JP2007149651A - Electrolyte film and method of manufacturing same, and its application - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrolyte film with a low fuel crossover and a small humidity dependency of ionic conductivity, and to provide a film electrode composite and a fuel cell quickly rising from a fuel depletion state to generate by supplying fuel and capable of attaining high output even in a state of high temperature and low humidification. <P>SOLUTION: The electrolyte film 3 contains an acidic group AH with a PKa value between -17.0 and 5.0 and a water alternative group B with a PKb value between -6.0 and 4.0. The manufacturing method for the electrolyte film comprises a process impregnating or filling a material containing the water alternative group B and/or a material containing a water alternative group B precursor and/or a material containing the acidic group AH and/or a material containing an acidic group AH precursor in the electrolyte film comprising the acidic group AH and/or the water alternative group B. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electrolyte membrane, a process for producing the same, a membrane electrode assembly using the same, and a fuel cell.

  A fuel cell is a power generation device with low emissions, high energy efficiency, and low burden on the environment. For this reason, it is in the spotlight again in recent years to the protection of the global environment. Compared to conventional large-scale power generation facilities, this is a power generation device expected in the future as a relatively small-scale distributed power generation facility, and as a power generation device for mobile objects such as automobiles and ships. It is also attracting attention as a power source for small mobile devices, robots, and portable devices, and is expected to be installed in mobile phones and personal computers in place of secondary batteries such as nickel metal hydride batteries and lithium ion batteries.

  In polymer electrolyte fuel cells, in addition to conventional polymer electrolyte fuel cells using hydrogen gas as fuel (hereinafter sometimes referred to as PEFC), fuel such as methanol is directly used. Direct fuel cells to be supplied are also attracting attention. The direct fuel cell has a lower output than the conventional PEFC, but the fuel is liquid and does not use a reformer, so the energy density is high and the usage time of the portable device per filling is long. There is an advantage.

  In a polymer electrolyte fuel cell, an anode electrode and a cathode electrode in which a reaction responsible for power generation occurs, and a polymer electrolyte membrane serving as a proton conductor between the anode and the cathode constitute a membrane electrode assembly (MEA). A cell in which this MEA is sandwiched between separators is configured as a unit. Here, the electrode is composed of an electrode substrate (also referred to as a gas diffusion electrode or a current collector) that promotes gas diffusion and collects (supply) electricity, and an electrode catalyst layer that actually becomes an electrochemical reaction field. ing. For example, in the anode electrode of PEFC, a fuel such as hydrogen gas reacts in the catalyst layer of the anode electrode to generate protons and electrons, and the electrons are conducted to the electrode substrate, and the protons are conducted to the polymer electrolyte membrane. For this reason, the anode electrode is required to have good gas diffusivity, electron conductivity, and proton conductivity. On the other hand, in the cathode electrode, an oxidizing gas such as oxygen or air is reacted with protons conducted from the polymer electrolyte membrane and electrons conducted from the electrode base material in the catalyst layer of the cathode electrode to produce water. For this reason, in the cathode electrode, it is necessary to efficiently discharge the generated water in addition to gas diffusibility, electron conductivity, and proton conductivity.

  Among PEFCs, a direct fuel cell using methanol or the like as a fuel requires performance different from that of a conventional PEFC using hydrogen gas as a fuel. That is, in a direct type fuel cell, a fuel such as a methanol aqueous solution reacts with the catalyst layer of the anode electrode to produce protons, electrons, and carbon dioxide at the anode electrode, and the electrons are conducted to the electrode substrate, and the protons are polymer electrolyte. The carbon dioxide passes through the electrode substrate and is released out of the system. For this reason, in addition to the required characteristics of the anode electrode of the conventional PEFC, fuel permeability such as aqueous methanol solution and carbon dioxide emission are also required. Further, in the cathode electrode of the direct type fuel cell, in addition to the reaction similar to that of the conventional PEFC, fuel such as methanol that has permeated through the electrolyte membrane and oxidizing gas such as oxygen or air are mixed with carbon dioxide in the cathode electrode catalyst layer. Reactions that produce water also occur. For this reason, since generated water becomes more than conventional PEFC, it is necessary to discharge water more efficiently.

  Conventionally, a perfluoro proton conductive polymer membrane represented by “Nafion (registered trademark)” (manufactured by DuPont, trade name) has been used as a polymer electrolyte membrane. However, these perfluoro proton conductive polymer membranes have a problem that the direct fuel cell has a large permeation of fuel such as methanol, and the cell output and energy efficiency are not sufficient. In addition, there is a problem that the ionic conductivity in the low water content state is insufficient. That is, since proton conduction is conducted through water in the cluster channel, the ionic conductivity largely depends on the moisture content of the membrane due to humidity. Furthermore, the perfluoro proton conductive polymer is very expensive because it uses fluorine.

  Non-perfluoro proton conductive polymer film different from the conventional perfluoro proton conductive polymer film, an inorganic component having an organosiloxane skeleton and a metal element and / or metalloid element whose PKa is 3 or less as an acidic oxide A proton conductor containing a polymer (Patent Document 1), a proton conductive material containing a polymer having a mesogenic group and an acidic group having a PKa of 1.5 or less (Patent Document 2), and conventional techniques described in these documents It is done.

  In Patent Document 1, a functional group having a PKa of 3 or less is essential, but there is no description of its definition, measurement or calculation method, and a fuel cell that can withstand practical use in terms of the balance of conductivity and strength of the proton conductor obtained. Could not be produced.

Even in Patent Document 2, as in Patent Document 1, there is no description of definition, measurement or calculation method of PKa, and the PKa value of the polymer mentioned in the examples is not clear. In addition, the acidic group contained was a proton donating group having a PKa of 1.5 or less, and it was estimated that proton conduction would decrease under a low water content, and a fuel cell that could withstand practical use could not be produced.
JP 2002-245846 A JP 2004-323805 A

  The present invention provides an electrolyte membrane having a low fuel crossover and a small dependency of ion conductivity on humidity in view of the background of the prior art, and further, rising from the fuel depleted state until power is generated by supplying fuel. In addition, the present invention intends to provide a membrane electrode assembly and a fuel cell that can achieve high output even under high temperature and low humidity conditions.

  The present invention employs the following means in order to solve such problems. That is, the electrolyte membrane of the present invention includes an acidic group AH having a PKa value defined by the formula S1 of −17.0 to 5.0 and a PKb value defined by the formula S2 of −6.0 to 4 It is characterized by containing a water substitution group B of 0.0 or less.

(AH: acidic group, B: water substitute group, PKa and PKb: logarithm of equilibrium constant, []: concentration)
In addition, the membrane electrode assembly and the fuel cell of the present invention are configured using such an electrolyte membrane.

  According to the present invention, it is possible to provide an electrolyte membrane having a low fuel crossover and a small humidity dependency of ionic conductivity, and a high-power fuel cell is provided by using a membrane electrode assembly made of such an electrolyte membrane. It becomes possible.

  Hereinafter, preferred embodiments of the present invention will be described.

  The electrolyte membrane of the present invention includes an acidic group AH having a PKa value defined by the formula S1 of −17.0 to 5.0 and a PKb value defined by the formula S2 of −6.0 to 4.0. It is necessary to contain the following water substitute group B.

(AH: acidic group, B: water substitute group, PKa and PKb: logarithm of equilibrium constant, []: concentration)
The acidic group AH having a PKa value of −17.0 or more and 5.0 or less is essential as a proton donating group, and the water substitute group B having a PKb value of −6.0 or more and 4.0 or less is a water-containing group even in a low water content state. Essential for conducting protons through the alternative group B. Furthermore, the water substitution group B is present in the electrolyte membrane, so that the water content can be reduced and the fuel crossover is reduced.

  When the PKa value is −17.0 or more and 5 or less, the proton conductivity is good. The PKa value is more preferably from −17.0 to 0.0.

  If the PKb value is −6.0 or more, protons are easily released as much as water, and if the PKb value is 4.0 or less, protons are easily received as much as water. The PKb value is more preferably −5.0 or more and 3.0 or less.

  The PKa value of the present invention can be measured by the following method.

In the present invention, the PKa value is defined by the S1 expression. However, since pH = −log [H ⁺ ], the S1 expression can be rewritten as pKa = −log ([A ⁻ ] / [AH]) + pH. . From this equation, the pH in the state of −log ([A ⁻ ] / [AH]) = 0, that is, [A ⁻ ] / [AH] = 1 is pKa.

As a specific measuring method example, an aqueous solution of the electrolyte membrane material containing an acidic group AH, by adding an alkali such as NaOH aqueous solution having a predetermined concentration, by conventional known neutralization titration, performed pH measurements, [A ^- ] = [AH], that is, the pH when neutralization of 50% proceeds is defined as the pKa value. The pH at which 50% neutralization has progressed is the value when the slope of the neutralization titration curve is minimized.

