JP4849892B2 - Method for manufacturing diaphragm for direct liquid fuel cell - Google Patents

Description

  The present invention relates to a method for producing a diaphragm for a direct liquid fuel cell.

  Ion exchange membranes are widely used as membranes for batteries such as polymer electrolyte fuel cells, redox flow cells, zinc-bromine cells, and dialysis membranes. Among these, a polymer electrolyte fuel cell using an ion exchange membrane as an electrolyte is a clean and highly efficient power generation system that continuously supplies fuel and an oxidant, and extracts chemical energy as electricity when they react. In recent years, it has become increasingly important for automobile use, home use and portable use from the viewpoint of low temperature operation and miniaturization. A polymer electrolyte fuel cell generally has a gas diffusion electrode having a catalyst supported on both sides of a solid polymer diaphragm acting as an electrolyte, and a chamber (fuel chamber) on the side where one gas diffusion electrode exists. ) Is supplied with a liquid fuel such as hydrogen gas or methanol, and an oxygen-containing gas such as oxygen or air as an oxidant is supplied to the chamber on the other gas diffusion electrode side. By connecting an external load circuit, the fuel cell is operated. Above all, direct liquid fuel cells that use methanol or the like as direct fuel are not only easy to handle because the fuel is liquid, but also are inexpensive fuels, especially as a relatively small output power source for portable devices. Expected.

  The basic structure of such a direct liquid fuel cell is shown in FIG. In the figure, (1) is a battery partition, (2) is a fuel flow hole, (3) is an oxidant gas flow hole, (4) is a fuel chamber side diffusion electrode, (5) is an oxidant chamber side gas diffusion electrode, (6) shows a solid polymer electrolyte membrane. In this direct liquid fuel cell, protons (hydrogen ions) and electrons are generated in the fuel chamber side diffusion electrode (4) from the liquid fuel such as alcohol supplied to the fuel chamber (7), and this proton is used as the solid polymer electrolyte. (6) Conducts the inside, moves to the other oxidant chamber (8), reacts with oxygen in the air or oxygen gas, and generates water. At this time, the electrons generated in the fuel chamber side diffusion electrode (4) move to the oxidant chamber side gas diffusion electrode (5) through the external load circuit to obtain electric energy.

  In the direct liquid fuel cell having such a structure, a cation exchange membrane is usually used for the diaphragm, but the cation exchange membrane has not only low electrical resistance and high physical strength, The characteristic that the permeability | transmittance of the liquid fuel used as a fuel is low is requested | required. For example, when the permeability of the liquid fuel is high, when the ion exchange membrane is used as a diaphragm for a fuel cell, the liquid fuel in the fuel chamber cannot be sufficiently prevented from diffusing to the oxidation chamber side, Large battery output cannot be obtained.

  Conventionally, as a cation exchange membrane used as a diaphragm for a fuel cell, for example, a polyolefin-based or fluororesin porous membrane is used, and a polymerizable unit having a functional group capable of introducing a cation-exchange group into this is used. A film obtained by a method in which a polymerizable composition comprising a monomer and a crosslinkable polymerizable monomer is filled and polymerized, and an ionic group relating to a functional group capable of introducing the cation exchange group is introduced, is relatively inexpensive. In addition, it is known as suitable because it has low electrical resistance, low hydrogen gas permeability, and little deformation due to swelling or the like (for example, Patent Documents 1 and 2).

JP 2001-135328 A Japanese Patent Laid-Open No. 11-310649

  However, even in these cation exchange membranes, when used as a diaphragm for a direct liquid fuel cell, the permeability of liquid fuel such as alcohol is not sufficiently suppressed. There was a problem that fuel diffusion occurred and the battery performance deteriorated. In order to improve this, in the polymerizable composition for polymerizing the cation exchange resin constituting the cation exchange membrane, the content of the crosslinkable polymerizable monomer is increased, and the hydrophilic cation exchange group is reduced. A technique of reducing the amount of introduction to increase the hydrophobicity of the film and increasing the degree of crosslinking of the film to form a dense film is effective to some extent, but in this case, the electrical resistance of the film increases. As a result, a problem that the battery output decreases is caused, and the fuel cell membrane that is practically satisfactory cannot be obtained.

