JPH0785879A - Phosphoric acid fuel cell matrix - Google Patents

Abstract

(57) [Abstract] [Purpose] To improve phosphoric acid retention and electronic insulation. [Structure] Two layers including a phosphoric acid holding layer having a matrix arranged on the fuel electrode side and an electronic insulating layer arranged on the air electrode side,
Alternatively, an electronic insulating layer is formed on both upper and lower main surfaces of the phosphoric acid holding layer,
By constructing each of the electronic insulating layers as three layers arranged on the fuel electrode side and the air electrode side, respectively, the electronic insulating property of the matrix can be secured and at the same time, the phosphoric acid retaining ability can be enhanced. In the layer structure, the electronic insulating layer arranged on the air electrode side suppresses the migration of phosphoric acid to the air electrode side, which is more sensitive to phosphoric acid, and prevents the catalyst layer from being excessively wetted by phosphoric acid. , Making the migration of phosphoric acid from the matrix difficult.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a phosphoric acid fuel cell matrix.

[0002]

2. Description of the Related Art A single cell of a phosphoric acid type fuel cell generally has a structure in which a fuel electrode (anode) and an air electrode (cathode) are arranged on both upper and lower sides of a matrix which holds phosphoric acid which is an electrolyte. FIG. 5 is a partial schematic sectional view showing the structure of a single cell of a phosphoric acid fuel cell. In FIG. 5, this single cell is composed of a fuel electrode 1 composed of a carbon base material 1a and a catalyst layer 1b, a matrix 2, and an air electrode 3 composed of a carbon base material 3a and a catalyst layer 3b. For convenience of description below, regarding the matrix 2,
The constituent materials are schematically shown and the constituent materials are not shown for both electrodes.

The catalyst layers 1b and 3b generally use a material having a large specific surface area such as carbon black as a carrier, and catalyst particles having platinum supported thereon and water repellency and even in a phosphoric acid atmosphere at about 200 ° C. A film formed by mixing stable polytetrafluoroethylene (hereinafter referred to as PTFE) or the like is used. Commonly used carbon carriers include, for example, acetylene black and furnace black, and in each case, primary particles have a particle size of several hundred angstroms, and these particles are aggregated into particles of the order of several microns. The catalyst layers 1b and 3b made of these materials have different characteristics depending on the manufacturing method.
There are many very small pores of 1 micron or less.
On the other hand, the matrix 2 is prepared by mixing silicon carbide 4 having a particle size of several microns or less, which is relatively stable in a phosphoric acid atmosphere at high temperature and has an electronic insulating property, with PTFE 5, which is a chemically stable binder. It is formed into a film and holds phosphoric acid as an electrolyte.

The matrix 2 is manufactured as follows. First, for example, silicon carbide 4 (product number GC # 3, manufactured by Fujimi Abrasives Co., Ltd., having a particle size of about 3 μm)
000) 5 g and a particle diameter of about 0.3 μ manufactured by Shin-Etsu Chemical Co.
Silicon Carbide 4a (trade name Nano Fine-
Weigh 5 g of β), add 200 ml of deionized water to this, and mix for about 20 minutes. Furthermore, for example, the product name Teflon 30J manufactured by Mitsui DuPont Fluorochemicals, that is, PT
Add 1.0 ml of FE5 and mix for about 10 minutes. Then, 100 ml of isopropyl alcohol is added to coagulate the material, and then the cake is collected by centrifugation. The obtained cake is formed into a sheet by a calender roll method, and the matrix 2 can be obtained by baking this at 250 ° C. for 15 minutes.

Fuel electrode 1 (anode) and air electrode 3
At the (cathode) the following reactions occur. Reaction of fuel electrode 1 H ₂ → 2H ⁺ + 2e ⁻ (1) Reaction of air electrode 3 (1/2) O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O (2) Total reaction H ₂ + (1/2) O ₂ → H ₂ O (3) That is, in the fuel electrode 1 , as in the formula (1), hydrogen supplied from the outside is separated into protons and electrons by the action of the catalyst layer 1b. The protons move toward the air electrode 3 in the electrolyte (phosphoric acid) impregnated in the matrix 2 sandwiched between the fuel electrode 1 and the air electrode 3 . On the other hand, the electrons move to the air electrode 3 through the external circuit. In the air electrode 3, and the oxygen in the air supplied from the outside, and protons having moved through the electrolyte from the fuel electrode 1, in contact with the electron which have moved from the fuel electrode 1 through an external circuit, a catalyst layer It reacts by the action of 3b to produce water. [Reaction of formula (2)].

