JP2006185629A - Gas-liquid separation membrane for fuel cell, and fuel cell using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable to maintain power generation efficiency of a fuel cell and to carry out safe and stable operation for a long period by efficiently discharging carbon dioxide outside the system, which is generated at a fuel electrode of a direct methanol fuel cell (DMFC). <P>SOLUTION: By using a gas-liquid separation membrane 12 in which a permeation amount of carbon dioxide at 50°C is 10,000 cm<SP>3</SP>/m<SP>2</SP>24 hr atm or more and permeation amount of methanol is 25,000 g/m<SP>2</SP>24 hr or less, or by using the gas/liquid separation membrane composed of ultrahigh-molecular weight polyolefin and/or 4-methyl-1-pentene (co)polymer, carbon dioxide generated at the fuel electrode is discharged outside the system. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a gas-liquid separation membrane suitably used in the field of fuel cells. In particular, the present invention relates to a gas-liquid separation membrane suitably used for a fuel cell in which an aqueous solution of an organic liquid such as methanol is directly supplied as fuel, among polymer electrolyte fuel cells that can be downsized and operated at low temperatures. Furthermore, the present invention relates to a liquid fuel direct supply type fuel cell using such a gas-liquid separation membrane.

Fuel cells have been actively developed in recent years because of their features such as high power generation efficiency, high energy density, and low environmental load. Polyelectrolyte fuel cells (PEFC) are attracting attention for automotive or household cogeneration applications, but there are problems in the storage and supply of fuel hydrogen for portable electronic devices such as notebook computers and digital cameras. Therefore, among the polymer electrolyte fuel cells, a liquid fuel direct supply type fuel cell that supplies liquid fuel and directly generates hydrogen from the liquid fuel with a catalyst at the fuel electrode is considered promising as a portable electronic device application.
As the fuel for this type of fuel cell, aqueous solutions of methanol, ethanol, dimethyl ether, etc. have been studied. However, methanol is regarded as the primary fuel because of its high theoretical energy density, and is called a direct methanol fuel cell (DMFC). It is.
In the following, a DMFC using a methanol aqueous solution as a fuel will be described as a representative example, but the gas-liquid separation membrane for a fuel cell developed in the present invention can be suitably used for other liquid fuels such as ethanol and dimethyl ether. Needless to say.

The DMFC generates power by a chemical reaction between a methanol aqueous solution (CH ₃ OH + H ₂ O) and oxygen (O ₂ ). A methanol aqueous solution serving as a fuel is decomposed into hydrogen ions (H ⁺ ), electrons (e ⁻ ), and carbon dioxide (CO ₂ ) by an anode (fuel electrode) catalyst.
And power generation by is extracted from the external electrode, H ⁺ will reach the polymer electrolyte membrane and into the cathode (air electrode), O ₂ is the O dissociated by a catalyst of the air electrode ^{- -} this time occurs e react with H ₂ O is discharged from the air electrode.
A single cell, which is the smallest structural unit, has a structure in which a polymer electrolyte membrane represented by a product name “Nafion” manufactured by DuPont is sandwiched between both electrodes of a fuel electrode and an air electrode. Both electrodes have a porous structure so that the aqueous methanol solution and oxygen diffuse, and are in contact with the polymer electrolyte membrane through the catalyst layer.

In DMFC, the electrode reaction of CH ₃ OH + H ₂ O → 6H ⁺ + CO ₂ + 6e ⁻ proceeds by the Pt / Ru catalyst at the fuel electrode. _CH 3 OH adsorbed on Pt surface sequentially ^{H +} and e ^- CO next via aldehyde while releasing, OH _{H 2} O occurs dissociate adsorbed on Ru ^- the CO which group is adsorbed onto the Pt oxidized to CO _2.
The reaction is continued by newly supplying CH ₃ OH to the catalyst surface from which CO ₂ has been desorbed. However, as the CO ₂ concentration in the vicinity of the fuel electrode increases, the desorption rate decreases and the reaction for producing H ⁺ is slow. Therefore, removal of CO ₂ is important to maintain the power generation efficiency of DMFC.

