JP2011014334A - Method for manufacturing electrode paste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve dispersion of an electrolyte resin in an electrode paste used in the manufacture of a fuel cell electrode.SOLUTION: The method for manufacturing an electrode paste used in the manufacture of a fuel cell electrode includes a process to generate microbubbles in the electrolyte solution.

Description

  The present invention relates to an electrode paste for a fuel cell.

  In general, an electrode of a fuel cell contains an electrolyte resin. In the process of manufacturing an electrode for a fuel cell, a catalyst (for example, platinum) supported on a catalyst carrier (for example, carbon) and an electrolyte solution containing an electrolyte resin are kneaded to form an electrode paste (also referred to as electrode ink). ) Is included. Since the electrolyte resin has a property of being aggregated and stabilized, many electrolyte resins contained in the electrolyte solution have a large particle diameter. Thus, when the electrolyte resin is aggregated, it is difficult to form a three-phase interface where the catalyst carrier, the catalyst, and the electrolyte resin are in contact with each other. As a result, the utilization rate of the catalyst may decrease, and power generation efficiency may decrease.

  In order to solve such a problem, there has been proposed a technique for loosening the aggregation of the electrolyte resin by adding a strongly alkaline reagent to the electrolyte solution (see, for example, Non-Patent Documents 1 and 2). In addition, when manufacturing the electrode paste, the electrolyte is adjusted by adjusting the technique of kneading with a weak shearing force that does not cause aggregation of the electrolyte resin (see, for example, Patent Document 1), the number of revolutions during kneading, the stirring time, and the like. A technique (for example, see Patent Document 2) that suppresses aggregation of the resin has been proposed.

JP 2003-100305 A Japanese Patent Laid-Open No. 2006-210181 JP 2006-331968 A

Journal of Power Sources Volume 165 (2007) p. 128-133 Journal of Power Sources Volume 169 (2007) p. 271-275

  However, as described in non-patent literature, when a strongly alkaline reagent is used, the surface of carbon as a catalyst carrier is modified to be hydrophilic, so that water generated by power generation of the fuel cell is generated in the catalyst layer. There is a risk that the fuel cell performance may be deteriorated due to retention in the inside and flooding.

  This invention is made | formed in view of the said subject, and it aims at providing the technique which improves the dispersibility of electrolyte resin in the electrode paste used for manufacture of the electrode for fuel cells.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

Application Example 1 An electrode paste manufacturing method used for manufacturing a fuel cell electrode,
A method for producing an electrode paste, comprising a step of generating microbubbles in an electrolyte solution containing an electrolyte resin.

  Bubbles are negatively charged. Therefore, when air bubbles enter the electrolyte solution, the hydrophobic group part becomes hydrophilic, and the solvent (alcohol) enters the part where the hydrophobic groups gather and aggregate. Thereby, aggregation of electrolyte resin is loosened. Even if the microbubbles are removed thereafter, the electrolyte is not aggregated because the solvent has entered. Therefore, the dispersibility of the electrolyte resin can be improved in the electrode paste used for manufacturing the fuel cell electrode.

  The present invention can be realized in various forms. For example, a method for manufacturing a fuel cell electrode, a method for manufacturing a fuel cell, a fuel cell manufactured by the method, and a vehicle equipped with the fuel cell Or the like.

It is process drawing which shows the manufacturing method of the membrane electrode assembly as one Example of this invention. It is a figure which shows the average particle shape of electrolyte resin in the electrolyte solution which performed the microbubble generation process. It is a table | surface which shows the particle diameter distribution of electrolyte solution. It is a figure which shows the cyclic voltammogram of the oxygen electrode of MEA of a present Example. It is a table | surface which shows the quantity of electricity required for ionization of hydrogen in the hydrogen electrode of MEA of a present Example. It is a figure which shows the current-voltage characteristic of the fuel cell using MEA of a present Example.

  FIG. 1 is a process diagram showing a method for producing a membrane electrode assembly (hereinafter abbreviated as “MEA”) as one embodiment of the present invention. In step S102, microbubbles are generated in the electrolyte solution by a pressurized and reduced pressure method. In this example, a Nafion (registered trademark) 1100 solution (SE-5142 manufactured by DuPont) is used as the electrolyte solution. In step S102, for example, the microbubble generator is operated for 30 minutes in a mixed solution of Nafion (registered trademark) 1100 solution 100 g and a dispersion medium (water 25 g, ethanol 25 g). Thereby, aggregation of the electrolyte resin in the electrolyte solution can be loosened. In this embodiment, a Foamest column type 300 (manufactured by NAC) is used as a microbubble generator. This microbubble generator generates microbubbles by adding a compressed gas to a porous polymer film. Other microbubble generators may be used.

