JP2009289692A - Method of manufacturing electrode layer for fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode layer of a structure easy in intrusion and diffusion of fuel and an oxidizing agent, by enlarging the substantially surface area participating in catalyst reaction as the electrode layer for a fuel cell, and a method capable of forming this electrode layer by an ultrasonic spray device. <P>SOLUTION: This electrode layer 22 is composed of a porous assembly formed by gathering a further larger number of porous catalyst secondary particles 23 formed by gathering a large number of catalyst primary particles composed of a catalyst carrying particle and an ion conductive polymer. This electrode layer can be provided by drying an ink particle so that the ink particle sprayed from the ultrasonic spray device sticks to a target surface in a substantially dried state, when applying catalyst ink including the catalyst carrying particle, the ion conductive polymer and a solvent to a high polymer film or a gas diffusing film by the ultrasonic spray device. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electrode layer of a solid polymer electrolyte fuel cell, a method for manufacturing the same, and a fuel cell including the electrode layer. The surface area of the electrode layer is increased, the reaction area is increased, and cell characteristics are improved. It has been made.

FIG. 10 shows an example of a membrane electrode assembly (MEA) which is a reaction part of a solid polymer electrolyte fuel cell.
In FIG. 10, reference numeral 1 denotes a polymer electrolyte membrane. A membrane-like anode electrode layer 2 having a thickness of about 20 μm is joined to one surface of the polymer electrolyte membrane 1, and a membrane-like cathode electrode layer 3 having a thickness of about 20 μm is joined and integrated to the other surface. A diffusion layer such as carbon paper (not shown) is provided on the surfaces of the anode electrode layer 2 and the cathode electrode layer 3 to form a membrane electrode assembly.

The polymer electrolyte membrane 1 is a film made of a perfluorosulfonic acid polymer having a thickness of about 30 to 70 μm.
For the anode electrode layer 2 and the cathode electrode layer 3, a catalyst ink is applied to a carbon paper serving as a diffusion layer and dried. For the catalyst ink, for example, catalyst-carrying particles in which catalyst particles such as platinum fine particles having a diameter of about 2 to 5 nm are carried on conductive particles such as carbon particles having a diameter of about 30 nm are prepared. , Isopropanol, water or the like dispersed in a polymer electrolyte solution is used.

The carbon paper on which the anode electrode layer 2 and the cathode electrode layer 3 are formed is bonded to both surfaces of the polymer electrolyte membrane 1 to form a membrane electrode assembly.
In addition, there is a manufacturing method in which catalyst ink is applied to both surfaces of the polymer electrolyte membrane 1 to form the electrode layers 2 and 3, and then a diffusion layer is joined thereto to form a membrane electrode assembly.

  As a method of applying the catalyst ink to the diffusion layer or the polymer electrolyte membrane (hereinafter collectively referred to as a target), an air spray method has been conventionally used, but a recent method of applying an ultrasonic spray device has been proposed. Has been. The coating method using an ultrasonic spray apparatus is considered to have an advantage that the dispersion of catalyst-carrying particles in the obtained electrode layer is uniform.

  However, in the case of using the ultrasonic spray device, the catalyst-supporting particles grow together as in the case of the conventional air spray device, and an electrode layer in a state where the grown particles are bonded by the ion conductive polymer is obtained. There wasn't.

Regarding the formation of an electrode layer for a fuel cell using an ultrasonic spray device, there are the following patent documents.
JP 2006-210200 A JP 2006-236881 A JP 2007-16993 A JP 2007-165075 A JP 2007-213841 A JP 2007-258051 A JP 2007-265734 A

  An object of the present invention is to obtain an electrode layer having a structure in which a substantial surface area involved in a catalytic reaction is large as an electrode layer for a fuel cell and in which a fuel and an oxidant can easily enter and diffuse, and to apply ultrasonic waves It is to obtain a method that can be formed by a spray device.

To solve this problem,
The invention according to claim 1 is a method of forming an electrode layer for a fuel cell by applying a catalyst ink containing catalyst-carrying particles, an ion conductive polymer and a solvent to a target made of a polymer film or a diffusion film by an ultrasonic spray device. Because
A method for producing an electrode layer for a fuel cell, wherein the ink particles are dried such that the ink particles sprayed from an ultrasonic spray device adhere to the target surface in a substantially or completely dried state.

