JP2009059694A - Catalyst ink for fuel cell, its manufacturing method, and fuel cell electrode using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst ink for a fuel cell capable of having a larger amount of electrolyte adsorption to a catalyst holding conductor and stably maintaining diameters of colloidal particles and a dispersed state, a manufacturing method capable of effectively forming such catalyst ink, and a fuel cell electrode. <P>SOLUTION: The catalyst ink for a fuel cell is provided by dispersing colloidal particles wherein catalyst holding conductor particles for adsorbing a solid polymer electrolyte are condensed and further, the solid polymer electrolyte is adsorbed on the outer periphery of a condensed body, and a median diameter of the colloidal particles is 3 to 15 μm. The catalyst ink can be obtained by dispersing catalyst holding conductors by ultrasonic waves at a low energy level or by using ionomer resin obtained by drying commercial ionomer solution as a solid polymer electrolyte. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a catalyst ink in which a catalyst-carrying conductor applied to a catalyst layer of a fuel cell such as a solid high-molecular fuel cell is highly dispersed, a method for producing the same, and a fuel cell electrode using the same.

  A polymer electrolyte fuel cell includes an electrolyte membrane composed of an ion exchange membrane, a membrane electrode assembly (MEA) composed of a catalyst layer and a gas diffusion layer disposed on both sides thereof, a separator laminated on the membrane electrode assembly, etc. Is provided. For the formation of the catalyst layer, a catalyst ink is used in which carbon particles carrying a catalyst such as platinum (catalyst carrying conductor) and a solid polymer electrolyte that is an ion exchange resin are dispersed in a solvent, and this catalyst ink is used as an electrolyte. Many so-called wet methods are employed in which the film or gas diffusion layer is applied and dried.

  In order to improve the cell performance of the polymer electrolyte fuel cell, hydrogen and oxygen from the separator are uniformly and rapidly supplied to the interface between the electrolyte membrane and the catalyst layer (three-layer interface), and at the same time, the oxygen electrode The water produced on the side must be discharged quickly to the separator. Therefore, it is desirable that a well-balanced three-layer interface in which electron conductivity, a gas diffusion path, and a proton conduction path of the catalyst material are sufficiently formed is formed in the catalyst material (catalyst particles).

  For this purpose, Patent Document 1 proposes to use a solid polymer electrolyte in the form of a colloid in a catalyst ink. That is, a dispersion in which a catalyst-carrying conductor is dispersed in an organic solvent is obtained, and the dispersion and a solid polymer electrolyte alcohol solution are mixed to form a solid polymer electrolyte colloid, and the colloid is supported by the catalyst. It is made to adsorb | suck to a conductor, and it is set as a liquid mixture, and it applies to the single side | surface of a gas diffusion layer, and produces an electrode.

  By generating a solid polymer electrolyte colloid, the catalyst-supported conductor (carbon powder supporting a noble metal catalyst) and the solid polymer electrolyte can be sufficiently brought into contact with each other. It is described that it is possible to disperse the carbon fine particles and the solid polymer electrolyte in a state in which they are sufficiently adhered to each other, and a good three-layer interface is formed in the catalyst layer.

In general, the solid polymer electrolyte colloid having the catalyst-supported conductor as the core obtained in this way is agglomerated from the outside by a solvent. Therefore, the colloidal solid polymer electrolyte is not necessarily uniformly formed on the catalyst-supported conductor. It cannot be adsorbed. Therefore, it cannot be said that the amount of electrolyte adsorption on the catalyst particles is large, and the material utilization rate cannot be increased.
JP-A-8-264190

  The present invention has been made in view of the above circumstances, and has a large amount of electrolyte adsorbed on a catalyst-carrying conductor and can stably maintain an appropriate colloidal particle diameter and dispersion state. It is an object of the present invention to provide an ink, a production method capable of efficiently forming such a catalyst ink, and a fuel cell electrode.

  The fuel cell catalyst ink of the present invention is a fuel cell catalyst ink comprising a dispersion medium and colloidal particles dispersed in the dispersion medium, wherein the colloidal particles carry a catalyst carrying an adsorbed solid polymer electrolyte. Conductive particles are aggregated, and the solid polymer electrolyte is further adsorbed on the outer periphery of the aggregate, and the median diameter of the colloidal particles is 3 to 15 μm. Here, the median diameter is a particle diameter in which the particle size distribution is divided into right and left parts, and the larger side and the smaller side are equal.

  The method for producing a fuel cell catalyst ink according to the present invention includes a mixed liquid preparation step of mixing at least a catalyst-carrying conductor, a solid polymer electrolyte, and a dispersion medium to obtain a mixed liquid, and sonicating the mixed liquid. A dispersion step of obtaining a dispersion in which the catalyst-carrying conductor is dispersed, and aggregating dispersed particles of the catalyst-carrying conductor adsorbing the solid polymer electrolyte by stirring the dispersion for a predetermined time, An agitation step of forming colloidal particles adsorbing the solid polymer electrolyte on the outer periphery of the aggregate, and the dispersion step reduces the temperature of the mixed solution in contact with the vibrator of the ultrasonic disperser to 40 ° C. or less. The ultrasonic treatment is performed so as to hold.

  In such a fuel cell catalyst ink manufacturing method, the temperature of the mixed solution in contact with the vibrator is more preferably maintained at 0 to 30 ° C., and the temperature of the mixed solution in contact with the vibrator is maintained at 2 to 30 ° C. More preferably.