  In this embodiment, the microbubble means a fine bubble having a diameter of 10 micrometers to several tens of micrometers when bubbles are generated. A bubble having a smaller bubble diameter such as a “micro nano bubble” having a diameter of several hundred nanometers to 10 micrometers or a “nano bubble” having a diameter of several hundred nanometers or less may be used.

  The electrolyte resin is not limited to Nafion (registered trademark), and other fluorine-based sulfonic acid resins such as Aciplex (registered trademark) and Flemion (registered trademark) may be used. Further, for example, a fluorine-based phosphonic acid resin, a fluorine-based carboxylic acid resin, a fluorine-based graft resin, a hydrocarbon-based graft resin, an aromatic resin, or the like may be used.

  In step S104, the electrolyte solution containing microbubbles created in step S102 (hereinafter also referred to as “microbubble-containing electrolyte solution”), a fuel cell catalyst (hereinafter also simply referred to as “catalyst”), a dispersion A kneading liquid is prepared by kneading the medium. In this embodiment, platinum is used as the catalyst. Platinum as a catalyst is supported on carbon black. In this embodiment, the dispersion medium contains water and a lower alcohol such as ethanol. Specifically, the microbubble-containing electrolyte solution, the catalyst, and the dispersion medium were placed in a stirrer and kneaded (stirred) for several tens of seconds to several minutes. In addition, a human may knead by hand without using a stirrer.

  The catalyst is not limited to platinum, and in addition, rhodium, palladium, iridium, osmium, ruthenium, rhenium, gold, silver, nickel, cobalt, lithium, lanthanum, strontium, yttrium, etc. Two or more kinds may be used. Moreover, you may use the alloy which combined these 2 or more types.

  The catalyst carrier is not limited to carbon black, and various other carbon materials such as natural graphite powder, artificial graphite powder, mesocarbon microbeads (MCMB), and multi-walled carbon nanotubes (MWCNT) can be used.

  In step S106, a carbon black in the kneaded liquid prepared in step S104 was dispersed (pulverized and mixed) using an ultrasonic homogenizer (manufactured by UH-600 SMT) to prepare a catalyst ink. Instead of the ultrasonic homogenizer, a jet mill, a ball mill, a vibration ball mill, a micro cutter, or the like may be used.

  In step S108, a catalyst layer is formed on the electrolyte membrane. Specifically, the catalyst ink created in step S106 is applied onto the base sheet to form a catalyst layer, and a base sheet with a catalyst layer is created. Thereafter, the base sheet with the catalyst layer is superposed so that the catalyst layer side is in contact with the electrolyte membrane, and hot-pressed at 130 ° C. to transfer the catalyst layer onto the electrolyte membrane. When the catalyst layer is joined to the electrolyte membrane by transfer, bubbles in the catalyst layer disappear. Even when the bubbles disappear, the dispersion of the electrolyte resin is maintained. In this example, the electrolyte membrane formed with the catalyst layer formed in step S108 is referred to as “CCM (Catalyst Coated Membrane)”.

  In this embodiment, the catalyst layer is formed on the electrolyte membrane by transfer, but the catalyst layer may be formed on the electrolyte membrane by a printing means such as a spray method, an ink jet method, or screen printing. When a catalyst layer is formed on the electrolyte membrane by a method other than transfer, heat treatment may be performed at 130 ° C. or higher after the catalyst layer is formed on the electrolyte membrane.

  In step S110, the MEA is created by superposing the diffusion layer sheet on the CCM created in step S108 and hot-pressing it below 130 ° C.

  FIG. 2 is a diagram showing an average particle shape of the electrolyte resin in the electrolyte solution subjected to the microbubble generation treatment. In FIG. 2, microbubbles were generated in the mixed solution of the electrolyte solution and the dispersion medium for 30 minutes (similar to the treatment in step S102), then left at room temperature for 12 hours to remove the bubbles, and then zeta plus (Brookhaven). The average particle | grains of electrolyte resin were measured using Instrument Corporation. In FIG. 2, a microbubble generation process is performed for 30 minutes (the manufacturing method of the present embodiment) is indicated as a, and a microbubble generation process is not performed as a comparative example as b.

