JP2005174861A - Manufacturing method for membrane electrode assembly for solid polymer fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method for a membrane electrode assembly for a solid polymer fuel cell capable of obtaining high output voltage by efficiently covering catalyst powder with a cation exchange resin to increase a reaction site in a three-phase zone. <P>SOLUTION: This manufacturing method comprises a step preparing a coating solution with solid concentration of 0.1-20 mass% and positive (plus) zeta potential of the particles in the liquid by preparing a dispersion liquid by mixing a cation exchange resin and a dispersion medium containing alcohol, then warming at temperature of 40-120°C so that a zeta potential of the cation exchange resin in the dispersion liquid changes from negative (minus) to positive (plus), in that condition, adding and mixing catalyst powder into the dispersion liquid so that the mass ratio of the catalyst powder and the cation exchange resin in solid content conversion is 50:50-85:15, a step forming a catalyst layer by applying the coating solution on a base material and drying it and a step arranging the catalyst layer adjacent to a polymer electrolyte film as at least one catalyst layer of a cathode and an anode. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing a membrane electrode assembly for a polymer electrolyte fuel cell.

  A fuel cell is a cell that directly converts the reaction energy of the gas used as fuel into electrical energy. In particular, the hydrogen / oxygen fuel cell has no influence on the global environment because its reaction product is essentially water only. It is known for almost nothing. In particular, for polymer electrolyte fuel cells that use a polymer electrolyte membrane as an electrolyte, polymer electrolyte membranes having high ionic conductivity have been developed in recent years, and can operate at room temperature and achieve high output density. Therefore, with increasing social demand for energy problems and global environmental problems, there is a great expectation as a power source for mobile vehicles for electric vehicles, small cogeneration systems, and the like.

  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 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 as a fuel and a gas containing oxygen (such as air) as an oxidant, Electric power is generated by supplying the anode and cathode respectively.

  Usually, an electrode used for a polymer electrolyte fuel cell is a catalyst powder made of metal particles or carbon particles carrying metal particles coated with an ion exchange resin (hereinafter referred to as catalyst powder). The catalyst layer is composed of a gas diffusion layer that supplies a reaction gas to the catalyst layer and collects charges generated in the catalyst layer. In the catalyst layer, there are voids composed of fine pores formed between the secondary particles of the above-described metal particles or carbon particles supporting the metal particles, and these voids are the reaction gas. Functions as a diffusion flow path. 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.

  As a basic method for forming this catalyst layer, after preparing a coating liquid for forming a catalyst layer by mixing a solid polymer electrolyte solution in a dispersion in which the above catalyst powder is dispersed, Examples thereof include a method of coating on a Teflon (registered trademark) substrate and heat-pressing on the solid polymer electrolyte membrane, and a method of directly coating the coating liquid on the solid polymer electrolyte membrane. However, for catalyst powders, particularly catalyst powders in which metal particles are supported on carbon, the pores of the carbon carrier are usually developed, and ion exchange resin is used for the metal fine particles supported in the fine pores. It was difficult to coat, and the reaction area that worked effectively for power generation was very small compared to the surface area of all metal particles.

  For this reason, in order to further increase the three-phase interface in the catalyst layer, it is necessary that the metal particles in the catalyst powder be efficiently coated with the ion exchange resin.

  However, in general, in a dispersion of an ion exchange resin having a cation exchange group such as a sulfonic acid group represented by Nafion solution (manufactured by Aldrich) or Flemion solution (manufactured by Asahi Glass), the cation exchange group is usually outside. It is considered that the zeta potential shows a negative (minus) value because it is oriented in the dispersion and dispersed in the dispersion. In addition, even in ordinary catalyst powders, it is known that the zeta potential shows a negative value in a dispersion containing water or alcohol. In particular, carbon particles carrying metal particles are quinone on the surface of the particles. Since it contains surface functional groups such as a functional carbonyl group, a phenolic hydroxyl group, and a lactone ring, it exhibits a small negative zeta potential. For this reason, in the conventional manufacturing method, both the ion exchange resin and the catalyst powder are dispersed with a negative zeta potential in the coating liquid, and in this case, both of them repel each other electrostatically. Therefore, it is not easy to efficiently coat the catalyst powder particles with the ion exchange resin.

  For this reason, conventionally, as a method for increasing the three-phase interface and expanding the reaction site, a method of preventing the particles from aggregating by bonding basic functional groups to the surface of carbon particles carrying metal particles (Patent Document 1). ), A method of imparting hydrophilicity to carbon particles carrying metal particles, and orienting sulfonic acid groups of an ion exchange resin (Patent Document 2) and the like have been proposed.

