JP2007103293A - Membrane electrode assembly, its manufacturing method, and polymer electrolyte fuel cell using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a membrane electrode assembly in which high performance of a polymer electrolyte fuel cell can be maintained for a long period, and to provide its manufacturing method. <P>SOLUTION: This is the membrane electrode assembly which uses a liquid fuel and has an anode electrode catalyst layer and a cathode electrode catalyst layer containing Ru elements on both sides of the solid polymer electrolyte membrane, and in which after a current of 50 mA/cm<SP>2</SP>is impressed for 100 hours, the ratio of an amount occupied by the Ru element having zero valence out of the whole amount of the Ru element existing in the anode electrode catalyst layer is 40% or more within 5 μm or less from the surface of the solid polymer electrolyte membrane, while the whole amount of the Ru element existing in the cathode electrode catalyst layer is 2% or less of the whole amount of the Ru element existing in the anode electrode catalyst layer. This is the manufacturing method of the electrode assembly wherein a process in which the catalyst containing the Ru element is immersed into water solutions and/or organic solvents having different pHs for a plurality of times and dried, a process in which the catalyst containing a dried Ru element is kneaded with a polymer solution, and a process in which the kneaded catalyst containing the Ru element is coated on the electrode base material or on the solid polymer electrolyte membrane to fabricate the anode electrode catalyst layer are all carried out under nitrogen atmosphere. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a polymer electrolyte fuel cell using a membrane electrode assembly and a liquid fuel.

  A fuel cell is a power generation device with low emissions, high energy efficiency, and low environmental burden.

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

  In the polymer electrolyte fuel cell, in addition to a conventional polymer electrolyte fuel cell (hereinafter referred to as PEFC) using hydrogen gas as a fuel, a direct methanol fuel cell (hereinafter referred to as PEFC) that directly supplies a methanol aqueous solution of liquid fuel. (Referred to as DMFC). Although the DMFC has a lower output than the conventional PEFC, the fuel is liquid and does not use a reformer. Therefore, the energy density is high, and the use time of the portable device per filling is long. is there.

  In a fuel cell, an anode electrode and a cathode electrode in which a reaction responsible for power generation occurs and an electrolyte membrane serving as an ion conductor between the anode and the cathode constitute a membrane-electrode complex (MEA), and this MEA is a separator. A cell sandwiched between the two is configured as a unit. Here, the electrode is an electrode base material (also referred to as a gas diffusion electrode or a current collector) that supplies fuel liquid or gas, discharges a product, and collects (supply) electricity, and actually becomes an electrochemical reaction field. And an electrode catalyst layer.

  For example, in an anode electrode of a polymer electrolyte fuel cell, a fuel such as a methanol aqueous solution reacts with a catalyst layer of the anode electrode to generate protons, electrons, and carbon dioxide, and electrons are transferred to the electrode substrate and protons are transferred to the polymer solid electrolyte. Carbon dioxide is discharged out of the system. For this reason, the anode electrode is required to have good liquid fuel penetration, gas diffusivity, electronic conductivity, and ionic conductivity, and to maintain these performances chemically and physically. Stability is required.

  On the other hand, in the cathode electrode, an oxidizing gas such as oxygen or air reacts with protons conducted from the polymer solid electrolyte and electrons conducted from the electrode base material in the cathode electrode catalyst layer to produce water. For this reason, in the cathode electrode, it is necessary to efficiently discharge the generated water in addition to gas diffusibility, electron conductivity, and ion conductivity. In particular, in the DMFC, a reaction in which methanol and oxygen or oxygen such as air that has passed through the electrolyte membrane generate carbon dioxide and water in the catalyst layer of the cathode electrode also occurs. For this reason, more water is generated than conventional PEFC, so it is necessary to discharge water more efficiently, and, like the anode, chemical and physical stability is required to maintain these performances. .

  In particular, in a DMFC using liquid fuel, it has been found that Ru in the anode electrode catalyst layer is dissolved and deposited at the cathode. These may cause a decrease in durability.

  However, the catalysts used in current anodes contain large amounts of soluble ruthenium compounds.

  Under such circumstances, various studies have been conducted for the purpose of improving the durability of DMFC. As an example, there has been proposed a membrane electrode assembly comprising an electrode catalyst layer characterized by comprising a three-dimensional crosslinked structure containing silane and carbon fine particles supporting a noble metal catalyst (see Patent Document 1).

  In addition, there are some examples in which a polymer containing no ionic group is used for the electrode catalyst layer binder, and all of them are used in a mixture with a polymer containing an ionic group. For example, a catalyst layer is proposed in which a mixture of a suspension in which a fluororesin not containing ionic groups is dispersed in a solvent and a polymer containing ionic groups is used as a binder (see Patent Document 2). As a polymer therein, a mixture of a solvent-soluble fluoropolymer substantially free of ion exchange groups and a solvent-soluble fluoropolymer having an ionic group has been proposed (see Patent Document 3).

