JP2010061917A - Method for manufacturing catalytic electrode of fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To fix a catalytic electrode layer on an electrolyte membrane in a short time without giving a thermal and physical damage on the catalytic electrode layer and the electrolyte membrane at the manufacturing of the catalytic electrode of a solid polymer fuel cell. <P>SOLUTION: In the method for manufacturing the catalytic electrode 3 of a polymer electrolyte fuel cell, a catalytic electrode powder 2 containing catalyst carrying conductive particles and a binder is prepared and the catalytic electrode powder 2 is coated on the electrolyte membrane 1 by a xerography method, and by light energy emitted from a flash lamp 10, the binder is melted on the electrolyte membrane 1 in a very short time, and the catalytic electrode powder 2 coated on the electrolyte membrane 1 is fixed to the electrolyte membrane 1. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing a catalyst electrode (referred to as a “catalyst electrode layer” as appropriate) of a fuel cell. More specifically, the present invention relates to a production method for forming a catalyst electrode layer on an electrolyte membrane in producing a polymer electrolyte fuel cell (PEFC).

In recent years, polymer electrolyte fuel cells have been widely used as electric power for automobiles, homes, mobile phones and the like.
This polymer electrolyte fuel cell generally includes a membrane electrode assembly (MEA) comprising an electrolyte membrane and two catalyst electrode layers that carry the electrolyte membrane from both sides, and two diffusion layers that carry the MEA from both sides. have.

By the way, there is a prior art method for forming a MEA by supporting a catalyst electrode layer on an electrolyte membrane during the production of the polymer electrolyte fuel cell.
It is a method disclosed in Patent Documents 1 and 2, in which a powder containing catalyst-supporting carbon particles is transferred to an electrolyte membrane as a catalyst electrode layer by an electrostatic copying method, and then the transferred catalyst The electrode layer is heated and pressed with a heat roll (that is, hot pressing) to form a catalyst electrode layer on the electrolyte membrane (hereinafter, this method is referred to as “heat roll method”).

However, in this heat roll method, heating and pressurization for a certain time is inevitable, and the following problems occur.
First, according to the same method, the heating time is relatively long as 4 minutes and 5 minutes, so that the electrolyte resin in the electrolyte membrane and the catalyst electrode layer is deteriorated by heating and pressurization during this time, or the electrolyte membrane Wrinkles and kinks are generated, the ability of hydrogen ions (protons) to pass through is reduced, and the power generation performance and durability of the fuel cell are reduced.
Second, according to the same method, the heating temperature is set to, for example, about 140 ° C. to about 160 ° C., and is directly applied as heat to the electrolyte membrane and the catalyst electrode layer, not as radiant heat. The heating temperature combined with the heating time deteriorates the electrolyte resin in the electrolyte membrane and the catalyst electrode layer.
Thirdly, according to the same method, pressurization is performed at a relatively high value, for example, 30 kgf / cm ² . Under such a pressure, the catalyst-carrying conductive particles (for example, platinum-carrying carbon particles) strongly contact the electrolyte membrane, so that the particles damage the electrolyte membrane and cause mechanical damage. Therefore, the adhesiveness (bonding property) between the catalyst electrode layer and the electrolyte membrane is lowered, unnecessary electric resistance is generated, and the voltage is lowered.

As described above, as long as the heat roll method is employed, the first, second, and third problems occur, but it is determined that it is difficult to solve these problems for the following reason.
For the first problem, since the catalyst electrode layer is heated by heat conduction, it takes a long time for heat to be conducted from the heat roll to the catalyst electrode layer or the electrolyte membrane.
The second problem is that when the catalyst electrode layer is fixed to the electrolyte membrane, the temperature is as close as possible to the softening temperature of the electrolyte membrane (for example, DuPont Nafion (product name) is used as the electrolyte membrane). Must be 140 to 160 ° C.).
For the third problem, since the electrolyte resin in the electrolyte membrane and the catalyst electrode layer is in a solid state (solid) at the start of pressurization and heating by a heat roll, the adhesion between the electrolyte membrane and the catalyst electrode layer (bonding) Is difficult. Therefore, for example, it is necessary to improve the adhesion stability at the adhesion boundary between the two. In that case, since the protrusion-like adhesion | attachment which improved mechanical adhesiveness is requested | required, the pressure value of the said pressurization must be made high.
JP-A-8-329962 JP 2004-281221 A

Therefore, in view of the above problems, the present invention adopts an electrostatic copying method when transferring the catalyst electrode layer to the electrolyte membrane, and thereafter, the catalyst membrane is not damaged by the electrolyte membrane. It aims at providing the manufacturing method of the catalyst electrode layer (catalyst electrode) of a fuel cell.
Various aspects of the method of manufacturing a fuel cell according to the present invention, and their operations and effects will be described in detail in the section of the aspect of the invention below.

