JP2007234302A - Manufacturing method of diaphragm for direct liquid type fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a direct liquid type fuel cell diaphragm having both high proton conductivity and high alcohol impermeability. <P>SOLUTION: A polymerizable composition containing at least (a) a monocyclic aromatic polymerizable monomer prepared by bonding one polymerizable group, one or more methyl groups and one or more hydrogen atoms to a benzene ring and by bonding one of the methyl groups to the polymerizable group at a para position, (b) a cross-linking polymerizable monomer and (c) a polymerization initiator is brought into contact with a porous film to fill the polymerizable composition in void parts of the porous film, thereafter the polymerizable composition is polymerized and hardened, and thereafter a cation exchange group is introduced into the benzene ring originated from the monocyclic aromatic polymerizable monomer, whereby this direct liquid type fuel cell diaphragm is manufactured. For the monocyclic aromatic polymerizable monomer, p-methylstyrene is preferable. <P>COPYRIGHT: (C)2007,JPO&INPIT

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. Then, a 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 oxygen as an oxidant is supplied to the chamber on the side where the other gas diffusion electrode exists. And oxygen-containing gas such as air. 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 fuel are evaluated because they are easy to handle because the fuel is liquid, and the fuel is inexpensive, especially for portable devices. It is expected to be a power source with a small output scale.

  The basic structure of a direct liquid fuel cell is shown in FIG. In the figure, 1a and 1b are battery partition walls formed on both sides of the solid polymer electrolyte membrane 6 with a solid polymer electrolyte membrane 6 used as a diaphragm interposed therebetween, and 2 is a fuel formed on the inner wall of one battery partition wall 1a. The flow holes 3 are oxidant gas flow holes 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 this third copolymer 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 above background, the present invention has low permeability of liquid fuel such as alcohol, particularly methanol permeability, low electrical resistance of the diaphragm, stable high battery output, hardly deformed such as swelling, It aims at providing the manufacturing method of the diaphragm for fuel cells which consists of a cation exchange membrane.

  The present inventors have conducted extensive research in view of the above problems. As a result, when an aromatic polymerizable monomer having a methyl group at the para position with respect to the polymerizable group is used as the main component of the polymerizable composition filled in the voids of the porous membrane, the ortho position or As compared with the case of using an aromatic polymerizable monomer having a methyl group at the meta position, it has been found that the permeability of liquid fuel can be specifically reduced without increasing the membrane resistance, and the present invention is completed. It came to.

Therefore, the present invention
a) one polymerizable group, at least one methyl group, and at least one hydrogen atom bonded to the benzene ring, and one of the methyl groups is para-positioned relative to the polymerizable group A monocyclic aromatic polymerizable monomer formed by bonding 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 voids of the porous film, and then the polymerizable composition is polymerized and cured, and then the monocyclic aroma A method for producing a diaphragm for a direct liquid fuel cell, wherein a cation exchange group is introduced into a benzene ring derived from a group-based polymerizable monomer.

  The present invention also includes the case where the monocyclic aromatic polymerizable monomer is p-methylstyrene.

  According to the method for producing a diaphragm of the present invention, as a polymerizable monomer for introducing a cation exchange group into a polymerizable composition for forming a cation exchange resin, a methyl group at a para position with respect to the polymerizable group. Therefore, the cation exchange resin constituting the obtained diaphragm is moderately increased in hydrophobicity and reduces the permeability of the liquid fuel. Furthermore, the reason is unknown, but since a polymerizable monomer having a methyl group at the para position relative to the polymerizable group is used, a monomer having a methyl group at the ortho position or the meta position is used. Compared to the case, the permeation suppression effect of liquid fuel is high.

  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 using the diaphragm obtained by the manufacturing method of the present invention has a low internal resistance of the cell and suppresses the crossover of liquid fuel such as methanol, so that a high battery output can be obtained.