  The invention according to claim 2 adjusts the distance between the ultrasonic spray device and the target so that the ink particles sprayed from the ultrasonic spray device adhere to the target surface in a substantially or completely dried state. 2. The method for producing a fuel cell electrode layer according to claim 1, wherein the ink particles are dried.

  The invention according to claim 3 heats the space between the ultrasonic spray device and the target so that the ink particles sprayed from the ultrasonic spray device adhere to the target surface in a substantially or completely dried state. 2. The method for producing a fuel cell electrode layer according to claim 1, wherein the ink particles are dried.

  According to a fourth aspect of the present invention, there is provided a fuel cell electrode layer according to the first aspect, in which an anti-scattering body for preventing ink particles from scattering is provided between the ultrasonic spray device and the target for spraying. It is a manufacturing method.

  A fifth aspect of the present invention is a fuel cell electrode layer manufactured by the manufacturing method according to any one of the first to fourth aspects.

The invention according to claim 6 is an electrode layer for a fuel cell manufactured by the manufacturing method according to any one of claims 1 to 4,
An electrode layer for a fuel cell comprising a porous aggregate formed by aggregating a large number of porous secondary catalyst particles composed of a large number of catalyst primary particles composed of catalyst-carrying particles and an ion conductive polymer. .

  The invention according to claim 7 is the electrode layer for a fuel cell according to claim 5 or 6, wherein the shape of the catalyst secondary particles is spherical.

  The invention according to claim 8 is a fuel cell comprising the electrode layer for fuel cell according to any one of claims 5 to 7.

According to the present invention, the electrode layer is formed by aggregating a large number of catalyst secondary particles in an independent form and has a large number of voids inside, and the catalyst secondary particles themselves are also numerous inside. Therefore, it is possible to obtain an electrode layer having a structure in which the substantial surface area involved in the catalytic reaction is large and the fuel and the oxidant can easily enter and diffuse.
For this reason, the fuel cell provided with this electrode layer has high performance.

FIG. 1 schematically shows an example of an electrode layer obtained by the method for producing an electrode layer of the present invention.
In FIG. 1, the code | symbol 21 shows the diffusion layer which consists of carbon paper etc., and the code | symbol 22 shows the electrode layer formed in this diffusion layer 21 surface. The electrode layer 22 is an anode electrode layer or a cathode electrode layer of the membrane electrode assembly.

  The electrode layer 22 is in the form of a film having a thickness of about 10 to 20 μm, and is composed of an aggregate of innumerable catalyst secondary particles 23, 23. The catalyst secondary particles 23 are aggregated in a state close to point contact with each other, and there are an infinite number of minute spaces between the catalyst secondary particles 23, 23... It is highly porous. The catalyst secondary particles 23 are bonded to each other by an ion conductive polymer.

The catalyst secondary particles 23 are spherical or indeterminate particles having a particle diameter of about 1 to 30 μm, the surface has innumerable irregularities, and innumerable cavities communicating with the internal space are opened. The catalyst secondary particles 23 themselves are also porous.
One catalyst secondary particle 23 is composed of an aggregate in which an infinite number of catalyst primary particles are aggregated.

The primary catalyst particles are particles having a particle size of 10 to 100 nm, and are composed of catalyst-supporting particles and a resin film made of an ion conductive polymer such as an ionomer that covers the surface thinly.
The catalyst-carrying particles are particles in which catalyst metal fine particles such as platinum, palladium and iridium having a diameter of 1 to 5 nm are attached and supported on the surface of a carrier made of conductive fine particles such as carbon powder having a diameter of 10 to 80 nm.

  In the electrode layer 22 having such a structure, since the electrode layer 22 is porous and there is a space between the individual catalyst secondary particles 23, 23..., And the catalyst secondary particles 23 are also porous, The substantial surface area involved in the reaction of the entire layer becomes extremely large, and many of the catalyst-carrying particles face the space, so that the catalytic function is maximized and the catalytic reaction with the fuel or oxidant is performed. Proceed efficiently.

In addition, the fuel and the oxidant easily enter and diffuse into this space, and the water generated by the electrode reaction can be easily removed.
Furthermore, moisture permeates through the space to the polymer electrolyte membrane, the wettability of the polymer electrolyte membrane is maintained, and the hydrogen ion conductivity is improved.

