JP2006185849A - Solid polymer electrolyte film for fuel cell and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid polymer electrolyte film having excellent durability by suppressing the formation of pin holes in the solid polymer electrolyte film. <P>SOLUTION: In this solid polymer electrolyte film for a fuel cell, the distribution of the concentration of hydrophobic segments in the thickness direction of the solid polymer electrolyte film for the fuel cell is increased from its center toward both surfaces thereof. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a solid polymer electrolyte membrane for a fuel cell, and more particularly to a solid polymer electrolyte membrane for a fuel cell having excellent durability.

  In recent years, in response to social demands and trends against the background of energy and environmental problems, fuel cells that can operate at room temperature and obtain high output density have attracted attention as power sources for electric vehicles and stationary power sources. A fuel cell is a clean power generation system in which the product of an electrode reaction is water in principle and has almost no adverse effect on the global environment. Fuel cells include polymer electrolyte fuel cells (PEFC), phosphoric acid fuel cells (PAFC), alkaline fuel cells (AFC), solid oxide fuel cells (SOFC), and molten carbonate fuel cells (MCFC). )and so on. Among them, the polymer electrolyte fuel cell is expected as a power source for electric vehicles because it operates at a relatively low temperature and obtains a high output density.

  The polymer electrolyte fuel cell generally has a structure in which a membrane-electrode assembly (hereinafter also simply referred to as “MEA”) is sandwiched between separators. The MEA is formed by sandwiching a solid polymer electrolyte membrane between a pair of electrode catalyst layers and a gas diffusion layer.

  The electrode catalyst layer is a porous layer formed by a mixture of a solid polymer electrolyte and an electrode catalyst in which catalyst particles are supported on a conductive carrier. In addition, a gas diffusion layer is used in which a carbon water repellent layer composed of carbon particles, a water repellent and the like is formed on the surface of a gas diffusion base material such as carbon cloth.

  In the polymer electrolyte fuel cell, the following electrochemical reaction proceeds. First, hydrogen contained in the fuel gas supplied to the anode-side electrode catalyst layer is oxidized by the electrode catalyst into protons and electrons as shown in the following formula (1). Next, the generated protons pass through the solid polymer electrolyte contained in the anode-side electrode catalyst layer, and further through the solid polymer electrolyte membrane in contact with the anode-side electrode catalyst layer, and reach the cathode-side electrode catalyst layer. The electrons generated in the anode-side electrode catalyst layer include a conductive material constituting the anode-side electrode catalyst layer, and a gas diffusion layer in contact with a different side of the anode-side electrode catalyst layer from the solid polymer electrolyte membrane The cathode side electrode catalyst layer is reached through the separator and the external circuit. The protons and electrons that have reached the cathode-side electrode catalyst layer react with oxygen contained in the oxidant gas supplied to the cathode side by the electrode catalyst as shown in the following formula (2) to generate water. In the fuel cell, electricity can be taken out through the above-described electrochemical reaction.

  The solid polymer electrolyte membrane is required to have high proton conductivity and a function as a separator sandwiched between electrodes.

  In addition, attempts have been made to reduce the thickness of conventional solid polymer electrolyte membranes from the viewpoint of reducing the internal resistance of the battery and increasing the output. However, in addition to the reduction in mechanical strength of the solid polymer electrolyte membrane itself due to the reduction in thickness, pinholes and the like are likely to occur during the production of the solid polymer electrolyte membrane. The occurrence of pinholes causes a gas leak to the counter electrode of fuel gas and oxidant gas, leading to a decrease in battery output.

Therefore, Patent Document 1 discloses a solid polymer electrolyte membrane in which a plurality of polymer membranes including a surface modified membrane are laminated. Specific examples of the surface modified membrane include those obtained by subjecting the surface of the solid polymer electrolyte membrane to imide crosslinking treatment, fluorination treatment, and the like. The surface modification film is strengthened by the surface modification treatment, and it becomes possible to improve the mechanical strength of the solid polymer electrolyte membrane even if the film thickness is thin, and defects such as pinholes may be generated. In addition, gas leakage can be suppressed.
JP 2003-272663 A

  Examples of the mechanism for generating pinholes in the solid polymer electrolyte membrane further include the following. That is, when a gas with low humidity is supplied due to operation stop or load change from a state in which the solid polymer electrolyte membrane is wetted and swollen by supplying a humidified gas, it is applied to the electrode catalyst layer. Moisture is deprived from the surface of the solid polymer electrolyte membrane in contact with it, and only the vicinity of the membrane surface contracts. Thus, if the shrinkage is not uniform between the surface and the inside of the solid polymer electrolyte membrane, cracks are likely to occur on the membrane surface due to tensile stress, and the swelling / shrinkage of the solid polymer electrolyte membrane due to wetting / drying is repeated. As a result, a pinhole is generated starting from a crack.