In the stage where CO ₂ accumulation is not progressing, the generated CO ₂ is dissolved in the methanol aqueous solution of the fuel, but when the saturation solubility is reached, it is generated as bubbles in the fuel liquid. The saturation solubility depends on the methanol concentration, temperature, and pressure.
If air bubbles are generated in the fuel liquid, for example, it adheres to the fuel liquid concentration sensor, liquid level sensor, etc., and these measured values are deviated, and there is a problem that the operating conditions of the fuel cell deviate from the optimum values and the power generation efficiency decreases. .
In a small DMFC for a portable device, since the flow path of the fuel liquid is narrow, the supply of fuel is hindered by the generated bubbles, and the power generation may be stopped.
If the fuel cell is a closed system, the internal pressure may increase in the worst case, and the fuel cell itself may be destroyed. Even if it does not lead to destruction, the joint may peel off and the fuel may leak, and the leaked fuel may adversely affect the portable electronic device on which the fuel cell is mounted.

As described above, in order to operate the DMFC stably and safely, it is necessary to appropriately remove carbon dioxide generated from the fuel electrode. In order to meet such demands, it has been proposed to seal a portion where the anode is in contact with outside air with a gas-liquid separation membrane that blocks liquid and allows gas to permeate (see, for example, Patent Document 1).
JP 2003-317773 A

The conventionally proposed gas-liquid separation membrane is a porous membrane made of a synthetic resin material with excellent chemical resistance and water repellency, such as polyethylene terephthalate and polytetrafluoroethylene, and the surface is further subjected to water repellency treatment. Etc. However, these materials are not necessarily suitable as gas-liquid separation membranes for fuel cells. When gas cannot be exhausted sufficiently or when used for a long time, liquid leakage, gas accumulation, etc. There was a case where the phenomenon occurred. Therefore, it has been strongly desired to realize a gas-liquid separation membrane for a fuel cell that has both sufficient liquid barrier properties and sufficient gas permeability.

As a result of intensive studies, the present inventors have found that a film having specific physical properties solves the above problems and is suitable as a gas-liquid separation membrane for a fuel cell, and has led to the first embodiment of the present invention. It was. Further, the present inventors have found that a film made of a specific material system solves the above problems and is suitable as a gas-liquid separation membrane for a fuel cell, and has led to the second embodiment of the present invention. The present inventors have further found out a preferred embodiment of the gas-liquid separation membrane of the present invention and a preferred embodiment of a fuel cell using the gas-liquid separation membrane of the present invention, and these are referred to as preferred embodiments of the present invention. It is what we propose.

That is, the first aspect of the present invention is
[1] The permeation amount of carbon dioxide at 50 ° C. measured by a differential pressure method gas permeation test is 10,000 cm ³ / m ² · 24 hr · atm or more, and the methanol permeability at 50 ° C. measured by the cup method is 25, The present invention relates to a gas-liquid separation membrane for fuel cells, which is 000 g / m ² · 24 hr or less.

[2] below is one of the preferred embodiments of the present invention.
[2] The gas-liquid separation membrane for fuel cells according to [1], comprising an ultrahigh molecular weight polyolefin and / or a 4-methyl-1-pentene (co) polymer. Here, “consisting of” means that the gas-liquid separation membrane is entirely composed of ultrahigh molecular weight polyolefin and / or 4-methyl-1-pentene (co) polymer, and the gas-liquid separation. When a part of the film is composed of ultrahigh molecular weight polyolefin and / or 4-methyl-1-pentene (co) polymer, it is intended to include both.

The second aspect of the present invention is
[3] The present invention relates to a fuel cell gas-liquid separation membrane comprising an ultrahigh molecular weight polyolefin and / or a 4-methyl-1-pentene (co) polymer. Here, “consisting of” means that the gas-liquid separation membrane is entirely composed of ultrahigh molecular weight polyolefin and / or 4-methyl-1-pentene (co) polymer, and the gas-liquid separation. When a part of the film is composed of ultrahigh molecular weight polyolefin and / or 4-methyl-1-pentene (co) polymer, it is intended to include both.

