JPH0613085A - Manufacture of electrode catalytic layer for fuel cell - Google Patents

Abstract

PURPOSE:To provide a method for manufacturing an electrode catalytic layer for fuel cell having a high cavity rate, a fine porous structure, and a high physical strength. CONSTITUTION:A method for manufacturing an electrode catalytic layer for fuel cell comprises the processes of mixing a catalyst fine particle suspension with a dispersion of fluorine resin, co-coagulating the catalyst fine particle and the fluorine resin in the mixture, kneading the coagulated body, and rolling the kneaded material. In this time, a low boiling point organic solvent having a boiling point lower than that of water and a high boiling point organic solvent having a boiling point higher than that of water are contained in the coagulated body.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing an electrode catalyst layer of a fuel cell. More specifically, it relates to a method for producing an electrode catalyst layer for a fuel cell, which has a fine porous structure, a high porosity, and a high physical strength.

[0002]

2. Description of the Related Art A fuel cell electrode catalyst layer is formed on the surface of an electrode such as a carbon electrode, and a fuel cell is constructed by providing a phosphoric acid electrolyte matrix layer between positive and negative electrodes provided with this catalyst layer. . The fuel cell electrode catalyst layer is
It consists of a fine porous structure in which an aggregate of catalyst fine particles in which noble metal fine particles such as platinum are supported on the surface of a catalyst carrier such as carbon black is held in a network of fibrillated fluororesin and is formed in the catalyst layer. At the three-phase interface of the liquid-gas phase, hydrogen gas, oxygen gas, and the electrolyte are chemically reacted by utilizing the catalytic action to extract electric energy.

Various methods have been conventionally proposed as a method for producing such an electrode catalyst layer for a fuel cell. For example, in Japanese Unexamined Patent Publication No. 63-48757, catalyst fine particles dispersed in water are mixed with a dispersion of fine fluororesin particles, and an organic solvent such as ethylene glycol is added to the mixture to add fine catalyst particles and fluororesin in the mixture. It is described that after co-aggregating and, the aggregate is kneaded, extruded and molded, and then rolled. According to this method, since an organic solvent having a high boiling point such as ethylene glycol is used, there is an advantage that the organic solvent is present during kneading and rolling, and fibrillation of the fluororesin is promoted, while rolling Since there is a large amount of high-boiling point organic solvent during the process, the plasticizing effect on the fluororesin is too strong, and the compaction of the catalyst layer progresses during rolling, which makes it difficult to obtain a catalyst layer with a high porosity. .

As another method for producing a fuel cell electrode catalyst layer, Japanese Patent Laid-Open No. 63-48756 discloses that catalyst fine particles dispersed in water are mixed with a dispersion of a fluororesin.
After adding a hydrophilic organic solvent such as acetone to the mixed solution to coaggregate the catalyst fine particles and the fluororesin in the mixture, the aggregate is filtered and once dried to remove the hydrophilic organic solvent. Describes a method of adding an organic solvent such as glycerin and ethylene glycol, kneading and rolling. In this method, an organic solvent having a high boiling point such as glycerin and ethylene glycol is used, and like the method described in JP-A-63-48757, a large amount of organic solvent is present during the rolling step. However, it is difficult to obtain a catalyst layer having a fine porous structure and a high porosity.

Yet another method for producing an electrode catalyst layer for a fuel cell is disclosed in JP-A-63-245864. In this method, the catalyst fine particles dispersed in water are mixed with a dispersion of a fluororesin, and then an organic solvent such as methyl alcohol, ethyl alcohol, isopropyl alcohol or ethylene glycol is added to the dispersion in two steps to form an organic solvent. It is intended to prevent the generation of bubbles when a solvent is added to the dispersion system and to realize the uniform dispersion of the catalyst fine particles and the fluororesin in the aggregate. In this method, an organic solvent such as methyl alcohol, ethyl alcohol, isopropyl alcohol, and ethylene glycol is used, but an organic solvent such as methyl alcohol, ethyl alcohol, and isopropyl alcohol has a low boiling point of 100 ° C. or lower. It is an organic solvent that has, and when only this is used, the vaporization of the organic solvent proceeds excessively in the rolling process, and the fluidity of the kneaded product necessary for rolling, that is, the plasticity of the fluororesin is rapidly increased. However, it is difficult to consolidate the sheet, and a high porosity can be maintained, but on the other hand, there is a drawback that the sheet cannot withstand the pressure during rolling and cracks or cracks occur. On the other hand, an organic solvent such as ethylene glycol has a high boiling point of 100 ° C. or higher, and when only this is used, a large amount of the organic solvent exists until the end of the rolling process, which is high as in the previous example. This has resulted in the difficulty of obtaining a catalyst layer having a porosity.

