JP4950539B2 - Diaphragm for direct liquid fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a diaphragm for a direct liquid type fuel cell endowed with high proton conductivity and high alcohol non-permeability, and with little occurrence of cracks due to thermal press or the like at formation of an electrode. <P>SOLUTION: The diaphragm for direct liquid type fuel cell is made by filling crosslinking ion exchange resin with a cation exchange group covalent bonded in holes of a porous film, with a thickness of the porous film of 40 to 120 &mu;m, a void ratio of 45% or more, and a ratio of tensile breaking strength (PMD/PTD) of a tensile breaking strength PMD in a film-flowing direction of the porous film to a tensile breaking strength PTD in a direction crossing the film-flowing direction of the porous film of 10 or less. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to a diaphragm for a direct liquid fuel cell in which pores of a porous film are filled with a cation exchange resin. The diaphragm has low permeability of fuel liquid such as methanol and high proton conductivity.

  Ion exchange membranes are widely used as battery membranes such as polymer electrolyte fuel cells, redox flow cells, zinc-bromine cells, and dialysis membranes. A polymer electrolyte fuel cell that uses an ion exchange membrane as an electrolyte membrane is a clean and highly efficient power generation system that continuously supplies fuel and oxidant to the fuel cell and extracts the chemical energy when they react as power. one of. In recent years, polymer electrolyte fuel cells can be expected to operate at low temperatures and can be miniaturized, and thus are becoming increasingly important for automobiles, households, and portable applications.

  2. Description of the Related Art A polymer electrolyte fuel cell generally has a structure in which an electrode carrying a catalyst is bonded to both surfaces of a solid polymer diaphragm that acts as an electrolyte. When power is taken out from the polymer electrolyte fuel cell, a fuel composed of a fuel liquid such as hydrogen gas or methanol is supplied to the chamber (fuel chamber) on the side where one electrode exists, and the other gas diffusion electrode exists. An oxygen-containing gas such as oxygen or air, which is an oxidant, is supplied to each chamber (oxidant chamber). In this state, by connecting an external load circuit between the two diffusion electrodes, the fuel cell operates and power is supplied to the external load circuit.

  Among solid polymer fuel cells, a direct liquid fuel cell using methanol or the like as a direct fuel is evaluated because it is easy to handle because the fuel is liquid, and the fuel is inexpensive. It is expected to be used as a power source with a small output scale.

  The basic structure of a direct liquid fuel cell is shown in FIG. In the figure, reference numerals 1a and 1b denote battery partition walls, which are provided on both sides of the solid polymer electrolyte membrane 6 with a solid polymer electrolyte membrane 6 acting as a diaphragm interposed therebetween. 2 is a fuel flow hole formed in the inner wall of one battery partition wall 1a, and 3 is an oxidant gas flow hole formed in the inner wall of the other battery partition wall 1b. 4 is a fuel chamber side diffusion electrode, and 5 is an oxidant chamber side gas diffusion electrode.

  In this direct liquid fuel cell, when a fuel liquid such as alcohol is supplied to the fuel chamber 7, protons (hydrogen ions) and electrons are generated in the fuel chamber side diffusion electrode 4. The generated protons conduct in the solid polymer electrolyte membrane 6 and move to the other oxidant chamber 8, where they react with oxygen in the air or oxygen gas to generate water. On the other hand, electrons generated in the fuel chamber side diffusion electrode 4 are sent to the oxidant chamber side gas diffusion electrode 5 through an external load circuit (not shown), and at this time, electric energy is given to the external load circuit.

  In the direct liquid fuel cell having the above structure, a cation exchange membrane is usually used for the solid polymer electrolyte membrane 6. The cation exchange membrane is required to have low electric resistance, high physical strength, and low permeability of the fuel liquid used. When the permeability of the fuel liquid to the cation exchange membrane is high, the fuel liquid supplied to the fuel chamber diffuses and moves toward the oxidation chamber, resulting in a decrease in battery output.

