JPH0636776A - Solid polymer electrolyte type fuel cell - Google Patents

Abstract

PURPOSE:To make an electrolyte layer thin after a fuel cell is formed and improve the performance of the electrolyte type fuel cell by coating and impregnating an electrolyte liquid dispersed and mixed with solid acid grains carrying the sulfuric acid group on the insulator of an inorganic material on the surface of an electrode. CONSTITUTION:Hydrophilic reaction layers 2 made of hydrophilic and hydrophobic carbon black and polyethylene tetrafluoride and hydrophobic gas diffusion layers 3 made of hydrophobic carbon black and polyethylene tetrafluoride are laminated, pressed, and sintered, platinum acid chloride is coated on the surfaces of the reaction layers 2 for oxidation and hydrogen reduction process to obtain a catalyst carrying gas diffusion electrode carrying a platinum catalyst. A solution dispersed with solid acid grains having the sulfuric acid group containing titanium oxide as a base material in a Nafion solution is coated and impregnated on the reaction layer faces of the electrode. Two electrodes are heated and pressed with the impregnated faces faced to each other to obtain an electrode provided with a thin electrolyte layer l having a large ion exchange capacity.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a solid polymer electrolyte fuel cell.

[0002]

2. Description of the Related Art A solid polymer electrolyte fuel cell uses an ion exchange resin membrane, which is a solid polymer membrane, as an electrolyte, and electrodes are bonded to both sides of this membrane. The main features of the fuel cell are: It is as follows. (1) The maximum operating temperature is about 100 to 120 ° C., and the operation can be performed at almost room temperature. (2) Since the internal resistance of the fuel cell can be remarkably reduced by making the electrolyte membrane thin, it is possible to operate at a high current density. (3) Therefore, the battery becomes compact. (4) Since the polymer membrane is essentially gas impermeable, the operating pressure can be arbitrarily set for the cathode and the anode. As described above, since the solid polymer electrolyte fuel cell uses the polymer membrane as the electrolyte, the internal resistance of the cell is remarkably reduced due to the low temperature operation, the differential pressure operation between the cathode and the anode, and the thinning of the polymer membrane. A major feature is the reduction.

As the polymer membrane for this fuel cell, a styrene-divinylbenzene resin, which was widely used as an ion exchange resin membrane in the early stage of development, was used as a core, and an ion exchange group was introduced into this. However, the cell life was not sufficient because it was physically or chemically unstable with respect to electrochemical phenomena and reactions occurring on the surface and inside of the polymer membrane of the fuel cell. Therefore, in recent years, perfluorocarbon resins having a sulfonic acid group as an ion-exchange group have come to be generally used because they are physically and chemically more durable.

A perfluorocarbon resin having a sulfonic acid group as an ion exchange group, that is, a perfluorocarbon sulfonic acid resin has the following structure.

[0005]

[Chemical 1] As a film-shaped product, Nafion 117 (Nafio
n 117: a product name manufactured by Du Pont Co., Ltd.) is often used conventionally. A gas diffusion electrode having a catalyst supported on the electrode surface is used as the electrode. Next, the prior art of the fuel cell will be described in more detail with reference to manufacturing examples of the polymer electrolyte fuel cell by these conventional means.

(Conventional example) By roll rolling, a hydrophilic reaction layer (about 40 to 50 μm) comprising hydrophilic carbon black, hydrophobic carbon black and polytetrafluoroethylene.
And a hydrophobic gas diffusion layer (about 400 to 500 μm) composed of hydrophobic carbon black and polytetrafluoroethylene are laminated and pressure-bonded, and hot press (380 ° C., 175 kg /
Cm ² for 3 seconds) to obtain a gas diffusion electrode having water repellency. Next, chloroplatinic acid is applied to the surface of the reaction layer by suction, and oxidation and hydrogen reduction treatments are performed to obtain 2 mg / cm 2.
Supports ² platinum catalysts. The catalyst-supporting gas diffusion electrode thus obtained and the electrolyte membrane Nafion 117 (about 0.175 mm
Thickness) and are joined by hot pressing at 130 to 145 ° C. for 60 seconds to obtain a conventional electrode. At the time of power generation, an oxidizing agent such as air and a fuel composed of hydrogen gas are caused to flow through the cathode and the anode, respectively, and an electric current is obtained while maintaining the cell temperature at 100 ° C. or lower. Table 1 shows an example of the power generation performance evaluation conditions.

