JP2002231265A - Fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell capable of preventing catalytic activity and fuel utilization efficiency from being lowered by crossover of fuel from the negative electrode side to the positive electrode side, in a direct type fuel cell using methanol or dimethyl ether for its fuel. SOLUTION: This fuel cell is formed by disposing a palladium membrane or a palladium alloy membrane at any position between a contact surface where the negative electrode is in contact with fuel and water and a contact surface where the positive electrode is in contact with an oxygen-containing gas. Or, this fuel cell is formed by using two electrolyte membranes and disposing the palladium membrane or the palladium alloy membrane between those electrolyte membranes.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell which uses methanol or dimethyl ether as a fuel and directly produces an electrochemical reaction of the fuel to obtain electric power. More specifically, the present invention relates to a fuel cell in which the fuel supplied to a negative electrode is used. The present invention relates to a fuel cell that can prevent a decrease in catalytic activity caused by reaching a positive electrode through an electrolyte membrane, and a decrease in utilization efficiency of these fuels.

[0002]

2. Description of the Related Art A fuel cell has electrodes on both sides of an electrolyte membrane, supplies a fuel (reducing agent) such as hydrogen or hydrocarbon to one electrode, and supplies an oxygen-containing gas such as oxygen or air to another electrode. (Oxidizing agent) to generate electricity by causing an electrochemical reaction. There are several types of fuel cells. For example, an inorganic oxide is used for the electrolyte membrane.
A solid electrolyte fuel cell operated at around 00 ° C., an alkaline fuel cell operated at a temperature of room temperature to 240 ° C. using an alkaline aqueous solution as an electrolyte, a phosphoric acid fuel cell operated at around 200 ° C. using phosphoric acid as an electrolyte, There is a polymer electrolyte fuel cell or the like that operates at a temperature of about room temperature to about 130 ° C. using a polymer electrolyte membrane.

[0003] Among these fuel cells, a direct methanol fuel cell using methanol directly as fuel and a direct fuel cell using dimethyl ether directly as fuel, many fuel cells reform hydrogen or hydrocarbons. Compared to using the hydrogen-containing gas obtained as a fuel, it is easier to handle the fuel, the system configuration of the fuel cell is simpler, and the operation of the fuel cell itself is easy for home use, It is expected to be used not only for industrial purposes but also as a power source for mobile objects.

That is, these direct type fuel cells have a structure in which a porous negative electrode having a platinum-based catalyst layer provided on both sides of an electrolyte membrane and a positive electrode are sandwiched, and methanol or dimethyl ether is directly supplied to the negative electrode together with water. And a structure for supplying an oxygen-containing gas such as oxygen or air to the positive electrode. At the negative electrode, methanol or dimethyl ether electrochemically reacts with water to generate protons, electrons, and carbon dioxide, and the electrons reach the positive electrode after working via an external circuit. After the protons reach the positive electrode through the electrolyte membrane, oxygen, protons, and electrons react to generate water.

As described above, these direct fuel cells can directly extract electricity from an oxygen-containing gas such as methanol or dimethyl ether, water, oxygen or air. Is expected, and has been studied in various technical fields,
Characteristics sufficient for practical use have not yet been obtained. The major reason is that methanol or dimethyl ether supplied to the negative electrode passes through the electrolyte membrane as it is and reaches the positive electrode, so-called crossover occurs. This is because there is a disadvantage that the efficiency is significantly reduced.

Various direct fuel cells have been proposed as solutions to the problem of methanol crossover. For example, a fuel cell in which cross-over of methanol is reduced by impregnating a solid polymer electrolyte membrane with alcohol and water other than methanol (JP-A-11-3711)
No. 25), a fuel cell in which two solid polymer electrolyte membranes are used as electrolyte membranes, an electrolyte solution such as a sulfuric acid aqueous solution is passed between these electrolyte membranes, and methanol crossover is extracted to the outside. (Japanese Patent Laid-Open No. 11-
No. 3724), a fuel cell using a catalyst having low reactivity with methanol for the positive electrode (JP-A-11-7964), and an oxidation catalyst layer for oxidizing methanol is buried between two solid electrolyte membranes. Fuel cell which prevents crossover of methanol to the positive electrode side by
No. 936). A direct fuel cell that has solved the problem of dimethyl ether crossover has not been proposed so far.

