JP2006277984A - Manufacturing method of membrane electrode assembly - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrolyte membrane and a catalyst layer to such an extent that thermocompression bonding is not required, despite the method of forming a catalyst layer using an electrophoresis method capable of forming a catalyst layer in a relatively short time. Membrane electrode that can sufficiently improve the adhesion between and the electrolyte membrane, and therefore can prevent the destruction of the electrolyte membrane due to thermocompression bonding, and can improve the utilization efficiency of the catalyst and achieve excellent fuel cell characteristics To provide a method for manufacturing a joined body.
A fuel cell having an anode 3 and a cathode 4 each having catalyst layers 5 and 5a containing catalyst powder and a cation exchange resin, and a solid electrolyte membrane 2 disposed between the anode 3 and the cathode 4. A method for producing a membrane electrode assembly 1 for use,
The temperature of the dispersion liquid in a state where the solid electrolyte membrane 2 is in contact with the dispersion liquid containing at least one of the anode 3 and the cathode 4 and the catalyst powder, the cation exchange resin, and the alcohol. Is maintained at 35 ° C. or lower and formed by electrophoresis. A method for producing a membrane electrode assembly,
[Selection] Figure 2

Description

  The present invention relates to a method for producing a membrane electrode assembly. More specifically, the present invention relates to a manufacturing technique of a membrane electrode assembly applicable to fuel cells having a wide variety of solid electrolyte membranes.

  A fuel cell is a chemical power generation device that directly converts the reaction energy of gas used as fuel into electrical energy. In particular, a hydrogen / oxygen fuel cell has a reaction product that is essentially water only. Known to have very little direct impact. In particular, solid electrolyte fuel cells (SOFC) and polymer electrolyte fuel cells (PEFC), which are solid electrolytes, include electrolytes such as molten salt fuel cells, phosphoric acid fuel cells, and alkaline fuel cells. Unlike liquid fuel cells, there is no problem of electrolyte dissipation, so a relatively simple battery structure can be employed. In particular, fuel cells that operate at medium and low temperatures are highly expected as a power source for mobile vehicles such as electric vehicles and small cogeneration systems, as social demands for energy and global environmental issues increase. . Currently, solid polymer fuel cells that use perfluorosulfonic acid membranes with excellent chemical stability are mainly used in the development of fuel cell systems. Cost reduction, expansion of operating temperature range, improvement of reliability, etc. are indispensable, and research and development related to cost reduction of electrolytes, development of new electrolyte membranes, and reduction of platinum catalyst usage are active.

  In a polymer electrolyte fuel cell, a proton conductive ion exchange membrane is usually used as a solid polymer electrolyte, and in particular, an ion exchange membrane made of a perfluorocarbon polymer having a sulfonic acid group has excellent basic characteristics. It has been known. In such a polymer electrolyte fuel cell, a catalyst layer and gas diffusion layers are arranged on both sides of an ion exchange membrane, and a gas containing hydrogen (fuel) and a gas containing oxygen (oxidizer) (air) Etc.) are supplied to the anode and cathode, respectively, to generate electricity.

  Usually, electrodes used in polymer electrolyte fuel cells contain metal particles or carbon particles carrying metal particles (hereinafter collectively referred to as “catalyst powder”) coated with an ion exchange resin. And a gas diffusion layer for supplying a reaction gas to the catalyst layer and collecting charges generated in the catalyst layer. In the catalyst layer, there is a void portion composed of fine pores formed between the secondary particles of the catalyst powder. The void portion functions as a reaction gas diffusion channel. Yes. It is known that the reaction at the electrode part of the polymer electrolyte fuel cell proceeds only at the three-phase interface where the electrolyte, catalyst and gas (hydrogen or oxygen) are present simultaneously. In order for this three-phase interface to function effectively, it is necessary that the electrolyte membrane and the catalyst layer are sufficiently bonded. When the catalyst layer and the electrolyte membrane are bonded, the heat is often higher than the glass transition temperature of the electrolyte. A step of crimping is included.

  As a basic method for forming such a catalyst layer, for example, as described in Non-Patent Document 1, a catalyst is prepared by mixing a solid polymer electrolyte solution in a dispersion in which the above-described catalyst powder is dispersed. After preparing a dispersion liquid for forming a layer (so-called catalyst ink), for example, a catalyst layer obtained by applying the dispersion liquid onto a polytetrafluoroethylene substrate, for example, is thermocompression-bonded on an electrolyte membrane (transfer method), A method in which a catalyst layer obtained by applying a catalyst ink on a carbon porous body or a so-called diffusion layer with a carbon powder or the like on the surface thereof is thermocompression-bonded on the electrolyte membrane, or the catalyst ink is directly applied to the electrolyte membrane. The method of coating on top is mentioned.

  However, in the method using thermocompression bonding as described above, in the case of a thin film or a poorly flexible electrolyte membrane, if the bonding strength at the time of bonding is increased in order to improve the bonding between the catalyst layer and the electrolyte membrane, the electrolyte membrane However, there is a problem in that the electrode pores are reduced by thermocompression bonding and the improvement of the fuel cell characteristics is hindered. In addition, platinum catalysts with the highest activity and stability are frequently used at present, and improving their utilization is extremely important for reducing the cost of fuel cell systems. However, catalyst ink is directly sprayed onto the electrolyte membrane by spraying or the like. The coating method has the disadvantages that it is difficult to increase the utilization rate of the expensive catalyst due to the scattering of ink around the ink, and there is a limit to the improvement of the catalyst layer formation rate.

  On the other hand, Patent Document 1 describes a method in which a solid polymer electrolyte membrane is formed by electrodeposition or casting after a mixture of a polymer electrolyte and catalyst-supported carbon is deposited on carbon paper as an electrode by electrodeposition. ing. However, according to such an electrophoresis method, the catalyst layer can be formed in a relatively short time, but the adhesion between the electrolyte membrane and the catalyst layer is weak, and it is necessary to finally perform thermocompression bonding. Therefore, there has been a problem that the electrolyte membrane is broken by thermocompression bonding, or the electrode pores are reduced to hinder the improvement of the fuel cell characteristics.