  However, in the above-described method for treating carbon particles carrying metal particles, there is a possibility that the activity of the catalytic metal may be reduced, the resistance value may be increased, and the cost is increased. there were.

  In addition, there is a method in which an aqueous solution of a platinum compound and a ruthenium compound is reduced by applying pressure and heating in a dispersion containing an ion exchange resin to form an alloy of platinum and ruthenium in the dispersion. Although it is mentioned (Patent Document 3), in this method, the concentration of the catalyst must be a very low coating solution, and conversely, when trying to obtain a coating solution having a high concentration, the catalyst particles aggregate. The problem that it is not practical because of the problems such as.

JP-A-8-78021 (Claims) JP 2002-324557 A (Claims) JP 2003-123775 A

  The present invention relates to a method for producing a membrane electrode assembly for a polymer electrolyte fuel cell, which can increase the reaction sites at the three-phase interface by efficiently coating the catalyst powder with a cation exchange resin and obtain a high output voltage. The purpose is to provide.

  The present invention relates to a membrane for a polymer electrolyte fuel cell comprising a cathode and an anode having a catalyst layer containing a catalyst powder and a cation exchange resin, and a polymer electrolyte membrane disposed between the cathode and the anode. A method for producing an electrode assembly, wherein a dispersion liquid containing the cation exchange resin and a dispersion medium containing alcohol is prepared, and then heated to a temperature of 40 to 120 ° C., whereby particles in the dispersion liquid are produced. The zeta potential is changed from negative (minus) to positive (plus), and in this state, the dispersion has a mass ratio of the catalyst powder to the cation exchange resin in terms of solid content of 50:50 to 85:15. The catalyst powder is added and mixed so that a solid content concentration of 0.1 to 20% by mass and a zeta potential of particles in the liquid is positive (plus); Apply the working fluid on the substrate and dry it A solid polymer fuel cell comprising: a step of forming a catalyst layer, and a step of arranging the catalyst layer adjacent to the polymer electrolyte membrane as at least one of a cathode and an anode catalyst layer. A method for producing a membrane electrode assembly for use is provided.

  The present invention also provides a solid polymer fuel cell comprising a cathode and an anode having a catalyst layer containing a catalyst powder and a cation exchange resin, and a polymer electrolyte membrane disposed between the cathode and the anode. A method for producing a membrane electrode assembly for a catalyst, wherein the catalyst powder and the cation exchange are prepared so that a mass ratio of the catalyst powder and the cation exchange resin in terms of solid content is 50:50 to 85:15 The resin and the dispersion medium containing alcohol are mixed, heated to a temperature of 40 to 120 ° C., and stirred, so that the solid content concentration is 0.1 to 20% by mass and the zeta potential of the particles in the liquid is positive. A step of producing a (plus) coating solution, a step of forming a catalyst layer by coating the coating solution on a substrate and drying, and at least one of a cathode and an anode catalyst layer. As next to the polymer electrolyte membrane To provide a method of manufacturing a solid polymer electrolyte fuel cell membrane electrode assembly, characterized in that through the process, it is placed in.

  According to the present invention, since the catalyst powder can be efficiently coated with a cation exchange resin, the three-phase interface can be increased, and it is excellent in initial power generation performance and at the same time is stable even after long-term power generation. A membrane electrode assembly for a battery can be obtained.

  FIG. 1 shows a cross-sectional view of one embodiment of a membrane electrode assembly for a polymer electrolyte fuel cell obtained by the present invention. Hereinafter, the membrane electrode assembly 7 will be described with reference to FIG. The membrane electrode assembly 7 includes a solid polymer electrolyte membrane 1, an anode catalyst layer 2 and a cathode catalyst layer 3 in close contact with the membrane surface of the electrolyte membrane 1, and gas diffusion layers 4, 4 ′ in close contact with these catalyst layers. And the gas seal body 6. On the outside of the membrane electrode assembly 7, a separator 5 in which a groove to be a gas flow path 5a is formed is disposed. For example, hydrogen gas obtained by reforming a fuel such as methanol or natural gas is supplied to the anode side through a groove of the separator.

  The solid polymer electrolyte membrane 1 has a role of selectively transmitting protons generated in the anode catalyst layer 2 to the cathode catalyst layer 3 along the film thickness direction. The solid polymer electrolyte membrane 1 also has a function as a diaphragm for preventing hydrogen supplied to the anode and oxygen supplied to the cathode from being mixed.