The following [4] to [8] are each one of preferred embodiments of the present invention.
[4] The gas-liquid separation membrane for a fuel cell according to any one of [1] or [3], wherein the thickness is 1 μm to 100 μm.
[5] A fuel cell comprising the gas-liquid separation membrane according to any one of [1] to [4].
[6] The fuel cell according to the above [5], wherein in the fuel cell, a perforated support is laminated on the outside of the fuel cell outside the gas-liquid separation membrane for the fuel cell.
[7] The fuel cell according to [5] or [6] above, wherein methanol is used as a fuel.

[8] A portable electronic device incorporating or using the fuel cell according to any one of [5] to [7].

According to the present invention, in the field of fuel cell gas-liquid separation membrane, a fuel cell gas-liquid separation membrane having both sufficient liquid blocking properties and sufficient gas permeability is provided.
By applying the present invention, it is possible to provide a fuel cell and a portable electronic device having excellent performance.

Hereinafter, the present invention will be described in detail. First, a gas-liquid separation membrane for a fuel cell according to a first embodiment of the present invention will be described.
The gas-liquid separation membrane for a fuel cell according to the first aspect of the present invention has a carbon dioxide permeation amount of 10,000 cm at 50 ° C. measured in accordance with a differential pressure method gas permeation test defined as method A of JIS K7126. ³ / m ² · 24 hr · atm or more, and the methanol permeability at 50 ° C. measured by the cup method is 25,000 g / m ² · 24 hr or less.
The permeation amount of carbon dioxide is defined as the permeation amount of carbon dioxide per unit pressure, unit time, and unit area at 50 ° C. Specifically, the carbon dioxide permeation amount is determined by using a differential pressure method gas permeation tester (MTC-3 type, manufactured by Toyo Seiki Co., Ltd.), a test temperature of 50 ° C., a test humidity of 0% RH, and a measurement area of 38.46 cm ² Since the transmittance is high, it is measured by manual measurement.

When the carbon dioxide permeation amount is 10,000 cm ³ / m ² · 24 hr · atm or more, for example, when the gas-liquid separation membrane of the present invention is used as the sealing material on the fuel electrode side of the fuel cell, the carbon dioxide is generated at the fuel electrode. It is possible to effectively discharge gas such as carbon dioxide to the outside of the fuel container to prevent an increase in the internal pressure of the battery, maintain the cell performance when the fuel cell is operated for a long time, and liquid such as fuel This is preferable because it is possible to prevent leakage.

The carbon dioxide permeation amount of the gas-liquid separation membrane of the present invention is preferably 10,000 cm ³ / m ² · 24 hr · atm or more, more preferably 15,000 cm ³ / m ² · 24 hr · atm or more. From the viewpoint of achieving the main object of the present invention, the permeation amount of carbon dioxide of the gas-liquid separation membrane of the present invention is preferably as high as possible, and there is no particular upper limit, but contamination of fuel, oxidant, each electrode, etc. is avoided. From the viewpoint, it is preferably 1,000,000,000 cm ³ / m ² · 24 hr · atm or less, preferably 100,000,000 cm ³ / m ² · 24 hr · atm or less.

Methanol permeability is defined as the amount of methanol per unit time per unit area at 50 ° C. Specifically, the methanol permeability is measured by the cup method. More specifically, 20 ml of methanol is placed in a stainless steel cup having a diameter of 30 mm (permeation area = 0.00707 m ² ), and a gas-liquid separation membrane sample having a diameter of 40 mm or more is placed through a polytetrafluoroethylene packing, and the stainless steel is placed. Use a ring-shaped flange made of steel, and fix it with screws. The cup is turned upside down and in contact with the gas-liquid separation membrane sample, put in a high-temperature bath at 50 ° C., taken out at regular intervals, and weighed to calculate the amount of methanol permeated. Since the screw head protrudes from the flange, when it is turned upside down, a gap is formed between the gas-liquid separation membrane sample and the high-temperature bath by the height of the screw head, and methanol permeated through the gap is dissipated.