[0007]

However, the fuel cell has a disadvantage that the effect of preventing the crossover of methanol is not maintained. In addition, the fuel cell has disadvantages in that the configuration is complicated and that the methanol extracted by the electrolyte solution must be recovered. In addition, in the above method, the types of the catalysts are limited, and there is a disadvantage that it is impossible to prevent a decrease in the utilization efficiency of methanol due to crossover. Further, there is a disadvantage that the method cannot prevent a decrease in the utilization efficiency of methanol. Therefore, the problem to be solved by the present invention is that, in a direct fuel cell using methanol or dimethyl ether as a fuel, it is possible to prevent a decrease in catalytic activity and a decrease in fuel utilization efficiency due to crossover of these fuels, and to improve the efficiency. It is to provide a fuel cell capable of generating power.

[0008]

The present inventors have made intensive studies to solve these problems, and as a result, in a direct fuel cell using methanol or dimethyl ether as a fuel, a palladium membrane or a palladium membrane having proton diffusion permeability. By disposing a palladium alloy film between the contact surface of the anode and the fuel and water and the electrolyte membrane, or by disposing two electrolyte membranes between these electrolyte membranes, it is possible to prevent fuel crossover, and By arranging the membrane or palladium alloy membrane between the oxygen-containing gas contact surface of the positive electrode and the electrolyte membrane, even if the fuel permeates the electrolyte membrane and reaches the positive electrode, the fuel is held at the oxygen-containing gas contact surface of the positive electrode. It has been found that the catalyst does not come into contact with the catalyst, and that a reduction in catalyst activity and a reduction in fuel use efficiency can be prevented.

That is, the present invention relates to a fuel cell having a structure in which a negative electrode is provided on one side of an electrolyte membrane and a positive electrode is provided on the other side, methanol or dimethyl ether is supplied as fuel to the negative electrode together with water, and an oxygen-containing gas is supplied to the positive electrode. A fuel cell characterized in that a palladium film or a palladium alloy film is disposed at any position between a contact surface of a negative electrode with fuel and water and a contact surface of a positive electrode with an oxygen-containing gas.

Further, the present invention has a negative electrode comprising a porous support holding a platinum group catalyst on one side of an electrolyte membrane and a positive electrode comprising a porous support holding a platinum group catalyst on the other side. A fuel cell having a configuration in which methanol or dimethyl ether is supplied to the negative electrode together with water as a fuel and an oxygen-containing gas is supplied to the positive electrode, wherein a palladium film or palladium is provided between the porous support of the negative electrode or the positive electrode and the electrolyte membrane. The fuel cell also includes an alloy film.

Further, the present invention relates to a fuel cell having a structure in which methanol or dimethyl ether is supplied to a negative electrode together with water as a fuel, and an oxygen-containing gas is supplied to a positive electrode.
A palladium film or a palladium alloy film is disposed between two electrolyte films, and a negative electrode is provided on one side of the electrolyte film that is not in contact with the palladium film or the palladium alloy film, and is not in contact with another palladium film or a palladium alloy film. A fuel cell is also characterized in that a positive electrode is provided on one side of the fuel cell.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention has a structure in which a negative electrode is provided on one side of an electrolyte membrane and a positive electrode is provided on the other side, water is supplied to the negative electrode together with methanol or dimethyl ether as a fuel, and an oxygen-containing gas is supplied to the positive electrode. Applied to direct fuel cells. The first embodiment of the fuel cell of the present invention is a method of forming a palladium membrane or a palladium alloy membrane having proton diffusion and permeability between a contact surface of a negative electrode with fuel and water and a contact surface of a positive electrode with an oxygen-containing gas. It is a configuration arranged at the position. Thus, when the membrane is arranged on the negative electrode side of the electrolyte membrane, by preventing fuel crossover, when the membrane is arranged on the positive electrode side of the electrolyte membrane, the fuel permeated through the electrolyte membrane and the positive electrode catalyst are separated. By preventing the contact, the fuel cell can be operated while maintaining the positive electrode catalyst in a highly active state. Further, the second embodiment of the fuel cell of the present invention has a configuration in which two electrolyte membranes are used, and a palladium membrane or a palladium alloy membrane having proton diffusion permeability is arranged between these two electrolyte membranes. In addition, by preventing the fuel crossover, the fuel cell can be operated while maintaining the positive electrode catalyst in a highly active state.

