JPH04215255A - Manufacture of electrode for fuel cell - Google Patents

Abstract

PURPOSE:To obtain a high-strength sheet not shrunk when dried, improve its mechanical strength and production efficiency, and stabilize the battery characteristic by molding a high-viscosity solid kneaded with a catalyst, fluororesin and a solvent in the heated state to manufacture a sheet-shaped catalyst layer to be pressed to an electrode. CONSTITUTION:A catalyst, dispersion or fine powder of fluororesin (PTFE) and a small quantity of a high-boiling point solvent of petroleum or alcohol are added to obtain a high-viscosity kneaded material, the kneaded material is extruded in the heated state to facilitate the fibrillation of the fluororesin, at least one method of extrusion molding and roll molding is used, and a high- shearing stress and high-strength sheet can be obtained.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing fuel cell electrodes.

0002

[Prior Art] A fuel cell is a device that directly converts the chemical energy of fuel into electrical energy, and a pair of electrodes placed one above the other with an electrolyte layer in between is supplied with fuel gas from an external gas supply system. It is a type of power distribution device that supplies oxidizing gas, causes the fuel gas and oxidizing gas to electrochemically react on the electrode catalyst layer of each electrode, and as a result extracts electrical energy outside the system.

FIG. 4 is a schematic vertical cross-sectional view showing the structure of the electrode and electrolyte layer. In FIG. 4, the electrodes 1 are arranged one above the other with the electrolyte layer 2 in between, but only one of the electrodes 1 is shown here for convenience. The electrode 1 is constructed by adhering an electrode catalyst layer 4 on a porous carbon base material 3, and the electrode catalyst layer 4 consists of catalyst particles 7 carrying noble metal fine particles 6 on the surface of a catalyst carrier 5, and fluororesin particles. It is formed by binding with 8. The electrolyte layer 2 contains SiC in the electrolyte 9.
The fine particles 10 are dispersed therein. and electrode catalyst layer 4
Inside, the gas from the carbon base material 3 side and the electrolytic solution 9 from the electrolytic solution layer 2 come into contact, a three-phase interface is formed, and an electrochemical reaction progresses. In order to carry out this electrochemical reaction efficiently, it is necessary to make the catalyst particles 7 supporting the noble metal fine particles 6 and the fluororesin particles 8 as fine as possible, and also to make the catalyst particles 7 and the electrolyte 9 that are easily wetted by the electrolyte 9. The catalyst particles 7 (
It is necessary to increase the number of three-phase interfaces where the electrolytic solution 9 (solid phase), reaction gas (not shown) (gas phase), and electrolytic solution 9 (liquid phase) are in contact.

For this purpose, conventionally, fine catalyst particles 7 are dispersed in water containing a surfactant using ultrasonic waves or the like, and a dispersion of fine fluororesin particles 8 is added thereto to disperse the catalyst particles 7 and the water containing a surfactant. A uniform dispersion state of the fluororesin particles 8 is obtained. In order to manufacture the electrode catalyst layer 4, an ink in which catalyst particles 7 and fluororesin particles 8 are uniformly dispersed is applied onto the porous carbon base material 3, and then dried and fired, or an organic solvent is used. The catalyst particles 7 and the fluororesin particles 8 are co-agglomerated using as an auxiliary agent, and after solid-liquid separation, the solid content is kneaded,
This is rolled to form a sheet-like catalyst layer, then dried, fired, and fixed onto a porous carbon base material 3 to form an electrode 1. FIG. 5 is a schematic diagram showing the situation in which the solid content is rolled, and 11 represents a calender roll and 12 represents a sheet-like catalyst layer.

[0005] However, as fuel cells are about to be commercialized and demands for reliability and cost reduction of fuel cell electrodes are increasing, there are the following problems regarding the production of the electrode catalyst layer 4.

[0006]

[Problems to be Solved by the Invention] The problem is that the conventional method of applying an ink of catalyst particles 7 and fluororesin particles 8 on a porous carbon substrate 3 has a weak mechanical strength of the electrode catalyst layer 4. Cracks are likely to occur in the electrode catalyst layer 4 during or after the manufacturing process, and this causes significant deterioration in battery characteristics due to gas leakage, electrolyte 9 leakage, and the like. Therefore, by forming the catalyst particles 7 and the fluororesin particles 8 into a rolled sheet, it is possible to mechanize manual work and reduce costs by reducing man-hours, as well as improve the mechanical strength of the electrode catalyst layer 4 and improve reliability. However, there is still a problem that it is not strong enough and it is difficult to mechanize it.

Therefore, the mechanical strength of the electrode catalyst layer 4 must be further increased, and in the drying process of the sheet catalyst layer, heat drying is more advantageous than vacuum drying in terms of drying efficiency. However, when we tried this method, there was a problem that the area of the sheet-like catalyst layer decreased due to shrinkage during drying and wrinkles appeared.To prevent this, we tried fixing the edges of the sheet-like catalyst layer, but the drying time still increased. Inconveniences such as cracks occur due to shrinkage.

The present invention has been made in view of the above points, and its object is to reduce the shrinkage during drying by molding a highly viscous paste of a catalyst, a fluororesin, and a lubricant in a heated state. It is an object of the present invention to provide a method for producing a fuel cell electrode that obtains a sheet-like electrode catalyst layer with high strength.

[0009]

[Means for Solving the Problems] In order to solve the above-mentioned problems, the method of the present invention uses high-boiling point petroleum-based or alcohol-based materials to form a sheet-like catalyst layer on its raw materials, the catalyst and fluororesin (PTFE). Add a small amount of solvent to create a highly viscous kneaded material,
In order to facilitate fibilization of the fluororesin, it is made into a sheet by applying high shear stress by using at least one of extrusion molding and rolling molding in a heated state.

