JP2007123122A - Electrolyte membrane for fuel cell and membrane electrode assembly - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrolyte membrane which has a concentration distribution of particulates with very short steps in a direction of membrane thickness. <P>SOLUTION: The particulate-containing electrolyte membrane for a fuel cell has a concentration gradient of particulates in a membrane in a direction of membrane thickness by utilizing an interaction of a base plate and the particulates. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electrolyte membrane for a fuel cell and a membrane electrode assembly (hereinafter also simply referred to as MEA).

  Fuel cells that generate electricity through the electrochemical reaction of gas have high power generation efficiency, and the exhausted gas is clean and has very little impact on the environment. The use of is expected. Fuel cells can be classified according to their electrolytes. For example, phosphoric acid fuel cells, molten carbonate fuel cells, solid oxide fuel cells, solid polymer fuel cells, and the like are known. In particular, the polymer electrolyte fuel cell can be operated at a temperature of about 80 ° C., and therefore it is relatively easy to handle and has a very high output density compared to other types of fuel cells. Therefore, its use is expected. A polymer electrolyte fuel cell is usually configured by stacking a large number of cells using a cell having a pair of electrodes on both sides of a solid polymer electrolyte membrane, which is a proton conductive polymer membrane, as a power generation unit. . Then, hydrogen gas or the like as fuel is supplied to an electrode (fuel electrode), and oxygen gas or air is supplied to the other electrode (air electrode) to obtain an electromotive force. As the solid polymer electrolyte membrane used as the electrolyte, a polymer membrane such as a perfluorinated sulfonic acid membrane is used.

The temperature at which the polymer electrolyte fuel cell is operated is a relatively high temperature of about 80 ° C. as described above. In addition, it is desired to further increase the operating temperature from the viewpoints of improvement in catalyst activity, effective use of exhaust heat, improvement in cooling efficiency, and the like. However, when the battery is operated at a high temperature, the strength of the solid polymer electrolyte membrane made of a polymer material becomes a problem. That is, at a high temperature, there is a risk that the elastic modulus of the solid polymer electrolyte membrane is lowered and the strength of the membrane is lowered.

  As one of the attempts to improve the strength of the solid polymer electrolyte membrane, Patent Document 1 discloses, as a method for producing an inorganic material composite polymer membrane, a raw material that is a compound in which a solute is a raw material for the inorganic material in the polymer membrane. A film solution direction by moving the solute by bringing the second liquid into contact with at least one of the surfaces of the raw material solution impregnating step for impregnating the solution and the polymer film impregnated with the raw material solution. The concentration of the inorganic fine particles in the film thickness direction includes a solute concentration gradient adjusting step for adjusting the concentration gradient of the solute and an inorganic material precipitation step for reacting the solute to precipitate fine particles of the inorganic material. A fine particle dispersed electrolyte membrane having a gradient and a method for producing the same have been proposed.

In this inorganic material composite polymer membrane, fine particle inorganic material is dispersed in the polymer membrane with a concentration gradient. Therefore, by adjusting the concentration gradient, the strength of the membrane can be improved and the water management property of the membrane can be improved. The electrolyte membrane meets various requirements such as good adhesion to the electrode.
JP 2002-352818 A

  However, the manufacturing method described in Patent Document 1 has a problem in that the manufacturing steps of the inorganic material composite polymer film are divided into three stages, and the number of steps increases, resulting in an increase in manufacturing cost. In addition, this method has a problem that it is necessary to disperse the inorganic material before the reaction, and the width of the applicable inorganic material is limited.

  Accordingly, an object of the present invention is to obtain an electrolyte membrane and an electrolyte membrane-electrode assembly having a fine particle concentration distribution in the film thickness direction in a very short step compared to the conventional art.

  Therefore, the present inventor has made it possible to create a concentration gradient of fine particles in the film during the film forming process. As a result, it has been found that the film can be formed in one step without increasing the number of manufacturing steps, and the present invention has been completed.

  That is, the object of the present invention is achieved by a fuel cell fine particle-containing electrolyte membrane characterized in that the concentration gradient of the fine particles in the film is provided in the film thickness direction by utilizing the interaction between the substrate and the fine particles.

  According to the present invention, it is possible to control and disperse the fine particle concentration in the electrolyte membrane in the thickness direction during the film formation process, so that it is possible to produce a fine particle dispersed electrolyte membrane in a very short step without increasing the number of steps. It becomes.

  Further, in the present invention, by utilizing the interaction between the substrate and the fine particles, hydrophilic fine particles are unevenly distributed in the concentration direction of the fine particles in the film in the film thickness direction, for example, in the outer direction of the electrolyte membrane (or MEA). When attached in such a manner (see FIGS. 1 to 3), the drainage effect from the central portion of the electrolyte membrane (and also the MEA) is increased, and flooding is effectively suppressed.

  Further, in the present invention, by utilizing the interaction between the substrate and the fine particles, the concentration gradient of the fine particles in the film is in the film thickness direction, for example, the gradient of the hydrophilic fine particles in the entire thickness direction of the electrolyte membrane (or MEA). When is attached, moisture can be moved in an arbitrary direction in the thickness direction of the electrolyte membrane (and also MEA). In the above description, the effect of using the hydrophilic fine particles has been described. However, the concentration gradient of the hydrophobic fine particles in the film is set so that the same effect can be exhibited even when the hydrophobic fine particles are used. It can be applied in the film thickness direction.

  The fine particle-containing electrolyte membrane for fuel cells of the present invention is characterized in that the concentration gradient of fine particles in the electrolyte membrane is provided in the film thickness direction by utilizing the interaction between the substrate and the fine particles.

  According to the present invention, the concentration gradient of the fine particles (for example, hydrophilic fine particles) in the electrolyte membrane is utilized in the film thickness direction by utilizing the interaction between the substrate and the fine particles, for example, in the center direction of the electrolyte membrane (further, MEA). By making the hydrophilic fine particles unevenly distributed and providing a concentration gradient, water can be retained in the electrolyte membrane (and also the MEA), and an effect of suppressing dryout during fuel cell power generation can be obtained.

  In addition, according to the present invention, by utilizing the interaction between the substrate and the fine particles, the concentration gradient of the fine particles in the film is increased in the film thickness direction, for example, the hydrophilic fine particles are applied in the outer direction of the electrolyte membrane (or MEA). By providing a concentration gradient by uneven distribution (see FIGS. 1 to 3), the drainage effect from the central portion of the electrolyte membrane (and also the MEA) is increased, and the effect of suppressing flooding can be obtained.

  Furthermore, according to the present invention, by utilizing the interaction between the substrate and the fine particles, the concentration gradient of the fine particles in the film is increased in the film thickness direction, for example, the hydrophilic fine particles in the entire thickness direction of the electrolyte membrane (or MEA). By providing the concentration gradient, moisture can be moved in any direction in the thickness direction of the MEA.

  Moreover, according to the present invention, it is possible to control and disperse the fine particle concentration in the electrolyte membrane in the thickness direction during the film forming process. Therefore, the fine particle dispersed electrolyte membrane can be produced in a very short step without increasing the number of steps. As a result, a cheaper electrolyte membrane can be provided as compared with the conventional fine particle-dispersed electrolyte that requires a plurality of steps.

  Here, as the interaction between the substrate and the fine particles, for example, hydrophilic-hydrophilic interaction, hydrophobic-hydrophobic interaction, π-π interaction, electrostatic interaction (including electrostatic repulsion), charge transfer interaction ( Interaction between electron donor and electron acceptor), dipole-dipole interaction (hydrogen bond, permanent dipole interaction, permanent dipole-induced dipole interaction, temporary dipole-induced dipole) Interactions, van der Waals forces, etc.), coordination bonds, and affinity interactions. Such interaction may use one kind of interaction alone, or may use two or more kinds of interactions in appropriate combination.

  Hereinafter, an example using the hydrophilic-hydrophilic interaction will be mainly described as an example of the embodiment of the present invention. However, the present invention is not limited to these, and other interactions can be performed in the same manner as the hydrophilic-hydrophilic interaction.

I. First Embodiment: Form Utilizing Hydrophilic-Hydrophilic Interaction As a form utilizing the hydrophilic-hydrophilic interaction between the substrate and the fine particles, for example, a hydrophilic material is used for both the substrate and the fine particles. , Intermolecular force (attraction) is exerted. For example, hydrophilic silica fine particles and hydrophilic silica substrates (both piranha treatment, etc.) may be mentioned, but are not limited thereto. According to this embodiment, it is excellent in that the concentration distribution can be easily controlled only by adjusting the substrate when it is desired to disperse hydrophilic fine particles or when a hydrophilic concentration gradient is desired in the film thickness direction. Yes.

(I) Fine particles The fine particles may be either hydrophilic (also simply referred to as hydrophilic fine particles) or imparted with hydrophilicity (also simply referred to as hydrophilic fine particles). In the present embodiment, these fine particles may be used alone or in combination of two or more.

These fine particles are, for example, hydroxyl group (—OH), —carboxyl group (—COOH), amino group (—NH ₂ ), carbonyl group (—CO), sulfone group, sulfonic acid group (—SO ₃ H). ), a peptide bond (-CONH-), ether bond (-COO-), a cyano group (-CN), polyoxyethylene group a thiol group (-SH), aldehyde group (-COH), amide groups (-CONH ₂ ), Imide group, imidazole (heterocyclic) group, ester bond (—O—), phosphodiester bond (—O—P (═O) OH—O—), etc. (however, these functional groups) Are preferably formed (or contained) by a compound having one or more types on the surface or inside thereof.

  The material of the fine particles is not particularly limited as long as the material can be stably present in the electrolyte membrane when the fuel cell used as the electrolyte membrane containing the fine particles is operated. . Fine particles formed of any organic or inorganic compound may be used. In the case of organic fine particles, in addition to hydrophilic-hydrophilic interaction, depending on the material used, π-π interaction, electrostatic interaction, etc. can be used effectively, and surface control is easy and can be used. It is excellent in that there are an infinite number of compounds. In addition, in the case of organic fine particles, even if they are present in the vicinity of the surface of the electrolyte membrane compared to inorganic fine particles, extremely good adhesion can be expressed between the electrolyte membrane and the electrode, and the battery reaction Is excellent in that it can sufficiently proceed. As a result, it is possible to provide a fuel cell with high MEA durability and excellent battery characteristics. However, in the present invention, as shown in each embodiment to be described later, since the surface of the inorganic fine particles is modified so as to obtain various interactions, it exhibits extremely high adhesiveness similar to that of organic fine particles. In many cases, it can be made to. On the other hand, when the fine particles are unevenly distributed in the center direction of the MEA due to the interaction between the substrate and the fine particles, the electrode and the electrolyte membrane can be adhered well regardless of the adhesion between the fine particles and the electrode. Therefore, since the particulate material is not restricted, a desired interaction between the substrate and the particulate can be selected. Therefore, for example, if a hydrophilic substrate and hydrophilic fine particles are used so that a hydrophilic-hydrophilic interaction can be selected between the substrate and the fine particles, the hydrophilic fine particles can be unevenly distributed in the center direction of the MEA. Dryout during power generation can be suppressed. On the other hand, in the case of inorganic fine particles, in addition to oxidation resistance and dimensional stability, inorganic fine particles that are excellent in heat resistance, mechanical strength, etc. are immobilized in the electrolyte membrane, so that the strength of the electrolyte membrane is improved. Can do. Even when used at high temperatures, the inorganic fine particles having excellent heat resistance can exert the effect of reinforcing the three-dimensional structure of the electrolyte membrane, so that high strength can be maintained over a long period of time. Is excellent in terms of. Therefore, these organic and inorganic fine particles may be properly used or used together depending on the intended use. The requirement is not limited to the present embodiment, and other embodiments described later, and can be applied to the present invention in general.