However, the above technique cannot suppress ruthenium dissolution and does not essentially improve the durability problem.
JP 2003-178770 A JP 2003-109603 A JP 2001-357858 A

  As described above, none of the conventional techniques can solve the dissolution and precipitation of Ru in the electrode catalyst layer in a fuel cell using liquid fuel.

  In view of the background of such prior art, the present invention does not provide a membrane electrode assembly for a polymer electrolyte fuel cell capable of maintaining high performance for a long time, a method for producing the same, and a polymer electrolyte fuel cell using the same. It is what.

The present invention employs the following means in order to solve such problems.
That is, the membrane electrode composite according to the present invention is a membrane electrode composite for a polymer electrolyte fuel cell using a liquid fuel having an anode electrode catalyst layer containing Ru element and a cathode electrode catalyst layer on both sides of a solid polymer electrolyte membrane. After applying a current of 50 mA / cm ² for 100 hours, the proportion of zero-valent Ru elements in the Ru electrocatalyst layer within 5 μm from the surface of the solid polymer electrolyte membrane is 40%. %, And the total amount of Ru elements present in the cathode electrode catalyst layer is 2% or less of the total amount of Ru elements present in the anode electrode catalyst layer.

  Further, the method for producing a membrane electrode assembly of the present invention includes a step of immersing a catalyst containing Ru element in an aqueous solution and / or an organic solvent having different pHs and drying it, a catalyst containing the dried Ru element in a polymer solution And the step of coating the catalyst containing the kneaded Ru element on the electrode substrate or the solid polymer electrolyte membrane to produce the anode electrode catalyst layer are all carried out in a nitrogen atmosphere. The method for producing a membrane electrode assembly according to the present invention.

  The polymer electrolyte fuel cell of the present invention is a polymer electrolyte fuel cell comprising the membrane electrode assembly according to the present invention described above.

  ADVANTAGE OF THE INVENTION According to this invention, the membrane electrode assembly which can provide the fuel cell excellent in durability compared with the past, its manufacturing method, and also a fuel cell are provided.

  In the present invention, the membrane electrode assembly for a polymer electrolyte fuel cell capable of maintaining the above-mentioned problem, that is, high performance for a long time, has been intensively studied and found that the following configuration is effective.

An anode side membrane for an anode electrode catalyst layer after applying a current of 50 mA / cm ² for 100 hours in an anode and cathode electrode catalyst layer for a polymer electrolyte fuel cell using a liquid fuel in contact with a solid polymer electrolyte membrane The proportion of the Ru element present in the anode electrode catalyst layer within 5 μm within the surface from the zero valence is 40% or more, and the total amount of Ru elements present in the cathode catalyst layer is the total amount of Ru elements present in the anode catalyst layer. It was clarified that the problem can be solved by making the amount of element 2% or less.

  It has been found from conventional studies that introduction of Ru into the anode electrode catalyst layer in the electrode catalyst layer of a polymer electrolyte fuel cell using liquid fuel leads to high output.

  However, it has been found that, in actual use, Ru in the anode electrocatalyst layer is dissolved and deposited at the cathode. These may cause a decrease in durability. On the other hand, the catalyst used for the current anode contains a large amount of a soluble ruthenium compound. Further, ruthenium was previously present in the cathode as a measure against methanol crossover, and it was difficult to improve durability.

As a result of intensive studies, the present inventors have investigated the anode electrode catalyst layer after applying a current of 50 mA / cm ² for 100 hours in an anode and cathode electrode catalyst layer for a polymer electrolyte fuel cell using liquid fuel. The proportion of the zero valence of Ru elements existing in the anode electrode catalyst layer within 5 μm from the anode side membrane surface is 40% or more, and the total amount of Ru elements existing in the cathode side catalyst layer is present in the anode catalyst layer. The present inventors have found that the durability can be enhanced and the output can be sufficiently obtained by applying the membrane electrode assembly having 2% or less of the total amount of Ru elements.

  This is thought to be because the chemical stability of the Ru element in the anode was significantly improved by removing the dissolved Ru component and then forming the catalyst layer in a nitrogen atmosphere. At the same time, it is considered that Ru precipitation at the cathode can be suppressed, and water, that is, polymer deterioration promotion at the cathode can also be suppressed.

Specifically, with respect to the anode electrode catalyst layer after applying a current of 50 mA / cm ² for 100 hours in the anode and cathode electrode catalyst layer of the membrane electrode composite of the present invention, the anode electrode within 5 μm from the anode side membrane surface The ratio of the Ru element present in the catalyst layer to the zero valence needs to be 40% or more. From the viewpoint of durability, the ratio is more preferably 45% or more, and even more preferably 50% or more.

  In addition, the total amount of Ru elements present in the catalyst layer on the cathode side needs to be 2% or less of the total amount of Ru elements present in the anode catalyst layer, and may be 1% or less from the viewpoint of durability. More preferably 0.5% or less.

  The ratio of the zero valence of the Ru element existing in the anode electrocatalyst layer within 5 μm from the anode side membrane surface is obtained by obtaining the profile of the Ru element within the measurement range by X-ray photoelectron spectroscopy (XPS). The amount of Ru depending on each valence is obtained from the peak division, and the ratio of the zero valence can be obtained.