  Conventionally, as a cation exchange membrane used as a fuel cell membrane, for example, a polymerizable monomer having a functional group capable of introducing a cation exchange group into a pore portion of a porous film made of polyolefin or fluorine resin. By a method in which a polymerizable composition comprising a polymer and a crosslinkable polymerizable monomer is charged and polymerized, and then a cation exchange group is introduced into a functional group capable of introducing the cation exchange group of a resin obtained by polymerization. The obtained diaphragm is known (for example, patent documents 1 to 3). According to this method, the diaphragm for a fuel cell is manufactured at a relatively low cost, and the obtained diaphragm has a low electrical resistance, a low hydrogen gas permeability, and a small swelling and deformation with respect to the fuel liquid.

As a method for producing a porous film filled with a polymerizable composition, for example, a polyolefin or fluorine resin is dispersed in a filler such as silica or a water-soluble salt crystal to form a film. After stretching, there is a stretching / opening method in which a porous film is obtained by dissolving and removing a filler in a film in a solvent soluble in the filler as necessary. As another method for producing a porous film, a mixture of a polyolefin-based or fluororesin and paraffin is formed in a molten state, and this is cooled to phase-separate fine paraffin particles in the formed film. Then, there is a phase separation method in which a porous film is obtained by solvent extraction of phase-separated paraffin.
JP 2001-135328 A Japanese Patent Laid-Open No. 11-310649 Japanese Patent Laying-Open No. 2005-5171

  The proton conductivity of the cation exchange membrane used for the diaphragm for a direct liquid fuel cell varies depending on conditions such as the film thickness and porosity of the porous film. When the film thickness is thin and the porosity is high, it is considered that protons easily move in the diaphragm and the proton conductivity of the diaphragm increases. However, it is considered that fuel liquids such as methanol are likely to pass through the diaphragm under the above-described high conductivity conditions. Therefore, it is very difficult to achieve both high conductivity and low fuel liquid permeability.

  In order to solve the above problems, the present inventors have made various studies. As a result, it was recognized that the thickness and porosity of the porous film constituting the fuel cell membrane, proton conductivity, and fuel liquid permeability were all in a first-order correlation. However, focusing on the porosity of the porous film, it was discovered that the rate of increase in proton conductivity is several times greater than the rate of increase in the permeability of the fuel liquid with respect to the increase in porosity. Accordingly, it has been found that when a fuel cell is constructed using a high porosity and thick membrane for a fuel cell, proton conductivity can be increased while keeping the permeability of the fuel liquid relatively low.

  On the other hand, as a method of producing a membrane-electrode assembly using an ion exchange membrane, both sides of the ion exchange membrane are obtained by drying a catalyst electrode layer formed on a support such as polytetrafluoroethylene after drying the ion exchange membrane. There is a method in which a catalyst electrode is formed on both surfaces of an ion exchange membrane by thermal transfer.

  However, the present inventors have found that an ion exchange membrane produced using a porous film having a large thickness and a high porosity is likely to crack in the ion exchange membrane during drying or formation of a catalyst electrode. It was. When a diaphragm with cracks is used directly in a liquid fuel cell, the impermeability of methanol begins to deteriorate even at a minute stage where cracks are difficult to visually confirm. The liquid leaks from the fuel chamber to the oxidizer chamber and power generation becomes impossible.

  As a result of further investigations to solve the above problems, the present inventors have found that a diaphragm formed of a thick film and a porous film having a high porosity has a low tensile fracture strength along the in-plane direction of the porous film. It was found that uniformity is greatly involved in the generation of cracks.

  The present invention has been completed on the basis of the above findings, and the object of the present invention is from a cation exchange membrane having a low permeability of fuel liquid such as alcohol, particularly methanol, and a high proton conductivity of the diaphragm. An object of the present invention is to provide a diaphragm for a fuel cell.

  The present invention for solving the above problems is described below.

  [1] A membrane for a fuel cell in which pores of a porous film are filled with a crosslinked ion exchange resin having a covalently bonded cation exchange group, the porous film having a thickness of 40 to 120 μm and a porosity of 45% or more, the tensile breaking strength ratio (PMD / PTD) of the tensile breaking strength PMD in the film flow direction of the porous film and the breaking strength PTD in the direction perpendicular to the film flow direction of the porous film is 10 or less directly A diaphragm for liquid fuel cells.

  [2] The diaphragm for a direct liquid fuel cell according to [1], wherein the average pore diameter of the pores is 0.01 to 2 μm.

  The diaphragm of the present invention is a diaphragm for a direct liquid fuel cell having a predetermined film thickness, a porosity, and a tensile fracture strength ratio and having both high fuel liquid impermeability and high proton conductivity.