In the fuel cell of the present invention, methanol or dimethyl ether as fuel reacts electrochemically with water at the negative electrode to generate protons, electrons and carbon dioxide, and the electrons work via an external circuit. And then reaches the positive electrode. Further, after the protons reach the positive electrode through the palladium film or the palladium alloy film and the electrolyte film, oxygen, protons, and electrons react to generate water. With such a configuration, the fuel cell of the present invention can generate power with high output and high fuel efficiency.
In the present invention, the fuel and water supplied to the negative electrode are:
It may be in a liquid state or a gas state.

Hereinafter, a first embodiment of the fuel cell of the present invention will be described in detail. The first embodiment of the fuel cell of the present invention is generally composed of a porous support holding a platinum group catalyst as a negative electrode on one side of an electrolyte membrane and a porous support holding a platinum group catalyst as a positive electrode on the other side. Using a support, a palladium membrane or a palladium alloy membrane is arranged between any of the porous supports and the electrolyte membrane, and these are brought into contact with each other. The fuel, water, and oxygen-containing gas are supplied to the negative electrode or the positive electrode on the side of the porous support that is not in contact with the membrane.

In the first embodiment of the fuel cell of the present invention, a palladium film or a palladium alloy film can be used on either the negative electrode side or the positive electrode side of the electrolyte membrane, but is preferably used on the negative electrode side. The reason is that when a palladium film or a palladium alloy film is used on the negative electrode side of the electrolyte membrane, the electrolyte membrane does not come into contact with methanol or dimethyl ether as a fuel, so that the deterioration of the electrolyte membrane can be prevented. The reason is that the catalyst component can be selected from a wide range without considering corrosion resistance since the anode catalyst held on the contact surface with water does not contact the strongly acidic electrolyte membrane. In addition, the palladium film or the palladium alloy film functions as a collector electrode regardless of whether it is used on the negative electrode side or the positive electrode side, so that power can be efficiently generated.

In the fuel cell of the present invention, a metal film made of palladium alone may be used. However, since the operation and stop of the fuel cell are repeated, permanent deformation of the palladium film or breakage of the film is likely to occur. It is preferable to use a palladium alloy film. Incidentally, the palladium alloy film means an alloy film containing other metals to the extent that metal palladium can maintain the diffusion and permeability of protons, and a metal type that forms an alloy with palladium is used. Is not particularly limited to, for example, palladium, gold, silver, copper, platinum, yttrium, nickel, iron,
It is an alloy film made of at least one metal selected from cobalt and zirconium. The ratio of the metal other than palladium in the palladium alloy is not particularly limited, but the weight ratio of the metal other than palladium is usually 2 to 50%, preferably about 5 to 40%. Among them, a silver-palladium binary alloy comprising 10 to 35% of silver and 90 to 65% of palladium, 1 to 10% of gold, and 5 to 25 of silver
%, And a ternary gold-silver-palladium alloy comprising 94 to 65% palladium.

The palladium film or palladium alloy film in the present invention may be a film obtained by rolling palladium or a palladium alloy, and may be plated, vapor-deposited or CV-coated on the surface of an electrolyte membrane or a porous support.
It may be a film obtained by the method D or the like, and is not particularly limited by the manufacturing method. The thickness of the palladium film or the palladium alloy film is not particularly limited, but is usually 0.1 to 200 μm, preferably about 0.5 to 40 μm. When the thickness of the palladium film or the palladium alloy film is less than 0.1 μm, the strength of the film may be weak and the film may be damaged. When the thickness exceeds 200 μm, diffusion and permeability of protons are reduced and sufficient power cannot be obtained. Causes inconvenience.

