JP2003086192A - Fuel cell and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance a cell's characteristics, simplify its arrangement, and reduce the amounts of noble metals used, particularly by improving an oxidant electrode to prevent the cell's performance from being decreased by the permeation of liquid fuel such as hydrogen or methanol to an oxidant. SOLUTION: A generating element comprises a fuel electrode 2, a catalyst/ oxide/polymer electrolyte thin layer 4 and a metal catalyst layer 5 serving as the oxidant electrode 4A, and an electrolyte membrane 3 formed of a polymer membrane sandwiched inbetween. Gas flow distribution panels 8 and 9 which respectively form a fuel flow passage and an oxidant flow passage are provided on the respective outer surfaces of the fuel electrode 2 and the oxidant electrode 4A serving as generating elements, to constitute a unit cell. The catalyst/oxide/ polymer electrolyte thin layer 4 is composed of a surface-modified oxide having at least one selected from oxides or from among an SO3 H group, a COOH group, a PO3 H group and an OH group; a catalyst in which at least one kind of metal selected from among platinum, palladium, rhodium and iridium is dispersed and supported on at least either a carbon powder or carbon fiber; and a solid polymer electrolyte material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell having a fuel electrode, an electrolyte layer and an oxidant electrode, and more particularly to a fuel cell which can bring high performance characteristics to the oxidant electrode and a method for producing the same. .

[0002]

2. Description of the Related Art A fuel cell is a generator for supplying electric power by supplying a hydrogen-containing gas, an organic alcohol or the like and a gas containing oxygen to a porous electrode provided with a catalyst. Hydrogen is oxidized on the electrode, and hydrogen ions conduct through the electrolyte and move to the cathode side. At the cathode, the supplied oxygen reacts with the transferred hydrogen ions to produce water. In addition, the electrons generate electric energy by flowing through the external circuit.

Among the fuel cells, a solid polymer fuel cell using a solid polymer membrane having a hydrogen ion conductor as an electrolyte is compact, has high output density, and can be operated by a simple system. , Is attracting attention as a mobile power source for on-site use for space and stationary, and for vehicles. That is, in this fuel cell, a fuel electrode, an oxidizer electrode, and an electrolyte membrane composed of a polymer membrane sandwiched between them constitute a power generating element. A unit cell is configured by providing a gas distribution plate that forms the agent flow path. As the polymer electrolyte membrane, a perfluorocarbon sulfonic acid membrane (for example, Nafion product name, manufactured by DuPont) is used.

This polymer film has a thickness of about 50 to 100 μm and exhibits hydrogen ion conductivity in a state of containing water, but when dried, it becomes an insulator and does not function as an electrolyte. In a polymer electrolyte fuel cell, hydrogen is passed through one side of this polymer membrane and air or oxygen is passed through the other side to generate electricity, but hydrogen and oxygen pass through the polymer electrolyte membrane (crossover phenomenon). There is a characteristic. In particular, it is known that in a wet state where the polymer membrane functions, the amount of hydrogen permeated is large, which causes consumption of hydrogen and drastic deterioration of battery characteristics.

Conventionally, various techniques have been proposed for this gas crossover (for example, JP-A-7-9011).
No. 1, etc.). In these technologies, a method of mixing and dispersing platinum or an oxide in a polymer film to generate water by the reaction of hydrogen and oxygen in the film to reduce humidification of the film and gas crossover is disclosed. Has been done. However, in the conventional method, since the reaction proceeds in the membrane, the heat generation thereof causes microdestruction or thermal melting of the membrane, which is not a desirable configuration from the viewpoint of extending the life of the battery. In addition, since the diffusion of oxygen is slower than that of hydrogen, the diffusion of oxygen in the film is rate-determining and the noble metal catalyst cannot be effectively used, and it is necessary to mix a large amount of the noble metal catalyst into the film. There's a problem.

[0006]

As described above, in the prior art, there are various problems to be solved from the viewpoint of extending the life of the battery or effectively utilizing the noble metal catalyst.

The present invention has been made in view of the above circumstances, and in particular, by improving the oxidizer electrode, the characteristics are improved and the structure is improved by preventing the deterioration of the performance due to the permeation of liquid fuel such as hydrogen or methanol to the oxidizer side. It is an object of the present invention to provide a fuel cell capable of simplifying the manufacturing process and reducing the amount of precious metal used.

