JP2013051173A - Composition, membrane-catalyst layer assembly, and method for manufacturing membrane-catalyst layer assembly - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composition improving battery characteristics and raising output of a fuel cell, and also capable of preventing an occurrence of flooding under high humidification conditions and preventing deterioration in catalyst activity under low humidification conditions.SOLUTION: A catalyst ink according to the present invention is a coating liquid which includes catalyst-supporting carbon, a fluorine-containing ion exchange resin and a dispersant, and is coated on a polymer electrolyte membrane for forming a catalyst layer in a polymer electrolyte fuel cell. In the catalyst ink, the catalyst-supporting carbon is contained in a state of an aggregate, an agglomerate, and an associated aggregate, and, when a particle size distribution in the catalyst ink is measured by a laser scattering/diffraction method, the particle size distribution has a main peak in a range corresponding to particle sizes of the associated aggregate.

Description

  The present invention relates to an electrode assembly (membrane catalyst layer assembly) of a polymer electrolyte fuel cell. In particular, the present invention relates to a catalyst ink (composition) applied to a polymer electrolyte membrane in order to form a catalyst layer of an electrode assembly.

  In recent years, fuel cells have attracted attention as vehicle driving sources and stationary power sources in response to social demands and trends against the background of energy and environmental problems. Fuel cells are classified into various types depending on the type of electrolyte and the type of electrode.

  For example, representative types include alkali type, phosphoric acid type, molten carbonate type, solid electrolyte type, and polymer electrolyte type. Among these, as a low-pollution power source for automobiles, polymer electrolyte fuel cells (PEFC) that can operate without raising the temperature (usually below 100 ° C) are attracting attention, and development for practical use is underway. It has been. However, since the polymer electrolyte fuel cell can be operated without raising the temperature, it is difficult to effectively use the exhaust heat for auxiliary power.

  Therefore, in order to make up for the difficulty of effective use of exhaust heat, high energy conversion efficiency and high power density are achieved for polymer electrolyte fuel cells under operating conditions with high utilization rates of hydrogen and oxygen. Is required.

  In order for the polymer electrolyte fuel cell to meet this requirement, among the elements constituting the cell, in particular, an electrode comprising a fuel cell electrode and an ion exchange membrane (polymer electrolyte membrane) having the electrode disposed on both surfaces thereof The joined body is important.

  Here, the fuel cell electrode is formed by directly applying a viscous mixture (catalyst ink) having the following configuration on the surface of the ion exchange membrane, or by applying a layer obtained by applying it to another sheet base material on the surface of the ion exchange membrane. It is formed by transferring or pasting.

  This catalyst ink is composed of a catalyst-supporting carbon that promotes an electrode reaction, a fluorine-containing ion exchange resin for enhancing conductivity and preventing clogging (flooding) of a porous body due to condensation of water vapor, and an alcohol such as ethanol. It is dissolved or dispersed in a solvent.

  Therefore, in order to satisfy the above-described requirements, improvement of the catalyst component in the catalyst ink, catalyst component loading method, protection and stabilization of the supported catalyst by coating with an ion exchange resin, etc. have been studied, and various improvements have been proposed. Yes.

  For example, the relationship between the particle size distribution of catalyst particles coated with an ion exchange resin, the particle size distribution of aggregates of supported catalyst particles, and battery characteristics has been reported (for example, Patent Document 1).

  That is, in the electrode constituent raw material disclosed in Patent Document 1, the aggregates of particles having different particle size distributions so that the aggregates of the supported catalyst particles carrying the catalyst metal of the fuel cell electrode constituent material have two particle size distribution peaks. It is adjusted by mixing. More specifically, the two particle size distribution peaks have a particle size distribution peak between 0.1 and 1.0 μm and between 1.0 and 10 μm. Agglomerates of particles exhibiting a distribution of up to 1.0 μm account for 25 percent of the total volume.

  By having two types of particle size distributions in this way, the electrode constituent raw material disclosed in Patent Document 1 reduces the pore volume when the particle size is too small, and decreases the catalyst utilization when the particle size is too large. Thus, it is possible to compensate for each of the disadvantages that the battery characteristics deteriorate.

  Furthermore, the proportion of the particle size distribution of the particle size of the coating liquid (catalyst ink) containing the catalyst-supporting carbon (catalyst particles) and the fluorine-containing ion exchange resin and having a dispersion medium is 30% volume frequency. A method of manufacturing a fuel cell electrode manufactured as described above has been proposed (for example, Patent Document 2).

JP-A-8-227716 JP 2003-109612 A

  However, the above-described prior art is operated when introducing a highly humidified reaction gas (relative humidity of 80% or more) into at least one electrode, or low humidification (relative humidity of 40% relative to at least one electrode). There is a problem that sufficient characteristics cannot be obtained when the reaction gas is introduced and operated.

  More specifically, in the electrode constituent raw material disclosed in Patent Document 1, aggregates of catalyst-carrying carbon (catalyst particles) showing a distribution between 1.0 and 10 μm account for 75% of the total volume, By containing many aggregates of catalyst-carrying carbon having a large diameter, the pore volume of the electrode can be secured, and the flooding of the porous body due to condensation of water vapor is prevented. However, when a fuel cell manufactured using the electrode constituent raw material of Patent Document 1 is operated by introducing a low humidified gas into at least one of the electrodes, the inside of the catalyst layer is in an atmosphere where condensation due to water vapor hardly occurs. Therefore, the catalyst cannot be activated sufficiently and the output of the battery cannot be fully exhibited.