  Further, the ratio of the Ru amount in the cathode catalyst layer to the Ru amount in the anode catalyst layer is determined by scraping each of the cathode electrode catalyst layer and the anode electrode catalyst layer from the cut-out MEA, treating them at a high temperature, and treating the residue with alkali. Ru in each electrode catalyst layer can be quantified by dissolving each solution with an acid and analyzing each solution by ICP emission spectrometry. The Ru amount per unit area can be determined from the area of the cut electrode catalyst layer and the amount of Ru contained therein, and the ratio of the Ru amount in the cathode catalyst layer to the Ru amount in the anode catalyst layer can be determined.

Specific measurement examples are given below, but the measurement is not particularly limited as long as a current of 50 mA / cm ² can be applied for 100 hours. In a 5 cm ² MEA, a 10% methanol aqueous solution was flowed to the anode electrode at a flow rate of 1 ml / cm ² , the cell temperature was adjusted to 40 ° C., and air was flowed to the cathode at a flow rate of 50 ml / cm ² , 50 mA / cm ² or more. Is applied for 100 hours. Thereafter, the ratio of the Ru element present in the anode electrode catalyst layer to the zero valence is determined by X-ray photoelectron spectroscopy (XPS). Further, the Ru amount of each catalyst layer is obtained from the cut-out MEA by ICP emission analysis.

  The anode electrode catalyst layer of the membrane electrode assembly of the present invention is not particularly limited with respect to the polymer used, and any polymer such as a polymer solid electrolyte or a polymer having no ionic group can be used.

  As a specific example, a polymer in which the catalyst particles are well dispersed, does not swell, deform or dissolve in the fuel and does not deteriorate in the oxidation-reduction atmosphere in the fuel cell is preferable.

  Such polymers include polytetrafluoroethylene (PTFE), polytetrafluoroethylene-perfluoroalkyl ether copolymer (PFA), polytetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene- Fluorine-containing resins such as ethylene copolymer (ETFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), and copolymers thereof, polyimide (PI), polyphenylene sulfide sulfone (PPSS), polysulfone ( PSF), polyphenylene sulfide (PPS), polyphenylene oxide (PPO), polyether ketone (PEK), polyether ether ketone (PEEK), polyether sulfone, polybenzimidazole (PBI), poly Carbonate, polyimide, heat and oxidation resistance polymers such as polybenzoxazole (PBO), silicone resins such as polyorganosiloxanes, polystyrene, polyethylene, such as a general purpose polymers and derivatives thereof, such as polypropylene. Among these polymers, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polytetrafluoroethylene-perfluoropolymer-perfluoroethylene-perfluoroethylene-perfluoroethylene-perfluoroethylene-perfluoroethylene-perfluoroethylene-perfluoroethylene in terms that they can be dissolved or dispersed in a solvent and can be dispersed with a catalyst or a conductive agent. Fluorine-containing polymers such as fluoroalkyl ether copolymer (PFA), polytetrafluoroethylene-hexafluoropropylene copolymer (FEP), or “Cytop” (registered trademark) manufactured by Asahi Glass Co., Ltd., polyimide (PI), polyphenylene Sulfide sulfone (PPSS), polysulfone (PSF), polyphenylene sulfide (PPS), polyphenylene oxide (PPO), polyether ketone (PEK), polyether ether ketone (PEEK), polyether sulfone, polybenzoy Indazole (PBI), polycarbonate, polyimide, polybenzoxazole (PBO) hydrocarbon type polymer is excellent in heat resistance and oxidation resistance, such as is preferably used.

  In addition, those containing an anionic group as a derivative of the above polymer are effective in improving the output, but may decrease in durability, so the content of the anionic group is adjusted according to the use conditions There is a need to.

  The catalyst used for the anode electrode catalyst layer in the present invention needs to contain Pt and Ru, but may contain other elements besides this. For example, noble metals or transition metals such as gold, palladium, iridium, cobalt, nickel, iron, titanium and silver are preferably used. It is also preferable to combine three or more elements as described above, and it may be included particularly from the viewpoint of improving durability.

  Preferred examples of such include platinum, ruthenium and iridium, platinum, ruthenium and rhodium, platinum, ruthenium and palladium. The catalyst may be a metal-only particle or may be supported on carbon, and even if these are mixed, this is a preferred embodiment. When the catalyst is a mixture of metal-only particles and supported carbon, the mixing ratio is not particularly limited. When the catalyst is supported carbon, the carbon material is the same as the carbon used for the conductive agent listed below.

  The conductive agent contained in the anode electrode catalyst layer in the present invention is not particularly limited as long as it has excellent electron conductivity and excellent durability in the electrode catalyst layer, and various conductive agents can be used. . For example, carbon, metal, metal compound, alloy, metalloid, organic conductive material and the like are preferably used.