  Since the direct liquid fuel cell using the diaphragm of the present invention suppresses the crossover of fuel liquid such as methanol, a high battery output can be obtained.

  The porous film used in manufacturing the diaphragm for a direct liquid fuel cell according to the present invention is a resin film having pores such as pores inside thereof, and at least the pores through the pores The front and back of the porous film communicate with each other. As such a film, a known resinous porous film can be used without limitation.

  The film thickness of the porous film is 40 μm or more and 120 μm or less, preferably 45 to 110 μm, and more preferably 50 to 105 μm. When the film thickness of the porous film is less than 40 μm, the strength is insufficient. On the other hand, when the film thickness exceeds 120 μm, proton conductivity tends to decrease.

  From the viewpoint of imparting high proton conductivity, the porosity of the porous film is 45% or more, preferably 47% or more. Although there is no restriction | limiting in particular in the upper limit of a porosity, In order to maintain the intensity | strength of a diaphragm, 95% or less of a porosity is preferable and 75% or less is more preferable.

  The average pore diameter of the pores of the porous film is preferably from 0.01 to 2 μm, more preferably from 0.015 to 0.4 μm. When the pore is less than 0.01 μm, the filling amount of the cation exchange resin is lowered. When the pore diameter exceeds 2 μm, the alcohol permeability increases. In addition, in this invention, the average hole diameter of the hole of the said porous film says the value measured by the bubble point method according to JISK3832.

  The air permeability (JIS P-8117) is preferably 1500 seconds or less, and more preferably 1000 seconds or less. By using a porous film having an air permeability in this range, the proton conductivity of the obtained fuel cell membrane is increased, and high physical strength can be imparted to the membrane.

  The surface smoothness is preferably 10 μm or less, more preferably 5 μm or less, expressed as a roughness index. By using a smooth porous film in this range, high impermeability to alcohol can be imparted to the resulting fuel cell membrane.

  Tensile breaking strength ratio between the tensile breaking strength (PMD) in the film flow direction (MD direction, long direction) of the porous film and the tensile breaking strength (PTD) in the direction orthogonal to the MD direction (TD direction, width direction) (PMD / PTD) is 10 or less. This point will be described with reference to FIG. That is, the tensile breaking strength of the porous film in the MD direction from the point A of the porous film 200 along the surface of the porous film is defined as PMD. Further, the tensile rupture strength of the porous film in the TD direction along the surface of the porous film perpendicular to the MD direction from A is defined as PTD.

  This tensile fracture strength ratio is preferably 7 or less from the viewpoint of increasing methanol permeability due to the occurrence of cracks, and further preventing leakage of fuel liquid from the fuel chamber to the oxidant chamber. Most preferably: Here, when the film is stretched in the production stage of the porous film, the tensile fracture strength ratio between the MD direction and the TD direction increases depending on the degree of stretching.

  That is, when manufactured by a manufacturing method typified by a porous film stretching opening method, the porous film is often stretched in the MD direction, and in this case, the tensile breaking strength in the MD direction is the maximum. become.

  If the film is not stretched in the porous film production stage, that is, if it is produced by a production method represented by a phase separation method, the tensile strength at break is substantially uniform in any direction. .

  The tensile fracture strength ratio between the MD direction and the TD direction is 10 or less by appropriately adjusting the stretch ratio during the production of the porous film, the porosity of the porous film, the average molecular weight of the polymer constituting the porous film, and the like. It can be. Many porous films having a tensile rupture strength ratio of 10 or less in the MD direction and the TD direction have a low stretch ratio during film production. Since this film has little molecular orientation bias, when a fuel cell membrane is manufactured using a porous film having a thick film and a high porosity, there is no generation of cracks during electrode formation.

  From the viewpoint of maintaining the strength of the porous film, at least the tensile breaking strength in the MD direction is preferably 1 MPa or more, and more preferably 4 MPa or more.

  The material of the porous film is not particularly limited as long as it has the above-described film thickness, porosity, and tensile fracture strength ratio, and examples thereof include thermoplastic resins and thermosetting resins. The material of the porous film is preferably a thermoplastic resin composition. The use of a thermoplastic resin facilitates the production of a porous film. And there exists an advantage with high adhesive strength with the ion exchange resin mentioned later.