Similarly, for the PKb value, the equation S2 can be rewritten as pKb = −log ([B] / [BH ⁺ ]) + pH, and an acid such as HCl is added to the aqueous solution of the electrolyte membrane material containing the water substitute group B. Then, generally known neutralization titration is carried out, and the pH when 50% neutralization progresses, that is, when the slope of the neutralization titration curve is minimized is defined as the pKb value.

  In the measuring method of pKa value and pKb value, the amount of electrolyte membrane powder dispersed, the type of acid and alkali used for titration, concentration, pH measurement, titration device, instrument, etc. are determined experimentally as appropriate, and are generally known. You can use the method.

  In addition, when the raw material of the electrolyte membrane containing the acidic group AH and / or this precursor or the water substitute group B and / or this precursor is used in advance, Pliego, JR, Jr .; Riveros, JM Phys. Chem. Chem. Phys. 2002, 4, 1622. and Iwanami Lecture Modern Chemistry 9 Acid-base and redox (Iwanami Shoten), Chemical Handbook (Basic) Maruzen The raw material to be used can be selected using the pKb value.

  In addition, when measuring the pKa value and pKb value of an electrolyte membrane containing an acidic group AH and a water substitution group B, the electrolyte membrane is pulverized with a freeze pulverizer or the like, and an electrolyte powder of 500 nm or less is added to a predetermined amount of water. A dispersed dispersion can be prepared and used as a sample for the neutralization titration.

As the acidic group AH having a PKa value of −17.0 or more and 5.0 or less in the present invention, one having proton exchange ability is preferable. Examples of such a functional group, a sulfonic acid group (-SO ₂ (OH)), a sulfuric acid group (-OSO ₂ (OH)), a sulfonimide group (-SO ₂ NHSO ₂ R (R represents an organic group.) ), A phosphonic acid group (—PO (OH) ₂ ), a phosphoric acid group (—OPO (OH) ₂ ), a carboxylic acid group (—CO (OH) 2), and salts thereof are preferred. Can be adopted. These acidic groups can be contained in two or more types, and may be preferable by combining them. The combination is appropriately determined depending on the structure of the polymer. Among them, it is more preferable to have at least one of a sulfonic acid group, a sulfonimide group, and a sulfuric acid group from the viewpoint of high proton conductivity, and most preferable to have at least a sulfonic acid group from the viewpoint of hydrolysis resistance.

  When the electrolyte membrane of the present invention has a sulfonic acid group, the sulfonic acid group density is preferably 0.1 to 5.0 mmol / g, more preferably 0.5 to 0.5 from the viewpoint of proton conductivity and fuel crossover suppression. 3.5 mmol / g, more preferably 1.0 to 3.5 mmol / g. When the sulfonic acid group density is 0.1 mmol / g or more, conductivity, that is, the output performance of the fuel cell can be maintained, and when it is 5.0 mmol / g or less, it is used as an electrolyte membrane for a fuel cell. In this case, sufficient fuel barrier properties and mechanical strength when containing water can be obtained.

  Here, the sulfonic acid group density is the molar amount of the sulfonic acid group introduced per unit dry weight of the electrolyte membrane, and the larger the value, the higher the degree of sulfonation. The sulfonic acid group density can be measured by elemental analysis, neutralization titration or nuclear magnetic resonance spectroscopy. Elemental analysis is preferable from the viewpoint of ease of measurement of sulfonic acid group density and accuracy, and analysis is usually performed by this method. However, the neutralization titration method is used when it is difficult to accurately calculate the sulfonic acid group density by the elemental analysis method such as when a sulfur source is included in addition to the sulfonic acid group. Furthermore, when it is difficult to determine the sulfonic acid group density by these methods, it is possible to use a nuclear magnetic resonance spectrum method.

Examples of the water substitution group B having a PKb value of −6.0 or more and 4.0 or less in the present invention include —OH, —O—Si (OH) ₃ , —COOH, —Ar ₁ —NH ₂ , — (NO _{2). 2} ) Ar ₂ —NH ₂ , —SO ₂ —NH ₂ , —CO—NH ₂ (Ar ₁ , Ar ₂ represents an arylene group) is preferable, and protons are transferred. Select from -OH, -O-Si (OH) ₃ , -Ph-NH ₂ ,-(NO ₂ ) ₂ PhNH ₂ , -CO-NH _{2 because the} capacity is closer to water (PKb = -1.74) More preferably, it is composed of one or more kinds.

  Specific examples having a water substitute group include one or more polymers, copolymers, and oligomers selected from vinyl alcohol, vinylaniline, tetraethoxysilane, tetramethoxysilane, acrylamide, carboxymethylcellulose hydroxypropylcellulose, and the like. Alternatively, condensates and the like can be mentioned, but there are many compounds other than the examples given here, and there is no particular limitation as long as the PKb value is within the scope of the present invention.

  The acidic group AH and the water substitute group B in the present invention may exist in the electrolyte membrane as a functional group of the polymer, or may exist as an additive. Moreover, the polymer which has both group of acidic group AH and water alternative group B, or the composite of the polymer which has separately may be sufficient. In particular, an electrolyte membrane or porous membrane having an acidic group AH is impregnated or filled with a monomer or compound having a water substitute group B, and these are polymerized or reacted to form an electrolyte membrane or porous membrane having an acidic group AH. It is preferably immobilized on a membrane. Conversely, in an electrolyte membrane having a water substitute group B by impregnating or filling a monomer or compound having an acidic group AH into an electrolyte membrane or porous membrane having a water substitute group B, and polymerizing or reacting them. Or may be immobilized on a porous membrane.

  In the present invention, the polymer for the electrolyte membrane having an acidic group AH is preferably a polymer excellent in hydrolysis resistance, fuel resistance, and heat resistance when it is assumed that the fuel cell is operated at a high temperature.

  Specific examples thereof include acidic group-containing polyphenylene oxide, acidic group-containing polyether ketone, acidic group-containing polyether ether ketone, acidic group-containing polyether sulfone, acidic group-containing polyether ether sulfone, acidic group-containing polyether phosphine oxide, Acid group-containing polyether ether phosphine oxide, acid group-containing polyphenylene sulfide, acid group-containing polyamide, acid group-containing polyimide, acid group-containing polyether imide, acid group-containing polyimidazole, acid group-containing polyoxazole, acid group-containing polyphenylene, etc. And an aromatic hydrocarbon polymer having an acidic group. Here, the acidic group is as described above.

  The method for synthesizing these polymers is not particularly limited as long as the above properties and requirements can be satisfied. For example, an acidic group or a derivative thereof may be introduced into a polymer obtained by polymerization, and an acidic group or a derivative thereof may be introduced into a monomer. After the introduction, the monomer may be polymerized.

  From the viewpoint of reducing fuel crossover, the electrolyte membrane is a component derived from 9,9-bis (4-hydroxyphenyl) fluorene, a component derived from phenolphthalein, and a component derived from 4,4′-dihydroxytetraphenylmethane. It is preferable to contain at least one selected from the group consisting of a polyetheretherketone skeleton.

  When the polymer electrolyte membranes of the present invention and they have a non-crosslinked structure, the weight average molecular weight by GPC method is preferably 10,000 to 5,000,000, more preferably 30,000 to 1,000,000. By setting the weight average molecular weight to 10,000 or more, it is possible to obtain mechanical strength that can be practically used. On the other hand, by setting it to 5 million or less, sufficient solubility can be obtained, and it is possible to prevent the solution viscosity from becoming too high and maintain good processability.

  As an example of the present invention, an electrolyte membrane or porous membrane having an acidic group AH is impregnated or filled with a monomer or compound having a water substitute group B, and these have an acidic group AH by polymerization or reaction. An embodiment in the case of immobilization in an electrolyte membrane or a porous membrane will be described.

First, an electrolyte membrane and a porous membrane having an acidic group AH will be described. As a method for converting a polymer having, for example, a sulfonic acid group into an acidic group AH into a membrane, -SO ₃ M type (M is a metal) A method of forming a film of the polymer from a solution state, then heat-treating it at a high temperature, and substituting protons to form a film. The metal M may be any salt as long as it can form a salt with sulfonic acid, but Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Zr, Mo, W, and the like are preferable. Among these, Li, Na, K, Ca, Sr, and Ba are more preferable, and Li, Na, and K are more preferable.

The temperature of the heat treatment is preferably 200 to 500 ° C., more preferably 250 to 400 ° C., and further preferably 300 to 350 ° C. in terms of fuel cutoff, and the heat treatment time includes proton conductivity and productivity. Is preferably 1 minute to 24 hours, more preferably 3 minutes to 1 hour, and even more preferably 5 minutes to 30 minutes.