  Another method for producing a fuel cell catalyst ink of the present invention is to obtain a solidified ionomer resin by drying an ionomer solution obtained by dissolving an ionomer, which is a solid polymer electrolyte, in water and / or a lower alcohol such as ethanol. Mixing of a liquid mixture to obtain a liquid mixture by mixing a drying process, an ionomer dispersion process in which the ionomer resin is dispersed in a dispersion medium to obtain an ionomer dispersion liquid, a catalyst-supported conductor, the ionomer dispersion liquid, and a dispersion medium A colloid in which dispersed particles of the catalyst-carrying conductor adsorbing the solid polymer electrolyte are agglomerated by subjecting the mixed solution to ultrasonic treatment, and the solid polymer electrolyte is further adsorbed on the outer periphery of the aggregate And an ultrasonic treatment step for forming particles.

  In addition, the fuel cell electrode of the present invention is formed using the fuel cell catalyst ink.

  The fuel ink catalyst ink of the present invention is obtained by aggregating dispersed particles of a catalyst-supporting conductor adsorbing a solid polymer electrolyte, and further dispersing colloidal particles adsorbing the solid polymer electrolyte on the outer periphery of the aggregate. Therefore, a large amount of the solid polymer electrolyte is stably adsorbed on the catalyst-carrying conductive particles. Since the median diameter of the dispersed colloidal particles changes to 3 to 15 μm depending on the amount of the electrolyte, the electrolytic mass per colloidal surface area is constant regardless of the amount of the electrolyte. Therefore, the three-layer interface where the catalyst metal, the conductor and the electrolyte are in contact with each other inside the catalyst layer of the electrode formed with this catalyst ink is increased, and the reaction efficiency can be improved. That is, according to the catalyst ink of the present invention, the fuel metal material utilization rate of the catalyst metal can be increased, high power generation performance can be achieved with less electrolytic mass than before, and higher power generation performance can be achieved if the electrolytic mass is the same. Can be obtained.

  The method for producing a fuel cell catalyst ink of the present invention can be carried out in the same manner as in the prior art except that the catalyst-carrying conductor is ultrasonically dispersed with low energy in the dispersing step, so that the conventional process is greatly changed. The desired fuel cell catalyst ink can be produced easily and efficiently.

  In addition, other methods for producing the fuel cell catalyst ink of the present invention can be carried out in substantially the same manner as in the prior art, except that a commercially available ionomer solution is used as a solid polymer electrolyte. A desired fuel cell catalyst ink can be easily and efficiently produced without greatly changing the process.

Preferred embodiments of the present invention will be described below with reference to the drawings.
(Catalyst ink)
The fuel cell catalyst ink of the present invention (hereinafter simply referred to as catalyst ink) is a fuel cell catalyst ink comprising a dispersion medium and colloid particles dispersed in the dispersion medium, wherein the colloid particles are solid. The catalyst-supported conductor particles (hereinafter also referred to as catalyst particles) adsorbing a polymer electrolyte (also referred to simply as an electrolyte) are aggregated, and the solid polymer electrolyte is further adsorbed on the outer periphery of the aggregate. The median diameter of the colloidal particles is 3 to 15 μm.

  FIG. 9 (b) shows a preferred embodiment of the catalyst ink of the present invention. FIG. 9B schematically shows the colloidal particles 40 dispersed in the dispersion medium 30 of the catalyst ink 3. The colloidal particles 40 aggregate the catalyst particles 10 that have adsorbed the electrolyte 20 into aggregates 60, and further adsorb the electrolyte 20 on the surface of the aggregates 60. For this reason, in the catalyst layer formed using this catalyst ink 3, the three-layer interface where the catalyst, the conductor and the electrolyte are in contact with each other is increased, and the reaction efficiency can be improved. Further, since colloidal particles 40 are formed on the surface of the aggregate 60 by further adsorbing the electrolyte 20, the adsorption power of the electrolyte to the catalyst particles is large. Accordingly, as shown in the photograph of FIG. 8B, the dispersion state of the colloidal particles 40 dispersed in the dispersion medium 30 can be stably maintained.

  In the present embodiment, the median diameter of the colloidal particles 40 in the catalyst ink 3 is 3 to 15 μm. If the median diameter is less than 3 μm, there may be a catalyst that does not contribute to the reaction because the colloidalization of the electrolyte 20 is incomplete. On the other hand, if it exceeds 15 μm, the catalyst particles 10 may be over-agglomerated to cause a flooding phenomenon in which the produced water stays in the catalyst layer. The colloidal particle diameter of the catalyst ink 1 is more preferably 7 to 10 μm.

  If the colloidal particle diameter of the colloidal particles 40 in the catalyst ink 3 is in the above range, the three-layer interface is necessary and sufficient, so that the amount of available catalyst such as Pt is always constant.

  In such a catalyst ink 1, the catalyst particles 10 and the electrolyte 20 are dispersed while maintaining a constant electrolyte adsorption amount. For this reason, the segregation of the electrolyte 20 hardly occurs, and blockage of pores (gap between colloids) due to liquid water is suppressed. For this reason, the generated water can be easily discharged to the outside, and the gas can be easily introduced to the catalyst surface. As a result, the diffusion resistance is lowered and the reaction proceeds smoothly.