(Aspect of the Invention)
Hereinafter, embodiments of the invention will be shown and described. Each of the items (1), (2), and (3) corresponds to each of claims 1, 2, and 3.

(1) A method for producing a catalyst electrode for a polymer electrolyte fuel cell, comprising: a powder production step for producing a powder for a catalyst electrode containing catalyst-supporting carbon particles and a binder; An electrostatic copying process in which the powder is applied to the electrolyte membrane by an electrostatic copying method, and the binder electrode is melted by the light energy of a flash lamp, and the powder for the catalyst electrode applied to the electrolyte membrane is And a light fixing step for fixing the electrolyte film.

  According to the aspect of this section, the light fixing for fixing the powder for the catalyst electrode applied to the electrolyte membrane to the electrolyte membrane by the light energy emitted from the flash lamp is directly contacted as in the heat roll method. It is non-contact and non-pressurized, and therefore there is no pressurization to the catalyst electrode layer or the electrolyte membrane, so there is virtually no mechanical damage due to the catalyst electrode particles coming into contact with the electrolyte membrane. .

Further, according to the aspect of this section, the binder can be melted on the electrolyte membrane by the light energy emitted from the flash lamp. Further, since the light absorption rate of the electrolyte membrane is as low as about 35%, the heat effect on the electrolyte membrane due to the light energy is remarkably reduced as compared with the heat roll method.
Further, according to the aspect of this section, the catalyst electrode layer and the electrolyte are obtained by melting a binder having a sharp particle size distribution in a range of about 5 μm to 13 μm by light energy emitted from a flash lamp that is instantaneously emitted. Bond the membrane. As a result, since the binder is fine powder, the heat capacity is small, so that light energy is easily transferred to each particle of fine powder. In addition, since the particle size of the fine powder is uniform to some extent, if the binder is irradiated with light energy uniformly, the particles of the fine powder are also melted uniformly. With such a feature, for example, since the heat treatment of the binder electrolyte membrane is completed in a very short time of 1 millisecond or less, according to the aspect of this section, the deterioration of the electrolyte membrane is caused by the catalyst electrode layer. Compared to the heat roll method in which the heating time of 4 to 5 minutes is long, the time is significantly reduced.
Further, according to the aspect of this section, the heating temperature of the catalyst electrode layer by light emitted from the flash lamp instantaneously reaches about 500 ° C., but is instantaneous (for example, about 0.3 milliseconds). Yes, the heating temperature immediately becomes a low temperature of 100 ° C. or lower. For this reason, damage to the electrolyte membrane due to heating is remarkably reduced as compared with the heat roll method.

  Furthermore, if the binder is made of a solution that does not contain an organic solvent and is mainly made of a fluororesin such as PTFE, the fluororesin is emitted from a flash lamp because of its flame retardancy compared to an organic solvent. In order to prevent burning with light energy, it is not necessary to make the surrounding atmosphere inactive or vacuum atmosphere (non-flammable atmosphere) as shown in Patent Document 1, and the equipment cost is not so much.

(2) The manufacturing method according to (1), wherein, in the powder production step, the powder for the catalyst electrode further includes a pore forming agent, and the porous catalyst is formed using the pore forming agent. A method for producing a powder for an electrode.
According to this section, in the photofixing step of (1), the catalyst electrode layer is already impregnated with a certain amount of the electrolyte resin from the electrolyte membrane, and further, for example, a structure containing an alkali salt such as calcium carbonate. From the beginning, the pore agent is added to the powder for the catalyst electrode. Then, for example, a solution containing an acid such as nitric acid is reacted with calcium carbonate, the reaction product is removed, and many pores are formed. This porous portion functions effectively at the time of impregnation with the electrolyte resin solution in the following (3) (see below).