  That is, the catalyst-carrying carbon aggregates having a large particle size have a range that is not coated with an ion exchange resin such as an ionomer resin (ionomer resin) inside, and as a result, a range that is activated in the catalyst-carrying carbon. It gets smaller. That is, as the proportion of the aggregate of the catalyst carrier carbon having a large particle size increases, the range not covered with the ion exchange resin increases, and the activation range in the catalyst-supported carbon further decreases. For this reason, under low humidification conditions where flatting is unlikely to occur, the activation of the catalyst is reduced in the electrode constituent raw material of the cited document 1 as compared with the conventional electrode constituent raw material.

  On the other hand, in the method for producing a polymer electrolyte fuel cell electrode of Patent Document 2, the proportion of aggregates having a particle size of 1.0 μm or less is 30% volume frequency or more. That is, it contains many aggregates having a small particle diameter of 1.0 μm or less, and as a result, the pores become small. Therefore, when a fuel cell manufactured using the electrode constituent material of Patent Document 2 is operated by introducing a highly humidified gas into at least one of the electrodes, flattening easily occurs. For this reason, under the high humidification condition, it is affected by the flatting, and there arises a problem that the output of the battery cannot be sufficiently exhibited.

  The present invention has been made in view of the above-described problems of the prior art, and improves battery characteristics, enhances the output of a fuel cell, prevents flattening under high humidification conditions, and catalyzes under low humidification conditions. Provided are a composition capable of preventing a decrease in activity, a membrane catalyst layer assembly, and a method for producing a membrane catalyst layer assembly.

  In order to solve the above problems, the composition according to the present invention includes a catalyst-supporting carbon, an ion exchange resin, and a dispersion medium, and is applied to a polymer electrolyte membrane to form a catalyst layer in a fuel cell. In the composition, the catalyst-supported carbon is composed of aggregates of primary aggregates formed by combining particles of the catalyst-supported carbon, and secondary aggregates formed by collecting a plurality of the aggregates. Aggregate of aggregates, and an aggregate state intermediate between the aggregate and the agglomerate, including aggregate aggregates that are formed by aggregation of a plurality of aggregates and have a particle size in a predetermined particle size range When the particle size distribution in the composition is measured by a laser scattering / diffraction method, the particle size distribution has a main peak in the predetermined particle size range of the aggregate. That.

  A membrane catalyst layer assembly according to the present invention is a membrane catalyst layer assembly comprising a polymer electrolyte membrane and a catalyst layer disposed on the polymer electrode membrane in order to solve the above-described problems, The catalyst layer includes a catalyst-carrying carbon, an ion exchange resin, and a dispersion medium. The catalyst-carrying carbon is an aggregate of primary aggregates formed by combining particles of the catalyst-carrying carbon, and the aggregate is Agglomerates of secondary aggregates formed by aggregating, and agglomerates that are in an intermediate agglomerated state between the aggregate and the agglomerate and are formed by aggregating a plurality of aggregates and having a particle size in a predetermined particle size range. In a particle size distribution that is included in a state of an aggregate and is obtained by measurement by a laser scattering / diffraction method, the particle size distribution may be within a predetermined particle size range of the aggregate. A composition having a peak is formed by coating the polymer electrolyte membrane.

  In order to solve the above-mentioned problems, a method for producing a membrane / catalyst layer assembly according to the present invention prepares a polymer electrolyte membrane, and on this polymer electrolyte membrane, a catalyst-supporting carbon, an ion exchange resin, and a dispersion As agglomeration state of the aggregate formed by combining the primary particles of the catalyst-supporting carbon, the aggregate of primary aggregates formed by combining the particles of the catalyst-supported carbon, and a plurality of the aggregates are collected Agglomerates of secondary agglomerates formed in this way, and agglomerates that are agglomerated between the aggregates and the agglomerates, are formed by aggregating a plurality of aggregates, and have a particle size in a predetermined particle size range In a particle size distribution obtained by measurement by a laser scattering / diffraction method, the main peak is within a predetermined particle size range of the aggregate. Coating the composition with.

  The present invention is configured as described above, improves battery characteristics, increases fuel cell output, prevents flattening under high humidification conditions, and prevents a decrease in catalyst activity under low humidification conditions. There is an effect that can be.

It is a figure which shows an example of schematic structure of the fuel cell single cell which concerns on this Embodiment. It is a figure which shows an example of the single aggregate which is the aggregate of the carbon particle which concerns on this Embodiment. It is a figure which shows an example of the agglomerate which is the aggregate of the carbon particle which concerns on this Embodiment. It is a figure which shows an example of the aggregation aggregate which is the aggregate of the carbon particle which concerns on this Embodiment. It is a graph which shows the particle size distribution of the aggregate of the carbon particle in the catalyst ink which concerns on this Embodiment. It is a figure which shows an example of the state which the single aggregate connected between the association aggregates in the dispersion medium of the catalyst ink which concerns on this Embodiment. It is a flowchart which shows an example of the manufacturing process of the catalyst ink which concerns on this Embodiment. It is a graph which shows an example of the relationship between the shear time with respect to the catalyst carrying | support carbon which concerns on this Embodiment, the particle size of the aggregate, and its volume frequency.

(Single fuel cell)
The configuration of the single fuel cell 1 according to this embodiment will be described with reference to FIG. FIG. 1 is a diagram illustrating an example of a schematic configuration of a fuel cell single cell 1 according to the present embodiment. In addition, the fuel cell single cell 1 which concerns on this Embodiment is demonstrated as a cell of a polymer electrolyte fuel cell (PEFC).

