JP2018181676A - Method for producing catalyst layer for fuel cell and electrode catalyst mixture - Google Patents

Abstract

An object of the present invention is to provide a method for producing an electrode catalyst layer which can improve battery performance under dry conditions while maintaining battery performance under wet conditions.
A catalyst carrier and an electrode catalyst composed of a catalyst metal supported on the catalyst carrier are brought into contact with a dispersion medium containing water as a main component, and then a polymer electrolyte is further mixed to obtain a composition. Forming the catalyst layer using the composition, wherein the contact is maintained until the cumulative volume fraction of the electrode catalyst particle size of 1 μm or less is more than 0%. Production method.
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Description

  The present invention relates to a method of producing a catalyst layer for a fuel cell and an electrode catalyst mixture.

  A polymer electrolyte fuel cell (PEFC) using a proton conductive solid polymer membrane has a low temperature as compared to other types of fuel cells such as, for example, solid oxide fuel cells and molten carbonate fuel cells Operate. For this reason, the polymer electrolyte fuel cell is expected as a stationary power source and a power source for mobile bodies such as automobiles, and its practical use has also been started.

  The configuration of the PEFC generally has a structure in which a membrane-electrode assembly (MEA) is sandwiched by separators. An MEA generally has a structure in which a gas diffusion layer, a cathode catalyst layer, a solid polymer electrolyte membrane, an anode catalyst layer, and a gas diffusion layer are stacked.

  In MEA, the following electrochemical reactions proceed. First, hydrogen contained in the fuel gas supplied to the anode (fuel electrode) side is oxidized by the catalyst to become protons and electrons. Next, the generated protons pass through the polymer electrolyte contained in the anode catalyst layer and the solid polymer electrolyte membrane in contact with the anode catalyst layer to reach the cathode (air electrode) catalyst layer. In addition, the electrons generated in the anode catalyst layer are a conductive carrier constituting the anode catalyst layer, and a gas diffusion layer, a gas separator and an external circuit in contact with the anode catalyst layer on the side different from the solid polymer electrolyte membrane. Reaches the cathode catalyst layer. Then, the protons and electrons reached the cathode catalyst layer react with oxygen contained in the oxidant gas supplied to the cathode catalyst layer to generate water. In the fuel cell, electricity can be extracted to the outside through the above-described electrochemical reaction. The catalyst used for the catalyst layer usually comprises a catalyst metal such as platinum or platinum alloy supported on a catalyst carrier such as a carbon material.

  As a method for producing an electrode catalyst layer, representatively, an electrode catalyst slurry prepared by mixing an electrode catalyst and a solid polymer electrolyte solution is applied to a substrate and dried, and the method can be mentioned. . For example, Patent Document 1 describes that an alcohol is added to a dispersion aqueous solution in which catalyst-supporting particles and water are mixed, and then an ionomer solution is added.

JP, 2014-192070, A

  However, the method described in Patent Document 1 has a problem that although the battery performance under the wet condition is relatively high, the battery performance under the dry condition is deteriorated.

  Then, an object of this invention is to provide the manufacturing method of the electrode catalyst layer which can improve the battery performance under dry conditions, maintaining the battery performance under wet conditions.

  Another object of the present invention is to provide an electrode catalyst mixture capable of improving cell performance under dry conditions while maintaining cell performance under wet conditions.

  In the present invention, a composition is obtained by bringing a catalyst carrier and an electrode catalyst composed of a catalyst metal supported on the catalyst carrier into contact with a dispersion medium containing water as a main component, and then further mixing a polymer electrolyte. Forming a catalyst layer using the composition, and maintaining the contact until the cumulative volume fraction of the electrode catalyst particle diameter of 1 μm or less is more than 0%; is there.

  The present invention is also a catalyst mixture comprising a catalyst support and an electrode catalyst for a fuel cell comprising a catalyst metal supported on the catalyst support, and a dispersion medium containing water as a main component, and the particle size of the electrode catalyst is 1 μm. An electrocatalyst mixture, wherein the cumulative volume fraction below is greater than 0%.

  By applying the electrode catalyst layer obtained by the method for producing an electrode catalyst of the present invention or an electrode catalyst layer formed using the electrode catalyst mixture of the present invention to a membrane electrode assembly, battery performance under wet conditions Cell performance under dry conditions can be improved.

It is a figure explaining the mechanism by this invention. BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic sectional drawing which shows the basic composition of the polymer electrolyte fuel cell which concerns on one Embodiment of this invention. It is a figure which shows the proton transport resistance of the membrane electrode assembly obtained by the Example and the comparative example.

  In the first embodiment of the present invention, a catalyst carrier and an electrode catalyst composed of a catalyst metal supported on the catalyst carrier are brought into contact with a dispersion medium containing water as a main component, and then a polymer electrolyte is further mixed. A composition for forming a catalyst layer using the composition, wherein the contact is maintained until the cumulative volume fraction of the electrode catalyst particle size of 1 .mu.m or less is more than 0%. It is a manufacturing method of a catalyst bed.

  A second embodiment of the present invention is a catalyst mixture comprising a catalyst carrier and a fuel cell electrode catalyst composed of a catalyst metal supported on the catalyst carrier, and a dispersion medium containing water as a main component, It is an electrode catalyst mixture in which the cumulative volume fraction of the particle diameter of 1 μm or less of the catalyst is more than 0%.

  Hereinafter, an electrode catalyst for a fuel cell consisting of a catalyst carrier and a catalyst metal supported on the catalyst carrier may be simply referred to as an electrode catalyst, and a dispersion medium containing water as a main component may be referred to simply as a dispersion medium.

  By applying the electrode catalyst layer obtained by the method for producing the electrode catalyst of the first embodiment or the electrode catalyst layer formed using the electrode catalyst mixture of the second embodiment to a membrane electrode assembly under wet conditions The battery performance under dry conditions can be improved while maintaining the battery performance under The mechanism by which both embodiments produce such an effect is presumed as follows. The technical scope of the present invention is not limited to the following mechanism.

  Fuel cell performance (activity) is influenced by the transport properties of the reactive gas (eg, protons) to the catalytic metal in addition to the activity of the catalytic metal itself. Therefore, from the vicinity of the catalyst metal to the catalyst layer, the formation of structures on various scales becomes the governing factor of the fuel cell performance (activity) through the influence on the reaction gas transport characteristics.

  The protons generated on the anode side are transported to the cathode side through the polymer electrolyte and the polymer electrolyte membrane in the electrode catalyst. At this time, for example, in a perfluorocarbon sulfonic acid-based polymer such as Nafion (registered trademark, manufactured by DuPont), protons move through a sulfonic acid group in the polymer. Under dry conditions, the mobility of the polymer electrolyte side chain having a sulfonic acid group responsible for proton transport is reduced, and thus the proton transportability via the polymer electrolyte is reduced. For this reason, generally, under dry conditions, proton transport is disadvantageous, which tends to cause deterioration of the cell performance.

  On the other hand, a carbon material generally used as a catalyst carrier constituting an electrode catalyst has a primary particle diameter on the order of several tens of nm, and is easily aggregated by van der Waals attraction, and has a hydrophobic surface. In the solvent, aggregation tends to occur due to the hydrophobic effect. When the electrode catalyst is aggregated, the catalytically active component present inside the electrode catalyst aggregate can not contribute to the reaction, which causes a decrease in battery performance.

  In the present embodiment, it is intended to gently loosen the aggregates of the electrode catalyst by bringing the electrode catalyst into contact (immersion) with the dispersion medium. Since the dispersion medium contains water as a main component, it is difficult to adsorb to the catalyst carrier having a hydrophobic surface originally, and the dispersion medium does not easily permeate between the particles. However, when the electrode catalyst is immersed in the dispersion medium for a relatively long time, water is adsorbed between the particles of the aggregate of the catalyst support, and further, it is considered that the aggregate is broken by water entering between the particles. . In addition, the water which has entered enters into the electrode catalyst particles (see FIG. 1). It is considered that the adsorbed water adsorbed to the particles repels the surface of the catalyst carrier which is hydrophobic, and repulsion that occurs can suppress the particles from being reaggregated.

  Further, as described above, the presence of the adsorbed water on the electrode catalyst makes it easy for the side chain of the polymer electrolyte to approach the electrode catalyst. By forming an electrode catalyst layer using such a composition, an electrode catalyst layer in which a sulfonic acid group in a side chain approaches the electrode catalyst can be obtained. Therefore, the side chain in the vicinity of the electrode catalyst suppresses the decrease in proton transportability even under dry conditions.

  Therefore, the catalyst metal present on the electrode catalyst particles can be effectively utilized by breaking up the aggregates of the electrode catalyst and maintaining the state. Further, by forming the catalyst layer using a composition in which water exists around the electrode catalyst, it is considered that the transportability of protons is improved, and the battery performance is improved even under dry conditions.