Another object of the present invention is to provide a method of manufacturing a fuel cell, which can improve the cell performance and manufacturing quality by paying particular attention to the oxidizer electrode.

[0009]

In order to achieve the above object, in the invention according to claim 1, power generation is performed by a fuel electrode, an oxidizer electrode, and an electrolyte membrane composed of a polymer membrane sandwiched between them. In the fuel cell constituting the unit cell, the oxidant electrode is made of an oxide by forming a device and providing a gas distribution plate forming a fuel flow path and an oxidant flow path on the outer surface of the power generation element. And a catalyst / oxide comprising a solid polymer electrolyte material and a catalyst in which at least one metal selected from platinum, palladium, rhodium and iridium is supported and dispersed on at least one of carbon powder and carbon fiber. Provided is a fuel cell including a thin polymer electrolyte layer.

According to a second aspect of the invention, in the fuel cell according to the first aspect, the catalyst, the oxide, and the oxide of the thin polymer electrolyte layer are at least one selected from zirconia, tin oxide, titania, and ceria. And a mixture containing at least one of these oxides.

According to a third aspect of the invention, in the fuel cell according to the first or second aspect, the oxide of the catalyst / oxide / polymer electrolyte thin layer is SO ₃ H group, COOH group, PO ₃ H group.
There is provided a fuel cell, which is a surface-modified oxide having at least one selected from a group and an OH group.

In the invention according to claim 4, claims 1 to 3
In the fuel cell according to any one of the above items, a metal catalyst layer or a carbon layer is formed between the catalyst / oxide / polymer electrolyte thin layer and the gas distribution plate forming the oxidant channel. Provide a fuel cell.

According to a fifth aspect of the invention, in the fuel cell according to the fourth aspect, the amount of the metal catalyst layer is 0.2 to 4 mg.
There is provided a fuel cell characterized by being in the range of / cm ² .

In the present invention, the amount of the metal catalyst layer (b) is in the range of 0.2 to 4 mg / cm ² is 0.2 mg.
This is because if it is less than / cm ² , the predetermined function cannot be obtained, and conversely, if the amount of the metal catalyst layer is more than 4 mg / cm ² , gas flow is hindered.

In the invention according to claim 6, claims 1 to 5
In the oxidant electrode according to any one of items 1 to 5, there is provided a fuel cell, wherein the content of the solid polymer electrolyte material in the catalyst / oxide / polymer electrolyte thin layer is 10% or more by weight concentration. To do.

In the present invention, the reason for setting the concentration of the solid polymer electrolyte material to 10 wt% is to ensure ionic conductivity in the catalyst / oxide / polymer electrolyte thin layer.
That is, the relationship between the mass of the polymer electrolyte and the ionic conductivity is that if the content of the mass of the polymer electrolyte in the catalyst / oxide / polymer electrolyte thin layer is less than 10 wt%, the effect cannot be exerted, and 10 wt% or more. By setting 0.2
This is because the voltage drop at A / cm ² exhibits a resistance corresponding to 5 mV or less. The concentration of the solid polymer electrolyte material is 8
When it exceeds 0 wt%, the gas flow path is blocked by the generated water and the battery characteristics are deteriorated.

According to a seventh aspect of the invention, in the fuel cell according to any one of the first to sixth aspects,
Provided is a fuel cell characterized in that the oxide / polymer electrolyte thin layer has a thickness of 5 to 30 μm.

In the present invention, the reason why the thickness of the catalyst / oxide / polymer electrolyte thin layer (a) is in the range of 5 to 30 μm is that the catalyst / oxide / polymer electrolyte thin layer (a) has a thickness of 5
If it is less than μm, the desired function cannot be obtained.
This is because if it exceeds m, the circulation of air is hindered.

According to the invention of claim 8, claims 4 to 7
The method for producing a fuel cell according to any one of 1 to 3, wherein a liquid composition of a catalyst / oxide / polymer electrolyte thin layer is directly applied to the surface of a metal catalyst layer or a carbon layer to form an oxidizer electrode. And a fuel electrode and an electrolyte membrane are integrated with each other.

In the invention according to claim 9, claims 4 to 7
The method for producing the fuel cell according to any one of 1 to 3, wherein a liquid composition of the catalyst, oxide, and polymer electrolyte thin layer is applied to a resin sheet having releasability in advance and dried, and the metal is used after drying. Provided is a method for producing a fuel cell, which comprises thermocompression-bonding to the surface of a catalyst layer or a carbon layer to form an oxidant electrode, which is integrated with a fuel electrode and an electrolyte membrane.