  In the method for producing a cation exchange membrane for a fuel cell membrane known as the prior art, the cation exchange group is used as a monomer component constituting the polymerizable composition for polymerizing the cation exchange resin. A polymerizable monomer having no functional group capable of introducing a cation exchange group such as acrylonitrile, acrolein, methyl vinyl ketone, etc. in addition to a polymerizable monomer having a functional group capable of introducing a monomer or a crosslinkable polymerizable monomer It has also been shown to contain the body as a third copolymer component. However, the polymerizable monomers that are clearly specified as the third copolymerization component are all monomers having strong hydrophilicity, and cation exchange membranes obtained by copolymerizing these are the result. Only membranes with high hydrophilicity were obtained, and these membranes could only be used as fuel cell membranes and had no significant effect on the permeability of liquid fuel such as alcohol.

  In the background described above, the present invention is a cation exchange membrane conventionally used as a membrane for fuel cells. The permeability of liquid fuel such as alcohol, particularly methanol permeability is low, membrane resistance is low, and the battery output is high. An object of the present invention is to provide an ion exchange membrane that can be stably obtained and hardly deforms such as swelling.

  The present inventors have conducted extensive research in view of the above problems. As a result, it was found that the permeability of the liquid fuel can be remarkably reduced without increasing the membrane resistance by introducing a specific amount of hydrophobic site in the membrane, and a simple method for producing these membranes. The headline and the present invention have been proposed.

That is, the present invention relates to 30 to 90 mol% of a polymerizable monomer having a functional group capable of introducing a cation exchange group, and a hydrophobic polymerizable monomer 1 having no functional group capable of introducing the cation exchange group. A polymerizable composition containing 60 mol%, a polymerizable monomer component consisting of 1 to 40 mol% of a crosslinkable polymerizable monomer, and an effective amount of a polymerization initiator component, is made of a thermoplastic resin (crosslinked) what is excluded) a is in contact with the porous membrane, the polymerizable composition is polymerized and cured after filling the void portion having a said porous membrane, then the functional group capable of introducing the cation-exchange group A method for producing a diaphragm for a direct liquid fuel cell, wherein a cation exchange group is introduced.

Furthermore, the present invention is a polymerization comprising 30 to 90 mol% of a polymerizable monomer having a cation exchange group, 1 to 60 mol% of a hydrophobic polymerizable monomer, and 1 to 40 mol% of a crosslinkable polymerizable monomer. A polymerizable composition comprising a polymerizable monomer component and an effective amount of a polymerization initiator component is contacted with a porous membrane whose material is a thermoplastic resin (excluding those crosslinked), and the polymerizable composition also provides method for producing a direct liquid fuel cell membrane, characterized in that the polymerization cured after being filled in the void portion having a said porous membrane.

  According to the method of the present invention, a polymerizable monomer for introducing a cation exchange group into a polymerizable composition for forming a cation exchange resin, and a crosslinkable polymerizable monomer for making the resin crosslinkable. Since the hydrophobic polymerizable monomer is contained in an amount of 1 to 60 mol% separately from the body, the hydrophobic cation exchange resin constituting the obtained cation exchange membrane has a hydrophobic polymerizable property separately from the crosslinking site. The amount of the hydrophobic portion attributed to the monomer is introduced. Therefore, this cation exchange membrane has a highly enhanced hydrophobic property while maintaining a certain ion exchange capacity and appropriate crosslinking for suppressing deformation such as membrane swelling. As a result, the cation exchange membrane obtained by this method greatly reduces the permeability of liquid fuel, particularly methanol, without excessively increasing the electrical resistance of the membrane when used directly as a diaphragm for a liquid fuel cell. It becomes possible. That is, it is possible to obtain a direct liquid fuel cell diaphragm that is difficult to achieve in the past and has both high liquid fuel impermeability and high proton conductivity.

  The direct liquid fuel cell manufactured using the diaphragm obtained by the method of the present invention has a low cell internal resistance and suppresses the crossover of fuel fuel such as methanol. It is obtained and is extremely useful.

  In the production method of the present invention, as a polymerizable composition for forming a cation exchange resin, 30 to 90 mol% of a polymerizable monomer having a functional group capable of introducing a cation exchange group, the cation exchange group can be introduced. 1 to 60 mol% of a hydrophobic polymerizable monomer having no functional group, a polymerizable monomer component consisting of 1 to 40 mol% of a crosslinkable polymerizable monomer, and an effective amount of a polymerization initiator component A polymerizable composition is used.