[0006]

The present invention has been made in view of the above circumstances, and has a high porosity, a fine porous structure, and a high physical strength, and is an electrode catalyst for a fuel cell. It is intended to provide a method for producing a layer.

[0007]

In order to achieve the above object, in the invention according to claim 1, "a step of mixing a catalyst fine particle suspension and a dispersion of a fluororesin, and a mixed solution" In the method for producing a fuel cell electrode catalyst layer comprising a step of coaggregating the catalyst fine particles and a fluororesin therein, a step of kneading the aggregate, and a step of rolling the kneaded material, in the aggregate, A low-boiling point organic solvent having a boiling point lower than that of water, and a high-boiling point organic solvent having a boiling point higher than that of water are included in the method for producing an electrode catalyst layer for a fuel cell. I made it a summary. According to the invention of claim 2, "a method for producing an electrode catalyst layer for a fuel cell, characterized in that the boiling point difference between the low boiling point organic solvent and the high boiling point organic solvent is at least 10 ° C or more" And The gist of the invention according to claim 3 is "a method for producing an electrode catalyst layer for a fuel cell, wherein the rolling temperature in the rolling step is 40 to 80 ° C".

The method for producing the fuel cell electrode catalyst layer of the present invention will be described in more detail below. The catalyst fine particles are obtained by supporting precious metal fine particles such as platinum on the surface of a catalyst carrier such as carbon black, and the catalyst fine particles are uniformly dispersed in water by using a dispersing means such as ultrasonic waves or a surfactant. A catalyst fine particle suspension is obtained. On the other hand, the dispersion of fluorine resin is polytetrafluoroethylene (PT
A fluororesin such as FE) is dispersed in water, and a dispersion medium can be used to enhance dispersibility, or a method such as ultrasonic dispersion can be used. After this, these are mixed uniformly. The amount of fluororesin is preferably 20 to 60% with respect to the weight of the catalyst layer. I mean,
When the amount of the fluororesin is less than 20%, it becomes difficult to keep the catalyst in a stable state, and the physical strength of the catalyst layer decreases. On the other hand, if it is more than 60%, the amount of catalyst fine particles that can be relatively retained becomes small, and a sufficient catalytic effect cannot be obtained.

Next, an aggregating agent is added to the above mixed solution to coaggregate the catalyst fine particles and the fluororesin. The aggregating agent may be any hydrophilic organic solvent. Next, the agglomerates are taken out from the liquid containing the agglomerates obtained in this step by a separation method such as filtration, and the agglomerates are kneaded and rolled.

The kneading is carried out by a kneading machine such as a kneading stirrer, a kneader, a Banbury mixer, a roll mixer, a screw mixer. The fluororesin has a property of becoming fibrillated into a fine fibrous substance having tackiness by applying a shearing force, and the fluororesin in the aggregate is fibrillated by the shearing force at the time of kneading. At the same time, this kneading forms a uniform mixture of the agglomerates of the fluororesin and the agglomerates of the catalyst fine particles.

Rolling is performed by a calender roll or a press. By this rolling, the fibrillation of the fluororesin in the kneaded material proceeds, and the fibrillated fibrous material is oriented, so that its physical strength can be increased. In order to further increase the physical strength, the rolling step may be repeated, especially when a calender roll is used,
The strength can be increased by changing the rolling direction.