  As shown in FIG. 1, the fuel cell single cell 1 has two electrodes (a fuel electrode 3 and an air electrode 4) formed on both sides of a polymer electrolyte membrane 2, and these are MEA (membrane electrode assembly) 5. It is the structure formed by integrating. The electrodes are a catalyst layer (fuel electrode catalyst layer 31 and air electrode catalyst layer 41) disposed on the polymer electrolyte membrane 2 side, and a gas that is a porous member having conductivity disposed outside the catalyst layer. Diffusion layers 32 and 42 are provided. This electrode contains a catalyst-supporting carbon and a fluorine-containing ion exchange resin.

  In addition, separators 6 and 7 that serve as supply passages for reaction gases such as hydrogen and oxygen are disposed outside the gas diffusion layers 32 and 42, and the MEA 5 is sandwiched between the separators 6 and 7.

As the catalyst for forming the catalyst layer (the fuel electrode catalyst layer 31 and the air electrode catalyst layer 41), a substance that promotes the electrode reaction at the anode and the cathode is used, and a platinum group metal such as platinum or an alloy thereof is particularly suitable. . As the catalyst, metal particles may be used as they are, but in the present embodiment, catalyst-supporting carbon having a specific surface area of 300 m ² / g or more is used as a catalyst. The metal loading is preferably 10 to 70% by mass with respect to the total mass of the catalyst-carrying carbon.

  The polymer electrolyte membrane 2 (ion exchange membrane) adjacent to and sandwiched by the two electrodes preferably has an ion exchange capacity of 0.6 to 2.2 meq / g, particularly 1 .1 to 1.6 meq / g is preferable. Further, the thickness of the electrode of the fuel cell is preferably 1 to 50 μm, particularly preferably 10 to 30 μm.

  The material constituting the polymer electrolyte membrane 2 is preferably the same as that exemplified as the fluorine-containing ion exchange resin used for forming the electrode. That is, the fluorine-containing ion exchange resin is preferably composed of a copolymer containing a polymer unit based on tetrafluoroethylene and a polymer unit based on perfluorovinyl ether having a sulfonic acid group.

The perfluorovinyl ether having a sulfonic acid _{group, CF 2 = CF- (OCF 2} CFX) m -O p - in (CF2) _n -SO ₃ H (wherein, m is 0 to 3, n is 1 to 12, P is preferably 0 or 1, and X is F or CF ₃ ).

  In addition, separators 6 and 7 that also serve as supply passages for reaction gases such as hydrogen and oxygen are disposed outside the gas diffusion layers 32 and 42, and the MEA 5 is sandwiched between the separators 6 and 7. is there.

  By the way, in the polymer electrolyte fuel cell, the performance of the MEA 5 is important in order to realize high energy conversion efficiency and high power density even under operating conditions with high utilization rates of hydrogen and oxygen. In particular, the performance depends on the catalyst ink (composition) that forms the catalyst layers (fuel electrode catalyst layer 31 and air electrode catalyst layer 41) of the electrodes (fuel electrode 3 and air electrode 4). In the present specification, the fuel electrode catalyst layer 31 and the air electrode catalyst layer 41 are simply referred to as catalyst layers unless there is a need to distinguish between them. Further, when it is not necessary to distinguish between the fuel electrode 3 and the air electrode 4, they are referred to as electrodes.

  The catalyst ink is composed of a catalyst-supporting carbon that promotes an electrode reaction, a fluorine-containing ion exchange resin for enhancing conductivity and preventing fluttering due to water vapor aggregation, alcohol, ether, dialkyl sulfoxide as a dispersion medium, and A dispersion medium containing one or more kinds from the group consisting of water is used.

  The catalyst ink is applied directly to the polymer electrolyte membrane 2 or a layer obtained by applying the catalyst ink to another sheet-like substrate is transferred or pasted to the surface of the polymer electrolyte membrane 2.

  Details of the catalyst ink applied to the polymer electrolyte membrane 2 will be described below.

(Catalyst ink)
First, the fluorine-containing ion exchange resin contained in the catalyst ink preferably has an ion exchange capacity of 0.6 to 2.2 meq / g from the viewpoint of conductivity and gas permeability. Those having 1.6 meq / g are preferred. The fluorine-containing ion exchange resin is preferably made of a copolymer containing a polymer unit based on tetrafluoroethylene and a polymer unit based on perfluorovinyl ether having a sulfonic acid group.

The perfluorovinyl ether having a sulfonic acid _{group, CF 2 = CF (OCF 2} CFX) m -O p - (CF 2) are preferably those represented by -SO ₃ H. Here, X is a fluorine atom or a trifluoromethyl group, m is an integer of 0 to 3, n is an integer of 1 to 12, and p is 0 or 1. More preferable specific examples include the following compounds. In the following formula, q and r are integers of 1 to 8, and t is an integer of 1 to 3.

CF ₂ = CFO (CF ₂ ) _q SO ₃ H
CF ₂ = CFOCF ₂ CF (CF ₃ ) O (CF ₂ ) _r SO ₃ H
_{CF 2 = CF (OCF 2 CF} (CF 3)) t O (CF 2) 2 SO 3 H
In addition, the catalyst-carrying carbon and the fluorinated ion exchange resin contained in the electrode have a mass ratio of catalyst-carrying carbon: fluorinated ion exchange resin = 60: 40 to 70:30. It is preferable from the viewpoint of transportation. In addition, the catalyst carrying | support carbon here shall include the case of only a catalyst.