  On the other hand, under wet conditions, oxygen transport in the catalyst layer is generally disadvantageous. According to the configuration of the present embodiment, in the composition for forming the electrode catalyst layer, the hydrophobic polymer electrolyte main chain can not approach the electrode catalyst due to the presence of the adsorbed water on the surface of the electrode catalyst. Therefore, the reaction gas can be directly supplied to the catalyst metal at a predetermined ratio or more without interposing the polymer electrolyte, and oxygen gas can be transported to the catalyst metal more quickly and more efficiently. Therefore, it is considered that oxygen transportability is improved and high power generation performance can be maintained even under wet conditions.

  Therefore, a membrane electrode assembly and a fuel cell having an electrode catalyst layer obtained by the method for producing an electrode catalyst according to the first embodiment, or an electrode catalyst layer formed using the electrode catalyst mixture according to the second embodiment are wet While maintaining high power generation performance under conditions, high power generation performance can be exhibited even under dry conditions.

  Hereafter, each process in the manufacturing method of the catalyst layer for fuel cells of 1st embodiment is demonstrated. In the present specification, “X to Y” indicating a range includes X and Y, and means “X or more and Y or less”. Moreover, unless otherwise indicated, measurement of operation, a physical property, etc. is performed on the conditions of room temperature (20-25 degreeC) / relative humidity 40-50% RH.

(I) A step of contacting an electrode catalyst and a dispersion medium containing water as a main component and maintaining the contact until the cumulative volume fraction of the particle diameter of 1 μm or less of the electrode catalyst becomes more than 0% to obtain an electrode catalyst mixture Prepare an electrode catalyst.

  The electrode catalyst comprises a catalyst carrier and a catalyst metal supported on the catalyst carrier.

  The catalyst support functions as a support for supporting the above-described catalyst component and an electron conduction path involved in the exchange of electrons between the catalyst component and other members. The catalyst support may have any specific surface area for supporting the catalyst particles in a desired dispersed state and have sufficient electron conductivity as a current collector, but it has conductivity and durability. From the viewpoint, the catalyst support is preferably a carbon material. Specific examples of the carbon material include carbon blacks such as acetylene black, channel black, oil furnace black, gas furnace black (eg, Vulcan), lamp black, thermal black, black pearl, ketjen black (registered trademark); Black pearl, graphitized acetylene black, graphitized channel black, graphitized oil furnace black, graphitized gas furnace black, graphitized lamp black, graphitized thermal black, graphitized ketjen black, graphitized black pearl, carbon nanotube, carbon nanotube Examples include nanofibers, carbon nanohorns, carbon fibrils, activated carbon, coke, natural graphite, artificial graphite and the like. In addition, as a conductive support, zeolite template carbon (ZTC) having a structure in which nano-sized band-shaped graphenes are regularly connected in a three-dimensional manner can also be mentioned. These may be used alone or in combination of two or more. The term "carbon material" as used herein means to contain carbon atoms as the main component, and is a concept including both carbon atoms only and carbon atoms substantially, and elements other than carbon atoms are included. It may be done. "Consisting essentially of carbon atoms" means that incorporation of impurities of about 2 to 3% by weight or less is acceptable.

The BET specific surface area of the catalyst carrier may be a specific surface area sufficient for supporting the catalyst in a highly dispersed manner. The BET specific surface area of the catalyst carrier (the catalyst carrier precursor before supporting the catalyst) is preferably 500 m ² / g or more, and more preferably 550 m ² / g or more. If the specific surface area is in the range as described above, the catalyst is sufficiently dispersed in the catalyst carrier to obtain sufficient power generation performance, and the catalyst can be sufficiently used effectively and the oxygen transport resistance can be easily controlled low. The upper limit of the BET specific surface area of the catalyst carrier is preferably at 2000 m ² / g or less, and more preferably less 1500 m ² / g. The catalyst carrier may be a commercially available product, or may be produced by a known method described in, for example, JP 2010-208887 A, WO 2009/075264, and the like.

In the present specification, “BET specific surface area (m ² / g catalyst support)” is measured by a nitrogen adsorption method. Specifically, about 0.04 to 0.07 g of a sample (carbon powder, catalyst powder) is precisely weighed and sealed in a sample tube. The sample tube is predried at 90 ° C. for several hours in a vacuum dryer to obtain a measurement sample. For weighing, an electronic balance (AW 220) manufactured by Shimadzu Corporation is used. In the case of a coated sheet, a net weight of about 0.03 to 0.04 g of a coated layer obtained by subtracting the weight of Teflon (substrate) of the same area from the total weight of the coated sheet is used as a sample weight . Next, the BET specific surface area is measured under the following measurement conditions. By creating a BET plot from the range of relative pressure (P / P0) of about 0.00 to 0.45 on the adsorption side of the adsorption / desorption isotherm, the BET specific surface area is calculated from the slope and the intercept.

  Besides the above-mentioned carbon materials, porous metals such as Sn (tin) and Ti (titanium), and further conductive metal oxides can be used as the carrier. In view of the effects of the present embodiment, the catalyst carrier is preferably particles.

  Further, the size of the catalyst carrier is not particularly limited, but from the viewpoints of ease of loading, catalyst utilization, and control of the thickness of the electrode catalyst layer in an appropriate range, the average primary particle diameter is 5 to 200 nm, Preferably, it is about 10 to 100 nm. The average primary particle diameter is a value calculated as an average value of particle diameters of particles observed in several to several tens of fields using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM) Shall be adopted.

  In the electrode catalyst in which the catalyst metal is supported on the catalyst carrier, the loading amount of the catalyst metal is preferably 10 to 80% by weight, more preferably 20 to 60% by weight, with respect to the total amount of the electrode catalyst. If the loading amount of the catalyst metal is a value within such a range, the balance between the degree of dispersion of the catalyst metal on the catalyst carrier and the catalyst performance can be appropriately controlled. In the present invention, the “catalyst metal supporting ratio” is a value obtained by measuring the weight of the carrier before supporting the catalyst metal and the catalyst after supporting the catalyst metal.

  The catalyst metal which comprises an electrode catalyst has the function to catalyze the electrochemical reaction. The catalyst metal used in the anode catalyst layer is not particularly limited as long as it has a catalytic effect on the oxidation reaction of hydrogen, and known catalysts can be used in the same manner. The catalyst metal used in the cathode catalyst layer is also not particularly limited as long as it has a catalytic action for the reduction reaction of oxygen, and known catalysts can be used in the same manner. Specifically, metals such as platinum, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, copper, silver, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, and alloys thereof It can be selected from

  Among these, those containing at least platinum are preferably used in order to improve catalytic activity, poisoning resistance to carbon monoxide and the like, heat resistance and the like. That is, the catalyst metal is preferably platinum or contains platinum and a metal component other than platinum, and more preferably platinum or a platinum-containing alloy. Such catalytic metals can exhibit high activity. Although the composition of the alloy depends on the type of metal to be alloyed, the content of platinum is preferably 30 to 90 atomic%, and the content of metal to be alloyed with platinum is preferably 10 to 70 atomic%. In addition, an alloy is generally a metal element to which one or more metal elements or nonmetal elements are added, and is a generic term for alloys having metallic properties. The structure of the alloy includes a eutectic alloy which is a so-called mixture in which component elements become separate crystals, one in which component elements completely dissolve and a solid solution, and a component element is an intermetallic compound or a compound of metal and nonmetal. There are those which are formed, and any of them may be used in the present invention. At this time, the catalyst metal used for the anode catalyst layer and the catalyst metal used for the cathode catalyst layer can be appropriately selected from the above. In the present specification, unless otherwise specified, descriptions of catalyst metals for the anode catalyst layer and the cathode catalyst layer have the same definitions for both. However, the catalyst metals of the anode catalyst layer and the cathode catalyst layer do not have to be the same, and can be appropriately selected so as to exert the desired action as described above.

  The shape and size of the catalyst metal (catalyst component) are not particularly limited, and the same shape and size as those of known catalyst components may be employed. As the shape, for example, granular, scaly, layered and the like can be used, but is preferably granular. At this time, the average particle size of the catalyst metal particles is preferably 1 to 30 nm, more preferably 2 to 10 nm. When the average particle size of the catalyst metal particles is a value within such a range, the balance between the catalyst utilization rate and the ease of support related to the effective electrode area in which the electrochemical reaction proceeds can be appropriately controlled. In the present specification, “the average particle size of catalyst metal particles” refers to the crystallite radius determined from the half width of the diffraction peak of the catalyst metal component in X-ray diffraction, and the catalyst examined from transmission electron microscopy (TEM) It can be measured as the average value of the particle radius of metal particles. In the present specification, the “average particle diameter of catalyst metal particles” is a crystallite radius determined from the half-width of the diffraction peak of the catalyst metal component in X-ray diffraction.