  The anode catalyst layer 2 and the cathode catalyst layer 3 are disposed between the gas diffusion layers 4, 4 ′ and the solid polymer electrolyte membrane 1. Thereby, a membrane electrode assembly for a polymer electrolyte fuel cell is obtained. Hereinafter, the present invention will be described in detail.

  In the present invention, a coating liquid for forming a catalyst layer (hereinafter simply referred to as a coating liquid) contains a catalyst powder, a cation exchange resin, and a dispersion medium containing alcohol, as described in detail below. It includes a step of bringing the zeta potential of the particles in the coating liquid into a positive (plus) state. Further, the coating liquid is adjusted so that the solid content concentration 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. It is also characterized. Thereby, a cation exchange resin can coat | cover a catalyst powder efficiently, and when a conjugate | zygote is produced, since a three-phase interface can be increased, it is preferable. The coating liquid of the present invention can be used in forming any of the cathode and anode catalyst layers, and is particularly preferably used for both the cathode and anode catalyst layers. Here, the particles in the coating liquid are composed of catalyst powder particles and cation exchange resin particles.

  In the present invention, a cation exchange resin is used. Examples of the cation exchange group in the cation exchange resin include a sulfonic acid group, a carboxylic acid group, a phosphonic acid group, and a sulfonimide group. As the cation exchange resin, those having a sulfonic acid group are particularly preferable.

  In the present invention, the cation exchange resin 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 may increase during power generation, which is not preferable. If it is more than milliequivalent / g dry resin, the water content of the obtained catalyst layer is increased, the resin layer tends to swell, and the pores may be clogged. The ion exchange capacity is particularly preferably 0.8 to 1.2 meq / g dry resin.

The cation exchange _{resin, CF 2 = CF- (OCF 2} CFX) m -O p - (CF 2) a perfluorovinyl compound represented by n -SO ₃ H (m is an integer of 0 to 3, n represents an integer of 1 to 12, p represents 0 or 1, and X represents a fluorine atom or a trifluoromethyl group.) and a copolymer comprising a polymer unit based on tetrafluoroethylene It is preferable that

Preferable examples of the fluorovinyl compound include compounds represented by the following formulas (1) to (3). However, in the following formula, q is an integer of 1 to 8, r is an integer of 1 to 8, and t is an integer of 1 to 3.
_{CF 2 = CFO (CF 2)} q -SO 3 H ··· (1)
_{CF 2 = CFOCF 2 CF (CF} 3) O (CF 2) r -SO 3 H ··· (2)
_{CF 2 = CF (OCF 2 CF} (CF 3)) t O (CF 2) 2 -SO 3 H ··· (3).

  Specific examples of the cation exchange resin include Nafion (trade name: manufactured by Aldrich) and Flemion (trade name: manufactured by Asahi Glass).

  In the present invention, a dispersion medium containing alcohol is used. In addition to alcohol, other solvents can be mixed with the dispersion medium containing alcohol as needed. Examples of other solvents include water and acetone. Other solvents and alcohol can be mixed and used at a ratio of 10: 1 to 1:10.

  In the present invention, the alcohol is not particularly limited, but an alcohol having 1 to 5 carbon atoms and containing one or more OH groups in the molecule 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. The alcohol is particularly preferably a straight chain having one OH group in the molecule, and ethanol is particularly preferable.

  In the present invention, the catalyst powder is made of metal particles or metal particles supported on carbon. Further, the catalyst powder in the present invention exhibits a negative (minus) value of zeta potential in the above-mentioned alcohol. When using metal particles as a catalyst as they are, platinum or an alloy with platinum is preferable. As a metal used as an alloy with platinum, gold, silver, ruthenium, palladium, rhodium, iridium, cobalt, iron, manganese, chromium and the like are preferable, but not necessarily limited thereto.

  Further, in the case of catalyst powder in which metal particles are supported on carbon, any metal can be used, and the metal particles are not particularly limited, and are 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 preferred. In the case of catalyst powder in which metal particles are supported on carbon, the metal particles used are preferably an alloy with platinum, and an alloy of platinum and ruthenium is particularly preferable because the activity of the catalyst is stable.

Further, in the case of a catalyst powder in which metal particles are supported on carbon, the carbon serving as a carrier preferably has a specific surface area of 50 to 1500 m ² / g. If it is less than a specific surface area of 50 m 2 / ^g, it is difficult to increase the loading of metal particles as a catalyst, it is not preferred since the output characteristics of the obtained catalyst layer are likely to decrease, the specific surface area of 1500 m ² / If it exceeds g, since the pores are too fine, coating with a cation exchange resin becomes difficult, and the output characteristics of the obtained catalyst layer may be deteriorated. The specific surface area is particularly preferably 200 to 900 m ² / g.