Examples of the fine particles having hydrophilicity (hydrophilic fine particles) include, for example, a hydroxyl group (—OH), a —carboxyl group (—COOH), an amino group (—NH ₂ ), a carbonyl group (—CO), a sulfone group, Sulfonic acid group (—SO ₃ H), peptide bond (—CONH—), ether bond (—COO—), cyano group (—CN), polyoxyethylene group, thiol group (—SH), aldehyde group (—COH) ), Amide group (—CONH ₂ ), imide group, imidazole (heterocyclic) group, ester bond (—O—), phosphodiester bond (—O—P (═O) OH—O—), etc. Examples thereof include fine particles formed of a compound having one or more types of functional groups (but not limited to these functional groups) on the surface or inside of the fine particles. Examples thereof include hydrophilic polymer fine particles synthesized by dispersion polymerization of a hydrophilic monomer. For example, hydrophilic polymer fine particles can be synthesized by dispersion polymerization of a hydrophilic monomer containing acrylamide as a main component and N-methylolacrylamide, 2-hydroxyethyl methacrylate, and acrylic acid as a comonomer. In the synthesis, poly (oxyethylene) metal acrylate or the like can be used as a reactive dispersion stabilizer, and a hydrophilic organic solvent can be used as a dispersion medium. As a result, submicron-sized fine particles are obtained, and the particle size depends on the dispersion medium SP, the copolymerization amount of poly (oxyethylene) metallate, and the chain length. Also, under specific conditions, the relationship between the polymerization rate and the volume per particle is primary, and monodispersed fine particles are obtained. However, the present invention is not limited to these, and various hydrophilic fine particles can be mentioned.

  Other hydrophilic polymers include, for example, polyvinyl pyrrolidone, copolymers of polyvinyl pyrrolidone, poly (2-methyl-2-oxazoline) polymers, poly (2-ethyl-2-oxazoline) polymers, combinations thereof, and Although these derivatives etc. are mentioned, it does not restrict | limit at all to these.

  Examples of the fine particles having hydrophilicity (hydrophilic fine particles) include hydrophilic treatment techniques such as piranha treatment, radiation graft treatment, chemical vapor adsorption treatment (CVD treatment), and vacuum ultraviolet light treatment (VUV treatment). In addition, there may be mentioned those obtained by modifying the hydrophilic functional group as described above on the surface or inside of the fine particles. For example, in the case of piranha treatment, inorganic fine particles such as silica gel fine particles are heated with a piranha solution (a mixed solution of hydrogen peroxide (31%): concentrated sulfuric acid = 3: 7 by volume). To obtain hydrophilized microparticles obtained by immersing them in a solution for a predetermined period of time and introducing (providing) a number of hydroxyl groups (—OH groups) on the surface (or inside the pores) of the microparticles. Can do. The fine particle material suitable for the hydrophilization treatment is an inorganic compound such as zirconium phosphate, silica, titania, zirconia, or alumina. This is because the piranha solution reacts explosively with organic matter. In this way, optimal conditions and materials may be appropriately selected for each hydrophilic treatment. In addition, the surface modification of the fine particles (further, a substrate described later) is not particularly limited as long as it can adjust hydrophilicity (further, the hydrophobicity or surface charge described later). The surface modification method can be generally used. For example, a silane coupling agent containing an alkoxysilane such as octadecyltrimethoxysilane, a method using a coupling agent such as a titanium coupling agent, a method using a bond between a thiol and a noble metal, or a sol-gel method to coat a thin film on the surface A method, a method of applying a polymer film such as polyimide or polypropylene, a method of further spreading the surface-modified particles on the wall surface of the substrate surface (applicable for surface modification of the substrate described later), and a treatment with a surfactant. Or the like can be used.

  The shape of the fine particles used in the present invention is not limited at all. Specific examples include a circular cross section (spherical), an elliptical cross section, a cylindrical shape, a prismatic shape, a needle shape (bar shape), and an indefinite shape. The requirement is not limited to the present embodiment, and other embodiments described later, and can be applied to the present invention in general.

  The size (average particle size) of the fine particles used in the present invention is in the range of 1 nm to 100 μm, preferably 1 nm to 0.1 μm. When the size (average particle size) of the fine particles is less than 1 nm, it is difficult to handle and the cohesive force is high, so that it is difficult to stably disperse the particles, and it is difficult to produce the fine particles themselves, which tends to be expensive. If the size of the fine particles (average particle size) exceeds 100 μm, the proton conductivity of the electrolyte may be significantly reduced. The size (average particle diameter) of the fine particles can be measured by dynamic light scattering measurement. This requirement is not limited to this embodiment, and other embodiments described later, and can be applied to the present invention in general.

  The content of the fine particles used in the present invention is 0.01 to 50 wt%, preferably 1 to 5 wt%. When the content of the fine particles is less than 0.01 wt%, it is difficult to control the desired moisture, and it may be difficult to have a sufficient fine particle concentration gradient (concentration distribution) in the film thickness direction. . When the content of the fine particles exceeds 50 wt%, it is difficult to maintain the form and mechanically brittle, and the smooth movement of protons in the electrolyte membrane may be slightly restricted. This requirement is not limited to this embodiment, and other embodiments described later, and can be applied to the present invention in general.

  The fine particles used in the present invention may be those in which a plurality of these are collected (aggregated or the like) to form secondary particles, or may be monodispersed without aggregation of the fine particles. The shape of the secondary particles is not particularly limited, and examples thereof include a spherical shape (lump shape), an elliptical cross section, a spiral shape (string shape), a tuft shape, a layer shape, and an indefinite shape. These may be used alone or in combination of two or more. This requirement is not limited to this embodiment, and other embodiments described later, and can be applied to the present invention in general.

(Ii) Substrate The substrate may be either a substrate having hydrophilicity (also simply referred to as a hydrophilic substrate) or a substrate having hydrophilicity (also simply referred to as a hydrophilic substrate).

Further, these substrates are, for example, hydroxyl groups (-OH), - a carboxyl group (-COOH), a amino _(-NH 2), carbonyl group (-CO), sulfone group, a sulfonic acid group (-SO ₃ H), peptide bond (—CONH—), ether bond (—COO—), cyano group (—CN), polyoxyethylene group, thiol group (—SH), aldehyde group (—COH), amide group (—CONH) ₂ ), hydrophilic functional groups such as imide group, imidazole (heterocyclic) group, ester bond (—O—), phosphodiester bond (—O—P (═O) OH—O—) (however, these functions) It is desirable that it is composed (formed) of a compound having one or more types on the surface or inside thereof. These are not particularly limited only to the hydrophilic substrate of this embodiment, but can be applied to a hydrophilic substrate or a substrate used in other embodiments.

  In the present invention, from the viewpoint of interaction with the fine particles in the membrane (electrolyte membrane), it is sufficient that at least the base material surface is treated so as to be a hydrophilic substrate or a hydrophilic substrate. Therefore, for example, a hydrophilic substrate or a hydrophilic substrate may be bonded to a hydrophobic substrate that is not a hydrophilic substrate or a hydrophilic substrate, or a concentration gradient of the degree of hydrophilicity is provided in the thickness direction of the substrate. It may be formed as described above.

  Further, in the present invention, the substrate (surface) may be formed so that the hydrophilicity of the entire substrate (surface) is uniform, or formed so as to have an appropriate concentration gradient in the surface direction of the substrate (surface). It may be what was done. By having a concentration gradient of the degree of hydrophilicity in the surface direction of the substrate, it is possible to have a similar concentration gradient of the degree of hydrophilicity in the surface direction of the electrolyte membrane obtained by interaction with the fine particles, for example, A concentration gradient of the degree of hydrophilicity can be provided from the inlet side to the outlet side of the fuel-containing gas or oxygen-containing gas.

Examples of the substrate having hydrophilicity (hydrophilic substrate) include, for example, hydroxyl group (—OH), —carboxyl group (—COOH), amino group (—NH ₂ ), carbonyl group (—CO), sulfone group, Sulfonic acid group (—SO ₃ H), peptide bond (—CONH—), ether bond (—COO—), cyano group (—CN), polyoxyethylene group, thiol group (—SH), aldehyde group (—COH) ), Amide group (—CONH ₂ ), imide group, imidazole (heterocyclic) group, ester bond (—O—), phosphodiester bond (—O—P (═O) OH—O—), etc. Examples thereof include a substrate formed of a compound having one or more kinds of functional groups (however, these functional groups are not limited to these functional groups) on the surface or inside of the substrate. For example, a hydrophilic polymer is synthesized by polymerization of a hydrophilic monomer containing acrylamide as a main component and N-methylolacrylamide, 2-hydroxyethyl methacrylate, and acrylic acid as a comonomer, and this is applied and dried. Thus, a desired substrate can be obtained.

  As a substrate having hydrophilicity (hydrophilic substrate), for example, by hydrophilization processing techniques such as piranha processing, radiation graft processing, chemical vapor adsorption processing (CVD processing), vacuum ultraviolet light processing (VUV processing), etc. And those obtained by modifying the hydrophilic functional group as described above on the surface or inside of the substrate. Since the piranha treatment is the same as that described for the hydrophilic microparticles, the description thereof is omitted here.

  The shape thickness of the substrate is not particularly limited, and may be a film shape or a plate shape. The requirement is not limited to the present embodiment, and other embodiments described later, and can be applied to the present invention in general.

  The thickness of the substrate is not particularly limited, and an optimum thickness may be selected as appropriate according to the shape. The thickness may be in the range of 10 to 100 μm for the film shape, and 0.1 mm for the plate shape. It may be in the range of -10 cm. This requirement is not limited to this embodiment, and other embodiments described later, and can be applied to the present invention in general.