  Next, the dispersion medium contained in the catalyst ink will be described. The dispersion medium is preferably an aqueous dispersion medium containing water, particularly a mixed solvent of water and alcohol. Alcohols and ethers preferably have 1 to 6 carbon atoms, and dialkyl sulfoxides preferably have 2 to 6 carbon atoms. Preferable specific examples of the solvent corresponding to the above include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 1,4-dioxane and the like.

  Examples of the dialkyl sulfoxide include dimethyl sulfoxide and diethyl sulfoxide.

  Furthermore, the catalyst ink contains carbon particles (catalyst-carrying carbon) as catalyst particles carrying the catalyst, and in this embodiment, the aggregate in which the carbon particles (domains) are bonded with a strong force is mainly used. As shown in FIGS. 2 to 4, the following three types of aggregates having different particle sizes are classified. The minimum unit of carbon particles is 10 to 50 (0.01 to 0.05 μm) nm size.

  First, the first type of aggregate is an aggregate which is a primary aggregate obtained by aggregating several carbon particles with a strong force as shown in FIG. Hereinafter, this aggregate is referred to as a single aggregate in order to distinguish it from other aggregates. FIG. 2 is a diagram showing an example of a single aggregate that is an aggregate of carbon particles according to the present embodiment. The particle size of this single aggregate is about 300 nm (about 0.3 μm). This single aggregate is considered to be produced by further bonding hydrocarbons to a skeleton formed by melting and bonding liquid crystal particles in the reaction process and then carbonizing.

  Next, as shown in FIG. 3, the second type of aggregate is an agglomerate that is a secondary aggregate obtained by aggregating single aggregates that are primary aggregates by van der Waals force, force due to simple aggregation, entanglement, or the like. . FIG. 3 is a diagram showing an example of an agglomerate that is an aggregate of carbon particles according to the present embodiment. The particle size of the agglomerate is about a dozen μm to a few hundred μm.

  As shown in FIG. 4, the third type of aggregate is an aggregate in which several single aggregates are aggregated by van der Waals force, simple aggregation, entanglement, etc., and an intermediate aggregate between the aggregate and the agglomerate. It is an aggregate that becomes a state. In the present specification, this aggregate is referred to as an association aggregate. FIG. 4 is a diagram showing an example of an association aggregate that is an aggregate of carbon particles according to the present embodiment. The particle size of the aggregate is in the range of about 0.5 μm to 1.5 μm. In the present embodiment, the aggregate aggregate is defined so as to be distinguished from the agglomerate by the particle size.

  That is, in the catalyst ink according to the present embodiment, the above-described single aggregate, association aggregate, and agglomerate are present in a predetermined ratio, respectively. In the particle size distribution measured by the laser scattering / diffraction method, The main peak of this particle size distribution comes in the range of the particle size of the aggregate. That is, the volume frequency of the association aggregate is the highest in the catalyst ink.

  Here, the particle size distribution was measured by a laser scattering / diffraction method, specifically using a particle size distribution apparatus HRA model 9320-X100 manufactured by Microtrac (registered trademark).

  By the way, the applicant stated that the performance of the polymer electrolyte fuel cell using the fuel cell electrode produced by applying this catalyst ink differs due to the particle size distribution of the aggregates of the carbon particles in the catalyst ink. I found it.

  In particular, as shown in FIG. 5 as the particle size distribution of the aggregates of carbon particles in the catalyst ink, there are single aggregates, associated aggregates, and agglomerates, in which the proportion of the aggregate aggregate particles is totally dispersed. It has been found that the fuel cell performance is improved by increasing the volume frequency relative to the particles. FIG. 5 is a graph showing the particle size distribution of the aggregates of carbon particles in the catalyst ink according to the present embodiment.

  As shown in FIG. 5, there is a large volume frequency peak indicating an aggregate aggregate before and after the particle size becomes 1 μm, and a single aggregate and an agglomerate respectively before and after the particle size of 0.3 μm and tens of μm. appear.

  The catalyst-supporting carbon and the fluorine-containing ion exchange resin and the dispersion medium are mixed so that the agglomerates exist according to the particle size distribution as shown in FIG. 5, and an ultrasonic disperser, a stirring deaerator, a wet jet mill, etc. If it is dispersed using a disperser, good battery output can be achieved.

(Relationship between aggregate particle size distribution and battery output)
Hereinafter, the relationship between the particle size distribution of aggregates in the catalyst ink and the battery output of the polymer electrolyte fuel cell will be described more specifically.

  First, in the presence of single aggregate, association aggregate, and agglomerate as a dispersion of catalyst-supported carbon in the catalyst ink, when the volume frequency of the single aggregate relative to the whole is the highest, flatting is performed under high humidification conditions. Is likely to occur. That is, when the ratio of the single aggregate is high, the pores for allowing the gas to pass through become small, and as a result, the battery output is not sufficiently exhibited due to the influence of flatting.

  On the other hand, when the ratio of the agglomerate, that is, the volume frequency of the agglomerate with respect to the whole, becomes the highest, the catalyst activity decreases under low humidification conditions, and the output of the fuel cell decreases. That is, when the ratio of agglomerate is high, the inside of the aggregate is not coated with a fluorine-containing ion exchange resin such as an ionomer, and thus the catalytic activity is low.

  When the ratio of the aggregate aggregate, that is, the volume frequency of the aggregate aggregate with respect to the whole is the highest, and preferably 2.5 to 4.0% or more, it is possible to form an ionomer coating thickness that is optimal for securing a three-phase interface. .

  That is, when a single aggregate, association aggregate, and agglomerate are dispersed in a dispersion medium by a dispersion device in the presence of a fluorine-containing ion exchange resin, a relatively large aggregate such as agglomerate has a large volume. The frequency of collisions between them increases. For this reason, since the agglomerate tends to be subjected to a shearing force and the amount of the coated fluorine-containing ion exchange resin is scraped off, the coating thickness of the fluorine-containing ion exchange resin becomes relatively thin in the whole particle.

