JP2001167775A - Ion conductive film, method of manufacturing the same, and fuel cell using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a novel ion conductive film that can suppress methanol crossover, while maintaining ion conductivity in order to solve the problems in the conventional fuel cell, and a fuel cell, particularly a fuel cell of small size hat can supply a stable output. SOLUTION: An-ion conductive single film (not a composite film) in which the conductivity within the depth of 50 μm from at least one of its main surfaces is lower than the conductivity inside the film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an ionic conductive film,
The present invention relates to a manufacturing method thereof and a fuel cell using the same.

[0002]

2. Description of the Related Art Conventional methanol fuel cells are classified into two types, a liquid supply type and a vaporization supply type, depending on the method of supplying liquid fuel. Among them, the vaporization supply type has high activity and high performance because the electrode reaction is performed with a gaseous fuel, but on the other hand, the system is extremely complicated and it is difficult to reduce the size. On the other hand, in the case of the liquid supply type, the fuel electrode and the oxidant electrode face each other via the electrolyte membrane and utilize capillary force or the like for fuel supply. It is suitable for miniaturization without requiring any other means. Here, the electrolyte membrane is made of perfluorosulfonic acid (trade name: Na
When a proton-conductive solid polymer membrane such as fion Du Pont) is used as the electrolyte, a crossover occurs in which a liquid organic fuel such as methanol permeates the electrolyte membrane toward the oxidant electrode. If this phenomenon occurs, the liquid fuel and the oxidant react directly, and energy cannot be output as electric power. Therefore, there is a decisive problem that a stable output cannot be obtained.

[0003]

In the conventional fuel cell, the ionic conductivity was not sufficient to suppress the crossover of methanol, and a stable output could not be supplied.

[0004] The present invention has been made in view of the above problems, and has as its object to provide a new ionic conductive membrane capable of suppressing methanol crossover while maintaining ionic conductivity. It is an object to provide a fuel cell capable of supplying a stable output.

[0005]

In order to solve the above-mentioned problems, in the ionic conductive film according to the present invention, the conductivity on the surface is set lower than the conductivity on the inside, and the electrolyte of the fuel cell is improved. It is characterized by being used for applications.

According to a second aspect of the present invention, in the first aspect, the ionic conductive film is a polymer comprising a fluororesin skeleton and sulfonic acid.

According to a third aspect of the present invention, in the ion conductive film according to the second aspect, the polymer is a polybenzimidazole derivative, an amino-containing polymer, a polyaniline derivative,
It is selected from the group consisting of a silanol-containing polymer and a hydroxyl-containing polymer.

According to a fourth aspect of the present invention, there is provided a method for manufacturing an ion conductive film.
A step of preparing a conductive membrane used for an electrolyte of a fuel cell,
Irradiating the surface of the conductive film with an electron beam to modify the conductivity on the surface to be lower than the conductivity inside the conductive film.

A fuel cell according to a fifth aspect of the present invention provides an electrolyte membrane, a fuel electrode formed adjacent to the electrolyte membrane, and an oxidant adjacent to the electrolyte membrane and opposed to the fuel electrode via the electrolyte membrane. In a fuel cell including a pole, the electrolyte membrane is an ion conductive membrane whose conductivity on the surface is set lower than conductivity on the inside.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION An ionic conductive film having a basic structure of a fluorinated resin represented by Nafion exhibits excellent ionic conductivity. Since this high ionic conductivity is exerted through a water-containing cluster network, in a fuel cell using methanol, there is a problem that methanol is mixed with water from the anode, diffuses through the cluster network to the cathode, and lowers the output voltage. Was. On the other hand, a method of introducing a crosslinked structure or the like to suppress swelling is generally used, but there is a problem that when the entire film is crosslinked, the conductivity is greatly reduced. Therefore, in order to maintain conductivity and suppress crossover of methanol, only the surface thin film layer of a single film is densified or made hydrophobic, and while maintaining ionic conductivity, permeation selectivity between water and methanol is improved. The present invention has been proposed.

That is, the ion conductive film of the present invention can be described as follows.

At least one surface layer of the film having ionic conductivity is modified by physically or chemically modifying such as electron beam irradiation, and the conductivity is lower than the internal conductivity. Use an ion conductive film or an ion conductive film whose swelling in water, a solvent, or an electrolyte is lower than that of the inside. Here, the modified region on the surface is desirably at least one surface layer having a depth within 50 μm.

