JP6988143B2 - Method for manufacturing catalyst layer for fuel cell and electrode catalyst mixture - Google Patents

Description

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

Solid polymer electrolyte fuel cells (PEFCs) using proton conductive solid polymer membranes are colder than other types of fuel cells, such as solid oxide fuel cells and molten carbonate fuel cells. Operate. Therefore, polymer electrolyte fuel cells are expected as a stationary power source and a power source for mobile bodies such as automobiles, and their practical use has also started.

The structure of the PEFC is generally such that a membrane-electrode assembly (MEA) is sandwiched between separators. The 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 laminated.

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, and reach the cathode (air electrode) catalyst layer. Further, the electrons generated in the anode catalyst layer are the conductive carrier constituting the anode catalyst layer, the gas diffusion layer, the gas separator and the external circuit which are in contact with the side different from the solid polymer electrolyte membrane of the anode catalyst layer. It reaches the cathode catalyst layer through. Then, the protons and electrons that have reached the cathode catalyst layer react with oxygen contained in the oxidant gas supplied to the cathode catalyst layer to generate water. In a fuel cell, electricity can be taken out to the outside through the above-mentioned electrochemical reaction. The catalyst used for the catalyst layer is usually formed by supporting a catalyst metal such as platinum or a platinum alloy on a catalyst carrier such as a carbon material.

As a typical method for producing the electrode catalyst layer, there is a method in which an electrode catalyst slurry prepared by mixing an electrode catalyst and a solid polymer electrolyte solution is applied to a substrate and dried. .. For example, Patent Document 1 describes that an ionomer solution is added after adding alcohol to a dispersed aqueous solution in which catalyst-supported particles and water are mixed.

Japanese Unexamined Patent Publication No. 2014-192070

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

Therefore, an object of the present invention is to provide a method for manufacturing an electrode catalyst layer capable of improving the battery performance under dry conditions while maintaining the battery performance under wet conditions.

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

In the present invention, an electrode catalyst made of a catalyst carrier and a catalyst metal supported on the catalyst carrier and a dispersion medium containing water as a main component are brought into contact with each other, and then a polymer electrolyte is further mixed to obtain a composition. A method for producing a catalyst layer for a fuel cell, which comprises forming a catalyst layer using a composition, and maintaining contact with a catalyst layer having a particle size of 1 μm or less until the cumulative body integration rate exceeds 0%. be.

The present invention is also a catalyst mixture containing a catalyst carrier, an electrode catalyst for a fuel cell made of a catalyst metal supported on the catalyst carrier, and a dispersion medium containing water as a main component, wherein the particle diameter of the electrode catalyst is 1 μm. The following cumulative body integral ratio is an electrode catalyst mixture of more than 0%.

By applying the electrode catalyst layer obtained by the method for producing an electrode catalyst of the present invention or the electrode catalyst layer formed by using the electrode catalyst mixture of the present invention to a membrane electrode assembly, battery performance under wet conditions can be obtained. It is possible to improve the battery performance under dry conditions while maintaining the above.

It is a figure explaining the mechanism by this invention. It is a schematic sectional drawing which shows the basic structure 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 in an Example and a comparative example.

In the first embodiment of the present invention, an electrode catalyst composed of a catalyst carrier and a catalyst metal supported on the catalyst carrier is brought into contact with a dispersion medium containing water as a main component, and then a polymer electrolyte is further mixed. The catalyst layer is formed using the composition, and the contact is maintained until the cumulative body integration rate of the electrode catalyst having a particle diameter of 1 μm or less becomes more than 0%, for a fuel cell. This is a method for manufacturing a catalyst layer.

Further, the second embodiment of the present invention is a catalyst mixture containing a catalyst carrier, an electrode catalyst for a fuel cell made of a catalyst metal supported on the catalyst carrier, and a dispersion medium containing water as a main component, and is an electrode. An electrode catalyst mixture having a catalyst particle size of 1 μm or less and a cumulative body integration rate of more than 0%.

Hereinafter, the catalyst carrier and the electrode catalyst for a fuel cell made of 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 simply referred to as a dispersion medium.

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

The performance (activity) of the fuel cell is influenced by the transport characteristics of the reaction gas (for example, protons) to the catalyst metal in addition to the activity of the catalyst metal itself. Therefore, the structure formation at various scales from the vicinity of the catalyst metal to the catalyst layer becomes a controlling factor of the performance (activity) of the fuel cell through the influence on the reaction gas transport characteristics.

The protons generated on the anode side are transported to the cathode side through the polyelectrolyte and the polyelectrolyte 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 to the sulfonic acid group in the polymer. Under dry conditions, the mobility of the side chain of the polyelectrolyte having a sulfonic acid group responsible for proton transport is reduced, so that the proton transport property via the polyelectrolyte is lowered. Therefore, in general, under dry conditions, proton transport becomes disadvantageous and tends to cause deterioration of battery performance.

On the other hand, the carbon material generally used as a catalyst carrier constituting the electrode catalyst has a primary particle size of several tens of nm, so that it easily aggregates due to van der Waals attraction and has a hydrophobic surface, so that it is water-based. It tends to aggregate in a solvent due to its hydrophobic effect. When the electrode catalyst aggregates, the catalytically active component existing inside the electrode catalyst aggregate cannot contribute to the reaction, which causes deterioration of battery performance.

The present embodiment is intended to gently loosen the aggregates of the electrode catalyst by contacting (immersing) the electrode catalyst with the dispersion medium. Since the dispersion medium contains water as a main component, it is difficult to adsorb to a catalyst carrier having a hydrophobic surface, and it is difficult for the dispersion medium to permeate between particles. However, it is considered that by immersing the electrode catalyst in the dispersion medium for a relatively long time, water is adsorbed between the particles of the aggregate of the catalyst carrier, and further, water enters between the particles to loosen the aggregate. .. Further, the water that has entered is adsorbed on the electrode catalyst particles (see FIG. 1). It is considered that the adsorbed water adsorbed on the particles repels the surface of the catalytic carrier, which is hydrophobic, and the generated repulsive force can prevent the particles from aggregating again.

Further, as described above, the presence of the adsorbed water on the electrode catalyst makes it easier for the side chain of the polymer electrolyte to approach the electrode catalyst due to the adsorbed water. By forming the electrode catalyst layer using such a composition, an electrode catalyst layer in which the sulfonic acid group of the side chain is close to 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, by breaking the aggregate of the electrode catalyst and maintaining the state, the catalyst metal existing on the electrode catalyst particles can be effectively utilized. Further, it is considered that by forming the catalyst layer using the composition in which water is present around the electrode catalyst, 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 within the catalyst layer is generally disadvantageous. According to the configuration of the present embodiment, in the composition for forming the electrode catalyst layer, the presence of adsorbed water on the surface of the electrode catalyst prevents the hydrophobic polymer electrolyte main chain from approaching the electrode catalyst. Therefore, the reaction gas can be directly supplied to the catalyst metal at a certain ratio or more without going through the polymer electrolyte, and the 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, the membrane electrode assembly and the fuel cell having the electrode catalyst layer obtained by the method for producing the electrode catalyst of the first embodiment or the electrode catalyst layer formed by using the electrode catalyst mixture of the second embodiment are wet. High power generation performance can be maintained even under dry conditions, and high power generation performance can be exhibited even under dry conditions.