  The catalyst powder particles preferably have an average particle size of 0.05 to 5 μm. If the average particle size is less than 0.05 μm, the resulting catalyst layer has a dense structure and it is difficult to discharge generated water at the cathode or anode. Since it is difficult to coat with an exchange resin and the coating area is reduced, the performance of the catalyst layer may be lowered, which is not preferable.

  In this invention, a coating liquid is produced by the method of either of the two aspects shown below.

  First, as a 1st aspect, after mixing a cation exchange resin and the dispersion medium containing alcohol and producing a dispersion liquid, it heats at the temperature of 40-120 degreeC, and sets the zeta potential of a cation exchange resin. By reversing from a negative state to a positive state and then maintaining the state, the catalyst powder is added to the dispersion and mixed. Accordingly, in the present invention, when the catalyst powder and the cation exchange resin form particles, the cation exchange resin having a positive zeta potential with respect to the catalyst powder particles having a negative zeta potential is electrostatically charged. It can be adsorbed on the surface and the coverage can be increased.

  In the present invention, the mechanism by which the zeta potential of the cation exchange resin in the dispersion containing the cation exchange resin is reversed from negative to positive has not been elucidated and is not clear. The ion exchange groups of the cation exchange resin present in the liquid gather inside the aggregate, and the hydrophobic group of the alcohol is coordinated to the skeleton of the hydrophobic ion exchange resin oriented to the outside, and is located outside the alcohol. It is considered that the zeta potential shows a positive value because H of the OH group is positively charged. If the temperature exceeds 120 ° C., the molecular motion of the resin or alcohol becomes intense, the above-mentioned blending cannot be performed, and the zeta potential of the particles in the dispersion may not be positive. The temperature for heating after mixing a cation exchange resin and alcohol to prepare a dispersion is particularly preferably 45 to 80 ° C.

  The dispersion containing the cation exchange resin is preferably mixed with the catalyst powder in a state where the zeta potential of the cation exchange resin is +10 to +160 mV. This is preferable because the catalyst powder can be efficiently coated with the cation exchange resin and a catalyst layer with excellent performance can be obtained. The zeta potential of the cation exchange resin is particularly preferably +10 to +80 mV.

  On the other hand, as a 2nd aspect which produces a coating liquid, it is based on the method of stirring, mixing catalyst powder, a cation exchange resin, and the dispersion medium containing alcohol, and hold | maintaining at the temperature of 40-120 degreeC. . Also in this method, as in the above-described method, the cation exchange resin whose zeta potential is reversed from negative to positive in the coating solution can efficiently coat the catalyst powder having a negative zeta potential. In the case of this method, it is preferable to carry out dispersion and stirring operations for about 3 to 30 hours in order to promote coating with the cation exchange resin. The stirring operation time is not particularly limited as long as it does not cause aggregation of the catalyst powder particles. As for the temperature which heats a coating liquid, 45-80 degreeC is especially preferable.

  In the present invention, if necessary, the catalyst powder can be dispersed in water and then mixed with a dispersion containing a cation exchange resin. When the catalyst powder is dispersed in water, the solid content concentration is preferably 3 to 20% by mass.

  In the present invention, the coating liquid needs to have a solid content concentration of 0.1 to 20% by mass. When the solid content concentration is less than 0.1% by mass, a catalyst layer having a predetermined thickness cannot be obtained unless it is repeatedly applied to produce a catalyst layer by applying a coating solution. Becomes worse. On the other hand, if the solid content concentration is more than 20% by mass, the viscosity of the coating liquid increases, and the catalyst layer obtained by coating may become non-uniform. The solid content concentration is particularly preferably 1 to 10% by mass.

  Moreover, in this invention, it is necessary to produce a coating liquid so that mass ratio of catalyst powder and cation exchange resin may be 50: 50-85: 15. If the amount of the catalyst is less than 50:50 at this mass ratio, the pores of the catalyst support are crushed by the cation resin, and the reaction field is reduced, so that the performance as a polymer electrolyte fuel cell may be deteriorated. . Further, when the amount of the catalyst is larger than 85:15 in this mass ratio, the coating of the catalyst powder with the cation exchange resin may be insufficient, and the performance as a solid polymer fuel cell may be deteriorated. . It is particularly preferable that the mass ratio of the catalyst powder and the cation exchange resin is 60:40 to 80:20.