  As a preferable conductive material contained in the anode electrode catalyst layer of the present invention, a carbon material is preferable from the viewpoint of a large specific surface area and corrosion resistance, and among them, carbon black and nanocarbon materials are particularly preferable.

  As specific carbon black, channel black, thermal black, oil furnace black, acetylene black and lamp black are preferable. As oil furnace black, Vulcan (registered trademark) XC-72R, Vulcan P, Black Pearls (manufactured by Cabot Corporation) (Registered Trademark) 880, Black Pearls (Registered Trademark) 1100, Black Pearls (Registered Trademark) 1300, Black Pearls (Registered Trademark) 2000, Regal (Registered Trademark) 400, Ketchen Black (Registered Trademark) EC manufactured by Lion, Mitsubishi Chemical # 3150, # 3250, etc. manufactured by the company are used, and Denka Black (registered trademark) manufactured by Denki Kagaku Kogyo Co., Ltd. is used as the acetylene black. Among these, in particular, Vulcan (registered trademark) XC-72R manufactured by Cabot Corporation is particularly preferably used.

  As the nanocarbon material, carbon nanotubes, carbon nanohorns, fullerenes and the like are preferably used. It is also preferable to use a surface treated product or a mixture of these carbon materials. In addition to such carbon black, artificial graphite obtained from organic compounds such as natural graphite, pitch, coke, polyacrylonitrile, phenol resin, furan resin, carbon, gold, palladium, and the like can also be used. These conductive materials may be in the form of particles or fibers.

  Moreover, it is also possible to use a conductive material obtained by post-processing these carbon materials. The amount of these conductive materials added to the electrode catalyst layer is preferably 1 to 80%, more preferably 5 to 50% as a weight ratio. The mixing ratio of the catalyst, the conductive material, and the polymer in the electrode catalyst layer of the present invention should be appropriately determined according to the required electrode characteristics, and is not particularly limited, but the weight of the conductive material and the polymer The ratio of (conductive material) / (polymer) = 50/50 to 95/5 is preferable.

  It is important that the thickness of the anode electrode catalyst layer in the present invention is a thickness that does not hinder the movement of a liquid or gas of a reaction product such as an aqueous methanol solution or carbon dioxide. For this reason, it is preferably 150 μm or less, more preferably 100 μm or less, and particularly preferably 50 μm or less. On the other hand, if the thickness of the anode electrode catalyst layer is too thin, it becomes difficult to make the catalyst uniformly present. Therefore, the thickness is preferably 1 μm or more, more preferably 5 μm or more, and particularly preferably 10 μm or more.

  The thickness of the electrode catalyst layer is about 100 to 1000 times with a scanning electron microscope (SEM) or transmission electron microscope (TEM), and 5 cross-sections are measured per 1 cm, and the thickness is measured at each observation point. The average value is a representative value at each observation point. The average value of the representative values is defined as the electrode catalyst layer thickness.

  The anode electrode catalyst layer of the present invention is not particularly limited except that it is produced under a nitrogen atmosphere.

  Specific examples of the electrode catalyst layer forming method will be described below. The electrocatalyst coating liquid is kneaded with a triple roll, ultrasonic wave, homogenizer, wet jet mill, dry jet mill, mortar, stirring blade, satellite (rotation and revolution type) stirrer, or the like. The kneaded electrode catalyst coating solution is applied and dried by using a knife coater, bar coater, spray, dip coater, spin coater, roll coater, die coater, curtain coater flow coater or the like. The coating method is appropriately selected according to the viscosity and solid content of the coating solution. Moreover, the electrode catalyst layer coating liquid can be applied to either an electrode base material or an electrolyte membrane described later. Moreover, it is also possible to form a catalyst layer independently, and it peels, after apply | coating to a glass base material etc., drying. Furthermore, an anode catalyst layer produced separately may be transferred or sandwiched between an electrode substrate and a polymer solid electrolyte. As the transfer substrate in this case, a polytetrafluoroethylene (PTFE) sheet, or a glass plate or a metal plate whose surface is treated with a fluorine or silicone release agent is also used.

  In order to improve the durability, the anode electrode catalyst of the present invention is immersed in an aqueous solution and / or an organic solvent having different pHs in a nitrogen atmosphere and dried several times. It is believed that this removes Ru having high solubility and further suppresses Ru components that are easily oxidized by treatment in a nitrogen atmosphere, thereby improving durability. Although the pH solution used for the treatment is not particularly limited, the acid solution is preferably an inorganic acid such as hydrochloric acid, sulfuric acid, nitric acid or aqua regia and a mixture thereof, an organic acid such as acetic acid or citric acid and a mixture thereof. . As the basic solution, various organic alkalis can be used in addition to inorganic alkalis such as sodium hydroxide and potassium hydroxide. The treatment can be carried out by immersing in the liquid under a nitrogen atmosphere or contacting with a vapor, but is not limited thereto. Further, mixing the organic solvent reduces the surface tension of the solution used for the treatment, which is effective for mixing and dispersing the catalyst particles, particularly the supported carbon catalyst particles. Furthermore, heating is also effective means for promoting dissolution of the solvent Ru. Among them, the method of immersing in a sodium hydroxide aqueous solution or a potassium hydroxide aqueous solution is preferable because it can selectively remove Ru having high solubility.

