JP2016195046A - Electrolyte membrane for solid polymer type fuel battery, solid polymer type fuel battery and method of manufacturing electrolyte membrane for solid polymer type fuel battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrolyte membrane that enables a solid polymer type fuel battery to operate under a high temperature condition and a low humidity condition.SOLUTION: An electrolyte membrane for a solid polymer type fuel battery is obtained by bonding an ion exchange group to a graft chain of aromatic hydrocarbon-based polymer resin containing inorganic filler. Aromatic hydrocarbon polymer type polymer resin is preferably polyether ether ketone or a derivative thereof. The solid polymer type fuel battery contains a membrane electrode assembly obtained by bonding a fuel electrode to one membrane surface of the electrolyte membrane for the solid polymer type fuel battery, and bonding an air electrode to the other membrane surface.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an electrolyte membrane used for a polymer electrolyte fuel cell. In particular, the present invention relates to an electrolyte membrane for a polymer electrolyte fuel cell produced by bonding an ion exchange group to an aromatic hydrocarbon polymer resin.

  A polymer electrolyte fuel cell is a high-efficiency power generator that extracts, as electric power, chemical energy at the time of reaction between a fuel supplied into the cell and an oxidant. Since it can be operated at a relatively low temperature, there is a great demand for electric vehicle use, home use, portable device use, and the like. BACKGROUND ART A polymer electrolyte fuel cell (hereinafter sometimes referred to as “fuel cell”) is composed of a cell including a membrane electrode assembly (MEA). MEA is a joined body in which a fuel electrode is joined to one membrane surface of an electrolyte membrane and an air electrode is joined to the other membrane surface. The fuel electrode and the air electrode are each a laminate in which at least a gas diffusion layer and a catalyst layer are laminated.

  When fuel such as hydrogen or methanol is supplied to the fuel electrode, the fuel reaches the catalyst layer after being diffused in the gas diffusion layer in the fuel electrode. When the fuel comes into contact with the catalyst layer, protons (hydrogen ions) and electrons are generated. The generated electrons move to the air electrode through an external circuit. On the other hand, protons move through the electrolyte membrane and reach the air electrode. An oxygen-containing gas such as oxygen or air is supplied to the air electrode as an oxidizing agent. In the catalyst layer of the air electrode, the reaction between protons and oxygen moved from the fuel electrode is promoted, and water is generated. The fuel cell uses chemical energy generated by the above reaction as electric energy.

  In order to improve the battery characteristics of the polymer electrolyte fuel cell, the electrolyte membrane is conventionally made of a fluorine-based resin having good proton conductivity and high conductivity. However, the fluorine-based resin has a property that it tends to be liquefied as the amount of ion-exchange group bonds increases. Therefore, there is a limit to improving proton conductivity.

  In addition, the fluororesin must be sufficiently humidified to maintain proton conductivity under high temperature conditions. That is, a polymer electrolyte fuel cell using an electrolyte membrane made of a fluororesin is not suitable for continuous operation under high temperature conditions and low humidification conditions. In order to improve the strength of the electrolyte membrane, when a reinforcing material such as a fiber is mixed with the fluororesin, the manufacturing cost increases. Furthermore, since the fluororesin requires special treatment at the time of disposal, the treatment cost is high.

  Examples of the material for the electrolyte membrane that can replace the fluororesin include aromatic hydrocarbon polymer resins. In particular, polyetheretherketone (PolyEtherEtherKetone, PEEK) has high heat resistance and chemical stability, and is therefore suitable for fuel cell applications compared to fluororesins.

  Patent Document 1 discloses a polymer electrolyte membrane in which a functional monomer having a sulfonic acid group or the like is bonded using PEEK or the like as a base material. The polymer electrolyte membrane disclosed in Patent Document 1 is manufactured using a radiation graft polymerization method. When the radiation graft polymerization method is used, it is advantageous in that the preparation of the substrate and the provision of the ion exchange function can be performed in separate steps. However, in order to realize a high-performance fuel cell under high temperature conditions and low humidification conditions, further improvement in proton conductivity of an electrolyte membrane using an aromatic hydrocarbon polymer resin is required.

JP 2009-67844 A

  An object of the present invention is to provide an electrolyte membrane capable of operating a polymer electrolyte fuel cell under high temperature conditions and low humidification conditions.

  The present invention relates to an electrolyte membrane for a polymer electrolyte fuel cell (hereinafter referred to as “electrolyte membrane”) in which an ion exchange group is bonded to a graft chain of an aromatic hydrocarbon polymer resin containing an inorganic filler. There is.) In the present invention, the aromatic hydrocarbon polymer resin is preferably polyetheretherketone or a derivative thereof. The present invention includes a polymer electrolyte fuel cell including a membrane electrode assembly in which a fuel electrode is joined to one membrane surface of an electrolyte membrane for a polymer electrolyte fuel cell and an air electrode is joined to the other membrane surface. To do.

  A film forming step for producing an aromatic hydrocarbon polymer resin film by dispersing an inorganic filler in a molten aromatic hydrocarbon polymer resin and then forming the aromatic hydrocarbon polymer resin into a film; And a method for producing an electrolyte membrane for a polymer electrolyte fuel cell, comprising a graft polymerization step of irradiating the aromatic hydrocarbon polymer resin membrane with radiation to graft polymerize an ion exchange group-containing monomer.

  The electrolyte membrane of the present invention can operate a polymer electrolyte fuel cell under high temperature conditions and low humidification conditions.

It is a schematic diagram of the membrane electrode assembly applied to the fuel cell of the present invention. It is a figure which shows the current-voltage characteristic of the fuel cell of this invention. It is a figure which shows the voltage characteristic of the fuel cell of this invention.

[Electrolyte membranes for polymer electrolyte fuel cells]
In the present invention, water content can be improved by using an aromatic hydrocarbon polymer resin as a base material and adding an inorganic filler to the aromatic hydrocarbon polymer resin. In a polymer electrolyte fuel cell (hereinafter sometimes referred to as “fuel cell”) using the present invention, even when used in an operating environment where the relative humidity is relatively low under a high temperature condition, from the fuel electrode side. The supplied proton can be quickly moved to the air electrode side.