The invention according to claim 10 is a method for producing the fuel cell according to any one of claims 4 to 7, wherein the catalyst / oxide / polymer electrolyte thin layer is preliminarily formed into a sheet shape. Further, there is provided a method for producing a fuel cell, which comprises sandwiching this sheet between a metal catalyst layer or carbon layer and an electrolyte membrane and thermocompression-bonding the sheet and integrating the sheet with a fuel electrode.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a fuel cell and a method of manufacturing the same according to the present invention will be described below with reference to the drawings.

First Embodiment (FIGS. 1, 2, and 3) FIG. 1 is a schematic view of a cell structure of a fuel cell according to the first embodiment of the present invention. As shown in FIG. 1, the cell of the present embodiment includes a fuel electrode 2 and a catalyst as an oxidant electrode 4A.
The oxide / polymer electrolyte thin layer 4 and the metal catalyst layer 5 and the electrolyte membrane 3 made of a polymer membrane sandwiched between them constitute a power generating element. Gas distribution plates 8 and 9 for forming a fuel flow path and an oxidant flow path are formed on the outer side surfaces of the fuel electrode 2 and the oxidizer electrode 4A as the power generating elements, respectively.
And the gas diffusion layer 1 facing the fuel flow path and the oxidant flow path 1,
6 are provided, and a unit cell is configured by this.

The catalyst / oxide / polymer electrolyte thin layer 4 was constituted to contain carbon particles supporting palladium as a catalyst, zirconia as an oxide, and a fluorine-based sulfonic acid polymer as a polymer electrolyte. Further, the metal catalyst layer 5 contains platinum.

More specifically, the electrolyte membrane 3 is a cation exchange polymer membrane (hereinafter simply referred to as "polymer membrane") having a sulfonic acid group as an ion exchange group so that hydrogen ions can be conducted. Ions are selectively transmitted in the film thickness direction. This is a fluorinated sulfonic acid exchange membrane (for example, trade name: Nafion membrane, manufactured by Du Pond) and has a thickness of 50 μm.

The electrolyte membrane 3, the metal catalyst layer 5 and the catalyst
Oxidizer electrode 4A consisting of oxide / polymer electrolyte thin layer 4
And the fuel electrode 2 are integrated through thermocompression bonding by hot pressing. The gas diffusion layers 1 and 6 are formed of porous porous carbon and have a porosity of 70 to 95%. The gas diffusion layer 1,
For 6, a thin layer containing carbon powder having pores smaller than the pore diameter of the porous carbon and a fluororesin may be formed on the surface of the porous carbon. Further, the porous carbon may be made to contain a fluororesin, sinter it, and impart water repellency thereto.

The fuel electrode 2 was manufactured by the following steps. That is, as the gas diffusion layer 1, water repellent carbon paper (polytetrafluoroethylene content 25w
t%) was prepared and the catalyst paste was applied thereto. The catalyst paste is a cation exchange resin solution in which carbon particles supporting 40 wt% of platinum as a catalyst, for example, the same fluorinated sulfonic acid polymer resin liquid as the electrolyte membrane 3 (resin content 5 wt% is a mixed solution of propanol and water). It is a paste. This paste was applied in an amount such that platinum was 0.4 mg / cm ² , and dried at 70 ° C. to remove the solvent.

Next, the oxidizer electrode 4A is the same as that of the fuel electrode 2.
In the same manner as in the case of manufacturing, it was manufactured by the following steps. Sanawa
Then, as the gas diffusion layer 6, a water-repellent carbon paper is used.
Per (polytetrafluoroethylene content 25 wt%) is used
Then, the catalyst paste was applied thereto. Catalyst paste
Is a carbon particle supporting 40 wt% platinum as a catalyst
Cation exchange resin solution for the child, for example, the same as the electrolyte membrane 3
Fluorinated sulfonic acid polymer resin liquid (resin content 5 wt%
(Dissolved in a mixed solution of propanol and water)
It was made into a paste. This paste is platinum
Is 0.2 mg / cm ^TwoAnd apply at 70 ℃
The solvent was removed by drying.

Next, catalyst / oxide / polymer electrolyte thin layer 4
The manufacturing method of is described.