Examples of the base material of the ion conductive film include a polybenzimidazole film, a polystyrene sulfonic acid copolymer film, a polyvinyl sulfonic acid copolymer film, a fluoropolymer film composed of a fluororesin skeleton and sulfonic acid, and the like. Among them, a fluoropolymer film composed of a fluororesin skeleton and sulfonic acid having durability, film strength and ionic conductivity is most suitable.

The method of manufacturing the ion conductive film can be obtained by irradiating the surface of the base material of the ion conductive film with an electron beam to modify the surface. Generally, since EB reaches the deep part of the film, it is necessary to irradiate the electron beam at an acceleration voltage of 100 KV or less. 1
If it is more than 00KV, the damage of the film is too large,
The EB reaches the deep part, and a membrane usable as an electrolyte membrane of a target fuel cell cannot be obtained. The acceleration voltage is preferably 20 KV or more, and below that, a sufficient effect as an electrolyte membrane of a fuel cell cannot be obtained. Although it may be in an inert atmosphere or air, it is more reproducible and more realistic in an inert gas. According to the above-mentioned method, hydrophobicity and densification are achieved by a crosslinking reaction on the membrane surface and elimination of sulfonic acid groups. It is important to reduce the thickness of these surface-modified layers to such an extent that sufficient strength is maintained.

The above-mentioned ionic conductive film has an increased surface strength at the time of swelling, and in some cases, there is a concern that contact with the electrode may be deteriorated. However, the surface of the film further swells with water, a solvent, or an electrolytic solution. By laminating an easy ion conductive film, the improvement can be easily made.

Another ionic conductive film of the present invention can be described as follows.

A first ionic conductive film having high ionic conductivity; and a second ionic conductive film having a maximum swelling area at 25 ° C. of less than 5% and having a nitrogen or hydroxyl group. Is a complex. The first ion conductive film has at least one property of high methanol permeability but high ion conductivity. Further, the second ion conductive film is a composite with at least one polymer (B) having a lower methanol permeability but a lower ion conductivity as compared with the ion conductive film (hereinafter referred to as (A)). Consists of In order to reduce the methanol permeability while maintaining the conductivity, (hereinafter referred to as (B)) needs to be thinner than (A). The film thickness of (A) is usually 10 μm to 500 μm, and considering the balance between mechanical strength and conductivity, it is 50-200 μm.
m is preferred. As for (B), the thinner the film, the less the decrease in conductivity, usually 0.01-10 μm, preferably 0.1-1 μm.
μm is desirable. (B) may be coated on at least one surface of (A) or may be inserted in a sandwich shape inside. (B) has a function of preventing swelling of (A) and improving methanol permeability. Therefore, (B) requires a proton conductivity of 1 × 10 ⁻¹⁰ S / cm or more. Preferably, a conductivity of 1 × 10 ⁻⁵ S / cm is desired. These films are also formed by a coating method, a laminating method, a dipping method or the like, and may be subjected to a press or other heat treatment. These may be doped with an acid such as phosphoric acid or sulfuric acid to increase conductivity.

As the ion conductive film, a polystyrene sulfonic acid copolymer film, a polyvinyl sulfonic acid copolymer film,
Crosslinked alkyl sulfonic acid derivatives, fluoropolymer membranes made of fluororesin skeleton and sulfonic acid, etc. can be used. Among them, fluoropolymer membranes made of fluororesin skeleton and sulfonic acid that combine durability, film strength and ionic conductivity are most suitable. is there.

Examples of the film having nitrogen or hydroxyl groups include polybenzimidazole derivatives, polybenzoxazole derivatives, crosslinked polyethyleneimine, polysilamine derivatives, amine-substituted polystyrene represented by polydiethylaminoethyl polystyrene, and nitrogen represented by diethylaminoethyl polymethacrylate. Examples include substituted polyacrylates, silanol-containing polysiloxanes, hydroxyl-containing polyacrylic resins represented by hydroxyethyl polymethylacrylate, and hydroxyl-containing polystyrene resins represented by parahydroxypolystyrene. Further, as shown below, a crosslinkable substituent, for example, a vinyl group, an epoxy group, an acryl group, a methacryl group, a cinnamoyl group, a methylol group, an azide group, a naphthoquinonediazide group and the like may be substituted.