As a method for forming a film of —SO ₃ M type polymer from a solution state, for example, after pulverizing —SO ₃ M type polymer is immersed in an aqueous solution of M salt or M hydroxide and thoroughly washed with water Illustrates a method of drying, then dissolving in an aprotic polar solvent, etc. to prepare a solution, applying the solution on a glass plate or film by an appropriate coating method, removing the solvent, and acid treatment be able to.

  As the coating method, methods such as spray coating, brush coating, dip coating, die coating, curtain coating, flow coating, spin coating, and screen printing can be applied.

  The solvent used for film formation may be any solvent that dissolves the polymer compound and can be removed thereafter. For example, N, N-dimethylacetamide, N, N-dimethylformamide, N-methyl-2-pyrrolidone, Aprotic polar solvents such as dimethyl sulfoxide, sulfolane, 1,3-dimethyl-2-imidazolidinone and hexamethylphosphontriamide, ester solvents such as γ-butyrolactone and butyl acetate, carbonates such as ethylene carbonate and propylene carbonate Solvents, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, alkylene glycol monoalkyl ethers such as propylene glycol monoethyl ether, or alcohols such as isopropanol Lumpur solvent is preferably used.

  As the thickness of the electrolyte membrane of the present invention, a membrane having a thickness of 3 to 2000 μm is usually preferably used. A thickness of more than 3 μm is preferable to obtain a membrane strength that can withstand practical use, and a thickness of less than 2000 μm is preferable in order to reduce membrane resistance, that is, improve power generation performance. A more preferable range of the film thickness is 5 to 1000 μm, and a more preferable range is 10 to 500 μm.

  The film thickness can be controlled by various methods. For example, when forming a film by the solvent casting method, it can be controlled by the solution concentration or the coating thickness on the substrate. For example, when forming the film by the cast polymerization method, it is prepared by the spacer thickness between the plates. You can also.

  In addition, an additive such as a plasticizer, a stabilizer, or a mold release agent used for a general polymer compound can be added to the electrolyte membrane of the present invention within a range not contrary to the object of the present invention.

  In the electrolyte membrane of the present invention, the polymer structure can be cross-linked by means such as irradiation with radiation as necessary. By crosslinking, an effect of further suppressing fuel crossover and swelling with respect to the fuel can be expected, and mechanical strength is improved, which may be more preferable. Examples of radiation irradiation include electron beam irradiation and γ-ray irradiation.

  The electrolyte membrane having an acidic group AH may be a porous membrane. The porous membrane preferably has an acidic group AH, a porosity of 5 to 80% by volume, and an average pore diameter of less than 50 nm from the viewpoint of fuel cutoff. The polymer constituting the porous body may be a thermosetting resin, a crystalline or amorphous thermoplastic resin, or may contain an inorganic substance, an inorganic oxide, an organic-inorganic composite, or the like. Although what is good is used, what is comprised so that the space | gap can be formed and the acidic group AH can exist in the inside of a space | gap is used.

  Therefore, at least one monomer constituting the polymer preferably has an acidic group AH or can be introduced with an acidic group AH by post-treatment. Here, “introduction” means a state where an acidic group AH is chemically bonded to the polymer itself, a state where a substance having an acidic group AH is strongly adsorbed on the polymer surface, or a substance having an acidic group AH. It means that the acidic group AH is not easily detached by physical means such as washing as in the case where the acid group A is removed.

  In addition, the repeating unit having the acidic group AH and the repeating unit not having the acidic group AH may coexist alternately, and the repeating continuity of the repeating unit having the acidic group AH is appropriately divided to such an extent that the proton conduction is not impaired. preferable. By doing so, the portion of the repeating unit having the acidic group AH can be prevented from containing excessive water or the like, that is, the fuel crossover can be kept low. In addition, the water resistance of the electrolyte membrane can be improved, and cracks can be prevented from occurring or collapsing.

  That is, a copolymer of a monomer having an acidic group AH or capable of being introduced and a monomer other than that is preferable. Furthermore, from the balance of fuel crossover and proton conductivity, it is preferable that units having acidic group AH and units not so are connected alternately, that is, there are many portions of alternating polymerization.

  As a means for realizing this idea, polymerization of a vinyl monomer can be mentioned. In particular, a copolymer having many repeating units of alternating copolymerization can be obtained by copolymerizing a vinyl monomer having a positive e value and a negative one. The e value here represents the vinyl state of the monomer and the charged state of the radical end, and is the e value of the Qe concept described in detail in “POLYMER HANDBOOK” (J. BRANDRUP et al.) And the like.

  Specific examples of the vinyl monomer include acrylonitrile, methacrylonitrile, styrene, α-methylstyrene, p-methylstyrene, o-ethylstyrene, m-ethylstyrene, p-ethylstyrene, p-tert-butylstyrene. , Chlorostyrene, 1,1-diphenylethylene, vinylnaphthalene, vinylbiphenyl, indene, acenaphthylene, and other aromatic vinyl monomers, methyl (meth) acrylate, cyclohexyl (meth) acrylate, isobornyl (meth) acrylate, adamantyl (meta ) Acrylate, phenyl (meth) acrylate, benzyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, lauric (Meth) acrylic monomers such as (meth) acrylate, stearyl (meth) acrylate, isooctyl (meth) acrylate, n-octyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, N-methylmaleimide, Nn-butylmaleimide, N-phenylmaleimide, N-o-methylphenylmaleimide maleimide, Nm-methylphenylmaleimide, Np-methylphenylmaleimide, N-o-hydroxyphenylmaleimide, Nm-hydroxyphenylmaleimide, Np-hydroxyphenylmaleimide, N-o-methoxyphenylmaleimide, Nm-methoxyphenylmaleimide, Np-methoxyphenylmaleimide, N-o-chlorophenylmaleimide, Nm - Lolophenylmaleimide, Np-chlorophenylmaleimide, N-o-carboxyphenylmaleimide, Nm-carboxyphenylmaleimide, Np-carboxyphenylmaleimide, N-o-nitrophenylmaleimide, Nm-nitrophenylmaleimide N-p-nitrophenylmaleimide, N-ethylmaleimide, N-isopropylmaleimide, N-isobutylmaleimide, N-tert-butylmaleimide, N-cyclohexylmaleimide, N-benzylmaleimide, maleic anhydride, acrylic acid, methacrylic acid , Crotonic acid, cinnamic acid, maleic acid, fumaric acid, citraconic acid, mesaconic acid, itaconic acid, methallylsulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, sulfomethylstyrene, p-styrene Sulfonic acid, sodium p-styrenesulfonate, potassium p-styrenesulfonate, vinylbenzoic acid, sodium vinylbenzoate, vinylbenzoic acid potassium salt, vinyl acetate, vinyl propionate, vinylsulfonic acid, vinylsulfuric acid, 2,2 , 2-trifluoroethyl (meth) acrylate, 2,2,3,3-tetrafluoropropyl (meth) acrylate, 1H, 1H, 5H-octafluoropentyl (meth) acrylate, 1H, 1H, 2H, 2H-hepta Examples thereof include fluorine-containing monomers such as decafluorodecyl (meth) acrylate.

  Of these, aromatic vinyl monomers such as styrene, α-methylstyrene, vinyl naphthalene, vinyl biphenyl, indene, and acenaphthylene are preferably used from the viewpoint of easy introduction of the acidic group AH and polymerization workability.

  In addition, as a combination, when an aromatic vinyl monomer such as styrene or α-methylstyrene having a negative e value is selected, a vinyl unit having a positive e value and difficult to introduce the acidic group AH for the reason described above. From the viewpoint of fuel crossover suppression effect, acrylonitrile, methacrylonitrile, N-phenylmaleimide, N-isopropylmaleimide, N-cyclohexylmaleimide, N-benzylmaleimide, 2,2,2-trifluoroethyl (Meth) acrylate, 2,2,3,3-tetrafluoropropyl (meth) acrylate, 1H, 1H, 5H-octafluoropentyl (meth) acrylate, 1H, 1H, 2H, 2H-heptadecafluorodecyl (meth) Fluorine-containing monomers such as acrylate are preferred.