  As an example of the first embodiment, FIG. 1 schematically shows a state of an electrolyte membrane in which a concentration gradient of fine particles in a film is applied in a film thickness direction by utilizing a hydrophilic-hydrophilic interaction between a substrate and fine particles. FIG. FIG. 1A is a schematic cross-sectional view schematically showing a state of a hydrophilic fine particle-containing electrolyte membrane for a fuel cell produced on a hydrophilic substrate, and FIG. 1B is a hydrophilic fine particle-containing electrolyte of FIG. 1A. It is a graph showing the relationship of the density distribution of hydrophilic fine particles with respect to the film thickness direction of a film | membrane (film | membrane).

  In the first embodiment, due to the hydrophilic-hydrophilic interaction between the substrate 300 and the fine particles 103, these various intermolecular forces (interactions) are exerted between the fine particles and the substrate as attractive or repulsive driving forces. The concentration distribution of the fine particles 103 is formed in the thickness direction of the electrolyte membrane 100.

  This is because a hydrophilic-hydrophilic process is performed in a state in which the fine particles 103 are movable from the application of the electrolyte solution in which the hydrophilic fine particles 103 are dispersed on the hydrophilic substrate 300 to the removal of the solvent. Make the interaction work. Specifically, by causing a hydrophilic-hydrophilic interaction to work between the hydrophilic functional group on the substrate side and the hydrophilic functional group on the fine particle side, a desired concentration gradient is formed on the fine particles 103 in the electrolyte membrane 100. Put in the direction. Thereafter, when the solvent is removed, the concentration gradient applied in the film thickness direction is fixed (stabilized). Thereby, a desired fine particle-dispersed electrolyte membrane can be obtained.

  Therefore, the substrate 300 does not need to be a constituent member of the fuel cell, and may be any substrate that can be used as a film-forming substrate used in the process of manufacturing the electrolyte membrane 100. For example, it may be an electrode catalyst layer (a constituent member of a fuel cell) used by being bonded to both surfaces of the electrolyte membrane, or may be a film-forming substrate (support) used only in the production stage. Preferably, it is a film-forming substrate (support). This is because the electrode catalyst layer can also exhibit a desired effect by dispersing the fine particles to provide a concentration gradient of the fine particles in the film thickness direction as the whole electrode-membrane assembly.

  Here, the concentration distribution (concentration gradient) can be easily controlled by adjusting the substrate. For example, it can be controlled by adjusting the density of the hydrophilic functional group on the substrate surface. However, it may be controlled by adjusting the fine particles.

  The concentration gradient (concentration distribution) of the hydrophilic fine particles 103 can be measured by, for example, an electron probe X-ray microanalyzer (EPMA), time-of-flight secondary ion mass spectrometry (TOF-SIMS), or Auger electron spectroscopy. it can.

II. Second Embodiment: Hydrophobic-Hydrophobic Interaction As a form using the hydrophobic-hydrophobic interaction between the substrate and the fine particles, for example, a hydrophobic material is used for both the substrate and the fine particles. (Attraction) to work. For example, fluorine-containing fine particles, fluorinated fine particles, and fluorine-treated substrates (such as organosilanes) can be mentioned, but are not limited thereto. According to this embodiment, it is excellent in that the concentration distribution can be easily controlled only by adjusting the substrate when it is desired to disperse hydrophobic fine particles or when a hydrophobic concentration gradient is desired in the film thickness direction. Yes.

(I) Fine particles The fine particles may be either hydrophobic (also simply referred to as hydrophobic fine particles) or imparted with hydrophobicity (also simply referred to as hydrophobic fine particles). In the present embodiment, these fine particles may be used alone or in combination of two or more.

  Further, the kind of the fine particle material is not particularly limited as long as it can stably exist in the electrolyte membrane when the fuel cell used as the electrolyte membrane containing the fine particle is operated. . Fine particles formed of any organic or inorganic compound may be used. In the case of organic fine particles, in addition to hydrophobic-hydrophobic interaction, depending on the materials used, π-π interaction and electrostatic interaction can be used effectively, and surface control is easy and compounds that can be used Is excellent in that there are an infinite number of types. On the other hand, inorganic fine particles are excellent in terms of oxidation resistance and dimensional stability. Therefore, these organic and inorganic fine particles may be properly used or used together depending on the intended use.

  Fine particles having hydrophobic properties (hydrophobic fine particles) include a fluorine skeleton, a hydrocarbon group such as an alkyl group, a fluorinated hydrocarbon group such as a fluoroalkyl group, a double bond (> C = C <), and an allyl group. A hydrophobic functional group represented by an acyl group, a phenyl group, an aromatic ring (benzene ring, etc.), a disulfide bond, a fluorine skeleton, etc. (however, these functional groups are not limited at all). Examples thereof include fine particles formed (or contained) by a compound having one or more kinds on the surface or inside. Examples thereof include hydrophobic polymer fine particles synthesized by dispersion polymerization of a hydrophobic monomer. Examples thereof include fluororesin microparticles (fluorine microparticles) such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyhexafluoropropylene, and tetrafluoroethylene-hexafluoropropylene copolymer (FEP). In addition, examples of the hydrophobic polymer include a copolymer of polyvinylidene fluoride, a terpolymer thereof, polyphenylene oxide, polysulfone, polyethersulfone, polyphenylsulfone, combinations thereof, and derivatives thereof. There is no limitation to these.

  Fine particles with hydrophobic properties (hydrophobic fine particles) include hydrocarbon groups such as alkyl groups, fluorinated hydrocarbon groups such as fluoroalkyl groups, hydrocarbon groups such as alkyl groups, and fluorinated carbonization such as fluoroalkyl groups. Hydrophobic functional groups such as hydrogen groups, double bonds (> C = C <), allyl groups, acyl groups, phenyl groups, aromatic rings (benzene rings, etc.), disulfide bonds, fluorine skeletons, etc. In particular, the fine particles are formed by a compound having one or more types on the surface or inside of the fine particles.

  As the fine particles to which hydrophobicity is imparted (hydrophobized fine particles), for example, a hydrophobic treatment technique such as fluorination treatment, alkylation treatment, surface graft treatment, or the like can be applied to the surface or inside of the fine particles. The thing etc. which modified the functional group are mentioned. For example, when hydrophobizing the surface of the fine particles, a method of performing a surface treatment while hydrolyzing the coupling agent while dispersing the fine particles in the aqueous medium so as to have a primary particle size can be used. . This hydrophobic treatment method can be carried out in the gas phase or in the liquid phase, but if carried out in the liquid phase, it is difficult for the fine particles to aggregate (secondary particles) and between the fine particles by the hydrophobic treatment. The charge repulsion action works, and the surface treatment of the fine particles can be performed in a state of almost primary particles. Fine particle materials suitable for the hydrophobizing treatment include vinyl polymer compounds such as polystyrene, polymethacrylic acid ester and acrylic acid ester, organic compounds such as silicon element-containing compounds such as organosilanes, silica, titanium oxide, Examples thereof include inorganic compounds such as alumina.

As said coupling agent, a silane coupling agent, a titanium coupling agent, etc. are mentioned, for example. More preferably used is a silane coupling agent having a general formula R _m SiY _n (wherein R represents an alkoxy group, m represents an integer of 1 to 3, Y represents an alkyl group, a vinyl group, a glycidoxy group) , A hydrocarbon group such as a methacryl group, and n is an integer of 1 to 3). For example, vinyltrimethoxysilane, vinyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, vinyltriacetoxysilane, methyltrimethoxysilane, methyltriethoxysilane, isobutyltrimethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, Examples thereof include trimethylmethoxysilane, hydroxypropyltrimethoxysilane, phenyltrimethoxysilane, n-hexadecyltrimethoxysilane, and n-octadecyltrimethoxysilane.

(Ii) Substrate The substrate may be either one having hydrophobicity (also simply referred to as a hydrophobic substrate) or one having hydrophobicity (also simply referred to as a hydrophobic substrate). These base materials include, for example, hydrocarbon groups such as alkyl groups, fluorinated hydrocarbon groups such as fluoroalkyl groups, double bonds (> C = C <), allyl groups, acyl groups, phenyl groups, aromatics It has one or more kinds of hydrophobic functional groups (but not limited to these functional groups) such as rings (benzene rings, etc.), disulfide bonds, fluorine skeletons, etc. on the surface or inside thereof. Those composed (formed) of compounds are desirable.

  In the present invention, from the viewpoint of interaction with hydrophobic fine particles in the membrane (electrolyte membrane), the hydrophobic substrate or at least the surface of the substrate to which the electrolyte solution is applied is treated to have hydrophobicity. Any substrate may be used. Accordingly, for example, a hydrophobic substrate or a hydrophobic substrate may be bonded to a hydrophilic substrate that is not a hydrophobic substrate or a hydrophobic substrate, or a concentration gradient of the degree of hydrophobicity is provided in the thickness direction of the substrate. It may be formed as described above.

  In the present invention, the substrate (surface) may be formed to have a uniform degree of hydrophobicity, or may have an appropriate concentration gradient in the surface direction of the substrate (surface). It may be what was done. By having a concentration gradient of the degree of hydrophobicity in the surface direction of the substrate, it is possible to have a similar concentration gradient of the degree of hydrophobicity in the surface direction of the electrolyte membrane obtained by interaction with the fine particles, for example, A concentration gradient of the degree of hydrophobicity can be provided from the inlet side to the outlet side of the fuel-containing gas or oxygen-containing gas.

  Examples of the substrate having hydrophobicity (hydrophobic substrate) include, for example, hydrocarbon groups such as alkyl groups, fluorinated hydrocarbon groups such as fluoroalkyl groups, double bonds (> C = C <), allyl groups, Hydrophobic functional groups such as acyl groups, phenyl groups, aromatic rings (benzene rings, etc.), disulfide bonds, fluorine skeletons, etc. (however, these functional groups are not limited in any way) on the surface or inside of the substrate. Examples include a substrate formed of a compound having one or more kinds. Specifically, substrates made of fluororesin such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyhexafluoropropylene, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polyethylene terephthalate, polyethylene Polyesters such as naphthalate, olefins such as polyethylene, polypropylene and polydicyclopentadiene, urethane resin, polystyrene resin, epoxy resin, acrylic resin, vinyl ester resin, maleic acid resin, urea resin, melamine resin, norbornene resin, etc. Etc.

