JP2003100305A - Method of manufacturing electrode for fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that aggregation of a resin potion generated by the shearing stress which is loaded during preparing a paste which forms a water repellent layer and a catalyst layer in an electrode, generates clogging in filter, lacks in coating film and so on, and also pinholes and cracks generated in the coating layer by air bubble involved in the process of making the paste result in short circuit failure and decline of cell output voltage. SOLUTION: Before adding the resin, strong shearing stress is loaded to accelerate the formation of secondary particles of a solid component, and after adding the resin, mixture processing is performed by weak shearing stress so as not to generate the aggregation of the resin, Also, the paste which forms the coating film layer is subject to decompression defoaming processing.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a polymer electrolyte membrane,
The present invention relates to a method for producing a fuel cell electrode in which a paste containing at least conductive material particles and a resin is applied to the surface of an electrode base material or the like to form a coating layer.

[0002]

2. Description of the Related Art For fuel cells for which high efficiency is desired, particularly solid polymer electrolyte fuel cells and direct methanol fuel cells, the surface of the polymer electrolyte membrane, electrode substrate or transfer support is used. Then, there is adopted an electrode manufacturing method in which a coating layer containing conductive material particles such as carbon particles is applied and formed. In order to form this coating layer, it is necessary to prepare and apply a paste containing conductive material particles. The coating layer does not necessarily have to be a single layer, and the coating layer may be provided so that the average particle size of the particles may be changed from the polymer electrolyte membrane side to the outside, or the water repellent layer and the hydrophilic layer. There is also proposed a multi-layer structure in which a coating layer is provided so as to exist.

[0003]

In order to prepare a paste for forming a coating film layer, a strong shearing force is applied in order to promote the formation of secondary particles of conductive material particles which are a part of the solid component of the coating film. It is necessary to mix them by force. Further, when manufacturing the electrode, it is common to add a water-repellent resin to the gas diffusion layer and an ion exchange resin to the catalyst layer. As the resin added here, a fluorine resin, an ion exchange resin,
A resin solution in which an acrylic / styrene-based copolymer resin, a styrene / butadiene-based copolymer resin, carboxymethyl cellulose, polyvinyl alcohol, a formal resin, an acetal resin or the like is dissolved or an emulsified resin solution can be used.

However, in general, an emulsion resin is a resin solution in which a synthetic resin such as a fluorine resin, a styrene / butadiene resin, an acrylic / styrene resin is dispersed in an aqueous solution with a surfactant or a dispersant, and shear stress, temperature and p
Due to a slight change in H, the synthetic resin itself tends to agglomerate, which requires careful handling. Here, aggregation is
It means that intermolecular and intramolecular interactions between resins existing in a colloidal state become stronger and entangled. Therefore, in the paste preparation process, if the solid components such as the conductive material are not sufficiently mixed before the addition of the emulsion resin, it becomes necessary to achieve secondary particle formation after the addition of the emulsion resin, and therefore a strong shearing force is required. When added, a problem occurs that the emulsion resin aggregates. In addition, when a paste in which resin agglomeration occurs is used, the agglomerates are clogged during the refining process and the coating process, the filter pressure increases, coating streaks occur, and the electrode is wound up to form a battery. In the case of (1), the resin originally necessary is removed during the refining process and the binding force is lost, which causes a problem such as a missing film.

Further, there is a problem that air bubbles are entrapped in the paste due to the mechanical stirring action of the mixing stirrer and the wetting of the powder in the step of preparing the paste. If coating is performed with the air bubbles still contained, pinholes may appear on the coating layer after coating and drying so that the base of the polymer electrolyte membrane, electrode substrate, etc. may be visible, or cracks may occur in the coating layer. There is such a problem. Therefore, a decrease in battery output voltage occurs due to the movement of charges in the pinhole portion being hindered,
The coating film may be missing from the cracked portion, causing defects due to a short circuit or lowering the output.