(3) The manufacturing method according to (2), wherein after the electrostatic copying step and the photofixing step, the porous catalyst electrode powder fixed on the electrolyte membrane by the photofixing step The manufacturing method characterized by including the electrolyte solution application | coating process which impregnates an electrolyte resin solution.
According to this section, since the electrolyte resin solution can be impregnated so as to be poured into many pores of the catalyst electrode powder produced in the section (2), the electrolyte resin and electrolyte contained in the catalyst electrode layer The membrane can be suitably bonded, and hydrogen ions can be moved more smoothly from the anode side of the electrolyte membrane to the other cathode side, while the three-phase reaction between the reaction gas, the electrolyte, and the catalyst electrode is preferably performed. Can be done.

  As described above, the process of photofixing the catalyst electrode layer on the electrolyte membrane with a flash lamp is a non-contact and substantially low-temperature heating method using instantaneous light. Therefore, as a whole, the thermal and mechanical damage of the electrolyte membrane is remarkably reduced as compared with the conventional heat roll method, and as a result, the durability of the electrode of the fuel cell is improved. Further, the light fixing is instantaneous and is a very short processing time, so that productivity is improved.

  According to the present invention, the catalyst electrode layer can be fixed to the electrolyte membrane in a short time without thermally and physically damaging the catalyst electrode layer and the electrolyte membrane, thereby improving the durability of the fuel cell. Can be made. Further, according to the present invention, the electrolyte component can be sufficiently spread over the entire region from the electrolyte membrane to the catalyst electrode layer, and the power generation performance of the fuel cell can be improved.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a diagram for illustrating a mode for carrying out a method of manufacturing a fuel cell according to the present invention. In the figure, the same reference numerals denote the same components, and the basic configuration is the same as the conventional one shown in the figure. The manufacturing method is not limited to the following embodiment, and it is needless to say that various modifications can be made without departing from the gist of the present invention.

FIG. 1 is a conceptual diagram for explaining a method for producing a catalyst electrode (catalyst electrode layer) of a polymer electrolyte fuel cell according to an embodiment of the present invention.
The manufacturing method will be described separately for the first embodiment and the second embodiment with reference to FIG.

First Embodiment : In the first embodiment, a powder production process for producing a powder for a catalyst electrode containing catalyst-carrying carbon particles and a binder, and an electrostatic copying method for producing the powder for the catalyst electrode An electrostatic copying process for applying to the electrolyte film by the above method, and a photofixing process for melting the binder by a flash lamp and fixing the powder for the catalyst electrode applied to the electrolyte film to the electrolyte film. It is a process.

Powder preparation step (not shown); The powder for the catalyst electrode is produced by a kneading and pulverizing method. This kneading and pulverizing method is composed of a process of measuring, mixing, kneading, pulverizing, classifying and sieving the material, and controls the fixing state of the powder material for the catalyst electrode to the electrolyte membrane and constitutes the powder. The basic characteristics of the size and shape of the particles are controlled, and the purpose is to make the quality of the coated surface of the powder on the electrolyte membrane constant by classification and sieving.
The composition of the powder material for the catalyst electrode is composed of a binder such as PTFE, PFA, FEP, and ETFE, which is melted by light energy from the flash lamp and fixed to the electrolyte membrane, platinum-supported carbon, nickel-supported carbon, And a catalyst-supporting conductive material (catalyst-supporting conductive powder) such as nickel-ruthenium-supported carbon.

  First, these materials are weighed according to a predetermined recipe and mixed with a mixer such as a Henschel mixer. The roughly mixed material is further kneaded in a kneader while being heated and melted at 330 ° C. to 350 ° C., and each composition is sufficiently micro-dispersed. The kneaded catalyst-carrying conductive material is cooled, coarsely pulverized while being cooled, and then finely pulverized from 5 μm to 13 μm by a dry jet mill. In order to sharpen the particle size distribution of the finely pulverized catalyst-supporting conductive powder, fine powder and coarse powder located at the bottom of the particle size distribution are removed by a centrifugal force classifier such as a cyclone. In this way, the catalyst-carrying conductive powder 2 is produced by the powder production process according to the first embodiment.