In a first embodiment of the fuel cell of the present invention,
Although a palladium film or a palladium alloy film may be used as it is, in order to enhance the surface activity of the palladium film or the palladium alloy film, a small amount of platinum, palladium, ruthenium, rhenium, rhodium,
It is preferable to use it in a state where fine particles of a platinum group metal such as iridium are attached.

Examples of a method for attaching platinum group metal fine particles to the surface of a palladium film or a palladium alloy film include a method in which an aqueous solution of a platinum group metal is electrolyzed using a palladium alloy film as a cathode, and a method in which hydrogen is applied to the palladium alloy film. There are a method of immersing in an aqueous solution of a platinum group metal in the occluded state for attachment, and a method of attaching by an electroless plating method, and the method is not particularly limited.
Incidentally, instead of the negative electrode or the positive electrode made of a porous support holding a platinum group catalyst, using this attachment method, the platinum group catalyst is directly held on a palladium film or a palladium alloy film and used as a negative electrode or a positive electrode. You can also.

In the present invention, the catalyst used for the negative electrode is not particularly limited, but is usually a particulate catalyst made of a platinum group metal, or platinum and ruthenium, rhodium, palladium, rhenium, iridium, chromium, gold, Silver, iron,
A mixed catalyst in the form of fine particles such as cobalt or nickel, or an alloy catalyst is used. These catalysts are used by being supported on a conductive porous support such as carbon paper, carbon nonwoven fabric, metal nonwoven fabric, and metal foam. You. Although the amount of the catalyst supported on the conductive carbon is not particularly limited, for example, 3 to 70% by weight of platinum is used by being used. These catalysts are usually dispersed in a solvent such as water, alcohol, and ketones together with an ion exchange resin solution to prepare a negative electrode catalyst solution, which is applied to a conductive porous support to form a negative electrode. A negative electrode can also be directly applied.

The positive electrode catalyst may have the same composition as that of the negative electrode catalyst.
Different catalyst compositions can also be used. A water-repellent component, such as polytetrafluoroethylene fine particles, can be added to the positive electrode catalyst solution in addition to the negative electrode catalyst solution component. The positive electrode in the present invention is usually formed by applying a platinum-based catalyst or the like to a conductive porous support such as carbon paper or carbon non-woven fabric like the negative electrode.

As the electrolyte membrane used in the present invention, a solid polymer electrolyte membrane (usually called an ion exchange membrane) is usually used, but a nonwoven fabric or the like impregnated with an electrolyte solution, or a zeolite or the like is used. Can be used, and the type of the electrolyte membrane is not particularly limited.
When a solid polymer electrolyte membrane is used, a commercially available one can be used. There is no particular limitation on the thickness of the solid polymer electrolyte membrane, the ion exchange capacity, and the like.

When a solid polymer electrolyte membrane is used as the electrolyte membrane, a palladium alloy membrane,
After laminating the negative electrode and the positive electrode, they are usually heated and compressed to form a membrane-electrode assembly. The membrane / electrode assembly is usually incorporated into a cell composed of a conductive current collector provided with a flow path for a fuel or an oxygen-containing gas to form a fuel cell. FIG. 1 shows an example of a fuel cell according to the present invention. Further, in the present invention, a plurality of cells can be stacked to form a fuel cell stack. In the case of a stack, a fuel cell is usually formed so as to electrically connect the stacked cells.

Next, a second embodiment of the fuel cell according to the present invention will be described. The second embodiment of the fuel cell of the present invention is a fuel cell in which two electrolyte membranes are used, and a palladium membrane or a palladium alloy membrane having proton diffusion permeability is arranged between these two electrolyte membranes. It is. In the second embodiment of the fuel cell of the present invention, usually on one side of the electrolyte membrane that is not in contact with the palladium membrane or palladium alloy membrane,
A negative electrode composed of a porous support holding a platinum group catalyst,
A positive electrode made of a porous support holding a platinum group catalyst is provided on one surface of the side not in contact with another palladium film or palladium alloy film. The same palladium film or palladium alloy film as that used in the first embodiment is used. Further, as the negative electrode catalyst, the positive electrode catalyst, the electrolyte membrane, and the like, those similar to those used in the first embodiment are used.