If the methanol permeability is 25,000 g / m ² · 24 hr or less, for example, leakage of fuel from the fuel cell can be effectively prevented, stable operation becomes possible, This is preferable because it can prevent adverse effects on the equipment and the like.
Methanol permeability of the gas-liquid separation membrane of the present invention is preferably 10,000g ^/ m 2 · 24hr or less, more preferably not more than 5,000g ^/ m 2 · 24hr. From the viewpoint of achieving the main object of the present invention, the lower the methanol permeability of the gas-liquid separation membrane of the present invention, the better.

  The gas-liquid separation membrane for a fuel cell according to the first aspect of the present invention is not particularly limited as long as the carbon dioxide permeation amount and the methanol permeation rate are within the above ranges. And / or consisting of 4-methyl-1-pentene (co) polymer.

Next, the gas-liquid separation membrane for fuel cells which is the 2nd form of this invention is demonstrated.
The gas-liquid separation membrane for a fuel cell according to the second embodiment of the present invention is made of ultrahigh molecular weight polyolefin and / or 4-methyl-1-pentene (co) polymer. Here, “consisting of” means that the gas-liquid separation membrane is entirely composed of ultrahigh molecular weight polyolefin and / or 4-methyl-1-pentene (co) polymer, and the gas-liquid separation. When a part of the film is composed of ultrahigh molecular weight polyolefin and / or 4-methyl-1-pentene (co) polymer, it is intended to include both.

It is preferably used in the gas-liquid separation membrane for fuel cells according to the first aspect of the present invention, and is used as one of two options in the gas-liquid separation membrane for fuel cells according to the second aspect of the present invention. The ultrahigh molecular weight polyolefin (A) is a homopolymer or copolymer of an α-olefin having 2 to 12 carbon atoms, and has an intrinsic viscosity [η] measured at 135 ° C. in a decalin solvent of 4.0 d1 / That which is more than g. The intrinsic viscosity [η] of the ultrahigh molecular weight polyolefin is preferably 5.0 d1 / g or more, more preferably 6.0 d1 / g or more.

An intrinsic viscosity [η] at 135 ° C. in a decalin solvent of 4.0 d1 / g or more is preferable because it has sufficient mechanical strength such as tensile strength, impact strength, and wear resistance. The upper limit of the intrinsic viscosity [η] is not particularly limited, but if it is 15.0 d1 / g or less, it is in a range where thin film molding can be performed by inflation molding or the like, and it is easy to mold into a gas-liquid separation membrane.
The intrinsic viscosity [η] at 135 ° C. in a decalin solvent is specifically measured according to ASTM D4020.

When the ultrahigh molecular weight polyolefin is used for the gas-liquid separation membrane for a fuel cell of the present invention, the gas-liquid separation membrane can achieve both sufficient gas permeability and strength, which is preferable.
The ultrahigh molecular weight polyolefin that can be used in the present invention is a homopolymer or copolymer of an α-olefin having 2 to 12 carbon atoms. Specific examples of such α-olefins include ethylene, propylene, 1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 4-methyl-1-pentene, and 3-methyl-1. -Pentene and the like. Among these, an ethylene homopolymer or a copolymer of ethylene and other α-olefins having ethylene as a main component is particularly preferable. The ultra-high molecular weight polyolefin that can be used in the present invention may be one obtained by copolymerizing monomers other than the various α-olefins as long as the object of the present invention is not impaired. The ultra-high molecular weight polyolefin that can be used in the present invention can be appropriately produced by a conventionally known method, and the production method is not particularly limited. For example, the ultra high molecular weight polyolefin can be produced by the method described in JP-A-06-234811. can do.

  In the gas-liquid separation membrane for a fuel cell of the present invention, one type of ultrahigh molecular weight polyolefin may be used alone, or two or more types may be used in combination. It can also be used in the form of a blend in combination with a polyolefin obtained from the same or different monomer having a lower molecular weight. Furthermore, in using the ultrahigh molecular weight polyolefin for the gas-liquid separation membrane for fuel cells of the present invention, a plasticizer, an antioxidant, an ultraviolet absorber, a stabilizer, a filler, and a pigment within the range not impairing the object of the present invention. One type or two or more types of additives selected from dyes, antistatic agents, antibacterial agents, antifungal agents, flame retardants, dispersants and the like can be added.