In any of the methods, the catalyst dispersion has extremely fine pores, and it is difficult to efficiently coat the metal particles supported inside the fine pores with an ion exchange resin. There is also a problem that the reaction area that effectively contributes to power generation is only about 20 to 30% of the total surface area of the metal particles.
Japanese Patent Laid-Open No. 2002-25566 SS Kocha, “Principles of MEA preparation”, Handbook of Fuel Cells, Vol. 3, John Wiley & Sons, Ltd., (2003) pp. 538-564.

  The present invention has been made in view of the above-described problems of the prior art, and is also a method of forming a catalyst layer using an electrophoresis method capable of forming a catalyst layer in a relatively short time. Regardless, the adhesiveness between the electrolyte membrane and the catalyst layer can be sufficiently improved to the extent that thermocompression bonding is not required, so that the destruction of the electrolyte membrane due to thermocompression can be avoided, and the utilization efficiency of the catalyst is improved. An object of the present invention is to provide a method for manufacturing a membrane electrode assembly (MEA) that can achieve excellent fuel cell characteristics.

  As a result of intensive studies to achieve the above object, the inventors of the present invention set the temperature of the dispersion at a predetermined temperature in a state where the solid electrolyte membrane is in contact with the dispersion containing the catalyst powder, the cation exchange resin, and the alcohol. The inventors have found that the above object can be achieved by forming a catalyst layer by electrophoresis while maintaining the following, and have completed the present invention.

  That is, the method for producing a membrane electrode assembly of the present invention comprises an anode and a cathode each having a catalyst layer containing catalyst powder and a cation exchange resin, and a solid electrolyte membrane disposed between the anode and the cathode. A method for producing a membrane electrode assembly for a fuel cell, wherein the catalyst layer of at least one of the anode and the cathode is made into a dispersion containing the catalyst powder, the cation exchange resin, and alcohol. The method is characterized in that the dispersion is formed by electrophoresis while keeping the temperature of the dispersion at 35 ° C. or lower in a state where the solid electrolyte membrane is in contact therewith.

  In the method for producing a membrane electrode assembly of the present invention, it is preferable that the catalyst layer is formed by electrophoresis in a state where the zeta potential (ζ potential) of the cation exchange resin in the dispersion is maintained negative. .

  Moreover, in the manufacturing method of the membrane electrode assembly of this invention, the solid content concentration in the said dispersion liquid is 0.1-20 mass%, And the said catalyst powder and said cation exchange resin in conversion of solid content, Is preferably 50:50 to 85:15.

Furthermore, as the cation exchange resin used in the method for producing a membrane electrode assembly of the present invention, the main chain contains a structure of —CF ₂ —CF ₂ — group as a repeating unit, and the side chain has a sulfonic acid group, phosphonic acid A copolymer having at least one group selected from the group consisting of a group and a sulfonimide group is more preferable.

  The catalyst powder used in the method for producing a membrane / electrode assembly of the present invention is preferably a catalyst powder in which metal particles are supported on a carbon support.

  In addition, the manufacturing method of the membrane electrode assembly of the present invention can sufficiently improve the adhesion between the electrolyte membrane and the catalyst layer, improve the utilization efficiency of the catalyst, and achieve excellent fuel cell characteristics. The reason for this is not necessarily clear, but the present inventors infer as follows. That is, when the zeta potential of the cation exchange resin in the dispersion containing the cation exchange resin, the catalyst powder, and the alcohol is 40 ° C. or higher, as shown in FIG. Inverted from negative to positive ((i) → (ii) → (iii) in FIG. 1) and found that when the temperature of the dispersion is lowered after the temperature rises, it shows some hysteresis and returns to the negative potential again. ((Iv) → (v) → (vi) in FIG. 1).

  Although the mechanism of such zeta potential reversal is not necessarily clear, the present inventors have found that the ultrasonic absorption in this dispersion corresponds to the temperature at which the reversal of zeta potential occurs. It is presumed that some structural change has occurred. Although details are still unknown, when the temperature rises, the ion exchange groups of the cation exchange resin present in the dispersion gather inside the aggregate, and the hydrophobic ion exchange resin skeleton is oriented to the hydrophobic structure of the hydrophobic ion exchange resin. It is inferred that the zeta potential shows a positive value because the group is coordinated and H of the OH group located outside the alcohol is positively charged.

  When a catalyst layer is formed by electrophoresis using such an alcohol-containing dispersion, the temperature of the dispersion is maintained at a temperature lower than the temperature at which the inversion of the zeta potential occurs, that is, 35 ° C. or lower. By maintaining this state, the adhesion between the resulting catalyst layer and the electrolyte membrane is improved, and the conventional thermocompression bonding becomes unnecessary. Furthermore, by maintaining the temperature conditions during electrophoresis in the above-described state, the catalyst powder can be efficiently coated with the cation exchange resin and the three-phase interface can be increased. The present inventors speculate that the initial fuel cell characteristics are improved and the battery characteristics become stable even when power is generated for a long time.

  According to the present invention, the electrolyte membrane is formed to such an extent that thermocompression bonding is not required despite the method of forming the catalyst layer using an electrophoresis method capable of forming the catalyst layer in a relatively short time. The adhesion between the catalyst layer and the catalyst layer can be sufficiently improved, so that the destruction of the electrolyte membrane due to thermocompression bonding can be avoided, and the utilization efficiency of the catalyst can be improved to achieve excellent fuel cell characteristics. It is possible to provide a method for manufacturing a membrane electrode assembly.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the following description and drawings, the same or corresponding elements are denoted by the same reference numerals, and duplicate descriptions are omitted.