[0006]

The present invention provides a step of preparing a paste containing conductive material particles and a resin, and applying the prepared paste to the surface of a polymer electrolyte membrane, an electrode substrate or a support. In the method for manufacturing a fuel cell electrode having a step of forming a membrane layer, the step of preparing the paste is a secondary treatment of the conductive material particles in the paste by mixing conductive material particles and a dispersion medium with a strong shearing force. The method is characterized by comprising a step of promoting particle formation, and then a step of adding a resin component and performing a mixing treatment with a weak shearing force such that the resin does not aggregate. Here, it is preferable to have a step of defoaming the paste before applying the paste to the surface of the polymer electrolyte membrane, the electrode substrate or the support.
The defoaming treatment is preferably performed under reduced pressure of 60 torr or less.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. FIG. 1 shows an example of a paste manufacturing process. First,
Carbon black of the conductive material particles is mixed with an aqueous solution of a surfactant which is a dispersion medium thereof, and the mixture is subjected to a first mixing treatment (mixing I). Then add an aqueous solution of a surfactant,
The same mixing process is performed (mixing II). Next, a water repellent emulsion resin is added and a second mixing process is performed (mix II
I). Then, it is subjected to vacuum defoaming treatment, filtered through a filter and purified. In this series of paste preparation steps, in the first mixing step (mixing I and II), the mixture is mixed with a strong shearing force to promote the secondary particle formation of carbon, which is a solid component in the paste. On the other hand, in the mixing process (mixing III) after the addition of the resin component, the mixing process is performed with a weak shearing force to prepare a paste so that the resin does not aggregate. This prevents aggregates from being clogged during the refining process and the coating process, increasing the filter pressure and causing coating streaks. Further, when a battery is manufactured through a process of winding an electrode having a coating layer made of such paste, the originally necessary resin is removed during the refining process and the binding force is lost, and therefore the coating film is missing. It is also possible to prevent problems such as being caused.

When the paste prepared as described above is subjected to defoaming treatment using a vacuum defoaming device, pinholes through which the paste is applied and dried can be seen so that the underlying layer is visible. It is possible to prevent problems such as the occurrence of cracks and cracks in the coating layer. As described above, before the addition of the resin component, the mixture is treated with a strong shearing force to promote the secondary particle formation of the solid component in the paste, and after the addition of the resin component, the mixture is treated with a weak shearing force to perform the mixing treatment of the resin. By preparing the paste so that agglomeration does not occur, it is possible to prepare a fuel cell electrode having no defects. In addition, by defoaming the paste under reduced pressure to defoam so that the foam bursts and collapses, it is possible to manufacture an electrode plate that does not have pinholes or cracks, and there is no short circuit failure and fuel with improved output voltage. You can get a battery.

[0009]

EXAMPLES Examples of the present invention will be described below. A paste for forming the water repellent layer of the electrode was prepared as follows. Acetylene black (trade name Denka Black manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive material, a 1 wt% aqueous solution of a surfactant as a dispersion medium, and polytetrafluoroethylene (hereinafter abbreviated as PTFE) as a resin of a water repellent agent. A PTFE emulsion resin (manufactured by Daikin Industries, Ltd., trade name D1) dispersed in water was used. First, in the step shown in FIG.
In the mixing I and mixing II steps, acetylene black and an aqueous surfactant solution are mixed, and in the mixing III step, PTFE is added.
The emulsion resin was mixed to prepare a paste.
A strong shearing force was applied in the mixing I and mixing II steps to form secondary particles of acetylene black. Mix III process is PT
Since the FE emulsion resin was added, a weak shear force was applied to prevent the resin from agglomerating.

In the above mixing steps I, II and III, a planetary mixer 3D-5 manufactured by Tokushu Kika Co., Ltd. was used as a stirring mixer. This is a mixing stirrer having a planetary mixer section in which two blades having a rotation and a revolution function are paired as a stirring mechanism, and a dissolver section that revolves while revolving in the same manner as the planetary section. The shearing force applied to the paste is, when the rotation speed is 20 rpm in the outermost peripheral portion of the blade of the planetary mixer,
The shear rate (peripheral speed) is about 15 m / s. In addition, the rotation speed is 2000 at the outermost periphery of the disc in the disperser section.
At rpm, the shear rate (peripheral speed) is about 15 m / s.
If the disk rotation speed of the disperser is lower than 2000 rpm, resin agglomeration is not seen and a good paste can be obtained, but if it is higher than 2000 rpm, resin agglomeration tends to occur. When using a disper, the load applied to the paste is affected by the liquid level height and viscosity of the paste, and resin agglomeration tends to occur especially when mixing and stirring under conditions where air bubbles are involved, and the shear rate is not always required. It is not limited by Further, in the mixer which was scaled up separately from the stirring mixer used in this example, no resin agglomeration was observed even when the peripheral speed of the disperser was 15 m / s.