Hereinafter, each step in the method for manufacturing the catalyst layer for a fuel cell of the first embodiment will be described. In addition, in this specification, "X to Y" indicating a range includes X and Y, and means "X or more and Y or less". Unless otherwise specified, operations and measurements of physical properties are performed under the conditions of room temperature (20 to 25 ° C.) / relative humidity of 40 to 50% RH.

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

The electrode catalyst consists of a catalyst carrier and a catalyst metal supported on the catalyst carrier.

The catalyst carrier functions as a carrier for supporting the above-mentioned catalyst component and as an electron conduction path involved in the transfer of electrons between the catalyst component and other members. The catalyst carrier may be any as long as it has a specific surface area for supporting the catalyst particles in a desired dispersed state and has sufficient electron conductivity as a current collector, but is conductive and durable. From the viewpoint, it is preferable that the catalyst carrier is a carbon material. Specific examples of the carbon material include carbon blacks such as acetylene black, channel black, oil furnace black, gas furnace black (for example, Balkan), lamp black, thermal black, black pearl, and 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 nanotubes; Carbon Nanofibers; carbon nanohorns; carbon fibrils; activated carbon; coke; natural graphite; artificial graphite and the like can be mentioned. Further, as the conductive carrier, zeolite template carbon (ZTC) having a structure in which nano-sized band-shaped graphene is regularly connected in a three-dimensional manner can also be mentioned. These may be used alone or in combination of two or more. The carbon material referred to here means that it contains a carbon atom as a main component, and is a concept including both a carbon atom and a substantially carbon atom, and includes elements other than the carbon atom. It may be. "Substantially composed of carbon atoms" means that impurities of about 2 to 3% by weight or less can be mixed.

The BET specific surface area of the catalyst carrier may be a specific surface area sufficient to support the catalyst in a highly dispersed manner. The BET specific surface area of the catalyst carrier (catalyst carrier precursor before supporting the catalyst) ^{is preferably 500 m 2} / g or more, and more preferably 550 m ² / g or more. When the specific surface area is within the above range, the catalyst is sufficiently dispersed in the catalyst carrier to obtain sufficient power generation performance, the catalyst can be sufficiently effectively used, and the oxygen transport resistance is low and easy to control. 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 produced by using a commercially available product or by a known method described in, for example, Japanese Patent Application Laid-Open No. 2010-2088887, International Publication No. 2009/0752664.

In the present specification, "BET specific surface area (m ² / g catalyst carrier)" 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. This sample tube is pre-dried at 90 ° C. for several hours in a vacuum dryer to prepare a sample for measurement. An electronic balance (AW220) manufactured by Shimadzu Corporation is used for weighing. In the case of a coated sheet, the net weight of the coated layer, which is obtained by subtracting the weight of Teflon (registered trademark) (base material) having the same area from the total weight of the coated sheet, is used as the sample weight of about 0.03 to 0.04 g. .. 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 intercept.

In addition to the above carbon materials, porous metals such as Sn (tin) and Ti (titanium), and conductive metal oxides can also be used as carriers. Considering the effect of this embodiment, the catalyst carrier is preferably particles.

The size of the catalyst carrier is not particularly limited, but the average primary particle diameter is 5 to 200 nm from the viewpoint of ease of support, catalyst utilization, and control of the thickness of the electrode catalyst layer within an appropriate range. It is preferably about 10 to 100 nm. The average primary particle size is a value calculated as the average value of the particle size 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 on which the catalyst metal is supported on the catalyst carrier, the amount of the catalyst metal supported is preferably 10 to 80% by weight, more preferably 20 to 60% by weight, based on the total amount of the electrode catalyst. When the amount of the catalyst metal supported is a value within such a range, the balance between the dispersity of the catalyst metal on the catalyst carrier and the catalyst performance can be appropriately controlled. The "catalyst metal loading ratio" in the present invention is a value obtained by measuring the weights of the carrier before supporting the catalyst metal and the catalyst after supporting the catalyst metal.

The catalytic metal constituting the electrode catalyst has a function of catalyzing an electric chemical reaction. The catalyst metal used for the anode catalyst layer is not particularly limited as long as it has a catalytic action on the oxidation reaction of hydrogen, and known catalysts can be used in the same manner. Further, the catalyst metal used for the cathode catalyst layer is also not particularly limited as long as it has a catalytic action on 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. Can be selected from.

Of these, those containing at least platinum are preferably used in order to improve catalytic activity, toxicity 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 catalyst metals can exhibit high activity. The composition of the alloy depends on the type of metal to be alloyed, but it is preferable that the content of platinum is 30 to 90 atomic% and the content of the metal alloyed with platinum is 10 to 70 atomic%. In addition, an alloy is generally a general term for a metal element to which one or more kinds of metal elements or non-metal elements are added and having metallic properties. The structure of the alloy includes a eutectic alloy, which is a so-called mixture in which the constituent elements are separate crystals, a solid solution in which the constituent elements are completely fused, and a compound in which the constituent elements are an intermetal compound or a compound of a metal and a non-metal. Some of them are formed, and in the present application, any of them may be used. 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, the description of the catalyst metal for the anode catalyst layer and the cathode catalyst layer has the same definition for both. However, the catalyst metal 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 exhibit 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 the known catalyst component can be adopted. As the shape, for example, a granular shape, a scaly shape, a layered shape, or the like can be used, but the shape 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 within such a range, the balance between the catalyst utilization rate and the ease of carrying with respect to the effective electrode area where the electrochemical reaction proceeds can be appropriately controlled. In the present specification, the "average particle size of the catalytic metal particles" is the crystallite radius obtained from the half-value width of the diffraction peak of the catalytic metal component in X-ray diffraction, or the catalyst examined by a transmission electron microscope (TEM). It can be measured as the average value of the particle radii of the metal particles. In the present specification, the "average particle size of the catalyst metal particles" is the crystallite radius obtained from the half width of the diffraction peak of the catalyst metal component in X-ray diffraction.

The method for producing the electrode catalyst (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 a liquid phase reduction method, an evaporative dry solid method, a colloidal adsorption method, a spray pyrolysis method, and a reverse micelle (microemulsion method) can be used. Alternatively, a commercially available product may be used as the electrode catalyst.