  Specific examples of the operating environment of the fuel cell of the present invention using a predetermined electrolyte membrane include a relative humidity of 20 to 80% RH under a temperature condition of 80 to 160 ° C. In the present invention, the fuel cell can be operated even in an operating environment where the relative humidity exceeds 80% RH under the same temperature condition. The temperature condition and the relative humidity are values set in a general fuel cell performance evaluation apparatus.

  In the present invention, the ion exchange group bonded to the aromatic hydrocarbon polymer resin only needs to be bonded to the graft chain, and may be bonded to the graft chain and the main chain. The graft chain is formed by radiation graft polymerization, chemical graft polymerization (chain transfer method, oxidation method, etc.) and the like. Since the ion exchange group is mainly bonded to the graft chain, the mechanical strength is not impaired even if the amount of the ion exchange group is increased. Therefore, this invention can improve proton conductivity by the increase in the amount of ion-exchange group bonds, and the inclusion of an inorganic filler.

[Aromatic hydrocarbon polymer resin]
In the present invention, a known aromatic hydrocarbon polymer resin having mechanical strength that can be used as an electrolyte membrane can be used. Preferably, an aromatic hydrocarbon polymer resin called a super engineering plastic is used. Further, those having a polyether ether ketone structure, a polyether ketone structure, a polyimide structure, a polysulfone structure, or a polybenzimidazole structure are preferable.

  More specific examples include polyphenylene sulfide (PPS), polyetheretherketone (PEEK), polyethylene naphthalate (PEN), super engineering plastic polysulfone (PSU), polyethersulfone (PES), polyarylate (PAR), polyamide Examples include imide (PAI), polyetherimide (PEI), and polyimide (PI). PEEK is particularly preferable because it is excellent in chemical stability and strong alkali resistance.

  The aromatic hydrocarbon polymer resin used in the present invention includes a polymer alloy obtained by mixing two kinds of aromatic hydrocarbon polymer resins. Examples of the polymer alloy include polymer alloys in which PEEK is mixed with other aromatic hydrocarbon polymer resin or fluorine polymer resin. As aromatic hydrocarbon polymer resin mixed with PEEK, polyphenylene sulfide (PPS), polysulfone (PSU), polyetherimide (PEI), as fluorine polymer resin, polytetrafluoroethylene (PTFE), And tetrafluoroethylene perfluoroalkyl vinyl ether copolymer (PFA). The polymer alloys exemplified above are preferable because the mechanical strength can be maintained even when the amount of ion-exchange group bonds increases, or the amount of ion-exchange group bonds can be positively increased. On the other hand, a normal hydrocarbon film is easily broken due to a decrease in film strength with an increase in the amount of ion-exchange group bonds.

  In the polymer alloy exemplified above, the content of the aromatic hydrocarbon polymer resin or fluorine polymer resin mixed with PEEK is preferably 0.1 to 50 parts by mass with respect to 100 parts by mass of the obtained polymer alloy, 0.5 -40 mass parts is more preferable, and 1-35 mass parts is further more preferable. When the content of the aromatic hydrocarbon polymer resin or fluorine polymer resin mixed with PEEK is less than 0.1 parts by mass, the mechanical strength of such a polymer alloy is compared with the case where PEEK is used alone. There is no significant improvement. When the content exceeds 50 parts by mass, the mechanical strength of the film may be lowered.

[Inorganic filler]
As the inorganic filler to be contained in the above aromatic hydrocarbon polymer resin, those capable of improving the water content of the obtained electrolyte membrane can be used without limitation. Silica is preferred as such an inorganic filler. In the present invention, the silica to be contained in the aromatic hydrocarbon polymer resin may be either hydrophilic silica or hydrophobic silica, more preferably hydrophilic silica. Further, the shape of silica may be spherical, scale-like, or needle-like, and spherical is preferred. The water content of the present invention can be improved by dispersing the silica in the hydrophilic part in the microphase separation structure of the aromatic hydrocarbon polymer resin. As a result, the electrolyte membrane of the present invention has good proton conductivity.

In the present invention, the hydrophilic silica refers to SiO ₂ fine particles not subjected to the hydrophobizing treatment described below. In the present invention, commercially available hydrophilic silica can be used. Examples of commercially available product names include Aerosil (registered trademark) 200 (manufactured by Nippon Aerosil Co., Ltd.), SFP-20M (manufactured by Denki Kagaku Kogyo Co., Ltd.), and the like.

As the hydrophobic silica, fine particles obtained by hydrophobizing the above hydrophilic silica are used. The hydrophobic treatment is a treatment in which a hydrophobic layer is formed by coating a hydrophobic compound. A silane coupling method or the like can be applied as a coating method. In the present invention, commercially available hydrophobic silica may be used. Examples of the commercial name include Aerosil (registered trademark) RX200 (manufactured by Nippon Aerosil Co., Ltd.). The particle diameter D ₅₀ of the hydrophobic silica is preferably 0.1 to 12 μm, and more preferably 0.1 to 6 μm.

The particle diameter D ₅₀ of the hydrophilic silica is preferably 0.1 to 12 μm, and more preferably 0.1 to 6 μm. When the particle diameter D ₅₀ exceeds 12 μm, the dispersibility in the aromatic hydrocarbon polymer resin becomes insufficient. Particle diameter D of the silica ₅₀ can be measured by a laser diffraction type particle size distribution measuring apparatus.

  The content of silica is preferably 1 part by mass or more and 5 parts by mass or less, and more preferably 3 parts by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the aromatic hydrocarbon polymer resin. By containing silica within the above preferred range, the water content of the electrolyte membrane of the present invention is 1 to 3 times or more the water content of an electrolyte membrane not containing silica produced under the same conditions. It becomes.