The paste for forming the electrode catalyst layer is carbon (made by Lion Corporation, trade name Ketjen Black E).
PFS in which C) is loaded with platinum in a weight ratio of 50:50, and perfluorosulfonate ionomer (hereinafter abbreviated as PFSI) is dispersed in alcohol as a resin.
I emulsion resin (PFSI emulsion resin manufactured by DuPont, USA, trade name Nafion) was used. even here,
Similar to the water-repellent layer forming paste, in the mixing step before resin addition, mixing treatment with strong shearing force promotes secondary particle formation of platinum-carrying carbon in the paste, and mixing after addition of the resin In the process, a paste was prepared by mixing with a weak shearing force to prevent resin agglomeration. As comparative examples, several kinds of catalyst layer pastes were prepared by changing the mixing conditions of Mix I, Mix II and Mix III.

The paste prepared as described above was defoamed by changing the target vacuum degree using a vacuum defoaming device. In this treatment, defoaming was performed by maintaining the reduced pressure for 10 minutes after the foam spontaneously burst and started to collapse.
Under the condition that collapse of foam due to spontaneous bursting was not observed, degassing was completed by maintaining a reduced pressure state for 10 minutes after reaching the target vacuum degree. In addition, as a comparative example, a paste without vacuum degassing was also prepared. The pinhole refers to a state in which a hole that allows the base material to be seen from the surface of the coating film is opened.
Foam refers to the bubbles that collect on the surface of the paste liquid. In the defoaming, not only foam is generated on the liquid surface of the paste to increase the volume, but also the volume of the entire paste may be increased due to expansion of air bubbles contained in the paste.

The water-repellent layer-forming paste produced as described above is carbon paper (trade name: TG, manufactured by Toray Industries, Inc.)
(PH060) was coated on one side using a doctor blade method, dried at 60 ° C. for 30 minutes, and then heat-treated at 380 ° C. for 15 minutes using a hot air dryer. Thus, a gas diffusion layer having a water repellent layer was produced. The catalyst layer-forming paste is applied to a support made of polyethylene terephthalate (hereinafter abbreviated as PET) (manufactured by Toray Industries, Inc.) using a coating machine,
Dried. The transfer support sheet on which this catalyst layer was formed was wound up on a roll.

Next, the catalyst layer on the support sheet unrolled from the roll was thermally transferred at 150 ° C. to both sides of an ion exchange membrane (Nafion 112, manufactured by DuPont, USA). Then, the gas diffusion layer was heat-welded to the ion exchange membrane at 150 ° C. for 10 minutes so that the water repellent layer side was in contact with the catalyst layer. The membrane-electrode assembly (MEA) produced in this manner is laminated via a conductive separator plate, both ends of which are sandwiched between end plates via a current collector plate and an insulating plate, and tightened with a predetermined load to fold the fuel cell. Was produced.

Tables 1 and 2 show the manufacturing conditions of the water-repellent layer forming paste and the catalyst layer forming paste, respectively.

[0016]

[Table 1]

[0017]

[Table 2]

The following evaluation was made on the fuel cell comprising the obtained paste, the water repellent layer and the catalyst layer produced by applying the paste, and the electrode plate produced by using the water repellent layer and the catalyst layer. went. (1) Clogged filter The paste prepared was filtered with a filter having a mesh size of 100 mesh before coating, and the clogged state of the filter was visually observed. (2) Generation of pinholes The state of generation of pinholes was confirmed by visually observing the water repellent layer and the catalyst layer. (3) Streaks were confirmed by visually observing the coating streak water-repellent layer and the catalyst layer. (4) Cracking of water repellent layer and catalyst layer The water repellent layer and catalyst layer were visually observed to confirm the occurrence of cracks. (5) Short circuit failure The internal resistance of 1000 MEAs in the fabricated fuel cell was measured, and the number of leaked cells was counted.

(6) Cell output voltage The prepared fuel cell was kept at 75 ° C., and hydrogen gas humidified so that the dew point became 70 ° C. on the fuel electrode side, and the dew point became 60 ° C. on the air electrode side. Humidified air is supplied, and the fuel gas is operated at a fuel gas utilization rate of 70% and an air utilization rate of 40%, and current densities of 200 mA / cm ² and 800 mA / c.
The battery output voltage at m ² was measured. Table 3 and Table 4
Shows the evaluation results of the water repellent layer and the catalyst layer, and Table 5 shows the evaluation results of the fuel cell.