Examples of the method for producing a catalyst by the liquid phase reduction method include a method in which a catalyst metal is deposited on the surface of the catalyst carrier precursor and then heat treatment is performed. Specific examples thereof include a method in which a catalyst carrier is immersed in a precursor solution of a catalyst metal, reduced with a reducing agent, and then heat-treated.

Here, the precursor of the catalyst metal is not particularly limited, and is appropriately selected depending on the type of the catalyst metal used. Specific examples thereof include chlorides, nitrates, sulfates, chlorides, acetates and amine compounds of catalyst metals such as platinum. More specifically, chlorides such as platinum chloride (hexachloroplatinic acid hexahydrate), palladium chloride, rhodium chloride, ruthenium chloride and cobalt chloride, nitrates such as palladium nitrate, rhodium nitrate and iridium nitrate, palladium sulfate and sulfuric acid. Sulfates such as rhodium, acetates such as rhodium acetate, ammine compounds such as dinitrodiammine platinum nitric acid and dinitrodiammine palladium are preferred and exemplified. Further, the solvent used for preparing 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 depending on the type of the precursor of the catalyst metal used. Specific examples thereof include water, acids, alkalis and organic solvents. 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. ..

Examples of the reducing agent include hydrogen, hydrazine, sodium borohydride, sodium thiosulfate, citric acid, sodium citrate, L-ascorbic acid, sodium borohydride, formaldehyde, methanol, ethanol, ethylene, carbon monoxide and the like. .. A substance that is gaseous at room 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 applied in the same manner.

The precipitation conditions are not particularly limited as long as the catalyst metal can be deposited on the catalyst carrier. For example, the precipitation temperature is preferably a temperature near the boiling point of the solvent, more preferably room temperature to 100 ° C. The precipitation time is preferably 1 to 10 hours, more preferably 2 to 8 hours. If necessary, the precipitation step may be performed while stirring and mixing. 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. Considering the effect of promoting the reduction of the catalyst metal precursor, it is preferable that the heat treatment step is performed in an atmosphere containing hydrogen gas, more preferably in a hydrogen atmosphere.

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

The main component of the dispersion medium containing water as the main component means that water is 80% by weight or more (upper limit 100% by weight) with respect to the dispersion medium, and water is preferably 90% by weight or more (upper limit 100% by weight). ), 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 repulsive force between the dispersion medium (particularly water) that has entered between the particles and the electrode catalyst becomes large, and it is possible to prevent the loosened aggregates from aggregating again. Furthermore, due to the high proportion of water in the dispersion medium, the presence of the dispersion medium (particularly water) adsorbed on the electrode catalyst makes it difficult for the polyelectrolyte to approach the electrode catalyst, and the proton transportability under dry conditions is improved. , Oxygen transportability under wet conditions is also maintained high.

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

The contact between the electrode catalyst and the dispersion medium is carried out until the cumulative volume fraction of the electrode catalyst having a particle diameter of 1 μm or less becomes more than 0%. That is, the process is carried out until particles having a diameter close to the primary particle size of the electrode catalyst appear. By maintaining the contact of the dispersion medium with the electrode catalyst, water enters the inside of the aggregate and breaks the aggregate, so that the catalyst particles become particles close to the primary particle size and adsorbed water on the particles. Is expected to exist. More preferably, the contact between the electrode catalyst and the dispersion medium is maintained such that the cumulative volume fraction of the electrode catalyst having a particle diameter of 1 μm or less is 2.5% or more (upper limit 100%), more preferably 3.5% or more. It is preferably carried out until it reaches 4.5% or more, and most preferably 5.0% or more. The larger the cumulative volume fraction of the electrode catalyst having a particle diameter of 1 μm or less is, the more preferable it is. Therefore, the upper limit thereof is not specified, but it is usually 40.0% or less.

In addition, "contact between the electrode catalyst and the dispersion medium is performed until the cumulative volume fraction of the electrode catalyst having a particle diameter of 1 μm or less exceeds 0%" means that the cumulative volume fraction of the electrode catalyst having a particle diameter of 1 μm or less is 0. If it exceeds%, it means that the maintenance of contact may be stopped at any time.

Further, it is preferable that the contact between the electrode catalyst and the dispersion medium is carried out until the peak particle size of the electrode catalyst becomes 95 or less, specifically, when the peak particle size of the electrode catalyst before contact is 100. As described above, the aggregation of the electrode catalyst is due to the van der Waals attraction between the particles and the hydrophobic effect in the dispersion medium. The agglutination before the contact with the dispersion medium is due to the van der Waals attraction between the particles, and is generally smaller than the peak particle size after the contact with the dispersion medium. Therefore, by contacting the electrode catalyst and the dispersion medium until the particle size becomes smaller than the peak particle size of the electrode catalyst before the contact with the dispersion medium, both the van der Waals attractive force between the particles and the hydrophobic effect in the dispersion medium can be obtained. It will be smaller than the peak particle size of the agglomerates formed due to this. By reducing the peak particle size in this way, the particle size of the electrode catalyst can be further reduced. Here, as the peak particle size of the electrode catalyst, a value calculated based on the particle size distribution measurement conditions described in the following examples is adopted. Further, when the peak particle size of the electrode catalyst before contact is set to 100, it is preferable to contact the electrode catalyst and the dispersion medium so as to be 90 or less, and contact the electrode catalyst and the dispersion medium so as to be 80 or less. Is more preferable. In the contact between the electrode catalyst and the dispersion medium, when the peak particle size of the electrode catalyst is set to 100, the contact is saturated at about 10 even if the contact is maintained. In one preferred embodiment, when the peak particle size 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 size of the electrode catalyst is 50 to 80.

The peak particle diameter of the electrode catalyst in the dispersion medium and the cumulative volume fraction of the electrode catalyst having a particle diameter of 1 μm or less are obtained as follows. A mixture of electrode catalyst and dispersion medium is 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 is measured under the following conditions. The particle size calculated according to the following particle size distribution measurement conditions is based on volume.

For the peak particle size of the electrode catalyst before contact with the dispersion medium, the particle size distribution is measured under the above particle size distribution measurement conditions.

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

Here, the method for controlling the cumulative volume fraction of the electrode catalyst of the electrode catalyst mixture having a particle diameter of 1 μm or less to exceed 0% is not particularly limited, but (1) the time for maintaining contact between the electrode catalyst and the dispersion medium, and (2) It was found 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 size of the electrode catalyst to be small. did. Hereinafter, the above will be described in detail. Needless to say, the method is not limited to the above methods (1) and (2).