[0007]

[Table 1]

Generally, the performance of a fuel cell is evaluated by the magnitude of the voltage drop (overvoltage) in the cell caused by the extraction of current during power generation. The smaller the overvoltage, the better the performance. In a polymer electrolyte fuel cell, the theoretical voltage is about 1.23 V, but when current is taken out, the voltage drops due to overvoltage in the cell. For example, the voltage is 0 when the current density is 0.3 A / cm ^2. 6 ~ 0.8V
Becomes The main ones of such overvoltages are as follows. (1) Reaction overvoltage mainly controlled by oxygen reduction reaction rate on the cathode side (2) Electric resistance overvoltage caused by the electric resistance of the electrode and ion transfer resistance of the electrolyte membrane (3) Movement of reaction gas in the electrode Concentration overvoltage due to resistance

Among these overvoltages, the concentration overvoltage of (3) becomes remarkable mainly on the high current side of about 1 A / cm ² or more, and can be improved by making the gas diffusion layer porous. The overvoltages of (1) and (2) can be reduced by improving the method of joining the electrode, the electrolyte constituent material, and the electrolyte membrane to the electrode, and contributes most to the improvement of battery performance. The reaction overvoltage of (1) becomes small if the reduction reaction rate of oxygen is improved. This reaction rate is mainly affected by the amount of catalyst supported, the contact area between the electrolyte and the catalyst (electrochemical reaction interface area), pH (hydrogen ion concentration) and oxygen partial pressure in the reaction part, and these values are The larger the value, the higher the reaction rate. The overvoltage of (2) can be reduced by lowering the electrical resistance of the electrode material. Further, the ion transfer resistance of the electrolyte membrane can be reduced by increasing the ion exchange capacity of the membrane material and thinning it.

Therefore, conventionally, the overvoltages of (1) and (2) have been reduced by the following method. (1) The reaction interfacial area per unit weight of the catalyst is increased by reducing the supported catalyst particle size as small as possible. Specifically, the reaction layer is formed using hydrophilic carbon black carrying fine particles of platinum. (2) A liquid electrolyte is applied to the surface of the reaction layer to increase the amount of contact with the catalyst. (3) An alloy with platinum is used as a catalyst material. (4) Increase the ion exchange capacity of the electrolyte. (5) Thin the electrolyte membrane.

Although each of the above methods has been conventionally applied in various ways, it has the following problems. (1) There is a limit to making platinum into fine particles, and when the particle size is reduced, the catalytic activity is significantly reduced due to sintering of the catalyst particles. (2) When a liquid electrolyte is applied to the reaction layer, the reaction interfacial area increases, but the electrolyte impregnated in the reaction layer prevents the reaction gas (oxygen gas) from diffusing onto the catalyst particles.
As the current density goes up, no improvement in performance is seen. (3) Although alloy materials with platinum have been studied, there are problems in durability and the like. (4) Since the moldability of the electrolyte from the electrolyte solution to the membrane deteriorates as the ion exchange capacity increases, there is a limit to the increase in the ion exchange capacity. (5) The thinning of the electrolyte membrane shortens the ion migration distance, which reduces the ion migration resistance and thus the electrical resistance. The electric resistance directly affects the voltage drop rate of the battery when increasing the current density, and the smaller the electric resistance, the smaller the voltage drop. However, reducing the thickness of the electrolyte membrane causes problems such as formation of pinholes on the membrane, pressure resistance during differential pressure operation, and reliability.

[0012]

In the above-mentioned conventional solid polymer electrolyte membrane fuel cell, various means are applied to reduce the overvoltage in the cell, but the conventional means for improvement are as described above. There were challenges.

In view of the above-mentioned state of the art, the present invention is to provide a solid polymer electrolyte fuel cell which solves the problems of the conventional solid polymer electrolyte fuel cells.

[0014]

Means for Solving the Problems The present invention is directed to the reaction layer surface of a catalyst-supporting gas diffusion electrode on which a catalyst is supported, in an organic solvent solution of a perfluorocarbon sulfonic acid resin or in a mixed solution of the organic solvent and water. Characterized by applying and impregnating a mixed dispersion solution in which solid acid particles supporting sulfuric acid groups are mixed and dispersed on an insulator made of a material, and then facing the coated surfaces of two electrodes by thermocompression bonding. And a solid polymer electrolyte fuel cell.