  The method for producing the gas-liquid separation membrane for a fuel cell of the present invention using an ultrahigh molecular weight polyolefin is not particularly limited, and a conventionally known film production method can be appropriately employed within a range not impairing the object of the present invention. it can. For example, methods described in Japanese Patent Publication No. 4-16330, Japanese Patent Publication No. 6-55433, or Japanese Patent Application Laid-Open No. 9-183156 can be appropriately employed.

  It is preferably used in the gas-liquid separation membrane for fuel cells according to the first aspect of the present invention, and is used as one of two options in the gas-liquid separation membrane for fuel cells according to the second aspect of the present invention. As the 4-methyl-1-pentene (co) polymer used, a homopolymer of 4-methyl-1-pentene or a copolymer of 4-methyl-1-pentene and other α-olefin is used. It is done. When a copolymer is used, other α-olefins that are copolymer components include ethylene, propylene, 1-butene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1- Examples thereof include α-olefins having 2 to 20 carbon atoms such as hexadecene, 1-octadecene, 1-eicosene and the like. Preferred copolymerization components are 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene or 1-eicocene. As the copolymer, a ternary or higher copolymer obtained by copolymerizing two or more α-olefins may be used. In particular, it is preferable to use a copolymer mainly composed of 4-methyl-1-pentene containing 4-methyl-1-pentene in an amount of 80% by weight or more. When the content of the copolymer component (other α-olefin) exceeds 20% by weight, the melting point of the 4-methyl-1-pentene (co) polymer is lowered and the heat resistance tends to be lowered. It is desirable to appropriately adjust the content of the copolymer component in relation to the purpose.

  Since 4-methyl-1-pentene (co) polymer has a relatively high gas permeability, carbon dioxide required in the present invention is not required to be porous or extremely thin. Permeability can be ensured. For this reason, it is possible to provide sufficient carbon dioxide permeability while avoiding liquid leakage due to porosity and reduction in mechanical strength due to extremely thin film thickness. It is suitable as a material for the film.

  The 4-methyl-1-pentene (co) polymer that can be used for the gas-liquid separation membrane of the present invention is a melt flow rate (MFR) measured under the conditions of a load of 5.0 kg and a temperature of 260 ° C. according to ASTM D1238. Is preferably in the range of 5 to 50 g / 10 min. In particular, it is preferably in the range of 7 to 30 g / 10 minutes. When MFR is in the above range, film forming is easy to carry out, which is preferable.

In the gas-liquid separation membrane for a fuel cell of the present invention, 4-methyl-1-pentene (co) polymer may be used alone or in combination of two or more. . It can also be used in the form of a blend or the like in combination with a polyolefin other than 4-methyl-1-pentene (co) polymer. Furthermore, when 4-methyl-1-pentene (co) polymer is used for the gas-liquid separation membrane for fuel cells of the present invention, other resins and / or plasticizers are used within the range not impairing the object of the present invention. , One or more additives selected from antioxidants, ultraviolet absorbers, stabilizers, fillers, pigments, dyes, antistatic agents, antibacterial agents, antifungal agents, flame retardants, dispersants, etc. Can be added.

The method for producing the gas-liquid separation membrane for a fuel cell of the present invention using 4-methyl-1-pentene (co) polymer is not particularly limited, and is a conventionally known film as long as the object of the present invention is not impaired. Manufacturing methods can be employed as appropriate. For example, the method described in JP-A-10-81710 or JP-A-2001-62896 can be appropriately employed.

The gas-liquid separation membrane for a fuel cell of the present invention preferably has a thickness of 1 μm to 100 μm. Further preferable thickness is 3 μm to 80 μm, particularly preferably 5 μm to 50 μm. When the film thickness is in the above range, it is preferable from the viewpoint of reducing the thickness of the fuel cell and balancing the gas separation performance and the breakage resistance.