  Here, in the present invention, conventionally known cation exchange groups are not particularly limited, and specific examples include sulfonic acid groups, carboxylic acid groups, phosphonic acid groups, and the like. A sulfonic acid group which is a strongly acidic group is particularly preferable in that the resistance can be lowered.

  As the polymerizable monomer having a functional group capable of introducing such a cation exchange group, known monomers having such a function can be used without particular limitation, but as the functional group capable of introducing a cation exchange group, The sulfonic acid group, which is a suitable cation exchange group, is a group that can be easily introduced, so that styrene, vinyl toluene, vinyl xylene, α-methyl styrene, acenaphthylene, vinyl naphthalene, α-halogenated styrene, α, β, β A radical polymerizable monomer having an aromatic hydrocarbon group such as' -trihalogenated styrene is preferred. In addition, a structure in which a vinyl group is directly bonded to the aromatic hydrocarbon group such as styrene is preferable because it is less susceptible to hydrolysis than a structure in which a (meth) acryl group is bonded.

  The content of the polymerizable monomer having a functional group capable of introducing such a cation exchange group is such that the obtained cation exchange membrane has sufficient proton conductivity as a diaphragm for a fuel cell. It is 30-90 mol% in a body component, Preferably it is 40-85 mol%. When the content of the polymerizable monomer having a functional group capable of introducing a cation exchange group is less than 30 mol%, a membrane having sufficient proton conductivity cannot be obtained, while the content is 90 mol%. Exceeds the above, it becomes impossible to sufficiently secure the content of the other polymerizable monomer component, which will be described later, that is, the hydrophobic polymerizable monomer and the crosslinkable polymerizable monomer. It becomes impossible to impart hydrophobicity or crosslinking sufficient to prevent swelling or the like to the film.

  In the present invention, as the crosslinkable polymerizable monomer, a conventionally known monomer used in the production of an ion exchange membrane is used without particular limitation. By using the crosslinkable polymerizable monomer in this way, the cation exchange membrane becomes a crosslinked type. Since the cross-linked ion exchange resin is essentially solvent-insoluble, even if a large amount of cation exchange groups are introduced, the stability of the resin, such as solubility in water and alcohol and swelling, is not reduced. Therefore, the amount of ion-exchange groups that can be introduced can be extremely large, and the membrane resistance can also be extremely small.

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

  The content of these crosslinkable polymerizable monomers is such that the resulting cation exchange membrane is provided with a crosslinkable property sufficient to sufficiently prevent liquid fuel impermeability and swelling, etc. It is 1-40 mol% in a monomer component, Preferably it is 2-30 mol%. When the content of the crosslinkable polymerizable monomer is less than 1 mol%, it is difficult to form a sufficient crosslink, and although the membrane resistance is low, the alcohol impermeability is lowered. On the other hand, when this content exceeds 40 mol%, other polymerizable monomer components, such as a polymerizable monomer having a functional group capable of introducing a cation exchange group, and a hydrophobic polymerizable monomer described later The body content cannot be sufficiently secured, and the membrane becomes unsatisfactory in terms of proton conductivity.

  The greatest feature of the present invention is that the polymerizable monomer component of the polymerizable composition for forming such a cation exchange resin is a polymerizable monomer having a functional group capable of introducing the cation exchange group described above or a cross-linking. Apart from the polymerizable monomer, a certain amount of a hydrophobic polymerizable monomer having no functional group capable of introducing a cation exchange group is contained. With this configuration, in the cation exchange membrane produced by the method of the present invention, the cation exchange resin portion has the above-described amount of the hydrophobic portion due to the hydrophobic polymerizable monomer separately from the crosslinking portion. . As a result, this cation exchange membrane has a substantially improved hydrophobic property of the liquid fuel while maintaining a certain ion exchange capacity and appropriate crosslinking for suppressing deformation such as membrane swelling. Impermeability is greatly improved.

  As described above, in a conventionally known method for producing a cation exchange membrane for a fuel cell membrane, a polymerizable monomer having a functional group capable of introducing a cation exchange group or a crosslinkable polymerizable monomer in a polymerizable composition. Although there are those disclosed to contain a third copolymer component in addition to the monomer, the polymerizable monomers as these third copolymer components are all highly hydrophilic monomers. However, the present invention is the first to specifically propose the inclusion of the hydrophobic polymerizable monomer.