(1) Time of contact state The contact between the electrode catalyst and the dispersion medium is preferably maintained for 24 hours or longer, more preferably 48 hours or longer. When the contact state is set to 24 hours or more, the dispersion medium is sufficiently spread in the electrode aggregates, the dispersion medium easily enters between the electrode catalyst particles, and the peak particle diameter of the electrode catalyst can be sufficiently reduced. The longer the contact is maintained, the smaller the peak particle size of the electrode catalyst can be, and therefore the upper limit thereof is not specified. However, the effect of maintaining contact saturates after a certain period of time. Therefore, the maintenance of contact is preferably 200 hours or less, more preferably 180 hours or less, in consideration of the saturation of the effect and productivity.

(2) Stirring conditions of the dispersion liquid in which the electrode catalyst is dispersed in the dispersion medium The contact is preferably maintained by standing or stirring, and more preferably under stirring.

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

At this time, since stirring is performed for a relatively long time in this embodiment, it is preferable to perform stirring under relatively gentle conditions with a shearing force that does not damage the electrode catalyst by stirring for a long time. Suitable stirrers used in this case include an overturning rotary stirrer: a mix rotor (manufactured by AS ONE Corporation), a magnetic stirrer, a stirrer with stirring blades, and the like. Above all, since the effect of the present invention is easily exhibited, it is preferable to maintain the contact under stirring using an overturning rotary stirrer.

The overturning rotary stirrer rotates the container at a certain angle, and the direction of rotation of the container is a revolution that rotates the entire container around the center point even if the container rotates around the container axis. May be good. Preferably, it is an overturning rotary type stirrer that rotates on its axis. However, the overturning rotary type stirrer referred to here does not include a rotation / revolution type stirrer that involves both rotation and revolution.

The stirring conditions for stirring using the overturning rotary stirrer may be appropriately set. For example, in the case of a rotating overturning rotary stirrer, the rotation speed is preferably 0.1 to 5 rotations / minute, and is 0. .5 to 3 revolutions / minute is more preferable.

Further, it is preferable to premix the electrode catalyst and the dispersion medium before maintaining the contact between the electrode catalyst and the dispersion medium. By performing the premixing, the electrode catalyst becomes more familiar with the dispersion medium, and the time for subsequent micronization can be shortened.

Examples of the stirring device for premixing include mixers such as a rotating revolution mixer, a planetary mixer, and a homomixer, and a disperser such as an ultrasonic disperser and a jet mill.

Above all, it is preferable to perform premixing with a rotation / revolution type stirrer such as a rotation / revolution mixer. Premixing with a rotating / revolving stirrer makes it easier for the electrode catalyst to become familiar with the dispersion medium, and it is possible to shorten the time for the agglomerates to loosen by subsequent immersion. A rotation / revolution type stirrer rotates the container clockwise and at the same time rotates the container counterclockwise, and the centrifugal force generated by high-speed rotation / revolution is used as a pressing force to act on the material in the container. , It is a method to disperse the material by continuously generating a spiral vertical convection. As a disperser for a rotating / revolving stirrer, Awatori Rentaro (registered trademark) (manufactured by Shinky Co., Ltd.) is used.

That is, in a preferred embodiment of the present embodiment, the electrode catalyst and the dispersion medium are premixed by a rotating / revolving stirrer, and then agitated under stirring, preferably under stirring using an overturning rotary stirrer, as a catalyst electrode catalyst. And a form that maintains contact with the dispersion medium.

Further, in a more preferable embodiment of the present embodiment, the catalyst electrode is prepared by premixing the electrode catalyst and the dispersion medium with a rotating / revolving stirrer, and then stirring, preferably under stirring using an overturning rotary stirrer. It is a form in which the contact state of the catalyst and the dispersion medium is maintained for 24 hours or more.

However, the rotating / revolving stirrer has a relatively strong stirring force, and long-term stirring may damage the electrode catalyst itself and reduce the catalytic activity. Therefore, the premixing time is preferably 5 minutes or less, and more preferably 2 minutes or less. Further, since the effect of premixing can be more easily obtained, the premixing time is preferably 10 seconds or longer, and more preferably 30 seconds or longer.

The stirring conditions of the rotation / revolution type stirrer may be appropriately set, but for example, the rotation speed of rotation is preferably 100 to 400 rotations / minute, and more preferably 200 to 300 rotations / minute. Further, the revolution speed is preferably 200 to 800 rotations / minute, and more preferably 400 to 600 rotations / minute.

In this way, an electrode catalyst mixture for a fuel cell, which comprises a catalyst carrier and a catalyst metal supported on the catalyst carrier, and a dispersion medium containing water as a main component (for forming a fuel cell catalyst layer) is obtained. Can be done.

The electrode catalyst mixture preferably has a cumulative volume fraction of the electrode catalyst having a particle size of 1 μm or less of more than 0%. That is, preferably, it is an electrode catalyst mixture containing a catalyst carrier, an electrode catalyst for a fuel cell made of a catalyst metal supported on the catalyst carrier, and a dispersion medium containing water as a main component, and the particle size of the electrode catalyst is 1 μm. The following is an electrode catalyst mixture (for forming a fuel cell electrode catalyst layer) having a cumulative body integration rate of more than 0%. Since the electrode catalyst mixture having a small particle size of 1 μm or less having a small particle size of 1 μm or less has a small amount of aggregates of the electrode catalyst, the catalyst metal on the catalyst carrier can be effectively used. Therefore, it has excellent power generation performance. In addition, the adsorbed water present on the electrode catalyst suppresses the aggregation of particles again, makes it difficult for the polyelectrolyte to approach the electrode catalyst, improves proton transportability under dry conditions, and under wet conditions. The oxygen transportability underneath is also maintained high. In the mixture, the cumulative volume fraction of the electrode catalyst having a particle diameter of 1 μm or less is 2.5% or more (upper limit 100%), more preferably 3.5% or more, more preferably 4.5% or more, and most preferably 5. It is 0% or more.

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

(II) Step (II) After step (I), a step of further mixing a polymer electrolyte to obtain a composition Then, the electrode catalyst mixture or an 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 (slurry, coating liquid) for forming a fuel cell catalyst layer. Therefore, it is preferable to include a viscosity adjusting solvent for adjusting the viscosity.

The polymer electrolyte is not particularly limited, but is preferably an ionic conductive polymer electrolyte. The polymer electrolyte is also called a proton conductive polymer because it plays a role of transmitting protons generated around the catalyst active material on the fuel electrode side.

The polymer electrolyte is not particularly limited, and conventionally known findings can be appropriately referred to. Polyelectrolytes are roughly classified into fluorine-based polyelectrolytes and hydrocarbon-based polyelectrolytes according to the type of ion exchange resin as a constituent material. Of these, a fluoropolymer electrolyte is preferable in terms of proton conductivity.