Comparing the catalyst layers 1b and 3b with the matrix 2, the particles composing the catalyst layers 1b and 3b have a much smaller particle size in terms of material and have the same wettability with phosphoric acid. , The catalyst layers 1b and 3b are
This makes it easier to draw in phosphoric acid than the matrix 2 which has to hold phosphoric acid as an electrolyte. Therefore, conventionally, the wettability to phosphoric acid is controlled by increasing the amount of PTFE contained in the catalyst layers 1b and 3b than the amount of PTFE5 contained in the matrix 2 or by changing the heat treatment conditions in the manufacturing process. ing.

[0007]

When the above reaction is focused on the matrix 2, the following problems can be considered. Since hydrogen and air are supplied to both sides of the matrix 2, a shortage of phosphoric acid in the matrix 2 causes a crossover phenomenon in which these gases easily permeate each other through the matrix 2, and as a result, hydrogen and air are generated. It reacts directly and significantly deteriorates the characteristics of the fuel cell.

Since protons move in the phosphoric acid retained in the matrix 2, if the phosphoric acid in the matrix 2 is insufficient, the migration distance of protons becomes long, the internal resistance increases, and the characteristics of the fuel cell deteriorate. . If the phosphoric acid retention in the matrix 2 is poor, the matrix 2 is in direct contact with the fuel electrode 1 and the air electrode 3 , so that more phosphoric acid moves to these electrodes and the diffusion of gas in these electrodes is hindered. As a result, the characteristics of the fuel cell are significantly deteriorated.

If the matrix 2 has an extremely poor electron insulating property, the electrons, which should originally move to the air electrode 3 through the external circuit, move to the air electrode 3 through the matrix 2 and the fuel The battery is internally short-circuited and the characteristics deteriorate. However, conventionally, the catalyst layers 1b, 3b
Compared to the constituent materials of
Since the matrix 2 was formed, in order to secure the phosphoric acid retaining property of the matrix 2, PTFE which is a water repellent is used.
The only way was to control the amount and the firing temperature. However, even in the matrix 2 thus obtained, the phosphoric acid retention is not sufficient, and the matrix 2 is often depleted of phosphoric acid, which results in the catalyst layers 1b and 3b.
Of the catalyst layer 1b, 3b to inhibit the diffusion of gas in the catalyst layers 1b and 3b to reduce the cell output, or the gas crossover occurs through the matrix 2, leading to a decrease in the cell output. There is a problem that the internal resistance of the cell increases due to lack of phosphoric acid and the output voltage of the cell decreases.

Therefore, the performance of the matrix 2 is that the fuel electrode 1 and the air electrode 3 have
Higher phosphoric acid retention, phosphoric acid does not easily move to these electrodes, and further has sufficient electronic insulating property corresponding to the above,
It is desired that the battery does not cause an internal short circuit. The present invention has been made in view of the above points, and an object thereof is to provide a matrix of a phosphoric acid fuel cell having a high phosphoric acid retention property and a good electronic insulation property.

[0011]

In order to solve the above-mentioned problems, the matrix of the phosphoric acid type fuel cell of the present invention comprises a phosphoric acid holding layer arranged on the fuel electrode side and an electronic insulating layer arranged on the air electrode side. Or two electron-insulating layers are formed on the upper and lower main surfaces of the phosphoric acid retaining layer, and each electron-insulating layer is formed on the fuel electrode side and the air electrode side.