  The cathode electrode catalyst layer of the membrane electrode assembly of the present invention can be applied to the same technique as the anode electrode catalyst layer described above, but is not limited to work in a nitrogen atmosphere.

  It is also a preferred embodiment that the electrode catalyst layer of the present invention is a membrane electrode assembly (MEA) together with an electrode substrate and an electrolyte membrane.

  As an electrode base material in the membrane electrode assembly of the present invention, an electrode base material generally used for a fuel cell is used without particular limitation. For example, a porous conductive sheet having a conductive inorganic substance as a main constituent material is used. Specific examples of the conductive inorganic substance include a fired body from polyacrylonitrile, a fired body from pitch, graphite, and expanded graphite. Carbon materials such as stainless steel, molybdenum and titanium are used. The form of the conductive inorganic material is not particularly limited, such as fibrous or particulate. Among them, carbon paper TGP series, SO series manufactured by Toray Industries, Inc., carbon cloth manufactured by E-TEK, etc. are preferably used.

  The solid polymer electrolyte membrane in the membrane electrode assembly of the present invention is not particularly limited as long as it is an electrolyte used in a normal fuel cell, but the solid polymer electrolyte membrane is used as a proton conductive polymer material. Is preferably used. The proton conductive anionic group is not particularly limited, such as a sulfonic acid group, a carboxylic acid group, and a phosphoric acid group.

  This solid polymer electrolyte membrane is composed of a hydrocarbon-based membrane having an anionic group such as a sulfonic acid group on a styrene-divinylbenzene copolymer or a heat-resistant engineering plastic, a fluoroalkyl ether side chain and a fluoroalkyl main chain. The copolymer is roughly divided into perfluoro-based copolymers, and should be appropriately selected according to the use and environment in which the fuel cell is used. A partial fluorine film partially substituted with fluorine atoms is also preferably used. Examples of the perfluoro membrane include DuPont's Nafion (registered trademark), Asahi Kasei's Aciplex (registered trademark), Asahi Glass Flemion (registered trademark), and the like. Examples include styrene sulfonic acid polymers and polyvinylidene fluoride introduced with sulfonic acid groups. Among these, a hydrocarbon polymer electrolyte membrane having an ionic group and excellent in hydrolysis resistance is preferable. Among these, specific examples of non-crosslinked hydrocarbon polymer electrolyte membranes include ionic group-containing polyphenylene oxide, ionic group-containing polyether ketone, ionic group-containing polyether ether ketone, and ionic group-containing polyether. Sulfone, ionic group-containing polyether ether sulfone, ionic group-containing polyether phosphine oxide, ionic group-containing polyether ether phosphine oxide, ionic group-containing polyphenylene sulfide, ionic group-containing polyamide, ionic group-containing polyimide, ion An aromatic hydrocarbon polymer having an ionic group such as an ionic group-containing polyetherimide, an ionic group-containing polyimidazole, an ionic group-containing polyoxazole, and an ionic group-containing polyphenylene. Here, the ionic group is not particularly limited as long as it is a negatively charged atomic group, but is preferably one having proton exchange ability. As such a functional group, a sulfonic acid group, a sulfuric acid group, a sulfonimide group, a phosphonic acid group, a phosphoric acid group, and a carboxylic acid group are preferably used.

  In addition, as the crosslinked hydrocarbon polymer electrolyte membrane, a crosslinked structure mainly composed of a vinyl monomer is preferably used. Specific examples of the vinyl monomer include acrylic monomers such as acrylonitrile, aromatic vinyl monomers such as styrene, N-phenylmaleimide, N-isopropylmaleimide, N-cyclohexylmaleimide, N-benzylmaleimide, 2 , 2,2-trifluoroethyl (meth) acrylate, 2,2,3,3-tetrafluoropropyl (meth) acrylate, 1H, 1H, 5H-octafluoropentyl (meth) acrylate, 1H, 1H, 2H, 2H -A fluorine-containing monomer such as heptadecafluorodecyl (meth) acrylate is preferable. In addition, as monomers having a plurality of vinyl groups, aromatic polyfunctional monomers such as divinylbenzene, polyhydric alcohols such as ethylene glycol di (meth) acrylate, bisphenoxyethanol (meth) full orange acrylate, etc. Di-, tri-, tetra-, penta- and hexa- (meth) acrylates are particularly preferred. In particular, it is more preferable to copolymerize the vinyl monomer.

  The polymer constituting the polymer electrolyte membrane of the present invention is preferably one in which the polymer molecular chain is constrained, and the method is not particularly limited, and the polymer having proton conductivity and water resistance / solvent A restraining effect is expressed by mixing a plurality of polymers having excellent properties. In particular, at the time of mixing, it is important that each polymer, specifically, a polymer having proton conductivity and a polymer having excellent water resistance and solvent resistance are compatible with each other. Further, the restraining effect can be obtained not only by mixing but also by a method such as crosslinking or internal penetrating polymer network.