  In the present invention, the hydrophobicity in the hydrophobic polymerizable monomer having no functional group capable of introducing a cation exchange group means that the logarithmic value (logPow) of water / octanol partition coefficient is 2.0 or more. Say. In order to fully exhibit the effects of the present invention, the logarithmic value (logPow) of the water / octanol partition coefficient is more preferably 3.0 or more. Here, the logPow value is a coefficient that expresses the polarity depending on the ease of distribution of substances into water and octanol as defined in Chemical Reviews vol.71 (6), 525 (1971), etc. It can be measured by the measuring method of Japanese Industrial Standard Z7260-107 (2000). With a polymerizable monomer having a logarithmic value (logPow) of the water / octanol partition coefficient of less than 2.0, the resulting cation exchange membrane should not exhibit a hydrophobic property that sufficiently reduces the alcohol permeability. Become.

  As such a polymerizable monomer having no functional group capable of introducing a hydrophobic cation exchange group, it may be appropriately selected from known monomers. Specific examples include vinylcyclopentane, vinylcyclohexane, octachlorostyrene, hexafluoropropylene, vinyltrimethylsilane, and vinyltrichlorosilane. In particular, vinylcycloalkane is preferable in that it is difficult to cause an undesirable chemical reaction such as hydrolysis during sulfonation or use as a fuel cell, and vinylcycloalkane having 5 to 8 carbon atoms of cycloalkane is most preferable.

  The content of the hydrophobic polymerizable monomer that does not have a functional group capable of introducing these cation exchange groups is such that the obtained cation exchange membrane has a hydrophobic property that sufficiently prevents liquid fuel non-permeability. In the polymerizable monomer component, it is 1 to 60 mol%, preferably 5 to 40 mol%. When the content of the hydrophobic polymerizable monomer is less than 1 mol%, it becomes difficult to impart sufficient hydrophobicity. On the other hand, when the content exceeds 40 mol%, other polymerizable monomers The content of the polymerizable monomer having a functional group capable of introducing the cation exchange group or the crosslinkable polymerizable monomer cannot be sufficiently ensured, and the proton conductivity and alcohol impermeability are satisfied. It becomes impossible film.

  In addition, each polymerizable monomer used in the polymerizable composition in the present invention is carbonized with a structure mainly composed of carbon and hydrogen from the viewpoint of production cost and impregnation into a polyolefin resin porous film described later. It is preferably a hydrogen-based polymerizable monomer. Of course, such a hydrocarbon-based polymerizable monomer may be present in a small amount of other atoms such as fluorine, chlorine, bromine, oxygen, nitrogen, silicon, sulfur, boron, and phosphorus, The amount is 40 mol% or less based on the total number of atoms constituting the monomer (excluding atoms constituting the cation exchange group in the polymerizable monomer having a cation exchange group described later), In particular, it is preferably 10 mol% or less.

  The polymerizable composition containing the polymerizable monomer component contains an effective amount of a polymerization initiator. The polymerization initiator is not particularly limited as long as it is a compound capable of polymerizing the polymerizable monomer, but is preferably an organic peroxide, such as octanoyl peroxide, Lauroyl peroxide, t-butylperoxy-2-ethylhexanoate, benzoyl peroxide, t-butylperoxyisobutyrate, t-butylperoxylaurate, t-hexylperoxybenzoate, di-t-butyl Examples thereof include radical polymerization initiators such as peroxides.

  The content of the polymerization initiator may be appropriately selected according to the composition of the polymerizable monomer to be used and the type of the polymerization initiator, from the range that is implemented as an effective usage for the same purpose. However, usually 0.1 to 20 parts by mass with respect to 100 parts by mass of the above-described polymerizable monomer component (including the content of other polymerizable monomer described later). More preferably, it is 0.5 to 10 parts by mass.

  In addition to the above-mentioned essential components, the polymerizable composition contains a small amount of other components as necessary in order to adjust the physical properties such as mechanical strength and polymerizability, as long as the effect is not greatly affected. You may mix | blend. Examples of such optional components include other polymerizable monomers such as acrylonitrile, acrolein, and methyl vinyl ketone, dibutyl phthalate, dioctyl phthalate, dimethyl isophthalate, dibutyl adipate, triethyl citrate, and acetyl tributyl citrate. And plasticizers such as dibutyl sebacate. Among these, when other polymerizable monomer is contained in the polymerizable monomer component, the content thereof is 50 mol% or less, particularly 20 mol% or less in the polymerizable monomer component. The amount of plasticizer used is preferably 50 parts by mass or less with respect to 100 parts by mass of the polymerizable monomer component.