Also in the second embodiment of the fuel cell of the present invention, when a solid polymer electrolyte membrane is used as the electrolyte membrane, the anode and the cathode are superposed on the solid polymer electrolyte membrane and then usually heated and compressed. Thus, a membrane-electrode assembly is formed.
The fuel cell is formed by incorporating the membrane / electrode assembly into a cell composed of a conductive current collector provided with a flow path for a fuel or an oxygen-containing gas, as described above. Further, also in the second embodiment of the fuel cell of the present invention, a plurality of cells can be overlapped to form a fuel cell stack. In the case of a stack, a fuel cell is formed so as to electrically connect the stacked cells in the same manner as described above.

A mixed solution or vapor of methanol or dimethyl ether as a fuel and water is supplied to the negative electrode side of the fuel cells of the first and second embodiments of the present invention configured as described above. On the other hand, oxygen or an oxygen-containing gas such as air is ventilated to the positive electrode side. On the negative electrode side, fuel and water are electrochemically oxidized to generate protons, electrons and carbon dioxide, and the protons diffuse and permeate through the palladium film or palladium alloy film and the electrolyte film to reach the positive electrode side. In addition, the electrons work outside via the negative electrode current collector, and then reach the positive electrode via the positive electrode current collector. At the positive electrode side, hydrogen ions and electrons are recombined and oxidized to produce water.

[0027]

Next, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.

Example 1 5% by weight of gold, 20% by weight of silver,
Using a 10 μm thick palladium alloy film composed of 75% by weight of palladium as a negative electrode and using a nickel plate as a positive electrode, 4%
Water electrolysis was performed at 25 ° C. in an aqueous sodium hydroxide solution, and hydrogen was absorbed by the palladium alloy film. This palladium alloy film was immersed in an aqueous solution containing palladium chloride and hydrochloric acid to form 0.05 mg of fine palladium particles on the front and back surfaces of the palladium alloy film.
/ Cm ² (palladium black treatment). Next, 1 part by weight of an alloy catalyst in which 60% by weight of platinum was supported as platinum at an atomic ratio of platinum-ruthenium on carbon black of 3: 2, and 0.5 part by weight of a cation exchange resin liquid as a pure component. Was dispersed in a mixed solvent of 2-propyl alcohol and water to prepare a negative electrode catalyst solution. This negative electrode catalyst solution is 190 μm thick.
1.9 mg / cm as platinum amount on carbon paper
² to obtain a negative electrode.

On the other hand, 1.0 part by weight of a platinum catalyst in which 60% by weight of platinum is supported on carbon black, 0.5 part by weight of a cation exchange resin solution as a pure component, and a dispersion of fine particles of tetrafluoroethylene as a pure component 0.15 parts by weight was dispersed in a mixed solvent of 2-propyl alcohol and water to prepare a positive electrode catalyst solution. This positive electrode catalyst solution was applied to carbon paper having a thickness of 190 μm so as to have a platinum amount of 0.5 mg / cm ² to obtain a positive electrode.

The negative electrode fabricated in this manner was superposed on the palladium alloy film so that the catalyst-coated surface was in contact therewith, and a 89 μm-thick cation exchange film was superposed on the other surface of the palladium alloy film. . The surface of the cation exchange membrane that was not in contact with the palladium alloy membrane was overlapped such that the catalyst-coated surface of the positive electrode was in contact with the cation exchange membrane. The negative electrode, the palladium alloy membrane, the cation exchange membrane, and the positive electrode were stacked in this order at 130 ° C. and 30 kg.
/ Cm ² for 5 minutes to prepare a membrane-electrode assembly.

Next, as shown in FIG. 1, the above membrane / electrode assembly was incorporated into a carbon cell having a flow channel on both the negative electrode side and the positive electrode side and having an electrode area of 16 cm ² , A fuel cell was formed. This fuel cell is
While maintaining the temperature at ° C, a mixed solution of methanol-water was supplied to the negative electrode, and humidified air was supplied to the positive electrode for 15 hours. During that time, the output density was measured while changing the load resistance, and a maximum output of 0.11 W / cm ² was obtained. Also,
During this time, in order to check for the presence or absence of methanol crossover from the negative electrode side to the positive electrode side, the gas at the air outlet was sampled and the concentration of methanol vapor was measured using a detector tube (detection lower limit: 0.2 ppm). Methanol could not be detected.