FIG. 1 is a cross-sectional view showing the configuration of a main part of a fuel cell using the above-described ion conductive membrane. In the figure, 1 is a fuel electrode (anode) 2 and an oxidizer electrode (cathode)
3 is an electrolyte plate sandwiched between them, and is formed into a plate shape as an electrolyte membrane. The electrolyte plate 1, the fuel electrode 2 and the oxidant electrode 3 constitute an electromotive section 4. Here, the fuel electrode 2 and the oxidant electrode 3 are formed of a conductive porous body in order to allow fuel and oxidant gas to flow and pass electrons.

In this fuel cell, each cell has a fuel infiltration portion 6 having a function of retaining liquid fuel, and a gaseous fuel held in the fuel infiltration portion 6 and having the liquid fuel vaporized is supplied to the fuel electrode 2.
Is provided with a fuel vaporizing section 7 for leading the fuel to the fuel cell. Reference numeral 10 denotes an electromotive section composed of an electrolyte plate 1, a fuel electrode 2, and an oxidant electrode 3. By stacking a plurality of unit cells including the electromotive unit 10, the fuel infiltration unit 6, and the fuel vaporization unit 7 via the separator 5, a stack 100 serving as a battery main body is configured. An oxidizing gas supply groove 8 for flowing an oxidizing gas is provided as a continuous groove on a surface of the separator 5 which is in contact with the oxidizing electrode 3. From fuel tank (not shown) to fuel permeation section 6
As a means for supplying liquid fuel to the
The liquid fuel introduction passage 4 is formed on at least one side surface of 00 along this surface. The liquid fuel introduced into the liquid fuel introduction passage 4 is supplied from the side surface of the stack 100 to the fuel permeation section 6, further vaporized by the fuel vaporization section 7, and supplied to the fuel electrode 2. At this time, by configuring the fuel infiltration portion with a member exhibiting a capillary phenomenon, the liquid fuel can be supplied to the fuel infiltration portion 6 by capillary force without using an auxiliary device. For that purpose, the liquid fuel introduced into the liquid fuel introduction passage 4 is
It is configured so as to directly contact the end face of the fuel infiltration portion.

When the cells 100 are stacked to form the stack 100 as shown in FIG. 1, the separator 5, the fuel infiltration section 6, and the fuel vaporization section 7 function as a current collecting plate for conducting generated electrons. Therefore, it is formed of a conductive material. Further, if necessary, a layered, island-like, or granular catalyst layer may be formed between the fuel electrode 2 or the oxidizer electrode 3 and the electrolyte plate 1, but the present invention relates to such a catalyst layer. There is no restriction on the presence or absence. Further, the fuel electrode 2 and the oxidant electrode 3 themselves may be used as the catalyst electrodes. The catalyst electrode,
The catalyst layer may be used alone, or may have a multilayer structure in which the catalyst layer is formed on a support such as conductive paper or cloth.

As described above, the separator 5 also has a function as a channel for flowing an oxidizing gas. As described above, by using the separator 5 having both functions of the separator and the channel, the number of components can be further reduced, and the size can be further reduced. Note that a normal channel can be used instead of the separator 5.

As a method of supplying the liquid fuel from the fuel storage tank to the liquid fuel introduction path 4, there is a method in which the liquid fuel in the fuel storage tank is naturally dropped and introduced into the liquid fuel introduction path 4. This method can reliably introduce the liquid fuel into the liquid fuel introduction passage 4 except for a structural restriction that the fuel storage tank must be provided at a position higher than the upper surface of the stack 10. As another method, there is a method of drawing liquid fuel from the fuel storage tank by the capillary force of the liquid fuel introduction path 4. According to this method, the connection point between the fuel storage tank and the liquid fuel introduction path 4, that is, the position of the fuel inlet provided in the liquid fuel introduction path 4 is determined by the stack 10
There is no need to make the height higher than the upper surface of the fuel tank. For example, in combination with the above-mentioned natural fall method, there is an advantage that the installation location of the fuel tank can be freely set.

However, in order to continuously supply the liquid fuel introduced into the liquid fuel introduction passage 4 by the capillary force to the fuel permeation portion 6 by the capillary force, the fuel permeation portion is formed by the capillary force of the liquid fuel introduction passage 4. It is important to set the capillary force to 6 to be greater. The number of the liquid fuel introduction passages 4 is not limited to one along the side surface of the stack 10, and the liquid fuel introduction passages 4 may be formed on the other stack side surface.