Next, a method for manufacturing the electrode layer 22 will be described.
FIG. 2 shows an example of a method for producing the electrode layer 22 of the present invention.
In FIG. 2, the code | symbol 31 shows an ultrasonic spray apparatus and the code | symbol 32 shows a target. The target 32 is a diffusion layer or a polymer electrolyte membrane.

  The ultrasonic spray device 31 is a device that applies ultrasonic vibration of about 20 to 100 kHz from an ultrasonic oscillator to a catalyst ink having a composition described later to make the catalyst ink a mist of fine particles. For example, a commercially available apparatus for painting can be used. The ultrasonic output of the ultrasonic spray device 31 is about 3 to 10 W, but is not limited to this range.

  As the catalyst ink, for example, noble metal fine particles such as platinum, palladium and iridium having a particle diameter of about 1 to 5 nm are supported on a carrier made of conductive particles such as carbon black having a primary particle diameter of 20 to 50 nm by about 30 to 60% by weight. The catalyst-carrying particles are dispersed in a solvent composed of an organic solvent such as isopropanol and water, and then a Nafion (trade name) solution, which is an ion conductive polymer, is used. 10% by weight mixed. The drying speed of the catalyst ink can be adjusted by changing the composition and content of the solvent.

The mist sprayed from the nozzle 31 </ b> A of the ultrasonic spray device 31 falls toward the target 32 disposed below the ultrasonic spray device 31 while floating in the air and adheres to the target 32. As a result, the electrode layer 22 is formed.
The particles constituting the mist are droplets that become the catalyst secondary particles 23 and are in a liquid state containing a solvent immediately after spraying, so that the shape becomes spherical due to surface tension.

  When the mist adheres to the surface of the target 32, the solvent volatilizes from the individual droplets constituting the mist, and the surface of the fine particles serving as the catalyst secondary particles 23 is in a dry state. is necessary. That is, the solvent gradually volatilizes from the spherical droplets, and while adhering to the target 32 while maintaining the spherical shape in a state where drying progresses, the catalyst secondary particles 23 are formed when adhering to the target 32. Thus, the catalyst secondary particles 23 are not fused together to become one particle.

Here, the substantially dry state means a state in which the surface of the droplet particles is dried and the inside is not dried, and the catalyst secondary particles are connected as particles. When the dry state is weak, an electrode layer having a structure in which umeboshi-shaped secondary catalyst particles 23 in which pleats are formed is connected instead of being spherical.
The electrode layer having this structure is also included in the technical scope of the present invention. In the electrode layer having this structure, the substantial surface area is larger than that in which the catalyst secondary particles are spherical, but the gas diffusivity is slightly reduced.

In the first method for satisfying this requirement, the distance D between the ultrasonic spray device 31 and the target 32 is appropriately adjusted, and the solvent is volatilized spontaneously from fine particles in the air. There is a method of attaching.
The appropriate distance depends on various operating conditions, such as ambient temperature, humidity, ultrasonic output, ultrasonic frequency, type of solvent in the catalyst ink, content, etc. A proper distance D is determined.
Usually, the suitable distance D is preferably in the range of about 50 to 70 cm, but is not limited thereto.

  In the second method, as shown in FIG. 3, a heat source 33 such as an infrared lamp is provided on the side between the ultrasonic spray device 31 and the target 32, and the mist is dropping the heat from the heat source 33. In other words, the solvent is volatilized from the fine particles of the catalyst ink to adhere to the target 32 in a state where the solvent is completely volatilized.

In this method, since the solvent is volatilized from the fine particles quickly, the distance D between the ultrasonic spray device 31 and the target 32 can be shortened.
The amount of heat from the heat source 33 depends on various operating conditions in the same manner as described above, and is determined by conducting a preliminary experiment.
In addition, when hot air is applied, the mist is scattered, which is not preferable.

  Further, since the mist sprayed from the ultrasonic spray device 31 descends toward the target 32 while floating in the air, a part of the mist flows to the outside due to the flow of air in the room, etc. Some do not adhere to 32. In this case, as a matter of course, catalyst ink containing an expensive platinum catalyst or the like is wasted.

In order to prevent the mist from scattering, a hood-like scattering prevention body 34 as shown in FIG. 4 can be disposed between the ultrasonic spray device 31 and the target 32. The scattering prevention body 34 may have a shape such as a conical cylinder.
By using this scattering prevention body 34, scattering and dissipation of the mist-like material are avoided, and the waste of the catalyst ink is eliminated.
In addition, the airflow generated in the scattering prevention body 34 increases the mist-like floating time, sufficiently volatilizes the solvent, and makes it easy to obtain the spherical catalyst secondary particles 23.