  On the other hand, a relatively small aggregate such as a single aggregate has a small volume, so that it is difficult to apply a shearing force, and the coating thickness of the fluorine-containing ion exchange resin is relatively thick in the entire particle.

  On the other hand, aggregates with a particle size located between an agglomerate such as an aggregate aggregate and a single aggregate have an appropriate volume and a moderate shearing force applied to the aggregate. The resin thickness is optimized, the three-phase interface is increased, the battery characteristics are improved, and the output of the fuel cell is increased.

  As described above, the volume frequency of the association aggregate is increased, so that the catalyst-supported carbon can be uniformly coated with the fluorine-containing ion exchange resin, and the three-phase interface is increased, so that the battery characteristics are improved and the fuel cell is improved. Output increases.

  Furthermore, although the volume frequency is lower than that of the associated aggregate, the presence of the single aggregate and agglomerate in the catalyst ink can bring about the following effects.

  For example, it is assumed that a single aggregate exists in the catalyst ink, and the single aggregate is connected between the association aggregates as shown in FIG. FIG. 6 is a diagram showing an example of a state where a single aggregate is connected between the aggregates in the dispersion medium of the catalyst ink according to the present embodiment.

  Here, as described above, the single aggregate is covered with the ionomer. On the other hand, the rate at which the aggregate aggregate is completely covered by the ionomer is considered to be about 80 percent of the surface area. For this reason, there is a portion that is not completely covered by the ionomer at the junction between the aggregates.

Therefore, when the single aggregate having a small particle diameter enters the gap formed in the joint portion, a state covered with the ionomer can be formed. Accordingly, as shown in FIG. 6, when the single aggregate is connected between the aggregate aggregates, the H ⁺ conductivity can be assisted by the single aggregate in which the ionomer is thickly coated.

  Further, by filling the gap at the junction between the aggregates with the single aggregate, electricity can be conducted through the single aggregate in the gap formed at the junction. That is, electrical conductivity is improved.

  On the other hand, the agglomerate has a structure capable of securing a gap as shown in FIG. For this reason, when agglomerates are present appropriately in the catalyst ink, gas diffusion and drainage can be ensured.

  Therefore, the presence of moderate aggregates and agglomerates in the catalyst ink can prevent flattening from occurring under high humidification conditions, and prevent the catalytic activity from decreasing under low humidification conditions.

(Catalyst ink manufacturing process)
Next, a manufacturing process of the catalyst ink according to the present embodiment will be described with reference to FIG. FIG. 7 is a flowchart showing an example of the manufacturing process of the catalyst ink according to the present embodiment.

  First, a catalyst (for example, platinum) -supporting carbon is wetted (step S11, hereinafter referred to as S11). That is, a solvent (dispersion medium) is added to the catalyst-supporting carbon to make a slurry.

  Next, a catalyst-carrying carbon crushing step is performed (S12). That is, commercially available powdered carbon is considered to exist in the form of secondary aggregates, that is, agglomerates. For this reason, it is considered that the slurry-supported carbon is in an agglomerate state. Therefore, the agglomerate catalyst-carrying carbon is loosened by a disperser and mechanically dispersed. Then, the shearing force and the shearing time are controlled so that the agglomerates are reduced so that the catalyst-supporting carbon maintains the aggregate structure and approaches the aggregated aggregate state.

  When the catalyst-carrying carbon is loosened in step S12, an ion exchange resin addition step is performed in which the fluorine-containing ion exchange resin is added to the loosened catalyst-carrying carbon to form an ink (S13). In addition, when adding a fluorine-containing ion exchange resin to catalyst carrying | support carbon and making it ink, you may mix an anionic surfactant with a fluorine-containing ion exchange resin.

  As described above, when the fluorine-containing ion exchange resin is added to the catalyst-carrying carbon, a particle size control step of the catalyst-carrying carbon is performed (S14). That is, the chemical dispersion of the catalyst ink is advanced by the fluorine-containing ion exchange resin that is a surfactant. Further, the dispersion state of the catalyst ink is controlled by adjusting the shear time so that the dispersion state becomes the main peak within the particle size range of the aggregate aggregate.

  Specifically, as shown in FIG. 8, in the catalyst ink, the relationship between the particle size of the aggregate and the volume frequency is determined by the length of the shear time for the catalyst-supported carbon. FIG. 8 is a graph showing the relationship between the shear time for the catalyst-supported carbon according to the present embodiment, the particle size of the aggregate, and the volume frequency thereof.

  That is, when the shear time is in the relationship of A <B <C, and when the shear time is short (when A), the volume frequency of the aggregate having a large particle size, that is, the agglomerate increases. On the other hand, when the shearing time is long (when C), the volume frequency of the aggregate having a small particle size, that is, the aggregate becomes large. For this reason, the shear time is set to B between A and C, and the dispersion is controlled so that the main peak is obtained in the aggregation aggregate (particle diameter is around 1 μm).

  As described above, in order for the ratio of the aggregate aggregate particles to be the highest in volume frequency with respect to the total dispersed particles, the catalyst-supporting carbon, the fluorinated ion exchange resin, and the dispersion medium are combined as described above. Mix. After that, control is performed so as to disperse by applying a shearing force using a roll mill, ultrasonic dispersion, stirring deaerator, wet jet mill or the like. Moreover, you may use the dispersing agent which consists of anionic surfactant and a nonionic surfactant suitably.