  In the solid polymer electrolyte membrane in which a plurality of surface-modified membranes described in Patent Document 1 are laminated, the mechanical strength at the initial stage of operation of the fuel cell is improved. However, the swelling / shrinking of the solid polymer electrolyte membrane is also repeated by repeating the above-described change in the gas wet state that occurs during transient operation including stopping when applied to an automobile or the like, and the solid polymer electrolyte membrane according to Patent Document 1 is repeated. However, there was a possibility that sufficient durability could not be obtained, such as pinholes due to a gradual decrease in mechanical strength.

  The present invention has been made paying attention to the above-mentioned problems, and its object is to provide a solid polymer electrolyte membrane having excellent durability by suppressing the generation of pinholes in the solid polymer electrolyte membrane. It is to provide.

  The present invention relates to a solid polymer electrolyte membrane for a fuel cell, wherein the concentration distribution of hydrophobic segments in the thickness direction of the solid polymer electrolyte membrane for a fuel cell increases from the center toward both surfaces. The above-mentioned problems are solved by a solid polymer electrolyte membrane for use.

  According to the present invention, the shrinkage of the solid polymer electrolyte membrane due to the change in the gas wet state can be made uniform between the inside and the surface of the solid polymer electrolyte membrane. As a result, the occurrence of cracks and pinholes on the membrane surface due to repeated swelling and shrinkage of the solid polymer electrolyte membrane can be suppressed, and a solid polymer electrolyte membrane having excellent durability can be obtained.

  By using the solid polymer electrolyte membrane, it is possible to provide a fuel cell that can exhibit stable power generation performance over a long period of time.

  A first aspect of the present invention is a solid polymer electrolyte membrane for a fuel cell, wherein the concentration distribution of the hydrophobic segment in the thickness direction of the solid polymer electrolyte membrane for a fuel cell is high from the center toward both surfaces. A solid polymer electrolyte membrane for a fuel cell (hereinafter also simply referred to as “solid polymer electrolyte membrane”).

  In the present invention, the hydrophobic segment is an atomic group having no hydrophilic functional group such as a quaternary ammonium group, a carboxyl group, a sulfonic acid group, a phosphonic acid group, or a phosphoric acid group on the skeleton. Desirably, the number of hydrophilic groups in the hydrophobic segment is an average of 0.013 or less per monomer unit constituting the hydrophobic segment.

  The hydrophobic segment is a highly hydrophobic hydrocarbon group such as a phenyl group, an alkyl group, or an allyl group; at least one hydrogen bonded to carbon in the alkyl group, cycloalkyl group, aryl group, or the like is substituted with fluorine. Those having a hydrophobic group are desirable. In the hydrophobic segment, the hydrocarbon group and / or the hydrophobic group may be the same or different. Among them, the hydrophobic segment preferably has the hydrophobic group because high hydrophobicity is obtained.

  Further, an atomic group having a hydrophilic functional group on the skeleton with respect to the hydrophobic segment is defined as a hydrophilic segment.

  For example, in a polymer electrolyte membrane made of Nafion (registered trademark), examples of the hydrophobic segment include atomic groups represented by the following formulas (1) to (3),

Examples of the hydrophilic segment include an atomic group represented by the following formula (2).

FIG. 1 shows a schematic diagram of the solid polymer electrolyte membrane of the present invention. The solid polymer electrolyte membrane 100 shown in FIG. 1 uses two solid polymer electrolyte membrane precursors 101 having a hydrophobic segment segregated on one surface and a hydrophilic segment segregated on the other surface. It is formed by laminating the segregated surface on the outer side. In FIG. 1, the hydrophobic segment is simply indicated by “F” and the hydrophilic segment is indicated by “SO ₃ H”, and the same applies to FIGS. 2 and 3 described later.

  In the solid polymer electrolyte membrane of the present invention, as shown in FIG. 1, the concentration distribution of hydrophobic segments in the thickness direction of the solid polymer electrolyte membrane 100 increases from the center toward both surfaces, and the membrane surface The hydrophobic segment concentration is high.

  As a result, the water content on the surface of the solid polymer electrolyte membrane can be reduced, and the difference in shrinkage between the surface and the inside of the solid polymer electrolyte membrane can be made uniform when the gas is wet. Therefore, it is possible to suppress the occurrence of cracks on the surface of the solid polymer electrolyte membrane that becomes the starting point of the pinhole.

  Furthermore, by reducing the water content on the surface of the solid polymer electrolyte membrane, it is possible to suppress the amount of water taken from the surface of the membrane when the gas is in a wet state, thereby greatly suppressing the swelling / shrinkage of the entire membrane. It is also possible.

  Therefore, according to the present invention, it becomes difficult to generate pinholes, and it is possible to provide a solid polymer electrolyte membrane having excellent durability.

  The material of the solid polymer electrolyte membrane of the present invention is not particularly limited, and any conventionally known material can be used without particular limitation. Specifically, the polymer skeleton is a fluorinated polymer in which all or a part of the polymer skeleton is fluorinated and has an ion exchange group, or a polymer polymer skeleton that does not contain fluorine. And solid polymer electrolytes having ion exchange groups.