Examples of the ion exchange resin constituting the fluoropolymer 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.) and the like. Perfluorocarbon sulfonic acid polymer, perfluorocarbon phosphonic acid polymer, trifluorostyrene sulfonic acid polymer, ethylene tetrafluoroethylene-g-styrene sulfonic acid polymer, ethylene-tetrafluoroethylene copolymer, polyvinylidene fluoride-per Fluorocarbon sulfonic acid-based polymers and the like can be mentioned. From the viewpoint of excellent heat resistance, chemical stability, durability, and mechanical strength, these fluoropolymer electrolytes are preferably used, and particularly preferably a fluoropolymer electrolyte composed of a perfluorocarbon sulfonic acid polymer. Is used.

Specific examples of the hydrocarbon-based electrolyte include sulfonated polyethersulfonate (S-PES), sulfonated polyaryletherketone, sulfonated polybenzimidazole alkyl, phospholated polybenzimidazole alkyl, sulfonated polystyrene, and sulfonated poly. Examples include ether etherketone (S-PEEK) and sulfonated polyphenylene (S-PPP). These hydrocarbon-based polyelectrolytes are preferably used from the viewpoint of manufacturing, such as low raw materials, simple manufacturing process, and high material selectivity. As for the above-mentioned ion exchange resin, only one kind may be used alone, or two or more kinds may be used in combination. Further, the material is not limited to the above-mentioned materials, and other materials may be used. Further, a commercially available electrolyte solution in which the electrolyte is prepared in advance in a solvent (for example, a DuPont Nafion solution: Nafion dispersed / suspended in 1-propanol at a concentration of 5 wt%) may be used. ..

In the polymer electrolyte responsible for the transfer of protons, the conductivity of protons is important. Here, if the EW of the polymer electrolyte is too large, the ionic conductivity of the entire catalyst layer is lowered. Therefore, the catalyst layer of the present embodiment preferably contains a polymer electrolyte having a small EW. Specifically, the catalyst layer of the present embodiment preferably contains a polyelectrolyte having an EW of 1500 g / mol or less, and more preferably contains 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, which makes it difficult for water to move smoothly. From such a viewpoint, the EW of the polymer electrolyte is preferably 600 g / mol or more. In addition, 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 an ion exchange group, and is expressed in units of "g / mol".

As for the mixing ratio of the polymer electrolyte and the composition A, the weight ratio (I / C ratio) of the polymer electrolyte (I) to the catalyst carrier (C) is preferably 0.4 to 1.6, and 0. It is more preferably 7 to 1.4.

The viscosity adjusting solvent is not particularly limited, and ordinary solvents used for forming the catalyst layer can be used in the same manner. Specific examples thereof include water, cyclohexanol, lower alcohols having 1 to 4 carbon atoms, propylene glycol, benzene, toluene, xylene and the like. In addition to these, butyl alcohol 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.

The water is not particularly limited, and tap water, purified water, ion-exchanged water, distilled water and the like can be used. Also, alcohol is not particularly limited. Specific examples thereof include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-methyl-1-propanol, 2-butanol, 2-methyl-2-propanol and cyclohexanol. Of these, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-methyl-1-propanol, 2-butanol and 2-methyl-2-propanol are preferable. By using a lower alcohol having such a high affinity, it is possible to prevent extreme uneven distribution of the electrolyte. Further, among the above alcohols, it is more preferable to use an alcohol having a boiling point of less than 100 ° C. Alcohols with a boiling point of less than 100 ° C include 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. An example is one selected from the group consisting of -2-propanol (boiling point: 83 ° C.). The above alcohols can be used alone or in combination of two or more.

The amount of the viscosity adjusting 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 electrode catalyst and the polymer electrolyte combined is preferably about 1 to 50% by weight, more preferably about 5 to 30% by weight in the composition.

As described above, the polyelectrolyte is roughly classified into a fluoropolymer electrolyte and a hydrocarbon-based polyelectrolyte according to the type of ion exchange resin as a constituent material. Of these, the electrolyte is preferably a fluoropolymer electrolyte. By using the hydrophobic fluoropolyelectrolyte in this way, a repulsive force acts between the water adsorbed on the electrode catalyst and the fluoropolymer electrolyte, and the fluoropolymer electrolyte becomes difficult to approach around the electrode catalyst. .. Therefore, the battery performance under dry conditions and wet conditions is high.

The order of adding the electrode catalyst, the polyelectrolyte and the solvent for adjusting the viscosity is not particularly limited, and all of them are mixed at once; after the electrode catalyst and the polyelectrolyte are mixed, the solvent for adjusting the viscosity is added and mixed. It may be in the form of.

The composition for forming the catalyst layer of the fuel cell includes, if necessary, a water repellent agent such as polytetrafluoroethylene, polyhexafluoropropylene, or tetrafluoroethylene-hexafluoropropylene copolymer, and a dispersant such as a surfactant. , Glycerin, ethylene glycol (EG), polyvinyl alcohol (PVA), propylene glycol (PG) and other thickeners, pore-forming agents and other additives may be contained.

When additives such as a water repellent, a dispersant, a thickener, and a pore-forming agent are used, these additives may be added to the composition. At this time, the amount of the additive added is not particularly limited as long as it does not interfere with the above-mentioned effect of the present invention. For example, the amount of the additive added is preferably 5 to 20% by weight, respectively, based on the total weight of the composition.

In this way, a composition containing an electrode catalyst 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, but the base material. It is preferable to apply a composition (catalyst ink) on the surface to form a catalyst layer.

The method for applying the composition to the substrate is not particularly limited, and a known method can be used. Specifically, it can be carried out by using a known method such as a spray (spray coating) method, a Gulliver printing method, a die coater method, a screen printing method, and a doctor blade method.

At this time, as the base material on which the composition is applied, a solid polymer electrolyte membrane (electrolyte layer) or a gas diffusion base material (gas diffusion layer) can be used. In such a case, after forming a catalyst layer on the surface of a solid polymer electrolyte membrane (electrolyte layer) or a gas diffusion base material (gas diffusion layer), the obtained laminate can be used as it is for manufacturing a membrane electrode assembly. It can be used. Alternatively, a peelable base material such as a polytetrafluoroethylene (PTFE) [Teflon (registered trademark)] sheet is used as the base material, the catalyst layer is formed on the base material, and then the catalyst layer portion is peeled off from the base material. Thereby, a catalyst layer may be obtained.

The amount of the catalyst ink applied to the coated substrate is not particularly limited. Specifically, the content (weight) (mg / cm ² ) of the catalyst metal per area of the catalyst layer 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 addition, in this specification, inductively coupled plasma emission spectroscopy (ICP) is used for measurement (confirmation) of "the content of platinum per area of a catalyst layer (mg / cm ^2)". A person skilled in the art can easily perform a method of reducing the desired "platinum content per catalyst layer area", and the amount can be adjusted by controlling the composition (catalyst concentration) and the coating amount of the slurry. 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 coating layer (film) of the catalyst ink is dried under an air atmosphere or an inert gas atmosphere at room temperature to 150 ° C. for 1 to 60 minutes.