  First, the membrane electrode assembly obtained by the production method of the present invention will be described. That is, the membrane electrode assembly produced by the present invention comprises an anode and a cathode each having a catalyst layer containing a catalyst powder and a cation exchange resin, and a solid electrolyte membrane disposed between the anode and the cathode. Have. The specific shapes and the like of the anode, the cathode and the solid electrolyte membrane are not particularly limited, but a schematic cross-sectional view of a preferred embodiment of a membrane electrode assembly for a polymer electrolyte fuel cell produced according to the present invention is shown. As shown in FIG.

  In the membrane electrode assembly 1 shown in FIG. 2, an anode 3 is disposed on one side of a solid electrolyte membrane (ion exchange membrane) 2 and a cathode 4 is disposed on the other side. The anode 3 is composed of an anode catalyst layer 5 that is in close contact with one surface of the electrolyte membrane 2 and a gas diffusion layer 6 that is in close contact with the outer surface of the anode catalyst layer 5. The cathode catalyst layer 5 ′ is in close contact with the other membrane surface of the electrolyte membrane 2, and the gas diffusion layer 6 ′ is in close contact with the outer surface of the cathode catalyst layer 5 ′. Further, a separator 7 having a groove 7 a formed as a gas flow path is disposed outside the membrane electrode assembly 1, and the membrane electrode assembly 1 is sealed in the separator 7 by a gas seal body 8. The anode catalyst layer 5 and the cathode catalyst layer 5 'are each composed of a catalyst powder and a cation exchange resin, and at least one of them is obtained by the method of the present invention described in detail below. The gas diffusion layers 6 and 6 ′ may not necessarily be provided, but the gas for efficiently supplying the function of the current collector and the fuel supplied from the separator 7 to the catalyst layers 5 and 5 ′. Since it has a function of diffusion, it is usually preferable to be provided.

  In the membrane electrode assembly 1 configured as described above, hydrogen gas obtained by reforming fuel such as methanol or natural gas is supplied to the anode 3 through the groove 7a of the separator 7, for example, and the cathode 4 is supplied with a gas containing oxygen such as air, and electrical energy is generated by a chemical reaction in the catalyst layers 5 and 5 '. At that time, the solid electrolyte membrane 2 has a role of selectively transmitting protons generated in the anode catalyst layer 5 to the cathode catalyst layer 5 ′ along the film thickness direction. Further, the solid electrolyte membrane 2 also has a function as a diaphragm for preventing hydrogen supplied to the anode 3 and oxygen supplied to the cathode 4 from being mixed.

  Next, the manufacturing method of the membrane electrode assembly of this invention is demonstrated. That is, the method for producing a membrane / electrode assembly of the present invention comprises a dispersion containing a catalyst powder, a cation exchange resin, and an alcohol, and an electrophoresis method in which the temperature of the dispersion is maintained at 35 ° C. or lower. In this method, at least one (particularly preferably both) of the anode catalyst layer 5 and the cathode catalyst layer 5 ′ is formed on the solid electrolyte membrane. Thereby, a membrane electrode assembly for a fuel cell that can firmly join a catalyst layer and an electrolyte membrane without performing a special thermocompression bonding operation and has excellent fuel cell characteristics with a high catalyst coverage by a cation exchange resin. Can be produced.

As the cation exchange resin used in the present invention, a fluorine-based cation exchange resin is preferable from the viewpoint of excellent chemical stability. Among them, a co-polymer containing a structure of —CF ₂ —CF ₂ — group as a repeating unit in the main chain is preferable. The coalescence is particularly preferred because it tends to be excellent in chemical stability. The cation exchange resin according to the present invention is more preferably a perfluoro ion exchange resin having at least one group selected from the group consisting of a sulfonic acid group, a phosphonic acid group and a sulfonimide group as an ion exchange group. Among them, a perfluorocarbon polymer having a sulfonic acid group (however, an etheric oxygen atom or the like may be contained) is particularly preferable.

As such a perfluorocarbon polymer having a sulfonic acid group, conventionally known polymers are widely employed. Among other things, the general formula:
_{CF 2 = CF (OCF 2 CFX} ) m -O p - (CF 2) n SO 3 H
(Where X is a fluorine atom or a trifluoromethyl group, m is an integer of 0 to 3, n is an integer of 0 to 12, p is 0 or 1, and n = 0. P = 0.)
A copolymer of perfluorovinyl compound represented by the following formula with perfluoroolefin or perfluoro (alkyl vinyl ether) is preferred. Specific examples of such a perfluorovinyl compound include compounds represented by any one of the following formulas 1 to 4. However, in a following formula, q is an integer of 1-9, r is an integer of 1-8, s is an integer of 0-8, z is 2 or 3.
CF ₂ = CFO (CF ₂ ) _q SO ₃ H Formula 1
CF ₂ = CFOCF ₂ CF (CF ₃ ) O (CF ₂ ) _r SO ₃ H Formula 2
CF ₂ = CF (CF ₂ ) _s SO ₃ H (Formula 3)
CF ₂ = CF [OCF ₂ CF (CF ₃ )] _z O (CF ₂ ) ₂ SO ₃ H (Formula 4)

Polymers comprising repeating units based on a perfluorovinyl compound having such a sulfonic acid group, typically polymerized using perfluorovinyl compound having -SO 2 _F groups, after polymerization -SO 2 _F group - Converted to SO ₃ H group. Although the perfluorovinyl compound having a —SO ₂ F group can be homopolymerized, since it has low radical polymerization reactivity, it is usually co-polymerized with a comonomer such as perfluoroolefin or perfluoro (alkyl vinyl ether) as described above. Used after polymerization. Examples of such a perfluoroolefin as a comonomer include tetrafluoroethylene, hexafluoropropylene, and the like. Usually, tetrafluoroethylene is preferably employed.