Examples of the ion-exchange group is not particularly _{limited, -SO 3 H, -COOH, -PO} (OH) 2, -POH (OH), - SO 2 NHSO 2 -, - Ph (OH) (Ph represents a phenyl group A cation exchange group such as —NH ₂ , —NHR, —NRR ′, —NRR′R ″ ⁺ , —NH ₃ ^{+ and the} like (R, R ′, R ″ represent an alkyl group, cycloalkyl Anion exchange groups such as a group, an aryl group, and the like.

  Specific examples of solid polymer electrolytes that are fluorine-based polymers and have ion exchange groups include Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Corporation), and Flemion (registered trademark). Perfluorocarbon sulfonic acid polymers such as Asahi Glass Co., Ltd., polytrifluorostyrene sulfonic acid polymers, perfluorocarbon phosphonic acid polymers, trifluorostyrene sulfonic acid polymers, ethylenetetrafluoroethylene-g-styrene sulfonic acid polymers Suitable examples include polymers, ethylene-tetrafluoroethylene copolymers, polytetrafluoroethylene-g-polystyrene sulfonic acid polymers, and polyvinylidene fluoride-g-polystyrene sulfonic acid polymers.

  Specific examples of the solid polymer electrolyte having the ion exchange group as the hydrocarbon polymer include polysulfone sulfonic acid polymer, polyether ether ketone sulfonic acid polymer, polybenzimidazole alkyl sulfonic acid polymer, Preferred examples include benzimidazole alkylphosphonic acid polymers, cross-linked polystyrene sulfonic acid polymers, polyethersulfone sulfonic acid polymers, and the like.

  The material of the solid polymer electrolyte membrane has a high ion exchange ability, and is excellent in chemical durability and mechanical durability. Therefore, the solid polymer electrolyte having the ion exchange group is the above-mentioned fluorine-based polymer. Among them, Nafion (registered trademark, manufactured by DuPont) and Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.) are more preferable.

  The solid polymer electrolyte membrane of the present invention has a concentration distribution that changes so that the concentration of the hydrophobic segment increases from the center toward both surfaces. At this time, the hydrophobic segment may increase from the central part to both surfaces so as to gradually increase without having a clear boundary line as shown in FIG. 1, and increases stepwise in at least two stages. May be. In addition, the inclination angle of the concentration gradient from the central portion to both surfaces in the solid polymer electrolyte membrane is not particularly limited, and may be appropriately determined so as to obtain a solid polymer electrolyte membrane having desired characteristics such as durability. Good.

  The content of the hydrophobic segment in the surface portion of the solid polymer electrolyte membrane is preferably 50 to 99.99 mass%, more preferably 90 to 99.99, with respect to all segments constituting the solid polymer electrolyte membrane. It is good to set it as the mass%. The surface portion of the solid polymer electrolyte membrane refers to a portion having a depth of 0.001 to 1 μm, preferably 0.001 to 0.01 μm from the surface of the solid polymer electrolyte membrane.

  If the content is less than 50% by mass, the water content on the surface of the solid polymer electrolyte membrane may not be sufficiently reduced, and cracks may occur, and if it exceeds 99.99% by mass, the solid polymer electrolyte The proton conductivity of the electrolyte membrane may be lowered.

  The content of the hydrophilic segment in the surface portion of the solid polymer electrolyte membrane is preferably 50% by mass or less, more preferably 0.01% by mass or less, with respect to all segments constituting the solid polymer electrolyte membrane. It is good to do.

  In the central part of the solid polymer electrolyte membrane, the content of the hydrophobic segment is preferably 0.01 to 50% by mass, more preferably 0.01 to 5%, based on all segments constituting the solid polymer electrolyte membrane. It is good to set it as 10 mass%. If the content is less than 0.01% by mass, the difference in the swelling ratio between the central part and the surface part becomes large, which may cause defects and the like, and if it exceeds 50% by mass, proton conductivity and the like decrease. There is a fear. The central portion of the solid polymer electrolyte membrane is a portion where the hydrophobic segment concentration is the lowest and the hydrophilic segment concentration is high.

  The thickness of the central portion, that is, the thickness in which the content of the hydrophobic segment within the solid polymer electrolyte membrane is within the above range is about 0.001 to 20 μm, preferably about 0.001 to 1 μm. Good.

  The content of the hydrophilic segment at the center of the solid polymer electrolyte membrane is preferably 50 to 99.99% by mass, more preferably 90 to 99.99, based on all segments constituting the solid polymer electrolyte membrane. It is good to set it as the mass%. If the content is less than 50% by mass, the proton conductivity may decrease, and if it exceeds 99.99% by mass, the difference in the swelling ratio between the central part and the surface part increases, and defects and the like are generated. There is a fear.

  The concentration gradient in the thickness direction of the hydrophobic segment and the hydrophilic segment in the solid polymer electrolyte membrane is determined by measuring the cross-section of the solid polymer electrolyte membrane using electron probe micro-partial analysis (EPMA), X-ray photoelectron spectroscopy ( It can be measured by elemental analysis using XPS).

