JP5010857B2 - 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. The diaphragm is formed by filling a void portion of a porous membrane with a cation exchange resin, and has low permeability of liquid fuel such as methanol.

  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.

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

  Among solid polymer fuel cells, direct liquid fuel cells that use direct methanol or the like as a fuel are evaluated as being easy to handle because the fuel is liquid, and the fuel is inexpensive. Expected to be a power source of 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 formed on both sides of the solid polymer electrolyte membrane 6 with the solid polymer electrolyte membrane 6 used 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 liquid fuel 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 produced 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 produce water. At this time, the 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) to obtain electric energy.

  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 electrical resistance, high physical strength, and low permeability for liquid fuel used as fuel. When the permeability of the liquid fuel to the cation exchange membrane is high, the liquid fuel supplied to the fuel chamber diffuses and moves toward the oxidation chamber, and as a result, the battery output decreases.

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 void of a porous membrane made of polyolefin or fluorine resin And a membrane obtained by a method of introducing a cation exchange group into a functional group capable of introducing the cation exchange group of the resin obtained by filling and polymerizing a polymerizable composition comprising a crosslinkable polymerizable monomer. Known (for example, Patent Documents 1 and 2). 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.
JP 2001-135328 A Japanese Patent Laid-Open No. 11-310649

  However, when these cation exchange membranes are directly used as a diaphragm for a liquid fuel cell, it is not possible to completely prevent liquid fuel such as alcohol from permeating through the cation exchange membrane. As a result, liquid fuel is diffused from the fuel chamber side to the oxidant chamber side, and the cell performance is degraded.

  In order to improve this problem, the amount of hydrophilic cation exchange groups introduced is relatively increased by increasing the content of the crosslinkable polymerizable monomer in the polymerizable composition filled in the voids of the porous membrane. The present inventors have studied to reduce it to a low level. According to this method, the hydrophobicity of the resulting cation exchange membrane is increased, and the degree of crosslinking of the membrane is also increased. As a result, a dense ion exchange membrane is obtained, which is effective to some extent for suppressing the permeation of liquid fuel. On the other hand, however, there is a problem that the electric resistance of the cation exchange membrane increases and the battery output decreases, and a fuel cell membrane that is practically satisfactory in this respect has not been obtained.

  In the method for producing a cation exchange membrane used in the fuel cell cited as the prior art, the cation exchange group can be introduced as a monomer component in the polymerizable composition filled in the voids of the porous membrane. In addition to polymerizable monomers and crosslinkable polymerizable monomers having various functional groups, polymerizable monomers having no functional group capable of introducing a cation exchange group such as acrylonitrile, acrolein, methyl vinyl ketone, etc. It has also been shown to be included as a tricopolymerization component. However, any of the polymerizable monomers described as these third copolymerization components is a highly hydrophilic monomer. Therefore, it was recognized that the cation exchange membrane obtained by copolymerizing these third copolymerization components has high hydrophilicity, and thus the permeation suppression effect of liquid fuel such as alcohol having high hydrophilicity has not been improved. That is, the cation exchange membrane in which the third copolymerization component is copolymerized is insufficient in terms of the permeation suppressing effect of liquid fuel such as alcohol when used as a fuel cell membrane.

  In the background described above, the present invention has low permeability of liquid fuel such as alcohol, particularly methanol permeability, appropriate electrical resistance of the diaphragm, stable and high battery output, and hardly undergoes deformation such as swelling. Another object of the present invention is to provide a method for producing a fuel cell membrane comprising a cation exchange membrane.

  The present inventors have conducted extensive research in view of the above problems. As a result, at least one alkyl group having 2 or more carbon atoms and at least one hydrogen atom are bonded to the aromatic ring as the main components of the polymerizable composition filled in the voids of the porous membrane. Compared with the case of using an aromatic polymerizable monomer having one methyl group, the use of an aromatic polymerizable monomer specifically increases the permeability of liquid fuel, particularly methanol. The present inventors have found that it can be reduced and have completed the present invention.

Therefore, the present invention
a) an aromatic polymerizable monomer in which one polymerizable group, at least one alkyl group having 2 or more carbon atoms, and at least one hydrogen atom bonded to an aromatic ring;
b) a crosslinkable polymerizable monomer, and c) a polymerization initiator,
The polymerizable composition containing at least a porous film is brought into contact with the porous film to fill the void in the porous film, and then the polymerizable composition is polymerized and cured, and then the aromatic polymerization is performed. A method for producing a diaphragm for a direct liquid fuel cell, wherein a cation exchange group is introduced into an aromatic ring derived from a functional monomer, wherein the aromatic ring of the aromatic polymerizable monomer is a benzene ring Including cases.