That is, by using the catalyst ink 3, it can be expected to obtain a fuel cell advantageous in terms of performance with a high material utilization rate.
(Method for producing catalyst ink)
Such a catalyst ink 3 can be manufactured as follows.
(First embodiment)
The first embodiment of the method for producing a catalyst ink for a fuel cell of the present invention includes a mixed liquid preparation step for mixing at least a catalyst-supporting conductor, a solid polymer electrolyte, and a dispersion medium to obtain a mixed liquid, and this mixed liquid. A dispersion step of obtaining a dispersion in which the catalyst-carrying conductor is dispersed by subjecting to sonication, and aggregating dispersed particles of the catalyst-carrying conductor adsorbing the solid polymer electrolyte by stirring the dispersion for a predetermined time; An agitation step for forming colloidal particles adsorbing solid polymer electrolyte on the outer periphery of the aggregate, and the dispersion step maintains the temperature of the liquid mixture in contact with the vibrator of the ultrasonic disperser at 40 ° C. or lower. Thus, ultrasonic treatment is performed.

  First, in the mixed solution preparation step, catalyst particles, an electrolyte, a dispersion medium, and, if necessary, a high-boiling anti-drying agent or additive are added and uniformly mixed and stirred to prepare a mixed solution.

  As the catalyst particles, for example, catalyst particles conventionally used for this type of catalyst ink can be arbitrarily used, such as carbon powder supporting a catalyst substance (for example, Pt). Similarly, electrolytes conventionally used in this type of catalyst ink such as perfluorocarbon sulfonic acid ionomer can be arbitrarily used.

  Moreover, as a dispersion medium, ethyl alcohol and water (pure water) can be used suitably, Furthermore, as desired, propylene glycol, ethylene glycol, (iso, n-) propylene alcohol, cyclohexanol, n -A desiccant or additive such as butyl acetate, n-acetic acid, n-butylamine, methylamine, or tetrahydrofuran can be used.

  In the present embodiment, the blending ratio of the catalyst particles, the electrolyte, and the dispersion medium is not particularly limited, and may be a blending ratio of the liquid mixture conventionally used for the catalyst ink that generates colloidal particles.

  For example, the total amount of the prepared mixed liquid is 100% by mass, and the catalyst particles are 3 to 15%, the electrolyte is 2 to 20%, and the dispersion medium is 50 to 95%. Moreover, as for the alcohol and water in a dispersion medium, it is desirable that the mass ratio (alcohol / water) is 1/3-1 / 0.5. If this ratio is less than 1/3, the electrolyte itself tends to colloid. If it exceeds 1 / 0.5, the adsorption may not proceed, which is not preferable. More preferably, it is 1/1 to 1.5 / 1.

  In the mixed liquid preparation step, the catalyst particles and the electrolyte may be mixed so that they are uniformly mixed in the dispersion medium, and the kneading / stirring method is not particularly limited. For example, the mixture may be rotated and mixed using a known method such as a well-known propeller type stirrer, a magnetic stirrer, a pot mill or the like and a conventional method such that the whole is uniformly stirred.

  In the mixed liquid 1 obtained in this way, as shown in a conceptual diagram in FIG. 1A, unbroken bulk catalyst particles 10 and the electrolyte 20 are randomly dispersed in the solvent 30. .

  Next, in the dispersion step, the obtained mixed solution is subjected to ultrasonic treatment, and the dispersed catalyst 2 is obtained by finely pulverizing the massive catalyst particles 10 by internal cutting and dispersing them in the dispersion medium 30.

  In this ultrasonic dispersion treatment, conventionally, a large amount of catalyst particles has been finely dispersed using a high output type (for example, 300 W) vibrator. However, in this embodiment, in order to reduce the energy applied from the outside, a low output vibrator of about 10 to 100 W (for example, 50 W) is used as the ultrasonic disperser, and the amount of energy given to the mixed liquid 1 Is 1/6 to 1/7 of the prior art.

  When energy is applied to the mixed liquid from the outside to disperse the catalyst particles, the temperature of the mixed liquid rises. This temperature rise causes a minute change in the mixed liquid, and the minute change greatly affects the properties of the catalyst ink when it is completed.

  That is, if the energy applied to the mixed liquid is large, the dispersion medium is likely to oxidize, and active points are easily formed on the surface of the catalyst particles, so that the electrolyte is easily separated from the surface of the catalyst particles in the stirring step after dispersion. May become catalyst ink. Therefore, a catalyst ink in which the electrolyte is strongly adsorbed on the catalyst particle surface cannot be obtained.

  In this embodiment, the amount of energy applied to the mixed liquid is reduced, and the dispersed state of the catalyst particles and the electrolyte after the dispersion treatment is made uniform and strong adsorption, and the catalyst ink adsorbs the electrolyte in the stirring step after dispersion. Colloidal particles with agglomerates of catalyst particles as nuclei are formed.

  An outline of the dispersion process is shown in FIG. In the dispersion step, ultrasonic dispersion treatment is performed by immersing the tip of the vibrator H in the mixed solution L. Here, J is a jacket for circulating cooling water, and T is a temperature sensor.

  As shown in FIG. 2, the temperature of the liquid mixture La (for example, immediately below the vibrator) La where the solution L and the vibrator H are in direct contact during the catalyst particle dispersion operation is the highest. Therefore, a good dispersion state is obtained by controlling the liquid temperature immediately below the vibrator during the catalyst particle dispersion operation.