In addition, as perfluoro (alkyl vinyl ether) as a comonomer,
_{CF 2 = CF- (OCF 2 CFY} ) t -O-R f
(Here, Y is a fluorine atom or a trifluoromethyl group, t is an integer of 0 to 3, and R ^f is a perfluoroalkyl group represented by linear or branched C _u F _{2u + 1} (1 ≦ u ≦ 12).)
The compound represented by these is preferable. Specific examples of such perfluoro (alkyl vinyl ether) include compounds represented by any of the following formulas 5 to 7. However, in the following formula, v is an integer of 1 to 8, w is an integer of 1 to 8, and x is 2 or 3.
CF ₂ = CFO (CF ₂ ) _v CF ₃ ... Formula 5
CF ₂ = CFOCF ₂ CF (CF ₃ ) O (CF ₂ ) _w CF ₃ ... Formula 6
CF ₂ = CF [OCF ₂ CF (CF ₃ )] _x O (CF ₂ ) ₂ CF ₃ Formula 7

In addition to perfluoroolefin and perfluoro (alkyl vinyl ether), fluorine-containing compounds such as 1,1,2,3,3,4,4-heptafluoro-4-[(trifluoroethenyl) oxy] -1-butene A monomer may also be copolymerized with a perfluorovinyl compound having a —SO ₂ F group as a comonomer.

  As such a perfluorocarbon polymer having a sulfonic acid group, commercially available products such as Nafion (trade name, manufactured by DuPont) and Flemion (trade name, manufactured by Asahi Glass) are preferably used. It is not specifically limited to.

  The cation exchange resin used in the present invention is preferably a dry resin having an ion exchange capacity of 0.5 to 1.5 meq / g. If the ion exchange capacity of the cation exchange resin is less than 0.5 meq / g dry resin, the resistance value of the resulting catalyst layer tends to increase during power generation, while the ion exchange capacity When the amount exceeds 1.5 meq / g dry resin, the water content of the obtained catalyst layer increases and the resin layer tends to swell, and the pores tend to be blocked. The ion exchange capacity of the cation exchange resin according to the present invention is particularly preferably 0.8 to 1.2 meq / g dry resin.

  As the catalyst powder used in the present invention, those that are stable in an acidic solution are used, and those made of metal particles or those in which metal particles are supported on a carbon support are commercially available and easily available. Such a catalyst powder has a relatively small absolute value of zeta potential in alcohol described later, and often shows a negative value. When the metal particles are used as a catalyst powder as they are, platinum or an alloy of platinum and other metals is preferable. Although it does not specifically limit as a metal used as an alloy with platinum, Gold, silver, ruthenium, palladium, rhodium, iridium, cobalt, iron, manganese, chromium, etc. are preferable.

  In addition, when the metal particles are supported on a carbon carrier and used as a catalyst powder, the metal particles are not particularly limited, and various metals can be used. Platinum, gold, silver, ruthenium, rhodium, palladium, osmium, iridium, chromium One or more selected from the group consisting of iron, titanium, manganese, cobalt, nickel, molybdenum, tungsten, aluminum, silicon, zinc and tin are preferable, and platinum or platinum is particularly preferable from the viewpoint of particularly stable catalytic activity. And other metals are preferred, and platinum and ruthenium alloys are particularly preferred.

In the case of a catalyst powder in which metal particles are supported on a carbon support, the carbon used as the support preferably has a specific surface area of 50 to 1500 m ² / g. When the specific surface area is less than 50 m ² / g, it is difficult to increase the loading ratio of the metal particles serving as the catalyst, and the output characteristics of the obtained catalyst layer tend to be reduced, while the specific surface area is 1500 m ² / g. If it exceeds, the pores are too fine, making it difficult to coat with a cation exchange resin, and the output characteristics of the resulting catalyst layer tend to deteriorate. The specific surface area of the carbon support according to the present invention is particularly preferably 200 to 900 m ² / g.

  Furthermore, the catalyst powder particles used in the present invention preferably have an average particle size of 0.05 to 5 μm. When the average particle size is less than 0.05 μm, the obtained catalyst layer tends to have a dense structure and it is difficult to discharge generated water at the cathode or anode. On the other hand, when the average particle size exceeds 5 μm, Since the powder is difficult to coat with an ion exchange resin and the coating area is reduced, the performance of the catalyst layer tends to be lowered.

  In the present invention, the catalyst powder can be dispersed in water as necessary, and then mixed with a dispersion containing a cation exchange resin. Thus, when dispersing a catalyst powder in water, it is preferable that solid content concentration is 3-20 mass%. Increasing the solid content concentration tends to increase the rate of formation of the catalyst layer during electrophoresis, but when the concentration exceeds 20% by mass, the dispersion state tends to become unstable.

  In the method for producing a membrane electrode assembly of the present invention, first, a dispersion liquid (hereinafter referred to as “catalyst ink”) containing the above-described catalyst powder, cation exchange resin and alcohol is prepared.

  Although it does not specifically limit as alcohol used as a dispersion medium in this invention, What contains 1 or more of OH groups in the molecule | numerator of C1-C5 is preferable. Specific examples include ethanol, n-propanol, isopropanol, n-butanol, isobutanol, n-pentanol, ethylene glycol, pentafluoroethanol, and heptafluorobutanol. These alcohols may be used alone or in combination of two or more. As the alcohol according to the present invention, a straight-chain alcohol having one OH group in the molecule is particularly preferable, and ethanol is particularly preferable.

  In the present invention, a mixture of alcohol and another solvent may be used as a dispersion medium. Examples of the other solvent in this case include water, acetone and the like. Thus, when mixing and using alcohol and another solvent, it is preferable that the mixing ratio (mass ratio) of alcohol and another solvent is the range of 10: 1 to 1:10. When the content of alcohol in the dispersion medium is less than the lower limit, the adhesion between the resulting catalyst layer and the electrolyte membrane is not sufficiently strong.

  In the catalyst ink according to the present invention, the solid content concentration is preferably 0.1 to 20% by mass, and more preferably 0.5 to 10% by mass. If the solid content concentration is less than the lower limit, the catalyst layer formation rate during electrophoresis tends to be low, and if the solid content concentration exceeds the upper limit, the dispersed state tends to become unstable.

