JP6281705B2 - Method for producing catalyst ink for fuel cell electrode - Google Patents

Description

  The present invention relates to a method for producing a catalyst ink used for a fuel cell electrode, and more particularly, to a method for producing a catalyst ink containing catalyst-supporting carbon and ionomer.

In the polymer electrolyte fuel cell electrode, a catalyst layer is provided on the polymer electrolyte membrane. This catalyst layer is formed by applying, transferring, or the like a catalyst ink containing carbon carrying a catalyst substance (for example, platinum, gold, etc.) and an aqueous solvent or an organic solvent (Patent Document 1). Here, it is known that when the catalyst ink has coarse particles (aggregates or undissolved components), fine irregularities are generated in the catalyst layer and the performance of the fuel cell electrode is deteriorated. Thus, for example, Patent Document 1 proposes removing coarse particles contained in the carrier as a pre-stage of the step of adjusting the catalyst ink. Specifically, it has been proposed to remove coarse particles by pressure filtration (pressure 3.5 kgf / cm ² (343 kPa)) using a mesh filter (pore diameter 10 μm).

JP 2004-241362 A

  However, when the catalyst ink contains a resin such as gel ionomer (polymer electrolyte) in the material, the gel ionomer coarse particles (aggregates and undissolved components) are filtered under pressure using a mesh filter. When trying to do so, the shape of the coarse particles is deformed by pressurization. In this case, the surface filtration type mesh filter cannot capture the deformed coarse particles, and passes through the holes of the mesh filter. When the catalyst layer of the fuel cell electrode is formed using such a catalyst ink, a coating surface defect occurs in the catalyst layer, and the initial performance and durability performance of the fuel cell electrode are remarkably deteriorated.

  On the other hand, if a filter with a small pore size (for example, a nonwoven fabric filter, a membrane filter, a sintered filter, etc.) is used, coarse particles of the deformed gel-like ionomer can be captured, but this time, it is not necessary to remove the catalyst-supported carbon. Most of them are captured and the yield decreases. Further, the compositional deviation of the catalyst ink occurs.

  The present invention has been made in view of the above background, and an object thereof is to provide a method for producing a catalyst ink for a fuel cell electrode, which can remove both catalyst-carrying carbon and coarse particles of an electrolyte ionomer. To do.

  In order to solve the above problems, according to a preferred aspect of the present invention, in a method for producing a catalyst ink for a fuel cell electrode, a preparation step of preparing a slurry containing catalyst-supporting carbon and an electrolyte ionomer; And a filtration step of filtering at a maximum filtration pressure of 100 kPa or less through a filter having a pore diameter not less than the diameter of the catalyst-supporting carbon and not more than 30 μm.

  According to the above production method, a filter having a pore diameter not less than the diameter of the catalyst-carrying carbon and not more than 30 μm is used, whereby coarse particles of the catalyst-carrying carbon can be captured by the filter. Moreover, since the maximum filtration pressure in a filtration process is 100 kPa or less, it is suppressed that the coarse particle of an ionomer deform | transforms during filtration. Therefore, the coarse particles of the ionomer can be captured by the filter. As a result, a catalyst ink from which both the catalyst-carrying carbon and the coarse particles of the electrolyte ionomer are removed can be obtained. The catalyst layer of the fuel cell electrode to which the catalyst ink is applied has a coating surface property with few coating surface defects, whereby the initial performance and durability performance of the fuel cell electrode can be improved.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the catalyst ink for fuel cell electrodes which can remove both the catalyst carrying | support carbon and the coarse particle of electrolyte ionomer can be provided.

It is a flowchart for demonstrating the manufacturing process of the catalyst ink which concerns on this embodiment. It is a schematic diagram for demonstrating the filtration apparatus used by the manufacturing process. It is a figure which shows the relationship between filtration pressure and defect size (major axis). It is a figure which shows the relationship between filtration pressure and defect size (area).

  Hereinafter, a method for producing a catalyst ink for a fuel cell electrode according to a preferred embodiment of the present invention will be described with reference to the accompanying drawings.

  In the manufacturing process in the present embodiment, the catalyst ink containing the catalyst-supporting carbon and the ionomer is filtered at a maximum filtration pressure of 100 kPa or less using a filter to remove coarse substances contained in the catalyst ink. The details will be described below with reference to FIGS.