  FIG. 3 shows the relationship between the liquid temperature immediately below the vibrator during the dispersion treatment and the median diameter of the colloidal particles obtained after the stirring treatment. From FIG. 3, it can be seen that colloidal particles having a large median diameter can be obtained after the stirring process if the temperature immediately below the vibrator is kept at 40 ° C. or lower. That is, the holding temperature of the mixed solution during the catalyst particle dispersion operation is 40 ° C. or less, more preferably 0 to 30 ° C., and further preferably 20 to 30 ° C.

  The state of the dispersion 2 after the dispersion step is shown in a conceptual diagram in FIG. The catalyst particles 10 are finely pulverized and dispersed in the dispersion medium 30, and some of the electrolyte 20 a is colloidal and includes (adsorbs) the catalyst particles 10 as nuclei. In such a dispersion 2, it is desirable that the median diameter of the catalyst particles 10 is 0.5 μm or less. If the median diameter of the catalyst particles after the dispersion treatment is larger than 0.5 μm, the catalyst particles 10 that are insufficiently crushed will be present in the colloid in the subsequent stirring treatment, and uniform colloidalization may not be possible. This is not preferable.

  Next, in the stirring step, the dispersion liquid 2 obtained above is stirred, and the catalyst particles 10 adsorbing the electrolyte 20 generated in the dispersing step are further aggregated by a bridging effect. Then, the colloidal particles 40 adsorbing a large amount of the electrolyte 20 are generated on the outer periphery of the aggregate 60 of the catalyst particles 10 adsorbing the electrolyte 20 as shown in FIG. The catalyst ink 3 is obtained by dispersing the colloidal particles 40 therein.

  Stirring can be performed in the same manner as before, and the temperature of dispersion 2 may be maintained at 10 to 30 ° C. and stirred for 12 to 24 hours.

  Thus, a catalyst ink 3 in which colloidal particles 40 having a median diameter of 3 to 15 μm are dispersed in the solvent 30 can be obtained. When the median diameter of the catalyst ink 3 is less than 3 μm, colloidalization is incomplete and a catalyst that does not depend on the reaction may be generated. On the other hand, if it exceeds 15 μm, the catalyst particles 10 may be excessively aggregated to cause a flooding phenomenon. Therefore, when the median diameter is less than 3 μm, for example, water is added to adjust the ethanol concentration to decrease, and when it exceeds 15 μm, for example, ethanol is added to break the colloid weakly, thereby colloidal particles. The median diameter of 40 can be adjusted to a desired size. Such adjustment may be performed, for example, when colloidalization has progressed excessively due to long-term storage or when the colloid diameter changes due to the physical properties of the material or specific catalyst surface.

  The median diameter of the colloidal particles of the catalyst ink obtained as described above varies depending on the content of the electrolyte contained in the catalyst ink. Therefore, the blending amount of the catalyst particles was constant and the blending amount of the electrolyte was changed to prepare a mixed solution, and seven-level catalyst inks containing different electrolytic masses were prepared according to the above procedure. Table 1 shows the mixing ratio of the mixed solution.

  The particle size distribution of the produced catalyst ink was measured, and the relationship between the median diameter and the electrolytic mass is shown in FIG. FIG. 4 shows that the particle size (median diameter) of the colloidal particles after aggregation decreases linearly with an increase in electrolytic mass, and there is a variable point when the electrolytic mass is 11.5%. This suggests that the aggregated form of colloidal particles is different when the electrolytic mass is 11.5% or more and less than 11.5%. That is, it is presumed that when the electrolytic mass is less than 11.5%, single-phase adsorption or aggregation occurs, and when it is 11.5% or more, double-phase adsorption or aggregation occurs.

  Here, the single-phase adsorption (or aggregation) means a state in which the electrolyte (or catalyst particles) is directly adsorbed on the catalyst surface, and the multi-phase adsorption (or aggregation) means that the electrolyte (or catalyst particles) is It means a state of being further adsorbed on the electrolyte. Therefore, a single phase adsorption state is desirable.

  Further, the adsorption amount of the electrolyte adsorbed on the catalyst particles was measured for these seven types of catalyst inks. The amount of adsorption was determined by the following procedure.

  First, a solution for preparing a 7-level calibration curve obtained by removing catalyst particles from each solution composition shown in Table 1 was prepared, and the viscosity of each solution was measured. RC550 manufactured by Eiko Seiki Co., Ltd. was used for viscosity measurement. From the viscosity measurement data obtained for each catalyst ink, the increase rate (gradient) of the shear stress with respect to the shear rate was determined, and a calibration curve was obtained by plotting this gradient against the electrolytic mass.

  Next, each of the prepared 7-level catalyst inks was filtered with a filter (Durapore, manufactured by Nihon Millipore Corporation), and the viscosity of the filtrate was measured in the same manner as described above. From the obtained data, a linear gradient with the shear rate as the horizontal axis and the shear stress as the vertical axis was determined, and the electrolytic mass contained in the filtrate was determined from this gradient and the calibration curve. The difference between the obtained electrolytic mass and the electrolytic mass at the time of blending was defined as the electrolytic mass adsorbed on the catalyst particles.