  According to the method for producing a diaphragm of the present invention, at least one alkyl group having 2 or more carbon atoms is used as a polymerizable monomer for introducing a cation exchange group into a polymerizable composition for forming a cation exchange resin. Since the individual polymerizable monomers are blended, the cation exchange resin constituting the obtained diaphragm is appropriately increased in hydrophobicity and effectively reduces the permeability of the liquid fuel.

  In this cation exchange membrane, the hydrophobicity of the membrane is greatly enhanced while maintaining a certain ion exchange capacity and appropriate crosslinking for suppressing deformation such as membrane swelling. As a result, when the cation exchange membrane obtained by this method is used directly as a diaphragm for a liquid fuel cell, the permeability of liquid fuel, particularly methanol, is greatly reduced without excessively increasing the electrical resistance of the membrane. In other words, the diaphragm according to the present invention is a direct liquid fuel cell diaphragm that has been difficult to achieve in the past and has both high liquid fuel impermeability and high proton conductivity.

  The direct liquid fuel cell manufactured by using the diaphragm obtained by the manufacturing method of the present invention has high battery output because the internal resistance of the cell is appropriate and crossover of liquid fuel such as methanol is suppressed. .

  In the method for producing a diaphragm for a direct liquid fuel cell according to the present invention (hereinafter sometimes abbreviated as the present diaphragm), after filling a predetermined polymerizable composition into a void formed in the porous film, The diaphragm is produced by introducing a cation exchange group into a resin obtained by polymerizing and curing the filled polymerizable composition and then polymerizing and curing.

(Polymerizable composition)
The polymerizable composition, which is a starting material for producing the diaphragm, contains a) an aromatic polymerizable monomer, b) a crosslinkable polymerizable monomer, and c) a polymerization initiator as essential components.

a) Aromatic polymerizable monomer The aromatic polymerizable monomer has one polymerizable group, at least one alkyl group having 2 or more carbon atoms, and at least one hydrogen atom as an aromatic ring. Is a compound bound to

  Examples of the aromatic ring include a monocyclic aromatic ring having a benzene skeleton and a polycyclic aromatic ring having a skeleton obtained by condensing a plurality of monocyclic aromatic rings such as naphthalene and anthracene. Among these, a monocyclic aromatic ring is preferable, and a benzene ring is particularly preferable in that it is easily available, has a high permeation suppressing effect on the liquid fuel of the obtained diaphragm, and can keep the electric resistance moderately low. .

  The alkyl group bonded to the aromatic ring preferably has 2 to 15 carbon atoms, and the hydrogen atom of the alkyl group may be substituted with a halogen atom. If the alkyl group has one carbon atom, the liquid fuel permeation suppressing effect is not sufficient. Examples of the alkyl group include ethyl group, n-propyl group, iso-propyl group, n-butyl group, iso-butyl group, tert-butyl group, n-heptyl group, n-hexyl group, n-pentyl group, n- Examples include an octyl group, an n-nonyl group, an n-decanyl group, a stearyl group, and a group in which these hydrogen atoms are substituted with a halogen atom. Among these alkyl groups, an alkyl group having 2 to 15 carbon atoms is preferable in that the permeation suppressing effect of liquid fuel is high, and the electric resistance of the obtained diaphragm is maintained in a normal preferable use range. An alkyl group having 2 to 10 carbon atoms is particularly preferable. Moreover, a linear alkyl group is preferable to a branched alkyl group in that the permeation suppressing effect of the liquid fuel is particularly high. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. Among these halogen atoms, a chlorine atom is preferable in view of availability.

  The maximum number of alkyl groups bonded to the aromatic ring varies depending on the number of rings in the aromatic ring. In any aromatic ring having any number of rings, one polymerizable group and at least one hydrogen atom must be bonded. As will be described later, this hydrogen atom is exchanged for a cation exchange group.

  As the polymerizable group, a hydrocarbon group having 2 to 5 carbon atoms having an unsaturated bond is preferable. Examples include a vinyl group, a propenyl group, a butylene group, and the like. A vinyl group is particularly preferred from the viewpoint of availability.