Next, a fuel cell which is a preferred embodiment of the present invention will be described.
A fuel cell which is a preferred embodiment of the present invention (hereinafter referred to as “preferred fuel cell”) has a carbon dioxide permeation amount at 50 ° C. measured by a differential pressure method gas permeation test of 10,000 cm ³ / m ² · 24 hr ·. The fuel cell gas-liquid separation membrane is atm or more and has a methanol permeability of 25,000 g / m ² · 24 hr or less at 50 ° C. measured by the cup method.

  There are no particular restrictions on the fuel used in the preferred fuel cell, and an aqueous solution of methanol, ethanol, dimethyl ether, etc., which are liquid fuels that can be used in ordinary fuel cells, can be used. However, cost, availability, reaction From the viewpoint of simplicity, energy density, etc., it is desirable to use methanol as the fuel. In particular, it is desirable to use a direct methanol type (DMFC) because peripheral auxiliary equipment such as a reformer is unnecessary and suitable for miniaturization.

Hereinafter, a preferred fuel cell will be described by taking DMFC as an example.
FIG. 1 illustrates a cross-sectional view of a DMFC which is an example of a preferred fuel cell. The fuel cell 1 may constitute a single cell with the housing 2 and may constitute a fuel cell stack in which the single cells are combined as necessary. A part of the housing 2 may be called a separator or a bipolar plate as a constituent member. The single cell has a structure in which the polymer electrolyte membrane 3 is sandwiched between an anode (fuel electrode 6) and a cathode (air electrode 7). This is a type that obtains electric power by supplying a methanol aqueous solution as a fuel directly to the anode (fuel electrode 6) and supplying air to the cathode (air electrode 7). A catalyst layer 4 containing a (Pt / Ru) catalyst is sandwiched between the fuel electrode 6 and the polymer electrolyte membrane 3, and a catalyst ( A catalyst layer 5 containing Pt) is sandwiched. Both the fuel electrode 6 and the air electrode 7 have a porous structure because methanol and water, oxygen or air must reach the catalyst layer. In many cases, an electrode including a catalyst layer is called an electrode, and a polymer electrolyte membrane, (both catalyst layers), and a laminate of a fuel electrode 6 and an air electrode 7 are used as a membrane electrode assembly (MEB). It is called.

The fuel electrode 6 and the air electrode 7 of the fuel cell 1 are electrically connected to the anode side external connection terminal 8 and the cathode side external connection terminal 9, respectively.
A fuel chamber 10 for storing fuel is provided on the fuel electrode 1 side of the fuel cell 1, and an air chamber 11 for storing air is provided on the air electrode 7 side of the fuel cell 1. The fuel chamber may be either a closed system or an open system, but in the open system, it is necessary to provide a mechanism for preventing fuel outflow when mounted on a portable device. The fuel may be supplied in batches or may be circulated and distributed using a pump or the like. Alternatively, a high-concentration methanol and water tank may be provided separately and mixed in advance so as to obtain an appropriate concentration before being supplied to the fuel chamber. Similarly, the air chamber may be a closed system or an open system, but normally air from outside is naturally circulated as an open system or forcedly circulated using a fan or the like.

A gas-liquid separation membrane 12 that discharges carbon dioxide (CO ₂ ) to the outside is disposed in a part of the fuel chamber 10. The location of the gas-liquid separation membrane provided in the fuel chamber 10 is not limited to the location of 12 in this example, and may be appropriately provided as long as the location can connect the fuel chamber 10 and the outside. it can. Here, in order to prevent deformation of the gas-liquid separation membrane for a fuel cell due to an increase in the internal pressure of the fuel cell, it is preferable to laminate a porous support outside the gas-liquid separation membrane.

In the fuel cell 1, an aqueous methanol solution is used as the fuel that fills / fuels or circulates / circulates in the fuel chamber 10. Air is supplied into the air chamber 11 via a filter (not shown).
The fuel is decomposed into hydrogen ions, electrons, and carbon dioxide by a catalytic reaction in the catalyst layer 6. The hydrogen ions pass through the polymer electrolyte membrane 3 and move to the air electrode 5, but the electrons flow between the external terminals 8 and 9 without passing through the polymer electrolyte membrane 3, thereby generating a current. Further, when the hydrogen ions and the like that have passed through the polymer electrolyte membrane 3 are catalytically burned with oxygen in the catalyst layer 5 on the air electrode 7 side, water (2H ₂ O) is generated.
That is, the cell reaction described above is “CH ₃ OH + 3/2 · O ₂ → CO ₂ + 2H ₂ O”, and carbon dioxide is discharged to the fuel chamber 10 side and water (water vapor) is discharged to the air chamber 11 side. The
Since the gas-liquid separation membrane of the present invention is excellent in carbon dioxide permeability, it is possible to reduce an increase in the internal pressure of the fuel cell due to the generation of carbon dioxide and to reduce or prevent fuel leakage.