The fuel storage tank as described above is
It can be detachable from the battery body. Thus, by replacing the fuel storage tank, the operation of the battery can be continued for a long time. Further, the supply of the liquid fuel from the fuel storage tank to the liquid fuel introduction path 4 may be configured such that the liquid fuel is pushed out by the above-described natural fall or the internal pressure in the tank, or the liquid fuel introduction path may be provided. It is also possible to adopt a configuration in which fuel is drawn out by the capillary force of 4.

The liquid fuel introduced into the liquid fuel introduction passage 4 is supplied to the fuel permeation section 6 by the above-described method. The form of the fuel infiltration section 6 is not particularly limited as long as it has a function of holding the liquid fuel therein and supplying only the vaporized fuel to the fuel electrode 2 through the fuel vaporization section 7. For example, it may have a passage for a liquid fuel and include a gas-liquid separation membrane at the interface with the fuel vaporization section 7. Further, when the liquid fuel is supplied to the fuel infiltration unit 6 by capillary force, the form of the fuel infiltration unit 6 is not particularly limited as long as the liquid fuel can be infiltrated by capillary force. In addition to a porous body, a nonwoven fabric manufactured by a papermaking method or the like, and a woven fabric woven with fibers, a narrow gap formed between glass and plastic plates or the like can be used.

The case where a porous body is used as the fuel infiltration section 6 will be described below. As the capillary force for drawing the liquid fuel into the fuel permeation portion 6 side, first, the capillary force of the porous body itself that becomes the fuel permeation portion 6 can be cited. When such a capillary force is used, a so-called continuous hole is formed by connecting the holes of the fuel permeable portion 6 which is a porous body, and the hole diameter is controlled, and the side surface of the fuel permeable portion 6 on the side of the liquid fuel introduction path 4 is controlled. To at least one other surface, the liquid fuel can be smoothly supplied by the capillary force even in the lateral direction.

The pore diameter and the like of the porous body that becomes the fuel infiltration section 6 are as follows:
It is not particularly limited as long as the liquid fuel in the liquid fuel introduction path 4 can be drawn in, and is not particularly limited, but is preferably about 0.01 to 150 μm in consideration of the capillary force of the liquid fuel introduction path 4. . Further, the volume of pores, which is an index of the continuity of pores in the porous body, is preferably about 20 to 90%. If the pore diameter is smaller than 0.01 μm, it becomes difficult to manufacture the fuel permeable portion 6, and if it exceeds 150 μm, the capillary force is reduced. Further, when the volume of the holes is less than 20%, the amount of continuous holes decreases and the number of closed holes increases, so that sufficient capillary force cannot be obtained. Conversely, the volume of the hole
If it exceeds 90%, although the amount of continuous pores increases, the strength becomes weak and the production becomes difficult. Practically, it is desirable that the pore size is in the range of 0.5 to 100 μm and the volume of the pores is in the range of 30 to 75%.

[0030]

The present invention can be understood more deeply by describing specific but non-limiting examples. Example 1 A 170 μm-thick Nafion 117 manufactured by DuPont was irradiated with an electron beam of 30 μC / cm 2 at an acceleration voltage of 50 KV to modify the surface. After standing in water for 1 hour, the surface conductivity was measured and found to be 1.1 × 10 ⁻⁶ S / cm. On the other hand, the surface is 30 μm
When the conductivity of the surface of the film after cutting was measured in the same manner, it was 4.5 × 10 ⁻² S / cm. Although the obtained film is a single film as intended, the internal conductivity is high,
It turned out that it is an ion conductive film with low surface conductivity.

A 10 μm surface of the ionic conductive film was cut out. Similarly, the inside was cut out from 90 μm to 100 μm, and the degree of swelling was measured after immersion in water for 1 hour.The degree of swelling of the surface layer was about 10%, whereas the degree of swelling of the inside was 22%. . The obtained film was found to be an ion conductive film having a high degree of swelling inside and a low swelling purity of the surface thin film layer, although it was a single film as intended.