  In the aromatic polymerizable monomer, it is preferable that at least one of the alkyl groups bonded to the aromatic ring is bonded to the polymerizable group in the para position.

  In addition, if the alkyl group having 2 or more carbon atoms, the polymerizable group, and the hydrogen atom are bonded to the aromatic ring within a range of numbers specified, the effect of the present invention is further added to the remaining bonding site. Other substituents that do not inhibit the binding may be bonded. Examples of such other substituents include halogen, cyano group, and nitro group.

  Monocyclic aromatic polymerizable monomers include p-ethylstyrene, p- (n-propyl) styrene, p- (iso-propyl) styrene, p- (n-butyl) styrene, p- (iso -Butyl) styrene, p- (tert-butyl) styrene, p- (n-heptyl) styrene, p- (n-hexyl) styrene, p- (n-pentyl) styrene, p- (n-octylstyrene), p- (n-nonyl) styrene, 2,4-diethylstyrene, 3,4-diethylstyrene, 2,3,4-triethylstyrene, 2-ethyl-4-methylstyrene, p-ethyl-α-methylstyrene, Examples thereof include p-chloroethylstyrene.

  Among these, p-ethylstyrene, p- (n-propyl) styrene, p- (n-butyl) are high in the permeation suppressing ability of the liquid fuel with respect to the obtained diaphragm and have an electric resistance within an appropriate range. ) Styrene, p- (tert-butyl) styrene, p- (n-heptyl) styrene, p- (n-hexyl) styrene, p- (n-pentyl) styrene, p- (n-octylstyrene) are particularly preferred. .

  The content of the aromatic polymerizable monomer in the polymerizable composition is not particularly limited, but is 10 to 99 mol% of the total amount of polymerizable monomers contained in the polymerizable composition. It is preferable that it is 40 to 98 mol% especially. When the content of the aromatic polymerizable monomer is within this range, the resulting cation exchange resin exhibits the effect of improving the impermeability of the liquid fuel more remarkably.

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. By blending the crosslinkable polymerizable monomer into the polymerizable composition, the resulting cation exchange resin becomes a crosslinkable type. Cross-linked ion exchange resins are essentially solvent insoluble. Therefore, there is no solubility in water or alcohol, swelling is minimized, and a large amount of cation exchange groups can be introduced into the resin. As a result, the diaphragm has a low electrical resistance.

  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. Among these, divinylbenzenes are particularly preferable.

  The content of the crosslinkable polymerizable monomer in the polymerizable composition is not particularly limited, but is 1 to 35 mol% of the total amount of polymerizable monomers contained in the polymerizable composition. It is preferable. By controlling the content of the crosslinkable polymerizable monomer within this range, the resulting cation exchange resin is imparted with sufficient crosslinkability to prevent non-permeability and swelling of the fuel liquid. The In particular, the content of the crosslinkable polymerizable monomer is preferably 2 to 20 mol%. By controlling the content of the crosslinkable polymerizable monomer within this range, the resulting cation exchange resin is further excellent in the effect of preventing liquid fuel impermeability and swelling, and the electrical resistance is particularly low. That is obtained and preferred.

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 aromatic 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 to be used and the kind of the polymerization initiator. Usually, 0.1-20 mass parts is mix | blended with respect to 100 mass parts of the said polymerizable monomer component sum total (When using the other polymerizable monomer mentioned later also including the content). It is preferably 0.5 to 10 parts by mass.

  In the polymerizable composition, a) an aromatic system in which one polymerizable group, at least one alkyl group having 2 or more carbon atoms, and at least one hydrogen atom are bonded to an aromatic ring. In addition to the polymerizable monomer, another aromatic polymerizable monomer capable of introducing a cation exchange group may be contained. Examples of such other aromatic polymerizable monomers include styrene, vinyl xylene, α-methyl styrene, vinyl naphthalene, α-halogenated styrenes, acenaphthylenes, and the like. The content thereof is preferably 89 mol% or less of the total amount of polymerizable monomers contained in the polymerizable composition, and particularly preferably 40 mol% or less.

  In addition to the above-mentioned essential components, the polymerizable composition may have a physical strength such as mechanical strength and a reactivity such as polymerizability, as required, within the limits not contrary to the object of the present invention. Other components may be blended in a small amount. 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.