[0020]

[Table 3]

[0021]

[Table 4]

[0022]

[Table 5]

In Mixes I and II, paste no. The coating lines 1 to 5 and 15 to 19 have coating streaks. In addition, in paste No. 3 where agglomeration occurred because a strong shearing force was applied in Mix III.
Those coated with 8 to 11 and 22 to 25 have streaks, pinholes, cracks and the like. On the other hand, in Mixes I, II and III, paste N applied with appropriate shearing force.
o. Those coated with 6, 7, 14, 20, 21, and 28 did not have defects such as stripes, pinholes, and cracks. As can be seen from Table 5, the water repellent layer paste N
o. 14 and catalyst layer paste No. The battery using No. 28 shows a high battery voltage without an internal short circuit.

In the mixing step before resin addition, a strong shearing force, for example, a shearing speed (peripheral speed) of 75 m / min is mixed to accelerate secondary particle formation of solid components in the paste, and in the mixing step after resin addition, Weak shear force, eg shear rate (peripheral speed) 11
By preparing a paste by mixing at m / min so that resin agglomeration does not occur, problems such as increased filter pressure, coating streak, and missing coating film occur. It has become possible to prevent it. Also,
By defoaming the paste, it is possible to prevent problems such as pinholes that make the underlying layer visible on the coating layer after coating and drying, and cracks in the coating layer. Became. Further, by promoting the secondary particle formation of the solid component in the paste by mixing with a strong shearing force in the mixing step before resin addition, the conductivity of the coating film is improved and weak in the mixing step after resin addition. By preparing the paste so that the resin is not aggregated by mixing with shearing force, it is possible to reduce the current density bias in the electrode,
Battery output voltage improved.

Although a planetary mixer was used as an agitator in the examples, kneading devices such as a continuous twin-screw kneader and a batch kneader, a pressure homogenizer, an ultrasonic homogenizer, a line mill, a sand mill, a bead mill, a bead mill, Planetary ball mills and other dispersers can also be used. Although the doctor blade method was used as the coating method, it is not limited to this method, and similar results can be obtained by other methods such as screen printing method, gravure printing method, coater coating method, and spray coating method. . Although hydrogen and air were used as the reaction gas in the examples, similar results were obtained with a fuel containing impurities such as carbon dioxide gas, nitrogen, and carbon monoxide as reformed hydrogen. Similar results are obtained using liquid fuels such as ethanol, ethanol and dimethyl ether and mixtures thereof. Further, the liquid fuel may be vaporized in advance and supplied as above.

The material of the gas diffusion layer is not limited to the carbon fine powder and carbon paper shown in the examples,
Other carbon particles, carbon cloth, carbon non-woven fabric, etc. can also be used. Further, the configurations of the catalyst layer and the membrane are not limited to those of the embodiment. The joined body of the polymer electrolyte and the electrode according to the present invention can be applied to a gas generator for oxygen, ozone, hydrogen and the like, a gas purifier, and various gas sensors such as an oxygen sensor and an alcohol sensor.

[0027]

As described above, according to the present invention, a fuel cell electrode having a coating film without defects can be obtained. As a result, it is possible to obtain a fuel cell in which a short circuit failure or a decrease in cell output voltage does not occur.

[Brief description of drawings]

FIG. 1 is a diagram showing a paste manufacturing process according to an embodiment of the present invention.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Eiichi Yasumoto             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Junji Morita             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Yasushi Sugawara             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. F-term (reference) 5H018 AA06 AS01 BB00 BB08 BB12                       EE05 EE17 HH09                 5H026 AA06 BB00 BB04 BB08 HH09

Claims (3)

[Claims] 1. A step of preparing a paste containing conductive material particles and a resin, and a step of applying the prepared paste to the surface of a polymer electrolyte membrane, an electrode substrate or a support to form a coating layer. A method of manufacturing a fuel cell electrode, wherein the step of preparing the paste comprises a step of mixing conductive material particles and a dispersion medium with a strong shearing force to promote secondary particle formation of the conductive material particles in the paste. And a step of adding a resin and then performing a mixing treatment with a weak shearing force that does not cause aggregation of the resin. 2. The method for manufacturing a fuel cell electrode according to claim 1, further comprising a step of defoaming the paste before the step of forming the coating layer. 3. The method for producing a fuel cell electrode according to claim 2, wherein the defoaming treatment is performed under a reduced pressure of 60 torr or less.