  In the method of the present invention, the polymerizable composition having the above composition is brought into contact with the porous film, and the polymerizable composition is filled in the voids of the porous film, followed by polymerization and curing. Thus, the fuel cell membrane comprising a cation exchange membrane based on a porous membrane increases the physical strength of the fuel cell membrane without sacrificing electrical resistance or the like because the porous membrane functions as a reinforcing part. Can be preferable.

  As such a porous membrane used as a base material, any known porous membrane can be used as long as at least a part of the pores communicate with each other so that a fuel cell membrane based on the porous membrane can be formed. Can be used without limitation. If the pores are too small, the filling property of the cation exchange resin is lowered. On the other hand, if the pores are too large, the impermeability of the alcohol may be lowered. Therefore, the average pore diameter is preferably 0.01 to 2 μm, particularly preferably. Those having pores of 0.015 to 0.4 μm are preferable.

  The porosity (also referred to as porosity) is preferably 20 to 95%, particularly preferably 30 to 90% because the electrical resistance of the fuel cell diaphragm can be lowered and high physical strength can be maintained. The air permeability (JIS P-8117) is preferably 1500 seconds or less, particularly preferably 1000 seconds or less. The thickness is preferably 5 to 150 μm, more preferably 10 to 120 μm, and particularly preferably 10 to 70 μm. Furthermore, in order to obtain high alcohol impermeability, the surface smoothness is preferably 10 μm or less, more preferably 5 μm or less in terms of roughness index.

Form of the porous film is not particularly limited, the porous film, woven fabric, nonwoven fabric, paper, an inorganic film or the like you can use without limitation. The material of the porous membrane, from the viewpoint of adhesion strength between the above-described cation exchange resin not only easy to manufacture of its high, the thermoplastic resin (those crosslinked excluded) Ru der.

  Examples of the thermoplastic resin include α- such as ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 3-methyl-1-butene, 4-methyl-1-pentene, and 5-methyl-1-heptene. Polyolefin resins such as olefin homopolymers or copolymers; vinyl chloride resins such as polyvinyl chloride, vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinylidene chloride copolymers, vinyl chloride-olefin copolymers; Such as polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-ethylene copolymer, etc. Fluorine resin; Polyamide such as nylon 6 and nylon 66 Resins. Among these, it is particularly preferable to use a polyolefin resin because it is excellent in mechanical strength, chemical stability, and chemical resistance, and is familiar with a hydrocarbon ion exchange resin. As the polyolefin resin, polyethylene or polypropylene resin is particularly preferable, and polyethylene resin is most preferable.

  Such a porous film can be obtained, for example, by a method described in JP-A-9-216964, JP-A-2002-338721, or the like, or a commercially available product (for example, Asahi Kasei “Hypore”, Ube Industries, Ltd.). "Eupor", Tonen Tapils "Setera", Nitto Denko "Exepor", Mitsui Chemicals "Hillette", etc.) are also available.

  The contact between the polymerizable composition and the porous film is not particularly limited as long as the polymerizable composition can enter the voids of the porous film. For example, the polymerizable composition can be applied to or sprayed on the porous film. Or a method of immersing the porous membrane in the polymerizable composition. In the case of immersion, the immersion time is generally 0.1 second to 20 minutes, although it depends on the type of the porous membrane and the composition of the suspension.

  The polymerization method of the polymerizable composition filled in the voids of the porous membrane in this way is not particularly limited, and a known method can be appropriately used depending on the composition of the polymerizable monomer used and the type of the polymerization initiator. Adopt it. When an organic peroxide as described above is used as a polymerization initiator, a heating method (thermal polymerization) is generally used. This method is preferable to other methods because it is easy to operate and can be relatively uniformly polymerized. In polymerization, in order to prevent polymerization inhibition by oxygen and to obtain surface smoothness, it is more preferable to perform polymerization after covering with a film of polyester or the like. Further, by covering with a film, excess polymerizable composition is removed, and a thin and uniform fuel cell membrane can be obtained. In addition, the polymerization temperature in the case of polymerization by thermal polymerization is not particularly limited, and may be appropriately selected and applied from known conditions, but is generally about 50 to 150 ° C, preferably about 60 to 120 ° C. . The polymerization time is about 10 minutes to 10 hours.