  In the present invention, when preparing the coating liquid, specifically, a method using a high-speed rotation such as using a stirrer such as a homogenizer or a homomixer, or using a high-speed rotating jet flow method or an attritor, a high pressure Examples thereof include a method of imparting elasticity to the dispersion by extruding the dispersion from a narrow portion under high pressure such as an emulsifier.

  The obtained coating liquid is preferably filtered. The filtration can remove aggregates of the catalyst powder particles in the coating liquid and has an effect of suppressing the aggregation of the coating liquid. Therefore, it is preferably performed immediately before coating when forming the catalyst layer. As a method of filtration, the coating solution may be pressurized and passed through a filter, or may be sucked and passed through a filter. It is preferable that the hole diameter of a filter is 5-100 micrometers. If the pore diameter is less than 5 μm, it is not preferable because it is difficult to filter and easily clogs, and if the pore diameter exceeds 100 μm, fine particles cannot be removed. The pore diameter is particularly preferably 20 to 60 μm.

  It is preferable that the coating liquids obtained by the above two production methods are applied in a state where the zeta potential of the particles in the coating liquid is kept positive. As described above, the obtained coating liquid is positively charged with a positively charged zeta potential, and the catalyst powder having a negative zeta potential is electrostatically adsorbed and its bond is strong. When bonded to form particles, it is considered that the particles basically exist stably in the dispersion medium. For this reason, even if the obtained coating liquid is cooled to room temperature, even if the catalyst layer is formed by coating on the substrate, the properties of the obtained catalyst layer are hardly deteriorated. preferable.

  Moreover, in this invention, it is preferable to apply in the state whose zeta potential of the particle | grains in a coating liquid is + 5- + 100 mV. If the zeta potential is less than +5 mV, the catalyst powder is not sufficiently covered with the cation exchange resin in the coating solution, and the properties of the obtained catalyst layer may be deteriorated. If the potential is more than +100 mV, the amount of catalyst powder in the coating solution is too small compared to the cation exchange resin, so that it is necessary to apply many times to form the catalyst layer, resulting in poor productivity. Therefore, it is not preferable. The zeta potential is particularly preferably +10 to +50 mV.

  In the present invention, examples of the method for producing a membrane electrode assembly include a method in which a coating solution is directly applied on an ion exchange membrane, and then dried to form a catalyst layer and sandwiched between gas diffusion layers. In addition, after applying a coating liquid on a base material to be a gas diffusion layer such as carbon paper, carbon cloth or carbon felt and drying to form a catalyst layer, this is applied to a solid polymer electrolyte membrane such as hot press A joining method can also be employed. In addition, the coating solution exhibits sufficient stability against the solvent contained in the coating solution, for example, on a base film such as polypropylene, polyethylene terephthalate, ethylene / tetrafluoroethylene copolymer, polytetrafluoroethylene, etc. It is also possible to employ a method in which the substrate film is coated, dried, hot-pressed onto a solid polymer electrolyte membrane, the substrate film is peeled off, and sandwiched between gas diffusion layers.

  As a coating method of the coating liquid when forming the catalyst layer, a method using an applicator, a bar coater, a die coater, a spray, etc., a screen printing method, a gravure printing method, or the like can be applied.

  The catalyst layer of the present invention preferably has a thickness of 3 to 30 μm. If the thickness is less than 3 μm, the gas supplied to the catalyst layer tends to permeate the membrane, and the strength of the resulting bonded body is reduced, which is not preferable. If the thickness exceeds 30 μm, the gas is supplied in the catalyst layer. Gas is difficult to diffuse and reaction is difficult to proceed. A thickness of 5 to 20 μm is particularly preferable.

  In addition, water repellents, pore formers, thickeners, diluting solvents, etc. may be added to the coating liquid as necessary to improve the drainage of water produced by electrode reactions, and to stabilize the shape of the catalyst layer itself. It is also possible to maintain the properties, improve coating unevenness during coating, and improve coating stability.

  In the polymer electrolyte fuel cell including the membrane electrode assembly of the present invention, a gas containing oxygen is supplied to the cathode, and a gas containing hydrogen is supplied to the anode. Specifically, for example, a separator in which a groove to be a gas flow path is formed is disposed outside both electrodes of the membrane electrode assembly, and gas is allowed to flow to the membrane electrode assembly by flowing gas through the gas flow path. To generate electricity. Examples of the material for the separator include metal, carbon, a material in which graphite and a resin are mixed, and the like can be used widely.

  Hereinafter, the present invention will be specifically described using Examples (Examples 1 and 5 to 7) and Comparative Examples (Examples 2 to 4 and Examples 8 to 10), but the present invention is not limited thereto.

