of the matrix material is attached to the fiber to produce the desired network-like electrolyte holding matrix. Although methanol is exemplified as an additive, micelle destruction occurs with any of ethanol, propanol, isopropanol, and isobutyl alcohol, and the same results as when methanol is used are obtained.

Next, an example will be explained.

Example 1 A suspension of polytetrafluoroethylene as a binder in 100y of silicon carbide as a matrix material, i.e. commercially available 6% by weight polytetrafluoroethylene particles and 6% by weight.
36 cc of Teflon 301J (manufactured by Mitsui Fluorochemical Co., Ltd.), which is a surfactant, and 30 cc of water were added and mixed with stirring, and the mixture was left in an open oven heated to 100°C to 150°C for 2 hours to remove moisture. I went to

Next, add 20 cc of methanol to the mixture from which water has been removed.
After stirring, the mixture was placed in an open chamber at 100°C and left to stand for 3 minutes to remove methanol water. Water was added to the resulting mixed material and kneaded into a single powder using a kneader kneader.
This kneaded material was rolled out into a sheet shape using a roller to form a matrix base material. This matrix base material was impregnated with a 95% phosphoric acid solution to obtain an electrolyte retention matrix. In addition, in the above manufacturing process, 3 to 100y of silicon carbide
Although 5% by weight of the binder was sufficient to spread into a sheet, if the matrix material and binder were kneaded without adding methanol and the binder was spread into a sheet, 2% by weight of the binder was added. Retention of electrolyte is poor. Example 2 Water was added to the mixed material obtained in Example 1 above and applied directly onto the electrode surface to form a matrix base material, and this matrix base material was impregnated with 95% phosphoric acid solution to form an electrolyte retention matrix. did.

With the electrolyte retention matrix obtained by this coating method, the envelope pressure was obtained from 0.7 kg/d to 1.05 k9/d.
When matrix material and binder are kneaded without adding methanol, 0.14k9/d to 0.21k9/Cl
．． It just turned out to be. Furthermore, when the matrix substrate shown in the above two examples was made into a seal with a thickness of 0.3 to 0.5 200 mm and hung by holding one end, it did not break due to its own weight, and the While mechanical strength was obtained, when a sheet of the matrix base material with the same dimensions as above was formed without adding methanol and suspended, it broke under its own weight. Further, using the electrolyte retention matrix shown in the above-mentioned example, a fuel cell having a unit cell size of 200 Wr1n square as shown in FIG. 1 was assembled and its characteristics were investigated.

In the figure, reference numeral 1 denotes an electrolyte holding matrix, and a fuel electrode 2 and an air electrode 3 each having a platinum catalyst are arranged on both sides of the electrolyte holding matrix 1, and a carbon vapor 4 is arranged on each electrode. A bipolar separator 7 forming a fuel passage 5 and an air passage 6 above the vapor 4
is located. The energization characteristics when hydrogen gas and air are supplied to the respective passages of the fuel cell constructed in this way and made to flow are as shown in FIG. 2.

In this figure, symbols 1 and ■ are the characteristic curves of the fuel cell having the electrolyte retention matrix shown in Example 1 and Example 2, respectively, and ■ is the characteristic curve of the fuel cell using the conventional electrolyte retention matrix. It has a curve. As can be seen from the figure, the voltage drop versus current density of the fuel cell using the electrolyte retention matrix according to the present invention is greatly improved. As described above, according to the present invention, by using a chemically stable, low-cost matrix material and a small amount of binder, it has excellent hydrophilicity and electrolyte retention, sufficient mechanical strength, etc., and excellent battery characteristics. It has the advantage that an electrolyte retention matrix that is greatly improved in width can be obtained through a simple process.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view schematically showing a fuel cell using an electrolyte retention matrix according to the present invention, and FIG. 2 is a characteristic diagram showing the current conduction characteristics of the fuel cell according to the present invention. 1... Electrolyte retention matrix, 2...
・Fuel electrode, 3... Air electrode.

Claims (1)

[Claims] 1 Mix an inorganic compound powder and a suspension of polytetrafluoroethylene, heat the mixture, and add at least one kind selected from methanol, ethanol, propanol, isopropanol, and isobutyl alcohol to the heated mixture. A method for producing an electrolyte retention matrix for a fuel cell, comprising: mixing additives, heating the mixture to remove the additives and moisture, and forming the resulting material into a predetermined thin plate shape. .