JP5427487B2 - Fuel cell - Google Patents

Description

  The present invention relates to a fuel cell, and in particular, has a catalyst electrode layer applied to an electrolyte membrane.

  A fuel cell is a device that converts chemical energy directly into electrical energy.

  Reducing substances such as hydrogen and methanol as fuel, and oxidizing gases such as air and oxygen as oxidants are supplied to the fuel electrode (anode) and the air electrode (cathode), respectively. And the electron which arises by the oxidation-reduction reaction which advances on the catalyst contained in an electrode layer is taken out, and it makes it electrical energy.

  The fuel cell can be divided into a solid polymer type, a phosphoric acid type, a molten carbonate type, a solid oxide type, etc., depending on the material of the electrolyte membrane and the operating temperature.

  Among them, a solid polymer electrolyte membrane having proton conductivity represented by perfluorosulfonic acid resin, sulfonated aromatic hydrocarbon resin, etc. is used to oxidize hydrogen on the anode side and oxygen on the cathode side. A polymer electrolyte fuel cell (PEFC) that generates electricity by reduction is known as a battery that can generate electricity at a relatively low temperature and has a high output density.

  In addition, direct methanol fuel cells (DMFC) using methanol as a fuel instead of hydrogen and methanol aqueous solution as a fuel have recently been attracting attention. DMFC is active type (forced supply of fuel and air), semi-active type (forced supply of either fuel or air), passive type (natural supply of fuel or air) depending on the fuel and air supply method And so on.

  The power generation of PEFC and DMFC is performed by a membrane-electrode assembly (MEA) having a configuration in which a solid polymer electrolyte membrane is sandwiched between an anode and a cathode. This MEA desirably has excellent durability against continuous power generation of PEFC and DMFC.

  However, during continuous power generation of PEFC and DMFC, a part of the electrolyte membrane in the electrode outer peripheral region is damaged, and fuel may cross-leak, so that stable power generation may not be continued.

  Analysis of the damaged electrolyte membrane revealed that there was no change in membrane composition or ion exchange capacity, and that its molecular weight was halved. This is particularly the case with DMFC power generation.

  In such MEAs for PEFC and DMFC, damage or breakage of the electrolyte membrane in the electrode peripheral portion is pointed out as a problem in Patent Documents 1 to 3.

  In Patent Document 1, the cause of the film breakage is stress concentration at the end of the electrode. However, the breakage observed in DMFC is caused by a decrease in the molecular weight of the solid polymer, and does not solve the problem.

  In Patent Document 2, cross-leaked hydrogen fuel and air cause a fuel reaction directly around the electrode without a catalyst, and the problem is to deteriorate the electrolyte membrane by this combustion heat, and a refractory layer made of carbon is provided around the electrode. A membrane electrode assembly is proposed. However, the carbonization region due to the combustion reaction was not confirmed at the membrane degradation site at the time of DMFC power generation, and it was confirmed that the membrane breakage occurred even when the membrane electrode assembly having the above configuration was used.

  Moreover, in patent document 3, in order to prevent the damage by direct contact of methanol fuel with a solid polymer electrolyte membrane, the membrane electrode assembly which provided the polymer membrane which added the plasticizer to the area | region larger than an electrode was used. However, there is no description about the mechanism of damage to the electrolyte membrane, and the membrane electrode assembly having the above-described configuration is not an effective means for solving this problem.

JP 2006-331718 A JP-A-7-201346 JP 2007-141832 A

  As a result of intensive studies, we found that hydrogen peroxide is generated at the electrode edge, and hydrogen peroxide and hydrogen peroxide radicals are solid around the electrode. It was ascertained that the degradation was caused by reducing the mechanical strength of the electrolyte membrane in the electrode outer peripheral region by decomposing the polymer electrolyte.

  When a membrane electrode assembly in which an electrolyte membrane is sandwiched between an anode and a cathode is sandwiched between a gasket and a separator, voids are likely to be generated in the electrode outer periphery and in a region surrounded by the gasket and the separator. When the DMFC operation is performed in such a configuration, the methanol aqueous solution that has permeated from the anode tends to stay in the gap in the outer peripheral region of the electrode on the cathode side. In this case, due to the Pt catalyst poisoning by methanol and the flooding phenomenon by water, the electrochemical potential at the cathode end tends to decrease, and the oxygen in the cathode gas is not completely oxidized and tends to be hydrogen peroxide.

  In addition, since hydrogen peroxide is easily dissolved in water, it reaches the electrolyte in the outer periphery of the electrode via an aqueous methanol solution staying in the void around the cathode, and the radical decomposes the solid polymer.

  Furthermore, it was confirmed that the presence of catalyst particles missing from the electrode end on the electrolyte membrane surface on the outer periphery of the electrode tends to lower the cathode potential particularly on the catalyst and promotes electrolyte membrane degradation due to the generation of hydrogen peroxide. Therefore, it is necessary to prevent the catalyst particles from being lost at the end portions of the electrodes.

  On the other hand, in the PEFC power generation, if water stays in the gap around the electrode, the hydrogen peroxide generated at the electrode is likely to stay without being decomposed, so that the electrolyte deterioration is likely to proceed in a region where the staying water is in contact. This can occur at both the anode and the cathode.

  Furthermore, the Pt catalyst exposed to a high potential tends to elute at the cathode during PEFC power generation, and the Pt cations naturally diffused in the electrolyte membrane react with the hydrogen molecules that have permeated from the anode, thereby reducing and depositing in the membrane. It has been reported. This is also the catalyst particles isolated from the electrode as described above, and easily generates hydrogen peroxide. Since the outer peripheries of the anode and cathode have a larger gas permeation amount than the electrolyte membrane sandwiched between these electrodes, if re-deposited Pt exists in the outer peripheries of the electrode, more hydrogen peroxide is generated and the deterioration of the electrolyte is accelerated. The

  Accordingly, an object of the present invention is to provide a membrane electrode assembly for PEFC and DMFC that prevents the generation and retention of hydrogen peroxide at the outer periphery of the electrode and suppresses electrolyte decomposition at the outer periphery of the electrode. It is in providing a structure and its manufacturing method.

A fuel cell membrane electrode assembly which is one of the embodiments according to the present invention is such that an anode comprising a catalyst and a solid polymer electrolyte and a cathode comprising a catalyst and a solid polymer electrolyte sandwich the solid polymer electrolyte membrane. In the membrane electrode assembly for a fuel cell to be formed, the anode and the cathode are embedded in the vertical direction of the membrane surface with respect to the electrolyte membrane, and the electrolyte membrane in the region sandwiched between the anode and the cathode The thickness t _in and the thickness of the electrolyte membrane located in the outer peripheral area of the anode and cathode are between t _out ,
t _out > t _in
Is established. In the present invention, the electrolyte membrane in the region sandwiched between the anode and the cathode is an electrolyte in which the anode catalyst layer and the cathode catalyst layer are arranged on both sides when the membrane electrode assembly is cut along the plane including the normal line. Refers to the membrane. In addition, when the membrane electrode assembly is cut along the plane including the normal line, the anode catalyst layer and the cathode catalyst layer are not arranged on both sides of the electrolyte membrane located in the outer peripheral region of the anode catalyst layer and the cathode catalyst layer. It refers to the electrolyte membrane. t _IN can be represented by the distance between the boundary line between the electrolyte membrane and the anode catalyst layer and the boundary line between the electrolyte membrane and the cathode catalyst layer in the cross section including the normal line of the membrane electrode assembly. The boundary line existing between the anode catalyst layer or cathode catalyst layer and the electrolyte membrane is determined by the presence or absence of a catalyst contained in the anode catalyst layer or cathode catalyst layer. The thickness of each region can be measured by a cross-sectional observation image including the normal line of the membrane electrode assembly. The thickness is measured at any three or more points in the corresponding region, and the arithmetic average value is expressed as t _in , t _out And Moreover, t _out can be defined as the thickness of the electrolyte membrane in which neither the anode catalyst layer nor the cathode catalyst layer is disposed in the relevant membrane electrode assembly, and can be measured using a micrometer.