  Furthermore, in the catalyst ink according to the present invention, the mass ratio of the catalyst powder and the cation exchange resin in terms of solid content is preferably in the range of 50:50 to 85:15, and 60:40 to 80 : More preferably, it is in the range of 20. If the ratio of the catalyst powder is less than the lower limit, the pores of the catalyst support in the resulting catalyst layer are crushed by the cation exchange resin, and the reaction field tends to decrease, so the fuel cell characteristics tend to be reduced. When the ratio of the catalyst powder exceeds the above upper limit, the catalyst powder is not sufficiently covered with the cation exchange resin in the obtained catalyst layer, and the three-phase interface tends to decrease, and the fuel cell characteristics tend to be deteriorated.

  The dispersion method employed when preparing the catalyst ink in the present invention is not particularly limited, for example, a method using a stirrer such as a homogenizer or a homomixer, a high-speed rotation such as a high-speed rotation jet flow method or a grinder. And a method of imparting elasticity to the dispersion by extruding the dispersion from a narrow portion under high pressure such as a high-pressure emulsifier.

  Moreover, it is preferable to filter the obtained catalyst ink. The filtration can remove the aggregates of the catalyst powder particles in the catalyst ink, and further has an effect of suppressing aggregation of the catalyst ink. Therefore, it is preferably performed immediately before forming the catalyst layer by the electrophoresis method described later. As a filtration method, the catalyst ink may be pressurized and passed through a filter, or may be sucked and passed through a filter. The pore size of such a filter is preferably 5 to 100 μm, and more preferably 20 to 60 μm. If the pore diameter is less than 5 μm, it tends to be difficult to filter and cause clogging. On the other hand, if the pore diameter exceeds 100 μm, fine particles tend not to be removed.

  Furthermore, a water repellent, a pore former, a thickener, a diluting solvent, etc. may be added to the catalyst ink according to the present invention as necessary, thereby enhancing the drainage of water generated by the electrode reaction. In addition, the shape stability of the catalyst layer itself can be further improved.

  Next, in the method for producing a membrane electrode assembly of the present invention, an anode catalyst is obtained by electrophoresis in a state in which the solid electrolyte membrane is brought into contact with the catalyst ink and the temperature of the catalyst ink is maintained at 35 ° C. or lower. At least one (particularly preferably both) of the layer and the cathode catalyst layer is formed on the solid electrolyte membrane.

  Although it does not specifically limit as a solid electrolyte membrane used in this invention, It is preferable to use the film | membrane which consists of an ion exchange resin similar to the ion exchange resin contained in a catalyst layer. Examples of the membrane made of such an ion exchange resin include an ion exchange membrane made of a perfluorocarbon polymer having a sulfonic acid group (for example, Nafion (trade name, manufactured by DuPont), Flemion (trade name, manufactured by Asahi Glass), etc.) , Partially fluorinated hydrocarbon sulfonic acid ion exchange membranes (for example, ETFE graft polymerized membranes having sulfonic acid groups), hydrocarbon sulfonic acid ion exchange membranes (for example, polyetheretherketone) And a membrane having a sulfonic acid group). Further, in the present invention, as the solid electrolyte membrane, a hydrocarbon membrane, a membrane obtained by adding an inorganic material or the like based on them, and an inorganic electrolyte membrane provided with ion conductivity based on an inorganic porous body or the like May be used.

  Moreover, the apparatus for carrying out the electrophoresis method in the present invention is not particularly limited. For example, an electrophoresis cell as shown in FIG. 3 is preferably used. In the electrophoresis cell 10 shown in FIG. 3, an anode 12 and a cathode 13 are installed in an electrophoresis tank 11 so as to face each other in parallel, and a DC stabilized power source for energizing between the anode 12 and the cathode 13. 14 is connected. Further, a solid electrolyte membrane 15 is disposed so as to partition the inside of the electrophoresis tank 11 into an anode side and a cathode side, and the surface to be treated of the solid electrolyte membrane 15 is put on the catalyst ink 16 put on the cathode side of the electrophoresis tank 11. Are arranged so as to contact each other.

  The anode 12 and the cathode 13 used in the electrophoresis cell 10 are not particularly limited, and a conductive substrate such as platinum or carbon is preferably used as the anode 12, and a metal substrate such as platinum or palladium is suitable as the cathode 13. Used for. Furthermore, the shape of the anode 12 and the cathode 13 is preferably a net shape, but may be a plate shape. The interval between the anode 12 and the cathode 13 is preferably 5 to 100 mm. If both poles are too close, there is a risk of a short circuit, and if they are too far apart, a higher voltage tends to be required for the DC power supply. Further, the positional relationship between the anode 12 and the cathode 13 may be horizontal or vertical as shown in FIG. 3, but when the catalyst particles or the like are likely to settle, the anode 12 is disposed below and the cathode 13 is disposed above. It is preferable.

  Moreover, the electrolyte solution 17 put in the anode side of the electrophoresis tank 11 is not specifically limited, For example, the electrolyte solution of perchloric acid aqueous solution, sulfuric acid aqueous solution, and phosphoric acid aqueous solution is used suitably.

  The voltage used for electrophoresis in the present invention is not particularly limited, but is basically preferably about 5 to 2000 V / cm, and depends on the distance between electrodes, the electrolyte solution, the composition of the catalyst ink, etc. About 1500V is more preferable. When this voltage is less than the lower limit, the catalyst layer formation rate tends to be slow. On the other hand, when the voltage exceeds the upper limit, heat generation due to energization increases and cooling for maintaining the temperature during electrophoresis at 35 ° C. or lower. There is a tendency for the cost required to become excessive.