  When the polymerizable monomer of other components is contained in the polymerizable composition, the content thereof may be 20 mol% or less, particularly 10 mol% or less of the total amount of all polymerizable monomer components. preferable. 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 membrane)
In the production method of the present invention, the polymerizable composition is brought into contact with a porous membrane. Thereby, the polymerizable composition is filled in the voids of the porous film. Thereafter, the polymerizable composition filled in the gap is polymerized and cured.

  As described above, the fuel cell membrane comprising a cation exchange membrane manufactured using a porous membrane as a base material can increase the physical strength without causing an increase in electrical resistance because the porous membrane functions as a reinforcing portion. it can.

  The porous membrane used as a substrate is a porous substrate having voids due to pores or the like inside thereof, and the front and back of the substrate communicate with each other through at least part of the voids through the voids. Any known porous substrate can be used without limitation.

  The average pore diameter of the voids of the porous substrate is preferably 0.01 to 2 μm, particularly preferably 0.015 to 0.4 μm. When the pore is less than 0.01 μm, the electrical resistance of the diaphragm obtained by decreasing the filling amount of the cation exchange resin increases. When the pore diameter exceeds 2 μm, the permeability of liquid fuel such as alcohol increases.

  The porosity (also referred to as porosity) of the porous membrane is preferably 20 to 95%, more preferably 30 to 90%.

In the present invention, the average pore diameter of the porous membrane refers to a value measured by a half dry method in accordance with ASTM-F316-86. Further, the porosity of the porous membrane is calculated by the following equation by measuring the volume (Vcm ³ ) and mass (Ug) of the porous membrane, and setting the density of the material of the porous membrane as X (g / cm ³ ). Value.

Porosity = [(V−U / X) / V] × 100 [%]
In the porous membrane, the air permeability (JIS P-8117) is preferably 1500 seconds or less, and more preferably 1000 seconds or less. By setting the air permeability within this range, the electric resistance of the obtained fuel cell membrane is lowered, and high physical strength is maintained.

  The thickness is preferably 5 to 150 μm, more preferably 10 to 120 μm, and particularly preferably 10 to 70 μm.

  The surface smoothness is preferably 10 μm or less, more preferably 5 μm or less in terms of roughness index. By setting the smoothness within this range, high impermeability to liquid fuel such as alcohol of the obtained fuel cell membrane is achieved.

  The form of the said porous membrane is not specifically limited, The thing of arbitrary forms, such as a porous film, a woven fabric, a nonwoven fabric, paper, an inorganic membrane, is used. Examples of the material for the porous film include thermoplastic resins, thermosetting resins, inorganic substances, and mixtures thereof. However, a thermoplastic resin is preferable from the viewpoint of not only easy production but also high adhesion strength with the above-described cation exchange resin.

  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 Resin, polyimide resin and the like.

  Among these, a polyolefin resin is particularly preferable because it is excellent in mechanical strength, chemical stability, and chemical resistance and has a good affinity with a hydrocarbon ion exchange resin.

  As the polyolefin resin, polyethylene or polypropylene resin is particularly preferable, and polyethylene resin is most preferable.

  Further, a porous film made of polyolefin resin is preferable, and a porous film made of polyethylene resin is particularly preferable in that it has a mean pore size and is easily available and excellent in strength.

  The porous membrane can also be obtained by the method described in JP-A-9-216964, JP-A 2002-338721, and the like. Alternatively, it can also be obtained as a commercial product (for example, Asahi Kasei “Hypore”, Ube Industries “Yupor”, Tonen Tapils “Setera”, Nitto Denko “Exepor”, Mitsui Chemicals “Hylet”, etc.).

(Contact between the polymerizable composition and the porous membrane)
The contact between the polymerizable composition and the porous membrane is not particularly limited as long as the polymerizable composition is brought into contact with the porous membrane by a method that can enter the voids. Examples thereof include a method in which the polymerizable composition is applied to or sprayed on the porous film, or a method in which the porous film is immersed in the polymerizable composition. When the porous film is immersed in and contacted with the polymerizable composition, 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 over ten minutes. It is.

(polymerization)
The polymerizable composition filled in the voids of the porous membrane is then polymerized, whereby the polymerizable composition filled in the voids of the porous membrane becomes a polymerized and cured polymer resin. 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 an organic peroxide as described above as a polymerization initiator, a 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, it is preferable that the porous film filled with the polymerizable composition is covered with a film such as polyester and then polymerized. By covering the porous membrane with a film, excess polymerizable composition is eliminated from the porous membrane, and a thin and uniform fuel cell membrane 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.