  Since the electrolyte membrane of the present invention uses a highly heat-resistant aromatic hydrocarbon polymer resin such as PEEK, it can be used under high temperature conditions in addition to temperature conditions of 25 to 80 ° C. As a specific example of the high temperature condition, the present invention can be used at a temperature condition of 80 to 160 ° C, more preferably 80 to 120 ° C. Further, since the moisture content is good by containing predetermined silica, the electrolyte membrane of the present invention has good proton conductivity even under low humidification conditions under the temperature conditions exemplified above.

  That is, the fuel cell using the electrolyte membrane of the present invention operates well under high temperature conditions and low humidification conditions. For example, a fuel cell using the electrolyte membrane of the present invention can be operated at a relative humidity of 30% RH (90 ° C.). When the content of silica with respect to 100 parts by mass of the aromatic hydrocarbon polymer resin is less than 3 parts by mass, it is not possible to obtain conductivity suitable for fuel cell applications. On the other hand, when it exceeds 5 mass parts, it becomes a cause which raises cost.

  Silica contained in the present invention also contributes to improvement of radical resistance of the electrolyte membrane. A chlorine radical is mentioned as a typical radical. Chlorine radical resistance can be evaluated by exposing the electrolyte membrane to chlorine and observing the deterioration state of the electrolyte membrane after a predetermined time has elapsed. In order to further improve radical resistance, in addition to silica, functional inorganic fillers having radical resistance improving functions such as talc, manganese dioxide, carbon black and radical scavenger are added to the aromatic hydrocarbon polymer resin. May be. In that case, the total content with respect to 100 parts by mass of the aromatic hydrocarbon polymer resin of silica and the above functional inorganic filler contained in the aromatic hydrocarbon polymer resin is preferably less than 40 parts by mass. . When the total content of silica or the like is 40 parts by mass or more, the mass of the aromatic hydrocarbon polymer resin relative to the total mass of the electrolyte membrane is relatively low, so that the mechanical strength of the electrolyte membrane is reduced.

[Ion exchange group]
In the present invention, the ion exchange group bonded to the aromatic hydrocarbon polymer resin may be either a cation exchange group or an anion exchange group, preferably a cation exchange group. Examples of the cation exchange group to be bonded include a sulfonic acid group (or sulfo group), a carboxylic acid group (or carboxy group), a phosphonic acid group (or phospho group), and a sulfonic acid group is more preferable. As the anion exchange group, an ammonium group or the like is bonded.

  From the viewpoint of improving the proton conductivity of the electrolyte membrane, the higher the ion exchange group content in the present invention, the better. Specifically, it is preferably contained so that at least the IEC of the electrolyte membrane is 1 meq / g or more, and more preferably 2 meq / g or more. In the present invention, an electrolyte membrane having the above-mentioned preferred IEC can be obtained by applying a radiation graft polymerization method to bond an ion exchange group to an aromatic hydrocarbon polymer resin.

  In the present invention, in order to maintain the mechanical strength of the aromatic hydrocarbon polymer resin, it is preferable to suppress the binding of ion exchange groups at the hydrophobic portion of the aromatic hydrocarbon polymer resin. From such a viewpoint, it is preferable that a graft chain is formed in the aromatic hydrocarbon polymer resin used in the present invention and an ion exchange group is bonded to the graft chain. However, the present invention does not exclude the structure in which the ion exchange group is bonded to the main chain of the aromatic hydrocarbon polymer resin.

  Since the ion exchange group of the present invention is mainly bonded to the graft chain, the higher the graft ratio, the more the ion exchange group can be bonded. Therefore, from the viewpoint of improving proton conductivity, the higher the graft ratio of the aromatic hydrocarbon polymer resin, the better. The specific graft ratio is preferably 50% or more, and more preferably 70% or more. When the graft ratio is less than 50%, the amount of ion-exchange group bonds decreases and the desired IEC cannot be obtained. The practical upper limit of the graft rate is 150 to 200%.

  The above aromatic hydrocarbon polymer resin containing the predetermined silica is used as a base material for the electrolyte membrane of the present invention after being formed into a film, a sheet or the like by a conventionally known method. The film thickness of the formed aromatic hydrocarbon polymer resin is preferably 5 to 200 μm, more preferably 10 to 120 μm. When the thickness is less than 5 μm, the electrolyte membrane is easily broken. When it exceeds 200 μm, it is difficult to obtain the conductivity required for fuel cell applications.

[Method for producing electrolyte membrane for polymer electrolyte fuel cell]
According to the method for producing an electrolyte membrane for a polymer electrolyte fuel cell of the present invention, a predetermined inorganic filler is dispersed in a molten aromatic hydrocarbon polymer resin, and then the aromatic hydrocarbon polymer resin is formed. A film forming process for forming an aromatic hydrocarbon polymer resin film by film formation, and a graft polymerization process for irradiating the aromatic hydrocarbon polymer resin film with radiation to graft polymerize an ion exchange group-containing monomer. Including. The method for producing an electrolyte membrane of the present invention will be described with reference to an example using silica as an inorganic filler.

  In the present invention, before irradiating an aromatic hydrocarbon polymer resin with radiation, the aromatic hydrocarbon polymer resin and a vinyl monomer are graft-polymerized, and a graft chain is formed on the aromatic hydrocarbon polymer resin. It is preferable to form. Thereby, the graft ratio of the ion exchange group containing monomer to the aromatic hydrocarbon polymer resin can be improved.

[Film formation process]
In this step, predetermined silica is added to and dispersed in the aromatic hydrocarbon polymer resin. In order to uniformly disperse the silica, it is preferable to add and knead the predetermined silica in a melted state until the viscosity of the aromatic hydrocarbon polymer resin becomes kneadable. The kneading temperature should just be more than melting | fusing point of the aromatic hydrocarbon type polymer resin used, for example, in the case of PEEK, 350-400 degreeC is preferable.