The conductivity between the opposing surfaces of the ionic conductive film was 1.5 × 10 ⁻³ S / cm, and the overall swelling purity when immersed in water was 13%. Analysis by infrared spectroscopy showed that the surface absorption of sulfonic acid was 15% lower than the internal absorption. A decrease in sulfonic acid groups was observed in the surface layer, and it was found that the swelling degree and the conductivity decreased due to a decrease in the sulfonic acid content along with crosslinking.
Furthermore, when the aqueous layer and water / methanol (1: 1 volume) were partitioned by the above-mentioned ionic conductive film, and the permeability coefficient of methanol was measured, the result was 7 × 10 ⁻⁸ cm 2 / s, which was 1.2 × 10 ⁻⁸ cm 2 / s before EB irradiation.
Compared with ^-6 cm2 / s, it was confirmed that methanol permeability was reduced.

Using the ionic conductive film described above, FIG.
A liquid fuel cell (unit cell) having the configuration shown in (1) was manufactured in the following manner. Although the fuel cell shown in FIG. 1 has a basic configuration, FIG. 2 shows an actually prepared fuel cell.

First, a 32 mm × 32 mm fuel electrode 22 having a Pt—Ru catalyst layer coated on a carbon cloth, and a 32 mm × 32 mm oxidizing electrode 23 having a Pt black catalyst layer coated on a carbon cloth
Then, the ion conductive film produced in Example 1 described above was cut out into a predetermined shape so that the catalyst layer was in contact with the electrolyte membrane, and was sandwiched as the electrolyte membrane 21. These were joined by hot pressing at 120 ° C. for 5 minutes at a pressure of 100 kg / cm 2. This electromotive section and an average pore diameter of 100 μm as the fuel vaporization layer 25,
A carbon porous plate having a porosity of 70%, and a carbon porous plate having an average pore diameter of 5 μm and a porosity of 40% as the fuel permeable layer 24,
A unit cell having a reaction area of 10 cm2 was fabricated by incorporating the inside of an oxidant electrode side holder 27 and a fuel electrode side holder 28 having an oxidant gas supply groove 26 having a depth of 2 mm and a width of 1 mm. In the liquid fuel cell obtained in this manner, methanol and water 1:
A 1 (molar ratio) mixture is introduced by capillary force from the side of the fuel permeable layer 25, and 1 atm of air as an oxidizing gas is flowed through the gas channel 26 at 100 ml / min under a load condition of 80 ° C. and 0.2 A / cm 2. Generated electricity. The initial voltage was 0.5V. There was no change in voltage after one day of operation. (Comparative Example 1) In Example 1, when a film irradiated with the same amount at an accelerating voltage of 200 KV was similarly analyzed, there was almost no difference in conductivity between the inside and the surface layer, and the swelling purity in water was 10%. Dropped. When the methanol permeability was examined in the same manner as in Example 1, it was found that the permeability was 6 × 10 ⁻⁸ cm 2 / s, which was significantly lower than that of Nafion117 before the treatment. However, the conductivity between the opposing surfaces was significantly reduced to 4.5 × 10 ⁻⁵ S / cm, and it was not possible to achieve both reduction in methanol permeability and maintenance of conductivity.

From these facts, the film of the present invention in which the swelling degree and conductivity of the surface thin film layer are reduced while maintaining the internal ionic conductivity is compared with a film in which the overall properties are changed uniformly. It has been found that permeation of methanol can be more effectively prevented while maintaining the original conductivity of the Nafion membrane.

An experiment was performed in the same manner as in Example 1 except that untreated Nafion 117 was used instead of the film produced in Example 1. The initial voltage was 0.4 V, but gradually decreased.
After running for hours, the load decreased until the load of 0.2 A / cm2 could not be taken.

From a comparison between Example 1 and Comparative Example 1, it was easily found that the membrane of the present invention was excellent as a solid electrolyte for a methanol fuel cell. (Comparative Example 2) A fuel cell having the same structure as in Example 5 except that untreated Nafion 117 was used instead of the membrane produced in Example 1 was driven, and the initial voltage was 0.4 V. Gradually lower, 0.2A by driving for 5 hours
/ cm2 decreased until the load could not be taken.