In addition, the configuration in which the cathode catalyst layer is completely embedded in the electrolyte membrane is particularly effective because the methanol aqueous solution can be completely prevented from staying around the cathode catalyst layer. In this case, when the thickness of the cathode catalyst layer and _{t CA t out ≧ t CA +} t relationship _in holds.

Further, even in a configuration in which the anode catalyst layer is completely embedded in the electrolyte membrane, methanol permeation is suppressed, so that it has an effect. In this case, when the thickness of the anode catalyst layer and t _AN, relationships t _out ≧ t _AN + t _in is established.

It is most preferable that both the anode catalyst layer and the cathode catalyst layer electrode are completely embedded in the electrolyte membrane. The thickness of the electrolyte membrane located in the outer peripheral area of the anode catalyst layer and the cathode catalyst layer is t _out , that the thickness of the layer t _CA, the thickness t _aN of the anode catalyst layer, the relationship between the anode catalyst layer and the thickness of the electrolyte film sandwiched between the cathode catalyst layer When _{t in t out ≧ t CA +} t aN + t in established It is.

  In a membrane electrode assembly for a fuel cell which is one of the embodiments according to the present invention, the fuel cell membrane electrode assembly is disposed on the outer periphery of a solid polymer electrolyte resin and an electrode constituting an electrolyte membrane in a region sandwiched between an anode catalyst layer and a cathode catalyst layer. The solid polymer electrolyte resins may be the same or different. Here, the solid polymer electrolyte located in the outer peripheral region of the electrode is arranged in a region where no electrode is arranged in a plan view of the membrane electrode assembly viewed from the anode side or the cathode side, and the membrane electrode assembly It is an electrolyte in contact with the side wall of the anode catalyst layer or the cathode catalyst layer in the cross-sectional image. The same electrolyte means that the polymer skeleton analyzed by nuclear magnetic resonance spectroscopy (NMR) is the same, the ion exchange capacity is within 5%, and analyzed by gel permeation chromatography (GPC). It means that the number average molecular weight and the weight average molecular weight of the polymer to be produced are within 10%.

  In a fuel cell membrane electrode assembly which is one of the embodiments according to the present invention, a solid polymer electrolyte constituting an electrolyte membrane sandwiched between opposing anodes and cathodes and a solid polymer electrolyte located in the electrode outer peripheral region are If the ion exchange capacity of the solid polymer electrolyte located in the outer peripheral area of the electrode is smaller than the ion exchange capacity of the solid polymer electrolyte sandwiched between the anode and the cathode, More specifically, the ion exchange capacity of the solid polymer electrolyte located in the outer peripheral region of the electrode is 95% of the ion exchange capacity of the solid polymer electrolyte sandwiched between the anode and the cathode. The following is desirable. The ion exchange capacity can be measured by NMR method or acid-base titration method.

  In a membrane electrode assembly for a fuel cell which is one of the embodiments according to the present invention, the solid polymer electrolyte in a portion where the contact angle of water with respect to the solid polymer electrolyte located in the outer peripheral region of the electrode is sandwiched between the anode and the cathode If it is larger than the contact angle with respect to water, the amount of methanol permeated through the outer periphery of the electrode can be reduced, which is desirable. In addition, the contact angle with water here means that the corresponding solid polymer electrolyte is varnished, formed into a film with a thickness of 10 μm or more, washed with water and dried, and then water droplets hung on the surface were observed from the cross-sectional direction. It is the angle between the water droplet and the film surface.

  In a fuel cell membrane electrode assembly which is one of the embodiments according to the present invention, the solid polymer electrolyte located in the outer peripheral region of the electrode is a π-conjugated polymer or a sulfonated π-conjugated polymer. It is desirable to include. By including π-conjugated polymer, even if the catalyst particles are isolated on the outer periphery of the cathode catalyst layer, the electron conduction between the electrode and the isolated particles is ensured, and the potential of the isolated particles does not decrease and hydrogen peroxide is generated. Can be suppressed.

  In a fuel cell membrane electrode assembly which is one of the embodiments according to the present invention, a solid polymer electrolyte located in the outer peripheral region of the electrode has a metal ion having an effect of capturing and decomposing hydrogen peroxide radicals and its oxidation. It is desirable to contain physical particles. In the membrane electrode assembly having such a configuration, even if water accumulates in a gap formed between the membrane electrode assembly, the gasket, and the gas diffusion layer, and hydrogen peroxide stays there, the electrolyte on the outer periphery of the electrode is overoxidized. It can be prevented from being decomposed into hydrogen radicals. Here, the metal ions having the effect of capturing and decomposing hydrogen peroxide radicals and oxide fine particles thereof may or may not be contained in the electrolyte membrane sandwiched between the anode and the cathode catalyst layer. However, it is desirable that it is not included from the viewpoint of proton conduction resistance of the membrane electrode assembly.

  In a fuel cell membrane electrode assembly which is one of the embodiments according to the present invention, the solid polymer electrolyte located in the outer peripheral region of the electrode contains an electrolyte or an additive having an effect of capturing Pt cations. It is desirable to prevent Pt cations that have been eluted and diffused from the electrode from being reduced and deposited in the electrolyte membrane on the outer periphery of the electrode, and to suppress the generation of hydrogen peroxide. Here, the electrolyte and additive having the effect of capturing the Pt cation may or may not be contained in the electrolyte membrane sandwiched between the anode and the cathode catalyst layer. From the viewpoint of proton conduction resistance of the joined body, it is desirable that it is not included.

  Further, in the membrane electrode assembly according to the present invention, when the solid polymer electrolyte located in the outer peripheral region of the electrode is an aromatic hydrocarbon electrolyte sulfonated or alkylsulfonated, the gas permeation amount at the outer peripheral portion of the electrode , It is desirable because the amount of methanol permeation can be suppressed.

  Further, in the membrane electrode assembly according to the present invention, the region sandwiched between the anode catalyst layer and the cathode catalyst layer is an aromatic hydrocarbon electrolyte that is sulfonated or alkylsulfonated, and is disposed on the outer periphery of the electrode. This is desirable because the bondability with an electrolyte having a low gas permeation amount and a low methanol permeation amount is enhanced.

  In the membrane electrode assembly which is one embodiment of the present invention, the resin composition in the electrolyte disposed in the outer peripheral region of the electrode and the resin composition in the electrolyte membrane sandwiched between the anode catalyst layer and the cathode catalyst layer are the same. For an electrolyte membrane obtained by applying a varnish in which a solid polymer electrolyte is dissolved, at least one of an anode catalyst layer and a cathode catalyst layer is formed on the electrolyte membrane before the water washing step. It can be manufactured by thermocompression bonding, drying, and washing.

  Among membrane electrode assemblies that are one embodiment of the present invention, the resin composition in the electrolyte disposed in the outer peripheral region of the electrode and the resin composition in the electrolyte membrane sandwiched between the anode catalyst layer and the cathode catalyst layer are different. For those, a different solid polymer electrolyte is selectively applied to the outer periphery of the region where at least one of the anode catalyst layer and the cathode catalyst layer is disposed, and the anode catalyst layer and the cathode catalyst layer are applied to the recesses on the electrolyte membrane. By doing so, it can be manufactured.