  Moreover, it is more preferable to have a crosslinked structure. By having a cross-linked structure, it is possible to suppress the spread between polymer chains with respect to moisture and fuel intrusion. Therefore, an excessive water content with respect to proton conduction can be suppressed to a low level, and swelling and collapse of the fuel can be suppressed. As a result, fuel crossover can be reduced. Further, since the polymer chain can be constrained, heat resistance, rigidity, chemical resistance and the like can be imparted. Further, when the acidic group AH is introduced after the polymerization, the acidic group AH can be efficiently and selectively introduced into the inner wall portion of the void. The crosslinking here may be chemical crosslinking or physical crosslinking. This cross-linked structure can be formed by, for example, copolymerization of polyfunctional monomers or irradiation with an electron beam or γ-ray. In particular, cross-linking with a polyfunctional monomer is preferable from an economical viewpoint.

  Specific examples of the polyfunctional monomer employed for forming the crosslinked structure include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, glycerol (di / tri) ( (Meth) acrylate, trimethylolpropane (di / tri) (meth) acrylate, pentaerythritol (di / tri / tetra) (meth) acrylate, dipentaerythritol (di / tri / tetra / penta / hexa) (meth) acrylate, Di-, tri-, tetra-, penta-, hexa- (meth) acrylates of polyhydric alcohols such as di (meth) acrylic acid biphenol, bisphenoxyethanol (meth) fluorene acrylate, polyethylene glycol di (meth) acrylate (Preferably Average molecular weight of polyethylene glycol moiety: about 400 to 1000), methoxypolyethylene glycol mono (meth) acrylate, di (meth) acrylate of bisphenol A ethylene oxide 30 mol adduct, di (meth) acrylate of glycerin ethylene oxide adduct, glycerin Tri (meth) acrylate of ethylene oxide adduct, di (meth) acrylate of trimethylolpropane ethylene oxide adduct, tri (meth) acrylate of trimethylolpropane ethylene oxide adduct, di (meth) acrylate of sorbitol ethylene oxide adduct , Di (meth) acrylate of sorbitol ethylene oxide adduct, tri (meth) acrylate of sorbitol ethylene oxide adduct, sorbitol ether Poly (oxy) polyethers such as tetra (meth) acrylate of a lenoxide adduct, penta (meth) acrylate of a sorbitol ethylene oxide adduct and hexa (meth) acrylate of a sorbitol ethylene oxide adduct, o-divinylbenzene, m -Aromatic polyfunctional monomers such as divinylbenzene, p-divinylbenzene, divinylbiphenyl, divinylnaphthalene, esters such as di (meth) acrylate, di (meth) acrylate diallyl ester, divinyl adipate, diethylene glycol Diallyl compounds such as bisallyl carbonate and diallyl phthalate, dienes such as butadiene, hexadiene, pentadiene, 1,7-octadiene, and dichlorophosphazene as raw materials. Examples thereof include a monomer having an introduced phosphazene skeleton, a polyfunctional monomer having a heteroatom cyclic skeleton such as triallyl diisocyanurate, bismaleimide, and methylene bisacrylamide.

  Of these, aromatic polyfunctional monomers such as divinylbenzene, ethylene glycol di (meth) acrylate, bisphenoxyethanol (meth) full orange, from the viewpoint of mechanical strength and chemical resistance when introducing the acidic group AH. Particularly preferred are di-, tri-, tetra-, penta- and hexa- (meth) acrylates of polyhydric alcohols such as acrylates.

  The molecular weight of the copolymer obtained from the above monomers is preferably 4000 or more in terms of weight average molecular weight from the viewpoint of maintaining the form. Moreover, since a crosslinked structure may be sufficient, there is no restriction | limiting in particular in an upper limit.

  Moreover, the polyfunctional monomer used for formation of a crosslinked structure may be used individually by 1 type, and may use 2 or more types together.

  In the porous film having a crosslinked structure, an acidic group AH is present inside the void. The interior refers to the inner surface of the void and the void portion itself. Preferably, the acidic group AH is present on the inner surface of the void. The acidic group AH may be present in a portion other than the inside of the void. The presence of the acidic group AH means that the acidic group AH is chemically bonded to the polymer itself, a state where a substance having the acidic group AH is strongly adsorbed on the polymer surface, or the acidic group AH. It means a state in which the substance has been held in the voids, and the acidic group AH is not easily detached from the voids by physical means such as washing.

  In introducing the acidic group AH into the porous film having the crosslinked structure, the monomer before polymerization may have the acidic group AH in advance, but the acidic group AH may be introduced after the polymerization. In view of the wide selectivity of raw materials and the ease of monomer preparation, it is preferable to introduce an acidic group AH after polymerization.

  That is, after obtaining a film-like polymer from a monomer composition containing a monomer capable of introducing an acidic group AH and a pore opening agent, or a polymer capable of introducing an acidic group AH and a pore opening agent After the film formation from the polymer composition containing, the step of removing the pore-opening agent from the film and the step of introducing the acidic group AH into the polymer are included.

  As the monomer capable of introducing the acidic group AH, as described above, an aromatic vinyl monomer such as styrene or α-methylstyrene having a negative e value among vinyl monomers can be employed. As polymerization of the above-mentioned vinyl monomer containing these, for example, radical polymerization is preferable from the viewpoint of workability. Examples of the radical generating initiator include various peroxide compounds, azo compounds, peroxides, cerium ammonium salts and the like.

  Specific examples thereof include 2,2′-azobisisobutyronitrile, 1,1′-azobis (cyclohexane-1-carbonitrile), 2,2′-azobis (4-methoxy-2,4-dimethylvalero). Nitrile), 2,2′-azobis (2-cyclopropylpropionitrile), 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2′-azobis (2-methylbutyronitrile), Azonitrile compounds such as 1-[(1-cyano-1-methylethyl) azo] formamide, 2-phenylazo-4-methoxy-2,4-dimethylvaleronitrile, 2,2′-azobis (2-methyl-N -Azoamidine compounds such as phenylpropionamidine) dibasic acid salt, 2,2'-azobis [2- (5-methyl-2-imidazolin-2-yl) propane] disalt Cyclic azoamidine compounds such as basic acid salts, azoamide compounds such as 2,2′-azobis {2-methyl-N- [1,1-bis (hydroxymethyl) -2-hydroxyethyl] propionamide}, 2,2 ′ -Alkylazo compounds such as azobis (2,4,4-trimethylpentane), potassium persulfate, ammonium persulfate, hydrogen peroxide, peroxides such as benzoyl peroxide, ceric ammonium sulfate, ceric ammonium nitrate, etc. Examples include cerium ammonium salts.

  In addition, polymerization by a photoinitiator using radiation, electron beam, ultraviolet ray, or the like can also be used. Photoinitiators include carbonyl compounds, peroxides, azo compounds, sulfur compounds, halogen compounds and metal salts.

  Moreover, when a polyfunctional monomer is included, shaping | molding and film formation by cast polymerization using a heat | fever and light are preferable. Cast polymerization is a mixture of various monomers, pore-opening agents, initiators, etc., injected between two plates, sheets, and films set to a predetermined clearance with gaskets and spacers. The polymerization is carried out by applying energy such as single wafer type or continuous type.

  For example, about 0.01 to 2 parts by weight of a photoinitiator represented by “Darocur (registered trademark)”, “Irgacure (registered trademark)” (manufactured by CIBA) or the like was added to the monomer composition to be used. The composition solution is injected between two sheets of quartz glass, polyethylene, polypropylene, or amorphous polyolefin, sealed, and irradiated with an ultraviolet lamp at an illuminance of about 0.01 to 100 mW / cm2, 0.1 Polymerization can be carried out by light irradiation for about 2 to 1 hour.

  In the case where proton conductivity is given priority as a characteristic required for the polymer, it is also preferable to introduce the acidic group AH into the polymer. For this purpose, the acidic group AH is introduced into the monomer before polymerization in advance. It is effective to carry out the polymerization after adding a pore-opening agent that assists. The pore opening agent need not itself have the ability to introduce the acidic group AH directly. That is, the penetration of a substance capable of introducing an acidic group AH into the polymer is replaced with a substance capable of introducing the acidic group AH by itself, decomposition, reaction, evaporation, sublimation, or outflow, or a solvent containing the same. By doing so, at least a part of the pore-opening agent is removed, and the acidic group AH is easily introduced not only into the surface layer of the polymer but also into the portion where the acidic group AH can be introduced inside the polymer.

  The pore-opening agent occupies a part of the monomer composition or polymer composition during polymerization or film formation, and removes this after polymerization or film formation to form voids in the porous body. Is.

  The types of pore-opening agents include compatibility with polymer materials, chemicals and solvents used for extraction and decomposition, and organic compounds by removing pore-opening agents such as heating, solvent immersion, light, electron beam, and radiation treatment, It can be suitably selected from solvents, soluble polymers, salts, metals and the like. The pore-opening agent may be in the form of a liquid or a powder, and a method that positively leaves an oligomer composed of the monomer used, an unreacted monomer or a by-product as a pore-opening agent. It may be taken.