Further, if the scattering prevention body 34 is made of a transparent material such as a glass plate or an acrylic resin plate, the internal situation can be visually confirmed, and heat from the heat source 33 such as an infrared lamp arranged outside can be introduced into the inside. it can.
Furthermore, as shown in FIG. 5, a heater 35 such as a nichrome wire can be wound around the scattering prevention body 34 to heat the internal space of the scattering prevention body 34.

  Further, when the target 32 has a large area, it is desirable to spray by arranging a plurality of ultrasonic spray devices 31 provided with the scattering prevention body 34 according to the size, shape, etc. of the target 32.

In the above manufacturing method, when the catalyst secondary particles 23, 23... Adhering to the surface of the target 32 are attached in a completely dry state, the adhesive force with the surface of the target 32 becomes insufficient, and in the subsequent process There is a risk of falling off the target 32.
For this reason, in the final stage of application, the distance D between the ultrasonic spray device 31 and the target 32 is reduced or heating is stopped so that undried fine particles adhere to the uppermost layer. The secondary catalyst particles 23, 23,... Are bonded to each other by the ion-conductive polymer in a dissolved state on the surface, and the fixing force to the target 32 is increased.
According to such an electrode layer manufacturing method, an electrode layer having a structure as shown in FIG. 1 can be obtained.

In JP-A No. 2001-185163, JP-A No. 2007-149503, JP-A No. 2007-323824, and JP-A No. 2008-27799, a catalyst ink is dried and granulated by a spray drying method. A technique is disclosed in which particles are adhered to a target surface by electrostatic force or the like, and then heated and pressurized to fix the particles to the target.
However, with this technique, the particles themselves are unlikely to be spherical, and since they are heated and pressurized for fixation to the target, the particles are deformed and the gaps between the particles are reduced, and the book shown in FIG. The electrode layer of the invention exhibits a different form (morphology).

The fuel cell of the present invention is provided with the electrode layer 22 produced by the manufacturing method as described above. That is, a cell in which a membrane electrode assembly (MEA) is formed by forming an electrode layer on the diffusion layer or polymer electrolyte membrane by the above-described manufacturing method, and this membrane electrode assembly and a plate-like spacer are combined through a gasket. It is a polymer electrolyte type fuel cell having
This fuel cell has high performance as described above.

Specific examples are shown below.
(Preparation of catalyst ink)
Catalyst-supported particles (TEC10V50TPM (manufactured by Tanaka Kikinzoku)) in which 50% by weight of platinum particles having an average particle diameter of 3 nm were supported on carbon black (Vulcan X72 (manufactured by Cabot)) having an average primary particle diameter of 30 nm were used. The catalyst-supported particles are dispersed in a solvent of isopropanol and water (4: 1 by weight), and then 5% by weight of a polymer electrolyte Nafion solution (manufactured by DuPont, trade name) is mixed. Produced.

(Conventional example)
Using the catalyst ink, the carbon paper serving as the diffusion layer was applied by a conventional air spray device.
FIG. 6 shows a scanning electron micrograph of the coated surface. From FIG. 6, it can be seen that the ink particles are fused to form a flat coating film, and a number of cracks are generated.

(Comparative example)
Using the catalyst ink, coating was performed by an ultrasonic spray device on carbon paper to be a diffusion layer. As the ultrasonic spray device, Ultrasonic atomizer US2 manufactured by LECHLER was used, the ultrasonic frequency was 58 kHz, the output was 8 W, and the distance between the nozzle and the carbon paper was 30 mm. The ambient temperature is 27 ° C.
FIG. 7 shows a scanning electron micrograph of the coated surface. As shown in FIG. 7, the catalyst secondary particles are fused with each other to form a highly uneven surface. This is because the distance is short, and the solvent of the catalyst ink remains in the form of carbon paper, which is then dried.

(Example 1)
Using the catalyst ink, coating was performed by an ultrasonic spray device on carbon paper to be a diffusion layer. As the ultrasonic spray device, Ultrasonic atomizer US2 manufactured by LECHLER was used, the ultrasonic frequency was 58 kHz, the output was 8 W, and the distance between the nozzle and the carbon paper was 500 mm. The ambient temperature is 27 ° C.
FIG. 8 shows a scanning electron micrograph of the coated surface. FIG. 8 clearly shows that the catalyst secondary particles dried in the air are individually deposited.
FIG. 9 is an enlarged view of the photograph in FIG. FIG. 10 is a scanning electron micrograph of the cut surface obtained by cutting the coated surface. 9 and 10 that spherical catalyst secondary particles are clearly present.