Example 2 23% by weight of silver, palladium 7
Platinum black treatment was performed on both surfaces of a 7% by weight palladium alloy film having a thickness of 20 μm in the same manner as in Example 1. The one side of the palladium alloy membrane an anode catalyst solution prepared in Example 1, were coated to a 1.5 mg / cm ² platinum amount was the coated surface of the negative electrode catalyst solution and the negative electrode. Next, a cation exchange membrane and a positive electrode prepared in the same manner as in Example 1 were overlaid on the other side of the palladium alloy membrane such that the catalyst-coated surface was in contact with the cation exchange membrane. The thus superimposed products are heated at 120 ° C. and 100 kg / cm ² for 10 minutes.
The mixture was heated and compressed for 1 minute to prepare a membrane-electrode assembly.

This membrane / electrode assembly was assembled in the same fuel cell as in Example 1, and the output characteristics were measured for 20 hours in the same manner as in Example 1. As a result, the maximum output was 0.13 W / cm ^2. Obtained. Also, during this time, in order to check for the presence or absence of crossover of methanol from the negative electrode side to the positive electrode side, sampling of the gas at the air outlet and measurement of the concentration of methanol vapor using a detector tube were attempted, but methanol could not be detected. Was.

Example 3 23% silver, 77% palladium
Was treated with palladium black on one side of the palladium alloy film having a thickness of 10 μm, and the other side was treated with platinum black-ruthenium black in the same manner as the palladium black treatment. Each deposition amount of platinum particles and ruthenium particles in this case 0.9 mg ^/ cm 2, was 0.5 mg / cm ^2.
A cation exchange membrane is superimposed on the palladium black-treated surface of this palladium alloy membrane, and a positive electrode prepared in the same manner as in Example 1 is coated with a catalyst on a surface of the cation exchange membrane that is not in contact with the palladium alloy membrane. They were superposed so that the surfaces were in contact with the cation exchange membrane. The thus laminated palladium alloy membrane, cation exchange membrane, and positive electrode were heated and compressed at 120 ° C. and 100 kg / cm ² for 5 minutes to form a membrane.
An electrode assembly was manufactured.

After this membrane / electrode assembly was assembled in the same cell as in Example 1 to form a fuel cell, the output characteristics over 15 hours were measured in the same manner as in Example 1. As a result, a maximum output of 0.09 W / cm ² was obtained. Also, during this time, in order to check for the presence or absence of crossover of methanol from the negative electrode side to the positive electrode side, sampling of the gas at the air outlet and measurement of the concentration of methanol vapor using a detector tube were attempted, but methanol could not be detected. Was.

Example 4 Palladium black treatment was performed on both surfaces of the same palladium alloy film as in Example 1 in the same manner as in Example 1. Next, this palladium alloy membrane was sandwiched between two cation exchange membranes. A negative electrode prepared in the same manner as in Example 1 was superposed on one side of the superposed ion exchange membrane not in contact with the palladium alloy membrane such that the catalyst-coated surface was in contact therewith. Further, the positive electrode prepared in the same manner as in Example 1 was superposed on the other side of the superposed cation exchange membrane that was not in contact with the palladium alloy membrane such that the catalyst-coated surface was in contact therewith. Thus, the negative electrode, the cation exchange membrane, the palladium alloy membrane, the cation exchange membrane, and the positive electrode were stacked in this order at 120 ° C. and 100 ° C.
The mixture was heated and compressed at kg / cm ² for 10 minutes to prepare a membrane-electrode assembly.

Using this membrane / electrode assembly, a fuel cell was formed in the same manner as in Example 1. While maintaining the fuel cell at 90 ° C., a mixed solution of methanol and water was supplied to the negative electrode side, and humidified air was supplied to the positive electrode side, and output characteristics were measured for 15 hours. As a result, the maximum output was 0.10 W /
cm ² was obtained. During this time, in order to check for the presence or absence of crossover of methanol from the negative electrode side to the positive electrode side, the gas at the air outlet was sampled and the concentration of methanol vapor was measured using a detector tube, but methanol could not be detected. Was.