[Example 1]
10.2 g of distilled water was added to and mixed with 2 g of a catalyst (trade name: TEC10E50E, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) in which platinum was supported on a carbon support (specific surface area 800 m ² / g) on 46.5% by mass of the total mass of the catalyst. A liquid was obtained. CF ₂ = CF ₂ / CF ₂ = CFOCF ₂ CF (CF ₃ ) O (CF ₂ ) ₂ SO ₃ H copolymer (ion exchange capacity 1.1 meq / g dry resin, hereinafter, After adding 11.2 g of a dispersion having a solid content concentration of 9% by mass in which polymer a) is dispersed in ethanol, the mixture is stirred using a homogenizer (manufactured by Kinematica, trade name: Polytron) to obtain a coating solution. Got. The zeta potential of the coating solution at this time was measured with a zeta potential analyzer (manufactured by Matec Applied Science, model: ESA9800, hereinafter the same) and found to be −31 mV at room temperature (temperature 20 ° C.). Next, after this coating liquid was dispersed for 8 hours by a dipping machine at a temperature of 50 ° C., the zeta potential was measured again, and it was +30 mV at a temperature of 50 ° C. The coating liquid was applied on a polypropylene base film with a bar coater while maintaining the temperature at 50 ° C., and then dried in a dryer at a temperature of 80 ° C. for 30 minutes to form a catalyst layer. In addition, when the amount of platinum per unit area contained in the catalyst layer was calculated by measuring the mass of only the base film before the catalyst layer formation and the base film after the catalyst layer formation, 0.5 mg / cm ² .

Next, as a solid polymer electrolyte membrane, 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 1.1 meq / g dry resin) ), The catalyst layers formed on the base film are arranged on both sides of the membrane, and transferred by a hot press method to form an anode catalyst layer and a cathode catalyst layer, and the electrode area is 25 cm ² A joined body comprising a solid polymer membrane and a catalyst layer was produced. Further, a membrane electrode assembly was produced by sandwiching between two gas diffusion layers.

(Evaluation)
The obtained membrane electrode assembly is assembled into a power generation cell, hydrogen (utilization rate 70%) / air (utilization rate 40%) is supplied at normal pressure, and the current density is 0.2 A / cm at a cell temperature of 70 ° C. Initial characteristic evaluation and durability evaluation of the polymer electrolyte fuel cell in No. ² were performed. Hydrogen and air were humidified and supplied to the cell with a dew point of 70 ° C. on the anode side and a dew point of 70 ° C. on the cathode side, respectively, and the relationship between the cell voltage at the initial stage of operation and the elapsed time after the start of operation and the cell voltage were measured. The results are shown in Table 1. Also, hydrogen gas is supplied to the anode side at 53 cm ³ / min, nitrogen gas is supplied to the cathode side at 2000 cm ³ / min, and a combination of potentiostat and function generator is used 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 an apparatus for the purpose. 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 CV measurement 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. Table 2 shows the measurement results of the amount of coulomb.

[Example 2]
Example 1 is the same as Example 1 except that the coating liquid is not applied for 8 hours in a dipping machine at a temperature of 50 ° C., and the coating liquid is applied on a substrate film at a temperature of 20 ° C. The membrane electrode assembly was produced by operating as described above. The results of evaluation in the same manner as in Example 1 using the obtained membrane / electrode assembly are shown in Tables 1 and 2.

[Example 3]
In Example 1, the zeta potential of the coating solution obtained is -32 mV by carrying out a dispersion treatment for 8 hours with a dipping machine at a temperature of 35 ° C. instead of a temperature of 50 ° C. Subsequently, a membrane / electrode assembly is produced by performing the same operation as in Example 1 except that the coating liquid is applied on the base film while maintaining the temperature at 35 ° C. Tables 1 and 2 show the results obtained by evaluating in the same manner as in Example 1 using this membrane / electrode assembly.

[Example 4]
In Example 1, instead of carrying out the dispersion treatment for 8 hours with a dipping machine at a temperature of 50 ° C., the coating solution was subjected to a dispersion treatment for 1 hour at a temperature of 125 ° C. in an autoclave and then allowed to stand at room temperature (temperature 20 ° C.) The zeta potential of the resulting coating solution is −30 mV by operating in the same manner except for cooling to. Subsequently, a membrane / electrode assembly is produced by performing the same operation as in Example 1 except that the coating liquid is applied to the base film while being maintained at a temperature of 20 ° C. Tables 1 and 2 show the results obtained by evaluating in the same manner as in Example 1 using this membrane / electrode assembly.