  In the above, the solvent (dispersion medium) is added to the catalyst-supporting carbon in the catalyst-supporting carbon wetting step in Step S11. However, the fluorine-containing ion exchange resin and the dispersion medium are mixed in advance, It may be added to the supported carbon. In this case, the ion exchange resin addition process of step S13 can be omitted.

  However, as described above, it is preferable to mix the fluorine-containing ion exchange resin with the catalyst-supported carbon dispersed in the dispersion medium because the obtained battery characteristics are improved.

  In addition, you may add another substance to the catalyst ink mentioned above as needed. For example, a thickener or a pore thickener for adjusting the viscosity may be added. As the thickener, cellosolve-based ones can be used, and as the diluent, water, hydrocarbons, fluorine-containing hydrocarbons and the like can be used. Silica, alumina, etc. can be used as the pore-increasing agent.

  In addition, when the electrode of the fuel cell is formed on the surface of the ion exchange membrane from the catalyst ink produced by the above-described catalyst ink production process, the catalyst ink is applied directly on the surface of the ion exchange membrane, or carbon paper is used. It was formed by transferring or affixing the layer obtained by applying to the sheet base material on the surface of the ion exchange membrane.

  Application of the catalyst ink to the ion exchange membrane or sheet substrate can be performed by an existing method such as a spray method, a die coater, a lip coater, a comma coater, a gravure coater, or screen printing. When an electrode is formed on a sheet-like base material and this is transferred or attached to an ion exchange membrane, a hot press method, an adhesion method, or the like can be used. The thickness of the electrode thus formed is preferably 1 to 50 μm, particularly 10 to 30 μm.

(Example)
Next, specific embodiments will be described in detail by Examples (Example 1) and Comparative Examples (Examples 2 and 3). In addition, this invention is not limited to this Example.

  First, a specific aspect of Example 1 will be described.

  In the catalyst-carrying carbon wetting step shown in step S11 of FIG. 7, 30.3 g of water was mixed.

  Further, 6.0 g of platinum-supported carbon in which platinum is supported on carbon black powder (platinum is 50% by mass in the total weight of the catalyst-supported carbon) is added. In the catalyst-carrying carbon pulverization step shown in step S12, this dispersion was dispersed for 30 seconds using a stirring deaerator.

  And after adding an ion exchange resin at the ion exchange resin addition process of step S13 and performing the particle size control process of step S14, the particle size distribution of the particle | grains of the dispersion liquid after dispersion | distribution is measured using a particle size distribution apparatus. did. At this time, the dispersion processing time in the stirring and defoaming device in the particle size control step in step S14 is set to 10 minutes.

Further, an ion exchange membrane (thickness 30 μm) made of a perfluorocarbon polymer having a sulfonic acid group is used as the polymer electrolyte membrane 2, and the above dispersion is applied to both the cathode side and the anode side with respect to this ion exchange membrane. Each was coated with a die coater so that the platinum content was 0.3 mg / cm ² .

  The catalyst ink may be applied after being left for at least one day before it is applied.

Subsequently, MEA (membrane / electrode assembly, (membrane catalyst layer) in which gas diffusion layers 32 and 42 having a thickness of about 10 μm are formed on both surfaces of the polymer electrolyte membrane 2 by drying at 80 ° C. for about 5 minutes to 10 minutes. Bonded body)) 5 (electrode area 196 cm ² ) was produced.

Next, the fuel cell single cell 1 is assembled using the produced MEA 5, and the cell temperature in the fuel cell single cell 1 is set to 90 ° C. Then, after supplying low-humidified hydrogen gas to the anode and low-humidified air to the cathode, loading is performed at a current density of 0.16 A / cm ² . Then, after performing current-voltage measurement at a constant current density for 12 hours, the cell temperature of the single fuel cell 1 is set to 65 ° C. this time. Then, after supplying highly humidified hydrogen gas to the anode and supplying low humidified air to the cathode, loading is performed at a current density of 0.24 A / cm ² . The current-voltage measurement was continuously performed at a constant current density over 12 hours. As a result, the obtained voltage value is set as 100 and is shown as Example 1 in Table 1.

  On the other hand, as a comparative example (Example 2), an MEA is manufactured under the following conditions, and a fuel cell single cell is assembled.

  That is, in both the cathode side and the anode side, in the adjustment of the dispersion to be applied, that is, in the particle size control step of step S14, the dispersion processing time in the stirring deaerator is set to 30 minutes. Except for this dispersion treatment time, MEA 5 was produced in the same manner as in Example 1 described above, fuel cell single cell 1 was assembled, and its performance and dispersion characteristics were similarly evaluated. The results are shown in Table 1.

  Further, as a comparative example (Example 3), an MEA is manufactured under the following conditions, and a fuel cell single cell is assembled.

  That is, on both the cathode side and the anode side, in the adjustment of the dispersion to be applied, that is, in the particle size control step of step S14, the dispersion processing time in the stirring deaerator is set to 3 minutes. Except for this dispersion treatment time, an MEA was produced in the same manner as in Example 1 described above, the fuel cell single cell 1 was assembled, and the performance and the properties of the dispersion were similarly evaluated. The results are shown in Table 1.

  As described above, when the fuel cell single cell 1 using the MEA 5 produced with a dispersion treatment time of 10 minutes in the stirring and defoaming apparatus is operated with both the anode and the cathode with low humidification (cell temperature 90 ° C.) It can be seen that stable results are obtained when the anode is operated with high humidification and the cathode is operated with low humidification (cell temperature is 65 ° C.).