  Examples of the thermoplastic resin composition include ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 3-methyl-1-butene, 4-methyl-1-pentene, and 5-methyl-1-heptene. Polyolefin resins obtained by homopolymerizing α-olefins or copolymerizing them; polyvinyl chlorides such as polyvinyl chloride, vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinylidene chloride copolymers, vinyl chloride-olefin copolymers Resin; polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-ethylene copolymer Fluorine diameter resin such as nylon 6, nylon 66, etc. Polyamide resins, such as polyimide resin.

  Among these resins, polyolefin resins are preferable because they are particularly excellent in mechanical strength, chemical stability, and chemical resistance and have high affinity with hydrocarbon ion exchange resins. Among polyolefin resins, polyethylene resin or polypropylene resin is particularly preferable, and polyethylene resin is most preferable.

  These porous films can be produced, for example, by the method described in JP-A-2002-338721. Alternatively, commercially available products (for example, Asahi Kasei “Hypore”, Tonen Tapils “Setera”, Mitsui Chemicals “Hilet”, etc.) having the above-mentioned tensile strength at break ratio can also be obtained.

  The diaphragm of the present invention is a diaphragm in which the pores of the porous film described above are filled with an ion exchange resin having a cation exchange group.

  In the method of filling the pores of the porous film with the ion exchange resin, the polymerizable composition containing a predetermined polymerizable monomer is filled into the pores formed in the porous film, and then the filled polymerization is performed. A method of polymerizing and curing the functional composition is preferred. When the polymerizable composition containing a predetermined polymerizable monomer already has a cation exchange group, a membrane in which the pores of the porous film are filled with an ion exchange resin having a cation exchange group can be obtained by the above method. In the case where the polymerizable composition containing the predetermined polymerizable monomer has not yet been introduced with a cation exchange group, by introducing a cation exchange group into a resin obtained by polymerization and curing, the pores of the porous film are introduced. A diaphragm filled with an ion exchange resin having a cation exchange group is obtained. In the latter case, the polymerizable monomer has a functional group that can later introduce a cation exchange group. This functional group is an aromatic group generally represented by a benzene ring.

  Hereinafter, it demonstrates in detail about an example of the manufacturing method of the diaphragm of this invention.

(Polymerizable composition)
The polymerizable composition which is a raw material for producing the diaphragm includes a) a polymerizable monomer having a functional group or a cation exchange group into which a cation exchange group can be introduced, b) a crosslinkable polymerizable monomer, c ) A polymerization initiator is an essential component.

a) Polymerizable monomer As the polymerizable monomer, a conventionally known monomer can be used without limitation. Examples of the monomer having a functional group into which a cation exchange group can be introduced include styrene, vinyl toluene, vinyl xylene, α-methyl styrene, vinyl naphthalene, acenaphthylene, and α-halogenated styrenes. . Monomers having a cation exchange group include sulfonic acid monomers such as α-halogenated vinyl sulfonic acid, styrene sulfonic acid, and vinyl sulfonic acid; carboxylic acid monomers such as methacrylic acid, acrylic acid, and maleic anhydride. Monomer; Phosphonic acid monomers such as vinyl phosphoric acid, salts thereof, esters and the like.

b) Crosslinkable polymerizable monomer As the crosslinkable polymerizable monomer to be blended in the polymerizable composition, a monomer used in the production of a conventionally known ion exchange membrane can be used without limitation. When the crosslinkable polymerizable monomer is blended in the polymerizable composition, the resulting cation exchange resin becomes a crosslinkable type. Cross-linked ion exchange resins are essentially insoluble in solvents. Therefore, there is no solubility in water or alcohol contained in the fuel liquid, swelling is minimized, and a large amount of cation exchange groups can be introduced into the resin. As a result, the proton conductivity of the diaphragm can be made extremely high.

  Specific examples of the crosslinkable polymerizable monomer include m-, p-, o-divinylbenzene, divinylsulfone, butadiene, chloroprene, isoprene, trivinylbenzenes, divinylnaphthalene, diallylamine, triallylamine, divinyl. And divinyl compounds such as pyridines.