First, a method for producing a paste for coating will be described. Carbon particles supporting 50 wt% of palladium were used as the catalyst. To this, water was added and stirred, zirconia fine powder (specific surface area 60 m ² / g) was added, and the same fluorine-based sulfonic acid polymer resin liquid used when manufacturing the fuel electrode 2 was added. Then, the paste was prepared by stirring. The mixture ratio of the pastes was such that the dry weight ratio was 50 wt% palladium-supported carbon: oxide: polymer electrolyte = 50: 30: 20 (weight percent). Further, water was appropriately adjusted and used so that the viscosity of the paste would be suitable for the coating operation.

The paste produced by the above method is
The palladium was applied to the surface of the metal catalyst layer 5 of the oxidizer electrode 4A so that the amount of palladium would be 0.2 mg / cm ² , and dried. In order to further smooth the surface, a roll having a predetermined thickness was passed.

The fuel electrode 2, the electrolyte membrane 3, and the oxidizer electrode 4A (metal catalyst layer 5 and catalyst / oxide / polymer electrolyte thin layer 4) thus manufactured were hot pressed (130 ° C.,
It was thermocompression bonded with 80 kg / cm ² ). Then, the fuel cell was completed by mounting it on a groove-shaped separator for supplying a reaction gas.

To the fuel cell thus completed, fuel gas (or liquid fuel such as methanol) and air (or oxygen) are humidified and supplied at a temperature 5 to 10 ° C. lower than the operating temperature of the cell. To generate electricity.

Next, performance evaluation of the completed fuel cell of this embodiment will be described.

As a fuel cell for comparison, an oxidizer electrode 4 was used.
A conventional fuel cell having a platinum content of A of 0.4 mg / cm ² was applied. That is, in this conventional fuel cell, the catalyst / oxide / polymer electrolyte thin layer 4 was excluded from the configuration of this embodiment, and conversely, the amount of platinum in the metal catalyst layer 5 was 0.4 mg / cm ^2. Is. The manufacturing process of this conventional fuel cell was manufactured by substantially the same process as this embodiment described above.

FIG. 2 shows a fuel cell (A) according to this embodiment.
And the current-voltage characteristics of the fuel cell (B) according to the second embodiment and the fuel cell (C) according to the comparative example described later (the characteristics of the second embodiment will be described later). The operating condition of the battery is that the cell temperature is 7
Pure hydrogen as a fuel and air as an oxidizer at 0 ° C. at each current density (however, 100 mA / cm ² or less is 100 mA.
/ Cm as ² identical flow rate) with hydrogen and oxygen utilization is 70% and 40%, was determined by adjusting the flow rate.

As shown in FIG. 2, in the fuel cell (A) according to the present embodiment, the open circuit voltage was higher than that in the fuel cell (C) according to the comparative example, and the voltage was high at each current density. Regarding the open circuit voltage, in the fuel cell of the comparative example, since the catalyst is used for hydrogen oxidation that has crossed over to the catalyst on the oxidant side, an internal current flows even in the open circuit state, which causes polarization, As a result, the open circuit voltage was low. On the other hand, in the fuel cell according to the present embodiment,
The presence of the oxide / polyelectrolyte thin layer 4 traps hydrogen, the oxygen from the oxidant is adsorbed by the oxide, and the presence of the noble metal catalyst causes the hydrogen that has crossed over with oxygen to react. Since the noble metal catalyst of the oxidizer electrode 4A is not used for the oxidation of hydrogen because it produces water, the reaction area is large and the polarization of the battery is small, and the open circuit voltage and the high current density are high. The voltage can be indicated.

The amount of noble metal in the fuel cell according to the present embodiment is the same as that in the fuel cell according to the comparative example per unit area of the cell, but the output is high and therefore the output per platinum amount is large. found. In addition, the catalyst of the oxide-free cathode was 0.2 mg / cm ² or more, the amount of palladium contained in the layer containing the oxide was kept constant, and the conventional fuel cell having the same amount of platinum was used. When compared with each other, the characteristics of this embodiment were high. Note that the total platinum amount was 4 mg / cm ²
When a cell as a comparative example having a value exceeding the above was made, the characteristics were the same as those of the conventional fuel cell, and the superiority of the cell of this comparative example could not be confirmed.