[Example 5]
In Example 1, the same procedure as in Example 1 was used, except that 20.2 g of a 5% Nafion solution (ion exchange capacity 0.91 meq / g dry resin) manufactured by Aldrich was used instead of copolymer a. By performing the operation, a coating solution having a zeta potential of −14 mV at a temperature of 20 ° C. is obtained. The coating solution is subjected to a dispersion treatment for 8 hours in a 50 ° C. dipping machine in the same manner as in Example 1, and then allowed to cool to room temperature (temperature 20 ° C.), whereby the zeta potential of the resulting coating solution is +15 mV. When this coating solution is used in the same manner as in Example 1, a membrane / electrode assembly is produced. Tables 1 and 2 show the results obtained by evaluating in the same manner as in Example 1 using this membrane / electrode assembly. In addition, when the amount of platinum per unit area contained in the catalyst layer was calculated in the same manner as in Example 1, it was 0.5 mg / cm ² .

[Example 6]
After adding 25.1 g of distilled water to 16.8 g of a dispersion having a solid content concentration of 11.7% by mass in which copolymer a is dispersed in ethanol, the mixture is heated to a temperature of 50 ° C. using a thermostatic water bath and ionized. A dispersion containing the exchange resin was obtained. When the obtained zeta potential of the dispersion containing the ion exchange resin solution was measured, it was +40 mV at a temperature of 50 ° C. Separately, 60.7 g of distilled water and 40.4 g of ethanol were added to 10 g of the same catalyst as in Example 1, and then stirred with the same homogenizer as in Example 1 to obtain a dispersion containing the catalyst. When the zeta potential of the resulting dispersion containing the catalyst was measured, it was -25 mV at a temperature of 20 ° C. A dispersion containing 40 g of this catalyst was added to the dispersion containing the ion exchange resin heated to a temperature of 50 ° C. prepared previously to obtain a coating solution. The resulting coating solution had a zeta potential of +35 mV at a temperature of 50 ° C. With this coating solution maintained at a temperature of 50 ° C., the same operation as in Example 1 was carried out to produce a membrane electrode assembly. The results of evaluation in the same manner as in Example 1 using the obtained membrane / electrode assembly are shown in Tables 1 and 2. In addition, when the amount of platinum per unit area contained in the catalyst layer was calculated in the same manner as in Example 1, it was 0.5 mg / cm ² .

[Example 7]
In Example 6, the same operation as in Example 6 was performed except that the temperature of the constant temperature water bath was set to 70 ° C., to obtain a dispersion containing an ion exchange resin. The dispersion containing the obtained ion exchange resin had a zeta potential of +45 mV at a temperature of 70 ° C. Subsequently, the same operation as in Example 6 was performed except that the temperature of the constant temperature water bath was set to 70 ° C. to obtain a coating solution. The resulting coating solution had a zeta potential of +38 mV at a temperature of 70 ° C. After the obtained coating liquid was lowered to a temperature of 50 ° C., the operation was performed in the same manner as in Example 1 while maintaining the temperature, and a membrane electrode assembly was produced. The results of evaluation in the same manner as in Example 1 using the obtained membrane / electrode assembly are shown in Tables 1 and 2.

[Example 8]
In Example 6, the operation is performed in the same manner as in Example 6 except that the operation is performed at room temperature (temperature of 20 ° C.) without using a constant temperature water bath to obtain a dispersion containing an ion exchange resin. The resulting dispersion containing the ion exchange resin has a zeta potential of −38 mV at a temperature of 20 ° C. Subsequently, an operation is performed in the same manner as in Example 6 except that the operation is performed at room temperature (temperature of 20 ° C.) without using a constant temperature water bath to obtain a coating liquid. The resulting coating liquid has a zeta potential of −33 mV at a temperature of 20 ° C. When this coating solution is maintained at a temperature of 20 ° C. and operated in the same manner as in Example 1, a membrane / electrode assembly is produced. Tables 1 and 2 show the results obtained by evaluating in the same manner as in Example 1 using this membrane / electrode assembly.

[Example 9]
In Example 6, the same operation as in Example 6 is performed except that the constant temperature water bath is set to a temperature of 35 ° C. to obtain a dispersion containing an ion exchange resin. The resulting dispersion containing the ion exchange resin has a zeta potential of −39 mV at a temperature of 35 ° C. Subsequently, the same operation as in Example 6 is performed except that the constant temperature water bath is set to a temperature of 35 ° C. to obtain a coating liquid. The resulting coating liquid has a zeta potential of −33 mV at a temperature of 35 ° C. When this coating solution is maintained at a temperature of 35 ° C. and operated in the same manner as in Example 1, a membrane electrode assembly is produced. Tables 1 and 2 show the results obtained by evaluating in the same manner as in Example 1 using this membrane / electrode assembly.