  Moreover, as what gave hydrophobicity to the board | substrate (hydrophobized board | substrate), the glass plate, a polyethylene terephthalate film, a stainless steel board, a stainless steel belt, a silicon wafer etc., for example specifically, are generally used conventionally. Hydrophobic treatment technology such as one in which the fluororesin is coated on the substrate surface or a substrate in which a hydrophobic functional group is bonded to the substrate surface, the hydrophilicity as described above is applied to the surface or inside of the substrate. Although what modified the functional group etc. are mentioned, it is not restrict | limited at all to these. For example, a substrate such as glass or stainless steel is immersed in a 3-mercaptopropionic acid-ethanol solution for 10 minutes to 3 days to form a hydrophobic substrate obtained by bonding hydrophobic functional groups. This operation is performed near room temperature (20 to 30 ° C.). Moreover, about 1 to 30 hours are preferable. Instead of using ethanol, methanol or an aqueous alkaline solution may be used. Further, instead of using 3-mercaptopropionic acid, a longer aliphatic ω-mercapto fatty acid (for example, 10-mercaptodecanoic acid), an aromatic compound such as 4-thiobenzoic acid, or the like can also be used. In addition, lipoic acid may be used. Alternatively, an epoxy adduct polyamidoamine or a polymer compound having a silanol group or a thiol group in the molecule may be used. As the compound having a silanol group, an alkylsilanol used as a coupling agent for subjecting the surface of the material to a hydrophobic treatment is preferable.

  Also in the second embodiment, an electrolyte membrane in which the concentration gradient of the fine particles in the film is provided in the film thickness direction can be formed in the same manner as that utilizing the hydrophilic-hydrophilic interaction between the substrate and fine particles in FIG.

  Also in the second embodiment, with reference to FIG. 1, the substrate 300 and the fine particles 103 are subjected to hydrophobic-hydrophobic interaction, and these various intermolecular forces (interactions) are used as attractive or repulsive driving forces to form the fine particles and the substrate. It can be considered that the concentration distribution of the fine particles 103 is formed in the thickness direction of the electrolyte membrane 100 on the substrate 300 by acting between the two.

  This is because the hydrophobic-hydrophobic interaction occurs in the film formation process, in which the fine particle 103 is in a movable state from the application of the electrolyte solution in which the fine particle 103 is dispersed on the hydrophobic substrate 300 to the removal of the solvent. Work. Specifically, by causing a hydrophobic-hydrophobic interaction to work between the hydrophobic functional group on the substrate side and the hydrophobic functional group on the fine particle side, a desired concentration gradient is formed on the fine particles 103 in the electrolyte membrane 100. Put in the direction. Thereafter, when the solvent is removed, the concentration gradient applied in the film thickness direction is fixed (stabilized). Thereby, a desired fine particle-dispersed electrolyte membrane can be obtained.

  Therefore, as described in the first embodiment, the substrate 300 does not have to be a constituent member of the fuel cell, and can be used as a film-forming substrate used in the process of manufacturing the electrolyte membrane 100. I just need it. For example, an electrode catalyst layer (a constituent member of a fuel cell) used by being bonded to both surfaces of the electrolyte membrane may be used, or a film-forming substrate used only in the manufacturing stage. Preferably, it is a film forming substrate. This is because the electrocatalyst layer can also exhibit a desired effect by dispersing the fine particles to provide a concentration gradient of the fine particles in the film thickness direction as the whole MEA.

  Here, the concentration distribution (concentration gradient) can be easily controlled by adjusting the substrate side. For example, it can be controlled by adjusting the water repellency of the substrate surface. However, it may be controlled by adjusting the degree of hydrophobicity on the fine particle side, the particle diameter, and the like.

  The concentration gradient (concentration distribution) of hydrophobic fine particles can be measured by, for example, an electron probe X-ray microanalyzer (EPMA), time-of-flight secondary ion mass spectrometry (TOF-SIMS), or Auger electron spectroscopy. .

  It is also possible to utilize the interaction between hydrophilic and hydrophobic. That is, the hydrophilic-hydrophilic interaction and the hydrophobic-hydrophobic interaction described above can be used to generate a hydrophilic-hydrophobic action between the substrate and the fine particles.

  Further, in the present invention, the interaction of the third to sixth embodiments described below is expected to show expression effects such as improvement of proton conductivity in addition to water retention and drainage of the electrolyte membrane. In order to enhance the effect of the hydrophilic-hydrophilic interaction or the hydrophobic-hydrophobic interaction of the above-described first and second embodiments, the third to sixth described below will be described using these interactions. It is desirable to perform the material and surface treatment of the fine particles so as to obtain a synergistic effect with the interaction of the embodiment. For example, as in the following third embodiment, the material may be a hydrophilic material or a hydrophobic material as fine particles as described in the first or second embodiment and having a π electron of an aromatic ring, or the first ˜Aromatic rings may be introduced into the surface of the fine particles by chemically modifying a part of the hydrophilic material or hydrophobic material described in the embodiment. On the contrary, as a fine particle, a hydrophilic or hydrophobic functional group is introduced to the surface of the fine particle by chemically modifying a part of the material having π electrons of the aromatic ring described in the following third embodiment. You may do it. The same applies to the other fourth to sixth embodiments. Hereinafter, the third to sixth embodiments will be described.

III. Third Embodiment: Form Utilizing π-π Interaction As a form utilizing π-π interaction between a substrate and fine particles, for example, the substrate and fine particles both have π electrons of an aromatic ring, or an aromatic ring The intermolecular force (attractive force) is exerted between the substrate and the fine particles using the π-π interaction between the π electron and the electron possessed by the functional group. This is because π-π interaction works between the aromatic ring and the aromatic ring, or between the aromatic ring and the functional group of the CH group, NH group or OH group. Therefore, as an example of the form utilizing the π-π interaction between the substrate and the fine particles, fine particles having an aromatic ring or aromatic compound-modified fine particles and an aromatic compound-treated substrate can be mentioned. Is not to be done.

(I) Fine particles The fine particles may be those having an aromatic ring (also simply referred to as aromatic ring fine particles) or those modified with an aromatic ring compound (also simply referred to as aromatic ring compound-modified fine particles). In the present embodiment, these fine particles may be used alone or in combination of two or more.

  The material of the fine particles is not particularly limited as long as the material can be stably present in the electrolyte membrane when the fuel cell used as the electrolyte membrane containing the fine particles is operated. . Fine particles formed of any organic or inorganic compound may be used. In the case of organic fine particles, in addition to the π-π interaction, depending on the materials used, hydrophilic-hydrophilic interaction or hydrophobic-hydrophobic interaction, electrostatic interaction, etc. can be used effectively, making it stronger. It is excellent in that the concentration gradient of fine particles can be controlled by using various interactions together. On the other hand, inorganic fine particles are excellent in terms of oxidation resistance and dimensional stability. Therefore, these organic and inorganic fine particles may be properly used or used together depending on the intended use.

  Examples of the fine particles having an aromatic ring (aromatic ring fine particles) include fine particles formed of polyesters such as polyethylene terephthalate and polyethylene naphthalate, and compounds having an aromatic ring such as polyphenylenes.

  Examples of fine particles modified with an aromatic ring compound (aromatic ring compound-modified fine particles) include aromatics such as polyesters having an aromatic ring such as polyethylene terephthalate and polyethylene naphthalate, and polyphenylenes such as polyphenyl ether. Examples of the surface modification technique using a ring compound include those obtained by modifying the surface or inside of fine particles with an aromatic ring compound or a functional group having an aromatic ring as described above.

(Ii) Substrate The substrate is one having an aromatic ring (including a heteroaromatic ring or multiple bond ring) (also simply referred to as an aromatic ring substrate), or an aromatic compound (including a heteroaromatic compound or multiple bond). Any of those modified (also simply referred to as an aromatic ring compound-modified substrate) may be used.

  In the present invention, from the viewpoint of interaction with fine particles in the membrane (electrolyte membrane), it is sufficient that at least the base material surface is treated so as to be an aromatic ring substrate or an aromatic ring compound modified substrate. Therefore, for example, an aromatic ring substrate or an aromatic ring compound modified substrate may be bonded to a substrate that is not an aromatic ring substrate or an aromatic ring compound modified substrate.

  Examples of the substrate modified with an aromatic ring compound (aromatic ring compound modified substrate) include aromatic rings such as piranha treatment, radiation grafting treatment, chemical vapor adsorption treatment (CVD treatment), vacuum ultraviolet light treatment (VUV treatment), etc. Examples of the surface modification treatment technique using a compound include those obtained by modifying the surface or inside of a substrate with an aromatic ring compound as described above. Since the piranha treatment is the same as that described for the hydrophilic microparticles, the description thereof is omitted here.

  The shape thickness of the substrate is not particularly limited, and may be a film shape or a plate shape.

  The thickness of the substrate is not particularly limited, and an optimum thickness may be selected as appropriate according to the shape. The thickness may be in the range of 10 to 100 μm for the film shape, and 0.1 mm for the plate shape. It may be in the range of -10 cm.

  Also in the third embodiment, an electrolyte membrane having a concentration gradient of fine particles in the film in the film thickness direction can be formed in the same manner as that utilizing the hydrophilic-hydrophilic interaction between the substrate and fine particles in FIG.

  In the third embodiment as well, with reference to FIG. 1, the substrate 300 and the fine particle 103 interact with each other using the various intermolecular forces (interactions) by attractive or repulsive driving force due to the π-π interaction. It can be considered that the concentration distribution of the fine particles 103 is formed in the thickness direction of the electrolyte membrane 100 on the substrate 300 by acting between the two.

  This is because π−π in the film forming process, the process in which the fine particles 103 are movable from the application of the electrolyte solution in which the hydrophilic fine particles 103 are dispersed on the hydrophilic substrate 300 to the removal of the solvent. Make the interaction work. Specifically, by causing a π-π interaction to work between the π electrons of the aromatic ring on the substrate side and the π electrons of the aromatic ring on the fine particle side, a desired concentration gradient is imparted to the fine particles 103 in the electrolyte membrane 100. Apply in the film thickness direction. Thereafter, when the solvent is removed, the concentration gradient applied in the film thickness direction is fixed (stabilized). Thereby, a desired fine particle-dispersed electrolyte membrane can be obtained.

  Therefore, as described in the first embodiment, the substrate 300 does not have to be a constituent member of the fuel cell, and can be used as a film-forming substrate used in the process of manufacturing the electrolyte membrane 100. I just need it. For example, an electrode catalyst layer (a constituent member of a fuel cell) used by being bonded to both surfaces of the electrolyte membrane may be used, or a film-forming substrate used only in the manufacturing stage. Preferably, it is a film forming substrate. This is because the electrocatalyst layer can also exhibit a desired effect by dispersing the fine particles to provide a concentration gradient of the fine particles in the film thickness direction as the whole MEA.