In order to confirm such a hydrogen trap effect, the result of measuring the change in open circuit voltage by pressurizing the hydrogen side to 10 kpa is shown in FIG. As shown in FIG. 3, in the fuel cell (A) according to the present embodiment, the open circuit voltage hardly changes even when the pressure of hydrogen increases, but in the fuel cell (B) according to the comparative example, the open circuit voltage greatly decreases. did.

This is because the presence of the catalyst / oxide / polyelectrolyte thin layer 4 increases the hydrogen pressure and adsorbs hydrogen even when the hydrogen permeation amount increases, and supplies the adsorbed oxygen by the oxide. This is because the hydrogen that has permeated is smoothly oxidized to water and the reaction area of the cathode catalyst is kept large, so that the open circuit voltage can be kept high.

Further, in this embodiment, the concentration of the polymer electrolyte in the mixture after drying was set to 20 wt%. This is to ensure the ionic conductivity in the catalyst / oxide / polymer electrolyte thin layer 4. The relationship between the mass of the polymer electrolyte and the ionic conductivity was investigated, and it was found that the catalyst / oxide / polymer electrolyte was When 10 wt% or more is present as a weight percentage of the thin layer 4, the voltage drop at 0.2 A / cm ² is 5 mV.
It has been found to exhibit resistance equivalent to: Therefore, the catalyst / oxide / polymer electrolyte thin layer 4 needs 10 wt% or more of electrolyte.

As described above, in the fuel cell of this embodiment, the surface of the oxidizer electrode 4A containing the metal catalyst contains the catalyst in which the oxide and the noble metal are supported and dispersed in the carbon powder, and the polymer electrolyte material. A thin film was formed. By forming a thin layer having such a composition on the platinum catalyst surface, hydrogen that has permeated the electrolyte membrane 3 is adsorbed by a noble metal such as palladium, and an oxide is oxygen in the air supplied to the cathode. The component is adsorbed. Then, the oxygen and hydrogen react with each other on the noble metal catalyst to generate water. Therefore, it is possible to prevent hydrogen from reaching the metal catalyst in which the oxygen reduction reaction occurs and hindering the oxygen reduction reaction, and it is possible to maintain the catalyst area for oxygen reduction in a large state. The polarization of the battery at 4 A can be kept small, and high performance of the battery can be realized.

Second Embodiment (FIGS. 4, 5, and 2) Next, the second embodiment will be described. The structure of the battery according to the second embodiment is shown in FIG.

FIG. 4 is a schematic view of the cell structure of the fuel cell according to the second embodiment of the present invention. As shown in FIG.
The cell of the present embodiment comprises a fuel electrode 2, a catalyst / oxide / polymer electrolyte thin layer 4 and a carbon layer 7 as an oxidant electrode 4A, and an electrolyte membrane 3 composed of a polymer membrane sandwiched therebetween. It constitutes a power generation element. Gas distribution plates 8 and 9 for forming a fuel flow path and an oxidant flow path, and a surface for the fuel flow path and the oxidizer flow path are formed on the outer surfaces of the fuel electrode 2 and the oxidizer electrode 4A as the power generating elements, respectively. Gas diffusion layers 1 and 6 are provided, and a unit cell is configured by this.

The carbon layer 7 is formed between the catalyst / oxide / polymer electrolyte thin layer 4 and the gas channel plate 9 forming the oxidant channel. That is, in this second embodiment,
The first embodiment is that the catalyst / oxide / polymer electrolyte thin layer 4 is formed directly on the surface of the gas diffusion layer 6 of the oxidant electrode 4A without the metal catalyst layer 5 of the oxidant electrode 4A. different.

In this embodiment, the oxidant electrode 4A is manufactured as follows.

First, a porous carbon porous material (porosity 85%, thickness 90 μm) of polytetrafluoroethylene and carbon powder (specific surface area 240 m ² / g) was applied to a thickness of 30 μm. This was heat-treated in air at 350 ° C. for 20 minutes. Water repellency could be imparted by this heat treatment.