(Example 5) A cation exchange membrane was superimposed on one side of a palladium alloy membrane whose both sides were treated with palladium black in the same manner as in Example 1. The negative electrode prepared in the same manner as in Example 1 was superposed on the surface of the superposed cation exchange membrane that was not in contact with the palladium alloy membrane such that the catalyst-coated surface was in contact therewith. A positive electrode prepared in the same manner as in Example 1 was superimposed on the surface of the palladium alloy membrane not in contact with the cation exchange membrane so that the catalyst-coated surface was in contact therewith. The negative electrode, the cation exchange membrane, the palladium alloy membrane, and the positive electrode were stacked in this order at 130 ° C. and 50 kg.
/ Cm ² for 5 minutes to prepare a membrane-electrode assembly.

This membrane / electrode assembly was assembled in the same cell as in Example 1 to form a fuel cell. This fuel cell
While maintaining the temperature at 0 ° C., a mixed solution of methanol-water was supplied to the negative electrode, and humidified air was supplied to the positive electrode for 15 hours, and the output characteristics were measured.
/ Cm ² was obtained. Also, during this time, in order to check for the presence or absence of crossover of methanol from the negative electrode side to the positive electrode side, sampling of the gas at the air outlet and measurement of the concentration of methanol vapor using a detector tube were attempted, but methanol could not be detected. Was.

Example 6 Palladium black treatment was performed on both surfaces of a 25 μm-thick palladium alloy film made of 40% by weight of copper and 60% by weight of palladium in the same manner as in Example 1. A cation exchange membrane was superimposed on one side of the palladium alloy membrane in the same manner as in Example 1. Next, the negative electrode prepared in the same manner as in Example 1 was overlaid on the surface of the palladium alloy membrane that was not in contact with the ion-exchange membrane so that the catalyst-coated surface was in contact therewith, and further contacted with the palladium of the cation-exchange membrane. The positive electrode prepared in the same manner as in Example 1 was superposed on the non-coated surface such that the catalyst-coated surface was in contact with the positive electrode. At this time, the coating amount of the catalyst on the negative electrode was 2.2 mg /
cm ² . At 120 ° C, 1
It was heated and compressed at 00 kg / cm ² for 10 minutes to prepare a membrane-electrode assembly.

This membrane / electrode assembly was assembled in the same cell as in Example 1 to form a fuel cell. This fuel cell is
While maintaining the temperature at 0 ° C, the negative electrode side was kept at 80 ° C for 5 hours.
Supply humidified dimethyl ether at 80
When the output characteristics were measured by passing oxygen humidified at a temperature of 0 ° C., a maximum output of 0.05 W / cm ² was obtained. Also, during this time, in order to inspect the presence or absence of dimethyl ether crossover from the negative electrode side to the positive electrode side, the gas at the air outlet was sampled and the concentration of dimethyl ether vapor was measured with a detector tube, but dimethyl ether could not be detected. Was.

[0042]

According to the direct fuel cell of the present invention using methanol or dimethyl ether as a fuel, the catalyst activity is reduced and the methanol utilization efficiency is reduced due to crossover of the fuel from the negative electrode side to the positive electrode side, which was difficult in the prior art. Can be completely prevented without complicating the configuration of the fuel cell. In the present invention, since the fuel does not come into contact with the positive electrode catalyst, the positive electrode catalyst is not affected by poisoning components such as carbon monoxide caused by the fuel. The power density can be obtained, and the fuel use efficiency can be improved.

Further, in the case of using a palladium film or a palladium alloy film on the negative electrode side, in particular, since the electrolyte film does not come into contact with methanol or dimethyl ether as a fuel, the deterioration of the electrolyte film can be prevented, and the negative electrode catalyst can be used. Since it does not come into contact with a strongly acidic electrolyte membrane, the catalyst component can be selected from a wide range without considering corrosion resistance. In addition, in the fuel cell of the present invention, the palladium film or the palladium alloy film also functions as a collecting electrode, so that power can be efficiently generated. Further, depending on the configuration in which the solid polymer electrolyte membrane is not used as the electrolyte membrane, the fuel cell can be operated at a high temperature.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a configuration example in a case where a palladium film or a palladium alloy film is used on a negative electrode side in a fuel cell of the present invention.