In this way, the catalyst layer for the fuel cell is obtained.

Hereinafter, one of a catalyst layer, a membrane electrode assembly (MEA), and a fuel cell obtained by using the catalyst layer obtained by the production method of the first embodiment or the electrode catalyst mixture of the second embodiment with reference to the drawings as appropriate. The embodiment will be described in detail. However, the present invention is not limited to the following embodiments. It should be noted that each drawing is exaggerated for convenience of explanation, and the dimensional ratio of each component in each drawing may differ from the actual one. Further, when the embodiment of the present invention is described with reference to the drawings, the same elements are designated by the same reference numerals in the description of the drawings, and duplicate description will be omitted.

[Fuel cell]
The fuel cell includes a membrane electrode assembly (MEA) and a pair of separators including an anode-side separator having a fuel gas flow path through which the fuel gas flows and a cathode-side separator having an oxidant gas flow path through which the 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. First, the PEFC 1 has a solid polymer electrolyte membrane 2 and a pair of catalyst layers (anode catalyst layer 3a and cathode catalyst layer 3c) sandwiching the solid polymer electrolyte membrane 2. The laminate of the solid polymer electrolyte membrane 2 and the catalyst layer (3a, 3c) is further sandwiched by a pair of gas diffusion layers (GDL) (anode gas diffusion layer 4a and cathode gas diffusion layer 4c). As described above, the solid polymer electrolyte membrane 2, the pair of catalyst layers (3a, 3c) and the pair of gas diffusion layers (4a, 4c) form the membrane electrode assembly (MEA) 10 in a laminated state.

In PEFC 1, the 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 shown so as to be located at both ends of the illustrated MEA 10. However, in a fuel cell stack in which a plurality of MEAs are stacked, the separator is generally used as a separator for adjacent PEFCs (not shown). In other words, in the fuel cell stack, the MEAs are sequentially stacked via the separator to form the stack. In the actual fuel cell stack, the gas seal portion is arranged between the separator (5a, 5c) and the solid polymer electrolyte membrane 2, or between the PEFC 1 and another PEFC adjacent thereto. , In FIG. 2, these descriptions are omitted.

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 an uneven shape as shown in FIG. The convex portion of the separator (5a, 5c) seen from the MEA side is in contact with the MEA 10. This ensures an electrical connection with the MEA 10. Further, the recesses (the space between the separator and the MEA caused by the uneven shape of the separator) seen from the MEA side of the separators (5a, 5c) are for circulating gas during the operation of PEFC 1. Functions as a gas flow path. Specifically, a fuel gas (for example, hydrogen) is circulated in the gas flow path 6a of the anode separator 5a, and an oxidant gas (for example, air) is circulated in the gas flow path 6c of the cathode separator 5c.

On the other hand, the recesses of the separators (5a, 5c) seen from the side opposite to the MEA side are used as a refrigerant flow path 7 for circulating a refrigerant (for example, water) for cooling the PEFC during the operation of the PEFC 1. To. Further, the separator is usually provided with a manifold (not shown). This manifold functions as a connecting means for connecting the cells when the stack is configured. With such a configuration, the mechanical strength of the fuel cell stack can be ensured.

In the embodiment shown in FIG. 2, the separators (5a and 5c) are formed into an uneven shape. However, the separator is not limited to such an uneven shape, and may be any shape such as a flat plate shape or a partially uneven shape as long as the functions of the gas flow path and the refrigerant flow path can be exhibited. May be good.

The fuel cell having the MEA of the present invention as described above exhibits excellent power generation performance. Here, the type of the fuel cell is not particularly limited, and in the above description, the polymer electrolyte fuel cell has been described as an example, but in addition to this, an alkaline fuel cell and a direct methanol fuel cell have been described. , Micro fuel cells and the like. Among them, a polymer electrolyte fuel cell (PEFC) is preferable because it is compact and can have high density and high output. Further, the fuel cell is useful as a power source for a mobile body such as a vehicle whose mounting space is limited, as well as a power source for stationary use. Above all, it is particularly preferable to use it as a power source for a mobile body such as an automobile, which requires a high output voltage after a relatively long operation stop.

The fuel used when 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. Of these, hydrogen and methanol are preferably used because they can increase the output.

The application of the fuel cell is not particularly limited, but it is preferably applied to the vehicle. The electrolyte membrane-electrode assembly of the present invention is excellent in power generation performance and durability, and can be miniaturized. Therefore, the fuel cell of the present invention is particularly advantageous when the fuel cell is applied to a vehicle from the viewpoint of in-vehicle performance. Therefore, the present invention provides a vehicle having the fuel cell of the present invention.

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

[Electrode catalyst layer (catalyst layer)]
The electrode catalyst layer (catalyst layer) is formed by the production method of the first embodiment, or is formed by 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, considering the necessity of improving the proton conductivity and the transport characteristics (gas diffusivity) of the reaction gas (particularly O ₂ ), at least the cathode catalyst layer is manufactured by the production method of the first embodiment or the second embodiment. It is preferably formed using the electrode catalyst mixture of the form. However, only the cathode catalyst layer may be formed by using the electrode catalyst mixture of the present invention, or both the cathode catalyst layer and the anode catalyst layer may be formed by using the electrode catalyst mixture of the present invention. It is not something that is done.

[Electrolyte membrane (polyelectrolyte membrane)]
The electrolyte membrane is roughly classified into a fluorine-based polyelectrolyte membrane and a hydrocarbon-based polyelectrolyte membrane according to the type of ion exchange resin as a constituent material. Examples of the ion exchange resin constituting the fluoropolymer electrolyte membrane 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.) and the like. Perfluorocarbon sulfonic acid polymer, perfluorocarbon phosphonic acid polymer, trifluorostyrene sulfonic acid polymer, ethylene tetrafluoroethylene-g-styrene sulfonic acid polymer, ethylene-tetrafluoroethylene copolymer, polyvinylidene fluoride- Perfluorocarbon sulfonic acid-based polymers and the like can be mentioned. From the viewpoint of improving power generation performance such as heat resistance and chemical stability, these fluoropolyelectrolyte films are preferably used, and particularly preferably a fluoropolyelectrolyte composed of a perfluorocarbon sulfonic acid polymer. A membrane is used.