Furthermore, a carb carrying 40 wt% platinum
Fiber (fiber diameter 50 nm) and titanium oxide (70 m^Two/
Add water to g) to adjust the viscosity and add 5 wt% of fluorine.
Carbide Carrying 50% by Weight Platinum Sulfonic Acid Polymer
Where: oxide: polyelectrolyte = 40:30:30 (weight ratio
Centrifuge) and stir to obtain a slurry liquid.
It was Apply this slurry on a polytetrafluoroethylene sheet.
Cloth and dry. The coating amount is 30 μm after drying.
Was adjusted so that This polytetrafluoroethylene thin film sheet
Put the gauze on the porous carbon prepared previously, 140
℃, 40kg / cm ^TwoHot press under the conditions of and oxidize
Agent electrode 4A was obtained. The platinum content of this electrode was 0.3.
5 mg / cm^TwoMet. Oxidizer electrode thus obtained
To form a fuel cell similar to that of the first embodiment,
The battery characteristics were measured.

FIG. 2 shows the current-voltage characteristics of the fuel cell (B) according to the second embodiment and the fuel cell (C) according to the comparative example, as described above.
As is clear from FIG. 2, the fuel cell according to the present embodiment showed better characteristics than the fuel cell according to the comparative example.

In the present embodiment, the catalyst layer itself of the oxidant electrode 4A adsorbs hydrogen, supplies oxygen, and oxidizes the permeated hydrogen. However, in the catalyst layer, oxygen adsorption occurs in the entire catalyst layer, and a sufficient amount is obtained. Since the adsorbed oxygen exists, the oxidation reaction of the permeated hydrogen takes place near the interface between the catalyst layer and the polymer membrane, so that the original reduction of oxygen has little effect on the catalytic effective surface area.

On the other hand, since water is generated on the surface as described above, the water gives moderate humidity to the polymer of the oxidizer electrode 4A, so that the polymer electrolyte existing in the catalyst is effectively given moisture. As a result, the activity of the electrode can be maintained for a long time. As shown in FIG. 5, the battery voltage (0.2 A / c
m ² ) was stable for a long time in the fuel cell according to the present embodiment as compared with the fuel cell according to the comparative example. This indicates that the catalyst / oxide / polyelectrolyte thin layer 4 is effectively acting for a long period of time, and it was confirmed that the characteristic stability is also improved by this.

In the fuel cell of the second embodiment described above, the air-gas diffusion layer is a thin layer containing an oxide and a catalyst in which platinum is carried and dispersed in carbon fiber and a solid polymer electrolyte material. Since it is formed on the surface of No. 6, oxygen can be easily adsorbed, and hydrogen that has permeated the electrolyte membrane 3 can be oxidized on the noble metal catalyst. Therefore, hydrogen easily reacts with oxygen to form water. To generate. In this case, since the adsorbed oxygen is present in a large amount due to the presence of the oxide, the water production reaction occurs in the immediate vicinity of the electrolyte membrane 3 and the oxidant electrode 4A because it depends on the concentration of adsorbed hydrogen. Therefore, most noble metal catalysts can be used for the reduction reaction of oxygen. Therefore, the oxygen reduction reaction can proceed smoothly, and the polarization of oxygen reduction can be reduced,
Higher battery performance can be achieved. In addition, since the generated water wets the polymer electrolyte in the catalyst, the effect of the catalyst is maintained for a long period of time, so that stable battery characteristics can be maintained for a long period of time.

Other Embodiments In the first and second embodiments described above, zirconia or titanium oxide is applied as the oxide of the catalyst / oxide / polymer electrolyte thin layer 4, but instead of these, tin oxide is used. Also, when ceria is applied, almost the same results as in the above-mentioned respective embodiments were obtained.

Further, as the oxide of the polymer electrolyte thin layer 4, the surface of zirconia, titanium oxide or tin oxide is S.
A surface modified oxide having O ₃ H, COOH, PO ₃ H, OH groups was applied. That is, (1) 100 g of fine powder (100 m ² / g) of zirconia (ZrO ₂ ) was immersed in a solution of fuming sulfuric acid / concentrated sulfuric acid = 1/4,
Heat treatment was performed for an hour, and the oxide was further heat-treated at 500 ° C. for 1 hour. Infrared analysis (FTIR) of the obtained powder confirmed the presence of surface —SO ₃ H. (2) A fine powder of titanium oxide is dipped in a 2 M / L alkaline solution, dried and then heat-treated (500 ° C.-1 hour), and then washed with water to remove excess alkali and dried to obtain a hydroxide. A titanium oxide powder surface-treated with (-OH) was obtained.
(3) by immersing the tin oxide condensed phosphoric acid (phosphoric acid concentration 105%), then dried and heat treated (300 ° C. -1 h), was washed with water, and surface treatment _(-PO 3 H) oxide Tin fine powder was obtained. A thin layer of catalyst / oxide / polymer electrolyte was formed using the oxide surface-treated as described above.