(Introduction of cation exchange groups)
A cation exchange group is then introduced into the membrane-like polymer produced by filling the voids of the porous membrane with a resin made of the polymer of the polymerizable composition as described above.

  The cation exchange group is introduced into the aromatic ring of the polymer resin filled in the voids of the porous membrane. This aromatic ring is derived from the aromatic ring of a monocyclic or polycyclic 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. The number of cation exchange groups introduced into the aromatic ring is not particularly limited, and as many cation exchange groups as the number of hydrogen atoms bonded to the aromatic ring are introduced as desired.

  Examples of the method for introducing a sulfonic acid group into an aromatic ring include a method in which a sulfonating agent such as concentrated sulfuric acid, fuming sulfuric acid, sulfur dioxide, chlorosulfonic acid, or the like is reacted with the produced membrane polymer.

  As a method of introducing a phosphone group into an aromatic ring, as an aromatic polymerizable monomer, in addition to the alkyl group having 2 or more carbon atoms, a halogenated alkyl group such as a chloromethyl group or a chloroethyl group is further included. And a method of reacting the obtained film-like material with phosphorus trichloride in the presence of anhydrous aluminum chloride, followed by a hydrolysis reaction in an alkaline aqueous solution.

  As a method of introducing a carboxylic acid group into the aromatic ring, the aromatic ring is halogenated by contacting with a halogen gas in the presence of a catalyst such as iron halide, and further reacted with alkyllithium, and then reacted with carbon dioxide. Methods and the like.

  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 void portion of the porous membrane with the cation exchange resin is washed and cut as necessary, and used as a diaphragm for a direct liquid fuel cell according to a conventional method. Used.

The diaphragm for a direct liquid fuel cell produced by the method of the present invention has a high cation exchange capacity of 0.1 to 6 mmol / g, particularly 0.1 to 5 mmol / g, as measured by a conventional method. ing. Therefore, it has high battery output, fuel liquid permeability, and membrane electric resistance is 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 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 ℃, 0.45Ω · cm ² or less expressed in the electrical resistance by the AC impedance method in a wet state, even 0.25 ohms · cm ² or less and Very small. Moreover, the permeability of the fuel liquid is extremely small. For example, when it is in contact with 30% by mass of methanol at 25 ° C., the permeability of methanol in the diaphragm is usually 1000 g / m ² · hr or less, particularly 10 to 700 g / hr. The range is m ² · hr.

  The fuel cell membrane obtained by the method of the present invention has such a low electrical resistance and a low fuel liquid permeability. Therefore, the fuel supplied to the fuel chamber when used directly as a diaphragm for a liquid fuel cell. It is possible to effectively prevent liquid from passing through the diaphragm and diffusing into the opposite chamber, and a high output battery can be obtained.

  The direct liquid fuel cell employing the diaphragm obtained by the method of the present invention is generally the one having the basic structure shown in FIG. 1, but the direct liquid fuel cell having another known structure. Of course, it can also be applied. 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 cation exchange capacity, water content, membrane resistance, methanol permeability, and fuel cell output voltage of the membrane (cation exchange membrane) were measured to evaluate the characteristics of the fuel cell membrane. These measurement methods will be described below.

1) 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 [%]

2) 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 apart from each other in parallel. 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]

3) Methanol permeability The cation exchange membrane was immersed in a 1 mol / L-HCl aqueous solution for 10 hours or more to obtain a hydrogen ion type, and then dried at room temperature for 24 hours or more. This cation exchange membrane is attached to the center of the fuel cell (diaphragm area 1 cm ² ), an aqueous solution having a methanol concentration of 30% by mass is supplied to one chamber with a liquid chromatograph pump, and argon gas is supplied to the opposite chamber at 300 ml / supplied in min. The measurement was performed in a constant temperature bath at 25 ° C. A certain amount of argon gas flowing out from the chamber on the opposite side of the diaphragm is directly introduced into the gas chromatograph (GC14B manufactured by Shimadzu Corporation) using a gas sampler, the methanol concentration in the argon gas is measured, and the amount of methanol that has permeated through the diaphragm is obtained. It was.