Specific examples of the hydrocarbon-based electrolyte include sulfonated polyethersulfonate (S-PES), sulfonated polyaryletherketone, sulfonated polybenzimidazole alkyl, phospholated polybenzimidazole alkyl, sulfonated polystyrene, and sulfonated poly. Examples include ether etherketone (S-PEEK) and sulfonated polyphenylene (S-PPP). These hydrocarbon-based polyelectrolyte membranes have advantages in manufacturing, such as low raw materials, simple manufacturing process, and high material selectivity. As for the above-mentioned ion exchange resin, only one kind may be used alone, or two or more kinds may be used in combination. Further, the material is not limited to the above-mentioned materials, and 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 diffusion of a gas (fuel gas or an oxidant gas) supplied through a separator flow path and a function as an electron conduction path, and is hydrophilic and porous. It has the function of supporting the stratum.

The material constituting the gas diffusion layer base material is not particularly limited, and conventionally known findings can be appropriately referred to. For example, a sheet-like material having conductivity and porosity such as a carbon woven fabric, a paper-like paper machine, felt, and a non-woven fabric can be mentioned. More specifically, carbon paper, carbon cloth, carbon non-woven fabric and the like are preferably mentioned. As the gas diffusion layer base material, a commercially available product can also be used, and examples thereof include a carbon paper TGP series manufactured by Toray Industries, Inc. and a carbon cloth manufactured by E-TEK.

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

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

Further, in order to further improve the water repellency, the gas diffusion layer may have a microporous layer (MPL layer) on the catalyst layer side of the gas diffusion layer base material. The microporous layer refers to a microporous layer having a large number of micropores, 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, and expanded graphite can 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 its excellent electron conductivity and large specific surface area. The average particle size of the carbon particles is preferably about 10 to 100 nm. As a result, high drainage can be obtained due to the capillary force, and the contact with the catalyst layer can be improved.

The microporous layer preferably contains a water repellent. Examples of the water repellent used for the microporous layer include the same as the above-mentioned water repellent. 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 the carbon particles and the water repellent in the microporous layer is about 90: 10 to 40:60 (carbon particles: water repellent) in consideration of the balance between water repellency and electron conductivity. Is 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 forming a catalyst layer on the surface of an electrolyte membrane (solid polymer electrolyte membrane) or a gas diffusion layer base material (gas diffusion layer), the obtained laminate is used as it is for manufacturing a membrane electrode assembly. can do. Alternatively, a peelable base material such as a polytetrafluoroethylene (PTFE) [Teflon (registered trademark)] sheet is used as the base material, the catalyst layer is formed on the base material, and then the catalyst layer portion is peeled off from the base material. Thereby, a catalyst layer may be obtained.

(Membrane electrode assembly)
According to a further embodiment of the present invention, there is provided a fuel cell membrane electrode assembly including the fuel cell electrode catalyst layer. That is, the solid polymer electrolyte membrane 2, the cathode catalyst layer 3c arranged on one side of the electrolyte membrane, the anode catalyst layer 3a arranged on the other side of the electrolyte membrane, the electrolyte membrane 2, and the anode catalyst layer 3a. And a membrane electrode junction for a fuel cell having a pair of gas diffusion layers (4a, 4c) sandwiching the cathode catalyst layer 3c are provided. 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, considering the necessity of improving the proton conductivity and the transport characteristics (gas diffusivity) of the reaction gas (particularly O ₂ ), at least the cathode catalyst layer may be the catalyst layer of the embodiment described above. preferable. However, the catalyst layer according to the above embodiment is not particularly limited, such as being used as an anode catalyst layer or being 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, a method of transferring or applying a catalyst layer to an electrolyte membrane by hot pressing and joining the gas diffusion layer to the dried material, or the microporous layer side of the gas diffusion layer (including the microporous layer). If not, two gas diffusion electrodes (GDE) are prepared by applying a catalyst layer on one side of the base material layer in advance and drying, and hot pressing the gas diffusion electrodes on both sides of the solid polymer electrolyte membrane. The method of joining with can be used. The coating and bonding conditions of hot press or the like may be appropriately adjusted depending on the type of the 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 the membrane electrode assembly of the above-described embodiment. That is, one embodiment of the present invention is a fuel cell having a pair of anode separators and a cathode separator that sandwich the membrane electrode assembly of the above embodiment.

(Separator)
The separator has a function of electrically connecting each cell in series when a plurality of single cells of a fuel cell such as a polymer electrolyte fuel cell are connected in series to form a fuel cell stack. The separator also has a function as a partition wall for separating the fuel gas, the oxidant gas, and the cooling agent from each other. In order to secure these flow paths, it is preferable that each of the separators is provided with a gas flow path and a cooling flow path, as described above. As the material constituting the separator, conventionally known materials such as dense carbon graphite, carbon such as carbon plate, and metal such as stainless steel can be appropriately adopted without limitation. The thickness and size of the separator, the shape and size of each flow path provided are not particularly limited, and can be appropriately determined in consideration of the desired output characteristics of the obtained fuel cell and the like.

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

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

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

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

The effects of the present invention will be described with reference to the following examples and comparative examples. In the examples, the display of "parts" or "%" may be used, but unless otherwise specified, it represents "parts by weight" or "% by weight". Unless otherwise specified, each operation is performed at room temperature (25 ° C.).

(Example 1)
(Manufacturing of electrode catalyst)
As the catalyst carrier A, Ketjen Black EC300J (manufactured by Ketjen Black International Co., Ltd.) having a BET specific surface area of 790 m ^{2 / g and a primary average particle size of about 40 nm was prepared.} A catalyst powder A was obtained by supporting platinum (Pt) having an average particle diameter of 2.5 nm as a catalyst metal on the catalyst carrier A so that the loading ratio was 50% by weight. That is, 46 g of carrier A was immersed in 1000 g (platinum content: 46 g) of a dinitrodiammine platinum nitric acid solution having a platinum concentration of 4.6% by weight, and after stirring, 100 ml of 100% ethanol was added as a reducing agent. This solution was stirred and mixed at boiling point for 7 hours, and platinum was supported on the catalyst carrier A. Then, by filtering and drying, a catalyst powder having a loading ratio of 50% by weight on the carrier was obtained. Then, in a hydrogen atmosphere, the temperature was maintained at 900 ° C. for 1 hour to obtain an electrode catalyst I. The peak particle size of the electrode catalyst I measured under the following particle size distribution measurement conditions was 13.2 μm.

(Manufacturing of electrode catalyst mixture)
Using a self-revolving mixer (Awatori Rentaro (registered trademark) AR-250, manufactured by Shinky Co., Ltd.) for 100 parts by weight of the electrode catalyst I and 500 parts by weight of purified water, the rotation: 200 rotations / minute, the revolution: 400 rotations / In minutes, mixed for 2 minutes.

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

The above stirring was performed by sealing the system in order to prevent evaporation of the solvent accompanying the stirring. The same applies to the following examples and comparative examples.

The particle size measurement conditions are as follows.

(Particle size measurement conditions)
A sample was prepared by diluting the dispersion liquid with the dispersion medium of the electrode catalyst with 2-propanol so that the solid content concentration became 1.0% by weight. 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), the cumulative volume fraction having a particle size of 1 μm or less was obtained.