  As shown in FIG. 1, the solid polymer electrolyte membrane having such a concentration gradient includes at least two solid polymer electrolyte membrane precursors 101 in which the concentration distribution of the hydrophobic segment increases in the thickness direction. , And may be laminated with the surface with the higher concentration of the hydrophobic segment facing outward.

  Further, another solid polymer electrolyte membrane precursor is further sandwiched between the two solid polymer electrolyte membrane precursors 101 so that the obtained solid polymer electrolyte membrane has a desired concentration gradient of the hydrophobic segment. Or a solid polymer electrolyte membrane having a plurality of solid polymer electrolyte membrane precursors, such as disposing another solid polymer electrolyte membrane precursor on both sides of two laminated solid polymer electrolyte membrane precursors 101. May be laminated.

  Another solid polymer electrolyte membrane precursor sandwiched between the solid polymer electrolyte membrane precursors 101 is not particularly limited, but includes a segment having a lower hydrophobicity than the polymer solid electrolyte membrane precursor 101. What is contained is mentioned. Further, another solid polymer electrolyte membrane precursor disposed on both sides of the two laminated solid polymer electrolyte membrane precursors 101 is not particularly limited, but more than the polymer solid electrolyte membrane precursor 101. Examples include those containing segments with high hydrophobicity.

  At this time, it is only necessary that the obtained solid polymer electrolyte membrane has a predetermined concentration gradient of the hydrophobic segment in the thickness direction, and the solid polymer electrolytes constituting the respective solid polymer electrolyte membrane precursors The types may be different and the same may be used.

  The thickness of the solid polymer electrolyte membrane of the present invention may be appropriately determined in consideration of proton conductivity, mechanical strength, etc. of the obtained solid polymer electrolyte membrane, preferably 5 to 300 μm, more preferably 10 It is good to set it as -200 micrometers, Most preferably, it is 15-150 micrometers. From the viewpoint of strength and durability during film formation, the thickness is preferably 5 μm or more, and from the viewpoint of proton conductivity, it is preferably 300 μm or less.

  A second aspect of the present invention is a fuel cell MEA (hereinafter also simply referred to as “MEA”) using the above-described first solid polymer electrolyte membrane of the present invention.

  The structure of the MEA includes an anode side gas diffusion electrode having an anode side electrode catalyst layer and an anode side gas diffusion layer on both sides of the solid polymer electrolyte membrane, and a cathode side having a cathode side electrode catalyst layer and a cathode side gas diffusion layer. The gas diffusion electrode is not particularly limited as long as it is a conventionally known one such as a configuration in which the gas diffusion electrodes are arranged to face each other.

  The MEA of the present invention is characterized in that the first solid polymer electrolyte membrane of the present invention is used as the solid polymer electrolyte membrane. The first solid polymer electrolyte membrane of the present invention has a structure in which hydrophobic segments are segregated on the membrane surface, so that the moisture content on the membrane surface is reduced and the solid polymer electrolyte membrane due to a change in the wet state of the gas It is possible to make the difference in shrinkage uniform between the surface and the inside. Furthermore, by arranging the surface where the hydrophobic segment of the solid polymer electrolyte membrane is segregated and the electrode catalyst layer adjacent to each other, the electrode catalyst layer can remove moisture from the solid polymer electrolyte membrane even in an environment where the MEA is easily dried. It can be prevented from taking away. As a result, swelling / shrinkage of the solid polymer electrolyte membrane can be suppressed, generation of pinholes due to cracks in the solid polymer electrolyte membrane can be significantly suppressed, and an MEA having excellent durability can be obtained. It becomes possible.

  The MEA of the present invention is characterized by using the first solid polymer electrolyte membrane of the present invention. Therefore, the structure of the MEA is not particularly limited except that the first solid polymer electrolyte membrane of the present invention is used, and various conventionally known techniques may be referred to as appropriate. Therefore, the detailed description regarding the electrode catalyst layer and the gas diffusion layer in the anode and the cathode is omitted here.

  A third aspect of the present invention is a fuel cell using the above-described second MEA of the present invention. According to the above-described MEA of the present invention, it is possible to provide a fuel cell that can exhibit excellent power generation performance over a long period of time.

  The type of fuel cell is not particularly limited as long as desired cell characteristics can be obtained, but it is preferably used as a polymer electrolyte fuel cell (PEFC) from the viewpoints of practicality and safety. Thereby, a highly reliable fuel cell can be obtained as a power source for moving bodies and a stationary power source.

  The structure of the fuel cell is not particularly limited, and examples thereof include a structure in which MEA is sandwiched between separators.

  The separator has a function of separating air and fuel gas, and any conventional separator can be used without particular limitation. As the separator, conventionally known separators such as those made of carbon such as dense carbon graphite and a carbon plate and those made of metal such as stainless steel can be used without particular limitation. Moreover, in order to ensure the flow path of air and fuel gas, a gas distribution groove | channel may be formed and a conventionally well-known technique can be utilized suitably. The shape of the separator is not particularly limited, and may be appropriately determined in consideration of the output characteristics of the obtained fuel cell.