  The method for producing the electrode catalyst (the method for supporting the metal catalyst on the catalyst carrier precursor) is not particularly limited, and a conventionally known method can be used. For example, known methods such as liquid phase reduction, evaporation to dryness, colloid adsorption, spray pyrolysis, reverse micelle (microemulsion) can be used. Alternatively, a commercially available product may be used as the electrode catalyst.

  As a method for producing a catalyst by liquid phase reduction, there is a method of performing heat treatment after depositing a catalyst metal on the surface of a catalyst support precursor. Specifically, for example, a method of performing heat treatment after immersing the catalyst carrier in a precursor solution of a catalyst metal, reducing using a reducing agent, and the like can be mentioned.

  Here, the precursor of the catalyst metal is not particularly limited, and is appropriately selected depending on the type of catalyst metal used. Specifically, chlorides, nitrates, sulfates, chlorides, acetates and amine compounds of catalyst metals such as platinum can be exemplified. More specifically, chlorides such as platinum chloride (hexachloroplatinic acid hexahydrate), palladium chloride, rhodium chloride, ruthenium chloride, cobalt chloride, etc., nitrates such as palladium nitrate, rhodium nitrate, iridium nitrate, palladium sulfate, sulfuric acid Sulfates such as rhodium, acetates such as rhodium acetate, dinitrodiammine platinum nitrate, ammine compounds such as dinitrodiammine palladium, etc. are preferred and exemplified. Moreover, the solvent used for preparation of the precursor solution of the catalyst metal is not particularly limited as long as it can dissolve the precursor of the catalyst metal, and is appropriately selected according to the type of the precursor of the catalyst metal used. Specifically, water, an acid, an alkali, an organic solvent etc. are mentioned. The concentration of the catalyst metal precursor in the catalyst metal precursor solution is not particularly limited, but is preferably 0.1 to 50% by weight, more preferably 0.5 to 20% by weight in terms of metal. .

  As the reducing agent, hydrogen, hydrazine, sodium borohydride, sodium thiosulfate, citric acid, sodium citrate, L-ascorbic acid, sodium borohydride, formaldehyde, methanol, ethanol, ethylene, carbon monoxide and the like can be mentioned. . Note that a gaseous substance at normal temperature such as hydrogen can also be supplied by bubbling. The amount of the reducing agent is not particularly limited as long as the precursor of the catalyst metal can be reduced to the catalyst metal, and known amounts can be similarly applied.

  The deposition conditions are not particularly limited as long as the catalyst metal can deposit on the catalyst carrier. For example, the deposition temperature is preferably a temperature near the boiling point of the solvent, more preferably room temperature to 100 ° C. Moreover, it is preferable that precipitation time is 1 to 10 hours, More preferably, it is 2 to 8 hours. In addition, the said precipitation process may be performed, stirring and mixing if needed. As a result, the precursor of the catalyst metal is reduced to the catalyst metal, and the catalyst metal is deposited (supported) on the catalyst carrier.

  As the heat treatment conditions, for example, the heat treatment temperature is preferably 300 to 1200 ° C., more preferably 500 to 1150 ° C., and particularly preferably 700 to 1000 ° C. The heat treatment time is 0.02 to 3 hours, more preferably 0.1 to 2 hours, and particularly preferably 0.2 to 1.5 hours. In consideration of the reduction promotion effect of the catalyst metal precursor, the heat treatment step is preferably performed in an atmosphere containing hydrogen gas, more preferably in a hydrogen atmosphere.

  Then, the electrode catalyst and a dispersion medium containing water as a main component are brought into contact with each other.

  The main component in the dispersion medium containing water as a main component means that the content of water is 80% by weight or more (upper limit 100% by weight) to the dispersion medium, preferably 90% by weight or more (upper limit 100% by weight). And more preferably 100% by weight of water, that is, the dispersion medium is water. When the proportion of water in the dispersion medium is high, the repulsion between the dispersion medium (in particular, water) and the electrode catalyst which enter between the particles becomes large, and it is possible to suppress the reaggregation of the loosened aggregate again. Furthermore, because the proportion of water in the dispersion medium is high, the presence of the dispersion medium (particularly water) adsorbed to the electrode catalyst makes it difficult for the polymer electrolyte to approach the electrode catalyst, thereby improving the proton transportability under dry conditions. The oxygen transportability under wet conditions is also maintained high.

  Here, water is not particularly limited, and tap water, purified water, ion exchanged water, distilled water and the like can be used. The dispersion medium may contain a hydrophilic solvent other than water. As the hydrophilic solvent, methanol, ethanol, isopropyl alcohol, ethylene glycol, diethylene glycol, propylene glycol and the like can be mentioned. The hydrophilic solvents may be used alone or in combination of two or more.

  The contact between the electrode catalyst and the dispersion medium is performed until the cumulative volume fraction of the particle diameter of 1 μm or less of the electrode catalyst is more than 0%. That is, the process is performed until particles close to the primary particle diameter of the electrode catalyst appear. By maintaining the contact of the dispersion medium with the electrode catalyst, water enters the inside of the aggregates and breaks up the aggregates, so that particles with a catalyst particle size close to the primary particle diameter will be present, as well as adsorbed water on the particles. Is considered to be present. More preferably, the contact between the electrode catalyst and the dispersion medium is maintained when the cumulative volume fraction of the particle diameter of 1 μm or less of the electrode catalyst is 2.5% or more (upper limit 100%), more preferably 3.5% or more It is preferable to carry out until it becomes 4.5% or more, most preferably 5.0% or more. The larger the cumulative volume fraction of the particle diameter of 1 μm or less of the electrode catalyst, the larger the better, so the upper limit is not specified, but it is usually 40.0% or less.

  In addition, “the contact of the electrode catalyst and the dispersion medium is performed until the cumulative volume fraction of the particle diameter of 1 μm or less of the electrode catalyst is more than 0%” means that the cumulative volume fraction of the particle diameter of 1 μm or less of the electrode catalyst is 0 If it becomes more than%, it means that maintenance of contact may be stopped at any time.

  When the peak particle diameter of the electrode catalyst before contact is 100, specifically, the contact of the electrode catalyst and the dispersion medium is preferably performed until the peak particle diameter of the electrode catalyst becomes 95 or less. As described above, the aggregation of the electrode catalyst may be due to van der Waals attraction between particles, or due to the hydrophobization effect in the dispersion medium. The aggregation prior to the dispersion medium contact is due to the van der Waals attraction between the particles, and is generally smaller than the peak particle size after the dispersion medium contact. Therefore, by making the contact of the electrode catalyst and the dispersion medium smaller than the peak particle diameter of the electrode catalyst before the dispersion medium contact, both the van der Waals attraction between particles and the hydrophobization effect in the dispersion medium can be obtained. It becomes smaller than the peak particle diameter of the aggregate formed due to it. By thus reducing the peak particle size, the particle size of the electrode catalyst can be further reduced. Here, as the peak particle diameter of the electrode catalyst, a value calculated based on the particle size distribution measurement conditions described in the following examples is employed. When the peak particle diameter of the electrode catalyst before contact is 100, the contact of the electrode catalyst and the dispersion medium is preferably 90 or less, and the contact of the electrode catalyst and the dispersion medium is 80 or less It is more preferable to In addition, in the contact of an electrode catalyst and a dispersion medium, when the peak particle diameter of an electrode catalyst is set to 100, even if it continues a contact, it saturates at about 10 about. In a preferred embodiment, when the peak particle diameter of the electrode catalyst before contact is 100, it is preferable to contact the electrode catalyst and the dispersion medium so that the peak particle diameter of the electrode catalyst is 50 to 80.

  The peak particle size of the electrode catalyst in the dispersion medium and the cumulative volume fraction of the particle size of 1 μm or less of the electrode catalyst are determined as follows. A sample is prepared by diluting the mixture of the electrode catalyst and the dispersion medium with 2-propanol to a solid concentration of 1.0% by weight. Next, the particle size distribution of this sample is measured under the following conditions. The particle diameter calculated by the following particle size distribution measurement conditions is volume based.

  In addition, the peak particle diameter of the electrode catalyst before contacting with the dispersion medium measures the particle diameter distribution under the above-described particle diameter distribution measurement conditions.

  From the obtained particle size distribution (particle size-volume fraction frequency curve), the cumulative particle volume and peak volume diameter and the cumulative volume fraction with a particle size of 1 μm or less are determined.

  Here, the method of controlling the cumulative volume fraction of the particle diameter of 1 μm or less of the electrode catalyst of the electrode catalyst mixture to 0% or more is not particularly limited, but (1) time for maintaining the contact of the electrode catalyst and the dispersion medium, (2) It has been revealed that controlling at least one selected from the group consisting of stirring conditions of the dispersion liquid in which the electrode catalyst is dispersed in the dispersion medium is particularly important for controlling the peak particle diameter of the electrode catalyst small. did. The above will be described in detail below. Needless to say, the method is not limited to the methods (1) and (2).