  As described above, the composition according to the present invention can have the following configuration. That is, the composition according to the present invention is a composition that contains a catalyst-supporting carbon, an ion exchange resin, and a dispersion medium, and is applied to a polymer electrolyte membrane to form a catalyst layer in a fuel cell. In the composition, the catalyst-supported carbon is composed of aggregates of primary aggregates formed by combining particles of catalyst-supported carbon, aggregates of secondary aggregates formed by aggregating a plurality of aggregates, and aggregates. It is an aggregated state intermediate to agglomerates, and is included in the state of aggregated aggregates that are formed by aggregating multiple aggregates and have a particle size in a predetermined particle size range. When the particle size distribution in the composition is measured, it has a main peak of the particle size distribution in a predetermined particle size range of the aggregate.

  Here, the composition is a paint applied to the polymer electrolyte membrane to form a catalyst layer, and includes a liquid or paste-like material.

  According to this configuration, in the composition, depending on the aggregated state of the aggregate formed by the primary particles of the catalyst-supporting carbon, the state of the aggregate alone and the state of the aggregate aggregate in which multiple aggregates are aggregated And an agglomerate state in which a plurality of aggregates are further aggregated. In the composition according to the present invention, as a result of measuring the particle size distribution in the composition by the laser scattering / diffraction method, it has a main peak of this particle size distribution in the particle size range of the aggregate. That is, the catalyst-supported carbon in the aggregated aggregate state is the most present in the composition. The particle size range of the aggregate is a range of 0.5 μm or more and 1.5 μm or less.

  Thus, the presence of the largest number of aggregates in the composition enables the catalyst-supporting carbon to be uniformly coated with the ion exchange resin, and the three-phase interface is increased to improve the cell characteristics and improve the fuel. The output of the battery can be increased.

In addition to the aggregate aggregate, the volume frequency is small, but aggregates exist, so this aggregate enters the gap at the junction between the aggregate aggregates, improving H ⁺ conductivity and electrical conductivity. Can be made.

  In addition, agglomerates having voids with a small volume frequency also exist, so that gas diffusibility and drainage can be ensured.

  Therefore, the composition according to the present invention can improve battery characteristics, increase the output of the fuel cell, prevent flatting under high humidification conditions, and prevent a decrease in catalytic activity under low humidification conditions. There is an effect.

  Moreover, as described above, the membrane catalyst layer assembly according to the present invention can have the following configuration.

  That is, the membrane / catalyst layer assembly according to the present invention is a membrane / catalyst layer assembly having a polymer electrolyte membrane and a catalyst layer disposed on the polymer electrode membrane. The catalyst layer includes a catalyst-carrying carbon, an ion exchange resin, and a dispersion medium. The catalyst-carrying carbon is an aggregate of primary aggregates formed by combining particles of the catalyst-carrying carbon, the aggregate Agglomerates of secondary agglomerates formed by a plurality of aggregates, and agglomerates that are in an intermediate agglomerated state between aggregates and agglomerates and are formed by aggregating a plurality of aggregates and having a particle size in a predetermined particle size range A composition having a main peak of the particle size distribution in a predetermined particle size range of the aggregate in the particle size distribution which is included in the state of the aggregate and obtained by measuring by a laser scattering / diffraction method. It is formed by coating on the electrolyte membrane.

  Here, the composition is a paint applied to the polymer electrolyte membrane in order to form a catalyst layer, and includes liquid and paste-like materials.

  According to this configuration, in the membrane-catalyst layer assembly according to the present invention, the aggregated state of the aggregate formed by the primary particles of the catalyst-supported carbon is aggregated as a single aggregate and a plurality of aggregates are aggregated. It is formed by coating a polymer electrolyte membrane with a composition in which a state of an aggregate aggregate and a state of an agglomerate in which a plurality of aggregates are further aggregated. And as a result of measuring the particle size distribution in the composition by the laser scattering / diffraction method, this composition has a main peak of this particle size distribution in a range corresponding to the particle size of the aggregate. That is, the catalyst-supported carbon in the aggregated aggregate state is the most present in the composition. Note that the range corresponding to the particle size of the aggregate is a range of 0.5 μm or more and 1.5 μm or less.

  Thus, the presence of the largest number of aggregates in the composition enables the catalyst-supporting carbon to be uniformly coated with the ion exchange resin, and the three-phase interface is increased to improve the cell characteristics and improve the fuel. The output of the battery can be increased.

In addition to the aggregate aggregate, the volume frequency is small, but aggregates exist, so this aggregate enters the gap at the junction between the aggregate aggregates, improving H ⁺ conductivity and electrical conductivity. Can be made.

  In addition, agglomerates having voids with a small volume frequency also exist, so that gas diffusibility and drainage can be ensured.

  Therefore, the membrane / catalyst layer assembly according to the present invention improves battery characteristics, increases the output of the fuel cell, prevents flattening under high humidification conditions, and prevents a decrease in catalyst activity under low humidification conditions. There is an effect that can be.

  Moreover, the manufacturing method of the membrane catalyst layer assembly which concerns on this invention as mentioned above shall include the following manufacturing methods.

  That is, the method for producing a membrane / catalyst layer assembly according to the present invention comprises preparing a polymer electrolyte membrane, and containing the catalyst-carrying carbon, the ion exchange resin, and the dispersion medium on the polymer electrolyte membrane, Aggregates of aggregates formed by combining primary particles of carbon and aggregates of primary aggregates formed by combining particles of catalyst-supported carbon, and secondary aggregates formed by aggregating multiple aggregates Agglomerates, and aggregate aggregates that are intermediate aggregate states of the aggregates and the agglomerates, are formed by aggregating a plurality of aggregates, and are aggregates having a particle size in a predetermined particle size range, and a laser In a particle size distribution obtained by measuring by a scattering / diffraction method, a composition having a main peak in a predetermined particle size range of the aggregate is applied. That.