  FIG. 5 shows the relationship between the blending amount (mass%) of the electrolyte and the adsorption amount (mass%). From FIG. 5, it can be seen that the amount of electrolyte adsorbed on the catalyst particles increases as the blending amount increases. However, the rate of increase is not uniform, and the amount of adsorption gradually increases to 4-6% until the blending amount is close to 12%, but the amount of adsorption increases rapidly when it exceeds 12%. This inflection point approximates the median diameter variable point in FIG. 4, and an increase in the amount of adsorption suggests an increase in colloidal particles with a small median diameter, that is, the colloidal structure of the catalyst ink is broken. I understand that.

  As described above, it was confirmed that the colloidal particle diameter after aggregation was changed by the added electrolytic mass, and that the change method had a strong correlation with the added electrolytic mass.

  Further, from FIG. 5, it was found that the amount of adsorption to the catalyst particles was almost constant regardless of the blending amount when the blending amount of the electrolyte was within a range of about 5 to 12%. That is, when the electrolytic mass increases, colloidal particles having a small particle diameter increase, and as a result, the total surface area of the colloidal particles increases. In addition, there is a region where the amount of adsorption (distribution) of the electrolyte to the aggregated individual catalyst particles is always constant, and more electrolyte can be adsorbed on the catalyst surface than in the past due to the strong suction force of the colloid.

Therefore, in a region where the increase in electrolytic mass is almost constant, particles having a uniform composition can always be produced by changing only the size. In addition, an electrolytic mass sufficient to maintain water retention and the like and necessary and sufficient for the catalytic reaction can be secured.
(Second Embodiment)
The second embodiment of the method for producing a fuel cell catalyst ink of the present invention is a solidified ionomer resin obtained by drying an ionomer solution obtained by dissolving an ionomer, which is a solid polymer electrolyte, in water and / or a lower alcohol such as ethanol. A drying step for obtaining a mixture, an ionomer dispersion step for dispersing the ionomer resin in a dispersion medium to obtain an ionomer dispersion, a catalyst-carrying conductor, the ionomer dispersion, and a dispersion medium for mixing to obtain a mixture The liquid preparation step and the mixed liquid are subjected to ultrasonic treatment to agglomerate dispersed particles of the catalyst-carrying conductor adsorbing the solid polymer electrolyte, and the colloidal particles further adsorbing the solid polymer electrolyte to the outer periphery of the aggregate And an ultrasonic treatment step for forming the structure.

  In general, a solid polymer electrolyte is commercially available as an ionomer solution in which an ionomer is dissolved in water and / or a lower alcohol such as ethanol. In the drying step, the commercially available ionomer solution is first dried to obtain an ionomer resin.

  In the present embodiment, as the electrolyte, an electrolyte conventionally used in this type of fuel cell catalyst ink, such as perfluorocarbon sulfonic acid ionomer, can be arbitrarily used. For example, Nafion Solution (trade name, manufactured by Aldrich) in which perfluorocarbonsulfonic acid ionomer is dissolved in water and / or lower alcohol such as ethanol can be suitably used.

There are no restrictions on the drying means, but for example, an ionomer solution is accommodated in a container having a wide opening area such as a petri dish or a tray in order to promote drying, and then a vacuum of 10 ⁻¹ to 10 ⁻⁴ Pa at 50 to 150 ° C. It is good also as drying. The dry state of the ionomer resin is determined by a change in weight. When the dry weight reaches 95% by weight or more of the solid content in the dispersion field, the drying may be completed.

  Next, the obtained ionomer resin is dispersed in a dispersion medium to prepare an ionomer dispersion. As the dispersion medium, ethyl alcohol and water (pure water) can be suitably used. Here, as for the alcohol and water in a dispersion medium, it is desirable that the mass ratio (alcohol / water) is 100 / 0-50 / 50. If the alcohol is less than 50/50, the ionomer resin is difficult to dissolve. More preferably, it is 80 / 20-70 / 30.

  The ionomer resin is mixed with such a dispersion medium in an amount of 10 to 20% by mass and mixed so as to be uniform using a normal stirrer. Thereafter, the mixed solution is subjected to ultrasonic treatment to uniformly disperse the ionomer in the dispersion medium. The ultrasonic treatment is performed for 5 minutes to 1 hour using a conventional high-power type (for example, 300 W) vibrator, and then the ionomer is uniformly dispersed in the dispersion medium by allowing to stand at room temperature for 2 hours or more. An ionomer dispersion can be obtained.

  Next, in the mixed liquid preparation step, the ionomer dispersion liquid, the catalyst particles, and the dispersion medium are mixed to prepare a mixed liquid.

  Here, as the catalyst particles, for example, catalyst particles conventionally used in this type of catalyst ink, such as carbon powder supporting a catalyst substance (for example, Pt), can be arbitrarily used.

  In the present embodiment, the mixing ratio of the catalyst particles, the ionomer dispersion, and the dispersion medium is not particularly limited. What is necessary is just to set it as the mixture ratio of the liquid mixture conventionally used for the catalyst ink which produces | generates a colloid particle. For example, the total amount of the prepared mixed liquid is 100% by mass, and the catalyst particles are 3 to 15%, the electrolyte (ionomer content in the ionomer dispersion) is 2 to 20%, and the dispersion medium is 50 to 95%. Moreover, as for the alcohol and water in a dispersion medium, it is desirable that the mass ratio (alcohol / water) is 2/3-1 / 0.5.