(1) Time of Contact State Maintaining the contact of the electrode catalyst and the dispersion medium is preferably 24 hours or more, and more preferably 48 hours or more. By setting the contact state to 24 hours or more, the dispersion medium is sufficiently spread in the electrode aggregate, and the dispersion medium is easily introduced between the electrode catalyst particles, and the peak particle diameter of the electrode catalyst can be sufficiently reduced. The upper limit of the contact maintenance is not particularly defined because the peak particle diameter of the electrode catalyst can be reduced as the time is longer. However, when the contact is maintained for a certain time or more, the effect is saturated. For this reason, the maintenance of the contact is preferably 200 hours or less, more preferably 180 hours or less, in consideration of saturation of effects and productivity.

(2) Stirring Conditions of Dispersion Liquid in which Electrode Catalyst is Dispersed in Dispersion Medium It is preferable that the maintenance of the contact be performed with standing or under stirring, more preferably under stirring.

  In addition, when maintaining a contact under stirring, in order to prevent evaporation of the solvent accompanying long-time stirring, it is preferable to carry out by a closed system.

  At this time, since stirring is performed for a relatively long time in the present embodiment, it is preferable to carry out under relatively mild conditions with a shear force that does not damage the electrode catalyst due to the stirring for a long time. As a suitable stirrer used at this time, a tip-to-bottom rotary stirrer: mix rotor (manufactured by As One Corporation), a magnetic stirrer, a stirrer with a stirring blade, etc. may be mentioned. Above all, since the effect of the present invention is easily exhibited, it is preferable to maintain the contact under stirring using a tip-to-bottom rotary stirrer.

  The overturning rotary agitator is a device that rotates the container at a certain angle, and the rotation direction of the container is a rotation that rotates the entire container around a central point, even if rotation is about the container axis. It is also good. Preferably, it is an overturning rotation type agitator of rotation. However, the overturn rotary stirrer herein does not include a rotation / revolution stirrer with both rotation and revolution.

  Stirring conditions for stirring using the overturning rotary stirrer may be set as appropriate, but for example, in the case of a rotating overturning rotary stirrer, it is preferable to set the rotation speed to 0.1 to 5 revolutions / minute, 0 It is more preferable to set it to .5 to 3 revolutions / minute.

  Moreover, it is preferable to perform pre-mixing of the electrode catalyst and the dispersion medium before maintaining the contact of the electrode catalyst and the dispersion medium. By performing the pre-mixing, the electrode catalyst can easily conform to the dispersion medium, and the time for subsequent micronization can be shortened.

  As a stirring apparatus in the case of pre-mixing, mixers, such as a rotation revolution revolution mixer, a planetary mixer, a homomixer, and dispersers, such as an ultrasonic dispersion machine and a jet mill, are mentioned.

  Among them, it is preferable to perform the pre-mixing using a rotation / revolution stirrer such as a rotation-revolution mixer. By pre-mixing with the rotation / revolution stirrer, the electrode catalyst can easily conform to the dispersion medium, and the time for which the aggregates are loosened by the subsequent immersion can be shortened. A rotation / revolution type agitator rotates the container itself counterclockwise while rotating the container clockwise, and acts on the material in the container using the centrifugal force generated by high-speed rotation / revolution as a pressing force. The material is dispersed by continuously generating vortex-like upper and lower convection. As a dispersing device of the rotation / revolution type stirrer, Awatori Neritaro (registered trademark) (made by Shinky Co., Ltd.) or the like is used.

  That is, according to a preferred embodiment of the present embodiment, after the electrode catalyst and the dispersion medium are premixed by the rotation / revolution stirrer, the catalyst electrode catalyst is stirred, preferably under stirring using the overturning rotary stirrer. And in the form of maintaining the contact of the dispersion medium.

  In a further preferred embodiment of the present embodiment, after the electrode catalyst and the dispersion medium are premixed by the rotation / revolution stirrer, the catalyst electrode is stirred under stirring, preferably under stirring using the overturn rotary stirrer. The contact state of the catalyst and the dispersion medium is maintained for 24 hours or more.

  However, the rotation / revolution stirrer has a relatively strong stirring power, and long-time stirring may damage the electrode catalyst itself, and the catalyst activity may be reduced. Therefore, the pre-mixing time is preferably 5 minutes or less, more preferably 2 minutes or less. In addition, the pre-mixing time is preferably 10 seconds or more, and more preferably 30 seconds or more, since the effect of the pre-mixing can be more easily obtained.

  The stirring conditions of the rotation / revolution type stirrer may be set as appropriate. For example, it is preferable to set the number of rotations of rotation to 100 to 400 rotations / minute, and more preferably 200 to 300 rotations / minute. Moreover, it is preferable to set it as 200-800 rotation / min, and, as for the rotation speed of revolution, it is more preferable to set it as 400-600 rotation / min.

  Thus, an electrode catalyst mixture (for forming a fuel cell catalyst layer) comprising a fuel cell electrode catalyst comprising a catalyst carrier and a catalyst metal supported on the catalyst carrier and a dispersion medium containing water as a main component is obtained. Can.

  The electrocatalyst mixture preferably has a cumulative volume fraction of the electrode catalyst having a particle diameter of 1 μm or less of more than 0%. That is, preferably, it is an electrode catalyst mixture comprising a fuel cell electrode catalyst comprising a catalyst carrier and a catalyst metal supported on the catalyst carrier, and a dispersion medium containing water as a main component, and the particle diameter of the electrode catalyst is 1 μm An electrode catalyst mixture (for forming a fuel cell electrode catalyst layer) having the following cumulative volume fraction of more than 0%: An electrode catalyst mixture in which small particles having a particle diameter of 1 μm or less are present at a certain level or less can effectively utilize the catalyst metal on the catalyst support since there are few aggregates of the electrode catalyst. Therefore, the power generation performance is excellent. In addition, the adsorbed water present on the electrode catalyst suppresses aggregation of the particles again, and the polymer electrolyte becomes difficult to approach the electrode catalyst, and the proton transportability under dry conditions is improved, and the wet conditions are also included. The oxygen transportability below is also maintained high. In the mixture, the cumulative volume fraction of the particle diameter of 1 μm or less of the electrode catalyst is 2.5% or more (upper limit 100%), more preferably 3.5% or more, more preferably 4.5% or more, most preferably 5. It is 0% or more.

  The electrode catalyst mixture may be mixed with a polymer electrolyte as it is, or the electrode catalyst may be separated from the dispersion medium by filtration or the like. From the viewpoint of workability, the electrode catalyst mixture is preferably mixed with the polymer electrolyte as it is in the form of an aqueous dispersion, and from the viewpoint of dispersibility, the electrode catalyst mixture is in the form of an aqueous dispersion and preferably a solvent (preferably It is more preferable to mix with a polymer electrolyte dispersed in water and a mixed solvent of lower alcohol having 1 to 4 carbon atoms.

(II) After step (I), the step of further mixing the polymer electrolyte to obtain a composition. Next, the electrode catalyst mixture or the electrode catalyst separated from the electrode catalyst mixture is mixed with the polymer electrolyte to obtain a composition. .

  The composition is preferably a catalyst ink for forming a fuel cell catalyst layer (slurry, coating solution). Therefore, it is preferable to include a viscosity adjusting solvent for viscosity adjustment.

  The polymer electrolyte is not particularly limited, but is preferably an ion conductive polymer electrolyte. The above-mentioned polymer electrolyte plays a role of transferring protons generated around the catalyst active material on the fuel electrode side, and hence is also called a proton conductive polymer.

  The said polymer electrolyte is not specifically limited, Conventionally well-known knowledge may be referred suitably. Polymer electrolytes are roughly classified into fluorine-based polymer electrolytes and hydrocarbon-based polymer electrolytes, depending on the type of ion exchange resin that is the constituent material. Among these, fluorine-based polymer electrolytes are preferred in view of proton conductivity.

  Examples of the ion exchange resin constituting the fluorine-based polymer electrolyte include Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.), Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.), etc. Perfluorocarbon sulfonic acid based polymer, perfluorocarbon phosphonic acid based polymer, trifluorostyrene sulfonic acid based polymer, ethylene tetrafluoroethylene-g-styrene sulfonic acid based polymer, ethylene-tetrafluoroethylene copolymer, polyvinylidene fluoride per par Fluorocarbon sulfonic acid polymers and the like can be mentioned. From the viewpoint of excellent heat resistance, chemical stability, durability, and mechanical strength, these fluorine-based polymer electrolytes are preferably used, and particularly preferably a fluorine-based polymer electrolyte composed of a perfluorocarbon sulfonic acid-based polymer Is used.