  Moreover, it is preferable to select a polymer that does not adversely affect the electrolyte membrane even if a part of the pore-opening agent remains in the polymer after introduction of the acidic group AH or even if a product generated by the reaction remains.

  Moreover, when mix | blending a pore opening agent before superposition | polymerization, the pore opening agent whose boiling point and decomposition temperature are higher than polymerization temperature is preferable.

  Specific examples of the pore opening agent include ethylene carbonate, propylene carbonate, methyl cellosolve, diglyme, toluene, xylene, trimethylbenzene, γ-butyrolactone, dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone and 1,4-dioxane. , Carbon tetrachloride, dichloromethane, nitromethane, nitroethane, acetic acid, acetic anhydride, dioctyl phthalate, di-n-octyl phthalate, trioctyl phosphate, decalin, decane, hexadecane, and the like. Alternatively, two or more types may be used in combination.

  Further, the amount of the pore-opening agent may be appropriately set depending on the combination of the pore-opening agent and the monomer to be used, the desired porosity, and the pore diameter, but 1 to 80% by weight in the total composition including the pore-opening agent. It is preferable to add, More preferably, it is 5 to 50 weight%, More preferably, it is 10 to 30 weight%. If it is 1% by weight or more, the acidic group AH is easily introduced into the polymer, and the proton conductivity is improved. Moreover, if it is 80 weight% or less, the low melting point water content will decrease and the amount of fuel permeation will become small, which is preferable.

  After obtaining a film-like polymer or after forming a film from the polymer composition, the pore-opening agent is removed from the film. This is because of void formation.

  As a means for removing the pore opening agent, for example, the film may be immersed in a solvent capable of removing the pore opening agent. The solvent capable of removing the pore-opening agent is appropriately selected from water and organic solvents. Examples of organic solvents include halogenated hydrocarbons such as chloroform, 1,2-dichloroethane, dichloromethane and perchloroethylene, nitrated hydrocarbons such as nitromethane and nitroethane, alcohols such as methanol and ethanol, and aromatics such as toluene and benzene. Aliphatic hydrocarbons such as aromatic hydrocarbons, hexane, heptane and decane, esters such as ethyl acetate, butyl acetate and ethyl lactate, ethers such as diethyl ether, tetrahydrofuran and 1,4-dioxane, nitriles such as acetonitrile, etc. Is preferred. Moreover, one of these may be used alone, or two or more may be used in combination.

  After removing the pore-opening agent from the polymer, the solvent may or may not be removed by drying or the like.

  Next, introduction of an acidic group AH into the polymer in the film will be described. In order to make a membrane formed from a polymer containing a pore-opening agent into an electrolyte membrane, it is preferable that the acidic group AH is present at least inside the voids in the membrane. For this purpose, the acidic group AH is introduced by the acidic group AH introducing agent. To introduce. The acidic group AH introduction agent here is a compound that can introduce the acidic group AH into a part of repeating units capable of acidic group AH constituting the polymer, and generally known ones can be used. . As a specific example of the acidic group AH introducing agent, when introducing a sulfonic acid group, concentrated sulfuric acid, chlorosulfonic acid, fuming sulfuric acid, sulfur trioxide and the like are preferable, from the viewpoint of ease of reaction control and productivity. Most preferred is chlorosulfonic acid. Moreover, when introducing a sulfonimide group, sulfonamide is preferable.

  In order to introduce the acidic group AH into the copolymer in the film, specifically, means for immersing the film in the acidic group AH introducing agent or the mixture of the acidic group AH introducing agent and the solvent may be employed. . The solvent mixed with the acidic group AH introducing agent can be used as long as it does not react with the acidic group AH introducing agent or does not react vigorously and can penetrate into the polymer. Examples of such solvents are preferably halogenated hydrocarbons such as chloroform, 1,2-dichloroethane, dichloromethane and perchloroethylene, nitrated hydrocarbons such as nitromethane and nitroethane, and nitriles such as acetonitrile. The solvent and the acidic group AH introduction agent may be single or a mixture of two or more.

  It is also preferable in terms of shortening the number of steps to remove the pore-opening agent from the membrane and introduce the acidic group AH into the polymer in the same step.

  More specifically, by immersing the membrane in a solution obtained by adding an acidic group AH introduction agent (for example, the sulfonating agent) to a solvent capable of removing the pore opening agent, It is preferable to simultaneously perform the removal and introduction (sulfonation) of the acidic group AH into the polymer. In this case, the pore-opening agent in the film is removed while being replaced with a solution containing the acidic group AH. This method is also preferable from the viewpoint that the degree of introduction of the acidic group AH can be accurately controlled. In this case, as the solvent capable of removing the pore-opening agent, a solvent that does not react with the acidic group AH introduction agent or does not react vigorously and can penetrate into the polymer is used. The solvent capable of removing the pore-opening agent may be a single system or a mixture of two or more types.

  Solvent capable of removing acidic group AH introduction auxiliary agent when acidic group AH introduction auxiliary agent for assisting introduction of acidic group AH is contained in the monomer / polymer composition before film formation It is preferable that

  From the above viewpoint, the solvent capable of removing the pore-opening agent includes, for example, halogenated hydrocarbons such as chloroform, 1,2-dichloroethane, dichloromethane and perchloroethylene, nitrated hydrocarbons such as nitromethane and nitroethane, and acetonitrile. Nitriles such as are preferred.

  In addition, the electrolyte membrane of the present invention can be copolymerized with other components or blended with other polymer compounds within a range that does not impair the object of the present invention. Add stabilizers such as hindered phenols, hindered amines, thioethers, and phosphorus antioxidants, as well as various additives typified by plasticizers and colorants, as long as the properties are not impaired. Can do.

  In addition, the electrolyte membrane of the present invention has various polymers, elastomers, fillers, fine particles, and the like for the purpose of improving mechanical strength, thermal stability, processability, etc. within a range that does not adversely affect the above-mentioned various properties. Various additives may be included.

  The electrolyte membrane of the present invention is used. In addition to the above-described film shape, the shape can take various forms such as a plate shape, a fiber shape, a hollow fiber shape, a particle shape, and a lump shape.

  Processing into such shapes can be performed by extrusion molding, press molding, cast polymerization, etc., but when a three-dimensional cross-linked structure is added to the electrolyte membrane, heating between a glass plate and a continuous belt is performed. A cast polymerization method using light or light is preferred.

  As a method of including a substance having a water substitute group B and / or a precursor of the water substitute group B in the electrolyte polymer containing the acidic group AH, when both are dissolved in a solvent, the solution is mixed. An electrolyte membrane can be obtained by forming a film. In addition, after preparing the electrolyte membrane containing the acidic group AH or the porous membrane containing the acidic group AH, the electrolyte membrane or the porous membrane is impregnated or filled with a substance having a water substitute group B or a solution thereof. Examples thereof include a method of applying and polymerizing or condensing a substance having a water substitute group B by heating or UV irradiation. In this case, the substance having the water substitute group B and the substance having the acidic group AH may be mixed.

  It is also a preferable example to impregnate an electrolyte polymer or membrane containing an acidic group AH with a supercritical liquid such as carbon dioxide gas with a substance having a water substitute group B and / or a precursor of the water substitute group B. . It is preferable that the water substitute group B exists uniformly throughout the electrolyte membrane because it can work efficiently as a water substitute group.

  The membrane electrode assembly of the present invention comprises the electrode comprising the electrode catalyst layer and the electrode substrate, using the electrolyte membrane of the present invention. The electrode catalyst layer is a layer containing an electrode catalyst that promotes an electrode reaction, an electron conductor, an ion conductor, and the like. As the electrode catalyst contained in the electrode catalyst layer, for example, a noble metal catalyst such as platinum, palladium, ruthenium, rhodium, iridium and gold is preferably used. One of these may be used alone, or two or more of them, such as alloys and mixtures, may be used in combination.

  As the electron conductor (conductive material) contained in the electrode catalyst layer, a carbon material or an inorganic conductive material is preferably used from the viewpoint of electron conductivity and chemical stability. Among these, amorphous and crystalline carbon materials are mentioned. For example, carbon black such as channel black, thermal black, furnace black, and acetylene black is preferably used because of its electron conductivity and specific surface area. Furnace Black includes “Vulcan (registered trademark) XC-72”, “Vulcan (registered trademark) P”, “Black Pearls (registered trademark) 880”, “Black Pearls (registered trademark) 1100”, “Black” manufactured by Cabot Corporation. “Pearls (registered trademark) 1300”, “Black Pearls (registered trademark) 2000”, “Regal (registered trademark) 400”, “Ketjen Black (registered trademark)” EC, EC600JD, Mitsubishi Chemical Examples of the acetylene black include “Denka Black (registered trademark)” manufactured by Denki Kagaku Kogyo Co., Ltd. In addition to carbon black, artificial graphite or carbon obtained from organic compounds such as natural graphite, pitch, coke, polyacrylonitrile, phenol resin, and furan resin can also be used. As the form of these carbon materials, in addition to irregular particles, fibers, scales, tubes, cones, and megaphones can also be used. Moreover, you may use what post-processed these carbon materials.