  Predetermined silica is added to the molten aromatic hydrocarbon polymer resin and kneaded. As long as the effect of the present invention is not impaired, one type of silica may be added, or two or more types of silica may be added. The amount of silica added to the fused aromatic hydrocarbon polymer resin corresponds to the content of silica contained in the obtained electrolyte membrane. Accordingly, an addition amount of silica corresponding to the desired content of silica contained in the electrolyte membrane may be added to the molten aromatic hydrocarbon polymer resin.

  The amount of silica added to the aromatic hydrocarbon polymer resin is preferably 0.1 parts by mass or more and 50 parts by mass or less, and more preferably 0.5 parts by mass or more and 40 parts by mass or less with respect to 100 parts by mass of the aromatic hydrocarbon polymer resin. Preferably, it is 1 to 35 parts by mass. When two or more kinds of silica are contained, the total addition amount of silica added is set to the addition amount in the above preferable range. As a specific example, hydrophilic silica and hydrophobic silica can be added at a mass ratio of 1:34 to 34: 1.

  After adding the silica, the aromatic hydrocarbon polymer resin is kneaded until the silica is uniformly dispersed. In the example of PEEK, the above kneading is preferably performed at 350 to 450 ° C. as the temperature at which the viscosity capable of kneading the aromatic hydrocarbon polymer resin can be maintained. As the kneading apparatus, for example, when a twin-screw kneading extruder (for example, HK25D manufactured by Parker Corporation) is used, the discharge speed is preferably 2 kg / hr to 8 kg / hr. The number of kneading is preferably 400 to 600 rpm. Silica can be homogeneously dispersed by kneading under the above kneading conditions.

  As the kneading apparatus, a conventionally known apparatus such as a twin-screw kneading extruder can be used. From the viewpoint of handleability, the aromatic hydrocarbon polymer resin after kneading is preferably pelletized. Alternatively, the pelletized silica-containing aromatic hydrocarbon polymer resin may be melted again and the kneading step may be repeated 2 to 10 times. Thereby, the dispersibility of a silica can be improved. In the above kneading step, a crosslinking agent or a dispersing agent may be added.

  After completion of the kneading, an aromatic hydrocarbon polymer resin in which silica is uniformly dispersed is formed using a sheet processing machine. The processing temperature during sheet molding is preferably 350 to 450 ° C. The aromatic hydrocarbon polymer resin film can be produced by quenching and curing the formed aromatic hydrocarbon polymer resin. The treatment temperature at the time of quenching is lower than the curing temperature of the aromatic hydrocarbon polymer resin to be used, and is preferably 80 to 140 ° C. As the sheet processing machine, a die coater or a T coater is used.

[Graft polymerization process]
In this step, an ion exchange group-containing monomer is graft polymerized to the obtained aromatic hydrocarbon polymer resin film. By attaching an ion exchange group to the graft chain of the aromatic hydrocarbon polymer resin, compared to the case where the same amount of ion exchange group is bonded to the main chain of the aromatic hydrocarbon polymer resin, it is aromatic. The water solubility of the hydrocarbon polymer resin film can be suppressed. Thereby, an ion exchange group can be combined without impairing the mechanical strength of the aromatic hydrocarbon polymer resin.

  In the present invention, it is preferable to polymerize a vinyl monomer on an aromatic hydrocarbon polymer resin film and then graft-polymerize the above ion exchange group-containing monomer. As a polymerization method of the vinyl monomer, a thermal graft polymerization method is preferable, and as another method, a radiation graft polymerization method is exemplified.

[Vinyl monomer polymerization process]
When applying the thermal graft polymerization method, first, a vinyl monomer reaction solution in which a vinyl monomer is dispersed is prepared. Solvents include ethers such as 1,4-dioxane and tetrahydrofuran, hydrocarbons such as toluene and hexane, alcohols such as methanol, ethanol and isopropyl alcohol, ketones such as acetone, methyl isopropyl ketone and cyclohexanone, and ethyl acetate. And esters such as butyl acetate, nitrogen-containing compounds such as isopropylamine, diethanolamine, N-methylformamide, and N, N-dimethylformamide.

The vinyl monomer used in the present invention may be any monomer that can form a graft chain on the main chain of a predetermined aromatic hydrocarbon polymer resin, and examples thereof include monomers represented by the following formula (1).
(In the above formula (1), X is H, OH, F, Cl, or a hydrocarbon. R is a hydrocarbon and its derivatives.)

  Examples of the monomer represented by the formula (1) include a monomer in which R contained in the formula (1) is a hydrocarbon having an aromatic ring or a hydrocarbon having a carbonyl group or an amide group. More specific examples include styrene and its derivatives, acrylic acid and its derivatives, acrylamides, vinyl ketones, acrylonitriles, vinyl fluorine-based monomers, or polyfunctional monomers thereof.

  Specific examples of the polyfunctional monomer include divinylbenzene, bisvinylphenylethane, 2,4,6-triallyloxy-1,3,5-triazine, triallyl-1,2,4-benzenetricarboxylate, triallyl -1,3,5-triazine-2,4,6-trione, divinyl sulfone, ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, cyclohexane dimethanol divinyl ether, phenylacetylene, diphenylacetylene, 1,4 -Diphenyl-1,3-butadiene, diallyl ether, butadiene, isobutene. These polyfunctional monomers are preferred because of their high thermal graft polymerizability. Moreover, since a crosslinked structure can be formed in the main chain of the aromatic hydrocarbon polymer resin, the mechanical strength of the electrolyte membrane can be improved.

An aromatic hydrocarbon polymer resin film containing silica is immersed in the above vinyl monomer reaction solution, and a polymerization reaction is performed in the air. The temperature condition is preferably 40 to 100 ° C, more preferably 50 to 80 ° C. The reaction time is preferably 0.2 to 1 hour. After completion of the reaction, the aromatic hydrocarbon polymer resin film on which the graft chain is formed is dried in an inert gas atmosphere. The graft ratio of the vinyl monomer in the vinyl monomer reaction step by the thermal graft polymerization method is 1 to 50%. The graft ratio of the vinyl monomer was determined by measuring the dry weight (W ₁ ) before the reaction of the aromatic hydrocarbon polymer resin film and the dry weight (W ₂ ) after the reaction as shown in the following formula (2) It can ask for.