  Specific examples of hydrocarbon-based electrolytes include sulfonated polyethersulfone (S-PES), sulfonated polyaryletherketone, sulfonated polybenzimidazole alkyl, phosphonated polybenzimidazole alkyl, sulfonated polystyrene, sulfonated poly Ether ether ketone (S-PEEK), sulfonated polyphenylene (S-PPP), etc. are mentioned. These hydrocarbon-based polymer electrolytes are preferably used from the viewpoint of production that the raw materials are inexpensive, the production process is simple, and the selectivity of materials is high. In addition, only 1 type may be used individually by 1 type of ion exchange resin mentioned above, and 2 or more types may be used together. Moreover, it is not limited only to the material mentioned above, Other materials may be used. Alternatively, a commercially available electrolyte solution (for example, Nafion solution manufactured by DuPont: dispersion / suspension of Nafion at a concentration of 5 wt% in 1-propanol) may be used, in which the electrolyte is previously prepared in a solvent. .

  In a polymer electrolyte responsible for proton transfer, the conductivity of protons is important. Here, when the EW of the polymer electrolyte is too large, the ion conductivity in the entire catalyst layer is lowered. Therefore, it is preferable that the catalyst layer of the present embodiment contains a polyelectrolyte having a small EW. Specifically, the catalyst layer in the present embodiment preferably contains a polyelectrolyte having an EW of 1,500 g / mol or less, more preferably a polyelectrolyte having an EW of 1200 g / mol or less. On the other hand, if the EW is too small, the hydrophilicity is too high, and the smooth movement of water becomes difficult. From such a viewpoint, the EW of the polymer electrolyte is preferably 600 g / mol or more. EW (Equivalent Weight) represents the equivalent weight of the exchange group having proton conductivity. The equivalent weight is the dry weight of the polyelectrolyte per equivalent of ion exchange group, and is expressed in units of "g / mol".

  The mixing ratio of the polymer electrolyte and the composition A is preferably such that the weight ratio (I / C ratio) of the polymer electrolyte (I) to the catalyst carrier (C) is 0.4 to 1.6. More preferably, it is 7 to 1.4.

  The solvent for viscosity adjustment is not particularly limited, and conventional solvents used to form a catalyst layer can be used in the same manner. Specifically, water, cyclohexanol, lower alcohols having 1 to 4 carbon atoms, propylene glycol, benzene, toluene, xylene and the like can be mentioned. Besides these, butyl acetate, dimethyl ether, ethylene glycol, etc. may be used as a solvent. These solvents may be used alone or in the form of a mixture of two or more.

  Water is not particularly limited, and tap water, purified water, ion exchanged water, distilled water and the like can be used. Also, the alcohol is not particularly limited. Specifically, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-methyl-1-propanol, 2-butanol, 2-methyl-2-propanol, cyclohexanol and the like can be mentioned. Among these, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-methyl-1-propanol, 2-butanol and 2-methyl-2-propanol are preferable. By using such a lower alcohol having high affinity, extreme uneven distribution of the electrolyte can be prevented. Moreover, among the above-mentioned alcohols, it is more preferable to use an alcohol having a boiling point of less than 100 ° C. As the alcohol having a boiling point of less than 100 ° C, methanol (boiling point: 65 ° C), ethanol (boiling point: 78 ° C), 1-propanol (boiling point: 97 ° C), 2-propanol (boiling point: 82 ° C), and 2-methyl What is selected from the group consisting of -2-propanol (boiling point: 83 ° C.) can be exemplified. The said alcohol can be used individually by 1 type or in mixture of 2 or more types.

  The amount of the viscosity control solvent added by necessity is not particularly limited as long as it can completely dissolve the electrolyte. Specifically, the concentration of the solid content of the combination of the electrode catalyst and the polymer electrolyte is preferably about 1 to 50% by weight, more preferably about 5 to 30% by weight in the composition.

  As described above, polymer electrolytes are roughly classified into fluorine-based polymer electrolytes and hydrocarbon-based polymer electrolytes, depending on the type of ion exchange resin that is the constituent material. Among these, the electrolyte is preferably a fluorine-based polymer electrolyte. Thus, by using the hydrophobic fluorine-based polymer electrolyte, a repulsive force is exerted between the water adsorbed to the electrode catalyst and the fluorine-based polymer electrolyte, and the fluorine-based polymer electrolyte becomes difficult to approach around the electrode catalyst. . Therefore, the battery performance under the dry condition and the wet condition is high.

  The order of addition of the electrode catalyst, the polymer electrolyte and the viscosity adjusting solvent is not particularly limited, and all are mixed at once; after mixing the electrode catalyst and the polymer electrolyte, the viscosity adjusting solvent is added and mixed, etc. It may be in the form of

  The composition for forming a fuel cell catalyst layer may be, if necessary, a water repellent such as polytetrafluoroethylene, polyhexafluoropropylene, tetrafluoroethylene-hexafluoropropylene copolymer, or a dispersant such as a surfactant. Additives such as thickeners such as glycerin, ethylene glycol (EG), polyvinyl alcohol (PVA), propylene glycol (PG), and a pore forming agent may be included.

  In addition, what is necessary is just to add these additives to a composition, when using additives, such as a water repellent, a dispersing agent, a thickener, and a pore making agent. Under the present circumstances, the addition amount of an additive will not be restrict | limited especially if it is a quantity which does not prevent the said effect of this invention. For example, the amount of additive added is preferably 5 to 20% by weight, based on the total weight of the composition.

  In this way, a composition comprising an electrocatalyst and a polyelectrolyte is obtained.

(III) Forming a catalyst layer using the composition obtained in step (II) The method for forming a catalyst layer using the composition obtained in step (II) is not particularly limited. It is preferable to apply a composition (catalyst ink) to the surface to form a catalyst layer.

  The method of applying the composition to the substrate is not particularly limited, and known methods can be used. Specifically, a known method such as a spray (spray application) method, a Gulliver printing method, a die coater method, a screen printing method, and a doctor blade method can be used.

  Under the present circumstances, a solid polymer electrolyte membrane (electrolyte layer) or a gas diffusion base material (gas diffusion layer) can be used as a base material which apply | coats a composition. In such a case, after forming a catalyst layer on the surface of a solid polymer electrolyte membrane (electrolyte layer) or a gas diffusion substrate (gas diffusion layer), the obtained laminate is used as it is for production of a membrane electrode assembly. It can be used. Alternatively, a peelable substrate such as polytetrafluoroethylene (PTFE) [Teflon (registered trademark)] sheet is used as a substrate, and after forming the catalyst layer on the substrate, the catalyst layer portion is peeled off from the substrate The catalyst layer may be obtained accordingly.

The application amount of the catalyst ink to the application substrate is not particularly limited. Specifically, the content (area weight) of catalyst metal per catalyst layer area (mg / cm ² ) is 0.5 mg / cm ² or less, preferably 0.4 mg / cm ² or less. The lower limit is not particularly limited as long as the power generation performance can be obtained, and is, for example, 0.01 mg / cm ² or more. In the present specification, inductively coupled plasma emission spectroscopy (ICP) is used to measure (confirm) the "content of platinum per catalyst layer area (mg / cm ² )". One skilled in the art can easily carry out the desired "content of platinum per area of catalyst layer" by adjusting the composition by controlling the composition of the slurry (catalyst concentration) and the amount applied. it can.

  Alternatively, the thickness (dry film thickness) of the catalyst layer is not particularly limited, but is preferably 1 to 20 μm, more preferably 2 to 15 μm. The above thickness is applied to both the cathode catalyst layer and the anode catalyst layer. However, the thicknesses of the cathode catalyst layer and the anode catalyst layer may be the same or different.

  Finally, the coated layer (film) of the catalyst ink is dried at room temperature to 150 ° C. for 1 to 60 minutes in an air atmosphere or an inert gas atmosphere.

  Thus, a fuel cell catalyst layer is obtained.

  Hereinafter, one of the catalyst layer obtained by the manufacturing method of the first embodiment or the electrode catalyst mixture of the second embodiment, the membrane electrode assembly (MEA), and the fuel cell, which are obtained by the manufacturing method of the first embodiment Embodiments will be described in detail. However, the present invention is not limited to the following embodiments. Each drawing is expressed exaggerated for convenience of explanation, and the dimensional ratio of each component in each drawing may differ from the actual. Further, in the case where the embodiment of the present invention is described with reference to the drawings, the same reference numerals are given to the same elements in the description of the drawings, and the overlapping description will be omitted.

[Fuel cell]
The fuel cell comprises a pair of separators comprising a membrane electrode assembly (MEA), an anode side separator having a fuel gas flow path through which a fuel gas flows, and a cathode side separator having an oxidant gas flow path through which an oxidant gas flows. Have. The fuel cell of this embodiment can exhibit high power generation performance.

  FIG. 2 is a schematic view showing a basic configuration of a polymer electrolyte fuel cell (PEFC) 1 according to an embodiment of the present invention. The PEFC 1 first has a solid polymer electrolyte membrane 2 and a pair of catalyst layers (anode catalyst layer 3a and cathode catalyst layer 3c) sandwiching the polymer electrolyte membrane 2. The laminate of the solid polymer electrolyte membrane 2 and the catalyst layers (3a, 3c) is further sandwiched by a pair of gas diffusion layers (GDL) (anode gas diffusion layer 4a and cathode gas diffusion layer 4c). Thus, the solid polymer electrolyte membrane 2, the pair of catalyst layers (3a, 3c), and the pair of gas diffusion layers (4a, 4c) constitute a membrane electrode assembly (MEA) 10 in a stacked state.