By these surface treatments, the water retention capacity (water adsorption capacity per gram of oxide) becomes higher than that of the oxide without surface treatment, and the water retention property in the catalyst is improved. This is effective for maintaining high ionic conductivity of the solid polymer required for the oxygen reduction reaction. The long term stability of the fuel cells according to these embodiments is due to the effect of using the surface treated oxide. According to these embodiments, the deterioration rate is lower than that of the oxide which is not surface-treated as in the conventional example shown in FIG. In particular, SO ₃ H
In the case of an oxide containing a group, the deterioration rate is about 7 times that of FIG.
It was 0%, and it was confirmed that a remarkable effect was obtained.

Further, the present invention is not limited to the above embodiment, and it goes without saying that it can be implemented in various modes. For example, although hydrogen is used as the fuel gas in each of the above-described embodiments, the present invention can be applied to the oxidant electrode 4A of a methanol supply type fuel cell using methanol solutions of various concentrations. At this time, instead of hydrogen, the permeating methanol can be oxidized to prevent the reduction of the catalytic effective area of the oxidizer electrode 4A.

In the above embodiment, platinum and palladium are used as the noble metal catalyst. However, rhodium or iridium having hydrogen oxidation and oxygen reduction ability is applied, or a porphyrin complex compound (especially cobalt metal) in a complex with various metals is used. Is desirable) is also applicable.

As the oxide, zirconia or titania was applied, but tin oxide or tin oxide having antimony or the like having electronic conductivity, or zirconia to change the surface basicity, ceria was used. It is also effective to add magnesium oxide, silicon oxide, or the like.

Further, the catalyst / oxide / polymer electrolyte thin layer 4
The production method is as follows: Polytetrafluoroethylene or other thermoplastic organic polymer is added as a binder to these mixtures, and the product is molded on a sheet, and then a gas diffusion layer 6 or a carbon porous layer coated with a metal catalyst is prepared. It is also possible to make a fuel cell by sandwiching between the body and the polymer membrane and further mounting the fuel electrode 2 thereon by thermocompression bonding means such as hot pressing to form a fuel cell.

By forming a thin layer having such a composition on the surface containing a metal catalyst, hydrogen that has permeated the electrolyte membrane 3 is adsorbed by a noble metal such as platinum, palladium, rhodium or iridium, and SO ₃ H group, COOH group, P
Oxygen components of the air supplied to the cathode are adsorbed by the oxide surface-modified to contain at least one of O ₃ H group and OH group. Then, by reacting this oxygen and the permeated hydrogen with the noble metal catalyst, water is produced. Therefore, it is possible to prevent hydrogen from reaching the metal catalyst in which the oxygen reduction reaction occurs and hindering the oxygen reduction reaction, and it is possible to maintain the catalyst area for oxygen reduction in a large state. The polarization of the battery at 4 A can be kept small.

Since the surface of the gas diffusion layer 6 contains an oxide or a surface-treated oxide, adsorption of oxygen is facilitated, and a noble metal catalyst capable of oxidizing hydrogen that has permeated the electrolyte membrane 3 is used. Because it contains hydrogen, hydrogen readily reacts with oxygen to produce water. In this case, since the adsorbed oxygen is present in a large amount due to the presence of the oxide, the water production reaction occurs in the immediate vicinity of the electrolyte membrane 3 and the oxidant electrode 4A because it depends on the concentration of adsorbed hydrogen. Therefore, most noble metal catalysts can be used for the reduction reaction of oxygen. Therefore, the oxygen reduction reaction can proceed smoothly, the polarization of oxygen reduction can be reduced, and high performance of the battery can be achieved.

[0062]

As described above, according to the fuel cell of the present invention, in particular, by improving the oxidizer electrode, it is possible to prevent deterioration of performance due to permeation of liquid fuel such as hydrogen or methanol to the oxidizer side. It is possible to improve, simplify the structure, and reduce the amount of precious metal used.

Further, according to the method for producing a fuel cell of the present invention, the cell performance and the production quality can be improved by paying particular attention to the oxidant electrode.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a unit cell of an oxidizer electrode according to a first embodiment of the present invention.