In the above kneading step and rolling step, the fibrillation of the fluororesin can be promoted by adding an organic solvent as a fibrillation aid. In the method for producing a fuel cell electrode catalyst layer of the present invention, in the aggregate, a low boiling organic solvent having a boiling point lower than that of water, and a high boiling organic solvent having a boiling point higher than that of water. Is included. As a method of adding these low boiling point organic solvent and high boiling point organic solvent, in the step of kneading,
Since it suffices that the low-boiling organic solvent and the high-boiling organic solvent are contained in the kneaded product, for example, after mixing the catalyst fine particle suspension and the dispersion of the fluororesin, the low-boiling organic solvent or the high-boiling organic solvent is mixed. Is added to co-aggregate the catalyst fine particles with the fluororesin, and the aggregate is filtered, and then a high-boiling organic solvent or a low-boiling organic solvent is added to the filter cake. Further, as another method, after mixing the catalyst fine particle suspension and the dispersion of the fluororesin, a low-boiling organic solvent and a high-boiling organic solvent are added together, or a filter after co-coagulating and filtering is added. There is a method of adding a low boiling point organic solvent and a high boiling point organic solvent when kneading the slag. Incidentally, in the case of adding a low-boiling point organic solvent and / or a high-boiling point organic solvent after the step of mixing in the above method, in the step of kneading and rolling the low-boiling point organic solvent and / or the high-boiling point organic solvent later. In addition to the action of, it also acts as an aggregating agent and is useful.

Examples of the low boiling point organic solvent having a boiling point lower than that of water include aliphatic saturated alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol and propyl alcohol. Further, as the high boiling point organic solvent having a boiling point higher than that of water, ethylene glycol monoether such as ethylene glycol ethyl ether, butyl alcohol, isobutyl alcohol,
There are aliphatic saturated alcohols such as n-amyl alcohol and isoamyl alcohol, and ethylene glycol.

In the kneading step, the low boiling point organic solvent and the high boiling point organic solvent accelerate the fibrillation of the fluororesin. Further, in the rolling step, the heat of rolling causes the vaporization of the low boiling point organic solvent to progress, and the whole amount or most of it is vaporized in the initial stage of rolling, and the amount of the organic solvent in the kneaded product is correspondingly increased. Decrease. Along with this, fluidization of the fluororesin is also reduced, and consolidation is less likely to occur, and voids generated by vaporization of water or the low boiling point organic solvent are easily retained. On the other hand, the high-boiling organic solvent is hard to be vaporized by the heat at the time of rolling, and the whole amount or most of it is present until the end of rolling, which promotes the fibrillation of the fluororesin and increases the orientation, thereby improving the physical strength. Measured.

The ratio of the organic solvent including the high boiling organic solvent and the low boiling organic solvent to water is preferably 2: 1 to 1: 2 (volume ratio). When the ratio of water is higher than this ratio, the cohesive force becomes insufficient or fibrillation during kneading does not proceed sufficiently. On the contrary, if the ratio of the high-boiling organic solvent and the low-boiling organic solvent is high, fibrillation proceeds, but ignition is likely to occur during the rolling step or pre-baking after rolling, which is not preferable. Further, the ratio of the high boiling point organic solvent and the low boiling point organic solvent is preferably 2: 1 to 1: 9 (volume ratio). More preferably, it is 1: 1 to 1: 4. When the ratio of the high boiling point organic solvent is larger than the above ratio, the fluidity of the fluororesin does not decrease even after the low boiling point organic solvent is vaporized in the initial stage of rolling, and since the plasticity is strong, it is consolidated to secure high voids. Becomes difficult. On the other hand, when the ratio of the low boiling point organic solvent is high, the low boiling point organic solvent is vaporized at the initial stage of rolling and the plasticity of the fluororesin is drastically lowered, so that cracks and cracks are likely to occur.

The boiling point difference between the high boiling point organic solvent and the low boiling point organic solvent is preferably 10 ° C. or more, and more preferably 20 ° C. or more. When the boiling point difference is 10 ° C. or less, it is not possible to expect sufficient action and effect due to the different boiling points of the high boiling point organic solvent and the low boiling point organic solvent.