  Furthermore, a stack in which a plurality of MEAs are stacked via a separator and connected in series may be formed so that the fuel cell can obtain a desired voltage or the like. The shape of the fuel cell is not particularly limited, and may be determined as appropriate so that desired battery characteristics such as voltage can be obtained.

  4th of this invention is a manufacturing method of the 1st solid polymer electrolyte membrane of this invention. That is, a step of producing a solid polymer electrolyte membrane precursor by coating and drying a solid polymer electrolyte solution on a hydrophobic support, and at least two sheets of the solid polymer electrolyte membrane precursor And a step of laminating the surface in contact with the support on the outside, and a method for producing a solid polymer electrolyte membrane for a fuel cell.

  First, a process for producing a solid polymer electrolyte membrane precursor by applying and drying a solid polymer electrolyte solution on a hydrophobic support will be described. In the above step, the solid polymer electrolyte membrane precursor is preferably prepared by a solution casting method using a solid polymer electrolyte solution.

  The solid polymer electrolyte solution is a solution containing a solid polymer electrolyte, and is usually obtained by dissolving the solid polymer electrolyte in a solvent. As the solid polymer electrolyte, the same materials as those listed as materials for the solid polymer electrolyte membrane in the first aspect of the present invention may be used.

  As the solvent used in the solid polymer electrolyte solution, any solvent can be used without particular limitation as long as it can dissolve the solid polymer electrolyte and can be removed thereafter. Specifically, aprotic polar solvents such as N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, dichloromethane, chloroform, 1,2-dichloroethane, chlorobenzene, di- Chlorinated solvents such as chlorobenzene, alcohols such as methanol, ethanol, propanol and isopropyl alcohol, and alkylene glycol monoalkyl ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether and propylene glycol monoethyl ether are suitable. Used for. These can be used singly, but two or more solvents can be mixed and used as necessary.

  In the solid polymer electrolyte solution, if the concentration of the solid polymer electrolyte is too high, the resulting solution has a high viscosity, and there is a possibility that a solid polymer electrolyte membrane having a desired concentration gradient of hydrophobic segments may not be obtained. If the concentration of the polymer electrolyte is too low, the proton conductivity, mechanical strength, etc. of the obtained solid polymer electrolyte membrane may be lowered. Therefore, the concentration of the solid polymer electrolyte in the solid polymer electrolyte solution is 1 to 20% by mass, preferably about 5 to 10% by mass.

  The solid polymer electrolyte solution has a range in which additives such as plasticizers, stabilizers, antioxidants, and compatibilizers that are usually used do not interfere with the formation of a concentration gradient of the hydrophobic segment, if necessary. May be included.

  In the method of the present invention, in order to produce a solid polymer electrolyte membrane having a desired concentration gradient of hydrophobic segments, a hydrophobic support is used as a support on which the solid polymer electrolyte solution is applied.

By applying the solid polymer electrolyte solution on the hydrophobic support, it is possible to segregate the hydrophobic segment on the support side. That is, as schematically shown in FIG. 2, the hydrophobic segment (F) that can be contained in the solid polymer electrolyte in the solid polymer electrolyte solution 201 cast and applied on the hydrophobic support 210. In addition to segregation on the support 210 side due to the affinity action, the hydrophilic segment (SO ₃ H) can be segregated on the opposite side of the support 210 relative to the segregation.

  The hydrophobic support is a support in which at least the surface to which the solid polymer electrolyte solution is applied is hydrophobic. Specifically, polytetrafluoroethylene (PTFE), polyvinylidene fluoride ( PVDF), polyhexafluoropropylene, tetrafluoroethylene-hexafluoropropylene copolymer (FEP) and other fluororesin support, urethane resin, polystyrene resin, epoxy resin, acrylic resin, vinyl ester resin, maleic acid resin, Examples of the support include urea resin, melamine resin, and norbornene resin. In addition, as the support, a surface of a support generally used such as a glass plate, a PET (polyethylene terephthalate) film, a stainless steel plate, a stainless steel belt, or a silicon wafer is coated with the fluororesin. May also be used.

  As a method of applying the solid polymer electrolyte solution onto the hydrophobic support, a spray method may be used, but these methods can be obtained because a uniform layer can be formed by using a bar coater method or a spin coater method. Is preferred.

  At this time, the segregation state of the hydrophobic segment is not particularly limited, but it is preferable to perform the segregation of the hydrophobic segment in a stationary state.

  After applying a solid polymer electrolyte solution on the hydrophobic support, the solid polymer electrolyte membrane precursor is obtained by drying to remove the solvent. The drying temperature is not particularly limited as long as the solvent can be removed to form a film, but it is usually sufficient if it is not lower than the melting point of the solvent and lower than the boiling point of the solvent. The humidity at the time of drying is below the relative humidity of atmospheric pressure. Moreover, the atmosphere at the time of drying is not particularly limited, but an inert gas atmosphere such as nitrogen, argon or helium is preferably used.