[0012]

The matrix of the present invention is a composite of two types of layers in which the phosphoric acid holding layer is made of the same material as the electrode and the amount of PTFE is adjusted, and the electronic insulating layer is made of the same material as the conventional matrix. Therefore, the electronic insulating property of the matrix can be secured, and at the same time, the phosphoric acid retaining capacity can be enhanced. Particularly, in the two-layer structure, by disposing the electronic insulating layer on the air electrode side, it is more sensitive to phosphoric acid. In the three-layer structure in which the phosphoric acid is prevented from moving to the air electrode side, the catalyst layer is prevented from being excessively wetted with phosphoric acid, and the phosphoric acid retaining layer is sandwiched by the electronic insulating layers, it is difficult to move phosphoric acid from the matrix.

[0013]

EXAMPLES The present invention will be described below based on examples. Figure 1
6 is a partial schematic cross-sectional view showing the configuration of the matrix according to the present invention, and the same reference numerals are used for the portions common to FIG. 5, but the illustration of the upper and lower electrode portions is omitted here.

[0014] Matrix 6 is a conventional matrix 2 differs from that shown FIG. 5 according to the present invention, as shown in FIG. 1, the matrix 6 of the present invention, two layers of phosphate retention layer 6a and an electron insulating layer 6b It was formed as a complex consisting of. This matrix 6 can be manufactured as follows. For example, first use 1 of furnace black 7 manufactured by Cabot under the trade name Vulcan XC-72.
Weigh 0 g and deionized water with surfactant 50
Add 0 ml and disperse by ultrasonic waves for about 5 minutes. After that, for example, 4.5 ml of Teflon 30J, a product name of PTFE manufactured by Mitsui DuPont Fluorochemical Co., Ltd., is added,
Mix and stir for about 10 minutes. Next, 100 ml of isopropyl alcohol was added to this dispersion and after stirring for 2 minutes,
Centrifuge to separate cake. The cake thus obtained is subjected to a calender roll machine to form a sheet having a thickness of 70 μm, which is baked in an air atmosphere at about 290 ° C. to form the phosphoric acid retaining layer 6a.

Next, for example, 5 g of silicon carbide 4a (trade name Nanofine-β) manufactured by Shin-Etsu Chemical Co., Ltd. and having a particle diameter of about 0.3 μm is weighed, and 100 ml of deionized water is added thereto.
And mix for about 10 minutes. In addition to this, for example, PT of Teflon 30J under the trade name of Mitsui DuPont Fluorochemicals
Add 0.4 ml of FE5 and mix for an additional 10 minutes.
The obtained dispersion is applied onto the phosphoric acid retaining layer 6a to form the electronic insulating layer 6b. By baking this at about 290 ° C. for 10 minutes, a matrix 6 having a thickness of about 90 μm and having two layers can be obtained. At this time, the electronic insulating layer 6
It is only necessary for b to be as thin as possible because it can only insulate electrons.

Thus, the matrix 6 of the present invention is
To increase the phosphoric acid retention, several hundred Å of furnace black 7 is used, and the phosphoric acid retention layer 6a in which the amount of PTFE 5 is smaller than in the case of the catalyst layer is used. The same two layers of the silicon carbide 4 and the electronic insulating layer 6b in which PTFE 5 is mixed are provided, and they have both the role of retaining phosphoric acid and the role of electronic insulating.

Although the case where the electron insulating layer 6b is formed on one surface of the phosphoric acid retaining layer 6a to form the matrix 6 has been described above, the matrix according to the present invention has the electron insulating layers 6b on the upper and lower surfaces of the phosphoric acid retaining layer 6a. It is also possible to form a composite having a three-layer structure in which the phosphoric acid retaining layer 6a is sandwiched between the electron insulating layers 6b. However, the illustration is omitted. In FIG. 2, portions common to FIG. 5 are represented by the same reference numerals, and the phosphoric acid retaining layer 6a is shown.
FIG. 3 is a partial schematic cross-sectional view of a single cell configured by using a matrix 6 in which an electronic insulating layer 6b is formed on one side of the above, in which case the electronic insulating layer 6b is provided on the air electrode 3 side. The provision of the electronic insulating layer 6b on the air electrode 3 side prevents the phosphoric acid from moving to the air electrode 3 side, which is more sensitive to phosphoric acid, and prevents the catalyst layer 3b from being excessively wetted by phosphoric acid. Because you can.