  In a fuel cell configured using a membrane electrode assembly, which is one embodiment of the present invention, a gas diffusion layer, a member for supplying air (oxygen), and a current collecting member, the gas diffusion layer is an anode. If the area is larger than the area of the catalyst layer and the cathode catalyst layer, the water retention portion formed between the membrane electrode assembly, the gas diffusion layer, and the gasket does not come into contact with the electrode end, and hydrogen peroxide is generated and retained. This is desirable because it can be prevented. Here, as a member for supplying fuel, a series of members for supplying fuel introduced by a pump or the like to the gas diffusion layer through the separator, and as a member for supplying air (oxygen), a blower or the like is used. 1 shows a series of members that supply air (oxygen) introduced by the above to a diffusion layer through a separator. The fuel is an aqueous methanol solution or hydrogen gas.

  Fuel is electrochemically oxidized at the anode, oxygen is reduced at the cathode, and a difference in electrical potential occurs between the electrodes. At this time, when a load is applied as an external circuit between the two electrodes, ion migration occurs in the electrolyte, and electric energy is extracted from the external load. For this reason, various fuel cells have high expectations for large power generation systems, small distributed cogeneration systems, electric vehicle power supply systems, and the like, and practical development is actively being developed.

  As described above, in the embodiment of the present invention, the structure of the membrane electrode assembly for suppressing the generation and retention of hydrogen peroxide at the outer periphery of the electrode and the deterioration and breakage of the electrolyte at the outer periphery of the electrode, and its constituent materials The present invention provides a manufacturing method thereof and a fuel cell using the same.

  According to the present invention, a membrane electrode assembly for a fuel cell having a long life can be provided by preventing deterioration and breakage of the electrolyte membrane on the electrode outer peripheral portion due to continuous power generation.

It is a schematic sectional drawing of the fuel cell demonstrated in the present Example. It is a cross-sectional schematic diagram of the conventional membrane electrode assembly for fuel cells. It is a cross-sectional schematic diagram of the membrane electrode assembly which concerns on a present Example. It is a cross-sectional schematic diagram of the membrane electrode assembly which concerns on a present Example. It is a cross-sectional schematic diagram of the membrane electrode assembly which concerns on a present Example. It is a cross-sectional schematic diagram of the membrane electrode assembly which concerns on a present Example. It is a cross-sectional schematic diagram of the membrane electrode assembly which concerns on a present Example. It is a cross-sectional schematic diagram of the membrane electrode assembly which concerns on a present Example. It is a schematic diagram of the portable information terminal concerning a present Example.

  Embodiments according to the present invention will be described below with reference to the drawings.

  FIG. 1 shows an example of a cell configuration of a fuel cell using a membrane electrode assembly.

  In FIG. 1, 11 is a separator, 13 is an anode catalyst layer, 12 is an anode diffusion layer, 14 is a solid polymer electrolyte membrane having proton conductivity, 15 is a cathode catalyst layer, 16 is a cathode diffusion layer, and 17 is a gasket. .

  The separator 11 has electronic conductivity, and as a material thereof, a dense graphite plate, a carbon plate formed by molding a carbon material such as graphite or carbon black with a resin, a metal such as stainless steel or titanium, or corrosion resistance and heat resistance thereof. It is desirable to use a material coated with an excellent conductive paint or precious metal plating.

  A combination of the anode catalyst layer 13, the cathode catalyst layer 15, and the solid polymer electrolyte membrane 14 is referred to as a membrane-electrode assembly (Membrane-Electrode-Assembly). In this case, the catalyst layer and the diffusion layer may be integrated.

  FIG. 2 shows a conventional MEA configuration. The anode catalyst layer and the cathode catalyst layer are arranged so as to sandwich the electrolyte membrane. In this configuration, a gap is generated between the electrode outer peripheral area of the anode catalyst layer and the cathode catalyst layer, the diffusion layer, and the seal portion by the gasket. Methanol and water stay in the tank. The stagnation of methanol or water at the outer periphery of the electrode causes a decrease in potential at the end of the cathode catalyst layer, and further causes the generated hydrogen peroxide to stay at the outer periphery of the electrode.

  This example relates to the structure and constituent materials of a membrane electrode assembly.

The configuration of this embodiment will be described with reference to FIGS.
In FIG. 3, the cathode catalyst layer (33) is partly embedded in the electrolyte membrane (32), and the thickness of the electrolyte membrane located on the outer periphery of the anode catalyst layer and the cathode catalyst layer is expressed as t _out anode. relationship t _out> t _in the thickness of the electrolyte membrane sandwiched between the catalyst layer and the cathode catalyst layer and t _in those that holds. With such a structure, the amount of methanol and water remaining in the periphery of the electrode can be reduced, so that a decrease in cathode potential at the electrode end and a hydrogen peroxide retention can be mitigated. Moreover, the gas permeation amount, methanol permeation amount, and water permeation amount can be reduced by increasing the electrolyte thickness at the outer periphery of the electrode.

  The same effect can be obtained by a structure in which only the anode catalyst layer is partially embedded in the electrolyte membrane, or a structure in which the anode catalyst layer and the cathode catalyst layer are partially embedded in the electrolyte membrane.

In FIG. 4, the cathode catalyst layer (43) is completely embedded in the electrolyte membrane (42), and the thickness of the electrolyte membrane located in the outer peripheral area of the anode catalyst layer and the cathode catalyst layer is t _out , the thickness t _CA of the cathode catalyst layer, in which relationship t _out ≧ t _CA + t _in the thickness of the sandwiched electrolyte membrane an anode catalyst layer and cathode catalyst layer and t _in holds. By adopting such a structure, water and methanol do not stay in the outer periphery of the cathode catalyst layer, and a decrease in cathode potential at the electrode end can be prevented. Further, the generated hydrogen peroxide can be prevented from diffusing and staying around the outer periphery of the electrode.

Further, even in a membrane / electrode assembly having a structure in which only the anode catalyst layer is completely embedded in the electrolyte membrane, fuel permeation from the anode electrode periphery can be suppressed, and hydrogen peroxide retention on the anode electrode periphery can also be suppressed. Therefore, the effect appears. In this case, when the thickness of the anode catalyst layer and t _AN, relationships t _out ≧ t _AN + t _in is established.

  The catalyst used for the anode and cathode according to the present embodiment may be any metal that promotes the oxidation reaction of fuel and the reduction reaction of oxygen, such as platinum, gold, silver, palladium, iridium, rhodium, Examples include ruthenium, iron, cobalt, nickel, chromium, tungsten, manganese, vanadium, titanium, or alloys thereof.

  Among such catalysts, in particular, a platinum (Pt) catalyst is used as a PEFC electrode catalyst and a DMFC cathode catalyst layer catalyst, and a platinum / ruthenium (Pt / Ru) catalyst is used as a DMFC anode catalyst layer catalyst. The particle size of the metal serving as the catalyst is usually 2 to 30 nm.

The catalyst metal according to this example is desirably supported on a carbon material having a large specific surface area. When the catalyst is finely divided, the specific surface area increases, so that the activity per unit weight increases. By supporting on carbon black, the catalyst can be maintained as fine particles without agglomerating. The specific surface area of the carbon black to be used is preferably selected from the range of 10 to 1000 m ² / g. If the specific surface area is too small, the effect of adding carbon black will not be obtained so much. If the specific surface area is too large, there will be many pores formed on the surface of the carbon black, and catalyst particles will enter the pores and become fine. This is because the catalyst particles that have entered the pores are less likely to contribute to the reaction during battery operation. For example, carbon black such as ketjen black, furnace black, channel black, acetylene black, fibrous carbon such as carbon nanotubes, activated carbon, graphite, etc. can be used, and these should be used alone or in combination. Can do.

  Among these, it is desirable to use ketjen black having a large specific surface area in order to increase the activity of the catalyst electrode layer.