  Next, in the method of the present invention, after preparing a solid polymer electrolyte membrane precursor having a hydrophobic segment segregated on one surface as described above, at least two of the solid polymer electrolyte membrane precursors were used. These are laminated with the surface in contact with the hydrophobic support facing outside. Thereafter, by removing the hydrophobic support, the concentration distribution of the hydrophobic segment in the thickness direction of the solid polymer electrolyte membrane is improved from the center toward both surfaces as schematically shown in FIG. Thus, a solid polymer electrolyte membrane is obtained.

  In addition, after peeling off from the hydrophobic support, the solid polymer electrolyte membrane precursor may be laminated with the surface in contact with the hydrophobic support facing outside.

  When laminating the solid polymer electrolyte membrane precursor, another solid polymer electrolyte membrane precursor is further interposed between the solid polymer electrolyte membrane precursors so that the obtained solid polymer electrolyte membrane has a desired hydrophobic segment concentration gradient. A solid polymer electrolyte membrane precursor may be sandwiched, or another solid polymer electrolyte membrane precursor may be disposed on both sides of two laminated solid polymer electrolyte membrane precursors.

  Another solid polymer electrolyte membrane precursor sandwiched between the solid polymer electrolyte membrane precursors is not particularly limited, but includes a segment having a lower hydrophobicity than the polymer solid electrolyte membrane precursor 101 And what to do. Further, another solid polymer electrolyte membrane precursor disposed on both sides of the two laminated polymer electrolyte membrane precursors is not particularly limited, but is more hydrophobic than the polymer solid electrolyte membrane precursor 101. And those containing segments having high properties.

  In the method of the present invention, it is preferable to perform hot pressing after laminating the solid polymer electrolyte membrane precursors, whereby the bondability of each solid polymer electrolyte membrane precursor can be improved. The hot pressing is not particularly limited, but is preferably performed at 110 to 170 ° C. and a pressing pressure of 1 to 5 MPa for 3 to 10 minutes.

  The time for hot pressing is not particularly limited, and may be performed immediately after the solid polymer electrolyte membrane precursor is laminated. The MEA is produced by laminating the solid polymer electrolyte membrane precursor. You may go after.

  In the above-described method for producing a solid polymer electrolyte membrane of the present invention, a hydrophobic support was used when producing the solid polymer electrolyte membrane precursor. However, the method of the present invention is not limited to the above method, and a method using a hydrophilic support is also preferably used when producing the solid polymer electrolyte membrane precursor.

  That is, the fifth of the present invention is a step of producing a solid polymer electrolyte membrane precursor by applying and drying a solid polymer electrolyte solution on a hydrophilic support, and the solid support from the hydrophilic support. And after laminating the polymer electrolyte membrane precursor, laminating at least two of the solid polymer electrolyte membrane precursors with the surface in contact with the hydrophilic support inside, the solid polymer electrolyte comprising It is a manufacturing method of a film | membrane.

  First, a process for producing a solid polymer electrolyte membrane precursor by applying and drying a solid polymer electrolyte solution on a hydrophilic support will be described. In the said process, it can carry out similarly to the 4th method of this invention mentioned above except using a hydrophilic support instead of a hydrophobic support as a support. Accordingly, only the hydrophilic support will be described below.

By casting the solid polymer electrolyte solution on the hydrophilic support, the hydrophilic segment can be segregated on the support side. That is, as schematically shown in FIG. 3, the hydrophilic segment (SO ₃ H) that can be contained in the solid polymer electrolyte in the solid polymer electrolyte solution 301 cast on the hydrophilic support 310. Is segregated to the support 310 side by the affinity action, and the hydrophobic segment (F) can be segregated to the opposite side of the support 310 relative to the segregation.

  The hydrophilic support is a support having hydrophilicity on at least the surface to which the solid polymer electrolyte solution is applied. Specifically, the quaternary ammonium group, carboxyl group, sulfonic acid group, phosphoric acid is used. And a support made of a hydrophilic resin having a hydrophilic functional group such as a group, a phosphonic acid group, a hydroxyl group, and a phenol group.

  As the support made of the hydrophilic resin, specifically, the solid polymer electrolyte listed as the material of the solid polymer electrolyte membrane in the first of the present invention, polyvinyl alcohol, polymethyl methacrylate, sodium polymethyl methacrylate, Containing hydrophilic polymers such as polyacrylic acid, sodium polyacrylate, polyvinylbenzoic acid, sodium polyvinylbenzoate, poly (2-hydroxyethyl) acrylate, poly-N-vinylpyrrolidone, poly-N-vinylacetamide Is mentioned.

  In addition, as the support made of the hydrophilic resin, a support made of a copolymer containing the hydrophilic structural unit is also preferably used. Examples of monomers that can be used in the copolymer include α-olefins such as ethylene, propylene, methyl vinyl ether, styrene, vinyl acetate, acrylic acid ester, methacrylic acid ester, and acrylonitrile, vinyl compounds, and vinylidene compounds. In addition to these vinyl polymers, polymers containing polyalkylene groups such as polyethylene oxide, starch-acrylic acid graft polymers, carboxylated methylcellulose, sodium alginate, arabic gum, collagen, etc. It may consist of molecular compounds.