  Here, the concentration distribution (concentration gradient) can be easily controlled by adjusting the substrate. For example, it can be controlled by adjusting the aromatic ring density on the substrate surface. However, it may be controlled by adjusting the fine particles.

IV. Fourth Embodiment: Form Utilizing Electrostatic Interaction As a form utilizing electrostatic interaction between a substrate and fine particles, for example, fine particles (for example, polystyrene sulfone) charged to plus (+) or minus (-) Intermolecular force between the substrate and the microparticle using electrostatic repulsion or electrostatic interaction with the oppositely charged substrate or the same charged substrate with an acid (PSS) microparticle, etc. (Attraction) is used, but it is not limited to these.

(I) Fine particles Examples of the fine particles include, but are not limited to, the various fine particles described in the above (I) to (III). Preferably, polystyrenesulfonic acid, polyaniline, etc., which are easily charged positively (+) or negatively (−), are desirable. In the present embodiment, such fine particles having the same charge may be used singly or in combination of two or more.

  The material of the fine particles is not particularly limited as long as the material can be stably present in the electrolyte membrane when the fuel cell used as the electrolyte membrane containing the fine particles is operated. . Fine particles formed of any organic or inorganic compound may be used. In the case of organic fine particles, electrostatic interaction, π-π interaction, hydrophilic-hydrophilic interaction or hydrophobic-hydrophobic interaction can be combined and used effectively. Is excellent in that it is infinite. On the other hand, inorganic fine particles are excellent in terms of oxidation resistance and dimensional stability. Therefore, these organic and inorganic fine particles may be properly used or used together depending on the intended use.

  As a method of charging the fine particles to plus (+) or minus (−), a general charging technique used for charging the fine particles can be used. Specific examples include a method of applying a voltage, but are not limited thereto. The charges (electrostatic charges) charged in the fine particles can be easily removed thereafter by an appropriate method.

(Ii) Substrate The substrate may be any material that can be charged and includes the various substrates described in (I) to (III) above, but is not limited thereto.

Examples of the method of applying a desired charge to the substrate include voltage application, but are not limited thereto. In the fourth embodiment, the hydrophilic-hydrophilic interaction between the substrate of FIG. An electrolyte membrane having a concentration gradient of fine particles in the membrane in the film thickness direction can be formed in the same manner as that used.

  In the fourth embodiment, the various intermolecular forces (interactions) act as attractive or repulsive driving forces between the microparticles and the substrate by electrostatic interaction between the microparticles and the microparticles. The fine particle concentration distribution is formed in the film thickness direction.

  This is because, during the film forming process, the fine particles can move from application of an electrolyte solution in which fine particles charged to + or − are dispersed to a substrate charged to + (or −) to removal of the solvent. Engage electrostatic interactions in the process. Specifically, by applying an electrostatic interaction between the substrate surface and the fine particles, a desired concentration gradient is given to the fine particles in the electrolyte membrane in the film thickness direction. After that, when the solvent is removed, the concentration gradient applied in the film thickness direction may be fixed (stabilized). Thereby, a desired fine particle-dispersed electrolyte membrane can be obtained.

V. Fifth Embodiment: Form using charge transfer interaction As a form using charge transfer interaction between a substrate and fine particles, an electron donor (donor; anthraquinone disulfonic acid, aromatic hydrocarbon, amine) is used on one of the substrate and fine particles. And the like using a charge transfer interaction in combination with an electron acceptor (acceptor; halogen-containing compound, quinone compound such as hydroquinone, nitro compound, cyano compound, etc.) An intermolecular force (attraction) is applied between the fine particles. Other examples include, but are not limited to, iodo and benzene, benzoquinone and hydroquinone, trinitrobenzene and hexamethylbenzene, tetracyanoethylene and benzene, hexamethylbenzene, or combinations thereof. It is not a thing.

(I) Fine particles When used as an electron donor, the fine particles include anthraquinone disulfonic acid, aromatic hydrocarbons, amines and the like as described above, but are not limited thereto. When used as an electron acceptor, examples thereof include halogen-containing compounds, quinone compounds such as hydroquinone, nitro compounds, and cyano compounds, but are not limited thereto. In this embodiment, such fine particles as an electron donor or electron acceptor may be used alone or in combination of two or more.

  The material of the fine particles is not particularly limited as long as the material can be stably present in the electrolyte membrane when the fuel cell used as the electrolyte membrane containing the fine particles is operated. Absent. Fine particles formed of any organic or inorganic compound may be used. In the case of organic fine particles, charge transfer interaction, π-π interaction, hydrophilic-hydrophilic interaction, hydrophobic-hydrophobic interaction, etc. can be combined and effectively function. It is excellent in that it is infinite. On the other hand, inorganic fine particles are excellent in terms of oxidation resistance and dimensional stability. Therefore, these organic and inorganic fine particles may be properly used or used together depending on the intended use.

(Ii) Substrate The substrate is not particularly limited as long as it can combine with the fine particles and can exhibit a charge transfer interaction, and examples thereof include electron donors and electron acceptors exemplified for fine particles. It is not something.

  Also in the fifth embodiment, an electrolyte membrane in which the concentration gradient of fine particles in the film is provided in the film thickness direction can be formed in the same manner as that utilizing the hydrophilic-hydrophilic interaction between the substrate and fine particles in FIG.

  In the fifth embodiment, these various intermolecular forces (interactions) are exerted between the fine particles and the substrate as attractive or repulsive driving forces by the charge transfer interaction between the fine particles and the fine particles. A concentration distribution of fine particles is formed in the film thickness direction.

  This is because, during the film forming process, for example, the fine particles move from the application of the electrolyte solution in which the fine particles composed of the electron acceptor are dispersed on the substrate composed of the electron donor to the removal of the solvent. Make charge transfer interactions work in a process that is possible. Specifically, by applying a charge transfer interaction between the substrate surface and the fine particles, a desired concentration gradient is applied to the fine particles in the electrolyte membrane in the film thickness direction. After that, when the solvent is removed, the concentration gradient applied in the film thickness direction may be fixed (stabilized). Thereby, a desired fine particle-dispersed electrolyte membrane can be obtained.

VI. Sixth Embodiment: Form using dipole-dipole interaction As a form using dipole-dipole interaction between a substrate and fine particles, for example, hydrogen produced by compounds having FON atomic groups on the substrate and fine particles. A dipole-dipole interaction such as a bond is used to exert an intermolecular force (attractive force) between the substrate and the fine particles, but is not limited thereto.

(I) Fine particles Examples of the fine particles include polar molecules such as compounds having FON atomic groups such as fluorinated cyanophenyl benzoate, polyurethane, polyether ether ketone, and polyurea, but are not limited thereto. It is not a thing. In particular, in the case of using a hydrogen bond, which is a particularly strong example of a dipole-dipole interaction, if the atom having a large electronegativity is not F (fluorine), O (oxygen), or N (nitrogen), the hydrogen bond Therefore, it is necessary to use the compound having the FON atomic group described above because it is impossible to induce the attractive force required for the above. From the viewpoint of dispersion in the electrolyte material, the fine particles are preferably aromatic polymers such as polyetheretherketone. In the present embodiment, these fine particles may be used alone or in combination of two or more.

  Further, the kind of the fine particles is not particularly limited as long as the fine particles can be stably present in the electrolyte membrane when the fuel cell used as the electrolyte membrane containing the fine particles is operated. Fine particles formed of any inorganic compound may be used. In the case of organic fine particles, π-π interaction, electrostatic interaction, hydrophilic-hydrophilic interaction or hydrophobic-hydrophobic interaction, etc. can be involved and act effectively, and the types of compounds that can be used Is excellent in that it is abundant. On the other hand, inorganic fine particles are excellent in terms of oxidation resistance and dimensional stability. Therefore, these organic and inorganic fine particles may be properly used or used together depending on the intended use.

(Ii) Substrate The substrate may be any substrate as long as a dipole-dipole interaction (attraction) such as a hydrogen bond acts between the fine particles, and the same FON atomic group as that exemplified for the fine particles may be used. Examples thereof include polar molecules such as compounds, but are not limited thereto.

  In the sixth embodiment as well, an electrolyte membrane in which the concentration gradient of fine particles in the film is provided in the film thickness direction can be formed in the same manner as that using the hydrophilic-hydrophilic interaction between the substrate and fine particles in FIG.

  In the sixth embodiment, for example, various intermolecular forces acting between the positive end of the polar molecule constituting the substrate and the negative end of the polar molecule constituting the fine particle due to the dipole-dipole interaction between the substrate and the fine particle. By causing (interaction) to act as an attractive or repulsive driving force between the fine particles and the substrate, a concentration distribution of the fine particles is formed in the thickness direction of the electrolyte membrane on the substrate.

  In the film forming process, for example, an electrolyte solution in which fine particles composed of a compound having FON atomic groups are dispersed on a substrate surface composed of a compound having FON atomic groups is applied, and then the solvent is removed. In the process in which the fine particles are movable until they are removed, a dipole-dipole interaction is exerted. Specifically, a desired concentration gradient is applied to the fine particles in the electrolyte film in the film thickness direction by causing a dipole-dipole interaction to work between the substrate surface and the fine particles. After that, when the solvent is removed, the concentration gradient applied in the film thickness direction may be fixed (stabilized). Thereby, a desired fine particle-dispersed electrolyte membrane can be obtained.

  This completes the description of the constituent features of the characteristic part of the fine particle-containing electrolyte membrane of the present invention. There are no particular restrictions on the other constituents (mainly electrolyte components) of the fine particle-containing electrolyte membrane of the present invention. Hereinafter, other constituent elements (mainly electrolyte components) will be briefly described, but the present invention is not limited thereto.

  That is, the fine particle-containing electrolyte membrane of the present invention is not particularly limited except that the fine particles described above are contained in the electrolyte membrane with a concentration gradient in the film thickness direction, and is a membrane made of a known electrolyte component. Any member having at least high proton conductivity may be used. Electrolyte components that can be used in this case are broadly classified into fluorine-based electrolytes that contain fluorine atoms in all or part of the polymer skeleton, and hydrocarbon-based electrolytes that do not contain fluorine atoms in the polymer skeleton.

  Specific examples of the fluorine electrolyte include perfluorocarbon sulfonic acids such as Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.), and Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.). Polymer, polytrifluorostyrene sulfonic acid polymer, perfluorocarbon phosphonic acid polymer, trifluorostyrene sulfonic acid polymer, ethylene tetrafluoroethylene-g-styrene sulfonic acid polymer, ethylene-tetrafluoroethylene copolymer, polyvinylidene A preferred example is a fluoride-perfluorocarbon sulfonic acid-based polymer.