  The content of the crosslinkable polymerizable monomer in the polymerizable composition is not particularly limited, but is preferably 1 to 40% by mass of the total amount of polymerizable monomers contained in the polymerizable composition. 2 to 30% by mass is more preferable. By controlling the content of the crosslinkable polymerizable monomer within this range, the resulting cation exchange resin has high fuel liquid impermeability, swelling and the like are minimized, and proton conductivity is particularly high. A high one is obtained.

c) Polymerization initiator The polymerizable composition contains a polymerization initiator. The polymerization initiator is not particularly limited as long as it is a compound that initiates polymerization of the polymerizable monomer and the crosslinkable polymerizable monomer.

  As the polymerization initiator, an organic peroxide is preferable. For example, octanoyl peroxide, lauroyl peroxide, t-butylperoxy-2-ethylhexanoate, benzoyl peroxide, t-butylperoxyisobutyrate, t-butylperoxylaurate, t-hexylperoxy Examples thereof include radical polymerization initiators such as benzoate and di-t-butyl peroxide.

  The content of the polymerization initiator is appropriately selected according to a conventional method depending on the composition of the polymerizable monomer used and the kind of the polymerization initiator. Usually, 0.1 to 20 parts by mass is blended with respect to 100 parts by mass of the total amount of the polymerizable monomer components (including the content of other polymerizable monomers described later). It is preferably 0.5 to 10 parts by mass.

  Furthermore, in addition to each of the above essential components, the polymerizable composition may be adjusted as necessary within the limits that do not contradict the purpose of the present invention in order to adjust the physical properties such as mechanical strength and the reactivity such as polymerizability. Other components may be mixed in a small amount. Examples of such optional components include polymerizable monomers such as acrylonitrile, acrolein, methyl vinyl ketone, vinyl cyclohexane, vinyl pyridine, and vinyl imidazole, dibutyl phthalate, dioctyl phthalate, dimethyl isophthalate, dibutyl adipate, and triethyl. Examples thereof include plasticizers such as citrate, acetyltributyl citrate, and dibutyl sebacate.

  As other components, when the polymerizable monomer is contained in the polymerizable composition, the content thereof is preferably 45% by mass or less, and 35% by mass or less of the total amount of all polymerizable monomer components. More preferred. The amount of the plasticizer used is preferably 50 parts by mass or less based on 100 parts by mass of the total polymerizable monomer components.

(Porous film)
In the manufacturing method of this diaphragm, the said polymeric composition is made to contact with the porous film mentioned above. Thereby, the polymerizable composition is filled in the pores of the porous film. Thereafter, the polymerizable composition filled in the pores is polymerized and cured.

  Thus, the fuel cell membrane made of a cation exchange membrane produced using a porous film as a base material has high physical strength without impairing proton conductivity because the porous film reinforces the strength.

(Contact between polymerizable composition and porous film)
The contact between the polymerizable composition and the porous film is not particularly limited as long as the polymerizable composition is contacted by a method capable of entering the pores of the porous film. For example, a method in which the polymerizable composition is applied to or sprayed on the porous film, or the porous film is immersed in the polymerizable composition is exemplified. When the porous film is immersed in the polymerizable composition and brought into contact therewith, the immersion time varies depending on the type of the porous film and the composition of the polymerizable composition, but is generally 0.1 second to 10 minutes or more. It is.

(polymerization)
The polymerizable composition filled in the pores of the porous film is then polymerized. The polymerization method is not particularly limited, and a known method may be appropriately employed depending on the composition of the polymerizable monomer used and the kind of the polymerization initiator. When using the said organic peroxide as a polymerization initiator, the polymerization method by heating (thermal polymerization) is common. This method is preferable to other methods because it is easy to operate and can be polymerized relatively uniformly.

  In the polymerization, in order to prevent polymerization inhibition due to oxygen and to obtain smoothness of the surface, the porous film filled with the polymerizable composition is covered with a film such as polyester, and the polymerization is performed in a state where both are in close contact with each other. Preferably, it is done. By covering the porous film with the film, excess polymerizable composition is excluded from the porous film, and a thin and uniform diaphragm for a fuel cell is produced.

  In the case of thermal polymerization, the polymerization temperature is not particularly limited, and a known temperature condition may be appropriately selected, but is generally 50 to 150 ° C, preferably 60 to 120 ° C. The polymerization time is preferably 10 minutes to 10 hours.