  The electrolyte membrane in the membrane electrode assembly of the present invention is also preferably an electrolyte membrane obtained by adding an inorganic material to the above-described hydrocarbon-based polymer electrolyte membrane, or an electrolyte membrane made of only an inorganic material. Examples of these inorganic materials include metal oxides such as alumina, silica, zeolite, titania, zirconia, and ceria, and carbon materials such as fullerenol.

  In addition, the electrolyte membrane in the membrane electrode assembly of the present invention is preferably one having a membrane shape in which a proton conductive electrolyte is filled in a support. Examples of the support include a porous polymer film, a porous inorganic material, a woven fabric, and a nonwoven fabric.

  The thickness of the electrolyte membrane in the membrane electrode assembly of the present invention is not particularly limited, and is determined according to the physical properties of the electrolyte membrane such as proton conductivity and the performance of the membrane electrode assembly (MEA) in which it is used. It should be done. Specifically, 5 μm to 500 μm is preferably used from the viewpoint of the physical properties of the electrolyte membrane, the performance of the MEA, and the manufacturing method.

  As a method for producing the membrane electrode assembly of the present invention, a step of immersing a catalyst containing Ru element in an aqueous solution and / or an organic solvent having different pHs and drying a plurality of times, a catalyst containing the dried Ru element and a polymer solution The step of kneading and the step of preparing an anode electrode catalyst layer by applying a catalyst containing a kneaded Ru element on an electrode substrate or a solid polymer electrolyte membrane are all performed under a nitrogen atmosphere. However, a conventional method can be applied except that all the steps are performed under a nitrogen atmosphere.

  When the electrode catalyst layer is formed on the electrode substrate, the electrode substrate with the electrode catalyst layer is bonded to an electrolyte such as a solid polymer electrolyte membrane. This bonding condition also depends on the characteristics of the fuel cell. Should be determined accordingly. In addition, when the electrode catalyst layer is formed on the electrolyte membrane, the electrolyte membrane with the electrode catalyst layer is joined to the electrode base material, and the joining conditions should be appropriately determined according to the characteristics of the fuel cell. Is.

  The electrode catalyst layer of the present invention and the membrane electrode assembly using the same can be suitably used for a solid polymer fuel cell, particularly a direct methanol fuel cell using a liquid fuel such as a methanol aqueous solution.

  Such a fuel cell is not particularly limited, but a power supply source of a mobile body or a portable device is preferably used. In particular, portable devices such as mobile phones, notebook computers, PDAs, digital cameras, and video cameras are preferable, and automobiles such as passenger cars, buses, and trucks, ships, and railways are also preferable mobiles.

  Hereinafter, the details of the present invention will be further described according to each procedure using examples. First, the evaluation method of what was produced in the Example below is demonstrated.

(MEA evaluation method)
MEA having an electrode size of 5 cm ² is sandwiched between cells manufactured by Electrochem, and a 20 wt% aqueous methanol solution is supplied to the anode side at 40 μl / cm ² / min, and air is supplied to the cathode side at 10 ml / cm ² / min, and constant temperature water at 60 ° C. The MEA was evaluated while the temperature was controlled at. In the evaluation, the current was gradually increased, and the voltage at that time was measured to obtain the output of the MEA.

(MEA durability)
Under the above MEA evaluation conditions, a constant current was applied to the MEA at 50 mA / cm ² , and after 100 hours of evaluation, the current was returned to zero, the current was gradually increased, and the voltage at that time was measured and output. The output retention rate was used as an index of durability.

(Analysis of Ru valence of anode electrode catalyst layer)
After evaluating the durability of the MEA, remove the MEA from the cell, cut out the center of the MEA, peel off the electrode catalyst layer on the anode surface little by little, and observe the cross-sectional form with a Hitachi Field Emission Scanning Electron Microscope S-800. Then, an anode catalyst layer having a thickness of 5 μm or less from the surface was prepared, and the anode catalyst layer was measured with an XPS apparatus ESCALAB 220iXL to obtain the number of elements for each valence of Ru.

(Measurement of the amount of Ru in the electrode catalyst layer)
The remainder of the MEA was cut off. Each of the cathode electrode catalyst layer and the anode electrode catalyst layer was scraped off from the cut-out MEA, and the weight was measured. The area of the electrode catalyst layer collected at this time was measured, these were treated at high temperature, and the residue was dissolved with alkali and acid.

  Each solution was analyzed with a sequential type ICP emission spectroscopic analyzer SPS400 manufactured by SII / Nanotechnology, and Ru in each electrode catalyst layer was quantified.

  The amount of Ru per unit area was determined from the area of the electrode catalyst layer and the amount of Ru contained therein, and the ratio of the amount of Ru in the cathode catalyst layer to the amount of Ru in the anode catalyst layer was determined.