  The present inventors have found that the temperature of the catalyst ink during electrophoresis has a great influence on the properties of the formed catalyst layer, and as a result of earnestly examining the temperature dependence of the catalyst ink involved, Electrophoresis is performed in a state where the temperature of the catalyst ink is maintained at 35 ° C. or lower (preferably 30 ° C. or lower, more preferably 25 ° C. or lower), thereby obtaining a catalyst layer having strong adhesion to the electrolyte membrane and excellent battery characteristics. I found out that Further, as described above, the present inventors have found that the zeta potential of the cation exchange resin is reversed from negative to positive when the temperature of the catalyst ink exceeds 35 ° C. and becomes about 40 ° C. or higher. In the invention, the catalyst layer is preferably formed by electrophoresis in a state where the zeta potential of the cation exchange resin in the catalyst ink is maintained negative. When the catalyst layer is formed using the electrophoresis method, the catalyst layer is not formed or formed unless the temperature of the catalyst ink is kept below the temperature at which the reversal of the zeta potential occurs, that is, 35 ° C. or lower. Even so, the adhesion to the electrolyte membrane is low, and good fuel cell characteristics cannot be obtained.

  In the method for producing a membrane / electrode assembly of the present invention, a catalyst layer having a practical thickness is formed in several minutes to several tens of minutes by performing the catalyst layer formation using electrophoresis under the above-described conditions. Can do. The thickness of the obtained catalyst layer is not particularly limited, but is preferably 3 to 30 μm, and particularly preferably 5 to 20 μm. When the thickness of the catalyst layer is less than 3 μm, the gas supplied to the catalyst layer tends to permeate the membrane, and the strength of the membrane electrode assembly obtained tends to decrease. On the other hand, when the thickness of the catalyst layer exceeds 30 μm, the gas supplied in the catalyst layer becomes difficult to diffuse and the progress of the chemical reaction tends to be hindered.

  In the method for producing a membrane / electrode assembly of the present invention, when the catalyst layers (the anode catalyst layer and the cathode catalyst layer) are formed on both surfaces of the solid electrolyte membrane by electrophoresis, the above-mentioned one side of the solid electrolyte membrane is After the catalyst layer is formed by this method, the solid electrolyte membrane is inverted and the catalyst layer may be formed on the other surface of the solid electrolyte membrane by the above method.

  As mentioned above, although the process of forming a catalyst layer using the electrophoresis method in the method for producing a membrane electrode assembly of the present invention has been described, specific examples of other steps for producing a membrane electrode assembly in the present invention are described. A method in particular is not restrict | limited, The general method for manufacturing the membrane electrode assembly for fuel cells can be applied suitably.

  As a general method for producing such a membrane electrode assembly, for example, a method in which a catalyst layer is formed on both surfaces of a solid electrolyte membrane and then sandwiched between gas diffusion layers can be mentioned. The gas diffusion layer used in the present invention is not particularly limited, and for example, a porous conductive substrate such as carbon cloth, carbon paper, carbon felt or the like can be used.

  Moreover, the separator used when obtaining a fuel cell using the membrane electrode assembly obtained by the present invention is not particularly limited, and for example, a wide range of materials made of metal, carbon, a material obtained by mixing graphite and resin, and the like are widely used. be able to.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.

Example 1
10.2 g of distilled water was added to 2 g of catalyst powder (platinum supported amount: 40 mass% of the total mass of the catalyst powder) on which platinum was supported on a carbon support (specific surface area 800 m ² / g) to obtain a mixed solution. To this mixed solution, CF ₂ = CF ₂ / CF ₂ = CFOCF ₂ CF (CF ₃ ) O (CF ₂ ) ₂ SO ₃ H copolymer (ion exchange capacity: 0.91 milliequivalent / (g) Dry resin (hereinafter referred to as “copolymer n”) is added to 112 g of a dispersion having a solid content concentration of 5% by mass in ethanol, ethanol is added, and a homogenizer (manufactured by Kinematica, trade name: Polytron) is added. Used and stirred to obtain a catalyst ink. The solid content concentration in the obtained catalyst ink was 0.07% by mass, and the mass ratio of the catalyst powder and the cation exchange resin in terms of solid content was 1: 2.8. The alcohol content in the dispersion medium in the catalyst ink was 99.8% by mass.

Next, the obtained catalyst ink was put into the electrophoresis cell shown in FIG. 3, and a solid electrolyte membrane Nafion 117 (trade name, DuPont) was used while the temperature of the catalyst ink was kept near 0 ° C. using a cooler. A catalyst layer was formed on one side of the membrane by electrophoresis. The intensity of the electric field during electrophoresis was 250 mVcm ⁻¹ and the electrophoresis time was 6 minutes. Next, the solid electrolyte membrane was inverted and a catalyst layer was formed on the opposite side of the membrane by electrophoresis in the same manner. As a result, a membrane / catalyst layer assembly (platinum amount: 0.8 mg / cm ² ) in which a catalyst layer having a uniform thickness of about 11 μm was formed on both surfaces of the solid electrolyte membrane was obtained.

  FIG. 4 shows an electron micrograph of a cross section of the catalyst layer formed on the solid electrolyte membrane. As is clear from FIG. 4, it was confirmed that the catalyst layer obtained in Example 1 was very excellent in thickness uniformity.

  In addition, when the adhesion between the catalyst layer and the solid electrolyte membrane was evaluated by a simple method of bending the produced joined body loosely, it was confirmed that the adhesion between the catalyst layer and the solid electrolyte membrane was very strong. It was done.

Subsequently, the membrane / catalyst layer assembly obtained as described above was sandwiched between two gas diffusion layers (carbon cloth having a thickness of 200 μm) to prepare a membrane / electrode assembly. Then, the obtained membrane electrode assembly is sandwiched between a pair of separators, and the separator and the membrane electrode assembly are tightened while arranging a gasket around the periphery, so that the effective electrode area for battery performance measurement is 25 cm ² . A single cell (power generation cell) for a polymer electrolyte fuel cell was completed.