  In addition, it is preferable in terms of electrode performance that the electron conductor is uniformly dispersed with the catalyst particles. For this reason, it is preferable that the catalyst particles and the electron conductor are well dispersed in advance as a coating liquid. Furthermore, it is also a preferred embodiment to use a catalyst-supporting carbon in which a catalyst and an electron conductor are integrated as an electrode catalyst layer. By using this catalyst-supporting carbon, the utilization efficiency of the catalyst is improved, which can contribute to the improvement of battery performance and cost reduction. Here, even when catalyst-supported carbon is used for the electrode catalyst layer, a conductive agent can be added to further increase the electron conductivity. As such a conductive agent, the above-described carbon black is preferably used.

  Various organic and inorganic materials are generally known as substances having ion conductivity (ion conductors) used for the electrode catalyst layer. However, when used for fuel cells, the ion conductivity is improved. A polymer having an ionic group such as a sulfonic acid group, a carboxylic acid group, or a phosphoric acid group (ion conductive polymer) is preferably used. Among these, from the viewpoint of the stability of the ionic group, a polymer having ion conductivity composed of a fluoroalkyl ether side chain and a fluoroalkyl main chain, or the polymer electrolyte material of the present invention is preferably used. As the perfluorinated ion conductive polymer, for example, “Nafion (registered trademark)” manufactured by DuPont, “Aciplex (registered trademark)” manufactured by Asahi Kasei Corporation, “Flemion (registered trademark)” manufactured by Asahi Glass Co., Ltd. and the like are preferably used. . These ion conductive polymers are provided in the electrode catalyst layer in the state of a solution or a dispersion. At this time, the solvent for dissolving or dispersing the polymer is not particularly limited, but a polar solvent is preferable from the viewpoint of the solubility of the ion conductive polymer.

  Since the catalyst and the electronic conductors are usually powders, the ionic conductor usually plays a role of solidifying them. It is preferable from the viewpoint of electrode performance that the ionic conductor is added in advance to a coating liquid mainly composed of electrode catalyst particles and an electron conductor when the electrode catalyst layer is produced, and is applied in a uniformly dispersed state. However, the ion conductor may be applied after the electrode catalyst layer is applied. Here, examples of the method for applying the ion conductor to the electrode catalyst layer include spray coating, brush coating, dip coating, die coating, curtain coating, and flow coating, and are not particularly limited. The amount of the ion conductor contained in the electrode catalyst layer should be appropriately determined according to the required electrode characteristics and the conductivity of the ion conductor used, and is not particularly limited. The range of 1 to 80% is preferable, and the range of 5 to 50% is more preferable. When the ion conductor is too small, the ion conductivity is low, and when it is too much, the gas permeability may be hindered.

  The electrode catalyst layer may contain various substances in addition to the catalyst, the electronic conductor, and the ionic conductor. In particular, in order to enhance the binding property of the substance contained in the electrode catalyst layer, a polymer other than the above-described ion conductive polymer may be included. Examples of such a polymer include fluorine atoms such as polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), polyhexafluoropropylene (FEP), polytetrafluoroethylene, and polyperfluoroalkyl vinyl ether (PFA). These copolymers, copolymers of monomer units constituting these polymers and other monomers such as ethylene and styrene, or blend polymers can be used. The content of these polymers in the electrode catalyst layer is preferably in the range of 5 to 40% by weight. When there is too much polymer content, there exists a tendency for an electronic and ionic resistance to increase and for electrode performance to fall.

  In addition, when the fuel is a liquid or a gas, the electrode catalyst layer preferably has a structure that allows the liquid or gas to easily permeate, and preferably has a structure that promotes the discharge of by-products due to the electrode reaction.

  As the electrode base material, one having a low electric resistance and capable of collecting or feeding power can be used. Moreover, when using the said electrode catalyst layer also as a collector, it is not necessary to use an electrode base material in particular. Examples of the constituent material of the electrode base material include carbonaceous and conductive inorganic substances. For example, a fired body from polyacrylonitrile, a fired body from pitch, a carbon material such as graphite and expanded graphite, stainless steel, molybdenum And titanium. These forms are not particularly limited, and are used, for example, in the form of fibers or particles. From the viewpoint of fuel permeability, fibrous conductive materials (conductive fibers) such as carbon fibers are preferable. As an electrode base material using conductive fibers, either a woven fabric or a non-woven fabric structure can be used. For example, carbon paper TGP series, SO series manufactured by Toray Industries, Inc., carbon cloth manufactured by E-TEK, etc. are used.

  As the woven fabric, a plain weave, a twill weave, a satin weave, a crest weave, a binding weave and the like are used without particular limitation. Moreover, as a nonwoven fabric, it does not specifically limit, such as a paper making method, a needle punch method, a spun bond method, a water jet punch method, and a melt blow method. It may also be a knitted fabric. In particular, when carbon fibers are used in these fabrics, carbonized plain fabric using flame-resistant spun yarn is carbonized or graphitized, and flame-resistant yarn is carbonized after being processed into a nonwoven fabric by the needle punch method or water jet punch method. Alternatively, a graphitized nonwoven fabric, a flameproof yarn, a carbonized yarn, or a mat nonwoven fabric by a paper making method using a graphitized yarn is preferably used. In particular, it is preferable to use a non-woven fabric because a thin and strong fabric can be obtained.

  When conductive fibers made of carbon fibers are used for the electrode substrate, examples of the carbon fibers include polyacrylonitrile (PAN) -based carbon fibers, phenol-based carbon fibers, pitch-based carbon fibers, and rayon-based carbon fibers.

  In addition, the electrode base material has a water repellent treatment for preventing gas diffusion / permeability deterioration due to water retention, a partial water repellent treatment for forming a water discharge path, a hydrophilic treatment, and a resistor for reducing resistance. Carbon powder can be added.

  In the polymer electrolyte fuel cell of the present invention, it is preferable to provide a conductive intermediate layer containing at least an inorganic conductive material and a hydrophobic polymer between the electrode substrate and the electrode catalyst layer. In particular, when the electrode base material is a carbon fiber woven fabric or a nonwoven fabric having a large porosity, by providing the conductive intermediate layer, it is possible to suppress performance degradation due to the electrode catalyst layer permeating into the electrode base material.

  A method for producing a membrane electrode assembly (MEA) using the electrode catalyst layer or the electrode catalyst layer and an electrode substrate using the polymer electrolyte membrane of the present invention is not particularly limited. Known methods (for example, the chemical plating method described in “Electrochemistry” 1985, 53, 269., “Journal of Electrochemical Science” (J. Electrochem. Soc.): Electrochemical Science and Technology, 1988, 135 (9), It is possible to apply the gas diffusion electrode hot press bonding method described in 2209. Although integration by hot pressing is a preferred method, the temperature and pressure may be appropriately selected depending on the thickness of the polymer electrolyte membrane, the moisture content, the electrode catalyst layer, and the electrode substrate. Alternatively, the polymer electrolyte membrane may be pressed in a water-containing state, or may be bonded with a polymer having ion conductivity.

  Examples of the fuel for the fuel cell of the present invention include organic compounds having 1 to 6 carbon atoms such as oxygen, hydrogen and methane, ethane, propane, butane, methanol, isopropyl alcohol, acetone, ethylene glycol, formic acid, acetic acid, dimethyl ether, hydroquinone, and cyclohexane. Examples thereof include a compound and a mixture of these with water, and one kind or a mixture of two or more kinds may be used. In particular, a fuel containing an organic compound having 1 to 6 carbon atoms is preferably used from the viewpoint of power generation efficiency and simplification of the entire battery system, and an aqueous methanol solution is particularly preferable in terms of power generation efficiency.

  The content of the organic compound having 1 to 6 carbon atoms in the fuel supplied to the membrane electrode assembly is preferably 1 to 99.8% by weight. When the content is 1% by weight or more, a practical high energy capacity can be obtained, and when the content is 99.8% by weight or less, the power generation efficiency is increased and a practical high output can be obtained.