Example 1
(1) Production and Evaluation of Electrolyte Membrane (A) Production of Polymer Electrolyte Polymer 109.1 g of 4,4′-difluorobenzophenone was reacted at 150 ° C. for 10 hours in 150 mL of fuming sulfuric acid (50% SO ₃ ). Thereafter, the mixture was poured little by little into a large amount of water, neutralized with NaOH, and 200 g of sodium chloride was added to precipitate the composite. The obtained precipitate was filtered off and recrystallized with an aqueous ethanol solution to obtain disodium 3,3′-disulfonate-4,4′-difluorobenzophenone (yield 181 g, yield 86%).

6.9 g of potassium carbonate, 14 g of 4,4 ′-(9H-fluorene-9-ylidene) bisphenol, 2.6 g of 4,4′-difluorobenzophenone, and the disodium 3,3′-disulfonate-4 Polymerization was carried out at 190 ° C. in N-methyl-2-pyrrolidone using 12 g of 4,4′-difluorobenzophenone. Purification was carried out by reprecipitation with a large amount of water to obtain polymer A. The density of the sulfonic acid group of the proton-substituted membrane of the obtained polymer A was 2.4 mmol / g and the weight average molecular weight was 240,000 according to elemental analysis.
(B) Production of polymer electrolyte membrane Polymer A obtained in (A) was dissolved in N, N-dimethylacetamide to obtain a coating solution having a solid content of 25%. The coating solution was cast on a glass plate and dried at 70 ° C. for 30 minutes and further at 100 ° C. for 1 hour to obtain a 56 μm film. Furthermore, after heat-treating under conditions of heating to 200 to 300 ° C. over 1 hour in a nitrogen gas atmosphere and heating at 300 ° C. for 10 minutes, the mixture was allowed to cool and immersed in 1N hydrochloric acid for 12 hours or more to perform proton substitution. The electrolyte membrane A was obtained by immersing it in a large excess of pure water for at least one day and thoroughly washing it.
(2) Production of membrane electrode assembly (MEA) and evaluation results (A) Production of anode electrode Using 30% polytetrafluoroethylene (PTFE) suspension on carbon paper TGP-H-060 manufactured by Toray Industries, Inc. After the water repellent treatment, firing was performed to prepare an anode electrode base material. Next, under a nitrogen atmosphere, catalyst pretreatment and electrode preparation were performed according to the following procedure.

  Prepare a 2-propanol / water mixed solution (2-propanol / water = 1/9 weight ratio) of sodium hydroxide 4% by weight as a pH 14 solution, adjust the temperature to 40 ° C., and then support Pt-Ru manufactured by Johnson Matthey Carbon and Pt—Ru particles were immersed in the mixed solution for 30 minutes and then washed with water. The catalyst was immersed in an aqueous HCl solution having a pH of 1 adjusted to 40 ° C. for 1 hour and then washed again with water. An anode electrode catalyst coating solution comprising this catalyst, polyvinylidene fluoride and dimethylacetamide was prepared, and applied to the anode electrode substrate and dried to prepare an anode electrode.

The thickness of the electrode catalyst layer of the obtained anode electrode was 28 μm, and the amount of Ru was 1.4 mg / cm ² .
(B) Production of Cathode Electrode Pt-supported carbon manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., Pt particles manufactured by Johnson Matthey Co., perfluoro membrane Nafion manufactured by DuPont (registered) A cathode electrode catalyst coating liquid made of a trademark solution was applied and dried to prepare a cathode electrode. The thickness of the electrode catalyst layer of the obtained cathode electrode was 45 μm, and the amount of Pt was 2.8 mg / cm ² .
(C) Production and evaluation results of MEA Membrane electrode composite by holding and pressing the polymer electrolyte membrane of the step (1) between the anode electrode and the cathode electrode produced in the steps (A) and (B) A body (MEA) was prepared. The MEA output was 40 mW / cm ² .
(3) Durability evaluation result of MEA, etc. Durability of MEA produced in (2) and (C) above, ratio of zero-valent Ru amount to Ru element amount of anode electrode catalyst layer, and Ru in anode catalyst layer The ratio of the amount of Ru in the cathode catalyst layer to the amount is summarized in Table 1.

Example 2
(1) Production of electrolyte membrane and evaluation results The same procedure as in (1) of Example 1 was performed.
(2) Production and evaluation results of membrane electrode assembly (MEA) Except that polymer A was used in place of polyvinylidene fluoride in the electrode catalyst coating solution when producing the anode electrode of (2) of Example 1, In the same manner as in Example 1 (2), electrodes and MEAs were produced and evaluated. The output of the obtained MEA was 43 mW / cm ² .
(3) Durability evaluation result of MEA, others The same as (3) of Example 1. The results are summarized in Table 1.

Example 3
(1) Production of electrolyte membrane and evaluation results The same procedure as in (1) of Example 1 was performed.
(2) Manufacture and Evaluation Results of Membrane Electrode Assembly (MEA) Soaked in 5% by weight 2-hydroxyl / water mixed solution of Example 2 (2), dried, and soaked in 2N HCl An electrode and an MEA were produced and evaluated in the same manner as (2) of Example 1 except that the series of steps was used after being performed twice. The output of the obtained MEA was 38 mW / cm ² .
(3) Durability evaluation result of MEA, others The same as (3) of Example 1. The results are summarized in Table 1.