[Ion exchange group-containing monomer graft polymerization step]
The aromatic hydrocarbon polymer resin film on which the graft chain is formed is irradiated with radiation after drying to generate radicals. By forming a graft chain in advance on the aromatic hydrocarbon polymer resin film as the base material by the vinyl monomer reaction step exemplified above, the amount of radical generation can be improved. The generated radical and the ion exchange group-containing monomer are reacted to bond the ion exchange group to the aromatic hydrocarbon polymer resin.

  Examples of the radiation graft polymerization method used in the present invention include a pre-irradiation method and a simultaneous irradiation method. The pre-irradiation method is a method of reacting a monomer containing an ion exchange group after irradiating the aromatic hydrocarbon polymer resin film with radiation. The simultaneous irradiation method is a method in which an aromatic hydrocarbon polymer resin film and an ion exchange group-containing monomer are irradiated with radiation at the same time to react with the monomer. In the present invention, any of the above methods may be applied.

  Further, examples of the pre-irradiation method include a polymer radical method and a peroxide method. The polymer radical method is a method in which an aromatic hydrocarbon polymer resin film is irradiated with radiation in an inert gas atmosphere. The peroxide method is a method in which an aromatic hydrocarbon polymer resin film is irradiated with radiation in the presence of oxygen. In the present invention, the polymer radical method is preferred.

  Examples of the type of radiation applied to the aromatic hydrocarbon polymer resin film include γ rays, X rays, electron beams, ion beams, ultraviolet rays, and the like. γ rays and electron beams are preferably used because radical generation is easy. The irradiation dose is preferably 1 kGy or more and 500 kGy or less, more preferably 5 kGy or more and 100 kGy or less, and further preferably 10 kGy or more and 60 kGy or less. If it is less than 1 kGy, the formation of graft chains becomes insufficient. If it exceeds 500 kGy, the aromatic hydrocarbon polymer resin film may break.

  In the reaction between the aromatic hydrocarbon polymer resin and the ion exchange group-containing monomer, the aromatic hydrocarbon polymer resin film is immersed in an ion exchange group-containing monomer reaction solution in which the ion exchange group-containing monomer is dispersed in a solvent. Can be done. Thereby, homopolymerization of the ion exchange group-containing monomer can be suppressed.

  An ion exchange group-containing monomer reaction solution in which a predetermined ion exchange group-containing monomer is dispersed in a solvent is prepared. The ion-exchange group-containing monomer dispersed in the solvent may be one type or two or more types. By diluting the above monomer with a predetermined solvent, the formation of a homopolymer can be suppressed.

As the ion exchange group-containing monomer, styrene sulfonic acid ethyl ester (ETSS), styrene sulfonic acid, sodium styrene sulfonate and the like are preferable.

  The concentration of the ion exchange group-containing monomer in the ion exchange group-containing monomer reaction liquid is preferably 20 to 80% by volume, more preferably 25 to 75% by volume. Solvents include ethers such as dioxane and tetrahydrofuran, hydrocarbons such as toluene and hexane, alcohols such as methanol, ethanol and isopropyl alcohol, ketones such as acetone, methyl isopropyl ketone and cyclohexanone, ethyl acetate, butyl acetate and the like And nitrogen-containing compounds such as isopropylamine, diethanolamine, N-methylformamide, and N, N-dimethylformamide.

  An aromatic hydrocarbon polymer resin film containing silica is immersed in the above-mentioned ion exchange group-containing monomer reaction solution, and a radiation graft polymerization reaction is performed in air or in an inert gas atmosphere. The oxygen concentration in the reaction atmosphere is preferably as low as possible from the viewpoint of suppressing radical deactivation, and more preferably 0.01% by volume or less. If it exceeds 0.01% by volume, the radicals are deactivated and the graft ratio is lowered. Nitrogen, argon or the like is used as the inert gas.

  The temperature condition during the polymerization is preferably 40 to 100 ° C, more preferably 50 to 80 ° C. Thereby, formation of homopolymer and radical deactivation can be suppressed. The reaction time is preferably 1 to 48 hours, more preferably 5 to 20 hours. The graft ratio of the ion exchange group-containing monomer in the ion exchange group-containing monomer graft polymerization step is about 50 to 200%.

[Ion exchange group activation process]
The ion exchange group bonded to the aromatic hydrocarbon polymer resin by the above-mentioned radiation graft polymerization method is made effective by the conventionally known method after washing and drying. Specific examples include a method of hydrolyzing an aromatic hydrocarbon polymer resin film by immersing it in pure water at 90 to 95 ° C. for 15 to 24 hours. Thereby, the electrolyte membrane for a polymer electrolyte fuel cell of the present invention can be produced.

  The IEC of the electrolyte membrane obtained by the production method of the present invention is 0.2 to 3.0 meq / g, more preferably 0.5 to 3.0 meq / g, still more preferably 1.0 to 3.0 meq / g, and 2.0 to 3.0. meq / g is most preferred. Since the electrolyte membrane of the present invention is based on an aromatic hydrocarbon polymer resin membrane, it is excellent in mechanical strength, strong alkali resistance, and chemical resistance. Moreover, the water content, radical resistance, and acid resistance of the electrolyte membrane can be improved by adding predetermined silica. Therefore, the electrolyte membrane of the present invention has good conductivity even under high temperature conditions and low humidification conditions, and is suitable for fuel cell applications.

[Polymer fuel cell]
The fuel cell of the present invention includes a membrane electrode assembly in which a fuel electrode is joined to one membrane surface of the electrolyte membrane for a polymer electrolyte fuel cell and an air electrode is joined to the other membrane surface. Since the electrolyte membrane is excellent in heat resistance and moisture content, the fuel cell of the present invention operates with high conductivity even under high temperature conditions and low humidification conditions.