FIG. 3 similarly shows a matrix 8 having a three-layer structure in which an electronic insulating layer 6b is formed on both upper and lower surfaces of a phosphoric acid retaining layer 6a.
FIG. 3 is a partial schematic cross-sectional view of a single cell configured using. This makes it difficult for phosphoric acid to move from the matrix 8 . FIG. 4 is a diagram showing the change over time in the terminal voltage of the unit cells using the matrix 6 and the matrix 8 , respectively, and the case of the unit cell using the conventional matrix is also shown for comparison. The curve (a) in FIG. 4 shows the characteristics of the single cell using the matrix 6 , the curve (b) shows the characteristics of the single cell using the matrix 8 , and the curve (c) shows the characteristics of the single cell using the conventional matrix. is there.

From FIG. 4, the matrix 8 having a three-layer structure is shown.
The use of the above-mentioned method increases the internal resistance by a slightly larger thickness and the terminal voltage is slightly lower than the case of using the two-layer structure matrix 6. However, a cell using the matrix of the present invention is In comparison, it can be seen that the stable characteristics are maintained for a long time.

[0020]

As described above in the examples, the matrix of the present invention is a composite having a layer acting as a phosphoric acid retaining layer and a layer acting as an electronic insulating layer. The phosphoric acid retaining layer and the electronic insulating layer are two-layered, and the electronic insulating layer is provided on the air electrode side.

The phosphoric acid retaining layer has a three-layer structure in which the upper and lower electronic insulating layers are sandwiched. As a result, since the composite having the layer acting as the electron insulating layer formed on at least one main surface of the layer acting as the phosphoric acid retaining layer, the retention of phosphoric acid in the matrix is prevented from being lowered, and the PTFE is prevented. Since the amount is small, even if the electronic insulating layer is cracked, the structure is such that sufficient phosphoric acid is retained in the phosphoric acid retaining layer, so the possibility of gas crossover is low and stable. It can operate various batteries.

Further, in the matrix having a two-layer structure of the phosphoric acid holding layer and the electron insulating layer, the electron insulating layer is provided on the air electrode side, so that the air electrode side, which is more sensitive to wetting by phosphoric acid, is formed on the air electrode side. The movement of phosphoric acid is suppressed, and the catalyst layer can be prevented from being excessively wetted with phosphoric acid. Furthermore, in the three-layer structure in which the phosphoric acid retaining layer is sandwiched by the electronic insulating layers, phosphoric acid from the matrix becomes difficult to move.

[Brief description of drawings]

FIG. 1 is a partial schematic sectional view showing a matrix having a two-layer structure according to the present invention.

FIG. 2 is a partial schematic cross-sectional view of a single cell using a two-layer matrix according to the present invention.

FIG. 3 is a partial schematic cross-sectional view of a single cell using a matrix having a three-layer structure according to the present invention.

FIG. 4 is a diagram showing changes over time in cell terminal voltage, which is shown in comparison between a matrix according to the present invention and a conventional matrix.

FIG. 5 is a partial schematic sectional view showing the structure of a single cell of a phosphoric acid fuel cell.

[Explanation of Codes] 1 fuel electrode 1a carbon base material 1b catalyst layer 2 matrix 3 air electrode 3a carbon base material 3b catalyst layer 4 silicon carbide 4a silicon carbide 5 PTFE 6 matrix 6a phosphoric acid retaining layer 6b electronic insulating layer 7 furnace black 8 matrix

Claims (3)

[Claims] 1. A matrix of a phosphoric acid fuel cell sandwiched between a fuel electrode and an air electrode, comprising a phosphoric acid retaining layer and an electronic insulating layer, wherein the electrons are formed on at least one main surface of the phosphoric acid retaining layer. A phosphoric acid fuel cell matrix, wherein an insulating layer is disposed on the air electrode side. 2. The matrix of a phosphoric acid fuel cell according to claim 1, comprising two layers, a phosphoric acid retaining layer arranged on the fuel electrode side and an electronic insulating layer arranged on the air electrode side. . 3. The matrix of a phosphoric acid fuel cell according to claim 1, which is composed of three layers in which electron insulating layers are formed on both upper and lower main surfaces of a phosphoric acid retaining layer.