  Here, the composition is a paint applied to the polymer electrolyte membrane in order to form a catalyst layer, and includes liquid and paste-like materials.

  According to this method, the aggregated state of the aggregate formed by combining the catalyst-supporting carbon particles includes the state of an aggregate alone, the state of an aggregate aggregate in which several aggregates are aggregated, and a plurality of aggregates. A membrane / catalyst layer assembly is formed by coating a polymer electrolyte membrane with a composition mixed with the state of agglomerates in which the agglomerates are aggregated.

  In this composition, as a result of measuring the particle size distribution in the composition by a laser scattering / diffraction method, the composition has a main peak of the particle size distribution in the particle size range of the aggregate. That is, the catalyst-supported carbon in the aggregated aggregate state is the most present in the composition. The particle size range of the aggregate is a range of 0.5 μm or more and 1.5 μm or less.

  Thus, the presence of the largest number of aggregates in the composition enables the catalyst-supporting carbon to be uniformly coated with the ion exchange resin, and the three-phase interface is increased to improve the cell characteristics and improve the fuel. The output of the battery can be increased.

In addition to the aggregate aggregate, the volume frequency is small, but aggregates exist, so this aggregate enters the gap at the junction between the aggregate aggregates, improving H ⁺ conductivity and electrical conductivity. Can be made.

  In addition, agglomerates having voids with a small volume frequency also exist, so that gas diffusibility and drainage can be ensured.

  Therefore, in the method for producing a membrane / catalyst layer assembly according to the present invention, the battery characteristics are improved, the output of the fuel cell is increased, the flattening under high humidification conditions is prevented, and the catalytic activity is exhibited under low humidification conditions. There exists an effect that a fall can be prevented.

  From the foregoing description, many modifications and other embodiments of the present invention are obvious to one skilled in the art. Accordingly, the foregoing description should be construed as illustrative only and is provided for the purpose of teaching those skilled in the art the best mode of carrying out the invention. The details of the structure and / or function may be substantially changed without departing from the spirit of the invention.

The polymer electrolyte fuel cell of the present invention is expected to be suitably used for mobile objects such as automobiles, distributed power generation systems, and home cogeneration systems.

1 Fuel Cell Single Cell 2 Polymer Electrolyte Membrane 3 Fuel Electrode 4 Air Electrode 5 MEA
6 Separator 7 Separator 31 Fuel Electrode Catalyst Layer 32 Gas Diffusion Layer 41 Air Electrode Catalyst Layer 42 Gas Diffusion Layer

Claims (6)

A composition comprising a catalyst-supporting carbon, an ion exchange resin, and a dispersion medium, which is applied to a polymer electrolyte membrane to form a catalyst layer in a fuel cell,
The catalyst-supported carbon in the composition includes an aggregate of primary aggregates formed by combining the particles of the catalyst-supported carbon, an agglomerate of secondary aggregates formed by collecting a plurality of the aggregates, and the aggregates. It is an intermediate aggregate state between the gate and the agglomerate, and is included in the state of an aggregate aggregate that is an aggregate formed by aggregating a plurality of aggregates and having a particle size in a predetermined particle size range,
A composition having a main peak of particle size distribution in a predetermined particle size range of the aggregate when the particle size distribution in the composition is measured by a laser scattering / diffraction method.   The composition according to claim 1, wherein the catalyst supported by the catalyst-supporting carbon is platinum or a platinum alloy. A membrane-catalyst layer assembly comprising a polymer electrolyte membrane and a catalyst layer disposed on the polymer electrode membrane,
The catalyst layer includes a catalyst-carrying carbon, an ion exchange resin, and a dispersion medium. The catalyst-carrying carbon is an aggregate of primary aggregates formed by combining particles of the catalyst-carrying carbon, and the aggregate is Agglomerates of secondary aggregates formed by aggregating, and agglomerates that are in an intermediate agglomerated state between the aggregate and the agglomerate and are formed by aggregating a plurality of aggregates and having a particle size in a predetermined particle size range. In a particle size distribution that is contained in a state of an aggregate and is obtained by measurement by a laser scattering / diffraction method, a composition having a main peak of the particle size distribution in a predetermined particle size range of the aggregate. A membrane-catalyst layer assembly formed by coating a polymer electrolyte membrane.   The membrane / catalyst layer assembly according to claim 3, wherein the catalyst supported by the catalyst-supporting carbon is platinum or a platinum alloy. Prepare a polymer electrolyte membrane,
On this polymer electrolyte membrane, the catalyst-supported carbon particles, the ion-exchange resin, and the dispersion medium, and the aggregated state of the aggregates formed by combining the primary particles of the catalyst-supported carbon, the catalyst-supported carbon particles are Aggregates of primary aggregates formed by combining, agglomerates of secondary aggregates formed by aggregating a plurality of aggregates, and agglomerated states intermediate between the aggregates and the agglomerates and aggregating a plurality of aggregates In the particle size distribution obtained by measurement by a laser scattering / diffraction method, and the predetermined particle size of the aggregate A method for producing a membrane catalyst layer assembly, which comprises applying a composition having a main peak in a range.   The method for producing a membrane / catalyst layer assembly according to claim 5, wherein the composition is applied onto the polymer membrane using a die coater, a lip coater, a comma coater, a gravure coater, screen printing, or a spray method.