  In PEFC 1, MEA 10 is further sandwiched by a pair of separators (anode separator 5a and cathode separator 5c). In FIG. 2, the separators (5a, 5c) are illustrated as being located at both ends of the illustrated MEA. However, in a fuel cell stack in which a plurality of MEAs are stacked, the separator is generally used also as a separator for an adjacent PEFC (not shown). In other words, in the fuel cell stack, MEAs constitute a stack by being sequentially stacked via the separators. In an actual fuel cell stack, a gas seal portion is disposed between the separator (5a, 5c) and the solid polymer electrolyte membrane 2, or between the PEFC 1 and another PEFC adjacent thereto. These descriptions are omitted in FIG.

  The separators (5a, 5c) can be obtained, for example, by pressing a thin plate having a thickness of 0.5 mm or less to form a concavo-convex shape as shown in FIG. The projections seen from the MEA side of the separators (5a, 5c) are in contact with the MEA 10. Thereby, the electrical connection with MEA 10 is secured. Further, the recesses (spaces between the separator and the MEA generated due to the uneven shape of the separator) seen from the MEA side of the separators (5a, 5c) allow the gas to flow during operation of the PEFC 1. It functions as a gas flow path. Specifically, a fuel gas (for example, hydrogen or the like) is caused to flow through the gas flow path 6a of the anode separator 5a, and an oxidant gas (for example, air or the like) is caused to flow through the gas flow path 6c of the cathode separator 5c.

  On the other hand, the recess seen from the side opposite to the MEA side of the separators (5a, 5c) is taken as a refrigerant flow path 7 for circulating a refrigerant (for example, water) for cooling the PEFC during operation of the PEFC 1. Ru. Furthermore, the separator is usually provided with a manifold (not shown). The manifold functions as a connecting means for connecting the cells when configuring the stack. With such a configuration, mechanical strength of the fuel cell stack can be secured.

  In the embodiment shown in FIG. 2, the separators (5a, 5c) are formed in a concavo-convex shape. However, the separator is not limited to only such a concavo-convex form, and may be any form such as a flat or a concavo-convex form as long as the functions of the gas flow path and the refrigerant flow path can be exhibited. It is also good.

  The fuel cell having the MEA of the present invention as described above exhibits excellent power generation performance. Here, the type of fuel cell is not particularly limited, and in the above description, a polymer electrolyte fuel cell has been described as an example, but in addition to this, an alkaline fuel cell, a direct methanol fuel cell And micro fuel cells. Among them, a polymer electrolyte fuel cell (PEFC) is preferably mentioned because of its small size, high density and high output. Further, the fuel cell is useful as a stationary power source or the like, as well as a power source for a mobile unit such as a vehicle whose mounting space is limited. Among them, it is particularly preferable to be used as a power source for mobile bodies such as automobiles where high output voltage is required after relatively long operation stop.

  The fuel used in operating the fuel cell is not particularly limited. For example, hydrogen, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, secondary butanol, tertiary butanol, dimethyl ether, diethyl ether, ethylene glycol, diethylene glycol and the like can be used. Among them, hydrogen and methanol are preferably used in that high output can be achieved.

  Further, the application application of the fuel cell is not particularly limited, but application to a vehicle is preferable. The electrolyte membrane-electrode assembly of the present invention is excellent in power generation performance and durability, and can be miniaturized. For this reason, the fuel cell of the present invention is particularly advantageous when the fuel cell is applied to a vehicle from the viewpoint of on-vehicle performance. Thus, the present invention provides a vehicle comprising the fuel cell of the present invention.

  The members constituting the fuel cell of the present embodiment will be briefly described below, but the technical scope of the present invention is not limited to only the following embodiments.

[Electrocatalytic layer (Catalytic layer)]
The electrode catalyst layer (catalyst layer) is formed by the manufacturing method of the first embodiment, or formed using the electrode catalyst mixture of the second embodiment. Here, the membrane electrode assembly has a cathode catalyst layer and an anode catalyst layer. At least one of the cathode catalyst layer and the anode catalyst layer may be formed using the catalyst mixture of the present invention. However, in consideration of the need to improve the proton conductivity and the transport characteristics (gas diffusibility) of the reaction gas (particularly O ₂ ), at least the cathode catalyst layer is produced according to the manufacturing method of the first embodiment, or Preferably, it is formed using a form of electrocatalyst mixture. However, only the cathode catalyst layer may be formed using the electrode catalyst mixture of the present invention, or both the cathode catalyst layer and the anode catalyst layer may be formed using the electrode catalyst mixture of the present invention. It is not something to be done.

[Electrolyte membrane (polymer electrolyte membrane)]
Electrolyte membranes are roughly classified into fluorine-based polymer electrolyte membranes and hydrocarbon-based polymer electrolyte membranes according to the type of ion exchange resin that is the constituent material. Examples of the ion exchange resin constituting the fluorine-based polymer electrolyte membrane include Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Corporation), Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.), etc. Perfluorocarbon sulfonic acid based polymers, perfluorocarbon phosphonic acid based polymers, trifluorostyrene sulfonic acid based polymers, ethylene tetrafluoroethylene-g-styrene sulfonic acid based polymer, ethylene-tetrafluoroethylene copolymer, polyvinylidene fluoride- Perfluorocarbon sulfonic acid polymers and the like can be mentioned. From the viewpoint of improving the power generation performance such as heat resistance and chemical stability, these fluorine-based polymer electrolyte membranes are preferably used, and particularly preferably a fluorine-based polymer electrolyte composed of a perfluorocarbon sulfonic acid-based polymer A membrane is used.

  Specific examples of hydrocarbon-based electrolytes include sulfonated polyethersulfone (S-PES), sulfonated polyaryletherketone, sulfonated polybenzimidazole alkyl, phosphonated polybenzimidazole alkyl, sulfonated polystyrene, sulfonated poly Ether ether ketone (S-PEEK), sulfonated polyphenylene (S-PPP), etc. are mentioned. These hydrocarbon-based polymer electrolyte membranes have manufacturing advantages such as inexpensive raw materials, simple manufacturing processes, and high material selectivity. In addition, only 1 type may be used individually by 1 type of ion exchange resin mentioned above, and 2 or more types may be used together. Moreover, it is not limited only to the material mentioned above, Other materials may be used.

  The thickness of the electrolyte membrane is usually about 5 to 100 μm.

[Gas diffusion layer]
The gas diffusion layer (gas diffusion layer base material) has a function of promoting the diffusion of the gas (fuel gas or oxidant gas) supplied through the separator flow path, and in addition to its function as an electron conduction path, hydrophilic porous It has a function to support the quality layer.

  The material which comprises a gas diffusion layer base material is not specifically limited, The conventionally well-known knowledge may be referred suitably. For example, sheet-like materials having conductivity and porosity, such as carbon woven fabrics, paper-like paper bodies, felts and non-woven fabrics, can be mentioned. More specifically, carbon paper, carbon cloth, carbon non-woven fabric and the like are preferably mentioned. A commercial item can also be used for a gas diffusion layer base material, for example, Toray Industries Inc. carbon paper TGP series, E-TEK company carbon cloth etc. are mentioned.

  The thickness of the gas diffusion layer substrate may be appropriately determined in consideration of the characteristics of the gas diffusion layer to be obtained, but may be about 30 to 500 μm. If the thickness of the substrate is a value within such a range, the balance between mechanical strength and diffusivity such as gas and water can be properly controlled.

  The gas diffusion layer substrate preferably contains a water repellent for the purpose of enhancing the water repellency and preventing the flooding phenomenon and the like. The water repellent agent is not particularly limited, but may be a fluorine-based polymer such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyhexafluoropropylene or tetrafluoroethylene-hexafluoropropylene copolymer (FEP). Molecular materials, polypropylene, polyethylene and the like can be mentioned.

  Further, in order to further improve water repellency, the gas diffusion layer may have a microporous layer (MPL layer) on the catalyst layer side of the gas diffusion layer substrate. The microporous layer refers to a microporous layer having a large number of fine pores, and is usually an aggregate of carbon particles.

  The carbon particles contained in the microporous layer are not particularly limited, and conventionally known materials such as carbon black, graphite, expanded graphite and the like may be appropriately adopted. Among them, carbon black such as oil furnace black, channel black, lamp black, thermal black and acetylene black can be preferably used because of excellent electron conductivity and large specific surface area. The average particle size of the carbon particles is preferably about 10 to 100 nm. This makes it possible to obtain high drainage performance by capillary force and to improve the contact with the catalyst layer.