4) Fuel cell output voltage The catalyst was applied to carbon paper having a thickness of 100 μm and a porosity of 80% that had been made water-repellent with polytetrafluoroethylene so that the catalyst would be 4 mg / cm ^2, and the pressure was reduced at 80 ° C. for 4 hours A gas diffusion electrode was obtained by drying. As the catalyst, carbon black carrying 50% by mass of an alloy catalyst of platinum and ruthenium (ruthenium 50 mol%) is used on the fuel chamber side, and carbon black carrying 50% by mass of platinum is used on the oxidant chamber side. The mixture was prepared by mixing 5% perfluorocarbon sulfonic acid dissolved in alcohol and water (manufactured by DuPont, trade name Nafion). The blending mass ratio of the catalyst-supporting carbon black and the perfluorocarbon sulfonic acid was 70:30 on both the fuel chamber side and the oxidant chamber side.

Next, the above-described oxidant chamber gas diffusion electrode is set on one side of the fuel cell diaphragm previously made into a hydrogen ion type, and the fuel chamber gas diffusion electrode is set on the other side. The pressure is 100 ° C. under a pressure of 5 MPa. After hot pressing for 2 seconds, it was left at room temperature for 2 minutes or longer. 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 atmospheric pressure air with a relative humidity of 80% 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.

Example 1
Polymerization was started in a polymerizable monomer composition composed of 90.5 mol% of p- (tert-butyl) styrene and 9.5 mol% of divinylbenzene so that the amount was 5 parts by mass with respect to 100 parts by mass of all monomers. The agent t-butylperoxyethyl hexanoate was added, and a porous film (made of polyethylene having a weight average molecular weight of 250,000, a film thickness of 25 μm, an average pore diameter of 0.03 μm, a porosity of 37%) was immersed therein for 5 minutes.

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

  The obtained film was immersed in a 1: 1 (mass ratio) mixture of 98% concentrated sulfuric acid and chlorosulfonic acid having a purity of 90% or more at 50 ° C. for 60 minutes to chlorosulfonate the benzene ring. It was immersed in a 5 mol / L sodium hydroxide aqueous solution for 15 hours to hydrolyze chlorosulfonic acid groups to sulfonic acid groups, thereby obtaining a fuel cell membrane of the present invention.

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

Examples 2-4
Using the polymerizable composition and porous membrane shown in Table 1, the fuel cell membrane of the present invention was obtained in the same manner as in Example 1. The results of evaluating the characteristics of the obtained fuel cell membrane are shown in Table 2.

Comparative Example 1
In place of p- (tert-butyl) styrene, styrene is used as the polymerizable monomer having no alkyl group, and the blending amount of the crosslinkable monomer in the polymerizable composition is adjusted to 9.5 mol%. A fuel cell membrane was obtained in the same manner as in Example 1. The results of evaluating the characteristics of the obtained fuel cell membrane are shown in Table 2.

Comparative Example 2
Instead of p- (tert-butyl) styrene, methyl styrene (equal mass mixture of p-form and m-form) is used as a polymerizable monomer having a methyl group having 1 carbon, and a polymerizable composition A fuel cell membrane was obtained in the same manner as in Example 1 with the blending amount of the crosslinkable monomer being adjusted to 9.5 mol%. The results of evaluating the characteristics of the obtained fuel cell membrane are shown in Table 2.

It is a conceptual diagram which shows the basic structure of a polymer electrolyte fuel cell.

Explanation of symbols

1a, 1b 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 membrane (cation ion exchange membrane)
7 Fuel chamber 8 Oxidant chamber

Claims (3)

a) one polymerizable group, at least one alkyl group having 2 to 10 carbon atoms, and at least one hydrogen atom bonded to the aromatic ring, and the alkyl group is para-positioned to the polymerizable group An aromatic polymerizable monomer bonded to
b) a crosslinkable polymerizable monomer, and c) a polymerization initiator,
The polymerizable composition containing at least a porous film is brought into contact with the porous film to fill the void in the porous film, and then the polymerizable composition is polymerized and cured, and then the aromatic polymerization is performed. A method for producing a diaphragm for a direct liquid fuel cell, wherein a cation exchange group is introduced into an aromatic ring derived from a functional monomer. The method for producing a diaphragm for a direct liquid fuel cell according to claim 1, wherein the number of carbon atoms of at least one of the alkyl groups bonded to the aromatic polymerizable monomer is 4 to 8. The method for producing a diaphragm for a direct liquid fuel cell according to claim 1 or 2 , wherein the aromatic ring of the aromatic polymerizable monomer is a benzene ring.

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