  When an acidic hydrogen ion conductive material is used as the solid polymer electrolyte used for the cathode catalyst layer (43) and the anode catalyst layer (41) and the solid polymer electrolyte used for the solid polymer electrolyte membrane (42), This is preferable because a stable fuel cell can be realized without being affected by the carbon dioxide gas contained therein. Examples thereof include perfluoroalkyl sulfonic acid electrolytes and hydrocarbon electrolytes having polar groups exhibiting proton conductivity. In particular, the hydrocarbon electrolyte membrane is excellent in methanol swelling resistance and methanol permeability, and it is desirable to use this. Examples of the polar group exhibiting proton conductivity include a sulfonic acid group, a phosphoric acid group, and a carboxyl group, and a sulfonic acid group is particularly desirable from the viewpoint of proton conductivity.

  Examples of hydrocarbon electrolytes include sulfonated engineering plastic electrolytes such as sulfonated polyetheretherketone, sulfonated polyethersulfone, sulfonated acrylonitrile / butadiene / styrene, sulfonated polysulfide, and sulfonated polyphenylene, and sulfoalkylation. Sulfoalkylated engineering plastics such as polyetheretherketone, sulfoalkylated polyethersulfone, sulfoalkylated polyetherethersulfone, sulfoalkylated polysulfone, sulfoalkylated polysulfide, sulfoalkylated polyphenylene, sulfoalkylated polyetherethersulfone, etc. An electrolyte can be used.

  Further, in order to improve the strength of the electrolyte membrane and the fuel permeation resistance, a structure in which a porous substrate is included in the electrolyte membrane can also be used.

In FIG. 5, not only the cathode catalyst layer (53) but also the anode catalyst layer (51) is embedded in the electrolyte membrane (52), and the electrolyte located in the outer peripheral area of the anode catalyst layer and the cathode catalyst layer. the thickness of the film t _out, the thickness t _CA of the cathode catalyst layer, the thickness t _aN of the anode catalyst layer, an anode catalyst layer and the thickness of the electrolyte film sandwiched between the cathode catalyst layer When t _in t _out ≧ t _CA relationship + t _AN + t _in is what is true. This is most desirable because it prevents the retention of methanol or water in the outer peripheral area of the electrode and suppresses the generation of hydrogen peroxide accompanying the potential drop at the cathode end and the retention of the generated hydrogen peroxide.

  4 and 5, the solid polymer electrolyte around the electrode, the anode catalyst layer, and the electrolyte membrane sandwiched between the cathode catalyst layers are the same, but the cathode catalyst layer as shown in FIG. (63) is surrounded by a solid polymer electrolyte (64), and the solid height of the electrolyte membrane (62) sandwiched between the solid polymer electrolyte (64), the anode catalyst layer, and the cathode catalyst layer. It may be different from the molecule in chemical composition and ion exchange capacity. Hereinafter, 62 is referred to as a solid polymer electrolyte membrane between electrodes, and 64 is referred to as a solid polymer electrolyte around the electrodes.

  In order to suppress permeation of aqueous methanol solution, hydrogen, and oxygen gas in the electrode outer peripheral region, it is desirable to use a material having low permeability of these substances for the solid polymer electrolyte (64) around the electrode, and its ion exchange capacity. Is preferably lower than the ion exchange capacity of the electrolyte membrane. On the other hand, if the ion exchange capacity is excessively lowered, the adhesion with the electrolyte membrane is lowered and there is a risk of peeling. From the above viewpoint, the ion exchange capacity of the solid polymer electrolyte (64) around the electrode is preferably in the range of 0.1 to 2, and more preferably in the range of 0.5 to 1.0.

  The solid polymer electrolyte (64) around the electrode is preferably made of a material having higher hydrophobicity than the electrolyte membrane (62) between the electrodes from the viewpoint of suppressing permeation of aqueous methanol solution from the electrode outer peripheral region. Hydrophobicity can be evaluated by forming each electrolyte into a film with a thickness of 10 μm or more, dropping a water drop on the electrolyte, and observing the angle (contact angle) formed by the liquid drop and the film surface. By using a highly hydrophobic material, methanol permeation can be suppressed, and further, the effect of suppressing water retention around the electrode by the structure of the present invention can be increased. However, it is not desirable to use an excessively hydrophobic material from the viewpoint of ensuring adhesion between the electrolyte membrane and the electrode.

  As such a material, in addition to the aforementioned engineered plastic electrolyte, the aromatic skeleton that is the basic skeleton is bonded with a fluorine-containing group such as (4,4'-hexafluoroisopropylidene) diphenol or decafluorobiphenol. Aromatic hydrocarbon electrolytes can also be used.

  Further, the solid polymer electrolyte (64) around the electrode may contain a π-conjugated solid polymer or a sulfonated π-conjugated solid polymer. These materials are desirable from the viewpoint of methanol permeation suppression. In addition, since these materials exhibit high electron conductivity when doped with sulfonic acid or the like, the solid polymer electrolyte (64) around the electrode exhibits electron conductivity. Even when some separation occurs between the solid polymer electrolyte (64) and isolated catalyst particles are generated in the solid polymer electrolyte, the isolated catalyst particles are interposed via the solid polymer electrolyte (64) showing electron conductivity. The cathode potential can be kept high, and the generation of hydrogen peroxide can be suppressed.

  Examples of such materials include polyaniline, polypyrrole, polythiophene, polyfluorene, polyphenylene, and sulfone oxides thereof.

  Moreover, it is desirable that the solid polymer electrolyte (64) around the electrode contains a material capable of capturing or decomposing hydrogen peroxide radicals. With this configuration, even when the generated hydrogen peroxide moves to the outer periphery of the electrode via the water in the diffusion layer, the solid polymer electrolyte layer around the electrode captures and decomposes the radicals. Therefore, it is possible to prevent the deterioration of the electrolyte in the outer periphery of the electrode.

  An example of the radical scavenger is a hindered phenol radical scavenger. Examples of hindered phenol radical scavengers include 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, pentaerythrityl-tetrakis [3. -(3,5-di-tert-butyl-4-hydroxyphenyl) propionate], 2-tert-butyl-6- (3-tert-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenyl acrylate 2- [1- (2-hydroxy-3,5-di-t-pentylphenyl) ethyl] -4,6-di-t-pentylphenyl acrylate, N, N′-hexamethylenebis (3,5- Di-t-butyl-4-hydroxy-hydrocinnamamide), 1,6-hexanediol-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propione 3,9-bis [2- [3- (3-t-butyl-4-hydroxy-5-methylphenyl) propionyloxy] 1,1-dimethylethyl] 2,4,8,10-tetraoxa Spiro [5.5] undecane, tris- (3,5-di-tert-butyl-4-hydroxybenzyl) isocyanurate, isooctyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate 4,4'-thiobis (6-tert-butyl-3-methylphenol), 6- [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propoxy] -2,4,8, Examples thereof include 10-tetra-t-butyldibenz [d, f] [1,3,2] dioxaphosphine, and are not particularly limited.

  Further, as the radical decomposing agent, metal cations such as Mn, Cr, Co, Cu, Ce, Rb, Co, Ir, Ag, Rh, Ti, Zr, Al, and Sb or oxide particles of these metals may be used. it can.

  The amount of radical scavenger and radical decomposer added in the present invention is not particularly limited, but the total amount of radical scavenger and radical decomposer added is 1 part by weight with respect to 100 parts by weight of the polymer electrolyte material. To 50 parts by weight is preferred. If the total addition amount is less than 1 part by weight, the durability against hydrogen peroxide radicals is insufficient, and if it exceeds 50 parts by weight, the mechanical properties of the electrolyte in the outer peripheral part and the bondability with the electrolyte (62) between the electrodes are poor. Since it falls, it is not preferable.

  Further, the amount of the radical scavenger and radical decomposer added to the electrolyte membrane (62) between the electrodes is not particularly limited, but these additives inhibit the proton conductivity of the electrolyte membrane (62) between the electrodes. Therefore, zero is desirable.