FIG. 2 is a cross-sectional view showing a configuration example in a case where a palladium film or a palladium alloy film is used between two electrolyte membranes in the fuel cell of the present invention.

FIG. 3 is a cross-sectional view showing a configuration example in the case where a palladium film or a palladium alloy film is used on the positive electrode side in the fuel cell of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cell 2, 2 'Ion exchange membrane 3 Palladium membrane or palladium alloy membrane 4 Negative electrode 5 Positive electrode 6 Flow path of fuel and water 7 Flow path of oxygen-containing gas 8 Fuel and water inlet 9 Unreacted fuel, water and carbon dioxide Outlet 10 inlet for oxygen-containing gas 11 outlet for water and exhaust gas 12 negative electrode terminal 13 positive electrode terminal

 ──────────────────────────────────────────────────続 き Continued on front page F term (reference) 5H018 AA06 AA07 AS01 BB03 BB05 BB07 DD01 DD05 DD06 DD08 EE02 EE03 EE04 EE05 EE10 5H026 AA06 AA08 BB02 BB04 CX01 CX03 CX04 CX05 EE02 EE05 EE08

Claims (10)

[Claims] 1. A fuel cell comprising a negative electrode on one side of an electrolyte membrane and a positive electrode on the other side, supplying methanol or dimethyl ether as fuel with water to the negative electrode, and supplying an oxygen-containing gas to the positive electrode, A fuel cell, wherein a palladium film or a palladium alloy film is disposed at any position between a contact surface of a negative electrode with fuel and water and a contact surface of a positive electrode with an oxygen-containing gas. 2. A negative electrode comprising a porous support holding a platinum group catalyst on one side of an electrolyte membrane and a positive electrode comprising a porous support holding a platinum group catalyst on the other side. A fuel cell configured to supply methanol or dimethyl ether as a fuel together with water and to supply an oxygen-containing gas to a positive electrode, wherein a palladium film or a palladium alloy film is disposed between a porous support of the negative electrode or the positive electrode and an electrolyte film. A fuel cell, comprising: 3. A fuel cell having a configuration in which methanol or dimethyl ether is supplied to a negative electrode together with water as a fuel and an oxygen-containing gas is supplied to a positive electrode, wherein a palladium film or a palladium alloy film is disposed between two electrolyte films. A fuel cell, characterized in that a negative electrode is provided on one surface of the electrolyte membrane not in contact with the palladium film or palladium alloy film, and a positive electrode is provided on one surface of the electrolyte membrane not in contact with the palladium alloy film. 4. The fuel cell according to claim 1, wherein the palladium film or the palladium alloy film is disposed between the fuel and water contact surface of the negative electrode and the electrolyte film. 5. The fuel cell according to claim 2, wherein a palladium membrane or a palladium alloy membrane is disposed between the porous support of the negative electrode and the electrolyte membrane. 6. The platinum group catalyst is a fine particle catalyst made of a platinum group metal, or platinum and ruthenium, rhodium, palladium, rhenium, iridium, chromium, gold,
3. The fuel cell according to claim 2, which is a particulate mixed catalyst or an alloy catalyst made of at least one metal selected from silver, iron, cobalt, and nickel. 7. The fuel cell according to claim 2, wherein the porous support is carbon paper, carbon nonwoven fabric, metal nonwoven fabric, or metal foam. 8. The fuel cell according to claim 1, wherein the palladium film or the palladium alloy film holds platinum group metal fine particles on the surface. 9. A palladium alloy membrane comprising: palladium;
The fuel cell according to any one of claims 1 to 3, wherein the fuel cell is an alloy film made of at least one metal selected from gold, silver, copper, platinum, yttrium, nickel, iron, cobalt, and zirconium. 10. The palladium film or palladium alloy film is a thin film formed by rolling, or a thin film formed by plating, vapor deposition, or CVD on the surface of an electrolyte membrane or a porous support. The fuel cell according to claim 3.