  By the method described above, a film-like polymer obtained by filling the pores of the porous film with the polymer resin of the polymerizable composition is obtained. When the resin of the membrane polymer is a cured product of a resin composition containing a monomer having a cation exchange group, it is used as it is as a fuel cell membrane. When the resin of the membrane polymer does not have a cation exchange group, the cation exchange group is introduced into the resin as described in the next introduction of the cation group, and then used as a fuel cell membrane.

(Introduction of cation exchange groups)
The cation exchange group is introduced into the aromatic ring of the resin filled in the pores of the porous film. This aromatic ring is derived from the aromatic ring of the aromatic polymerizable monomer blended in the polymerizable composition.

  As the cation exchange group introduced into the aromatic ring, a conventionally known cation exchange group is employed without any particular limitation. Specific examples include a sulfonic acid group, a carboxylic acid group, and a phosphonic acid group. A sulfonic acid group which is a strongly acidic group is particularly preferable in that the electric resistance of the obtained diaphragm is lowered.

  As a method for introducing a sulfonic acid group into an aromatic ring, for example, a method in which a sulfonating agent such as concentrated sulfuric acid, fuming sulfuric acid, sulfur dioxide, chlorosulfonic acid or the like is brought into contact with the produced film-like polymer and reacted. Is mentioned.

  As a method of introducing a phosphone group into an aromatic ring, a method of reacting a membrane polymer having an alkyl halide group with phosphorus trichloride in the presence of anhydrous aluminum chloride and then hydrolyzing in an alkaline aqueous solution. Etc.

  As a method of introducing a carboxylic acid group into an aromatic ring, a method of halogenating by contacting with a halogen gas in the presence of a catalyst such as iron halide and further reacting with alkyl lithium and then reacting with carbon dioxide, etc. Is mentioned.

  The method for introducing these cation exchange groups is a known method.

(Diaphragm for direct liquid fuel cell)
The cation exchange membrane obtained by filling the pores of the porous film with the cation exchange resin thus obtained is washed, cut as necessary, and directly separated according to a conventional method for a liquid fuel cell. Used as

The diaphragm for a direct liquid fuel cell of the present invention has a high cation exchange capacity of 0.1 to 5 mmol / g, particularly 0.1 to 4 mmol / g, as measured by a conventional method. Therefore, it has high battery output, low fuel liquid permeability, and sufficiently high proton conductivity of the membrane. In addition, as a result of using the polymerizable composition having the above composition, the diaphragm of the present invention has a moisture content of usually 5 to 90%, more preferably 10 to 80%, and an increase in electrical resistance due to drying, that is, proton. It is difficult for a decrease in conductivity to occur. Furthermore, an insoluble in the fuel liquid, the electrical resistance is usually, 40 ℃, 0.25Ω · cm ² or less represent an electric resistance by the AC impedance method in wet condition, even as small as 0.20Ω · cm ^2. Moreover, the permeability of the fuel liquid is extremely small. For example, the methanol permeability in the diaphragm when contacting with 30% by mass of methanol at 25 ° C. is usually 1000 g / m ² · hr or less, particularly 10 to 800 g / m. The range is ² · hr.

  Since the diaphragm for a fuel cell according to the present invention has such a low electrical resistance and a low fuel liquid permeability, the fuel liquid supplied to the fuel chamber is used when directly used as a diaphragm for a liquid fuel cell. Can be effectively prevented from diffusing to the opposite chamber and a high output battery can be obtained.

  The direct liquid fuel cell manufactured using the diaphragm of the present invention is generally one having the basic structure of FIG. 1, but of course also applies to other direct liquid fuel cells having a known structure. be able to. As the fuel liquid, methanol is the most common, and the effect of the present invention is most prominent. In addition, ethanol, ethylene glycol, dimethyl ether, hydrazine, and the like have the same excellent effect. Is done. Furthermore, the fuel is not limited to liquid, and gaseous hydrogen gas or the like can be used.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

  In Examples and Comparative Examples, the membrane thickness of the porous film, porosity, pore diameter, breaking strength, and cation exchange capacity, moisture content, membrane resistance, methanol permeation of fuel cell membranes prepared using them The characteristics of the fuel cell membrane were evaluated by measuring the fuel cell output voltage. These measurement methods will be described below.