  FIG. 1 is a flowchart for explaining the manufacturing process of the catalyst ink according to the present embodiment.

  First, a gel ionomer is prepared by heating and mixing an ionomer (polymer electrolyte) material (step S1). Here, as the ionomer, for example, a proton conductive ion exchange resin having a perfluorocarbon sulfonic acid polymer that is a fluorine resin, a BPSH (polyarylene ether sulfonic acid copolymer) that is a non-fluorine resin, or the like. Can be used. Perfluorocarbon sulfonic acid polymers and BPSH have sulfonic acid groups. That is, these resins have ionicity and are called “ionomer (ion + polymer)”.

  Next, a catalyst material is prepared (step S2). Specifically, the catalyst is supported on the carbon by mixing and dispersing the carbon in a mixture of the catalyst and the ion exchange water. As the catalyst, for example, a metal catalyst (Pt, Pt—Fe, Pt—Cr, Pt—Ni, Pt—Ru, Pt—Co, etc.) can be used. As carbon, for example, carbon containing V, F, Ni, and Ti as impurities can be used. In addition, the catalyst ink for anodes and the catalyst ink for cathodes can each be prepared by changing the components and composition ratios of the catalyst and carbon.

  Next, the gel ionomer prepared in step S1 and the catalyst-supported carbon prepared in S2 are mixed and emulsified to prepare a slurry (suspension) containing the catalyst-supported carbon and ionomer (step S3). .

  In this state, the catalyst ink contains coarse particles (aggregates and undissolved components) of the catalyst-carrying carbon and ionomer. When the catalyst layer of the fuel cell electrode is formed using the catalyst ink in which the coarse particles remain, a coating surface defect occurs in the catalyst layer, and the initial performance and durability performance of the fuel cell electrode are remarkably deteriorated. Therefore, in this embodiment, such coarse particles are removed in the next filtration step (step S4). First, the filtration apparatus 1 used at this filtration process is demonstrated using FIG.

  As shown in FIG. 2, the filtration device 1 includes a first tank 10, a second tank 20, a pressure control device 30, a filter support 40, and the like.

  The first tank 10 is a sealable container that stores the catalyst ink before filtration, and the second tank 20 is a container that is disposed below the first tank and stores the catalyst ink after filtration. To do.

The pressure control device 30 includes a gas cylinder 32 filled with a gas (for example, air or N ₂ ), a pipe 34 for supplying gas to the first tank 10, for example, a decompression device 36 including a plurality of regulators, a pressure gauge 38, and the like. ing. The pressure control device 30 depressurizes the gas supplied to the first tank 10 from the gas cylinder 32 via the pipe 34 by the decompression device 36. The pressure control device 30 includes a control unit (not shown). The control unit monitors the gas pressure measured by the pressure gauge 38 and opens / closes the decompression device 36 based on the gas pressure. By performing feedback control, the gas discharge pressure to the first tank 10 is adjusted to control the pressure in the first ink tank and the maximum filtration pressure (differential pressure).

  The filter support body 40 supports the filter 42 disposed between the first tank and the second tank. As the filter 42, for example, a metal mesh filter having a small distribution of filtration pore diameters can be used. For example, SUS316 or Ti having corrosion resistance is preferably used. The metal mesh filter is manufactured by a manufacturing method such as weaving, etching, or lithography, for example. The pore size of the filter 42 is set to a size capable of capturing coarse particles contained in the slurry, and is set to be not less than 30 μm and more preferably not less than 8 μm and not more than 12 μm in this case.

  Returning to the filtration step of step S4 in FIG. In the filtration step, first, a slurry (suspension) containing the catalyst-supporting carbon and the gel ionomer prepared in step S3 is charged into the first tank 10 of the filtration device 1. This initiates filtration. At this time, the pressure control device 30 of the filtration device 1 controls the discharge pressure of the gas to the first tank 10 so that the maximum filtration pressure in the filter 42 becomes sufficiently low. Specifically, the maximum filtration pressure is 100 kPa or less.