The DMFC shown in FIG. 1 has been described above as an example of a preferred fuel cell, but the gas-liquid separation membrane of the present invention can be suitably used for fuel cells of other systems and designs.
Although the fuel cell which is a preferred embodiment of the present invention has a small and relatively simple structure, it is possible to effectively prevent a decrease in cell performance, fuel leakage, etc. when used for a long time. For this reason, it is suitably used for portable electronic devices such as notebook computers, mobile phones, portable information terminals, digital cameras, and portable music terminals, and various electronic devices such as personal computers, AV devices, home appliances, and in-vehicle electronic devices. can do.

Hereinafter, the present invention will be specifically described by way of examples. The present invention is not limited to the following examples.
(Evaluation of gas-liquid separation membrane for fuel cells)
In the examples and comparative examples, the gas-liquid separation membrane for fuel cells was evaluated using the following films.
[Example 1]
Evaluation of films of brand names X-22 (melting point 222 ° C, MFR20), X-44 (melting point 228 ° C, MFR26), X-88 (melting point 236 ° C, MFR10) of OPULENT TPX film (Mitsui Chemicals) was carried out. . Table 1 shows the results.

[Example 2]
In the inflation film production apparatus disclosed in JP-A-10-306168, an ultrahigh molecular weight polyethylene inflation film was produced using an apparatus having the following specifications.
Specification of the apparatus The first screw outer diameter of the extruder 50 mmφ, the effective screw length 1100 mm, the flight pitch 30 mm constant, the screw compression ratio 1.8, the screw die effective length 1490 mm (L / L D = 28), die outlet outer die inner diameter 53 mmφ, die outlet mandrel outer diameter 45 mmφ, S 1 / S 2 = 1.17, S 2 / S 3 = 3.14, screw die second screw outer diameter 70 mmφ, second screw effective length 238 mm, flight pitch 25 mm constant, second screw compression ratio 1.0, stabilizer rod outer diameter 37 mmφ, stabilizer rod length 600 mm, 8 mmφ extending into the second screw, mandrel and stabilizer rod shaft It comprises a gas flow path, a stabilizer, a pinch roll, and a product winder.

<Preparation of ultra high molecular weight polyethylene film>
Ultra high molecular weight polyethylene [η]: 5.7 dl / g, bulk density: 0.45 g / cm ³ powder resin, extruder, joint part (J), die base part (D1) and die tip part (D2) Were set to 197 ° C., 191 ° C., 190 ° C. and 175 ° C., the first screw rotation speed was set to 21 rpm, the second screw rotation speed was set to 1.8 rpm, and a pinch roll at a speed of 8.7 m / min. While pulling, compressed air is blown from the 8 mmφ gas flow path extending inside the second screw, the mandrel and the stabilizer rod shaft, and the parison is expanded to 8.9 times the inner die inner diameter of 53 mmφ and folded. A high molecular weight polyethylene inflation film having a width of 710 mm and a thickness of 10 μm was prepared. This film was designated as experiment number 5.
Further, this film was stretched by a batch type biaxial stretching machine manufactured by Iwamoto Seisakusho at a stretching temperature of 146 ° C., a stretching ratio of 1.75 times in the TD direction, and a stretching speed of 1 m / min. Conducted for a minute. The film after stretching was designated as experiment number 6. Table 2 shows the results.