1) Porosity The apparent specific gravity d of the porous film was measured and calculated by the following formula using a specific gravity of polyethylene of about 0.9.

  Porosity (%) = [(0.9−d) /0.9] × 100

2) Average pore diameter Based on the bubble point method according to JIS K3832, it measured using the automatic aperture size distribution measuring machine.

3) Tensile strength at break The porous film was cut into a 1 cm wide and 10 cm long rectangle. The cut film was set in a tensile strength tester (manufactured by Shimadzu Corporation Autograph), and a break test was performed at a speed of 50 mm / min to obtain break strengths PMD and PTD.

4) Cation exchange capacity and water content After immersing the cation exchange membrane in a 1 mol / L-HCl aqueous solution for 10 hours or more to form a hydrogen ion type, the cation exchange membrane is immersed in a 1 mol / L-NaCl aqueous solution to form a hydrogen ion type. Was replaced with the sodium ion form. The liberated hydrogen ions were quantified with a potentiometric titrator (COMMITE-900, manufactured by Hiranuma Sangyo Co., Ltd.) using an aqueous sodium hydroxide solution (Amol).

  Next, after immersing the same cation exchange membrane in 1 mol / L-HCl aqueous solution for 4 hours or more, the membrane was taken out and sufficiently washed with ion exchange water. Thereafter, the moisture on the surface was wiped off with a tissue paper, and the mass (Wg) of the film when wet was measured. The membrane was further dried under reduced pressure at 60 ° C. for 5 hours, and then its mass was measured (Dg). Based on the above measured values, the cation exchange capacity and water content were determined by the following equations.

Cation exchange capacity = A × 1000 / D [mmol / g-dry mass]
Moisture content = 100 × (WD) / D [%]

5) Membrane resistance A strip-shaped sample diaphragm having a width of 2.0 cm wetted with pure water was pressed against the platinum wire using an insulating substrate in which five platinum wires having a line width of 0.3 mm were arranged parallel to each other. The sample was held in a constant temperature and humidity chamber of 40 ° C. and 90% RH, and the alternating current impedance was measured when an alternating current of 1 kHz was applied between the platinum wires. Each AC impedance when the distance between platinum wires was changed to 0.5 to 2.0 cm was measured.

  Although resistance due to contact occurs between the platinum wire and the diaphragm, this effect was excluded by calculating the specific resistance of the diaphragm from the distance between the platinum wires and the gradient of resistance. A good linear relationship was obtained between the distance between the platinum wires and the resistance measurement. The film resistance was calculated from the resistance gradient and film thickness by the following formula.

R = 2.0 × L ² × S
R: membrane resistance [Ω · cm ² ]
L: Film thickness [cm]
S: resistance-to-resistance gradient [Ω / cm]

6) Methanol permeability The fuel cell shown in FIG. 1 was assembled with only a membrane without using a gas diffusion electrode. An aqueous methanol solution having a concentration of 30% by mass was supplied to the fuel chamber with a liquid chromatograph pump, and conditioned air was supplied to the oxidizer chamber at 300 ml / min. The measurement was performed in a constant temperature bath at 25 ° C. A certain amount of humidity-controlling air flowing out from the oxidant chamber was directly introduced into a gas chromatograph (GC14B manufactured by Shimadzu Corporation) using a gas sampler, and the methanol concentration was measured. From the results, the amount of methanol that permeated the diaphragm was calculated. . For measurement, two points of 20% and 80% relative humidity at 25 ° C. were used as humidity control air, and the methanol permeability in each state was measured.

7) Fuel cell output voltage On carbon paper with a thickness of 100 μm and porosity of 80% treated with polytetrafluoroethylene for water repellency, the catalyst was applied to 4 mg / cm ² and decompressed at 80 ° C. for 4 hours. A gas diffusion electrode was obtained by drying. The applied catalyst dispersion was 5% perfluorocarbon sulfonic acid dissolved in carbon black carrying 50% by mass of an alloy catalyst of platinum and ruthenium (ruthenium 50 mol%), alcohol and water (trade name Nafion, manufactured by DuPont). ) Was mixed and prepared.