  When an aqueous methanol solution is used, the concentration of methanol is appropriately selected depending on the fuel cell system to be used. A concentration as high as possible is preferable from the viewpoint of long-time driving. For example, an active fuel cell having a system for sending a medium necessary for power generation, such as a liquid feed pump or a blower fan, to a membrane electrode assembly, or an auxiliary machine such as a cooling fan, a fuel dilution system, or a product recovery system has a methanol concentration of 30. It is preferable to inject a fuel of 100% or more by a fuel tank or a fuel cassette and dilute it to about 0.5-29% or send it directly to the membrane electrode assembly. A fuel having a methanol concentration in the range of 10 to 100% is preferred.

  Moreover, the membrane electrode assembly of the present invention may be used in the form of a stack of a plurality of sheets or in a state of being arranged. Further, the fuel cell may be built in the device to be used, or may be used as an external unit. From the viewpoint of maintenance, it is also preferable that the membrane electrode assembly is detachable from the fuel cell.

  In addition, a fuel cell for a portable device using a gas such as hydrogen as a fuel preferably has a structure in which those gases do not leak to the outside from the viewpoint of safety and long-time driving, and at least the anode side, which is the hydrogen electrode, is sealed. It is preferable to use it. The cathode preferably has a structure that naturally sucks air for the purpose of reducing peripheral devices and the like. The anode side is preferably a positive pressure, such as a hydrogen generator, a hydrogen cylinder, or a hydrogen storage alloy, and preferably 0.1 MPa to 0.0001 MPa. Preferably, it is 0.05 MPa to 0.001 MPa. Depending on the current to be extracted, natural convection can generate power.

  As a use of the fuel cell of the present invention, a power supply source of a moving body is preferable. In particular, mobile devices such as mobile phones, personal computers, PDAs, video cameras (camcorders), digital cameras, handy terminals, RFID readers, digital audio players, various displays, home appliances such as electric shavers and vacuum cleaners, electric tools, home use It is preferably used as a power supply source for automobiles such as power supply machines, passenger cars, buses and trucks, motorcycles, bicycles with electric assist, electric carts, electric wheelchairs, ships such as ships and railways, and various robots. Especially in portable devices, it is used not only for power supply sources, but also for charging secondary batteries installed in portable devices, and also suitable as a hybrid power supply source used in combination with secondary batteries, capacitors, and solar cells. Available to:

Hereinafter, the present invention will be described in more detail with reference to examples. However, these examples are for better understanding of the present invention, and the present invention is not limited thereto. (1) Ionic conductivity A
After immersing the sample in pure water at 25 ° C. for 24 hours, the sample was taken out in an atmosphere at 25 ° C. and a relative humidity of 50 to 80%, and the proton conductivity was measured by the constant potential AC impedance method as quickly as possible.

As a measuring apparatus, a Solartron electrochemical measurement system (Solartron 1287 Electrochemical Interface and Solartron 1255B Frequency Response Analyzer) was used. The sample was sandwiched between two circular electrodes (made of stainless steel) of φ2 mm and φ10 mm with a weight of 1 kg. The effective electrode area is 0.0314 cm2. A 15% aqueous solution of poly (2-acrylamido-2-methylpropanesulfonic acid) was applied to the interface between the sample and the electrode. A constant potential impedance measurement with an AC amplitude of 50 mV was performed at 25 ° C., and the ionic conductivity A in the film thickness direction was determined.
(2) Ionic conductivity B
The sample was measured for ionic conductivity B by a constant potential AC impedance method in a constant temperature and high humidity bath at 90 ° C. and a relative humidity of 50%.

As a measuring apparatus, a Solartron electrochemical measurement system (Solartron 1287 Electrochemical Interface and Solartron 1255B Frequency Response Analyzer) was used. As the sample, a membrane having a width of about 10 mm and a length of about 10 to 30 mm was used. The sample was left in a constant temperature and high humidity bath at 90 ° C. and 50% relative humidity until just before the measurement. As electrodes, platinum wires (two wires) having a diameter of 100 μm were used. The electrodes were arranged on the front side and the back side of the sample film so as to be parallel to each other and perpendicular to the longitudinal direction of the sample film. The electrolyte membrane part between the platinum wires was set to be exposed.
(3) Methanol Permeation A film-like sample was immersed in pure water at 25 ° C. for 24 hours, and then measured at 20 ° C. using a 30 wt% methanol aqueous solution.

A sample membrane was sandwiched between the H-type cells, pure water (60 mL) was placed in one cell, and 30 wt% aqueous methanol solution (60 mL) was placed in the other cell. The cell capacity was 80 mL each. Moreover, the opening part area between cells was 1.77 cm < ² >. Both cells were stirred at 20 ° C. The amount of methanol eluted in pure water at the time of 1 hour, 2 hours and 3 hours was measured and quantified with a gas chromatography (GC-2010) manufactured by Shimadzu Corporation. The methanol permeation amount per unit time was determined from the slope of the graph.

[Reference example]
(1) Synthesis example 1 of polymer material having ionic group
109.1 g of 4,4′-difluorobenzophenone was reacted at 100 ° C. for 10 hours in 150 mL of fuming sulfuric acid (50% SO ₃ ). Thereafter, the mixture was poured little by little into a large amount of water, neutralized with NaOH, and 200 g of sodium chloride was added to precipitate the composite. The resulting precipitate was filtered off and recrystallized with an aqueous ethanol solution to obtain disodium 3,3′-disulfonate-4,4′-difluorobenzophenone. (Yield 181 g, 86% yield).

  6.9 g of potassium carbonate, 16 g of 9,9-bis (4-hydroxyphenyl) fluorene, 6 g of 4,4′-difluorobenzophenone, and the disodium 3,3′-disulfonate-4,4′-difluoro Polymerization was performed at 190 ° C. in N-methyl-2-pyrrolidone using 6 g of benzophenone. Purification was carried out by reprecipitation with a large amount of water to obtain polymer A.

(2) Synthesis example 2 of polymer material having ionic group
6.9 g of potassium carbonate, 14 g of 4,4′-dihydroxytetraphenylmethane, 7 g of 4,4′-difluorobenzophenone, and the disodium 3,3′-disulfonate-4,4′- of Synthesis Example 1 Polymerization was carried out at 190 ° C. in N-methyl-2-pyrrolidone using 5 g of difluorobenzophenone. Purification was carried out by reprecipitation with a large amount of water to obtain polymer B.

(3) Preparation Examples of Electrolyte Membranes A and B The above polymer A and polymer B were each dissolved in N-methyl-2-pyrrolidone to obtain a coating solution having a solid content of 25%. The coating liquid was cast on a glass plate and dried at 70 ° C. for 30 minutes and further at 100 ° C. for 1 hour to obtain a film having a thickness of 72 μm. Furthermore, after heat-treating under conditions of heating to 200 to 300 ° C. over 1 hour in a nitrogen gas atmosphere and heating at 300 ° C. for 10 minutes, the mixture was allowed to cool and immersed in 1N hydrochloric acid for 12 hours or more to perform proton substitution. The electrolyte membrane A and the electrolyte membrane B were obtained by immersing in a large excess of pure water for at least one day and thoroughly washing.

(4) Production Example of Electrolyte Membrane 10 g of styrene, 5 g of divinylbenzene, 10 g of cyclohexylmaleimide, 30 g of propylene carbonate as a pore-opening agent, 2,2′-azobisisobutyronitrile as a polymerization initiator 1 g was charged, stirred with a magnetic stirrer and dissolved uniformly to obtain a monomer composition solution.

  Prepare a mold adjusted with a gasket so that the distance between two 30 cm × 30 cm glass plates with a thickness of 5 mm is 0.2 mm, and until the inside of the gasket is filled with the monomer composition solution between the glass plates Injected.

  Next, after polymerizing between plates in a hot air dryer at 65 ° C. for 8 hours, a polymer film was taken out between the glass plates.

  For removal of the pore-opening agent and introduction of ionic groups, the above film-like polymer was immersed in 1,2-dichloroethane to which 5% by weight of chlorosulfonic acid was added for 30 minutes, and then the cleaning solution became neutral. This was washed with water to obtain a polymer electrolyte membrane.

[Example 1]
Dissolve 1 g of 2-acrylamido-2-methylpropanesulfonic acid (AMPS) in 5 g of water, add 0.5 g of tetraethoxysilane, cool to 0 ° C., and stir until a uniform solution is obtained. A was obtained.

  The electrolyte membrane A cut to a predetermined size was put in a polyethylene bag, and a predetermined amount of the above-mentioned water-substituent group-containing solution A was added to make the electrolyte membrane A completely immersed, followed by sealing with a heat sealer. After immersion for 8 hours, the corner portion of the sealed polyethylene bag is cut, the excess water-substituent group-containing solution A is poured out, and then the polyethylene membrane and the electrolyte membrane A impregnated with the water-substituent group-containing solution A are placed on two glass plates Scissors were heated at 80 ° C. for 12 hours. Thereafter, the electrolyte membrane A impregnated with the water substitute group-containing solution A was taken out of the polyethylene bag and washed with water to obtain an electrolyte membrane D. The PKa of the acidic group AH, which is a sulfonic acid group, was −3.0, and the PKb of the water substitute group B derived from tetraethoxysilane was 0.42. In addition, Table 1 summarizes the values obtained by standardizing the ion conductivity A and B and the proton permeation amount with the measured value of “Nafion (registered trademark) 117” being 1.