From the comparison between Example 1 and Example 2, it is easily understood that the membrane of the present invention is excellent as a solid electrolyte for a methanol fuel cell. Example 2 A 170 μm thick Nafion 117 manufactured by DuPont was irradiated with an electron beam of 20 μC / cm 2 at an acceleration voltage of 35 KV to modify only the surface thin film layer. The methanol fuel cell shown in FIG. 2 was prepared and the output voltage was measured in the same manner as in Example 1 except that this ion conductive membrane was used. The output voltage was 0.5 V, and the output decrease after one day operation was 5%. Below, it was confirmed that cathode poisoning by methanol was reduced. (Example 3) DuPont's Nafion112 having a film thickness of about 100 µm was
An electron beam of 20 μC / cm2 was irradiated at an acceleration voltage of 35 KV to modify only the surface thin film layer. Untreated Nafion112 / Ion conductive membrane
/ Untreated Nafion 112 was laminated, and the methanol fuel cell was prepared and the output voltage was measured in the same manner as in Example 1. The output voltage was 0.55 V, and the output reduction after one day operation was within 5%. Example 4 A Nafion® film having a thickness of 190 μm was immersed in a 0.1% DMAc solution of polybenzimidazole at room temperature for 1 hour, dried at room temperature, and then dried at 125 ° C. and 100 kg / cm.
2 for 10 minutes, boil in pure water for 1 hour,
An ion conductive film of a composite film was prepared. A fuel cell was formed in exactly the same manner as in Example 1 except that this ion conductive membrane was used. Example 5 A 190 μm thick Nafion® film was immersed in a 0.1% solution of polyaniline in DMAc for 1 hour at room temperature, dried at room temperature, pressed at 125 ° C. and 100 kg / cm 2 for 10 minutes, and then boiled with pure water. One hour later, a composite ion-conductive film was prepared. A fuel cell was formed in exactly the same manner as in Example 1 except that this ion conductive membrane was used. Example 6 A Nafion® film having a thickness of 190 μm was immersed in a 1% DMAc solution of poly (dimethylaminoethylstyrene) at room temperature for 1 hour and dried at room temperature.
After pressing for 10 minutes at kg / cm2, boil in pure water 1
After a while, a composite membrane ionic conductive membrane was prepared. A fuel cell was formed in exactly the same manner as in Example 1 except that this ion conductive membrane was used. Example 7 A Nafion® film having a thickness of 190 μm was immersed in a 0.1% DMAc solution of polybenzimidazole for 1 hour at room temperature, dried at room temperature, and then dried at 125 ° C. and 100 kg / cm.
2 for 10 minutes, boil in pure water for 1 hour,
An ion conductive film of a composite film was prepared. Further, this film was immersed in a 1% aqueous solution of phosphoric acid for 5 hours to dope phosphoric acid. A fuel cell was formed in exactly the same manner as in Example 1 except that this ion conductive membrane was used. Example 8 A Nafion® film having a thickness of 190 μm was immersed in a 0.1% DMAC solution of polyaniline at room temperature for 1 hour, dried at room temperature, pressed at 125 ° C. and 100 kg / cm 2 for 10 minutes, and then boiled with pure water. One hour later, a composite ion-conductive film was prepared. Further, this film was immersed in a 1% aqueous solution of sulfuric acid for 5 hours to dope sulfuric acid. A fuel cell was formed in exactly the same manner as in Example 1 except that this ion conductive membrane was used. Example 9 A Nafion® film having a thickness of 190 μm was immersed in a 1% DMAc solution of poly (dimethylaminoethylstyrene) at room temperature for 1 hour, dried at room temperature, and then dried at 125 ° C. and 100 ° C.
After pressing for 10 minutes at kg / cm2, boil in pure water 1
After a while, a composite membrane ionic conductive membrane was prepared. Furthermore, 1% of polyparavinylbenzene sulfonic acid is added to this membrane.
It was immersed in the solution for 5 hours and doped with sulfonic acid. A fuel cell was formed in exactly the same manner as in Example 1 except that this ion conductive membrane was used. Example 10 Polyethylene cloth was impregnated with polystyrene / divinylbenzene into a polyethylene cloth, and a sulfonated ion exchange membrane was immersed in a 0.1% DMAc solution of polybenzimidazole at room temperature for 1 hour, dried at room temperature, and dried at 125 ° C. and 100 ° C.
After pressing for 10 minutes at kg / cm2, boil in pure water 1
After a while, a composite membrane ionic conductive membrane was prepared. A fuel cell was formed in exactly the same manner as in Example 1 except that this ion conductive membrane was used. Example 11 A Nafion® film having a thickness of 190 μm was immersed in a 0.1% DMAc solution of polybenzimidazole for 1 hour at room temperature and dried at room temperature. The temperature was 125 ° C. and 100 kg / cm 2.
For 10 minutes, and then boiled with pure water for 1 hour to produce a composite ion-conductive film. Further acceleration voltage 50K
EB irradiation was performed at a dose of V and a dose of 300 μC / cm2. A fuel cell was formed in exactly the same manner as in Example 1 except that this ion conductive membrane was used. A methanol fuel cell was produced using this ion conductive membrane in the same manner as in Example 1, and the output voltage was measured. The output voltage was 0.5 V, and the output reduction after one day of operation was 5% or less. As in Examples 3 to 10, it was possible to prevent a decrease in output, and it was confirmed that cathode poisoning by methanol was reduced. Comparative Example 3 Sample 1 A 190 μm thick Nafion® film was immersed in a 0.1% toluene solution of polystyrene at room temperature for 1 hour, dried at room temperature, and then heated at 125 ° C. and 100 kg / c.
After pressing at m2 for 10 minutes, the sample was boiled with pure water for 1 hour to prepare a composite membrane sample.