The rolling temperature in the rolling step is preferably 40 to 80 ° C. When the rolling temperature is lower than 40 ° C., the low boiling point organic solvent remains without being vaporized sufficiently, and the fluidity of the fluororesin is not sufficiently lowered,
A high porosity cannot be secured. If the rolling temperature is higher than 80 ° C, not only the low boiling point organic solvent and water but also the amount of the organic solvent in the kneaded product will be decreased, and the plasticity of the fluororesin will be drastically reduced, resulting in cracks and cracks. It tends to occur.

After the rolling step, the sheet is rolled between 130 and 20.
Preliminary calcination at a temperature of about 0 ° C. removes the high boiling point organic solvent and residual water in the sheet to obtain a catalyst layer having an appropriate pore distribution and high porosity.

[0019]

【Example】

Example 1 6.0 g of catalyst fine particles made of carbon black supporting platinum were uniformly dispersed in 1 liter of ultrapure water by using ultrasonic waves. Next, 10.0 g of polytetrafluoroethylene (PTFE) dispersion (30-J, manufactured by Mitsui Fluorochemical Co., Ltd.) was added dropwise to this dispersion and uniformly mixed. Then, a mixed solvent of 1 liter of ethyl alcohol and 0.5 liter of isobutyl alcohol was added to this mixed liquid to coagulate the catalyst fine particles and PTFE. By suction-filtering the liquid containing this aggregate, 6
0 g of filter cake was obtained. This filter cake was kneaded with a twin-arm kneader heated to 35 to 40 ° C to sufficiently fibrillate PTFE. Next, this kneaded product is rolled at a temperature of 50 ° C.
The thickness of the kneaded product is 14
A sheet having a thickness of 0 μm was obtained. This sheet is 150 ℃
The mixture was heated up to the temperature to evaporate mainly the solvent such as water and isobutanol remaining in the sheet to obtain a catalyst layer having a porosity of 76% by volume. The resulting catalyst layer had sufficient strength without being damaged by handling.

Example 2 6.0 g of catalyst fine particles made of carbon black carrying platinum was uniformly dispersed in 1 liter of ultrapure water by using ultrasonic waves. Next, a PTFE dispersion (Mitsui Fluorochemical Co., Ltd .: 30-J) was added to this dispersion.
4.3 g was added dropwise and mixed uniformly. Thereafter, 1.5 liters of isopropyl alcohol was added to this mixed solution to coagulate the catalyst fine particles and PTFE. After precipitation of the aggregates, 2 liters of the supernatant was removed, and 80 ml of isoamyl alcohol was added and mixed. On this occasion,
The volume ratio of water: isopropyl alcohol: isoamyl alcohol was 2: 3: 1. The liquid containing this aggregate was suction-filtered to obtain 42.9 g of a filter cake.
This filter cake was kneaded with a twin-arm kneader heated to 45 to 50 ° C. to sufficiently fibrillate PTFE. next,
This kneaded product was passed through a calender at a roll temperature of 60 ° C. alternately in the vertical and horizontal directions to perform rolling while mainly evaporating isopropyl alcohol in the kneaded product to obtain a sheet-shaped product having a thickness of 140 μm. Heat this sheet to 150 ° C,
A solvent such as isoamyl alcohol mainly remaining in the sheet was evaporated to obtain a catalyst layer having a porosity of 78% by volume. The resulting catalyst layer is not damaged by handling,
It had sufficient strength.

Example 3 6.0 g of catalyst fine particles made of carbon black supporting platinum were uniformly dispersed in 1 liter of ultrapure water by using ultrasonic waves. Next, a PTFE dispersion (Mitsui Fluorochemical Co., Ltd .: 30-J) 1 was added to the dispersion liquid.
0.0 g was added dropwise and mixed uniformly. Then, 1 liter of ethyl alcohol was added to this mixed solution to coagulate the catalyst fine particles and PTFE. After the liquid containing this aggregate was filtered by suction, the temperature was gradually raised to 110 ° C. to evaporate water and ethyl alcohol and dried. The dried mixture of catalyst fine particles and PTFE was pulverized with a ball mill to an average particle size of about 5 μm, and a mixed solution of 30 ml of water, 10 ml of isoamyl alcohol and 20 ml of isopropyl alcohol was added thereto.