  This is based on the knowledge of the present inventors that the maximum filtration pressure needs to be at least 100 kPa or less in order to prevent the coarse particles of ionomer being filtered from slipping out of the filter. . This point will be described below with reference to Table 1, FIG. 3 and FIG.

  Table 1 shows the relationship between the maximum filtration pressure in the filtration step and the coating surface defect size when the catalyst layer of the fuel cell electrode is formed using the catalyst ink after filtration. Here, a metal filter having a pore diameter of 10 μm is used as the filter. FIG. 3 shows the maximum filtration pressure [kPa] in Table 1 on the horizontal axis and the major axis [μm] of the coating surface defect on the vertical axis. In the figure, X is the average major axis of the defects, and Y is the maximum major axis and the minimum major axis. FIG. 4 shows the maximum filtration pressure [kPa] in Table 1 on the horizontal axis and the area ratio [%] of coating surface defects on the vertical axis. Z is the area ratio of coating surface defects.

  As apparent from Table 1, FIG. 3 and FIG. 4, the coating surface defects rapidly decrease at the maximum filtration pressure of 100 kPa (defect area ratio 7.0%). As apparent from Table 1 and FIG. 4, when the maximum filtration pressure is 60 kPa or less, the coating surface defects are remarkably reduced (defect area ratio 0.4%), and when the maximum filtration pressure is 40 kPa or less, the coating surface defects are almost eliminated (defect area ratio 0.1). %). In addition, the ratio that the coating surface defect contributes to the power generation efficiency is about 15% of the area ratio of the coating surface defect (1% reduction in efficiency when the area ratio of the coating surface defect is 15%). From the above, the maximum filtration pressure needs to be at least 100 kPa or less, preferably 60 kPa or less, more preferably 10 kPa or more and 40 kPa or less.

  The slurry thus filtered is accommodated in the second tank 20, and the filtration process is completed. In the filtration step, a filter having a pore size of the filter 42 not less than the diameter of the catalyst-carrying carbon and not more than 30 μm is used, so that coarse particles of the catalyst-carrying carbon are captured by the filter 42. Further, since the maximum filtration pressure is 100 kPa or less, deformation of the coarse particles of ionomer is suppressed during filtration. Therefore, coarse particles of ionomer are also captured by the filter 42. As a result, a catalyst ink from which coarse particles of both catalyst-carrying carbon and ionomer are removed can be obtained. As described above, the catalyst layer of the fuel cell electrode to which this catalyst ink has been applied has a good coating surface property with a small coating surface defect size, thereby improving the initial performance and durability performance of the fuel cell electrode.

<Modification>
Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and can be implemented in various modes without departing from the scope of the present invention.

  For example, although a metal mesh filter has been described as a filter, for example, a mesh filter having excellent chemical resistance such as PP, PTFE, or PFA may be used. In addition, for example, a mesh filter has a high porosity and a low filtration resistance, so it is suitable for a large amount of filtration in a short period of time. It is also possible to use a sintered filter or the like.

  Further, for example, as a mechanism for adjusting the maximum filtration pressure (differential pressure) in the filtration step, a method of adjusting the pressure of gas discharged to the first tank 10 (primary side) by the pressure control device 30 has been shown. However, it is not limited to this. For example, the second tank 20 (secondary side) may be sucked and depressurized. In order to precisely control the differential pressure, the second tank 20 (secondary side) is also the first tank 10 ( The pressure difference may be kept constant by applying a lower pressure compared to the primary side).

DESCRIPTION OF SYMBOLS 1 ... Filtration apparatus, 10 ... 1st tank, 20 ... 2nd tank, 30 ... Pressure control apparatus, 32 ... Gas cylinder, 34 ... Piping, 36 ... Pressure reducing device, 38 ... Pressure gauge , 40 …… Filter support, 42 …… Filter

Claims (1)

A preparation step of preparing a slurry containing a catalyst-supporting carbon and a gel ionomer, the slurry having a pore diameter through the diameter or on and 30μm following filters of the catalyst-carrying carbon, 10 kPa or more and 60kPa in the following filtration pressure A method for producing a catalyst ink for a fuel cell electrode, comprising: a filtration step of performing filtration to remove coarse particles of the catalyst-carrying carbon and the ionomer .

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