  Moreover, it is desirable that the solid polymer electrolyte (64) around the electrode contains a Pt cation scavenger that can trap Pt cations. Such a material is not particularly limited as long as it includes a functional group capable of coordinating with a Pt cation. Examples include 2,2'-bipyridine, 1,10'-phenanthroline, phthalocyanine, porphyrin, etc., where the nitrogen atom is a ligand, citric acid, succinic acid, malic acid, tartaric acid, etc. The thing made into a ligand etc. are mentioned. In addition to these, the use of a polymer such as polyaniline containing nitrogen element, polypyrrole, or carboxymethylcellulose containing a carboxyl group is also desirable because it is a high molecular weight substance, so that elution during continuous power generation is suppressed. .

  In addition, as shown in FIG. 7, a solid polymer electrolyte (75) having a chemical composition different from that of the electrolyte and an ion exchange capacity may be provided in the outer peripheral region of the anode catalyst layer. At this time, the structures of the solid polymer electrolytes around the electrodes in the anode catalyst layer and the cathode catalyst layer may be the same or different, but are preferably the same from the viewpoint of the balance of stress on both the anode and cathode. .

  In addition, as shown in FIG. 8, by arranging a gas diffusion layer having a larger area than the anode catalyst layer and the cathode catalyst layer of the membrane electrode assembly according to the present invention, the membrane electrode assembly and the diffusion layer, Even when water stays in the gap formed between the gaskets, contact between the staying water and the outer periphery of the electrode can be prevented, which is desirable. The size of the gas diffusion layer is not particularly limited, but it is preferable that the outer periphery of the gas diffusion layer is 1 mm or more away from the outer periphery of the anode catalyst layer and the cathode catalyst layer.

  Below, an example of the manufacturing method of the membrane electrode assembly concerning a present Example is shown. However, the manufacturing method is not limited to the following.

  In order to obtain a membrane-electrode assembly structure in which the anode catalyst layer or the cathode catalyst layer is embedded in the electrolyte membrane as shown in FIGS. 3 to 5, the varnish is applied to a flat substrate and dried. Then, an electrolyte membrane is prepared, and at least one of the anode catalyst layer and the cathode catalyst layer may be formed on the electrolyte membrane and thermocompression bonded before the water washing step. Before the electrolyte membrane is washed with water, the residual solvent remains in the electrolyte membrane, and the electrolyte membrane is plastically deformed in the thermocompression bonding process, so that the electrode is embedded. If the residual solvent necessary for plastic deformation of the electrolyte membrane in thermocompression bonding is washed with water as it is, many pores are generated in the electrolyte membrane, and free water is taken into the electrolyte membrane. Wash the entire electrode assembly with water.

  The solvent used for coating the electrolyte membrane in this production process is not particularly limited as long as it dissolves the electrolyte polymer and does not poison the catalyst after washing. For example, in addition to water, alkylene glycol monoalkyl ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether, n-propanol, iso-propanol, t-butyl alcohol, etc. Alcohols and highly polar solvents such as 1-methyl-2-pyrrolidone can be used. Alternatively, a mixture of two or more of these can be used.

  The electrode can be formed by direct application using a spray coating method or slit die coater method using an alcohol solution in which a catalyst and a solid polymer electrolyte are dispersed, and the electrode is applied in the form of a Teflon (registered trademark) sheet. It is also possible to press and heat the pressed product against an unwashed electrolyte membrane.

  In addition, by applying and drying the electrolyte varnish on the substrate with the projections corresponding to the electrode size during coating of the electrolyte membrane, an electrolyte membrane with depressions on one side is formed, and the periphery of the depressions is masked and directly in the depressions The membrane electrode assembly of the present invention can also be obtained by applying an electrode.

  In addition, as shown in FIGS. 6 and 7, in order to obtain a membrane electrode assembly in which a solid polymer electrolyte different from the electrolyte membrane (65 in FIG. 6) is arranged in the electrode peripheral portion (64 in FIG. 6), coating is performed. A composite electrolyte membrane that is recessed in the electrode placement area is obtained by pasting the electrolyte membrane that has been removed from the electrode membrane in a portion that corresponds to the electrode size to the dried and washed electrolyte membrane. What is necessary is just to apply | coat an electrode directly.

  In order to confirm whether the manufactured membrane electrode assembly is as in the embodiment of the present invention, a cross section of the obtained membrane electrode assembly may be observed with a scanning electron microscope (SEM). By mapping the composition with an energy dispersive X-ray spectrometer (EDX) attached to the SEM, the thickness of the electrolyte membrane, the thickness of the anode catalyst layer, and the thickness of the cathode catalyst layer can be evaluated.

  The sum of the thicknesses of the cathode catalyst layer, the anode catalyst layer, and the electrolyte membrane can be measured with a micrometer.

  The chemical composition and ion exchange capacity of the solid polymer electrolyte around the electrolyte membrane and the electrode can be analyzed by nuclear magnetic resonance (NMR) method by extracting only the relevant part.

  The molecular weight distribution can be evaluated using gel permeation chromatography (GPC).

  Further, the composition and crystal structure of additives contained in the solid polymer electrolyte between and around the electrodes can be evaluated by NMR, inductively coupled plasma (ICP), X-ray spectroscopy (XRD), or the like.

  In this embodiment, the gas permeation and methanol permeation at the electrode periphery can be suppressed by increasing the thickness of the electrolyte membrane at the periphery of the cathode catalyst layer and the anode catalyst layer, compared with the thickness of the electrolyte between the cathode and the anode. It is possible to prevent water and methanol from staying in the periphery. Therefore, generation of hydrogen peroxide at the electrode end and diffusion and retention of hydrogen peroxide on the electrode outer periphery can be suppressed, and as a result, deterioration and breakage of the electrolyte membrane on the electrode outer periphery can be prevented.

  Hereinafter, the present embodiment will be described in more detail. However, the present embodiment is not limited to the embodiment disclosed herein.

(Preparation of Pt / C catalyst slurry)
Ketjen Black carrying 67% by weight of platinum and Nafion (registered trademark) in a solvent containing propanol as a main component and Nafion (registered trademark) were added at a weight ratio of 1: 0.2, and the mixture was mixed with a magnetic stirrer. The mixture was stirred for a time to obtain a Pt / C catalyst slurry.

(Preparation of PtRu / C catalyst slurry)
Ketjen Black carrying 55% by weight of platinum ruthenium and Nafion (registered trademark) were added to a solvent containing propanol as a main component so that the weight ratio was 1: 0.6, and a magnetic stirrer was used. The mixture was stirred for 12 hours to obtain a PtRu / C catalyst slurry.

Example 1
(1-1) A sulfoalkylated polyethersulfone (Polymer A) was synthesized. The number average molecular weight of the polymer A was 72,000, and the weight average molecular weight was 261,000. The ion exchange capacity was 1.4 meg / g.
(1-2) 25 g of the polymer A prepared in (1-1) was dissolved in 75 g of N-methyl-2-pyrrolidone (NMP) to prepare a varnish (varnish A).
(1-3) The polymer A varnish produced in (1-2) was applied onto a PET film, dried at 80 ° C. for 10 minutes, and the formed electrolyte membrane A was peeled off from the PET film.
(1-4) A Pt / C catalyst slurry was applied on a PTFE sheet having a thickness of 100 μm and 50 mm × 50 mm, and a cathode catalyst layer was formed so that the platinum weight per unit area was 2 mg / cm ² . The electrode size was 30 mm × 30 mm.
(1-5) The PTFE sheet with the cathode catalyst layer obtained in (1-4) is bonded to one surface of the electrolyte membrane A obtained in (1-3) so that the cathode catalyst layer and the electrolyte membrane A are in contact with each other. A PTFE sheet was laminated on one side and pressed under the conditions of 120 ° C., 2 minutes, 12.5 MPa. Thereafter, the mixture was air-cooled, the residual solvent was removed under reduced pressure, and then washed with water and treated with diluted sulfuric acid.
(1-6) A 30 mm × 30 mm PtRu / C catalyst slurry is sprayed on the surface of the electrolyte membrane with a cathode obtained in (1-5) where there is no cathode catalyst layer so that the weight of platinum ruthenium is 2 mg / cm ^2. This was applied and pressed again under the conditions of 120 ° C., 2 minutes, 5 MPa, and this was used as an anode catalyst layer.
(1-7) of a cross-section of the MEA by cutting with a microtome method, was observed by SEM, the average thickness t _out of the electrolyte part not sandwiched by electrodes 74 .mu.m, the thickness t _in the electrolyte membrane portion 49 .mu.m, The cathode catalyst layer thickness (t _CA ) was 30 μm, and the anode catalyst layer thickness was 25 μm.