  In the mixed liquid preparation step, the catalyst particles and the electrolyte may be mixed so that they are uniformly mixed in the dispersion medium, and the kneading / stirring method is not particularly limited. For example, the mixture may be rotated and mixed using a known method such as a well-known propeller type stirrer, a magnetic stirrer, a pot mill or the like and a conventional method such that the whole is uniformly stirred. In addition, you may add a high boiling point drying inhibitor and additive to a liquid mixture as needed.

Subsequently, the mixed solution is subjected to ultrasonic treatment to agglomerate the dispersed electrolyte adsorption catalyst particles, and colloidal particles are further adsorbed on the outer periphery of the aggregate. An output type (for example, 300 W) can be used. By using a high-power type vibrator, the massive catalyst particles can be efficiently crushed and agglomerated for colloidalization. Therefore, the dispersion process may be terminated when the colloidal particle diameter reaches a desired size.

  According to this embodiment, colloidalization proceeds only by mixing an ionomer dispersion, catalyst particles (catalyst-supported conductor), and a dispersion medium. The obtained colloid is presumed to be a hydrocolloid, and the electrolyte is presumed to be stabilized in an adsorbed state in which the hydrophobic part is directed to the catalyst particle surface and the ionic group is directed to the dispersion medium side.

  With respect to the catalyst ink for fuel cells, changes in the colloidal particle diameter (median diameter) of the catalyst ink and the amount of electrolyte adsorbed depending on the amount of electrolyte added were confirmed. As in the first embodiment, seven-level catalyst inks having different electrolytic masses were prepared, and the median diameter and the amount of electrolyte adsorbed on each colloidal particle were measured. The results are shown in the graphs of FIG. 4 (◯) and FIG. 5 (●). From these graphs, as in the first embodiment, the colloidal particle diameter changes almost linearly depending on the amount of ionomer dispersed in the dispersion medium after drying. It can be seen that the amount of electrolyte adsorption per surface area is constant. Therefore, a constant catalytic reaction condition can always be created regardless of the added electrolytic mass.

  Each of the fuel cell catalyst inks obtained in the above embodiments can be applied to a perfluorosulfonic acid film, a carbon-hydrogen film, or the like as a paste-like mixed liquid and dried to form a catalyst layer. Alternatively, the catalyst layer may be formed by pulverizing by a known method such as freeze-drying and using an appropriate powder coating method. In such a catalyst layer, a good three-layer interface is formed even inside the catalyst particles, so that the performance of a fuel cell including an electrode having such a catalyst layer is also improved.

Hereinafter, the present invention will be described in more detail with reference to examples.
(Example 1)
Catalyst ink I was produced according to the procedure of the first embodiment.
<Procedure 1>
Catalyst particles (10-70 wt% Pt / C) 10% by mass, electrolyte (perfluorocarbon sulfonic acid ionomer) 6%, water 40%, ethanol 44% are uniformly kneaded and stirred with a magnetic stirrer (manufactured by ASONE). To obtain a mixed solution. At this time, the total weight of the ink after preparation was 20 g.
<Procedure 2>
The obtained mixed liquid was subjected to a dispersion treatment using a throwing type ultrasonic dispersion machine (manufactured by UH-300 SMT). A low output 50 W vibrator was used for the dispersion process. At this time, dispersion was performed while adjusting the output so that the liquid temperature directly below the vibrator was 30 ± 5 ° C. For dispersion, 100 s dispersion and 120 s cooling were alternately repeated 20 times. FIG. 6 shows changes in the output of the ultrasonic disperser and the liquid temperature immediately below the vibrator in this dispersion process. In addition, 5 degreeC cooling water was distribute | circulated to the jacket J (FIG. 2) provided in the outer side of the container which accommodates the dispersion liquid, and the dispersion liquid was cooled. Moreover, HA-400E (made by Anritsu Keiki Co., Ltd.) was used for the liquid temperature measurement.
<Procedure 3>
After completion of the dispersion treatment, the particle size distribution of the dispersed particles was measured using a particle size distribution meter (manufactured by MT3000 Micro Track), and it was confirmed that the median diameter was 0.5 μm or less.

Subsequently, the dispersion liquid temperature was maintained at 25 ° C. using a stirrer (RS-1A manufactured by ASONE Co., Ltd.), and a stirring process was performed for 12 hours to obtain catalyst ink I.
<Result>
The results are shown in FIG. 7 and FIG.

  FIG. 7 shows the result of measurement by the particle size distribution meter, where A is the particle size distribution of the catalyst ink I immediately after the dispersion treatment, and B is the particle size distribution of the catalyst ink I after the stirring treatment. The median diameter of A was 0.35 μm, and B was 8.5 μm.