An electrostatic copying process (FIG. 1 (1)): As shown in (1) in FIG. 1, the catalyst carrying conductive powder 2 prepared by the above powder manufacturing process, so as to surround the periphery of the developing roller 6 Then, it is stored in the storage cartridge 15. Then, the storage cartridge 15 is arranged so that the vertical portion 16 of the storage cartridge 15 is along the tangent line of the photosensitive drum 5.
Further, a charging electrode (not shown) is provided in the catalyst-carrying conductive powder 2 of the storage cartridge 15. The charging electrode is connected to a power source (not shown), and negatively charges the catalyst-carrying conductive powder 2 by the charge supplied from the power source. Then, the negatively charged catalyst-carrying conductive powder 2 physically adheres to the developing roller 6 and is sent to the surface of the photosensitive drum 5 by the rotation of the developing roller 6.

At this time, the photosensitive drum 5 is positively charged by the electrostatic roller 7. However, the portions exposed to the exposure unit 14 of the photosensitive drum 5 are neutralized. Accordingly, the negatively charged catalyst-carrying conductive powder 2 transported to the photosensitive drum 5 adheres to the photosensitive drum 5 with an electrostatic force at a portion where the charge is not removed. The catalyst-carrying conductive powder 2 attached to the photosensitive drum 5 is printed on the electrolyte membrane 1 side by the rotation of the photosensitive drum 5. Here, exposure may be performed by the exposure unit 14 using an appropriate mask according to the shape of the pattern on which the catalyst-carrying conductive powder 2 is to be printed on the surface of the electrolyte membrane 1 (the shape of the electrolyte membrane of the single cell 3). .
This process is intermittently performed every 3 unit cell portions, and after the exposure and printing of the unit cell portion 3 is finished, the tape-shaped electrolyte membrane 1 is moved in the direction of arrow A (upstream direction) with respect to the unit cell portion 3. Proceed to the next light fixing step.

Photofixing step (FIG. 1 (2)) : In the photofixing step sent from the electrostatic copying step, the catalyst-carrying conductive powder 2 on the electrolyte membrane 1 is emitted from a flash lamp 10 which is a heating fixing unit. The catalyst film (catalyst electrode layer) 3 is formed by heating and fixing to the electrolyte membrane 1 with light (in FIG. 1, only three powder particles are drawn for the sake of illustration only).
More specifically, when the catalyst-carrying conductive powder 2 is photofixed on the electrolyte membrane 1, the binder contained in the powder 2 is emitted from the flash lamp 10 (light energy). By heating at a high temperature of about 500 ° C. in a short time of about 0.3 milliseconds, the binder is melted, and the catalyst-carrying conductive powder 2 is bound to the electrolyte membrane 1, A catalyst electrode (catalyst electrode layer) 3 is formed. The melting point of the binder needs to be lower than about 500 ° C. Here, a material having a melting point of about 327 ° C., such as PTFE, is preferably used for the binder.

The conditions (capabilities) of the flash lamp 10 at this time are shown in Table 1. In addition, you may make it the said flash lamp 10 arrange | position to the focus of the reflector of the reference number 9 of FIG. By adding the back light of the parallel light of the lash lamp reflected by the inner wall (reflector) of the reflector to the front light of the flash lamp and irradiating the powder for the catalyst electrode electrostatically copied on the electrolyte membrane 1, Light can be emitted toward the powder efficiently.

Second Embodiment : The second embodiment is a powder production step of producing a powder for a catalyst electrode containing catalyst-carrying carbon particles and a binder, and a pore forming agent is further included in the powder. It is removed by pickling and rinsing, and the porous part is formed into a powder for the catalyst electrode. Immediately after the photofixing process, an electrolyte solution coating step is added, and the electrolyte solution is poured into the porous part. Further, the catalyst electrode layer already photofixed on the electrolyte membrane is further impregnated in the electrolyte solution spot. This point is different from the first embodiment. The second embodiment will be described below with a focus on differences from the first embodiment.