(Example 2)
(2-1) A membrane / electrode assembly was produced in the same manner as in Example 1 except that the pressing time in (1-5) was changed to 5 minutes.
(2-2) of a cross-section of the MEA by cutting with a microtome method, was observed by SEM, the average thickness t _out is 75μm of electrolyte portion not sandwiched by electrodes, the thickness t _in the electrolyte membrane portion 46 [mu] m, The cathode catalyst layer thickness (t _CA ) was 29 μm, and the anode catalyst layer thickness was 25 μm.

(Example 3)
(3-1) A 30 mm × 30 mm, 30 μm thick sheet was attached to the PET film. From this, the polymer A varnish produced in (1-2) was applied onto the PET film, and then at 80 ° C. for 30 minutes. After drying at 120 ° C. for 30 minutes, the membrane was peeled off from the PET film, washed with water and diluted with sulfuric acid to prepare an electrolyte membrane B having a recess on one side.
(3-2) Masking was performed on portions other than the recesses of the electrolyte membrane B, and a cathode catalyst slurry was applied thereon by a spray method to form a cathode catalyst layer in the recesses.
(3-3) A PtRu catalyst slurry is applied to the surface of the electrolyte membrane with a cathode catalyst layer obtained in (3-2) without a cathode catalyst layer so that the weight of platinum ruthenium is 2 mg / cm ² and is 30 mm × 30 mm. It spray-coated by the magnitude | size, and it pressed on the conditions of 120 degreeC, 2 minutes, and 5 MPa again.
(3-4) of a cross-section of the MEA by cutting with a microtome method, was observed by SEM, the average thickness t _out of the electrolyte part not sandwiched by electrodes 81Myuemu, the thickness t _in the electrolyte membrane portion 50 [mu] m, The cathode catalyst layer thickness (t _CA ) was 30 μm, and the anode catalyst layer thickness was 25 μm.

Example 4
(4-1) A PtRu / C slurry was applied on a PTFE film having a thickness of 100 μm and 50 mm × 50 mm, and an anode electrode layer was formed so that the weight of platinum ruthenium per unit area was 2 mg / cm ² . The electrode size was 30 mm × 30 mm.
(4-2) A PTFE sheet with a Pt / C catalyst layer obtained in (1-4) and a PtRu / C catalyst layer obtained in (4-1) from both sides of the electrolyte membrane A obtained in (1-3). The PTFE sheet was laminated so that the anode catalyst layer, the cathode catalyst layer, and the electrolyte membrane A were in contact with each other, and this was pressed at 120 ° C. for 5 minutes under the conditions of 12.5 MPa. The residual solvent was removed under reduced pressure, followed by washing with water and dilute sulfuric acid treatment.
(4-4) of a cross-section of the MEA by cutting with a microtome method, was observed by SEM, the average thickness t _out of the electrolyte part not sandwiched by electrodes 115 .mu.m, the thickness t _in the electrolyte membrane portion 50 [mu] m, The cathode catalyst layer thickness (t _CA ) was 35 μm, and the anode catalyst layer thickness was 30 μm.

(Example 5)
(5-1) The polymer A varnish produced in (1-2) was applied on a PET film and dried at 80 ° C. for 30 minutes and 120 ° C. for 30 minutes to obtain an electrolyte membrane B. The electrolyte membrane B was peeled off from the PET film, washed with water, and acid-treated. The thickness of the electrolyte membrane B measured with a micrometer was 50 μm.
(5-2) A sulfoalkylated polyethersulfone (Polymer B) was synthesized. The number average molecular weight of the polymer B was 73,000, and the weight average molecular weight was 251,000. The ion exchange capacity was 1.0 meg / g.
(5-3) 25 g of the polymer B prepared in (5-2) was dissolved in 75 g of N-methyl-2-pyrrolidone (NMP) to prepare a varnish (varnish B).
(5-4) Varnish B prepared in (5-3) was applied on a PET film and dried at 80 ° C. for 30 minutes to obtain an electrolyte membrane C with a PET film. The film thickness was 30 μm excluding the PET film.
(5-5) The electrolyte membrane C with a PET film obtained in (5-4) was cut into 50 mm × 50 mm, and a 30 mm × 30 mm region was cut from the center and removed.
(5-6) The electrolyte membrane C with the PET film obtained in (5-4) was attached from both surfaces of the electrolyte membrane B, and pressed under the conditions of 120 ° C., 5 minutes, 12 MPa to obtain a composite electrolyte membrane D. .
(5-7) Pt / C catalyst slurry, PtRu / C so that the thickness after drying is 30 μm at the portion where the electrolyte membrane B is exposed on both surfaces of the composite electrolyte membrane D obtained in (5-4). A catalyst slurry was applied. After drying, the PET film attached to both sides was removed and pressed under conditions of 120 ° C., 5 minutes, 5 MPa.

(Example 6)
(6-1) A polymer in which (4,4'-hexafluoroisopropylidene) diphenol was introduced into sulfonated polyethersulfone was synthesized (hereinafter referred to as polymer C). The number average molecular weight of the obtained polymer A was 59000, and the weight average molecular weight was 155000. The ion exchange capacity was 1.3 meq / g.
(6-2) 25 g of the polymer C prepared in (6-1) was dissolved in 75 g of N-methyl-2-pyrrolidone (NMP) to prepare a varnish.
(6-3) The polymer C varnish produced in (6-2) was applied onto a PET film and dried at 80 ° C. for 30 minutes to obtain an electrolyte membrane E with a PET film. The film thickness was 30 μm excluding the PET film.
(6-4) The electrolyte membrane E with a PET film obtained in (6-3) was cut to 50 mm × 50 mm, and a 30 mm × 30 mm region was cut from the center and removed.
(6-5) The electrolyte membrane E with the PET film obtained in (6-4) is attached from both surfaces of the electrolyte membrane B, and pressed under the conditions of 120 ° C., 5 minutes, 12.5 MPa, and the composite electrolyte membrane F is Obtained.
(6-6) Pt / C catalyst slurry, PtRu / C so that the thickness after drying of each part of the composite electrolyte membrane F obtained in (6-5) is 30 μm at the portion where the electrolyte membrane B is exposed. A catalyst slurry was applied. After drying, the PET film attached to both sides was removed and pressed under conditions of 120 ° C., 5 minutes, 5 MPa.

(Example 7)
(7-1) 25 g of polyaniline (manufactured by Aldrich) having a molecular weight of 10,000 was dispersed in 75 g of N-methyl-2-pyrrolidone (NMP).
(7-2) The polyaniline dispersion obtained in (7-1) and the polymer B varnish obtained in (5-3) were mixed at a weight ratio of 20:80 to obtain a mixed varnish C. It was. A membrane / electrode assembly was obtained in the same manner as in Example 4 except that the varnish of polymer B was changed to a mixed varnish.