That is, according to the present invention, a perfluorocarbon sulfonic acid resin which has been widely used in the past is used as an insulator of an inorganic material having a sulfuric acid group supported on the surface thereof, that is, a solid acid, which has an ion exchange capacity of the sulfonic acid resin. Disperse and mix the same as or larger than. Since the density of the solid acid particles is larger than that of the sulfonic acid resin, the ion exchange capacity per unit volume is larger than that of the resin alone.
A mixed solution of the solid acid and a sulfonic acid resin is applied to and impregnated on the surface of the catalyst-carrying gas diffusion electrode, and the application surfaces of the two electrodes are faced to each other by thermocompression to form a battery,
A battery is formed without previously molding the electrolyte into a membrane. As a result, an attempt is made to form an electrolyte and a mixed layer of a catalyst and an electrolyte having an ion exchange capacity larger than that of a conventional membrane.

[0016]

The electrode for a solid polymer electrolyte fuel cell according to the present invention configured as described above is used as a catalyst-supporting gas diffusion electrode in an organic solvent solution of perfluorocarbon sulfonic acid resin or a mixed solution of the organic solvent and water. The following effects can be expected by applying and impregnating a mixed dispersion solution in which solid acid particles having a sulfuric acid group are mixed and dispersed therein. (1) Since the formed electrolyte layer has a larger ion exchange capacity than the conventional electrolyte, it has the following effects. (A) Since the ion migration resistance in the electrolyte becomes small, the electric resistance becomes small. (B) Since the hydrogen ion concentration in the catalyst supporting region on the surface of the reaction layer is high, the reaction rate is high. Therefore, the reaction overvoltage becomes small. (C) Since the same performance can be obtained with a thicker membrane than the conventional membrane, it is not necessary to extremely thin the electrolyte membrane and the reliability of the membrane is improved. (2) Since the electrolyte is simply applied, impregnated, and thermocompression-bonded onto the electrode without being formed into a film, a relatively thin electrolyte layer can be formed, and electric resistance can be reduced. (3) Since the electrolyte is impregnated not only on the catalyst on the surface of the electrode but also on the catalyst existing inside the electrode near the surface, the reaction interface area is widened and the reaction resistance can be reduced.

The solution of the perfluorocarbon sulfonic acid resin used in the present invention is, for example, Aldrich Chemical C
Lower aliphatic alcohol (containing 10% water) containing 5% perfluorocarbon sulfonic acid resin sold as a Nafion Solution by ompany
There is a solution. Further, it is known that the affinity of the perfluorocarbon sulfonic acid resin with an organic solvent is dissolved in a lower aliphatic alcohol or another organic solvent having a high polarity when the ion exchange capacity is large. Further, the solid acid particles having a sulfate group used in the present invention are typically those in which a sulfate group and SO ₄ ²⁻ are carried on metal oxide particles such as TiO ₂ and ZrO ₂ . This is, for example, TiCl ₄
And water mixed and heated to TiCl ₄ + H ₂ O → Ti (OH)
The precipitation of Ti (OH) ₄ is obtained by the reaction of ₄ + 4HCl,
This dry powder is added to 1N H ₂ SO ₄ , filtered to remove excess H ₂ SO ₄ , and then dried, for example at 600 ° C.
It is obtained by firing for 3 hours to obtain SO ₄ ² -group-supporting TiO ₂ powder. For example, in a solid acid in which TiO ₂ carries a sulfate group, the ion exchange capacity is about 2 meq / g,
It is about twice as large as about 0.9 meq / g of Nafion.
Further, since the density of the solid acid is about 2.5 times larger, the ion exchange capacity per unit volume of the solid acid is about 5 times.
About twice as large.

Further, the catalyst-supporting gas diffusion electrode of the present invention is a gas diffusion electrode on which an electrode catalyst is supported. For example, a mixture of carbon black and polyfluorinated ethylene is molded on a sheet by rolling and then contains a catalyst component. There is an electrode which carries a catalyst by an oxidation or hydrogen reduction treatment after applying the solution, or an electrode which carries an electrocatalyst powder together with polyfluoroethylene on a porous carbonaceous substrate. The present invention is not limited to these gas diffusion electrodes.