  Specific examples of the hydrocarbon electrolyte include polysulfone, polysulfonic acid, polyaryl ether ketone sulfonic acid, polybenzimidazole alkyl sulfonic acid, polybenzimidazole alkylphosphonic acid, polystyrene sulfonic acid, polyether ether ketone sulfonic acid, poly A suitable example is phenylsulfonic acid.

  The polymer electrolyte preferably contains a fluorine atom because of its excellent heat resistance and chemical stability. Among them, Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.) Fluorine electrolytes such as Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.) are preferred.

  In addition, various Nafion (registered trademark of DuPont) manufactured by DuPont and perfluorosulfonic acid membranes represented by Flemion, ion exchange resins manufactured by Dow Chemical, ethylene-tetrafluoroethylene copolymer resin membrane, trifluoro Fluoropolymer electrolytes such as resin membranes based on styrene, hydrocarbon resin membranes with sulfonic acid groups, and other commonly available solid polymer electrolyte membranes and polymer microporous membranes A membrane impregnated with a liquid electrolyte, a membrane in which a porous body is filled with a polymer electrolyte, or the like may be used. Alternatively, the electrolyte membrane may be made of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), or the like in addition to the above-described fluorine-based polymer electrolyte or a membrane made of a hydrocarbon resin having a sulfonic acid group. You may use what formed the porous thin film impregnated with electrolyte components, such as phosphoric acid and an ionic liquid. In this case, it can be said that fine particles are added when forming a porous thin film so as to have a concentration gradient.

  The thickness of the electrolyte membrane may be appropriately determined in consideration of the properties of the obtained MEA, but is preferably 5 to 300 μm, more preferably 10 to 200 μm, and particularly preferably 15 to 100 μm. From the viewpoint of strength during film formation and durability during MEA operation, it is preferably 5 μm or more, and from the viewpoint of output characteristics during MEA operation, it is preferably 300 μm or less.

  The size of the electrolyte membrane may be appropriately determined in consideration of the characteristics of the obtained MEA. In particular, the present invention is excellent in that the cost of the membrane can be reduced because the membrane can be formed in one step without increasing the number of manufacturing steps in the process of forming the electrolyte membrane. For example, the price of a fuel cell for an automobile fuel cell is said to be 100 to 200 million yen, and it is said that it is difficult to achieve the same price as a current gasoline engine car only by the cost reduction effect by mass production. Yes. Therefore, development of parts and structures that contribute to cost reduction as well as improvement of fuel cell performance has become an important theme. This is one of the problems that can be said with respect to the membrane constituting the fuel cell. In particular, in the fluorine-based resin membrane that is one of the high-performance membranes, cost reduction is a major theme. Therefore, since the film forming process can be performed in a very short step as in the present invention, it is extremely excellent that a significant cost reduction effect can be expected because the cost of the film can be greatly reduced.

  Next, the MEA according to the present invention is obtained by sandwiching and laminating a catalyst layer from both surfaces of the above-described fine particle-containing electrolyte membrane of the present invention.

  Hereinafter, the embodiments of the MEA of the present invention will be described separately for each method of applying a concentration gradient in the film thickness direction of the fine particles in the fine particle-containing electrolyte membrane of the present invention.

  The first embodiment of the MEA of the present invention is obtained by laminating so that the concentration of fine particles increases toward the center in the thickness direction of the MEA electrolyte membrane. By adopting such a configuration, for example, when hydrophilic fine particles are unevenly distributed in the center direction of the MEA, water can be retained in the MEA, and the effect of suppressing dryout during fuel cell power generation can be exhibited or enhanced. Can do. On the contrary, when hydrophobic fine particles are unevenly distributed in the central direction of the MEA, the drainage effect from the central portion of the MEA is increased, and the effect of suppressing flooding can be expressed or enhanced.

  In the MEA of the present invention, an example in which the fine particle-containing electrolyte membrane is used is shown, but a fine particle-containing catalyst layer formed in the same manner as the fine particle-containing electrolyte membrane of the present invention may be used for the catalyst layer. By carrying out like this, it can be set as the structure by which hydrophilic microparticles were unevenly distributed in the center direction of MEA in the above-mentioned whole MEA, and it is excellent in the point which can raise the said effect further.

  The second embodiment of the MEA of the present invention is obtained by laminating so that the concentration of the fine particles increases toward the outside in the film thickness direction of the MEA. By adopting such a configuration, for example, when hydrophilic fine particles are unevenly distributed in the central direction of the MEA, the drainage effect from the central portion of the MEA is increased, and the effect of suppressing flooding can be expressed or enhanced. On the contrary, when hydrophobic fine particles are unevenly distributed in the center direction of the MEA, water can be retained in the MEA, and the effect of suppressing dryout during fuel cell power generation can be expressed or enhanced.

  The third embodiment of the MEA of the present invention is obtained by laminating so that the concentration of fine particles increases from one surface to the other surface in the film thickness direction of the MEA. By adopting such a configuration, for example, when there is a gradient of hydrophilic fine particles or hydrophobic fine particles throughout the thickness direction of the MEA, moisture can be moved in any direction in the thickness direction of the MEA. By providing such a configuration in an appropriate part of the MEA surface, the effect of suppressing the dry-out during fuel cell power generation can be expressed or enhanced, and the drainage effect from the central part of the MEA can be increased. The suppressing effect can be expressed or enhanced.

  The fuel cell fine particle-containing electrolyte membrane (and catalyst layer) of the present invention and the MEA using the same are not limited to the third embodiment of the MEA, but have a configuration in which the fine particles are unevenly distributed in the film thickness direction as described above. The portion to be taken may be formed on the entire electrolyte membrane (further, the catalyst layer) or MEA surface (electrolyte membrane or MEA surface direction). Or you may form only in the suitable location (area | region) of electrolyte membrane (further a catalyst layer) thru | or MEA surface (electrolyte membrane thru | or the MEA surface direction). Such a structure may be configured using, for example, a material (for example, a hydrophilic material) that interacts with the fine particles only at an applicable position on the substrate surface, or interacts with the fine particles only at an applicable position on the substrate surface. A surface treatment (such as a hydrophilic treatment) may be applied.

  The MEA of the present invention is not particularly limited with respect to the other constituent elements (mainly the catalyst layer and further the gas diffusion layer (GDL)) other than the above-described fine particle-containing electrolyte membrane of the present invention. . Hereinafter, these other constituent elements (mainly the catalyst layer and further the gas diffusion layer (GDL)) will be briefly described, but are not limited thereto.

(1) Catalyst layer The configuration of the catalyst layer includes (i) an electrode catalyst and (ii) an electrolyte.

(I) Electrode catalyst The electrode catalyst is formed by supporting catalyst particles on a conductive carrier.

  Here, the catalyst component used in the cathode catalyst layer is not particularly limited as long as it has a catalytic action in the oxygen reduction reaction, and a known catalyst can be used in the same manner. Further, the catalyst component used in the anode catalyst layer is not particularly limited as long as it has a catalytic action for the oxidation reaction of hydrogen, and a known catalyst can be used in the same manner. Specifically, it is selected from platinum, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum and the like, and alloys thereof. Is done. Among these, those containing at least platinum are preferably used in order to improve catalyst activity, poisoning resistance to carbon monoxide and the like, heat resistance, and the like. The composition of the alloy is preferably 30 to 90 atomic% for platinum and 10 to 70 atomic% for the metal to be alloyed, depending on the type of metal to be alloyed. The composition of the alloy when the alloy is used as a cathode catalyst varies depending on the type of metal to be alloyed and can be appropriately selected by those skilled in the art, but platinum is 30 to 90 atomic%, and other metals to be alloyed are 10 It is preferable to set it to -70 atomic%. In general, an alloy is a generic term for an element obtained by adding one or more metal elements or non-metal elements to a metal element and having metallic properties. The alloy structure consists of a eutectic alloy, which is a mixture of component elements that form separate crystals, a component element that completely dissolves into a solid solution, and a component element that is an intermetallic compound or a compound of a metal and a nonmetal. There is what is formed, and any may be used in the present application. At this time, the catalyst component used for the cathode catalyst layer and the catalyst component used for the anode catalyst layer can be appropriately selected from the above. In the following description, unless otherwise specified, the description of the catalyst component for the cathode catalyst layer and the anode catalyst layer has the same definition for both, and is collectively referred to as “catalyst component”. However, the catalyst components for the cathode catalyst layer and the anode catalyst layer do not need to be the same, and are appropriately selected so as to exhibit the desired action as described above.

  The shape and size of the catalyst component are not particularly limited, and the same shape and size as known catalyst components can be used, but the catalyst component is preferably granular. At this time, the smaller the average particle diameter of the catalyst particles used in the catalyst ink, the higher the effective electrode area where the electrochemical reaction proceeds, which is preferable because the oxygen reduction activity is also high, but in practice the average particle diameter is too small. On the other hand, a phenomenon in which the oxygen reduction activity decreases is observed. Therefore, the average particle diameter of the catalyst particles contained in the catalyst ink is preferably 1 to 30 nm, more preferably 1.5 to 20 nm, still more preferably 2 to 10 nm, and particularly preferably 2 to 5 nm. It is preferably 1 nm or more from the viewpoint of easy loading, and preferably 30 nm or less from the viewpoint of catalyst utilization. The “average particle diameter of the catalyst particles” in the present invention is the average value of the particle diameter of the catalyst component determined from the crystallite diameter or transmission electron microscope image obtained from the half-value width of the diffraction peak of the catalyst component in X-ray diffraction. Can be measured.

  The conductive carrier may have any specific surface area for supporting the catalyst particles in a desired dispersed state and has sufficient electronic conductivity as a current collector. The main component is carbon. Preferably there is. Specific examples include carbon particles made of carbon black, activated carbon, coke, natural graphite, artificial graphite and the like. In the present invention, “the main component is carbon” refers to containing a carbon atom as a main component, and is a concept including both a carbon atom only and a substantially carbon atom. In some cases, elements other than carbon atoms may be included in order to improve the characteristics of the fuel cell. In addition, being substantially composed of carbon atoms means that mixing of impurities of about 2 to 3% by mass or less is allowed.

The BET specific surface area of the conductive carrier may be a specific surface area sufficient to carry the catalyst component in a highly dispersed state, but is preferably 20 to 1600 m ² / g, more preferably 80 to 1200 m ² / g. Is good. When the specific surface area is 20 m ² / g or more, the dispersibility of the catalyst component and the polymer electrolyte in the conductive carrier is improved, which is excellent in that sufficient power generation performance can be obtained. On the other hand, when it is 1600 m ² / g or less, the catalyst component and the polymer electrolyte are excellent in that a high effective utilization rate can be effectively maintained.