(Example 2)
Using the catalyst ink, coating was performed by an ultrasonic spray device on carbon paper to be a diffusion layer. For the ultrasonic spray device, Ultrasonic atomizer US2 manufactured by LECHLER was used, the ultrasonic frequency was 58 kHz, the output was 8 W, and the distance between the nozzle and the carbon paper was 50 mm. The ambient temperature is 27 ° C.
FIG. 11 shows a scanning electron micrograph of the coated surface. From FIG. 11, the catalyst secondary particles are in a semi-dried state, and are attached to the carbon paper, the solvent is dried, and particles having wrinkles formed on the surface are deposited.

The graph of FIG. 12 compares the performance of the cell constructed using the electrode layer of Example 1 and the conventional example, and the test conditions are fuel: hydrogen, oxidant: air, temperature 80 ° C., humidification 122 %, Catalyst amount: platinum 1 mg / cm ² , cell area 25 cm ^{2.
From this graph, it can be seen that good performance can be obtained in the cell using the electrode layer of the present invention.}

It is the schematic sectional drawing which showed an example of the electrode layer of this invention typically. It is a schematic block diagram which shows the 1st method of the manufacturing method of the electrode layer of this invention. It is a schematic block diagram which shows the 2nd method of the manufacturing method of the electrode layer of this invention. It is a schematic block diagram which shows the other example of the 2nd method of the manufacturing method of the electrode layer of this invention. It is a schematic block diagram which shows the other example of the 2nd method of the manufacturing method of the electrode layer of this invention. It is a scanning electron micrograph which shows the result of a prior art example. It is a scanning electron micrograph which shows the result of a comparative example. 2 is a scanning electron micrograph showing the results of Example 1. FIG. 2 is a scanning electron micrograph showing the results of Example 1. FIG. 2 is a scanning electron micrograph showing the results of Example 1. FIG. 2 is a scanning electron micrograph showing the results of Example 2. FIG. It is a graph which shows the performance of the cell using the electrode layer of Example 1 and a comparative example. It is a schematic block diagram which shows the example of the membrane electrode assembly in the polymer electrolyte fuel cell concerning this invention.

Explanation of symbols

21 .... Diffusion layer, 22 .... Electrode layer, 23 ... Catalyst-supported particles, 31 ... Ultrasonic spray device, 32 ... Target, 33 ... Heat source, 34 ... Spattering prevention body, 35 ... Heater

Claims (8)

A method of forming an electrode layer for a fuel cell by applying a catalyst ink containing catalyst-carrying particles, an ion conductive polymer, and a solvent to a target composed of a polymer film or a diffusion layer using an ultrasonic spray device,
A method for producing an electrode layer for a fuel cell, wherein the ink particles sprayed from an ultrasonic spray device are dried so that the ink particles adhere to the target surface in a substantially or completely dried state.   The distance between the ultrasonic spray device and the target is adjusted, and the ink particles sprayed from the ultrasonic spray device are dried so that the ink particles adhere to the target surface in a substantially or completely dried state. The method for producing an electrode layer for a fuel cell according to claim 1.   The space between the ultrasonic spray device and the target is heated to dry the ink particles so that the ink particles sprayed from the ultrasonic spray device adhere to the target surface in a substantially or completely dried state. The method for producing an electrode layer for a fuel cell according to claim 1.   The method for producing an electrode layer for a fuel cell according to claim 1, wherein a spraying prevention body for preventing scattering of ink particles is provided between the ultrasonic spray device and the target for spraying.   The electrode layer for fuel cells manufactured with the manufacturing method in any one of Claims 1 thru | or 4. A fuel cell electrode layer manufactured by the manufacturing method according to claim 1,
An electrode layer for a fuel cell comprising a porous aggregate formed by further collecting a large number of porous catalyst secondary particles formed by aggregating a large number of catalyst primary particles composed of catalyst-carrying particles and an ion conductive polymer.   The electrode layer for a fuel cell according to claim 5 or 6, wherein the shape of the catalyst secondary particles is spherical.   A fuel cell comprising the fuel cell electrode layer according to claim 5.

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