[0019]

EXAMPLE An example of the solid polymer electrolyte fuel cell of the present invention will be given to explain the constitution and operation of the present invention in more detail. (Example 1) (1) From a hydrophilic reaction layer (about 40 to 50 μm) made of hydrophilic carbon black, hydrophobic carbon black and polytetrafluoroethylene by roll rolling, and from hydrophobic carbon black and polytetrafluoroethylene A hydrophobic gas diffusion layer (about 400 to 500 μm) is laminated, pressure-bonded, and sintered by hot pressing (380 ° C., 175 kg / cm ² , 3 seconds) to obtain a gas diffusion electrode having water repellency. Next, chloroplatinic acid is applied to the surface of the reaction layer by suction, and subjected to oxidation and hydrogen reduction treatment to obtain a catalyst-supporting gas diffusion electrode carrying ² mg / cm ² of platinum catalyst. (2) Using a suction type hot plate heated to about 70 to 90 ° C., 5 is applied to the reaction layer surface of the catalyst-supporting gas diffusion electrode.
% Nafion solution (Aldrich Chemical Company, USA)
Then, a solution in which solid acid particles having a sulfuric acid group and having titanium oxide as a base material were dispersed was applied and impregnated. (3) The solid acid-containing Nafion-coated catalyst-supporting gas diffusion electrode obtained in (2) was faced with the reaction layer surface, and 130 to 14
Bonding was performed by hot pressing at 5 ° C. for 60 seconds to obtain an electrode. (4) The cross section of the electrode obtained in (3) was observed with a microscope, the thickness of the electrolyte layer was about 100 μm, there was no penetration in the electrolyte layer, and the solid acid particles were dispersed almost uniformly in the electrolyte. It was confirmed that it was done. (5) A schematic view of the solid polymer electrolyte fuel cell obtained by the above method is shown in FIG. In FIG. 1, 1 is an electrolyte layer of solid acid-containing Nafion having a thickness of about 100 μm, 2 is a hydrophilic carbon black, Pt catalyst, and a hydrophilic reaction layer of polytetrafluoroethylene having a thickness of about 40 to 50 μm, and 3 is a hydrophobic carbon. About 4 consisting of black and polytetrafluoroethylene
It is a hydrophobic gas diffusion layer having a thickness of 00 to 500 μm.

Example 2 The reaction area of the electrode according to the present invention obtained in the item (1) of Example 1 and the conventional electrode obtained in the conventional example is 180
A power generation test was performed in a single cell of cm ² to obtain a current-voltage characteristic curve. The power generation test conditions are the same as those shown in Table 1. FIG. 2 shows a current density-voltage curve. It was revealed that the performance of the electrode was improved as shown in FIG.

(Example 3) Further, Table 2 shows the result of analysis of the power generation performance result in Example 2 by the power generation characteristic equation E = E ₀ -b log (i) -iR. In the trial formula, E ₀ is an equilibrium potential considering the catalytic activity, b is a Tafel b coefficient, and R is a differential electric resistance.

[0022]

[Table 2] It can be seen from the results in Table 2 that the electrode according to the present invention has a decreased reaction resistance and thus an increased E ₀ . Further, the decrease in the electric resistance R is large, which is considered to be due to the decrease in the electric resistance of the electrolyte layer, and the effect of the present invention is clear.

[0023]

According to the present invention, the electrode surface is coated and impregnated with an electrolyte solution prepared by dispersing and mixing solid acid particles carrying a sulfuric acid group on an insulator of an inorganic material without using a conventional polymer electrolyte membrane. The formed electrolyte layer becomes thin. Further, since the electrolyte layer has an ion exchange capacity larger than that of the polymer electrolyte, the electric resistance of the electrolyte layer becomes small, and the reaction rate increases and the reaction resistance decreases. With the above effects, it is possible to provide a solid polymer electrolyte fuel cell having excellent performance.

[Brief description of drawings]

FIG. 1 is a schematic view of a main part of a solid polymer electrolyte fuel cell according to an embodiment of the present invention.

FIG. 2 is a chart showing a performance comparison between the solid polymer electrolyte fuel cell of the present invention and a conventional one.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yuuo Hirata 4-6-22 Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture Mitsubishi Heavy Industries Ltd. Hiroshima Research Laboratory (72) Inventor Takuya Moriga 4 Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture 6-22 No. 6 Hiroshima Research Laboratory, Mitsubishi Heavy Industries, Ltd.

Claims (1)

[Claims] 1. A catalyst-supported gas diffusion electrode having a catalyst-supported reaction layer surface on an insulator made of an inorganic material in an organic solvent solution of a perfluorocarbon sulfonic acid resin or a mixed solution of the organic solvent and water. A solid polymer electrolyte type characterized by coating and impregnating a mixed dispersion solution in which solid acid particles carrying a sulfate group are mixed and dispersed, and then heating and press-bonding the coated surfaces of two electrodes facing each other. Fuel cell.