[Example 10]
In Example 6, instead of using a constant temperature water bath, a dispersion treatment was performed in an autoclave at a temperature of 125 ° C. for 1 hour, and then left to cool to room temperature (temperature of 20 ° C.). Operation is performed to obtain a dispersion containing an ion exchange resin. The resulting dispersion containing the ion exchange resin has a zeta potential of −35 mV at a temperature of 20 ° C. Subsequently, the same operation as in Example 6 is performed except that the operation is performed at room temperature (temperature 20 ° C.) without using a constant temperature water bath, to obtain a coating liquid. The resulting coating liquid has a zeta potential of −30 mV at a temperature of 20 ° C. When this coating solution is maintained at a temperature of 20 ° C. and operated in the same manner as in Example 1, a membrane / electrode assembly is produced. Tables 1 and 2 show the results obtained by evaluating in the same manner as in Example 1 using this membrane / electrode assembly.

Sectional drawing which shows the embodiment of the membrane electrode assembly for polymer electrolyte fuel cells of this invention.

Explanation of symbols

1: solid polymer electrolyte membrane,
2: Anode catalyst layer,
3: Cathode catalyst layer,
4, 4 ': Gas diffusion layer,
5: Separator,
5a: separator gas supply groove,
6: Gas seal body,
7: Membrane electrode assembly.

Claims (5)

A membrane electrode assembly for a polymer electrolyte fuel cell, comprising a cathode and an anode having a catalyst layer containing a catalyst powder and a cation exchange resin, and a polymer electrolyte membrane disposed between the cathode and the anode. A manufacturing method comprising:
The cation exchange resin and a dispersion medium containing alcohol are mixed to prepare a dispersion, and then heated to a temperature of 40 to 120 ° C., whereby the zeta potential of the particles in the dispersion is changed from negative (minus). In this state, the catalyst powder is changed so that the mass ratio of the catalyst powder to the cation exchange resin in terms of solid content is 50:50 to 85:15. Adding and mixing to produce a coating liquid in which the solid content concentration is 0.1 to 20% by mass and the zeta potential of particles in the liquid is positive (plus);
Applying the coating solution onto a substrate and forming a catalyst layer by drying;
And disposing the catalyst layer adjacent to the polymer electrolyte membrane as at least one of a cathode and an anode catalyst layer,
A process for producing a membrane / electrode assembly for a polymer electrolyte fuel cell, wherein   The method for producing a membrane electrode assembly for a polymer electrolyte fuel cell according to claim 1, wherein the catalyst powder is added to and mixed with the dispersion in a state where the zeta potential of particles in the dispersion is +10 to +160 mV. A membrane electrode assembly for a polymer electrolyte fuel cell, comprising a cathode and an anode having a catalyst layer containing a catalyst powder and a cation exchange resin, and a polymer electrolyte membrane disposed between the cathode and the anode. A manufacturing method comprising:
The catalyst powder, the cation exchange resin and a dispersion medium containing alcohol are mixed so that the mass ratio of the catalyst powder and the cation exchange resin in terms of solid content is 50:50 to 85:15, A step of producing a coating liquid in which the solid content concentration is 0.1 to 20% by mass and the zeta potential of particles in the liquid is positive (plus) by heating to a temperature of 40 to 120 ° C. and stirring;
Applying the coating solution onto a substrate and forming a catalyst layer by drying;
And disposing the catalyst layer adjacent to the polymer electrolyte membrane as at least one of a cathode and an anode catalyst layer,
A process for producing a membrane / electrode assembly for a polymer electrolyte fuel cell, wherein   The production of a membrane electrode assembly for a polymer electrolyte fuel cell according to any one of claims 1 to 3, wherein the coating liquid is applied in a state where the zeta potential of particles in the coating liquid is +5 to +100 mV. Method. The cation exchange _{resin, CF 2 = CF- (OCF 2} CFX) m -O p - (CF 2) a perfluorovinyl compound represented by n -SO ₃ H (m is an integer of 0 to 3, n represents an integer of 1 to 12, p represents 0 or 1, and X represents a fluorine atom or a trifluoromethyl group.) and a copolymer comprising a polymer unit based on tetrafluoroethylene The method for producing a membrane electrode assembly for a polymer electrolyte fuel cell according to any one of claims 1 to 4.

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