  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, comprises a) a monocyclic aromatic polymerizable monomer, b) a crosslinkable polymerizable monomer, and c) a polymerization initiator as essential components. To do.

a) Monocyclic aromatic polymerizable monomer The monocyclic aromatic polymerizable monomer has one polymerizable group, at least one methyl group, and at least one hydrogen atom as a benzene ring. Is a compound represented by the following chemical formula (1).

In the chemical formula (1), R ¹ represents an alkyl group having 1 to 5 carbon atoms, a halogen atom, a nitro group, a cyano group, or the like. Examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an iso-propyl group, an n-butyl group, an iso-butyl group, a ter-butyl group, and a pentyl group. Of these alkyl groups, a methyl group is preferred. 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.

n is an integer of 1-4. N is preferably 3 or 4, and n is particularly preferably 4 in that the permeation suppressing effect of the liquid fuel is high and the electric resistance of the obtained diaphragm is low. Moreover, the polymerizable monomer whose n is 4 is a preferable monomer also at the point which is easy to acquire. In the case where R ¹ is an alkyl group, n is preferably 3.

  A is a polymerizable 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 monocyclic aromatic polymerizable monomer represented by the chemical formula (1), at least one hydrogen atom is bonded to the aromatic ring. As will be described later, this hydrogen atom is exchanged for a cation exchange group.

  In the monocyclic aromatic polymerizable monomer represented by the chemical formula (1), at least one of the methyl groups bonded to the benzene ring is bonded to the polymerizable group A in the para position. Yes.

  As is clear from the data of Examples and Comparative Examples described later, a monocyclic aromatic polymerizable monomer in which a polymerizable group A and a methyl group bonded to a benzene ring are in a para-position to each other By using it as a starting material, it is possible to obtain the present diaphragm with high permeation suppression of liquid fuel and low electrical resistance of the obtained diaphragm. When a monocyclic aromatic polymerizable monomer in which the polymerizable group A and the methyl group do not have a para-position is used, the diaphragm is excellent in both suppression of permeation of liquid fuel and electrical resistance of the diaphragm Cannot be obtained.

  Monocyclic aromatic polymerizable monomers include p-methylstyrene, 2,4-dimethylstyrene, 1,2,4-trimethylstyrene, 1,3,4-trimethylstyrene, 2-ethyl-4- Examples include methylstyrene, 2-propyl-4-methylstyrene, 2-butyl-4-methylstyrene, 2-chloro-4-methylstyrene, p-methyl-α-methylstyrene, and the like.

  Among these, p-methylstyrene is particularly preferable in that the permeation suppressing power of the liquid fuel to the obtained diaphragm is high and the electric resistance is low.

  The content of the monocyclic aromatic polymerizable monomer in the polymerizable composition is not particularly limited, but is 10 to 10 of the total amount of polymerizable monomers contained in the polymerizable composition. It is preferable that it is 99 mass%, and it is especially preferable that it is 30-98 mass%. When the content of the monocyclic 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 an extremely 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.

  The content of the crosslinkable polymerizable monomer in the polymerizable composition is not particularly limited, but is 1 to 40% by mass of the total amount of polymerizable monomers contained in the polymerizable composition. It is preferable that it is 2-30 mass% especially. 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 the polymerization of the monocyclic 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 addition, in the polymerizable composition, in addition to the monocyclic aromatic polymerizable monomer in which one of the a) methyl groups is bonded to the polymerizable group in the para position, Another aromatic polymerizable monomer capable of introducing a 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 is preferably 89% by mass or less, and particularly preferably 68% by mass or less, based on the total amount of polymerizable monomers contained in the polymerizable composition.

  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 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% by mass or less, particularly 10% by mass 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 filling amount of the cation exchange resin is lowered. When the pore diameter exceeds 2 μm, the alcohol permeability increases.

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

  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 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 a cation exchange resin described later.

  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, 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.

  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 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. 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 group)
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 benzene ring of the resin filled in the voids of the porous membrane. In addition, this benzene ring is derived from the benzene ring of the monocyclic aromatic polymerizable monomer blended in the polymerizable composition.