<Fuel cell characteristic evaluation 1>
Hydrogen (80% humidification) / oxygen (20% humidification) is supplied to the power generation cell obtained above at normal pressure, and the initial characteristics (current density and cell voltage) of the fuel cell at a cell temperature of 80 ° C. Evaluation). The obtained results are shown in FIG. As is clear from FIG. 5, it was confirmed that the fuel cell using the membrane electrode assembly obtained in Example 1 was very excellent in cell characteristics.

<Fuel cell characteristic evaluation 2>
Hydrogen gas is supplied to the anode side of the power generation cell obtained above at 53 cm ³ / min and nitrogen gas is supplied to the cathode side at 2000 cm ³ / min. The potentiostat with the anode side as a reference electrode and the cathode side as a working electrode. The cyclic voltammetry (CV) on the cathode side was measured with a measuring device that combined a power generator and a function generator. Further, the membrane electrode assembly was removed and inverted, and hydrogen gas was supplied to the cathode side at 53 cm ³ / min and nitrogen gas was supplied to the anode side at 2000 cm ³ / min, and the CV on the anode side was measured in the same manner. The amount of electrochemical coulomb per unit area of the catalyst layer was measured for each of the cathode and anode. The obtained results are shown in Table 1.

(Comparative Example 1)
In this comparative example, a membrane / catalyst layer assembly having substantially the same amount of platinum was obtained in the same manner as in Example 1 except that electrophoresis was carried out without performing a special cooling operation. The temperature of the catalyst ink reached 40 ° C. during electrophoresis.

  An electron micrograph of a cross section of the catalyst layer formed on the solid electrolyte membrane is shown in FIG. As is clear from FIG. 6, it was confirmed that the catalyst layer obtained in Comparative Example 1 was inferior in thickness uniformity as compared with that obtained in Example 1.

  Further, when the adhesion between the catalyst layer and the solid electrolyte membrane obtained in Comparative Example 1 was evaluated in the same manner as in Example 1, the adhesion force between the catalyst layer and the solid electrolyte membrane was very weak. Was confirmed.

  Subsequently, a membrane / electrode assembly was produced in the same manner as in Example 1 using the membrane / catalyst layer assembly obtained in Comparative Example 1, and a power generation cell was completed. Characteristic evaluations 1 and 2 were performed. The results obtained in the fuel cell characteristic evaluation 1 are shown in FIG. 5, and the results obtained in the fuel cell characteristic evaluation 2 are shown in Table 1, respectively. As is clear from FIG. 5, it was confirmed that the fuel cell using the membrane electrode assembly obtained in Comparative Example 1 was inferior in battery characteristics as compared with that obtained in Example 1.

(Example 2)
A catalyst powder (trade name: TEC10E50E, trade name: TEC10E50E, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., platinum supported on a carbon support (specific surface area 800 m ² / g) of platinum on 2 g of distilled water 10 .2 g was added to obtain a mixed solution. To this mixed solution, a cation exchange resin CF ₂ ═CF ₂ / CF ₂ ═CFOCF ₂ CF (CF ₃ ) O (CF ₂ ) ₂ SO ₃ H copolymer (ion exchange capacity: 1.1 milliequivalent / After adding 11.2 g of a dispersion having a solid content concentration of 9% by mass in which a dry resin (hereinafter referred to as “copolymer f”) is dispersed in ethanol, a homogenizer (manufactured by Kinematica, trade name: Polytron) is used. And stirred to obtain a catalyst ink. The solid content concentration in the obtained catalyst ink was 13% by mass, and the mass ratio of the catalyst powder and the cation exchange resin in terms of solid content was 2: 1. The alcohol content in the dispersion medium in the catalyst ink was 50% by mass.

  The zeta potential of the catalyst ink at this point was measured with a zeta potential analyzer (manufactured by Matec Applied Science, model: ESA9800), and the catalyst ink temperature was −31 mV at 20 ° C.

  In this example, the catalyst ink obtained above was used, and an ion exchange membrane having a thickness of 50 μm made of a perfluorocarbon polymer having a sulfonic acid group (manufactured by Asahi Glass Co., Ltd., trade name: Flemion, ion exchange capacity 1. A membrane / catalyst layer assembly was obtained in the same manner as in Example 1 except that 1 milliequivalent / g dry resin) was used as the solid electrolyte membrane.

  Subsequently, a membrane / electrode assembly was produced in the same manner as in Example 1 using the membrane / catalyst layer assembly obtained in Example 2, and a power generation cell was completed. Characteristic evaluation 2 is performed. The obtained results are shown in Table 1.

(Comparative Example 2)
In this comparative example, a membrane / catalyst layer assembly is obtained in the same manner as in Example 2 except that electrophoresis is carried out without performing a special cooling operation. Subsequently, a membrane / electrode assembly was produced in the same manner as in Example 1 using the membrane / catalyst layer assembly obtained in Comparative Example 2, and a power generation cell was completed. Characteristic evaluation 2 is performed. The obtained results are shown in Table 1.

(Example 3)
In this example, Example 2 was used except that 20.2 g of 5% Nafion solution (ion exchange capacity 0.91 meq / g dry resin) manufactured by Aldrich was used instead of copolymer f. As in 2, a catalyst ink having a zeta potential of -14 mV at a catalyst ink temperature of 20 ° C. is obtained.

  Next, in this example, a membrane catalyst layer assembly was obtained in the same manner as in Example 2 except that the catalyst ink obtained in Example 3 was used, and the membrane catalyst layer assembly was further used. Then, a membrane / electrode assembly is prepared in the same manner as in Example 1, and a power generation cell is completed, and a fuel cell characteristic evaluation 2 is performed in the same manner as in Example 1. The obtained results are shown in Table 1.

(Comparative Example 3)
In this comparative example, a membrane / catalyst layer assembly is obtained in the same manner as in Example 3 except that electrophoresis is performed without performing any special cooling operation. Subsequently, a membrane / electrode assembly was produced in the same manner as in Example 1 using the membrane / catalyst layer assembly obtained in Comparative Example 3, and a power generation cell was completed. Characteristic evaluation 2 is performed. The obtained results are shown in Table 1.