  FIG. 1 is a schematic view showing a membrane electrode assembly (MEA) constituting the fuel cell of the present invention. In FIG. 1, an MEA 100 has a structure in which a fuel electrode 200 is joined to one membrane surface of an electrolyte membrane (electrolyte membrane) 300 for a polymer electrolyte fuel cell, and an air electrode 400 is joined to the other membrane surface. . The fuel electrode 200 and the air electrode 400 each have a structure in which a catalyst layer and a gas diffusion layer are joined. 201 is a catalyst layer of the fuel electrode 200, and 202 is a gas diffusion layer of the fuel electrode 200. 401 is a catalyst layer of the air electrode 400, and 402 is a gas diffusion layer of the air electrode 400.

  The catalyst layer 201 of the fuel electrode 200 is joined to the membrane surface of the electrolyte membrane 300 on the fuel electrode side. The gas diffusion layer 202 of the fuel electrode 200 is bonded to the surface of the catalyst layer 201 opposite to the surface where the catalyst layer 201 is bonded to the electrolyte membrane 300. The catalyst layer 401 of the air electrode 400 is joined to the air electrode side film surface of the electrolyte membrane 300. The gas diffusion layer 402 of the air electrode 400 is bonded to the surface of the catalyst layer 401 opposite to the bonding surface with the electrolyte membrane 300.

  The catalyst layer 201 of the fuel electrode 200 and the catalyst layer 401 of the air electrode 400 both have a catalyst supported on a carrier. The catalyst used for the catalyst layer 201 of the fuel electrode 200 may be metal particles that promote the oxidation reaction of the fuel. Preferably, platinum and platinum palladium are used. The catalyst used for the catalyst layer 401 of the air electrode 400 may be metal particles that promote the oxygen reduction reaction. Specific examples include platinum, gold, cobalt and the like and alloys thereof. Preferably, platinum is used.

  Carbon black or the like is used as the carrier. The catalyst layer may contain a known conductive agent or water repellent material. Known conductive agents include acetylene black, ketjen black and the like. Known water-repellent materials include polytetrafluoroethylene (PTFE) and the like. Examples of the method for forming the catalyst layer include a method in which a coating liquid in which at least a catalyst or a carrier is dispersed in an organic solvent is prepared, and the coating liquid is applied to a substrate using a screen printing method or the like and dried. Can be mentioned. When forming a catalyst layer using said coating liquid, the density | concentration of the catalyst in a coating liquid has preferable 30-70 mass%.

  Both the gas diffusion layer 202 of the fuel electrode 200 and the gas diffusion layer 402 of the air electrode 400 can be manufactured using conventionally known materials. Specific examples of the material include carbon non-woven fabric and carbon paper.

  A method for producing MEA 100 is not particularly limited, and a conventionally known hot press method or the like can be applied. As an example of a manufacturing method to which the hot press method is applied, the fuel electrode 200 is disposed so that the catalyst layer 201 is adjacent to one membrane surface of the electrolyte membrane 300. The air electrode 400 is disposed so that the catalyst layer 401 is adjacent to the other membrane surface of the electrolyte membrane 300. Thereafter, the fuel electrode 200, the electrolyte membrane 300, and the air electrode 400 are pressurized and integrated at a temperature condition of 100 to 250 ° C. and a pressure condition of 0.5 to 50 MPa, whereby the MEA 100 can be manufactured.

  In the cell of the fuel cell of the present invention, current collectors are disposed at both ends in the stacking direction of the MEA 100 in which the fuel electrode 200, the electrolyte membrane 300, and the air electrode 400 are stacked. The current collector joined to the fuel electrode side and the current collector joined to the air electrode side are connected to each other by an external circuit. The cell of the fuel cell of the present invention only needs to have a configuration including at least one MEA, and may have a configuration in which two or more MEAs are stacked via a separator. When two or more MEAs are stacked, the current collector may be joined to the fuel electrode and the air electrode located on the outermost side in the stacking direction.

  The electrolyte membrane used in the fuel cell of the present invention is produced by binding an ion exchange group to an aromatic hydrocarbon polymer resin such as PEEK containing silica. As a result, the water content of the electrolyte membrane and the amount of ion exchange groups can be improved, so that proton conductivity is good. High heat resistance and high mechanical strength. The fuel cell of the present invention using such a predetermined electrolyte membrane has 80-100% RH (70 ° C.), 80-100% RH (80 ° C.), relative humidity 20-40% RH (90 ° C.), relative humidity. It operates in any operating environment of 40 to 70% RH (110 ° C) and relative humidity 50 to 80% RH (120 ° C). Since the present invention operates under high temperature conditions and low humidification conditions, it is suitable for automotive applications. It also has high durability.

  The invention is further illustrated by the examples. However, the present invention is not limited to the examples described below.

[Production of electrolyte membrane]
(Example 1-4, Comparative Example 1)
(Film formation process)
PEEK powder as an aromatic hydrocarbon polymer resin and hydrophilic silica powder (primary particle size 12 nm, specific surface area 200 ± 25 m ² / g) are put into the kneader and PEEK is used at a temperature of 350 ° C or higher. The powder was kneaded with hydrophilic silica powder while melting. The content of the hydrophilic silica powder in the kneaded product of the PEEK powder and the hydrophilic silica powder was 5%. As the kneading apparatus, a twin-screw kneading extruder (HK25D) manufactured by Parker Corporation was used. After the kneading time, PEEK containing hydrophilic silica was pelletized. The pellets were again put into a kneading apparatus and melted, and hydrophilic silica and PEEK were further kneaded. Thereafter, the obtained pellets were dried.

  The dried pellets of hydrophilic silica-containing PEEK were put into a sheet processing machine, and sheet-molded to form a film while heating at a temperature condition of 400 ° C. The obtained hydrophilic silica-containing PEEK film was quenched and cured. The film thickness of the hydrophilic silica-containing PEEK film after curing was 16 μm.