  Further, the size of the conductive carrier is not particularly limited, but from the viewpoint of controlling the ease of loading, the catalyst utilization, and the thickness of the catalyst layer within an appropriate range, the average particle size is 5 to 200 nm, The thickness is preferably about 10 to 100 nm.

  In the electrode catalyst in which the catalyst component is supported on the conductive support, the supported amount of the catalyst component is preferably 10 to 80% by mass, more preferably 30 to 70% by mass with respect to the total amount of the electrode catalyst. Good. When the supported amount is 80% by mass or less, it is possible to effectively maintain an excellent degree of dispersion of the catalyst component on the conductive support, and to effectively improve the power generation performance corresponding to the increase in the supported amount. There is an advantage that can be expressed. Further, when the supported amount is 10% by mass or more, the catalyst activity per unit mass is excellent, and desired power generation performance corresponding to the supported amount can be obtained. Therefore, it is excellent in that the carrying amount design for ensuring the desired battery performance can be made relatively easily. The amount of the catalyst component supported can be examined by inductively coupled plasma emission spectroscopy (ICP).

  The catalyst component can be supported on the conductive carrier by a known method. For example, known methods such as impregnation method, liquid phase reduction support method, evaporation to dryness method, colloid adsorption method, spray pyrolysis method, reverse micelle (microemulsion method) can be used. Alternatively, a commercially available electrode catalyst may be used.

(Ii) Electrolyte The cathode catalyst layer / anode catalyst layer (also simply referred to as “catalyst layer”) of the present invention contains an electrolyte in addition to the electrode catalyst. The electrolyte is not particularly limited, and the same polymer electrolyte as that used for the membrane can be used. The electrolyte used for the membrane and the electrolyte used for each catalyst layer may be the same or different, but from the viewpoint of improving the adhesion between each catalyst layer and the membrane, the same one is used. Is preferred. That is, the electrolyte is not particularly limited, and a known one can be used, but any member having at least high proton conductivity may be used. Electrolytes that can be used in this case are broadly classified into fluorine-based electrolytes containing fluorine atoms in all or part of the polymer skeleton and hydrocarbon-based electrolytes not containing fluorine atoms in the polymer skeleton.

  Specific examples of the fluorine electrolyte include perfluorocarbon sulfonic acids such as Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.), and Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.). Polymer, polytrifluorostyrene sulfonic acid polymer, perfluorocarbon phosphonic acid polymer, trifluorostyrene sulfonic acid polymer, ethylene tetrafluoroethylene-g-styrene sulfonic acid polymer, ethylene-tetrafluoroethylene copolymer, polyvinylidene A preferred example is a fluoride-perfluorocarbon sulfonic acid-based polymer.

  Specific examples of the hydrocarbon electrolyte include polysulfone sulfonic acid, polyaryl ether ketone sulfonic acid, polybenzimidazole alkyl sulfonic acid, polybenzimidazole alkyl phosphonic acid, polystyrene sulfonic acid, polyether ether ketone sulfonic acid, polyphenyl. A suitable example is sulfonic acid.

  The polymer electrolyte preferably contains a fluorine atom because of its excellent heat resistance and chemical stability. Among them, Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.) Fluorine electrolytes such as Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.) are preferred.

(Iii) Fine Particles In the present invention, if necessary, the catalyst layer may be a fine particle dispersed catalyst layer in the same manner as the fine particle dispersed electrolyte membrane of the present invention. The specific configuration and production method can be performed in the same manner as described for the fine particle-containing catalyst layer (see FIG. 2 described in the examples).
That is, by using the interaction between the substrate and the fine particles, a fine particle-containing catalyst layer for a fuel cell, characterized in that a concentration gradient of fine particles in the catalyst layer is provided in the film thickness (layer thickness) direction. it can. The above interaction is a hydrophilic-hydrophilic interaction, a hydrophobic-hydrophobic interaction, a π-π interaction, an electrostatic interaction, a charge transfer interaction, and a combination of dipole-dipole interactions, etc., as appropriate. it can. In the case of utilizing the hydrophilic-hydrophilic interaction, the fine particles and the substrate can each be hydrophilic or imparted with hydrophilicity. Specifically, it may be a compound having one or more kinds of hydrophilic functional groups on the surface or inside thereof, or those having hydrophilicity by modifying hydrophilic functional groups on the surface or inside thereof. It may be. Similarly, in the case of utilizing the hydrophobic-hydrophobic interaction, the fine particles and the substrate can each have a hydrophobic property or a hydrophobic property. Specifically, it may be a compound having one or more kinds of hydrophobic functional groups on the surface or inside thereof, or a substance imparted with hydrophobicity by modifying a hydrophobic functional group on the surface or inside thereof. It may be. Since these details have already been described in the section of the fine particle dispersed electrolyte membrane, description thereof is omitted here.

  In addition, the catalyst layer, and further, the concentration gradient of the fine particles in the electrolyte membrane may be laminated so that the concentration of the fine particles increases toward the center in the thickness direction of the MEA electrolyte membrane and the catalyst layer. In addition, the layers may be laminated so that the concentration of the fine particles increases toward the outside in the MEA film thickness direction, or the concentration of the fine particles increases from one surface to the other surface in the MEA film thickness direction. It is only necessary to obtain an optimum configuration (concentration gradient) according to characteristics required for the MEA of the fuel cell. Note that these details are already described in the MEA section of the present invention, and thus the description thereof is omitted here.

(2) GDL
The GDL is disposed on the anode and cathode catalyst layers on both sides of the membrane. Specifically, the MEA (membrane + catalyst layer) can be further sandwiched by GDL, and if necessary, it can be obtained by sandwiching and joining by hot pressing.

  The GDL is not particularly limited, and known materials can be used in the same manner. For example, the base material is a sheet-like material having conductivity and porosity such as a carbon woven fabric, a paper-like paper body, a felt, and a non-woven fabric. Things. The thickness of the substrate may be appropriately determined in consideration of the characteristics of the obtained gas diffusion layer, but may be about 30 to 500 μm. If the thickness is less than 30 μm, sufficient mechanical strength or the like may not be obtained, and if it exceeds 500 μm, the distance through which gas or water permeates is undesirably increased.

  The GDL preferably contains a water repellent in the base material for the purpose of further improving water repellency and preventing a flooding phenomenon. Although it does not specifically limit as said water repellent, Fluorine-type, such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyhexafluoropropylene, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), etc. Examples thereof include polymer materials, polypropylene, and polyethylene.

(2 ′) Carbon particle layer (hereinafter also simply referred to as MIL)
In order to further improve water repellency, the GDL may have a MIL made of an aggregate of carbon particles containing a water repellent on the substrate.

  The carbon particles are not particularly limited, and may be conventional ones such as carbon black, graphite, and expanded graphite. Of these, carbon blacks such as oil furnace black, channel black, lamp black, thermal black, and acetylene black are preferred because of their excellent electron conductivity and large specific surface area. The particle size of the carbon particles is preferably about 10 to 100 nm. Thereby, while being able to obtain the high drainage property by capillary force, it becomes possible to improve contact property with a catalyst layer.

  Examples of the water repellent used for the MIL include the same water repellents as those described above used for the substrate. Of these, fluorine-based polymer materials are preferably used because of their excellent water repellency and corrosion resistance during electrode reaction.

  In the MIL, the mixing ratio of the carbon particles to the water repellent may be insufficient to obtain water repellency as expected when there are too many carbon particles. If there are too many water repellents, sufficient electron conductivity can be obtained. There is no fear. Considering these, the mixing ratio of the carbon particles and the water repellent in MIL is preferably about 90:10 to 40:60 in terms of mass ratio.

  The thickness of the MIL may be appropriately determined in consideration of the water repellency of the obtained GDL.

  When the GDL contains a water repellent, a general water repellent treatment method may be used. For example, after immersing the base material used for GDL in the dispersion liquid of a water repellent, the method of heat-drying in oven etc. is mentioned.

  When MIL is formed on a transfer mount in GDL, carbon particles, water repellent, etc. are dispersed in a solvent such as water, alcohol solvents such as perfluorobenzene, dichloropentafluoropropane, methanol, ethanol and the like. The slurry is prepared by applying the slurry onto a transfer mount and dried, or the slurry is once dried and pulverized to form a powder, and this is applied to the gas diffusion layer. Good. Then, it is preferable to heat-process at about 250-400 degreeC using a muffle furnace or a baking furnace.

  Hereinafter, the present invention will be specifically described based on examples. In addition, this invention is not limited only to these Examples. In the examples, “%” represents a mass percentage unless otherwise specified.

1. Preparation of hydrophilized fine particles Hydrophilic silica gel fine particles obtained by hydrophilizing silica gel fine particles by immersing silica gel fine particles with an average particle size of 0.05 μm in a piranha solution for 12 hours to give hydroxyl groups (—OH groups) to the surface. 103 was obtained.

2. Preparation of Hydrophilized Substrate As a substrate, the silicon substrate was immersed in a piranha solution (volume ratio of hydrogen peroxide solution (31%): concentrated sulfuric acid = 3: 7 mixed solution heated) for 12 hours. A hydrophilization treatment was performed to obtain a hydrophilized silicon substrate (also simply referred to as a hydrophilized silicon substrate) 300 having a hydroxyl group (—OH group) added to the surface. The water contact angle of the surface of the obtained hydrophilic silicon substrate 300 was 60 °.

3. Production of electrolyte membrane having concentration gradient of hydrophilized fine particles in thickness direction Disperse the above-mentioned hydrophilized silica gel fine particles at 5 wt% in Nafion solution (registered trademark DuPont DE520, Nafion content 5 wt%) as a hydrophilic fine particle dispersed electrolyte solution. The prepared solution was prepared. The obtained hydrophilic fine particle-dispersed electrolyte solution is cast-coated on the above-mentioned hydrophilized silicon substrate 300 as a support, and the solvent is removed at 25 ° C. for 24 hours in an air atmosphere. (Thickness 50 μm, area 10 cm × 10 cm) was produced. As shown in FIGS. 1A and 1B, the obtained hydrophilic fine particle-dispersed electrolyte membrane 100 has the highest hydrophilic fine particle concentration at the interface with the substrate 300. That is, the concentration of the hydrophilized fine particles 103 in the electrolyte membrane 100 is highest on the surface (bottom surface) 102 on the substrate side. The concentration (distribution) of the hydrophilic fine particles exists with a gradient that gradually decreases from the bottom surface 102 on the substrate side toward the upper surface 101 on the air side. The confirmation of having this concentration gradient can be calculated based on the EPMA measurement described later.

  Note that the concentration (distribution) of the hydrophilic fine particles shown in FIG. 1B can be controlled by changing the solvent removal rate (specifically, the drying temperature, etc.), the immersion time during the hydrophilization treatment, the temperature, and the like. It can be controlled.