Example 4
An aqueous solution containing 4.82 mol / kg, 6.49 mol / kg and 0.01 mol / kg of 2-acrylamido-2-methylpropanesulfonic acid, N, N-methylenebisacrylamide and ammonium peroxodisulfate, respectively, was injected into the porous polyimide membrane. After that, the composite film was obtained by heating at 60 ° C. for 1 hour for gelation. The obtained membrane was sandwiched between gold electrodes, and the proton conductivity was measured by an alternating current method in an atmosphere with a relative humidity of 90%. As a result, it was about 0.1 S / cm.

  In this example, a membrane catalyst layer assembly was obtained in the same manner as in Example 1 except that the composite membrane thus obtained was used as a solid electrolyte membrane, and the membrane catalyst layer assembly was further obtained. The membrane electrode assembly was produced in the same manner as in Example 1, and a power generation cell was completed. Fuel cell characteristic evaluation 2 was performed in the same manner as in Example 1. The obtained results are shown in Table 1.

(Example 5)
An aqueous solution similar to the aqueous solution used in Example 4 was vacuum impregnated into porous silica, and then left overnight in an atmosphere of 60 ° C. and 90% relative humidity to polymerize the gel to obtain composite particles. Next, the obtained composite particles were immersed in ultrapure water for 1 hour to sufficiently contain moisture, and then sandwiched between glass H-type cells.

  In this example, a membrane / catalyst layer assembly was obtained in the same manner as in Example 1 except that the composite particles sandwiched between cells were used as a solid electrolyte membrane. A membrane electrode assembly is prepared using the body in the same manner as in Example 1, and a power generation cell is completed, and fuel cell characteristic evaluation 2 is performed in the same manner as in Example 1. The obtained results are shown in Table 1.

  As is apparent from the results shown in Table 1, a fuel cell using a membrane electrode assembly in which the catalyst ink temperature during electrophoresis was maintained at 35 ° C. or lower by the method of the present invention to form a catalyst layer (Example) 1 to 5) are batteries as compared with fuel cells (Comparative Examples 1 to 3) using a membrane electrode assembly in which a catalyst layer is formed without maintaining the temperature of the catalyst ink during electrophoresis at 35 ° C. or lower. It was confirmed that the characteristics were very excellent.

  As described above, according to the method for manufacturing a membrane electrode assembly of the present invention, a method for forming a catalyst layer using an electrophoresis method capable of forming a catalyst layer in a relatively short time. Nevertheless, the adhesion between the electrolyte membrane and the catalyst layer can be sufficiently improved to the extent that thermocompression bonding is not required. Therefore, according to the present invention, the step of increasing the bonding strength between the electrolyte membrane and the catalyst layer by thermocompression is not required, and therefore the destruction of the electrolyte membrane by thermocompression can be avoided. Furthermore, since the utilization efficiency of the catalyst is improved in the membrane electrode assembly obtained by the method of the present invention, the present invention is very useful as a method for producing a membrane electrode assembly having excellent fuel cell characteristics.

It is a graph which shows the relationship between the zeta potential of cation exchange resin in the catalyst ink concerning this invention, and temperature. 1 is a schematic cross-sectional view showing a preferred embodiment of a membrane electrode assembly for a polymer electrolyte fuel cell produced according to the present invention. It is a schematic diagram which shows an example of the electrophoresis cell suitable for this invention. 2 is an electron micrograph showing a cross section of a catalyst layer formed on a solid electrolyte membrane in Example 1. FIG. 4 is a graph showing evaluation results of initial characteristics of fuel cells obtained in Example 1 and Comparative Example 1. 4 is an electron micrograph showing a cross section of a catalyst layer formed on a solid electrolyte membrane in Comparative Example 1. FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Membrane electrode assembly, 2 ... Solid electrolyte membrane, 3 ... Anode, 4 ... Cathode, 5 ... Anode catalyst layer, 5 '... Cathode catalyst layer, 6, 6' ... Gas diffusion layer, 7 ... Separator, 7a ... Gas Flow path, 8 ... gas seal body, 10 ... electrophoresis cell, 11 ... electrophoresis tank, 12 ... anode, 13 ... cathode, 14 ... power source, 15 ... solid electrolyte membrane, 16 ... catalyst ink, 17 ... electrolyte.

Claims (5)

A method for producing a membrane electrode assembly for a fuel cell, comprising: an anode and a cathode each having a catalyst layer containing a catalyst powder and a cation exchange resin; and a solid electrolyte membrane disposed between the anode and the cathode. There,
With the catalyst layer of at least one of the anode and the cathode, the temperature of the dispersion is set to 35 with the solid electrolyte membrane in contact with the dispersion containing the catalyst powder, the cation exchange resin, and alcohol. A method for producing a membrane / electrode assembly, wherein the membrane / electrode assembly is formed by electrophoresis while maintaining the temperature at or below.   The method for producing a membrane electrode assembly according to claim 1, wherein the catalyst layer is formed by electrophoresis in a state where the zeta potential of the cation exchange resin in the dispersion is maintained negative.   The solid content concentration in the dispersion is 0.1 to 20% by mass, and the mass ratio of the catalyst powder and the cation exchange resin in terms of solid content is 50:50 to 85:15. The method for producing a membrane electrode assembly according to claim 1 or 2, characterized in that The cation exchange resin includes a structure of a —CF ₂ —CF ₂ — group as a repeating unit in the main chain, and at least one selected from the group consisting of a sulfonic acid group, a phosphonic acid group, and a sulfonimide group in the side chain. It is a copolymer which has group, The manufacturing method of the membrane electrode assembly as described in any one of Claims 1-3 characterized by the above-mentioned.   The method for producing a membrane electrode assembly according to any one of claims 1 to 4, wherein the catalyst powder is a catalyst powder in which metal particles are supported on a carbon support.