(Graft polymerization process)
A test piece having a size of 2 cm × 3 cm was cut out from the obtained hydrophilic silica-containing PEEK membrane. The weight of the test piece in the dry state was measured and used as the dry weight (W ₁ ) of the hydrophilic silica-containing PEEK membrane before the reaction with the divinylbenzene (DVB) monomer. In Example 1, after a vinyl monomer was bonded to a hydrophilic silica-containing PEEK film by thermal graft polymerization to form a graft chain, ETSS monomer was further bonded by radiation graft polymerization.

First, a DVB reaction solution was prepared by adding DVB to 1,4-dioxane at a component weight ratio of 1: 3 in order to bind DVB monomers. The test piece and the DVB reaction solution were reacted in the glass container at 90 ° C. in the atmosphere to polymerize the DVB monomer into PEEK, thereby forming a graft chain on PEEK. After completion of the reaction, the test piece was dried for 1 hour under an argon atmosphere. The weight of the test piece in the dry state was measured and taken as the dry weight (W ₂ ) before irradiation of the hydrophilic silica-containing PEEK film after the reaction with the DVB monomer.

Subsequently, in order to bind the ETSS monomer, the dried test piece was placed in a glass container and irradiated with 30 kGy of γ rays in an argon atmosphere. Further, an ETSS reaction liquid in which styrene sulfonic acid ethyl ester (ETSS) was added to 1,4-dioxane at a component weight ratio of 1: 3 was prepared. The test piece was immersed in the ETSS reaction solution in the glass container. Thereafter, the test piece and the ETSS reaction solution were reacted for 24 hours under an argon atmosphere at a reaction temperature of 85 ° C., and the ETSS monomer was polymerized into PEEK to bond sulfonic acid groups to PEEK. After completion of the reaction, the test piece was washed and dried. The dry weight of the test piece bonded with the ETSS monomer after completion of the graft polymerization step was measured and taken as the weight (W ₃ ) after completion of the graft polymerization step. The grafting rate of the ETSS monomer was determined from equation (3). Table 1 shows the ETSS monomer graft ratio of Example 1.

(Ion exchange group validation process)
In the glass container, the test piece after completion of the graft polymerization step was immersed in pure water at 95 ° C. for 16 hours for hydrolysis treatment to obtain an electrolyte membrane of Example 1.

  An electrolyte membrane was prepared in the same manner as in Example 1 except that the addition rate of the hydrophilic silica powder in the kneaded mixture of PEEK powder and hydrophilic silica powder was 1% and 3%, respectively. It was.

(Example 4)
The film forming step was performed in the same manner as in Example 1 except that the hydrophobic silica powder (primary particle diameter 12 nm, specific surface area 140 ± 25 m ² / g) and PEEK powder were kneaded instead of the hydrophilic silica powder. . The content of the hydrophobic silica powder in the kneaded product of the PEEK powder and the hydrophobic silica powder was 5%. Thereafter, in the same manner as in Example 1, the graft polymerization step and the ion exchange group validation step were performed to produce an electrolyte membrane, and Example 4 was obtained.

(Comparative Example 1)
(Film formation process)
PEEK powder as an aromatic hydrocarbon polymer resin was charged into the kneading apparatus. As a kneading apparatus, a twin-screw kneading extruder (HK25D) manufactured by Parker Corporation was used. After the kneading time, PEEK was pelletized. The pellets were again put into a kneader and melted and further kneaded. Thereafter, the obtained pellets were dried.

  The dried PEEK pellets were put into a sheet processing machine, and the sheet was molded while heating at a temperature condition of 380 ° C. or higher. The obtained PEEK film was quenched and cured. The film thickness of the PEEK film after curing was 16 μm.

  A test piece having a size of 2 cm × 3 cm was cut out from a PEEK film to which silica was not added. The test piece was subjected to a graft polymerization step and an ion exchange group validation step in the same manner as in Example 1 to produce an electrolyte membrane, which was referred to as Comparative Example 1.

  For the test pieces of Example 1-4 and Comparative Example 1, the ETSS monomer graft ratio was determined by the formula (3). Table 1 shows the ETSS monomer graft ratios of Example 1-4 and Comparative Example 1.

[Moisture content]
The electrolyte membranes of Example 1-4 and Comparative Example 1 stored in water at room temperature were taken out and cut out with dimensions of 2 cm × 3 cm. After lightly wiping the surface of each cut-out electrolyte membrane, the wet weight (W ₄ ) was measured. Each wet electrolyte membrane was dried at 95 ° C. for 1 hour, and the dry weight (W ₅ ) was measured. Based on the obtained wet weight (W ₄ ) and dry weight (W ₅ ), the water content of each electrolyte membrane was determined by Equation (4).

[conductivity]
The electrolyte membranes of Examples 1-4 and Comparative Example 1 each having a film thickness of 16 μm were cut out with dimensions of 2 cm × 3 cm. About each cut-out electrolyte membrane, membrane resistance measurement was performed using the alternating current impedance meter, respectively. Membrane resistance was measured by wetting each electrolyte membrane with a 1M sulfuric acid aqueous solution, placing it between two Pt electrodes (distance between electrodes: 5 mm) as counter electrodes, and applying an alternating current of 100 kHz. Based on the obtained membrane resistance value Rm (Ω), the electrical conductivity of each electrolyte membrane was determined by Equation (5). In formula (5), d is the distance between the electrodes, and S is the membrane area of the electrolyte membrane.

[Ion exchange capacity (IEC)]
The electrolyte membranes of Example 1-4 and Comparative Example 1 after the conductivity measurement were each immersed in a 0.1 M sulfuric acid aqueous solution at 50 ° C. for 4 hours or longer to obtain a proton type. Further, it was immersed in a saturated saline solution at 50 ° C. for 4 hours to replace the H type with the —SO ₃ Na type. The saturated saline solution after each electrolyte membrane was taken out was neutralized and titrated with 0.1M NaOH, the substituted proton (H ⁺ ) was quantified, and the acid group concentration [n (acid group) obs of each electrolyte membrane ] Was requested.