[Creation of an electrocatalyst layer having a gradient of hydrophilic fine particles in the thickness direction]
Disperse the above-mentioned hydrophilized silica gel particles in 5 wt% in platinum-supporting carbon (TEC 10E50E, Tanaka Kikinzoku Kogyo Co., Ltd., TEC10E50E, platinum content 46.5%), Nafion (registered trademark) / isopropyl alcohol solution (DuPont, Nafion 5 wt%). 4.5 g of purified solution, 50 g of pure water, 40 g of 1-propanol (special grade reagent manufactured by Wako Pure Chemical Industries, Ltd.), 40 g of 2-propanol (special grade reagent manufactured by Wako Pure Chemical Industries, Ltd.) at 25 ° C. A catalyst ink was prepared by mixing and dispersing for 3 hours using a homogenizer in a glass container in a water bath set to hold. The catalyst ink was cast on the hydrophilized substrate 300 and the solvent was removed over 24 hours at 25 ° C. in an air atmosphere. A hydrophilic fine particle dispersed electrode catalyst layer 200 (thickness 20 μm, area 5 cm × 5 cm) Was made.

[Preparation of hydrophilic fine particle dispersed electrolyte assembly having hydrophilic fine particle gradient in the thickness direction]
As shown in FIG. 2, the hydrophilic fine particle-dispersed electrolyte membrane 100 and the hydrophilic fine particle-dispersed electrode catalyst layer 200 are used and laminated with the surface in contact with the hydrophilization treatment support inside, and the pressure is 130 MPa at a pressure of 3 MPa. By hot pressing at 10 ° C. for 10 minutes, a hydrophilic fine particle dispersed electrode assembly 400 was obtained.

[Preparation of hydrophilic fine particle dispersed electrolyte assembly having hydrophilic fine particle gradient in the thickness direction]
As shown in FIG. 3, the hydrophilic fine particle-dispersed electrolyte membrane 100 having a gradient of hydrophilic fine particles in the thickness direction, the anode catalyst layer 210, and the cathode catalyst layer 220 are used, and the surface in contact with the hydrophilic treatment support is The anode catalyst layer 210 and the electrolyte membrane 100 are laminated so as to be the interface 211, and hot pressing is performed at a pressure of 3 MPa at 130 ° C. for 10 minutes, thereby having a gradient of hydrophilic fine particles in the thickness direction. A hydrophilic fine particle dispersed membrane electrode assembly 400 having the highest concentration of hydrophilic fine particles at the interface of the anode catalyst layer was obtained. FIG. 3B is a drawing showing the concentration distribution of hydrophilic fine particles in the thickness direction in the membrane electrode assembly 400 obtained. As shown in FIGS. 3A and 3B, in this embodiment, fine particles are not blended in the anode catalyst layer 210 and the cathode catalyst layer 220, but the electrolyte membrane is formed by laminating the electrolyte membrane and the catalyst layer and hot pressing them. From this, it was confirmed that the fine particles were diffused also in the anode catalyst layer, and the concentration distribution of the hydrophilic fine particles was formed in the thickness direction of the anode catalyst layer.

  According to the combination of FIG. 3, since the hydrophilic fine particle concentration at the interface between the anode catalyst layer and the electrolyte membrane is the highest, evaporation from the anode interface to the anode gas phase side can be suppressed, and voltage drop due to anode dryout is suppressed. can do.

  FIG. 4 shows the Si to F intensity ratio distribution in the depth direction of the surface obtained by X-ray microanalyzer (EPMA: Electron Probe Micro-Analysis) measurement. Based on the fluorine atoms of Nafion (electrolyte membrane), the abundance ratio of Si atoms derived from silica gel particles (vs. fluorine) was calculated. When cast film formation was performed on a hydrophilized substrate, it was confirmed that the Si concentration on the hydrophilized substrate side was present with a gradient from the substrate side to the air side. Similarly, the concentration distribution of the fine particles shown in FIGS. 1B, 2B, and 3B can be calculated based on the EPMA measurement described above.

As an example of the first embodiment, FIG. 1 schematically shows a state of an electrolyte membrane in which a concentration gradient of fine particles in a film is applied in a film thickness direction by utilizing a hydrophilic-hydrophilic interaction between a substrate and fine particles. FIG. FIG. 1A is a schematic cross-sectional view schematically showing a state of a hydrophilic fine particle-containing electrolyte membrane for a fuel cell produced on a hydrophilic substrate, and FIG. 1B is a hydrophilic fine particle-containing electrolyte of FIG. 1A. It is a graph showing the relationship of the density distribution of hydrophilic fine particles with respect to the film thickness direction of a film. FIG. 2A is obtained by using the hydrophilic fine particle-dispersed electrolyte membrane and the hydrophilic fine particle-dispersed electrode catalyst layer produced in the examples, laminating with the surface in contact with the hydrophilization support inside, and hot pressing. FIG. 2 is a schematic cross-sectional view schematically showing a state of the hydrophilic fine particle dispersed membrane electrode assembly obtained. FIG. 2B is a graph showing the relationship of the concentration distribution of hydrophilic fine particles with respect to the film thickness direction of the hydrophilic fine particle dispersed membrane electrode assembly of FIG. 2A. FIG. 3A shows an example of a hydrophilic fine particle-dispersed electrolyte membrane having a gradient of hydrophilic fine particles in the thickness direction, an anode catalyst layer, and a cathode catalyst layer, which were prepared in Examples, and the surface in contact with the hydrophilization support was Laminated so as to be the interface between the catalyst layer and the electrolyte membrane, and obtained by hot pressing, has a gradient of hydrophilic fine particles in the thickness direction, and the interface between the electrolyte membrane and the anode catalyst layer is the most hydrophilic fine particles It is the cross-sectional schematic diagram which represented typically the mode of the hydrophilic fine particle dispersion membrane electrode assembly with a high density | concentration. FIG. 3B is a graph showing the relationship of the concentration distribution of hydrophilic fine particles with respect to the film thickness direction of the hydrophilic fine particle dispersed membrane electrode assembly of FIG. 3A. FIG. 4 is a graph showing the Si to F intensity ratio distribution in the depth direction of the surface obtained by X-ray microanalyzer (EPMA) measurement for the hydrophilic fine particle dispersed electrolyte membrane described with reference to FIG. 3 in the example. is there.

Explanation of symbols

100 hydrophilic fine particle-dispersed electrolyte membrane (electrolyte membrane having a gradient of hydrophilic fine particles in the thickness direction),
101 Of the surfaces on both sides of the electrolyte membrane, a surface having a hydrophilic fine particle concentration lower than the surface 102;
102 Of the surfaces on both sides of the electrolyte membrane, the surface having a hydrophilic fine particle concentration higher than the surface 101,
103 hydrophilized silica gel particles,
200 an electrode catalyst layer having a gradient of hydrophilic fine particles in the thickness direction;
201 surface having a hydrophilic fine particle concentration higher than 202 surface;
202 surface having a hydrophilic fine particle concentration lower than 201 surface;
210 anode catalyst layer,
211 Interface between anode catalyst layer and electrolyte membrane,
220 cathode catalyst layer,
221 interface between the cathode catalyst layer and the electrolyte membrane,
300 Hydrophilized substrate,
301 surface of a substrate subjected to hydrophilic treatment,
400 MEA having a gradient of hydrophilic fine particles in the thickness direction and having the highest hydrophilic fine particle concentration at the interface between the electrolyte membrane and the electrode catalyst layer (anode catalyst layer).

Claims (19)

  A fine particle-containing electrolyte membrane for a fuel cell, characterized in that a concentration gradient of fine particles in the film is provided in the film thickness direction by utilizing the interaction between the substrate and the fine particles.   2. The fine particle-containing electrolyte membrane for a fuel cell according to claim 1, wherein the interaction is a hydrophilic-hydrophilic interaction.   2. The fine particle-containing electrolyte membrane for a fuel cell according to claim 1, wherein the interaction is a hydrophobic-hydrophobic interaction.   The fine particle-containing electrolyte membrane for a fuel cell according to claim 1, wherein the interaction is a π-π interaction.   2. The fine particle-containing electrolyte membrane for a fuel cell according to claim 1, wherein the interaction is an electrostatic interaction.   The fine particle-containing electrolyte membrane for a fuel cell according to claim 1, wherein the interaction is a charge transfer interaction.   2. The fine particle-containing electrolyte membrane for a fuel cell according to claim 1, wherein the interaction is a dipole-dipole interaction.   3. The fine particle-containing electrolyte membrane for a fuel cell according to claim 2, wherein when the hydrophilic-hydrophilic interaction is used, the fine particles have hydrophilicity or are imparted with hydrophilicity.   9. The fine particle-containing electrolyte membrane for a fuel cell according to claim 2 or 8, wherein, when the hydrophilic-hydrophilic interaction is utilized, the substrate is hydrophilic or imparted with hydrophilicity.   4. The fine particle-containing electrolyte membrane for a fuel cell according to claim 3, wherein, when the hydrophobic-hydrophobic interaction is used, the fine particles have hydrophobicity or are imparted with hydrophobicity.   11. The fine particle-containing electrolyte membrane for a fuel cell according to claim 3, wherein, when the hydrophobic-hydrophobic interaction is used, the substrate has hydrophobicity or is imparted with hydrophobicity.   2. The fine particle-containing electrolyte membrane for a fuel cell according to claim 1, wherein the fine particles and / or the substrate is a compound having one or more kinds of hydrophilic functional groups on the surface or inside thereof.   2. The fine particle-containing electrolyte membrane for a fuel cell according to claim 1, wherein the fine particles and / or the substrate are provided with hydrophilicity by modifying a hydrophilic functional group on the surface or inside thereof.   2. The fine particle-containing electrolyte membrane for a fuel cell according to claim 1, wherein the fine particles and / or the substrate is a compound having one or more types of hydrophobic functional groups on the surface or inside thereof.   2. The fine particle-containing electrolyte membrane for a fuel cell according to claim 1, wherein the fine particles and / or the substrate are provided with hydrophobicity by modifying a hydrophobic functional group on the surface or inside thereof.   A membrane / electrode assembly obtained by sandwiching and laminating a catalyst layer from both surfaces of the fine particle-containing electrolyte membrane according to claim 1.   The membrane electrode assembly according to claim 16, obtained by laminating so that the concentration of fine particles increases toward the center in the thickness direction of the electrolyte membrane of the assembly.   The membrane electrode assembly according to claim 16, which is obtained by laminating so that the concentration of fine particles increases toward the outside in the film thickness direction of the assembly.   The membrane electrode assembly according to claim 16, obtained by laminating so that the concentration of fine particles increases from one surface to the other surface in the film thickness direction of the assembly.

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