これらの材料に対して、第１実施形態と同様な処理を行った後、触媒担持導電性材料中の造孔剤の炭酸カルシウムを、硝酸で洗浄後、水で洗浄し、乾燥し、除去する。これにより、除去された炭酸カルシウムに代わり、触媒担持導電性材料中に、多数の孔が造られる。これら孔を含む触媒担持導電性材料に、表２の追加する電解質樹脂のナフィオン（５％溶液）が含浸されるため、表２で、炭酸カルシウムとナフィオン（５％溶液）が同じ重量割合（２２ｗｔ％）となっている。
なお、造孔剤は、炭酸カルシウムに限られず、アルカリ塩、各種アルカリ微粉末等のアルカリ塩でもよい。この際は、それぞれについて適切な酸を用いるようにする。また、造孔剤としてＰＶＡを用いた場合には、水溶性なので水で溶解・除去が可能である。
（２）静電複写工程及び光定着工程（図１の（１））；実施例１と同様のためこの説明を省略する。 (1) Powder preparation step (not shown); Table 2 shows examples of starting materials for preparing the catalyst electrode powder of the second embodiment.

After these materials are treated in the same way as in the first embodiment, the pore-forming calcium carbonate in the catalyst-carrying conductive material is washed with nitric acid, then with water, dried and removed. . Thereby, instead of the removed calcium carbonate, a large number of pores are formed in the catalyst-carrying conductive material. Since the catalyst-supporting conductive material containing these pores is impregnated with Nafion (5% solution) of the electrolyte resin added in Table 2, in Table 2, calcium carbonate and Nafion (5% solution) have the same weight ratio (22 wt. %).
The pore-forming agent is not limited to calcium carbonate, and may be an alkali salt or an alkali salt such as various alkali fine powders. In this case, an appropriate acid is used for each. Further, when PVA is used as a pore-forming agent, it can be dissolved and removed with water because it is water-soluble.
(2) Electrostatic copying process and light fixing process ((1) in FIG. 1) ;

(3) Electrolyte solution application step ((3) in FIG. 1); The catalyst electrode material bound in the photofixing step is applied and impregnated with the electrolyte resin solution. In this step, the electrolyte solution to be prepared is a 5% solution of DuPont's Nafion (trade name). When the pore-forming agent “calcium carbonate” shown in Table 2 is removed by washing with nitric acid and water, a large number of pores are formed. The electrolyte solution is impregnated from the electrolyte solution application means 12 so as to spread over the entire catalyst electrode layer while being poured into the numerous holes. Thus, a catalyst electrode (catalyst electrode layer) is formed.
The catalyst electrode of the second embodiment is impregnated with the electrolyte resin solution so as to flow into many pores of the powder for the catalyst electrode as compared with that of the first embodiment. Can be included more. In addition to the fact that the electrolyte resin and the electrolyte membrane contained in the catalyst electrode layer are suitably joined, and hydrogen ions (protons) can be more preferably smoothly moved from the anode side to the other cathode side of the electrolyte membrane. Further preferably, a three-phase reaction of the reaction gas, the electrolyte, and the catalyst electrode can be performed.

  The manufacturing method of the catalyst electrode of the polymer electrolyte fuel cell (PEFC) according to the present invention is not limited to the aspect described in the above-described embodiment, and various modifications may be adopted by those skilled in the art. For example, the present invention can be applied to a method for manufacturing a catalyst electrode of a direct methanol fuel cell (DMFC).

  The present invention can be utilized when manufacturing a catalyst electrode of a fuel cell.

It is a conceptual diagram (manufacturing flow) for demonstrating embodiment which concerns on this invention.

Explanation of symbols

1: electrolyte membrane, 2: powder for catalyst electrode, 3: catalyst electrode, 10: flash lamp

Claims (3)

A method for producing a catalyst electrode of a polymer electrolyte fuel cell, comprising:
A powder production process for producing a powder for a catalyst electrode containing catalyst-supporting carbon particles and a binder;
An electrostatic copying process in which the powder for the catalyst electrode is applied to the electrolyte membrane by an electrostatic copying method;
A photofixing step of melting the binder by light energy of a flash lamp and fixing the powder for the catalyst electrode applied to the electrolyte membrane to the electrolyte membrane;
The manufacturing method characterized by including. It is a manufacturing method of Claim 1, Comprising: In the said powder preparation process,
The catalyst electrode powder further comprises a pore-forming agent, and a porous catalyst electrode powder is produced using the pore-forming agent. It is a manufacturing method of Claim 2, Comprising:
After the electrostatic copying step and the photofixing step, an electrolyte solution coating step of impregnating an electrolyte resin solution into the porous catalyst electrode powder fixed to the electrolyte film by the photofixing step is included. A featured manufacturing method.

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