  The microporous layer preferably contains a water repellent. As a water repellent used for a microporous layer, the thing similar to the water repellent mentioned above is mentioned. Among them, a fluorine-based polymer material can be preferably used because it is excellent in water repellency, corrosion resistance at the time of electrode reaction, and the like.

  The mixing ratio of carbon particles to the water repellent in the microporous layer is about 90:10 to 40:60 (carbon particles: water repellent) in weight ratio in consideration of balance between water repellency and electron conductivity. That's good. The thickness of the carbon particle layer is not particularly limited, and may be appropriately determined in consideration of the water repellency of the obtained gas diffusion layer.

  As described above, after the catalyst layer is formed on the surface of the electrolyte membrane (solid polymer electrolyte membrane) or the gas diffusion layer substrate (gas diffusion layer), the resulting laminate is used as it is for the production of a membrane electrode assembly can do. Alternatively, a peelable substrate such as polytetrafluoroethylene (PTFE) [Teflon (registered trademark)] sheet is used as a substrate, and after forming the catalyst layer on the substrate, the catalyst layer portion is peeled off from the substrate The catalyst layer may be obtained accordingly.

(Membrane electrode assembly)
According to a further embodiment of the present invention, there is provided a fuel cell membrane electrode assembly comprising the fuel cell electrode catalyst layer. That is, the polymer electrolyte membrane 2, the cathode catalyst layer 3c disposed on one side of the electrolyte membrane, the anode catalyst layer 3a disposed on the other side of the electrolyte membrane, the electrolyte membrane 2 and the anode catalyst layer 3a. And a fuel cell membrane electrode assembly having a pair of gas diffusion layers (4a, 4c) sandwiching the cathode catalyst layer 3c. And in this membrane electrode assembly, at least one of the cathode catalyst layer and the anode catalyst layer is the catalyst layer of the embodiment described above.

However, in consideration of the need for improving proton conductivity and transport characteristics (gas diffusibility) of the reaction gas (particularly O ₂ ), at least the cathode catalyst layer is the catalyst layer of the embodiment described above. preferable. However, the catalyst layer according to the above embodiment may be used as an anode catalyst layer, or may be used as both a cathode catalyst layer and an anode catalyst layer.

  The method for producing the membrane electrode assembly is not particularly limited, and a conventionally known method can be used. For example, as described above, the catalyst layer is transferred or coated on the electrolyte membrane by hot pressing, and the dried one is bonded to the gas diffusion layer, or the microporous layer side (including the microporous layer) of the gas diffusion layer If not, two gas diffusion electrodes (GDE) are prepared by applying and drying a catalyst layer on one side of the substrate layer in advance, and hot pressing this gas diffusion electrode on both sides of the solid polymer electrolyte membrane The method of joining at can be used. Coating conditions such as hot pressing and bonding conditions may be appropriately adjusted depending on the type of polymer electrolyte (perfluorosulfonic acid type or hydrocarbon type) in the solid polymer electrolyte membrane or the catalyst layer.

(Fuel cell)
According to a further embodiment of the present invention there is provided a fuel cell having a membrane electrode assembly of the above form. That is, one embodiment of the present invention is a fuel cell having a pair of anode separators and cathode separators sandwiching the membrane electrode assembly of the above-described embodiment.

(Separator)
The separator has a function of electrically connecting each cell in series when connecting a plurality of single cells of a fuel cell such as a polymer electrolyte fuel cell in series to constitute a fuel cell stack. The separator also has a function as a partition that separates the fuel gas, the oxidant gas, and the coolant from one another. In order to secure these flow paths, as described above, it is preferable that a gas flow path and a cooling flow path be provided in each of the separators. As a material which comprises a separator, conventionally well-known materials, such as carbons, such as a compact carbon graphite and a carbon board, and metals, such as stainless steel, can be suitably adopted without restriction. The thickness and size of the separator, and the shape and size of each flow path to be provided are not particularly limited, and can be appropriately determined in consideration of the desired output characteristics and the like of the obtained fuel cell.

  The method for producing a fuel cell is not particularly limited, and conventionally known findings in the field of fuel cells can be appropriately referred to.

  Furthermore, a fuel cell stack having a structure in which a plurality of membrane electrode assemblies are stacked and connected in series via a separator may be formed so that the fuel cell can exhibit a desired voltage. The shape or the like of the fuel cell is not particularly limited, and may be appropriately determined so as to obtain cell characteristics such as a desired voltage.

  The above-described PEFC and membrane electrode assembly use a catalyst layer which is excellent in power generation performance under both dry and wet conditions. Therefore, the said PEFC and membrane electrode assembly are excellent in power generation performance.

  The PEFC of the present embodiment and a fuel cell stack using the PEFC can be mounted, for example, in a vehicle as a driving power source.

  The effects of the present invention will be described using the following examples and comparative examples. Although the indication of "part" or "%" may be used in an Example, unless otherwise indicated, "part by weight" or "weight%" is represented. Also, unless otherwise stated, each operation is performed at room temperature (25 ° C.).

Example 1
(Production of electrode catalyst)
As catalyst carrier A, ketjen black EC300J (manufactured by ketjen black international Ltd.) having a BET specific surface area of 790 m ² / g and a primary average particle diameter of about 40 nm was prepared. This catalyst carrier A was loaded with platinum (Pt) having an average particle diameter of 2.5 nm as a catalyst metal so that the loading ratio was 50% by weight, to obtain a catalyst powder A. That is, 46 g of Carrier A was immersed in 1000 g (platinum content: 46 g) of a dinitrodiammine platinum nitrate solution having a platinum concentration of 4.6% by weight and stirred, and then 100 ml of 100% ethanol was added as a reducing agent. The solution was stirred and mixed at the boiling point for 7 hours to load platinum on the catalyst carrier A. Then, filtration and drying were performed to obtain a catalyst powder having a loading of 50% by weight on a carrier. Thereafter, in a hydrogen atmosphere, the temperature was maintained at 900 ° C. for 1 hour to obtain an electrode catalyst I. The peak particle diameter of the electrode catalyst I measured under the following particle size distribution measurement conditions was 13.2 μm.

(Production of electrode catalyst mixture)
Electrocatalyst I: 100 parts by weight and purified water 500 parts by weight using a self-revolution mixer (Awatori Neritaro (registered trademark) AR-250, manufactured by Shinky), autorotation: 200 revolutions / minute, revolution: 400 revolutions / Mix for 2 minutes in minutes.

  Thereafter, the mixture was stirred at a rotation number of 2 rotations / minute for 24 hours by a mix rotor (overturning stirring type stirrer) (BR-2 manufactured by AS ONE Corporation) to obtain an electrode catalyst mixture A-1. The electrode catalyst mixture A-1 after stirring had a peak particle size of 9.2 μm and a cumulative volume fraction of 1 μm or less of the particle size was 2.9%. Therefore, the peak particle diameter of the electrode catalyst after contact maintenance was 69.3 when the peak particle diameter before contacting with the dispersion medium was 100.

  The above-mentioned stirring was performed with the system closed in order to prevent evaporation of the solvent accompanying the stirring. The same applies to the following examples and comparative examples.

  Moreover, the particle size measurement conditions are as follows.

(Particle size measurement conditions)
The dispersion of the electrode catalyst in the dispersion medium was diluted with 2-propanol to a solid content concentration of 1.0% by weight to prepare a sample. Next, the particle size distribution of this sample was measured under the following particle size distribution measurement conditions. Based on the obtained particle size distribution (particle size-volume fraction frequency curve), a cumulative volume fraction with a particle diameter of 1 μm or less was determined.

(Particle size distribution measurement conditions)
Method: Laser diffraction / scattering method Device name: MT3000II (manufactured by Micro Track Bell)
(Example 2)
An electrode catalyst mixture A-2 was obtained in the same manner as in Example 1 except that the stirring time of the mix rotor (BR-2 manufactured by As One) was changed from 24 hours to 72 hours. The electrode catalyst mixture A-2 after stirring had a peak particle size of 8.0 μm and a cumulative volume fraction of particle sizes of 1 μm or less of 3.7%. Therefore, the peak particle diameter of the electrode catalyst after contact maintenance was 60.6 when the peak particle diameter before contact with the dispersion medium was 100.

(Example 3)
An electrode catalyst mixture A-3 was obtained in the same manner as in Example 1, except that the stirring time of the mix rotor (BR-2 manufactured by As One) was changed from 24 hours to 120 hours. The electrode catalyst mixture A-3 after stirring had a peak particle size of 7.6 μm and a cumulative volume fraction of particle sizes of 1 μm or less of 5.6%. Therefore, the peak particle diameter of the electrode catalyst after contact maintenance was 57.6 when the peak particle diameter before contacting with the dispersion medium was 100.