  In order to make the membrane polymer obtained by the above polymerization into a cation exchange membrane, a cation exchange group must be introduced into a group into which the cation exchange group can be introduced. This treatment may be performed appropriately depending on the type of the functional group in the polymerizable monomer having a functional group capable of introducing a cation exchange group. As described above, the cation exchange group for the fuel cell is preferably a sulfonic acid group. In this case, the polymerizable monomer having a functional group capable of introducing the cation exchange group has an aromatic hydrocarbon group. Things are used. Specific examples of the method for introducing a sulfonic acid group into the aromatic hydrocarbon group include a method of reacting a sulfonating agent such as concentrated sulfuric acid, fuming sulfuric acid, sulfur dioxide, and chlorosulfonic acid.

  The cation exchange membrane thus obtained may be used as a diaphragm for a direct liquid fuel cell according to a conventional method after washing and cutting as necessary.

  As described above, the diaphragm for a direct liquid fuel cell comprising the cation exchange membrane of the present invention is produced. This method uses a polymerizable monomer having a functional group capable of introducing a cation exchange group in a polymerizable composition as a polymerizable monomer for providing a cation exchange group. This is a production method of introducing a corresponding ionic group into a functional group capable of introducing the cation exchange group after polymerization into a molecule. In the present invention, as another method, a functional group capable of introducing the cation exchange group. In place of the polymerizable monomer having a cation exchange group, a polymerizable monomer having a cation exchange group is used, and this is carried out as a method for producing a target cation exchange membrane at the stage of polymerization into a membrane polymer. May be. That is, in the case of this method, the polymerizable composition has a polymerizable monomer having a cation exchange group of 40 to 90 mol%, a hydrophobic polymerizable monomer of 1 to 60 mol%, and a crosslinkable polymerizable monomer 1. A polymerizable composition comprising a polymerizable monomer component consisting of ˜40 mol% and an effective amount of a polymerization initiator component is used, and the polymerizable composition is brought into contact with the porous membrane to thereby remove the polymerizable composition from the porous membrane. This is a method of polymerizing and curing after filling the voids of

  This method is efficient in terms of operation because the introduction of a cation exchange group after polymerization of the membranous polymer can be omitted, but in general, a polymerizable monomer having a cation exchange group such as a sulfonic acid group. Is a solid, a solvent such as alcohol is required to permeate the polymerizable composition using this into the porous substrate, and the packing density of the cation exchange resin in the voids of the porous substrate is low. There is a possibility that the introduction density of ion exchange groups may not be increased or the introduction density of ion exchange groups may be difficult to increase. From these viewpoints, a method using a polymerizable monomer having a functional group capable of introducing the cation exchange group described above Is often more advantageous.

  Here, as the polymerizable monomer having a cation exchange group, styrene sulfonic acid, 2- (meth) acrylamide-2-methylpropane sulfonic acid, 3-sulfopropyl (meth) acrylic ester, vinyl sulfonic acid, vinyl Phosphonic acid, acrylic acid, methacrylic acid, maleic anhydride; further, α-halogenated vinyl sulfonic acid, α, β, β′-halogenated vinyl sulfonic acid, maleic acid, itaconic acid, styrenephosphonic acid, vinyl phosphorus Acid group-containing radical polymerizable monomers such as esters such as acids and salts corresponding to these may be mentioned.

  In addition, if the method uses a polymerizable monomer having a functional group capable of introducing the cation exchange group, even if it is a polymerizable monomer having a strong hydrophobicity, the introduction of the last cation exchange group A monomer in which a cation exchange group is introduced by the treatment cannot be used as a monomer for imparting a hydrophobic site to the polymerized cation exchange resin. In the method using a monomer, the monomer can also be used as a hydrophobic polymerizable monomer. As a result, as the hydrophobic polymerizable monomer used in this method, each hydrophobic polymerizable monomer that can be used in the method using a polymerizable monomer having a functional group capable of introducing a cation exchange group is used. In addition to the monomer, styrene, vinyltoluene, vinylxylene, α-methylstyrene, acetonaphthylene, vinylnaphthalene, α-halogenated styrene, α, β, β′-trihalogenated styrene, and the like can be suitably used.

  In addition, in this production method, the fine conditions are exactly the same as those in the method using a polymerizable monomer having a functional group capable of introducing a cation exchange group.