Thereafter, this mixture was kneaded with a twin-arm kneader heated to 45 to 50 ° C. to sufficiently fibrillate PTFE. Next, this kneaded product is rolled at a temperature of 60 ° C.
By passing through the calendar alternately in the vertical and horizontal directions, rolling is performed mainly while evaporating isopropyl alcohol in the kneaded product,
A sheet-like material having a thickness of 150 μm was obtained. This sheet-like material is heated to 150 ° C. to evaporate mainly water, a solvent such as isoamyl alcohol remaining in the sheet, and a porosity of 7
A 5% by volume catalyst layer was obtained. The resulting catalyst layer had sufficient strength without being damaged by handling.

Comparative Example 6.0 g of catalyst fine particles made of carbon black supporting platinum was uniformly dispersed in 1 liter of ultrapure water using ultrasonic waves. Then, after this dispersion, 10.0 g of polytetrafluoroethylene (PTFE) dispersion (30-J, manufactured by Mitsui Fluorochemical Co., Ltd.) was dropped and uniformly mixed. Thereafter, 1.5 liters of ethyl alcohol was added to this mixed solution to coagulate the catalyst fine particles and PTFE. The liquid containing this aggregate was suction-filtered to obtain 60 g of a filter cake. After that, when kneading and rolling were performed in the same manner as in Example 1, a large number of cracks were generated in the sheet-like material in the direction perpendicular to the traveling direction of the sheet during rolling.

[0024]

According to the present invention, the above-mentioned structure is provided.
In the method for producing a fuel cell electrode catalyst layer described, in the kneaded product, since a low boiling point organic solvent and a high boiling point organic solvent were included, in the rolling step, vaporization of the low boiling point organic solvent The whole amount of the low boiling point organic solvent or a large amount of it vaporizes in the early stage of rolling, so that the total amount of the organic solvent contained in the kneaded material decreases, the fluidity of the fluororesin also decreases, and consolidation As a result, it is less likely that the low boiling point organic solvent is vaporized and the voids generated by the vaporization of the low boiling point organic solvent are retained. On the other hand, the high boiling point organic solvent is
It exists without vaporization until the end of the rolling step to promote the fibrillation of the fluororesin and to orient the fibrillated fibrous material. As a result, it is possible to obtain a fuel cell electrode catalyst layer having a fine porous structure, a high porosity, and a high physical strength.

According to the method for producing an electrode catalyst layer for a fuel cell according to claim 2, the effect of promoting fibrillation during rolling of the high boiling point organic solvent contained in the agglomerate, and the initial rolling stage of the low boiling point organic solvent. It is possible to ensure the vaporization in.

According to the method for producing the fuel cell electrode catalyst layer of the third aspect, a high porosity can be reliably ensured, and cracks and cracks can be prevented from occurring.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akira Utsumi 1128 Katsube-cho, Moriyama-shi, Shiga Japan Shiba Plant, Japan Baileen Co., Ltd. (72) Inventor Yasuyuki Maeda 7 Kitatone, Sowa-machi, Sarushima-gun, Ibaraki Japan Vilene Tokyo Factory Co., Ltd.

Claims (3)

[Claims] 1. A step of mixing a catalyst fine particle suspension and a dispersion of a fluororesin, a step of coaggregating catalyst fine particles and a fluororesin in a mixed solution, a step of kneading an aggregate, and a kneaded product In the method for producing a fuel cell electrode catalyst layer comprising a step of rolling, in the aggregate, a low-boiling organic solvent having a boiling point lower than that of water, and a high-boiling point having a boiling point higher than that of water. A method of producing an electrode catalyst layer for a fuel cell, which comprises an organic solvent having a boiling point. 2. The method for producing an electrode catalyst layer for a fuel cell according to claim 1, wherein the boiling point difference between the low boiling point organic solvent and the high boiling point organic solvent is at least 10 ° C. or more. 3. The rolling temperature in the rolling step is 40-80.
3. The method for producing an electrode catalyst layer for a fuel cell according to claim 1, wherein the method is at a temperature of ° C.