FIG. 8 is a microscopic photograph in which particles inside the ink are directly observed with a microscope (manufactured by VH-7000 Keyence) to confirm aggregation. (A) is a state of the dispersion immediately after the dispersion treatment, (b ) Is the catalyst ink I (3) after the stirring treatment. As schematically shown in FIG. 9, immediately after the dispersion treatment, some of the electrolyte 20 is adsorbed on the catalyst particles 10, but the finely dispersed catalyst particles 10 and the electrolyte 20 are in the solvent 30. It exists apart. However, in the catalyst ink 3 after the stirring treatment, the catalyst particles 10 that have adsorbed the electrolyte 20 are aggregated, and the electrolyte 20 is further adsorbed on the outer periphery using the aggregate 60 as a nucleus to form colloidal particles 40. In FIG. 9, 50 is a catalyst metal such as Pt.
(Example 2)
A catalyst ink II was obtained in the same manner as in Example 1 except that the blending amount of the electrolyte in the mixed solution was 7% and the blending amount of ethanol was 43%. The median diameter of the dispersion liquid after the dispersion treatment was 0.35 μm, and the median diameter of the catalyst ink II after the stirring treatment for 12 hours was 8.5 μm.
(Example 3)
A catalyst ink III was obtained as follows in accordance with the procedure of the second embodiment.
<Procedure 1>
Ionomer solution (NafionR 20wt% Solution Aldrichi Co.) 100 g of the dish (opening area: 80 cm ²⁾ were taken into 50 ° C. × 1 ^hour, subjected to vacuum drying at ¹⁰ -1 Pa, the solidified 10g ionomer resin Obtained.
<Procedure 2>
The obtained ionomer resin (10 g), water and ethanol were uniformly kneaded and stirred with a magnetic stirrer (manufactured by ASONE) to obtain a mixed solution of an electrolyte. The formulation was by mass and water: ethanol: ionomer resin = 15: 65: 20.

The obtained ionomer mixed solution was subjected to a dispersion treatment for 1 hour using a throwing type ultrasonic dispersion machine (manufactured by UH-300 SMT). A high output 300 W vibrator was used for the dispersion process. After the dispersion treatment, the mixture was allowed to stand for 2 hours to obtain a re-dissolved ionomer dispersion.
<Procedure 3>
Catalyst particles (10-70 wt% Pt / C) 10% by mass ratio, electrolyte (ionomer in ionomer dispersion) 6%, water 40%, ethanol 44% are uniformly kneaded with a magnetic stirrer (manufactured by ASONE). The mixture was obtained by stirring. At this time, the total weight of the ink after preparation was 20 g.
<Procedure 4>
Dispersion treatment was carried out at 30 to 60 ° C. (temperature changes because cooling and dispersion are repeated) in the same manner as in the comparative example described later using a throwing type ultrasonic dispersion machine (UH-300 SMT). Was given. A high output 300 W vibrator was used for the dispersion process.
<Procedure 5>
After the dispersion treatment is completed, the particle size distribution of the dispersed particles is measured using a particle size distribution meter (manufactured by MT3000 Micro Track), and it is confirmed that the median diameter is 8 to 9 μm. Got. The dispersion processing time was 1.5 hours.
<Result>
The particle size distribution measurement results are shown in FIG.

  FIG. 12 shows the results of measurement using the above particle size distribution meter. C is the particle size distribution of the catalyst ink III, and D is the particle size distribution of the catalyst ink IV of the comparative example described later. The median diameter of C was 8.5 μm, and D was 0.35 μm.

Further, when the particles inside the catalyst ink III were directly observed with a microscope to confirm aggregation, it was confirmed that the colloidal particles of 7.5 to 9.5 μm were uniformly dispersed in the same manner as in FIG. 8B. .
(Comparative example)
The prior art was used as a comparative example. A liquid mixture having the same composition as in Example 2 was prepared, and the liquid mixture was subjected to a dispersion treatment using a high output type vibrator (300 W) of an ultrasonic disperser (manufactured by UH-600 SMT). Produced a catalyst ink IV of Comparative Example in the same manner as in Example 1. The liquid temperature at the time of dispersion treatment is measured in an arbitrary mixed liquid separated from the vibrator (for example, point P in FIG. 2), and an ultrasonic disperser is used so that this temperature is maintained at 40 ° C. or lower. The output of was adjusted. At this time, the liquid temperature of La just below the vibrator was 55 to 65 ° C.

FIG. 10 shows an observation photograph of particles inside the ink. (A) is the state of the dispersion liquid after completion of dispersion, and (b) is the catalyst ink IV after 12 hours of stirring treatment. The median diameter in FIG. 10 (a) was 0.38 μm, and (b) was 0.40 μm. That is, it can be seen that in the catalyst ink IV, the catalyst particles and the electrolyte are finely dispersed in the solvent without aggregation. For this reason, in the catalyst ink IV, the adsorption of the electrolyte to the catalyst particles is weak and the amount of adsorption is small, so that the utilization rate of the catalyst material is limited.
(Battery performance evaluation)
The obtained catalyst inks I, II, III, and IV were spray-coated on the electrolyte membrane (perfluorosulfonic acid) so that the weight of Pt was 0.3 mg / cm ² , thereby producing a battery electrode for evaluation. The battery performance was evaluated from the relationship between current density and voltage. The results are shown in FIG.

  The catalyst inks I (-□-), II (-Δ-) and III (-○-) of the examples all have battery performance superior to that of the catalyst ink IV (-◆-) which is a comparative example. I understand that

  For example, although the catalyst inks II and IV contain the same amount of electrolyte, the catalyst ink II (Example 2) shows higher power generation performance than the catalyst ink IV (Comparative Example).

  Further, in the catalyst ink I (Example 1) in which the electrolytic mass was reduced compared to the catalyst ink II (Example 2) in order to suppress flooding, an improvement in performance was observed over the entire current density range.