(Example 8)
(8-1) 10 mg of manganese nitrate hydrate (Mn (NO ₃ ) ₂ .6H ₂ O) was dissolved in 1 L of distilled water (aqueous solution A).
(8-2) 30 g of the polymer B powder obtained in (5-1) was immersed in the aqueous solution A and stirred at room temperature for 24 hours using a stirrer. 25 g of the filtrated product washed with water and dried was dispersed in 75 g of N-methyl-2-pyrrolidone (NMP) (varnish D).
(8-3) Varnish D obtained in (8-2) was applied onto a PET film and dried at 80 ° C. for 30 minutes to obtain an electrolyte membrane G with a PET film. The film thickness was 15 μm excluding the PET film.
(8-4) The electrolyte membrane G with a PET film obtained in (8-3) was cut into 50 mm × 50 mm, and a region of 30 mm × 30 mm was cut from the center.
(8-5) The electrolyte membrane G with the PET film obtained in (8-4) was attached from both sides of the electrolyte membrane B obtained in (5-1), and pressed under the conditions of 120 ° C., 5 minutes, 12 MPa. A composite electrolyte membrane H was obtained.
(8-6) The Pt / C catalyst slurry was applied to the exposed portions of the electrolyte membrane B in both surfaces of the composite electrolyte membrane H obtained in (8-5) so that the thickness after drying was 15 μm. After drying, the PET film attached to both sides was removed and pressed under conditions of 120 ° C., 5 minutes, 5 MPa.

Example 9
(9-1) 25 g of polythiophene (manufactured by Aldrich) having a molecular weight of 10,000 was dispersed in 75 g of N-methyl-2-pyrrolidone (NMP).
(9-2) A dispersion solution of polythiophene obtained in (9-1) and varnish B obtained in (5-3) were mixed at a weight ratio of 20:80 to obtain a mixed varnish E. A membrane / electrode assembly was obtained in the same manner as in Example 8 except that the varnish D was changed to the mixed varnish E.

(Comparative Example 1)
(10-1) The anode catalyst slurry and the cathode catalyst slurry were spray-coated on both surfaces of the electrolyte membrane B, respectively. The electrode size was 30 mm × 30 mm, the platinum ruthenium weight of the anode catalyst layer and the platinum weight of the cathode catalyst layer were 2 mg / cm ² , respectively.
(10-2) The obtained membrane / electrode assembly was pressed at 120 ° C. for 2 minutes under the condition of 5 MPa.
(10-3) When the thickness of the membrane electrode assembly obtained was measured, t _out = t _in = 50 μm, t _AN = 25 μm, and t _CA = 30 μm.

(Comparative Example 2)
(11-1) Similarly to Comparative Example 1, the anode catalyst slurry and the cathode catalyst slurry were spray-coated on both surfaces of the electrolyte membrane B, respectively. The electrode size was 30 mm × 30 mm, the platinum ruthenium weight of the anode catalyst layer and the platinum weight of the cathode catalyst layer were 2 mg / cm ² , respectively. At this time, Comparative Example 2 was obtained in which catalyst-supported carbon was formed in the periphery of the cathode-side electrode due to inadequate masking in the spray coating process.

(Comparative Example 3)
(12-1) Ketjen Black (made by Lion Co., Ltd., specific surface area 800 m ² / g), which is a main component of propanol, and Nafion (registered trademark, ion exchange) which is a solid polymer electrolyte A volume of 0.9) was added at a weight ratio of 1: 0.6, and the mixture was stirred with a magnetic stirrer for 12 hours.
(12-2) The carbon and solid polymer mixed solution obtained in (12-1) was spray-coated on both surfaces of the electrolyte membrane B to prepare an intermediate layer having a thickness of 35 mm × 35 mm and a thickness of 10 μm.
(12-3) The anode catalyst slurry and the cathode catalyst slurry were spray-coated on the carbon intermediate layer on the electrolyte membrane B obtained in (12-2), respectively. The electrode size was 30 mm × 30 mm, the weight of platinum ruthenium in the anode catalyst layer and the weight of platinum in the cathode were 2 mg / cm ² , respectively. The middle layer, the anode catalyst layer, and the cathode catalyst layer were aligned so that their centers were the same.
(12-4) The obtained membrane / electrode assembly was pressed at 120 ° C. for 2 minutes under the condition of 5 MPa.

(Comparative Example 4)
(13-1) 10 g of the polymer B prepared in (5-2) was dissolved in 90 g of N-methyl-2-pyrrolidone (NMP) to prepare a varnish.
(13-2) A polymer intermediate layer was applied on the electrolyte membrane so that the varnish obtained in (13-1) had a thickness of 35 mm × 35 mm and a thickness of 10 μm.
(13-3) The anode catalyst slurry and the cathode catalyst slurry were spray-coated on the polymer intermediate layer obtained in (13-2), respectively. The electrode size was 30 mm × 30 mm, the platinum ruthenium weight of the anode catalyst layer and the platinum weight of the cathode catalyst layer were 2 mg / cm ² , respectively. The polymer intermediate layer, the anode catalyst layer, and the cathode catalyst layer were aligned so that their centers were the same.
(13-4) The obtained membrane / electrode assembly was pressed at 120 ° C. for 2 minutes under the condition of 5 MPa.

(Comparative Example 5)
(14-1) A Pt / C catalyst slurry was sprayed onto both surfaces of the electrolyte membrane B. The electrode size was 30 mm × 30 mm, the platinum ruthenium weight of the anode catalyst layer and the platinum weight of the cathode catalyst layer were each 1 mg / cm ² .
(14-2) The obtained membrane / electrode assembly was pressed at 120 ° C. for 2 minutes under the condition of 5 MPa.
(14-3) When the thickness of the obtained membrane electrode assembly was measured, t _out = t _in = 50 μm and t _AN = t _CA = 15 μm.

(DMFC durability evaluation of membrane electrode assemblies)
DMFC durability of the membrane electrode assemblies of Examples 1 to 6 and Comparative Examples 1 to 4 was evaluated. Each fuel cell membrane / electrode assembly was sandwiched between carbon separators having fuel and air passages through a porous carbon diffusion layer to obtain a fuel cell for evaluation. At this time, the size of the diffusion layer was 35 mm square, and the area was larger than that of the anode catalyst layer and the cathode catalyst layer. A 4 mol / l aqueous methanol solution is supplied at 0.5 ml / min to the anode side of the evaluation fuel cell, and dry air (dew point -20 to -15 ° C.) is supplied to the cathode side at 500 ml / min. The temperature of the single cell was 60 ° C. Continuous power generation was performed under the condition of 0.2 A / cm ² . The maximum voltage was 1000 hours, and a plot of the cell voltage against the elapsed time was linearly approximated to calculate the voltage drop rate. In addition, when the membrane was broken during the measurement, the measurement was interrupted when a rapid increase in the fuel / air cross leak due to the breakage was confirmed. About MEA which completed evaluation, cross-sectional observation was performed and the presence or absence of the electrolyte thinning in the electrode outer peripheral area was confirmed. Moreover, the molecular weight distribution of the electrolyte of the outer peripheral part of an electrode and an electrode inner peripheral part was measured by GPC, and the presence or absence of electrolyte membrane deterioration was confirmed. In Examples 6 and 7, the number average molecular weight is obtained by removing the solid polymer electrolyte portion around the electrode.

(PEFC durability evaluation of membrane electrode assemblies)
The PEFC durability of the membrane electrode assemblies of Examples 8 to 9 and Comparative Example 5 was evaluated. Each fuel cell membrane / electrode assembly was sandwiched between carbon separators having fuel and air passages through a porous carbon diffusion layer to obtain a fuel cell for evaluation. At this time, the size of the diffusion layer was 35 mm square, and the area was larger than that of the anode catalyst layer and the cathode catalyst layer. Humidified hydrogen gas (dew point 80 ° C.) was supplied to the anode side at 60 mL / min, and humidified air (dew point 80 ° C.) was supplied to the cathode side at 260 mL / min. With the cell temperature kept at 80 ° C., continuous power generation was performed at 0.25 A / cm ² . The OCV after 100 hours of continuous power generation was measured, and the evaluation was terminated when a rapid drop in OCV was observed.