Next, the above gas diffusion electrodes were set on both surfaces of the fuel cell diaphragm to be measured, and hot pressed for 100 seconds under a pressure of 100 ° C. and a pressure of 5 MPa, and then allowed to stand at room temperature for 2 minutes. This was incorporated into a fuel cell having the structure shown in FIG. The fuel cell temperature was set to 25 ° C., a 30 mass% methanol aqueous solution was added to the fuel chamber side, and air at 25 ° C. and a relative humidity of 50% was supplied to the oxidizer chamber side at 200 ml / min. A power generation test was carried out and cell terminal voltages at current densities of 0 A / cm ² and 0.1 A / cm ² were measured.

Examples 1-3
90 parts by mass of styrene, 10 parts by mass of divinylbenzene, and 5 parts by mass of t-butyl peroxyethyl hexanoate as a polymerization initiator were mixed to obtain a polymerizable composition. 400 g of the polymerizable composition was placed in a 500 ml glass container, and the porous film shown in Table 1 was immersed therein.

  Subsequently, these porous films were taken out from the polymerizable composition, coated on both sides of the porous film using a 100 μm polyester film as a release material, and then heated and polymerized at 80 ° C. for 5 hours under nitrogen pressure of 0.3 MPa. did.

  The obtained membrane polymer was immersed in a 1: 1 mixture of 98% concentrated sulfuric acid and chlorosulfonic acid having a purity of 90% or more at 40 ° C. for 60 minutes to sulfonate the benzene ring to obtain a fuel cell membrane. It was.

  This fuel cell membrane was immersed in a 1 mol / L-hydrochloric acid aqueous solution for 3 hours while changing the solution once every hour, so that the counter ion of the sulfonic acid group was exchanged with hydrogen ion. Furthermore, in order to remove surplus hydrochloric acid existing in the membrane, washing was carried out by immersing in ion exchange water overnight. The washed fuel cell membrane was air-dried on a glass plate. The air-dried fuel cell membrane was visually checked for cracks. The air-dried fuel cell membrane was measured for cation exchange capacity, moisture content, membrane resistance, film thickness, methanol permeability, and fuel cell output voltage. The results are shown in Table 2.

Comparative Examples 1-4
The same operation as in Example 1 was performed except that the porous film shown in Table 1 was used to obtain a fuel cell membrane.

  About this fuel cell diaphragm, the same operation as description of Example 1 was performed, and the presence or absence of the crack was confirmed. The cation exchange capacity, water content, membrane resistance, film thickness, methanol permeability, and fuel cell output voltage were measured for the fuel cell membrane in which no cracks occurred. The results are shown in Table 2.

It is a conceptual diagram which shows the basic structure of a polymer electrolyte fuel cell. It is explanatory drawing of how to obtain | require the tensile breaking strength ratio of a porous film.

Explanation of symbols

1a, 1b Battery partition 2 Fuel flow hole 3 Oxidant gas flow hole 4 Fuel chamber side diffusion electrode 5 Oxidant chamber side gas diffusion electrode 6 Solid polymer electrolyte membrane (cation exchange membrane)
7 Fuel chamber 8 Oxidant chamber

Claims (3)

A membrane for a fuel cell in which a crosslinked ion exchange resin having an aromatic group covalently bonded to a cation exchange group is filled in pores of a porous film made of a polyolefin resin , wherein the porous film has a thickness of 40 to The tensile breaking strength ratio (PMD / PTD) between the tensile breaking strength PMD in the film flow direction of the porous film and the tensile breaking strength PTD in the direction perpendicular to the film flow direction of the porous film. ) Is a diaphragm for a direct liquid fuel cell, which is 10 or less.   The diaphragm for a direct liquid fuel cell according to claim 1, wherein the average pore diameter of the pores is 0.01 to 2 µm.   A porous film made of a polyolefin resin having a thickness of 40 to 120 μm and a porosity of 45% or more, which is perpendicular to the tensile breaking strength PMD in the film flow direction of the porous film and the film flow direction of the porous film In the pores of the porous film having a tensile breaking strength ratio (PMD / PTD) of 10 or less with the tensile breaking strength PTD in the direction of
  2. A cation exchange group is introduced after impregnating and polymerizing a polymerizable composition containing a monomer having a functional group into which a cation exchange group can be introduced, a crosslinkable polymerizable monomer, and a polymerization initiator. Or the manufacturing method of the diaphragm for direct liquid fuel cells of 2.

Images