In FIG. 11, the performance of Examples 1 to 3 is improved in the vicinity of 0.2 A / cm ^2, which shows catalytic activity as compared with the comparative example. Therefore, it is clear that the catalyst utilization is improved in Examples 1 to 3. In Examples 1 to 3, the performance is further improved in a high load region around 1.0 A / cm ² . Considering that colloids generally have a strong adsorptive power and an improvement in performance in the vicinity of 0.2 A / cm ² , this improvement in performance is a result of the electrolyte being strongly and uniformly adsorbed on the surface of the catalyst particles. Guessed.

  As described above, according to the catalyst ink of the present invention, the utilization factor of the catalyst material (particularly, Pt, etc.) can be increased. Therefore, it is possible to provide high power generation performance with less electrolysis mass and the same electrolysis mass. It can be expected that even higher power generation performance will be exhibited.

  The present invention can be suitably used for a catalyst ink for a fuel cell that forms a catalyst layer of a polymer electrolyte fuel cell.

It is a conceptual diagram which shows the form of the catalyst support conductor and solid polymer electrolyte in a liquid. (A) is a mixed liquid, (b) is a dispersion liquid after dispersion treatment, and (c) is a catalyst ink after stirring treatment. It is a schematic diagram which shows the ultrasonic dispersion processing method in a dispersion | distribution process. It is a graph which shows the relationship between the liquid temperature of La just under a vibrator | oscillator at the time of an ultrasonic treatment, and the median diameter of the colloid particle obtained after a stirring process. It is a graph which shows the relationship between the compounding quantity of a solid polymer electrolyte, and the median diameter of the colloid particle in a catalyst ink. It is a graph which shows the relationship between the compounding quantity of a solid polymer electrolyte, and the adsorption amount to a catalyst particle. It is a schematic diagram which shows the change of the ultrasonic output and liquid temperature in a dispersion | distribution process. It is a graph which shows the particle size distribution (A) of a dispersion liquid, and the particle size distribution (B) of the colloid particle in a catalyst ink. 2 is a microscopic observation photograph of catalyst ink I. (A) shows immediately after the dispersion treatment, and (b) shows after the stirring treatment. FIG. 2 is a schematic diagram for explaining (a) the form of a catalyst-carrying conductor and solid polymer electrolyte in a liquid before stirring treatment in catalyst ink I, and (b) colloidal particles generated after stirring treatment. It is a microscope observation photograph of catalyst ink IV. (A) is immediately after the dispersion treatment, and (b) is after the stirring treatment. It is a graph which shows a battery performance test result. It is a graph which shows the particle size distribution (C) of catalyst ink III, and the particle size distribution (D) of catalyst ink IV.

Explanation of symbols

1: Mixed liquid 2: Dispersion liquid 3: Catalyst ink 10: Catalyst-carrying conductor 20: Solid polymer electrolyte 30: Dispersion medium 40: Colloidal particles 50: Catalytic substance (catalytic metal) 60: Aggregate H: Vibrator J: Jacket for cooling L: Liquid mixture T: Temperature sensor

Claims (6)

A fuel cell catalyst ink comprising a dispersion medium and colloidal particles dispersed in the dispersion medium,
The colloidal particles are obtained by aggregating the catalyst-supported conductive particles adsorbing the solid polymer electrolyte and further adsorbing the solid polymer electrolyte on the outer periphery of the aggregate, and the median diameter of the colloidal particles is 3 to 15 μm. A fuel cell catalyst ink, wherein: A mixed liquid preparation step of mixing at least a catalyst-carrying conductor, a solid polymer electrolyte, and a dispersion medium to obtain a mixed liquid;
A dispersion step of subjecting the mixture to ultrasonic treatment to obtain a dispersion in which the catalyst-carrying conductor is dispersed;
By agitating the dispersion for a predetermined time, the dispersed particles of the catalyst-supported conductor adsorbing the solid polymer electrolyte are aggregated, and colloidal particles further adsorbing the solid polymer electrolyte are formed on the outer periphery of the aggregate And a stirring step to
In the dispersion step, the ultrasonic treatment is performed so that the temperature of the mixed solution in contact with the vibrator of the ultrasonic disperser is kept at 40 ° C. or lower.   The method for producing a catalyst ink for a fuel cell according to claim 2, wherein the temperature of the mixed solution in contact with the vibrator is maintained at 0 to 30 ° C.   The method for producing a catalyst ink for a fuel cell according to claim 2, wherein the temperature of the mixed solution in contact with the vibrator is maintained at 10 to 20 ° C. A drying step of obtaining a solidified ionomer resin by drying an ionomer solution obtained by dissolving an ionomer, which is a solid polymer electrolyte, in water and / or a lower alcohol such as ethanol;
An ionomer dispersion step of dispersing the ionomer resin in a dispersion medium to obtain an ionomer dispersion;
A mixed liquid preparation step of mixing the catalyst-supported conductor, the ionomer dispersion, and the dispersion medium to obtain a mixed liquid;
The mixed solution is subjected to ultrasonic treatment to aggregate the dispersed particles of the catalyst-carrying conductor adsorbing the solid polymer electrolyte, and colloidal particles adsorbing the solid polymer electrolyte are further formed on the outer periphery of the aggregate An ultrasonic treatment step for producing a catalyst ink for a fuel cell.   A fuel cell electrode comprising the fuel cell catalyst ink according to claim 1.