  Further, as the above-mentioned hydrophilic support, the above-described polymer film or the like on the surface of a conventionally used support such as a glass plate, a PET (polyethylene terephthalate) film, a stainless steel plate, a stainless steel belt, or a silicon wafer. May be formed.

  When a polymer film having a hydrophilic functional group is used, the surface coverage of the hydrophilic functional group on the support is preferably 50 to 100%, more preferably 90 to 100%. If the content is less than 50%, a desired concentration gradient of the hydrophobic segment in the solid polymer electrolyte membrane may not be formed.

  After producing the solid polymer electrolyte membrane precursor having a hydrophilic segment segregated on one side as described above, the solid polymer electrolyte membrane precursor was peeled from the hydrophilic support, and then the solid At least two polymer electrolyte membrane precursors are used and laminated with the surface in contact with the hydrophilic support inside.

  As a result, as schematically shown in FIG. 1, a solid polymer electrolyte membrane is obtained in which the concentration distribution of hydrophobic segments in the thickness direction of the solid polymer electrolyte membrane is improved from the center toward both surfaces. is there.

  In order to peel off the solid polymer electrolyte membrane precursor from the hydrophilic support, any method used in the conventional solution casting method can be used without particular limitation. For example, a spatula, tweezers, a needle, etc. It can peel using.

  To laminate the obtained solid polymer electrolyte membrane precursor, the fourth method of the present invention using a hydrophobic support, except that the surface in contact with the hydrophilic support is inside. You can do it in the same way.

  The solid polymer electrolyte membrane of the present invention is obtained by the above-described method using a solid polymer electrolyte membrane precursor produced using a hydrophilic support and a solid polymer electrolyte produced using a hydrophobic support. You may manufacture by laminating | stacking a film | membrane precursor.

  Hereinafter, the present invention will be described in more detail with reference to examples. In addition, this invention is not limited to the following Example.

<Example 1>
A Nafion solution (registered trademark: DuPont DE520, Nafion content: 5 wt%) as a solid polymer electrolyte solution was cast on a PTFE sheet (Nitrous Naflon sheet) as a support, and the atmosphere was 25 ° C. in an air atmosphere. The solvent was removed over 24 hours to prepare a solid polymer electrolyte membrane precursor 1 (thickness 25 μm, area 10 cm × 10 cm).

  By using two sheets of the solid polymer electrolyte membrane precursor 1 and laminating with the surface in contact with the PTFE sheet facing outside, and hot-pressing at 130 ° C. for 10 minutes at a pressure of 3 MPa, and then peeling the PTFE sheet A solid polymer electrolyte membrane 1 was obtained.

<Example 2>
As a solid polymer electrolyte solution, Nafion solution (registered trademark: DuPont DE520, Nafion content: 5 wt%) was cast on a hydrophilized silicon wafer as a support, and the solvent was used in the atmosphere at 25 ° C. for 24 hours. The solid polymer electrolyte membrane precursor 2 (thickness 25 μm, area 10 cm × 10 cm) was produced.

  In addition, the said support body was produced by immersing a silicon substrate in what heated the mixed solution of hydrogen peroxide solution: concentrated sulfuric acid (mass ratio) = 3: 7. The surface coverage of the hydroxyl group, which is a hydrophilic functional group, in the support was 80%.

  After the solid polymer electrolyte membrane precursor 2 is peeled from the support with tweezers, two solid polymer electrolyte membrane precursors 2 are used and laminated with the surface in contact with the support facing inward. A polymer electrolyte membrane 2 was obtained.

<Comparative Example 1>
A solid polymer electrolyte solution prepared by adjusting Nafion (registered trademark) / isopropyl alcohol solution (manufactured by DuPont, containing 5% by weight of Nafion) to a concentration of 5% by weight with isopropyl alcohol was cast and applied to a PET film as a support. The solvent was removed at 24 ° C. for 24 hours to produce a solid polymer electrolyte membrane 1 ′ (thickness 100 μm, area 10 cm × 10 cm).

<Evaluation>
Evaluation of the solid polymer electrolyte membrane produced in the said Examples 1-2 and the comparative example 1 was performed by producing the single cell for evaluation using each solid polymer electrolyte membrane, and measuring these durability. .

(1) Production of single cell for evaluation A carbon paper having a thickness of 270 μm (TGP-H-090 manufactured by Toray Industries, Inc.) was punched into 100 cm × 100 cm, and a PTFE dispersion (polyflon D-1E manufactured by Daikin Industries, 60 wt%) Then, PTFE was dispersed in the carbon paper by drying in an oven at 80 ° C. for 1 hour. At this time, the PTFE content was 25 wt%. As a result, a gas diffusion layer subjected to a water repellent treatment was obtained.