(Particle size distribution measurement conditions)
Method: Laser diffraction / scattering method Device name: MT3000II (manufactured by Microtrac 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 diameter of 8.0 μm and a cumulative volume fraction of 3.7% or less having a particle diameter of 1 μm or less. Therefore, when the peak particle size before the contact with the dispersion medium was 100, the peak particle size of the electrode catalyst after the contact was maintained was 60.6.

(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 diameter of 7.6 μm and a cumulative volume fraction of 5.6% with a particle diameter of 1 μm or less. Therefore, when the peak particle size before the contact with the dispersion medium was 100, the peak particle size of the electrode catalyst after the contact was maintained was 57.6.

(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 5.0% or less having a particle size of 1 μm or less. Therefore, when the peak particle size before contact with the dispersion medium was 100, the peak particle size of the electrode catalyst after maintaining contact was 65.9.

(Example 5)
An electrode catalyst mixture A-5 was obtained in the same manner as in Example 1 except that the premixing was not performed by the revolving mixer. The electrode catalyst mixture A-5 after stirring had a peak particle diameter of 13.6 μm and a cumulative volume fraction of 3.1% or less having a particle diameter of 1 μm or less. Therefore, when the peak particle size before contact with the dispersion medium was 100, the peak particle size of the electrode catalyst after maintaining contact 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 diameter of 10.4 μm and a cumulative volume fraction of 5.4% with a particle diameter of 1 μm or less. Therefore, when the peak particle size before the contact with the dispersion medium was 100, the peak particle size of the electrode catalyst after the contact was maintained 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 diameter of 9.9 μm and a cumulative volume fraction of 4.8% having a particle diameter of 1 μm or less. Therefore, when the peak particle size before the contact with the dispersion medium was 100, the peak particle size of the electrode catalyst after the contact was maintained was 75.0.

(Comparative Example 1)
(Manufacturing of electrode catalyst)
The electrode catalyst I was obtained in the same manner as in Example 1.

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

In Examples 1 to 7, the cumulative volume fraction having a particle size of 1 μm or less became more than 0% by immersing the electrode catalyst in water for a long time, specifically, immersing it for 24 hours or more. Further, by comparing Examples 1 and 5, it can be seen that the peak particle diameter of the electrode catalyst after the contact is maintained becomes smaller when the peak particle diameter before the contact with the dispersion medium is set to 100 by performing the premixing. It is considered that this is because water permeates more between the catalysts due to the premixing, and the catalysts are easily crushed in the subsequent steps.

On the other hand, in Comparative Example 1, since only the electrode catalyst and water were premixed and not immersed in water for a long time, the cumulative volume fraction having a particle size of 1 μm or less was 0%.

(Example 8)
In the composition A-3 obtained in Example 3, an ionomer dispersion as a polymer electrolyte (Nafion (registered trademark) D2020, EW = 1100 g / mol, manufactured by DuPont) was added to the electrolyte (ionomer) for a carbon carrier. The mixture was mixed so that the weight ratio (I / C ratio) was 0.9. Next, using the above mixture as a solvent, an aqueous solution of n-propyl alcohol (NPA) (water: NPA = 6: 4 (weight ratio)) is used so that the solid content (Pt + catalyst carrier + polymer electrolyte) is 7% by weight. Addition was made to prepare a catalytic ink.

Gasket around both sides of the polymer electrolyte membrane (DuPont, Nafion® NR211; thickness: 25 μm) (Teijin DuPont Film Co., Ltd., Theonex®, thickness: 25 μm (adhesive layer: 2710 μm)) Was placed. Next, the catalyst ink was applied to an exposed portion on one side of the polymer electrolyte membrane by a spray coating method to a size of 5 cm × 2 cm. The catalyst ink was dried by keeping the stage for spray coating 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, a membrane electrode assembly was obtained in which catalyst layers were formed on both sides of the electrolyte membrane by spray coating and drying treatment on the other surface 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 assembly obtained in Example 8 and Comparative Example 2.

(Power generation performance test 1: Dry condition)
Power was generated by supplying pure hydrogen to the anode and air (both 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%. The IV performance was measured under the above conditions.

(Power generation performance test 2: Wet condition)
Power was generated by supplying pure hydrogen to the anode and air (both 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%. The IV performance was measured under the above conditions.

Table 1 below shows the cell voltages (IR-free) of Examples and Comparative Examples at a current density of 1 A / cm ^{2 under Dry and Wet conditions.}

(Proton transport resistance test)
It was measured by electrochemical impedance spectroscopy. As the equipment used, the electrochemical measurement system HZ-3000 manufactured by Hokuto Denko Co., Ltd. and the frequency response analyzer FRA5020 manufactured by NF Circuit Design Block Co., Ltd. were used for evaluation according to the measurement conditions in Table 2 below. .. The results are shown in FIG.

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

1 ... Polymer electrolyte fuel cell (PEFC),
2 ... Solid polyelectrolyte 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)

An electrode catalyst made of a catalyst carrier and a catalyst metal supported on the catalyst carrier and a dispersion medium containing water as a main component are brought into contact with each other.
Then, the polymer electrolyte was further mixed to obtain a composition.
It has the ability to form 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 electrode catalyst having a particle diameter of 1 μm or less is 2.5% or more. The method for manufacturing a catalyst layer for a fuel cell according to claim 1, wherein the contact is maintained for 24 hours or more. The fuel cell according to claim 1 or 2, wherein when the peak particle size of the electrode catalyst before contact with the dispersion medium is 100, the contact is maintained until the peak particle size of the electrode catalyst becomes 95 or less. Method for manufacturing catalyst layer. The method for manufacturing a catalyst layer for a fuel cell according to any one of claims 1 to 3, wherein the contact is maintained under stirring using an overturning rotary stirrer. The method for manufacturing a catalyst layer for a fuel cell according to claim 4, wherein premixing is performed by a rotating / revolving stirrer before maintaining the contact. The method for producing a catalyst layer for a fuel cell according to any one of claims 1 to 5, wherein the dispersion medium is water. The method for producing a catalyst layer for a fuel cell according to any one of claims 1 to 6, wherein the catalyst carrier is a carbon material. An electrode catalyst mixture containing an electrode catalyst composed of a catalyst carrier and a catalyst metal supported on the catalyst carrier and a dispersion medium containing water as a main component (however, it does not contain a polymer electrolyte).
An electrode catalyst mixture having a cumulative volume fraction of 2.5% or more with a particle diameter of 1 μm or less of the electrode catalyst. The electrode catalyst mixture according to claim 8, wherein the dispersion medium is water. The electrode catalyst mixture according to claim 8 or 9, wherein the catalyst carrier is a carbon material.

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