[Comparative Example 1]
<Preparation of ultrahigh molecular weight polyethylene porous film>
A high-molecular-weight polyethylene blown film having a folding width of 710 mm and a thickness of 15 μm was produced in the same manner as in Example 2 except that the production apparatus of Example 2 was used and the sheet was drawn with a pinch roll at a speed of 6.3 m / min. Created. Using this film, a porous treatment was performed as follows. The inflation film was sandwiched between a pair of stainless steel metal frames, and fixed to the upper and lower metal frames with screws, thereby fixing the four sides of the film. In this state, it was immersed for 2 minutes in paraffin oil (Lyto manufactured by Witco) heated to 120.5 ° C. Subsequently, the film fixed to the metal frame taken out from the paraffin oil was put into a poor solvent HFE7200 (manufactured by 3M) in that state, and immersed at 60 ° C. for 5 minutes. This was taken out and air-dried at room temperature (23 ° C.), and then the film was removed from the metal frame to obtain a sample for stretching. Further, this film was stretched by a batch type biaxial stretching machine manufactured by Iwamoto Seisakusho at a stretching temperature of 120 ° C., a stretching ratio of 1.85 times in the TD direction, and a stretching speed of 1 m / min. Conducted for a minute. The obtained film had a film thickness of 25 μ, a porosity of 75%, an air permeability of 30 sec / 100 ml (JIS P8117), and an average pore diameter of 0.11 μm (ASTM F316). The ultra-high molecular weight polyethylene porous film after stretching was designated as experiment number 7. The results are shown in Table 3.

Since the carbon dioxide permeation amounts of the films obtained in the examples are sufficiently large, for example, an area of about 0.01 cm ^{2 to} 0.2 m ² (the area is appropriately selected depending on the output and cell size). A fuel cell provided with a membrane is sufficient to release carbon dioxide generated during operation of the fuel cell of each output set by the device used. Therefore, even when the fuel cell is continuously operated for a long time, it is possible to effectively suppress an abnormal increase in internal pressure due to the accumulation of carbon dioxide, a decrease in battery performance associated therewith, fuel leakage, and the like. Further, the methanol permeability of the films obtained in the examples is sufficiently low, and even when the internal pressure of the fuel cell rises to some extent, leakage of fuel and the like can be effectively suppressed.

On the other hand, the methanol permeability of the porous film obtained in the comparative example is too high for the purpose of the present invention. For this reason, when the porous film obtained by the comparative example is used for a fuel cell, fuel etc. leak. Such a fuel cell is difficult to operate continuously for a long time, and may damage peripheral precision equipment and precision parts.

It is sectional drawing which illustrates the structure of the fuel cell which has a gas-liquid separation membrane of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell single cell 2 Case 3 Polymer electrolyte membrane 4 Anode (fuel electrode) side Pt / Ru catalyst layer 5 Cathode (air electrode) side Pt catalyst layer 6 Anode (fuel electrode)
7 Cathode (Air electrode)
8 Anode (fuel electrode) side external terminal 9 Cathode (air electrode) side external terminal 10 Fuel chamber 11 Air chamber 12 Gas-liquid separation membrane 13 Housing opening

Claims (8)

The permeation amount of carbon dioxide at 50 ° C. measured by a differential pressure method gas permeation test is 10,000 cm ³ / m ² · 24 hr · atm or more, and the methanol permeability at 50 ° C. measured by the cup method is 25,000 g / m. ^A gas-liquid separation membrane for fuel cells, which is ² · 24 hr or less. The gas-liquid separation membrane for fuel cells according to claim 1, comprising an ultrahigh molecular weight polyolefin and / or a 4-methyl-1-pentene (co) polymer. A gas-liquid separation membrane for a fuel cell, comprising an ultrahigh molecular weight polyolefin and / or a 4-methyl-1-pentene (co) polymer.
The gas-liquid separation membrane for a fuel cell according to any one of claims 1 to 3, wherein the thickness is 1 µm to 100 µm. A fuel cell comprising the gas-liquid separation membrane according to any one of claims 1 to 4. 6. The fuel cell according to claim 5, wherein a porous support is laminated outside the gas-liquid separation membrane. The fuel cell according to claim 5 or 6, wherein methanol is used as a fuel. A portable electronic device using the fuel cell according to any one of claims 5 to 7.

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