Example 4
(1) Production and Evaluation Results of Electrolyte Membrane A commercially available Nafion (registered trademark) 117 membrane manufactured by DuPont was used after boiling in pure water for 1 hour.
(2) Production and evaluation results of membrane electrode assembly (MEA) An electrode and MEA were produced and evaluated in the same manner as (2) of Example 1.
The output of the obtained MEA was 39 mW / cm ² .
(3) Durability evaluation result of MEA, others The same as (3) of Example 1. The results are summarized in Table 1.

Comparative Example 1
(1) Production of electrolyte membrane and evaluation results The same procedure as in (1) of Example 1 was performed.
(2) Production of membrane electrode assembly (MEA) and evaluation results (A) Production of anode electrode Water repellent treatment using Toray carbon paper TGP-H-060 with 30% polytetrafluoroethylene (PTFE) suspension After firing, firing was performed to prepare anode electrode equipment. An anode electrode catalyst coating solution made of Johnson Matthey's Pt-Ru-supported carbon, Pt-Ru particles, polyvinylidene fluoride and dimethylacetamide is prepared in the atmosphere, and applied to the anode electrode equipment and dried to prepare an anode electrode. did.

The thickness of the electrode catalyst layer of the obtained anode electrode was 31 μm, and the amount of Ru was 1.5 mg / cm ² .
(B) Fabrication of cathode electrode, (C) Fabrication of MEA, and evaluation results were the same as in (2) of Example 1. The output of the obtained MEA was 38 mW / cm ² .
(3) Durability evaluation result of MEA, others The same as (3) of Example 1. The results are summarized in Table 1.

Comparative Example 2
(1) Production of electrolyte membrane and evaluation results The same procedure as in (1) of Example 1 was performed.
(2) Production and Evaluation Results of Membrane Electrode Assembly (MEA) Example 1 (2) except that the step of producing the anode electrode of (1) in Example 1 was performed in the air in the atmosphere. Similarly, an electrode and an MEA were produced and evaluated. The output of the obtained MEA was 37 mW / cm ² .
(3) Durability evaluation result of MEA, others The same as (3) of Example 1. The results are summarized in Table 1.

Comparative Example 3
(1) Production of electrolyte membrane and evaluation results It carried out similarly to Example 1 (1).
(2) Production of Membrane Electrode Assembly (MEA) and Evaluation Results The step of producing the anode electrode in Example 1 (2) under nitrogen atmosphere was carried out in the air, and polyvinylidene fluoride in the electrode catalyst coating solution An electrode and an MEA were prepared and evaluated in the same manner as in (2) of Example 1 except that polymer A was used instead of. The output of the obtained MEA was 39 mW / cm ² .
(3) Durability evaluation result of MEA, others The same as (3) of Example 1. The results are summarized in Table 1.

Comparative Example 4
(1) Production and Evaluation Results of Electrolyte Membrane A commercially available Nafion (registered trademark) 117 membrane manufactured by DuPont was used after boiling in pure water for 1 hour.
(2) Production and evaluation results of membrane electrode assembly (MEA) In the same manner as in (2) of Comparative Example 1, an electrode and MEA were produced and evaluated. The output of the obtained MEA was 39 mW / cm ² .
(3) Durability evaluation result of MEA, others The same as (3) of Example 1. The results are summarized in Table 1.

Claims (5)

A membrane electrode composite for a polymer electrolyte fuel cell using a liquid fuel having an anode electrode catalyst layer and a cathode electrode catalyst layer containing Ru element on both sides of a solid polymer electrolyte membrane, and having a current of 50 mA / cm ² After 100 hours of application, the proportion of zero-valent Ru element in the Ru element present in the anode electrode catalyst layer within 5 μm from the surface of the solid polymer electrolyte membrane is 40% or more. A membrane electrode assembly, wherein the total amount of Ru elements present is 2% or less of the total amount of Ru elements present in the anode electrode catalyst layer.   2. The membrane electrode assembly according to claim 1, wherein the solid polymer electrolyte membrane is a hydrocarbon-based solid polymer electrolyte membrane.   A step of immersing a catalyst containing Ru element in an aqueous solution and / or an organic solvent having different pH several times and drying, a step of kneading the dried Ru element containing catalyst with a polymer solution, and a catalyst containing the kneaded Ru element 3. The membrane electrode composite according to claim 1 or 2, wherein the step of coating the electrode substrate or the solid polymer electrolyte membrane to produce the anode electrode catalyst layer is all carried out in a nitrogen atmosphere. Production method.   A polymer electrolyte fuel cell comprising the membrane electrode assembly according to claim 1.   5. The polymer electrolyte fuel cell according to claim 4, wherein liquid fuel is used as fuel, and the liquid fuel is methanol.