Such a direct liquid fuel cell membrane produced by the method of the present invention has a cation exchange capacity of usually 0.1 to 3 mmol / g, particularly 0.1 to 2 mmol / g, as measured by a conventional method. is doing. Therefore, it has high battery output, fuel liquid permeability and membrane resistance are sufficiently low. 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 a decrease in proton conductivity due to drying. It is difficult to occur. Furthermore, it is insoluble in the fuel liquid, and the membrane resistance value is very small, 0.40 Ω · cm ² or less, and further 0.20 Ω · cm ² or less. Moreover, permeability of the fuel liquid is extremely small, for example, the transmittance of methanol to 100% methanol solution at 25 ° C. Usually 1000g ^{/ m} 2 · hr or less, in particular in the range 10~700g ^{/ m} 2 · hr.

  Since the diaphragm for a fuel cell obtained by the method of the present invention has such a low electrical resistance and a low fuel liquid permeability, the liquid supplied to the fuel chamber when used directly as a diaphragm for a liquid fuel cell. Can be prevented from permeating through the diaphragm and diffusing into the opposite chamber, and a high output battery can be obtained. As the direct liquid fuel cell employing the diaphragm obtained by the method of the present invention, the direct liquid fuel cell having the basic structure shown in FIG. 1 is generally used, but the direct liquid type fuel cell having another known structure is used. Of course, the present invention can also be applied to a fuel cell. 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.

  Hereinafter, examples will be given to describe the present invention in more detail, but the present invention is not limited to these examples.

  In addition, the measurement method of the cation exchange capacity | capacitance used for the characteristic evaluation of the fuel cell diaphragm in the Example and the comparative example, the water content, membrane resistance, methanol permeability, and a fuel cell output voltage is demonstrated below.

1) Cation exchange capacity and water content The ion exchange membrane was immersed in a 1 mol / L-HCl aqueous solution for 10 hours or more to form a hydrogen ion type, and then replaced with a sodium ion type with a 1 mol / L-NaCl aqueous solution to liberate hydrogen ions. Was quantified with a potentiometric titrator (COMITE-900, manufactured by Hiranuma Sangyo Co., Ltd.) using an aqueous sodium hydroxide solution (Amol). Next, the same ion exchange membrane is immersed in a 1 mol / L-HCl aqueous solution for 4 hours or more, washed thoroughly with ion exchange water, and then the membrane is taken out. The surface moisture is wiped off with tissue paper and the weight (Wg) when wet It was measured. Further, the membrane was dried under reduced pressure at 60 ° C. for 5 hours and its weight was measured (Dg). Based on the measured values, the ion exchange capacity and water content were determined by the following equations.

Ion exchange capacity = A × 1000 / D [mmol / g-dry weight]
Moisture content = 100 × (WD) / D [%]
2) Membrane resistance A strip-like sample membrane having a width of 2.0 cm wetted with pure water is pressed against a substrate on which platinum wires having a line width of 0.3 mm are placed at intervals of 0.5 cm. A sample is held in a constant temperature and humidity chamber at 40 ° C. and 90% RH, and an alternating current impedance of 1 kHz between the platinum wires is measured. Five platinum wires are arranged at intervals of 0.5 cm, and the AC resistance is measured by changing the distance between the electrodes to 0.5 to 2.0 cm. Although resistance due to contact occurs between the platinum wire and the film, this effect was excluded by calculating the specific resistance of the film from the interelectrode distance and the resistance gradient. A good linear relationship was obtained between the distance between the electrodes and the measured resistance value, and the film resistance was calculated from the slope and film thickness according to the following equation.

R = 2.0 × L ² × S
R: membrane resistance [Ω · cm ² ]
L: Film thickness [cm]
S: resistance-to-resistance gradient [Ω / cm]
3) Methanol permeability The membrane is sandwiched between fuel cells (electrolyte membrane area 5 cm ² ), a 30% by weight methanol concentration aqueous solution is supplied by a liquid chromatography supply pump, and argon gas is supplied to the opposite side of the membrane at 300 ml / min. To do. The measurement was performed at 25 ° C. in a constant temperature bath. The amount of methanol that permeated the electrolyte membrane was determined by measuring the methanol concentration in the argon gas collected in the gas collection container by gas chromatography.