Platinum-supported carbon (TEC10E50E, Tanaka Kikinzoku Kogyo Co., Ltd., TEC10E50E, platinum content 46.5 wt%) 10 g, Nafion (registered trademark) / isopropyl alcohol solution (DuPont, Nafion 5 wt% content) 4.5 g, pure water 50 g, 1-propanol (Wako Pure Chemical Industries, Ltd. special grade reagent) 40g, 2-propanol (Wako Pure Chemical Industries, Ltd. special grade reagent) 40g, in a glass container in a water bath set to hold at 25 ℃, homogenizer The catalyst ink was prepared by mixing and dispersing for 3 hours. Next, the catalyst layer ink was applied on one side of the gas diffusion layer that had been previously subjected to water repellent treatment using a screen printer, and dried in an oven at 100 ° C. for 30 minutes. Thus, an electrode catalyst layer having a thickness of 10 μm (the platinum weight per 1 cm ² area was 0.40 mg) was produced on the gas diffusion layer.

  Two gas diffusion layers were used and sandwiched between the polymer electrolyte membranes prepared in Examples 1 and 2 and Comparative Example 1 so that the electrode catalyst layer forming sides were opposed to each other, and the pressure was 3.8 MPa. The MEA was manufactured by hot pressing at 130 ° C. for 10 minutes. Further, the MEA was sandwiched between graphite separators, and sandwiched between gold-plated stainless steel current collector plates to obtain evaluation single cells.

(2) Evaluation of durability Hydrogen was supplied as fuel to the anode side of each evaluation single cell, and air was supplied as an oxidant to the cathode side. For both gases, the cell outlet pressure is set to atmospheric pressure, hydrogen is set to 70 ° C. and relative humidity 100%, air is set to 70 ° C. and relative humidity 100%, cell temperature is set to 70 ° C., hydrogen utilization rate is 67%, and air utilization rate. Was 40%. Under this condition, power generation was stopped after 3 minutes of power generation at a current density of 1 A / cm ² . After stopping, the supply of hydrogen and air was stopped, dry air was supplied to the single cell, the inside of the cell was replaced for 2 minutes, and then hydrogen gas was supplied to the anode side for 1 minute at the above utilization rate. Thereafter, air was supplied to the cathode side at the same utilization rate as above, and power was generated again. A power generation / stop cycle test was repeated for repeating this power generation / stop operation.

  In the single cell for evaluation using the solid polymer electrolyte membrane produced in Comparative Example 1, pinholes that cause gas leakage to the counter electrode of the fuel gas and the oxidant gas began to occur after 200 cycles, and the battery output decreased. On the other hand, in the evaluation single cell using the solid polymer electrolyte membrane produced in Examples 1 and 2, this was extended to 300 cycles, and the number of cycles until the performance was lowered due to the generation of pinholes was improved.

  From the above results, the evaluation unit cell using the solid polymer electrolyte membrane prepared in Examples 1 and 2 is more durable than the evaluation unit cell using the solid polymer electrolyte membrane prepared in Comparative Example 1. It is shown to be excellent. As a result, the solid polymer electrolyte membrane of the present invention is less susceptible to cracking and pinholes due to suppression of swelling / shrinkage of the solid polymer electrolyte membrane due to changes in the wet state of the gas. The evaluation single cell is considered to have improved durability.

  The solid polymer electrolyte membrane of the present invention is excellent in durability by suppressing the generation of pinholes, and provides a fuel cell that can exhibit stable power generation performance over a long period of time by using the solid polymer electrolyte membrane It becomes possible to do.

It is a schematic diagram which shows the state of the hydrophilic segment in the solid polymer electrolyte membrane of this invention, and a hydrophobic segment. It is a schematic diagram which shows the state of the hydrophilic segment in the solid polymer electrolyte solution apply | coated on the hydrophobic support body, and a hydrophobic segment. It is a schematic diagram which shows the state of the hydrophilic segment in the solid polymer electrolyte solution apply | coated on the hydrophilic support body, and the hydrophobic segment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100 ... Solid polymer electrolyte membrane, 101 ... Solid polymer electrolyte membrane precursor, 201 ... Solid polymer electrolyte solution, 210 ... Hydrophobic support, 301 ... Solid polymer electrolyte solution, 310 ... Hydrophilic support

Claims (5)

A solid polymer electrolyte membrane for a fuel cell,
A solid polymer electrolyte membrane for a fuel cell in which the concentration distribution of hydrophobic segments in the thickness direction of the solid polymer electrolyte membrane for a fuel cell increases from the center toward both surfaces.   A MEA for a fuel cell using the solid polymer electrolyte membrane for a fuel cell according to claim 1.   A fuel cell using the fuel cell MEA according to claim 2. Producing a solid polymer electrolyte membrane precursor by applying and drying the solid polymer electrolyte solution on a hydrophobic support; and
Laminating at least two sheets of the solid polymer electrolyte membrane precursor with the surface in contact with the hydrophobic support facing outside;
A method for producing a solid polymer electrolyte membrane for a fuel cell comprising: Producing a solid polymer electrolyte membrane precursor by applying and drying the solid polymer electrolyte solution on a hydrophilic support; and
After peeling off the solid polymer electrolyte membrane precursor from the hydrophilic support, at least two of the solid polymer electrolyte membrane precursors are laminated with the surface in contact with the hydrophilic support inside And the process of
A method for producing a solid polymer electrolyte membrane for a fuel cell comprising:

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