[Examples 2 and 3]
Except having changed the electrolyte membrane A of Example 1 into electrolyte membranes B and C, it carried out similarly to Example 1 and obtained electrolyte membranes E and F.

  The values obtained by normalizing the ion conductivity A, B and the proton permeation amount with the measured value of “Nafion (registered trademark) 117” as 1 are summarized in Table 1.

[Example 4]
Acrylamide (1 g), water (1 g), ethanol (0.5 g), and potassium persulfate (0.1 g) were mixed with stirring. An electrolyte membrane G was obtained in the same manner as in Example 1 except that the water substitute group-containing solution B and the water substitute group-containing solution A were changed. The PKa of the acidic group AH, which is a sulfonic acid group, was −3.0, and the PKb of the water substitution group B derived from acrylamide was 1.78. In addition, Table 1 summarizes the values obtained by standardizing the ion conductivity A and B and the proton permeation amount of the electrolyte membrane G with the measured value of “Nafion (registered trademark) 117” as 1.

[Example 5]
1 g of vinylaniline and 0.1 g of 2,2′-azobisisobutyronitrile were stirred and mixed, and stirred until a uniform solution was obtained, thereby obtaining a water substitute group-containing solution C. An electrolyte membrane H was obtained in the same manner as in Example 1 except that the water substitute group-containing solution C and the water substitute group-containing solution A were changed. The PKa of the acidic group AH, which is a sulfonic acid group, was −3.0, and the PKb of the water substitute group derived from vinylaniline was 3.68. In addition, Table 1 shows the values obtained by standardizing the ion conductivity A and B and the proton permeation amount of the electrolyte membrane H with the measured value of “Nafion (registered trademark) 117” as 1.

[Comparative Examples 1-3]
For electrolyte membranes A, B, and C that do not contain a water-substituting group, the ion conductivity A, B, and proton permeation amount were measured for comparison, and the measured value of “Nafion (registered trademark) 117” was normalized to 1. Are summarized in Table 1.

[Example 6] Membrane electrode composite A
Two carbon fiber cloth base materials were treated with a 20% ethylene tetrafluoride solution for water repellency, and then a carbon black dispersion containing 20% ethylene tetrafluoride was applied and baked to form an electrode base material. Produced.

  On one electrode substrate, an anode electrode catalyst coating solution composed of Pt—Ru-supported carbon and “Nafion (registered trademark)” solution was applied and dried to prepare an anode electrode.

  On the other electrode substrate, a cathode electrode catalyst coating solution composed of Pt-supported carbon and a “Nafion (registered trademark)” solution was applied and dried to prepare a cathode electrode.

  The electrolyte membrane D obtained above was held between an anode electrode and a cathode electrode, and heated and pressed to prepare a membrane electrode assembly A.

[Example 7] Membrane electrode composite B
Two carbon fiber cloth base materials were treated with a 20% ethylene tetrafluoride solution for water repellency, and then a carbon black dispersion containing 20% ethylene tetrafluoride was applied and baked to form an electrode base material. Produced.

  An electrode catalyst coating solution composed of Pt-supported carbon and a “Nafion (registered trademark)” solution was applied onto two electrode base materials, and dried to prepare an electrode.

  The electrolyte membrane G obtained above was held between two electrodes and heated and pressed to produce a membrane electrode assembly B.

Example 8 Evaluation of Fuel Cell A The obtained membrane electrode assembly A was set in a cell manufactured by Electrochem, and a fuel cell was prepared by flowing a 30% aqueous methanol solution on the anode side and air on the cathode side.

  The MEA using the electrolyte membrane D had better characteristics than the MEA using the “Nafion (registered trademark)” 117 membrane.

[Example 9] Evaluation of fuel cell B The obtained membrane electrode assembly B was set in an evaluation cell to produce a fuel cell. When this fuel cell was measured at a cell temperature of 90 ° C., fuel gas: hydrogen, oxidizing gas: air, gas utilization rate: anode 70% / cathode 40%, the current-voltage (IV) measurement was performed. The MEA using the NOA had better properties than the MEA using the “Nafion®” 117 membrane.

[Example 10]
The electrolyte membrane D was adjusted to a film thickness of 15 μm, and a membrane electrode assembly C was obtained in the same manner as in Example 7. This was set in a cell having an opening (passing through the cathode current collector plate) so that the cathode side can naturally inhale. An image of the cell is shown in FIGS. The hydrogen flow path on the anode side was serpentine. Hydrogen gas was supplied to the anode side at a pressure of 0.01 MPa, and the outlet was sealed to make it substantially sealed. Hydrogen gas was set to substantially no humidification and a cell temperature of 26 ° C., and current-voltage measurement was performed.

As a result, a maximum output of 250 mW / cm ² was obtained, and good power generation characteristics were exhibited even in a room temperature non-humidified state.

  As is clear from Table 1, the ionic conductivity B is better in the example than the comparative example, and the proton permeation amount can be reduced.

  The electrolyte membrane of the present invention can be applied to various electrochemical devices (for example, a fuel cell, a water electrolysis device, a chloroalkali electrolysis device, etc.). Among these devices, it is suitable for a fuel cell, and particularly suitable for a fuel cell using methanol aqueous solution or hydrogen as fuel.

  The use of the membrane electrode assembly and the fuel cell of the present invention is not particularly limited, but a power supply source for a mobile body is particularly preferable. In particular, mobile devices such as mobile phones, personal computers, PDAs, video cameras (camcorders), digital cameras, handy terminals, RFID readers, digital audio players, various displays, home appliances such as electric shavers and vacuum cleaners, electric tools, home use It is preferably used as a power supply source for automobiles such as power supply machines, passenger cars, buses and trucks, motorcycles, bicycles with electric assist, electric carts, electric wheelchairs, ships such as ships and railways, and various robots. Especially in portable devices, it is used not only for power supply sources, but also for charging secondary batteries installed in portable devices, and also suitable as a hybrid power supply source used in combination with secondary batteries, capacitors, and solar cells. Available to:

Perspective view of cathode current collector plate of evaluation cell Evaluation cell cross section

Explanation of symbols

1: Opening 2: Cathode current collector 3: Electrolyte membrane 4: Cathode electrode 5: Anode electrode 6: Gasket 7: Hydrogen gas supply port 8: Sealing material 9: Anode current collector 10: Lead

Claims (8)

A water substitute group containing an acidic group AH having a PKa value defined by the following formula S1 of -17.0 to 5.0 and a PKb value defined by the following formula S2 of -6.0 to 4.0. An electrolyte membrane comprising B.

(AH: acidic group, B: water substitute group, PKa and PKb: logarithm of equilibrium constant, []: concentration) The water substitution group B is —OH, —O—Si (OH) ₃ , —COOH, —Ar ₁ —NH ₂ , — (NO ₂ ) ₂ —Ar ₂ —NH ₂ , —SO ₂ —NH ₂ , —CO The electrolyte membrane according to claim 1, comprising at least one selected from —NH ₂ . (Ar ₁ and Ar ₂ represent an arylene group) The water substitute group B is composed of one or more selected from —OH, —O—Si (OH) ₃ , —Ph—NH ₂ , — (NO ₂ ) ₂ —Ph—NH ₂ , —CO—NH _2. The electrolyte membrane according to claim 1 or 2. (Ph represents phenylene)   The electrolyte membrane contains at least one selected from 9,9-bis (4-hydroxyphenyl) fluorene-derived components, phenolphthalein-derived components, and 4,4′-dihydroxytetraphenylmethane-derived components. The electrolyte membrane according to claim 1.   It is a three-dimensional crosslinked body, The electrolyte membrane in any one of Claims 1-4.   A method for producing an electrolyte membrane according to any one of claims 1 to 5, wherein a substance containing a water substitute group B and / or a substance containing a water substitute group B precursor is added to the electrolyte membrane containing an acidic group AH. And / or impregnating and / or impregnating and / or filling the electrolyte membrane containing the water substitute group B with the substance containing the acidic group AH and / or the substance containing the acidic group AH precursor. A method for producing an electrolyte membrane comprising one step.   A membrane electrode assembly using the electrolyte membrane according to any one of claims 1 to 5.   A fuel cell using the electrolyte membrane according to claim 1.

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