4) Fuel cell output voltage Carbon black carrying 50% by weight of platinum and a ruthenium alloy catalyst (ruthenium 50 mol%) on a carbon paper having a thickness of 100 μm and a porosity of 80% which has been subjected to water repellent treatment with polytetrafluoroethylene, A mixture of alcohol of perfluorocarbon sulfonic acid and 5% water solution (manufactured by DuPont, trade name Nafion) was applied so that the catalyst was 2 mg / cm ² and dried under reduced pressure at 80 ° C. for 4 hours to form a gas diffusion electrode It was.

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. 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.

5) Logarithm of water / octanol partition coefficient (logPow)
The logarithmic value (logPow) of the water / octanol partition coefficient was measured in accordance with “Measurement of partition coefficient (1-octanol / water) —flask shaking method” of Japanese Industrial Standard 7260-107 (2000).

Examples 1-4
According to the composition table shown in Table 1, various polymerizable monomers were mixed to obtain a polymerizable composition. 400 g of the resulting polymerizable composition was placed in a 500 ml glass container, and the porous membranes (A and B, 20 cm × 20 cm) shown in Table 1 were immersed therein.

Subsequently, these porous membranes were taken out from the polymerizable composition, coated on both sides of the porous membrane using a 100 μm polyester film as a release material, and then heated at 80 ° C. for 5 hours under nitrogen pressure of 3 kg / cm ^2. Polymerized.

  The obtained film-like material 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 obtain a direct liquid fuel cell membrane.

  The cation exchange capacity, water content, membrane resistance, film thickness, methanol permeability, and fuel cell output voltage of these fuel cell membranes were measured. The results are shown in Table 2.

Comparative Examples 1 and 2
The same operation as in Example 1 was carried out except that the polymerizable composition shown in Table 1 and the porous membrane were used to obtain a direct liquid fuel cell membrane.

  The cation exchange capacity, water content, membrane resistance, film thickness, methanol permeability, and fuel cell output voltage of this fuel cell membrane were measured. The results are shown in Table 2.

FIG. 1 is a conceptual diagram showing a basic structure of a polymer electrolyte fuel cell.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1; Battery partition 2; Fuel gas flow hole 3; Oxidant gas flow hole 4; Fuel chamber side gas diffusion electrode 5; Oxidant chamber side gas diffusion electrode 6; Solid polymer electrolyte (cation exchange membrane)
7; Fuel chamber 8; Oxidant chamber

Claims (6)

30 to 90 mol% of a polymerizable monomer having a functional group capable of introducing a cation exchange group, 1 to 60 mol% of a hydrophobic polymerizable monomer having no functional group capable of introducing the cation exchange group, crosslinkability A polymerizable composition containing a polymerizable monomer component consisting of 1 to 40 mol% of a polymerizable monomer and an effective amount of a polymerization initiator component is made of a thermoplastic resin (excluding those crosslinked). in contact with the porous membrane, the polymerizable composition is polymerized and cured after filling the void portion having a said porous membrane, then introducing a cation exchange group introduced functional group of the above cation exchange groups A method for producing a diaphragm for a direct liquid fuel cell. The membrane for a direct liquid fuel cell according to claim 1, wherein the hydrophobic polymerizable monomer having no functional group capable of introducing a cation exchange group has a logarithmic value of water / octanol partition coefficient of 2.0 or more. Method. 2. The method for producing a diaphragm for a direct liquid fuel cell according to claim 1, wherein the hydrophobic polymerizable monomer having no functional group capable of introducing a cation exchange group is vinylcycloalkane. A polymerizable monomer component comprising a cation exchange group-containing polymerizable monomer 30 to 90 mol%, a hydrophobic polymerizable monomer 1 to 60 mol%, and a crosslinkable polymerizable monomer 1 to 40 mol%; and a polymerizable composition comprising an effective amount of a polymerization initiator component, material is in contact with the porous membrane is a thermoplastic resin (excluding those crosslinked), the polymerizable composition of the porous membrane A method for producing a diaphragm for a direct liquid fuel cell, wherein the void portion is filled and then cured by polymerization. The method for producing a diaphragm for a direct liquid fuel cell according to claim 4, wherein the hydrophobic polymerizable monomer has a logarithmic value of water / octanol partition coefficient of 2.0 or more. The method for producing a diaphragm for a direct liquid fuel cell according to claim 4, wherein the hydrophobic polymerizable monomer is vinylcycloalkane.

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