FIG. 2 is a graph showing a characteristic comparison between a fuel cell according to an embodiment of the present invention and a fuel cell according to a comparative example.

FIG. 3 is a graph showing a comparison of the effects of the hydrogen pressure on the battery open circuit voltage between the first embodiment of the present invention and the comparative example.

FIG. 4 is a configuration diagram showing a unit cell of an oxidant electrode according to a second embodiment of the present invention.

FIG. 5 is a graph showing long-term characteristics comparison between the fuel cell according to the second embodiment of the present invention and the fuel cell according to the comparative example.

[Explanation of symbols]

1 gas diffusion layer 2 Fuel electrode (anode catalyst layer) 3 Electrolyte membrane 4A oxidizer electrode 4 Catalyst / oxide / polymer electrolyte thin layer 5 Metal catalyst layer (cathode catalyst layer) 6 Gas diffusion layer 7 carbon layer 8, 9 gas distribution plate

Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H01M 8/10 H01M 8/10 F term (reference) 5H018 AA06 AA07 AS02 AS03 BB01 BB03 BB05 BB06 BB08 BB13 CC06 DD05 DD06 DD08 EE03 EE05 EE12 EE18 EE19 HH03 HH05 5H026 AA06 AA08 BB02 BB03 BB04 CC03 CX02 CX05 EE02 EE05 EE12 EE18 HH03 HH05

Claims (10)

[Claims] 1. A fuel cell, an oxidant electrode, and an electrolyte membrane composed of a polymer membrane sandwiched between the fuel electrode, an oxidizer electrode, and a fuel cell. In a fuel cell that constitutes a unit cell by providing a gas distribution plate that forms a channel, the oxidizer electrode is an oxide and carbon powder of at least one metal selected from platinum, palladium, rhodium, and iridium. Alternatively, a fuel cell comprising a catalyst / oxide / polymer electrolyte thin layer composed of a solid polymer electrolyte material and a catalyst supported and dispersed on at least one of carbon fibers. 2. The fuel cell according to claim 1, wherein the oxide of the catalyst / oxide / polymer electrolyte thin layer is zirconia,
At least one oxide selected from tin oxide, titania and ceria, or at least one of these oxides
A fuel cell, which is a mixture containing two. 3. The fuel cell according to claim 1, wherein the oxide of the catalyst / oxide / polymer electrolyte thin layer is SO.
A fuel cell, which is a surface-modified oxide having at least one selected from a ₃ H group, a COOH group, a PO ₃ H group, and an OH group. 4. The fuel cell according to claim 1, wherein a metal catalyst layer or a metal catalyst layer is provided between the catalyst / oxide / polymer electrolyte thin layer and the gas distribution plate forming the oxidant channel. A fuel cell having a carbon layer. 5. The fuel cell according to claim 4, wherein the amount of the metal catalyst layer is in the range of 0.2 to 4 mg / cm ² . 6. The oxidant electrode according to claim 1, wherein the content of the solid polymer electrolyte material in the catalyst / oxide / polymer electrolyte thin layer is 10% or more by weight. A fuel cell characterized by being present. 7. The fuel cell according to any one of claims 1 to 6, wherein the catalyst / oxide / polymer electrolyte thin layer has a thickness of 5 to 30 μm. 8. A method for producing a fuel cell according to claim 4, wherein the liquid composition of the catalyst / oxide / polymer electrolyte thin layer is added to a metal catalyst layer or a carbon layer. A method for producing a fuel cell, characterized in that an oxidizer electrode is formed by directly coating the surface of the fuel cell, and the electrode is integrated with the fuel electrode and the electrolyte membrane. 9. A method for producing the fuel cell according to claim 4, wherein the liquid composition of the catalyst / oxide / polymer electrolyte thin layer is preliminarily peelable. On the surface of the metal catalyst layer or carbon layer by thermocompression bonding to form an oxidizer electrode,
A method for manufacturing a fuel cell, which comprises integrating this with a fuel electrode and an electrolyte membrane. 10. The method for producing the fuel cell according to claim 4, wherein the catalyst / oxide / polymer electrolyte thin layer is formed in a sheet shape in advance, and the sheet is formed. A method for producing a fuel cell, comprising sandwiching a metal catalyst layer or a carbon layer and an electrolyte membrane in a sandwich shape and thermocompression-bonding the resultant to an integrated fuel electrode.