Table 1 shows the conductivity and relative methanol permeability of each film in Examples 4 to 11 and Comparative Example 3. Methanol permeability of untreated Nafion membrane was 10
When the value is set to 0, it can be seen that the membrane used in Example 4-11 of the present invention has a low methanol permeability despite a small decrease in conductivity. On the other hand, as shown in the comparative example, when the surface was coated with polystyrene having neither nitrogen nor a hydroxyl group, a large increase in resistance was observed.

[Table 1] From these, while maintaining the internal ionic conductivity,
The film of the present invention in which the degree of swelling of the surface thin film layer and the conductivity have been reduced, compared to a film in which the overall properties are uniformly changed,
It was found that permeation of methanol can be more effectively prevented while maintaining the conductivity of the Nafion membrane. Example 16 A 190 μm thick Nafion® film was immersed in a 0.1% solution of polyaniline in DMAc at room temperature for 1 hour, dried at room temperature, pressed at 125 ° C. and 100 kg / cm 2 for 10 minutes, and then boiled with pure water. One hour later, a composite ion-conductive film was prepared. In addition, this membrane is
It was immersed in an aqueous solution for 5 hours and doped with sulfuric acid. Using this ion conductive film, untreated Nafion112 / ion conductive film /
Untreated Nafion 112 was laminated, a methanol fuel cell was produced in the same manner as in Example 1, and the output voltage was measured. The output voltage was 0.55 V, and the output decrease after one day operation was within 5%.

[0040]

As described above, the use of the ion conductive membrane of the present invention makes it possible to reduce the methanol crossover and to produce a stable and high-output fuel cell.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a fuel cell illustrating an embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating a main part of an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electrolyte plate 2 Fuel electrode 3 Oxidant electrode 4 Liquid fuel introduction path 5 Separator 6 Fuel permeation part 7 Fuel vaporization part 8 Oxidant gas supply groove 10 Electromotive part

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hideyuki Ogamu Toshiba-cho, Koyuki, Kawasaki-shi, Kanagawa Prefecture, Japan Inside Toshiba R & D Center (72) Inventor Hobson Lois Komukai, Koyuki-ku, Kawasaki-shi, Kanagawa 1F Toshiba-cho F-term in Toshiba R & D Center (reference) 4F073 AA02 AA07 CA42 5H026 AA08 CC03 CX05 EE18 EE19 HH06

Claims (5)

[Claims] 1. An ionic conductive membrane characterized in that its surface conductivity is set lower than its internal conductivity, and that it is used for electrolytes in fuel cells. 2. The ion conductive film according to claim 1, wherein said ion conductive film is a polymer comprising a fluororesin skeleton and sulfonic acid. 3. The method according to claim 2, wherein the polymer is selected from the group consisting of polybenzimidazole derivatives, amino-containing polymers, polyaniline derivatives, silanol-containing polymers, and hydroxyl-containing polymers. Ion conductive film. 4. A step of preparing a conductive film to be used as an electrolyte of a fuel cell, and irradiating the surface of the conductive film with an electron beam so that the surface has a conductivity within the conductive film. And a step of modifying the conductivity to be lower than the conductivity of the ion-conductive film. 5. A fuel comprising: an electrolyte membrane; a fuel electrode formed adjacent to the electrolyte membrane; and an oxidant electrode adjacent to the electrolyte membrane and facing the fuel electrode via the electrolyte membrane. A fuel cell according to claim 1, wherein the electrolyte membrane is an ion-conductive membrane whose surface conductivity is set to be lower than the internal conductivity.