  FIG. 3 is a table showing the particle size distribution of each electrolyte solution shown in FIG. The median diameter is a particle diameter corresponding to 50% of the cumulative distribution curve. Generally, when expressing the particle diameter of the electrolyte solution, the median diameter is used. As shown in FIG. 3, the median diameter of the electrolyte resin when the microbubble generation treatment is performed is 60 μm, and the median diameter of the electrolyte resin when the microbubble generation processing is not performed is 200 μm. As shown in FIGS. 2 and 3, when the microbubble generation process is performed, the distribution range of the electrolyte resin is narrower than when the microbubble generation process is not performed. That is, it can be said that the particle diameter of the electrolyte resin is reduced by performing the microbubble generation treatment. As a result, it can be said that the dispersibility of the electrolyte resin was improved by generating microbubbles in the electrolyte resin solution.

  FIG. 4 is a diagram showing a cyclic voltammogram of the oxygen electrode of an MEA manufactured by the manufacturing method in the present embodiment (hereinafter also simply referred to as “MEA of the present embodiment”). FIG. 5 is a table showing the amount of electricity required for ionization of hydrogen at the hydrogen electrode of the MEA of this example. The amount of electricity shown in FIG. 5 is calculated based on the calculation result of the surface area of the electrochemically active catalyst calculated from the cyclic voltammogram shown in FIG. The surface area of the electrochemically active catalyst is converted from the amounts of adsorbed hydrogen and adsorbed oxygen obtained from the peak areas of the oxidation current and reduction current in the cyclic voltammogram. 4 and 5, the MEA of the present embodiment is shown as a, and the MEA manufactured without performing the microbubble generation process is shown as b as a comparative example.

  As shown in FIG. 5, the MEA electrode of this example required 320 mQ of electricity to ionize hydrogen. On the other hand, when using the MEA of the comparative example, the amount of electricity required to ionize hydrogen was 250 mQ. That is, it can be said that the amount of hydrogen atoms adsorbed on the catalyst (platinum) was larger in the MEA electrode of this example. Therefore, it can be said that the dispersibility of the electrolyte resin in the catalyst layer is improved. In the MEA of this example and the MEA of the comparative example, the same amount of catalyst (platinum) is used, but the amount of electricity is 320 mQ and 250 mQ, respectively. That is, it can be said that the utilization rate of the catalyst (platinum) has improved by about 30%.

  FIG. 6 is a diagram showing current-voltage characteristics of a fuel cell using the MEA of this example. Also in FIG. 6, like FIG.4, 5, MEA of a present Example is shown as a, and MEA manufactured without performing a microbubble generation | occurrence | production process as a comparative example is shown as b. In FIG. 6, a fuel cell is configured by arranging separators on both sides of the MEA, and a current voltage measurement test is performed using an electronic load device FK400L (manufactured by Takasago Seisakusho) and a DC power supply device EX750 (manufactured by Takasago Seisakusho). Results are shown. The measurement conditions were as follows: hydrogen was supplied to the anode, air was supplied to the cathode, the hydrogen outlet pressure was 0.15 MPa, the air outlet pressure was 0.15 MPa, the operating temperature of the measurement cell was 80 ° C., and the dew point of the supplied hydrogen and oxygen was 80 Degree. As shown in FIG. 6, the fuel cell using the MEA of this example has improved fuel cell characteristics as compared with the fuel cell of the comparative example.

  As described with reference to FIGS. 2 to 6, according to the MEA manufacturing method of this embodiment, the dispersibility of the electrolyte resin is improved, and as a result, the utilization rate of the catalyst is improved and the performance of the fuel cell is improved. Is done.

  In addition, this invention is not restricted to said Example, In the range which does not deviate from the summary, it is possible to implement in various aspects. For example, in the above-described embodiment, microbubbles are generated in the electrolyte solution in step S102, but microbubbles may be generated at other timings. For example, in step S104, kneading may be performed while generating microbubbles. Further, in step S106, carbon black may be dispersed while generating microbubbles in the kneaded liquid.

Claims (1)

A method for producing an electrode paste used for producing a fuel cell electrode,
A method for producing an electrode paste, comprising a step of generating microbubbles in an electrolyte solution containing an electrolyte resin.

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