  As the cation exchange group introduced into the benzene ring, conventionally known cation exchange groups are 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.

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

  As a method for introducing a phosphonic group into a benzene ring, a film-like polymer having an alkyl halide group is reacted with phosphorus trichloride in the presence of anhydrous aluminum chloride, followed by a hydrolysis reaction in an alkaline aqueous solution. Methods and the like.

  As a method of introducing a carboxylic acid group into the benzene ring, there is a method of halogenation by contacting with a halogen gas in the presence of a catalyst such as iron halide, further reacting with alkyllithium, and then reacting with carbon dioxide. Can be 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 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 3 mmol / g, particularly 0.1 to 2 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, it is insoluble in the fuel liquid, and its electric resistance is usually very small as 0.45 Ω · cm ² or less, more preferably 0.25 Ω · cm ² or less in terms of electric resistance in a 3 mol / L-sulfuric acid aqueous solution. . In addition, the permeability of the fuel liquid is extremely small. For example, when 100% methanol contacts at 25 ° C., the methanol permeability in the diaphragm is usually 1000 g / m ² · hr or less, particularly 10 to 700 g / m ^2. -It is the range of 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 obtain a hydrogen ion type, the cation exchange membrane is immersed in a 1 mol / L-NaCl aqueous solution to obtain 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 one side of the fuel cell (diaphragm area 5 cm ² ) with the diaphragm attached in the center is supplied with an aqueous solution with a methanol concentration of 30% by mass using a liquid chromatograph pump, and the chamber on the opposite side of the diaphragm Argon gas was supplied at 300 ml / min. The measurement was performed in a constant temperature bath at 25 ° C. Argon gas flowing out from the chamber on the opposite side of the diaphragm was introduced into a gas collection container, and the methanol concentration in the argon gas collected in the gas collection container was measured by gas chromatography to determine the amount of methanol that permeated through the diaphragm. .

4) Fuel cell output voltage The catalyst was applied to a 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 was 2 mg / cm ^2, and the pressure was reduced at 80 ° C. for 4 hours A gas diffusion electrode was obtained by drying. The applied catalyst 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). It was prepared by mixing with the one.

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 20 mass% methanol aqueous solution was added to the fuel chamber side, and atmospheric oxygen 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, 2, 3
According to the composition table shown in Table 1, various monomers were mixed to obtain a monomer composition. 400 g of the obtained monomer composition was placed in a 500 ml glass container, 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, and a porosity of 37%) was immersed therein. .

  Subsequently, these porous membranes were taken out from the monomer 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 0.3 MPa. Polymerized.

  The obtained membrane 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.

  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.

Example 4
According to the composition table shown in Table 1, various monomers were mixed to obtain a monomer composition. 400 g of the obtained monomer 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 monomer 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 0.3 MPa. Polymerized. Further, the same operation as in Example 1 was performed to obtain a 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, 2, 3
The same operation as in Example 1 was performed except that the monomer composition and the porous membrane shown in Table 1 were used to obtain a 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.

Comparative Example 4
Using a perfluorocarbon sulfonic acid membrane (commercial product A), cation exchange capacity, water content, membrane resistance, film thickness, methanol permeability, and fuel cell output voltage were measured. These results are shown in Table 2.

It is a conceptual diagram which shows the 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 membrane (cation ion exchange membrane)
7 Fuel chamber 8 Oxidant chamber

Claims (2)

a) one polymerizable group, at least one methyl group, and at least one hydrogen atom bonded to the benzene ring, and one of the methyl groups is para-positioned relative to the polymerizable group A monocyclic aromatic polymerizable monomer formed by bonding 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 voids of the porous film, and then the polymerizable composition is polymerized and cured, and then the monocyclic aroma A method for producing a diaphragm for a direct liquid fuel cell, wherein a cation exchange group is introduced into a benzene ring derived from an aromatic polymerizable monomer. The method for producing a diaphragm for a direct liquid fuel cell according to claim 1, wherein the monocyclic aromatic polymerizable monomer is p-methylstyrene.

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