(Discussion)
Table 1 shows the durability evaluation results of DMFCs using the membrane electrode assemblies of Examples 1 to 6 and Comparative Examples 1 to 4. Table 2 shows the durability evaluation results of PEFCs using the membrane electrode assemblies of Examples 8 to 9 and Comparative Example 5.

  In Comparative Examples 1 to 3, since a large amount of methanol aqueous solution came out from the cathode exhaust gas during the power generation test, power generation was stopped at the time shown in Table 1. Each was disassembled and the electrolyte membrane was confirmed to be broken. As a result, the membrane was broken around the catalyst electrode layer. The molecular weight of the electrolyte membrane at the end of the electrode is less than half that before the test, and it is considered that the membrane strength decreased due to the progress of membrane decomposition, resulting in breakage.

  In Comparative Example 2 in which isolated catalyst particles existed around the cathode catalyst layer, the membrane breakage was observed in a shorter time than in Comparative Example 1. This is because the cathode potential is decreased by permeated methanol in the isolated catalyst particles. It is thought that it occurs remarkably.

  In Comparative Example 3 in which the carbon intermediate layer having a large area was inserted into the electrolyte membrane, the anode catalyst layer, and the cathode catalyst layer, the period until the membrane breakage was long, but the breakage occurred in 800 hours. Although this structure can suppress methanol permeation from the electrode end, it is porous, which means that suppression of liquid retention around the cathode catalyst layer is insufficient.

  In Comparative Example 4 in which a solid polymer intermediate layer having a large area was applied, continuous power generation for 1000 hours was possible, but thinning of the electrolyte membrane was confirmed from the cross-sectional SEM image, and the molecular weight at the end of the electrode was also reduced. It was seen. Although the methanol permeation is suppressed by application of a large area solid polymer intermediate layer, the effect is insufficient because the solid polymer intermediate layer is porous.

  In Examples 1 to 7, which are embodiments of the present invention, no membrane breakage is confirmed after 1000 hours of continuous power generation. This is because the outer peripheries of the cathode catalyst layer and the anode catalyst layer are protected by the electrolyte, so that methanol permeation from the periphery of the electrode is suppressed, and retention of methanol and water in the outer periphery of the cathode is suppressed. . In Example 1 in which a part of the cathode catalyst layer was embedded in the electrolyte membrane B, the electrolyte membrane was not damaged at the end of the electrode, but the average molecular weight at the outer periphery of the electrode was reduced by about 20%. . On the other hand, in Examples 2 and 3 in which the cathode catalyst layer is completely embedded in the electrolyte membrane B, it is possible to suppress a decrease in the molecular weight of the electrolyte on the outer periphery of the electrode. Further, in Examples 4 to 7 in which the solid polymer electrolyte is disposed also in the outer peripheral region of the anode catalyst layer, a decrease in molecular weight is hardly confirmed.

  In Table 2, in Example 8 in which the electrolyte in the electrode outer peripheral portion contains Mn cations having hydrogen peroxide radical decomposability, and in Example 9 in which polythiophene capable of trapping Pt cations is used, the electrode outer periphery even after continuous PEFC power generation for 2500 hours The electrolyte membrane in the region does not break, and the OCV maintains a high value of 950 mV. On the other hand, in Comparative Example 5, a rapid decrease in OCV was observed after 1000 hours of power generation, and when the cell was disassembled, film breakage at the electrode outer periphery was confirmed.

  FIG. 9 shows an example in which a membrane electrode assembly that is one embodiment of the present invention is mounted on a portable information terminal as an example of a fuel cell power generation system.

  This portable information terminal has a foldable structure in which two parts are connected by a hinge (97) that also serves as a holder for the fuel cartridge (96).

  One portion includes a display device (91) in which a touch panel type input device is integrated and a portion in which an antenna (92) is incorporated.

  One part is a main board (94) on which a fuel cell (93), a processor, a volatile and nonvolatile memory, a power control unit, a fuel cell and secondary battery hybrid control, an electronic device such as a fuel monitor, and an electronic circuit are mounted. It has a portion on which a lithium ion secondary battery (95) is mounted.

  The portable information terminal thus obtained can be used for a long time because the life of the fuel cell (93) is long.

  The present invention can be used for fuel cells represented by PEFC and DMFC.

11 Separator 12, 71 Anode diffusion layer 13, 21, 31, 41, 51, 61, 71, 82 Anode catalyst layer 14, 22, 32, 42, 52, 83 Solid polymer electrolyte membrane 15, 23, 33, 43, 53, 63, 73, 84 Cathode catalyst layer 16, 85 Cathode diffusion layer 17 Gasket 62, 72 Solid polymer electrolyte membrane 64, 74 between electrodes Solid polymer electrolyte around electrode 91 Display device 92 Antenna 93 Fuel cell 94 Main board 95 Lithium ion secondary battery 96 Fuel cartridge 97 Hinge

Claims (9)

A catalyst and an anode made of a solid polymer electrolyte formed to cover the catalyst;
A cathode comprising a catalyst and a solid polymer electrolyte formed so as to cover the catalyst,
In a membrane electrode assembly for a fuel cell formed by sandwiching a solid polymer electrolyte membrane,
Between the thickness t _in of the electrolyte membrane in the region sandwiched between the opposing anode and cathode and the thickness t _out of the electrolyte membrane located in the outer peripheral region of the anode and cathode,
The relationship t _out > t _in holds,
The ion exchange capacity of the solid polymer electrolyte in the electrolyte membrane portion sandwiched between the anode and the cathode is larger than the ion exchange capacity of the solid polymer electrolyte disposed in the outer peripheral region of at least one of the anode and the cathode,
A membrane / electrode assembly, wherein the solid polymer electrolyte membrane located in the outer peripheral region of at least one of the anode and the cathode contains a π-conjugated aromatic polymer.   2. The membrane electrode assembly according to claim 1, wherein a contact angle of the electrolyte membrane portion sandwiched between the anode and the cathode with respect to the water of the solid polymer electrolyte is disposed in at least one outer peripheral region of the anode or the cathode. A membrane electrode assembly having a smaller contact angle with respect to water of an electrolyte.   The membrane electrode assembly according to claim 1, wherein the solid polymer electrolyte disposed in the outer peripheral region of at least one of the anode and the cathode contains inorganic fine particles or metal cations having an action of decomposing hydroxy radicals. Membrane electrode assembly.   2. The membrane electrode assembly according to claim 1, wherein an electrolyte or additive having a Pt cation scavenging property is contained in a solid polymer electrolyte disposed in an outer peripheral region of at least one of an anode and a cathode. Electrode assembly.   5. The membrane electrode assembly according to claim 1, wherein the solid polymer electrolyte disposed in the outer peripheral region of at least one of the anode and the cathode includes an aromatic hydrocarbon electrolyte having a cation exchange group. A membrane electrode assembly.   6. The membrane electrode assembly according to claim 1, wherein the electrolyte membrane sandwiched between the anode and the cathode facing each other comprises an aromatic hydrocarbon electrolyte having a cation exchange group. .   7. The fuel cell having a structure in which the membrane electrode assembly according to claim 1 is sandwiched between gas diffusion layers on both sides thereof, wherein the area of the gas diffusion layer is larger than the areas of the anode and the cathode. A fuel cell.   8. The fuel cell according to claim 7, wherein alcohol is used as the fuel.   A fuel cell power generation system equipped with the fuel cell according to claim 7 or 8.

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