(Example 4)
An electrode catalyst mixture A-4 was obtained in the same manner as in Example 1 except that the stirring time of the mix rotor (BR-2 manufactured by As One) was changed from 24 hours to 168 hours. The electrode catalyst mixture A-4 after stirring had a peak particle size of 8.7 μm and a cumulative volume fraction of 1 μm or less of the particle size was 5.0%. Therefore, the peak particle diameter of the electrode catalyst after contact maintenance when the peak particle diameter before a dispersion medium contact is set to 100 was 65.9.

(Example 5)
An electrode catalyst mixture A-5 was obtained in the same manner as in Example 1 except that pre-mixing was not performed using a revolution-revolution mixer. The electrode catalyst mixture A-5 after stirring had a peak particle size of 13.6 μm and a cumulative volume fraction of 1 μm or less of the particle size was 3.1%. Therefore, the peak particle diameter of the electrode catalyst after contact maintenance when the peak particle diameter before a dispersion medium contact is set to 100 was 103.0.

(Example 6)
An electrode catalyst mixture A-6 was obtained in the same manner as in Example 5 except that the stirring time of the mix rotor (BR-2 manufactured by As One) was changed from 24 hours to 96 hours. The electrode catalyst mixture A-6 after stirring had a peak particle size of 10.4 μm and a cumulative volume fraction of particle sizes of 1 μm or less of 5.4%. Therefore, the peak particle diameter of the electrode catalyst after contact maintenance when the peak particle diameter before a dispersion medium contact is set to 100 was 78.7.

(Example 7)
An electrode catalyst mixture A-7 was obtained in the same manner as in Example 5, except that the stirring time of the mix rotor (BR-2 manufactured by As One) was changed from 24 hours to 168 hours. The electrode catalyst mixture A-7 after stirring had a peak particle size of 9.9 μm and a cumulative volume fraction of 1 μm or less of the particle size was 4.8%. Therefore, the peak particle diameter of the electrode catalyst after contact maintenance when the peak particle diameter before a dispersion medium contact is set to 100 was 75.0.

(Comparative example 1)
(Production of electrode catalyst)
An electrode catalyst I was obtained in the same manner as in Example 1.

(Production of Composition A)
Electrocatalyst I 100 parts by weight and 500 parts by weight of purified water are mixed for 2 minutes at a rotation speed of 200 revolutions / minute and a revolution speed of 400 revolutions / minute using a revolution-revolution mixer (AR-250, manufactured by Shinky). The composition A-8 was obtained. Composition A-8 after stirring had a peak particle size of 13.2 μm and a cumulative volume fraction of particle sizes of 1 μm or less of 0%. Therefore, the peak particle diameter of the electrode catalyst after pre-mixing when the peak particle diameter before contacting with the dispersion medium is 100 was 100.

  In Examples 1 to 7 above, by immersing water in the electrode catalyst for a long time, specifically by immersing for 24 hours or more, the cumulative volume fraction with a particle diameter of 1 μm or less became more than 0%. Further, it is understood from the comparison of Examples 1 and 5 that the pre-mixing reduces the peak particle diameter of the electrode catalyst after contact maintenance when the peak particle diameter before contact with the dispersion medium is 100. This is considered to be due to the fact that the pre-mixing allows more penetration of water between the catalysts and makes the catalysts more likely to be disintegrated in the subsequent steps.

  On the other hand, in Comparative Example 1, only the pre-mixing of the electrode catalyst and water was performed, and the immersion in water for a long time was not performed, so the cumulative volume fraction with a particle diameter of 1 μm or less was 0%.

(Example 8)
An ionomer dispersion (Nafion (registered trademark) D 2020, EW = 1100 g / mol, manufactured by DuPont) as a polymer electrolyte was added to the composition A-3 obtained in Example 3 as an electrolyte (ionomer) to a carbon carrier. It mixed so that a weight ratio (I / C ratio) might be 0.9. Next, using the above mixture as a solvent, n-propyl alcohol (NPA) aqueous solution (water: NPA = 6: 4 (weight ratio)) to a solid fraction (Pt + catalyst support + polymer electrolyte) of 7% by weight The catalyst ink was prepared by addition.

Gaskets (Teijin Dupont Film Co., Ltd., Theonex (registered trademark), thickness: 25 μm (adhesion layer: 2710 μm)) around both sides of a polymer electrolyte membrane (manufactured by Dupont, Nafion (registered trademark) NR 211, thickness: 25 μm) Placed. Next, the above catalyst ink was applied by spray coating to a size of 5 cm × 2 cm on the exposed portion on one side of the polymer electrolyte membrane. The catalyst ink was dried by maintaining the spray application stage at 60 ° C. for 10 minutes to obtain an electrode catalyst layer. The amount of platinum supported at this time was 0.35 mg / cm ² . The thickness of the catalyst layer was 10 μm. Next, in the same manner as described above, the other surface of the electrolyte membrane was spray-coated and dried to obtain a membrane / electrode assembly having the catalyst layers formed on both sides of the electrolyte membrane.

(Comparative example 2)
A membrane / electrode assembly was obtained in the same manner as in Example 8 except that the composition A-8 obtained in Comparative example 1 was used.

  The following power generation performance test and proton transport resistance test were performed using the membrane electrode assemblies obtained in Example 8 and Comparative Example 2.

(Power generation performance test 1: Dry condition)
Power generation was performed by supplying pure hydrogen to the anode and air (both at atmospheric pressure) to the cathode. The power generation conditions were a cell temperature of 80 ° C., an anode gas relative humidity of 40%, and a cathode gas relative humidity of 40%. Under the above conditions, I-V performance was measured.

(Power generation performance test 2: Wet condition)
Power generation was performed by supplying pure hydrogen to the anode and air (both at atmospheric pressure) to the cathode. The power generation conditions were a cell temperature of 80 ° C., an anode gas relative humidity of 100%, and a cathode gas relative humidity of 100%. Under the above conditions, I-V performance was measured.

The cell voltages (IR-free) of Examples and Comparative Examples at a current density of 1 A / cm ² under the dry conditions and wet conditions are shown in Table 1 below.

(Proton transport resistance test)
It was measured by electrochemical impedance spectroscopy. In addition, using the Hokuto Denko Co., Ltd. make, electrochemical measurement system HZ-3000 and the NF circuit design block Co., Ltd. make, frequency response analyzer FRA5020 were used as an apparatus used and evaluation was performed on the measurement conditions of following Table 2. . The results are shown in FIG.

  The membrane / electrode assembly produced using the electrode catalyst layer obtained by using the electrode catalyst mixture of the present invention obtained by the manufacturing method of the present invention is excellent in battery performance under both wet conditions and dry conditions. It also had excellent proton transportability.

1 ... polymer electrolyte fuel cell (PEFC),
2 ... Solid polymer electrolyte membrane,
3 ... catalyst layer,
3a ... anode catalyst layer,
3c ... cathode catalyst layer,
4a ... anode gas diffusion layer,
4c ... cathode gas diffusion layer,
5, ... separator,
5a ... anode separator,
5c ... cathode separator,
6a ... anode gas flow path,
6c: cathode gas flow path,
7 ... refrigerant flow path,
10: Membrane electrode assembly (MEA).

Claims (10)

Bringing an electrode catalyst composed of a catalyst carrier and a catalyst metal supported on the catalyst carrier in contact with a dispersion medium containing water as a main component;
Thereafter, the polymer electrolyte is further mixed to obtain a composition,
Forming a catalyst layer using the composition;
The method for producing a catalyst layer for a fuel cell, wherein the contact is maintained until the cumulative volume fraction of the particle diameter of 1 μm or less of the electrode catalyst is more than 0%.   The method for producing a fuel cell catalyst layer according to claim 1, wherein the maintenance of the contact is performed for 24 hours or more.   The fuel cell according to claim 1 or 2, wherein when the peak particle diameter of the electrode catalyst before contact with the dispersion medium is 100, the contact is maintained until the peak particle diameter of the electrode catalyst becomes 95 or less. Method for producing a catalyst layer.   The method for producing a fuel cell catalyst layer according to any one of claims 1 to 3, wherein the maintenance of the contact is performed under stirring using a tip-to-bottom rotary stirrer.   5. The method for producing a catalyst layer for a fuel cell according to claim 4, wherein pre-mixing is performed by a rotation / revolution stirrer before the contact is maintained.   The method for producing a fuel cell catalyst layer according to any one of claims 1 to 5, wherein the dispersion medium is water.   The method for producing a fuel cell catalyst layer according to any one of claims 1 to 6, wherein the catalyst support is a carbon material. An electrode catalyst mixture comprising: a catalyst support; an electrode catalyst composed of a catalyst metal supported on the catalyst support; and a dispersion medium containing water as a main component,
The electrode catalyst mixture whose cumulative volume fraction of particle diameter 1 micrometer or less of the said electrode catalyst is more than 0%.   The electrocatalyst mixture according to claim 8, wherein the dispersion medium is water.   The electrocatalyst mixture according to claim 8 or 9, wherein the catalyst support is a carbon material.