The IEC of each electrolyte membrane was determined by Equation (6) using the dry weight W ₃ of the electrolyte membrane after the graft polymerization step and the acidic group concentration [n (acidic group) obs].

  Table 2 shows the measurement results of moisture content, electrical conductivity at room temperature, and IEC for Example 1-4 and Comparative Example 1.

(Example 5)
[Fabrication of fuel cell]
[Production of catalyst layer]
In order to produce a catalyst layer constituting the fuel electrode, a coating solution was prepared by dispersing platinum, carbon black, Nafion solution, and PTFE solution in an aqueous methanol solution. The coating solution was prepared so that the concentration of the catalyst was 50%. The coating solution was applied to the substrate by a spray method and dried.

  In order to produce a catalyst layer constituting the air electrode, a coating solution was prepared by dispersing platinum, carbon black, Nafion solution, and PTFE solution in a methanol aqueous solution. The coating solution was prepared so that the concentration of the catalyst was 50%. The coating solution was applied to the substrate by a spray method and dried.

[Production of gas diffusion layer]
A coating solution in which the PTFE solution was dispersed was prepared, applied to carbon paper, and dried.

[Production of MEA]
A fuel electrode catalyst layer was laminated on one membrane surface of the electrolyte membrane of Example 3 having dimensions of 5 cm × 5 cm, and an air electrode catalyst layer was laminated on the other membrane surface. The laminate was hot-pressed under a temperature condition of 120 ° C. and a pressure condition of 1 MPa to integrate the fuel electrode catalyst layer, the electrolyte membrane, and the air electrode catalyst layer. After hot pressing, the base material of each catalyst layer was peeled off.

  Gas diffusion layers were laminated on the surfaces of the catalyst layers of the fuel electrode and the air electrode on which the base material was peeled off. Thereafter, hot pressing was performed at a temperature condition of 140 ° C. and a pressure condition of 2 MPa, and the gas diffusion layers were integrated at both ends in the stacking direction of the laminate. Thus, an MEA having a fuel electrode on one membrane surface of the electrolyte membrane and an air electrode on the other membrane surface was produced.

[Separation of separators]
A separator provided with a flow path capable of supplying hydrogen as a fuel was joined to the end face of the obtained MEA on the fuel electrode side. A separator provided with a flow path capable of supplying an oxygen-containing gas from a cylinder was joined to the end face on the air electrode side. The separator was also provided with a flow path for discharging water generated by the reaction between protons and oxygen. A current collecting plate and an insulating plate were further arranged and fixed on the fuel electrode side separator and the air electrode side separator, respectively. The obtained fuel cell was designated as Example 5.

  An MEA was produced in the same manner as in Example 5 using the electrolyte membrane of Example 4 having dimensions of 5 cm × 5 cm. Using this MEA, a fuel cell was produced in the same manner as in Example 5, and designated as Example 6. An MEA was produced in the same manner as in Example 5 using the electrolyte membrane in Comparative Example 1. Using this MEA, a fuel cell was produced in the same manner as in Example 5, and designated as Comparative Example 2. Using the obtained fuel cell cells of Example 5, Example 6, and Comparative Example 2, the respective battery characteristics were measured.

[Current-voltage characteristics]
The fuel cells of Example 5, Example 6, and Comparative Example 2 were set in the fuel cell performance evaluation apparatus. The cell temperature is 80 ° C, the relative humidity is 100% RH, hydrogen is supplied to the fuel electrode at 500cc / min, air is supplied to the air electrode at 2,000cc / min, and the current-voltage characteristics are measured while gradually taking out the current as a load. did. The measurement results are shown in FIG. As shown in FIG. 2, in Example 5 and Example 6, the use of an electrolyte membrane containing silica according to the present invention suppresses voltage drop as compared with Comparative Example 2.

[Voltage characteristics]
The fuel cells of Example 5, Example 6, and Comparative Example 2 were set in the fuel cell performance evaluation apparatus. The cell temperature is 90 ° C, the relative humidity is 30% RH, hydrogen is supplied to the fuel electrode at 500cc / min, air is supplied to the air electrode at 2,000cc / min, and a constant current density of 0.25A / cm ² is applied as a load. -Voltage characteristics were measured. The measurement results are shown in FIG. As shown in FIG. 3, Example 5 and Example 6 use at least 8 hours from the start of operation even under high-temperature and low-humidification conditions by using an electrolyte membrane containing silica according to the present invention. The same level of voltage can be maintained. In the above measurement, in Example 5, the voltage drop rate after 8 hours from the start of operation was 8.75 mV / hr. In addition, the voltage drop rate after 8 hours in Example 6 was 5 mV / hr.

100 Membrane electrode assembly
200 Fuel electrode
201 catalyst layer
202 Gas diffusion layer
300 Electrolyte membrane for polymer electrolyte fuel cell
400 air electrode
401 catalyst layer
402 Gas diffusion layer

Claims (4)

  An electrolyte membrane for a polymer electrolyte fuel cell, wherein an ion exchange group is bonded to a graft chain of an aromatic hydrocarbon polymer resin containing an inorganic filler.   2. The electrolyte membrane for a polymer electrolyte fuel cell according to claim 1, wherein the aromatic hydrocarbon polymer resin is polyether ether ketone or a derivative thereof.   A solid comprising a membrane electrode assembly in which a fuel electrode is joined to one membrane surface of the electrolyte membrane for a polymer electrolyte fuel cell according to claim 1 or claim 2 and an air electrode is joined to the other membrane surface Polymer fuel cell.   A film forming step for producing an aromatic hydrocarbon polymer resin film by dispersing an inorganic filler in a molten aromatic hydrocarbon polymer resin and then forming the aromatic hydrocarbon polymer resin into a film; A method for producing an electrolyte membrane for a polymer electrolyte fuel cell, comprising: a graft polymerization step of irradiating the aromatic hydrocarbon polymer resin membrane with radiation to graft polymerize an ion exchange group-containing monomer.