0010

[Function] By the method described above, the present invention supports two sides or the entire periphery of the sheet edge during heat drying when petroleum-based solvents are used to prevent the sheet from shrinking, and when alcohol-based solvents are used. can be vacuum-dried or freeze-vacuum-dried after washing with pure water, which can similarly prevent sheet shrinkage, and has high shear stress and high strength in the order of extruder and rolling machine. Sheets can be manufactured efficiently.

[0011]

[Examples] The present invention will be explained below with reference to Examples.

First, water containing a surfactant is added to a catalyst in which platinum is supported using acetylene black as a carrier, and ultrasonic waves are applied to the catalyst to sufficiently disperse the catalyst, and the average particle size is 0.2 μm. A dispersion of PTFE (polytetrafluoroethylene), which is a fluororesin, is added, mixed well, and vacuum dried to produce a mixed powder of catalyst and PTFE. Next, 20 to 70% by weight of a petroleum solvent having a boiling point of 180 to 250°C, such as kerosene (kerosene), is added and mixed to form a clay-like solid. Next, this clay-like solid material is rolled. At this time, hot water or steam is circulated inside the rolls of the rolling mill, and the roll temperature is set at 50 to 150 ° C.
A clay-like solid material is rolled to produce a sheet-like catalyst layer with a thickness of 200 μm. Next, the sheet-shaped catalyst layer is placed in a hollow frame or placed on a base material with two sides or the entire circumference fixed, and heated at 100 to 250°C in nitrogen gas.
After drying at 300℃, pre-baking at 350℃, 5
An electrode is obtained by heating and firing at ~10 kg/cm2.

In the above process, an alcohol-based solvent such as ethylene glycol (boiling point 192°C) is used instead of petroleum-based solvent.
You can also use The sheet-like catalyst layer obtained in this case is dried at 50 to 250°C and then pre-calcined at 300°C, and the sheet-like catalyst layer is washed with pure water and then vacuum-dried to form a porous catalyst layer. Since the alcohol inside can be replaced with pure water, the moisture freezes during vacuum drying, resulting in freeze-vacuum drying, which prevents shrinkage of the sheet catalyst layer and eliminates fixing on two sides or the entire circumference. It is also possible. Of course, it is also possible to heat dry at 100 to 250° C. in nitrogen gas with two sides or the entire circumference fixed.

[0014] Also, if the amount of petroleum-based solvent or alcohol-based solvent added is 20 to 70% by weight, the mixing condition with the catalyst and PTFE may be poor. A large amount of solvent is added and mixed uniformly to create a clay-like solid, which is placed on a filter and pressurized from the outside to remove excess solvent so that the amount of solvent is 20 to 70% by weight. As described above, electrodes can be produced through the same steps as those using petroleum-based solvents and alcohol-based solvents, respectively.

[0015] In the above example, a PTFE dispersion is used, but PTFE, which is an aqueous dispersion of PTFE, is used.
In order to mix and disperse the dispersion with the dry catalyst powder, it is necessary to first disperse the catalyst powder in water containing a surfactant, and then add the PTFE dispersion thereto. Then, in order to obtain a clay-like solid by adding and mixing a solvent, the mixture of PTFE and catalyst is once dried.
After removing the water, the amount of solvent necessary to form a clay-like solid is added and mixed. On the other hand, P
If TFE fine powder is used, since the PTFE finder is a dry particle, a clay-like solid can be obtained by mixing it with catalyst powder as it is and adding and mixing the required amount of solvent. That is, when using PTFE dispersion, a drying process is required to obtain a clay-like solid, but when using PTFE fine powder, a drying process is not required to obtain a clay-like solid. It is also effective to use fine powder of PTFE.

By the way, some of the PTFE particles in PTFE dispersions and fine powders become fibrous when shearing force is applied in the presence of an appropriate amount of organic solvent, and this fibrosis is accelerated by heating at 30° C. or higher. be done. Electrodes containing fibilized PTFE have increased mechanical strength. In the various electrode manufacturing methods described so far, the sheet-shaped catalyst layer is manufactured by rolling in order to facilitate fibilization of PTFE, but in the method of the present invention, only rolling is required. Instead, by performing extrusion processing as a preliminary step and performing a molding process that combines these, further effects can be achieved. In other words, when only rolling is performed,
The process of rolling → folding the sheet → rolling must be repeated to promote fibilization of PTFE and increase its mechanical strength. However, if extrusion is added as a pre-rolling process, the extrusion process will cause the fibilization of PTFE to increase. Since the material is advanced, mechanical strength can be ensured simply by rolling it as it is, and there is no need for repeated processing in a rolling mill.

FIG. 1 is a schematic diagram showing a state in which an extruder 13 is installed as a pre-stage of the rolling process shown in FIG. 5, and parts common to those in FIG. 5 are designated by the same reference numerals. In this way, it becomes possible to automate a series of continuous processing such as extrusion and rolling, and it is possible to simultaneously improve the mechanical strength of the sheet-like catalyst layer and the processing efficiency. At this time, in extrusion processing, it is difficult to obtain the width dimension as in rolling processing, and in rolling processing after extrusion processing, the sheet width tends to become smaller, so the extruder 13
It is necessary to consider increasing the dimensions of the cylinder and nozzle.

The mechanical strength of the sheet catalyst layer of the electrode obtained by the present invention is 600 to 1000 g/mm2, which is higher than the mechanical strength of the conventional sheet catalyst layer of 100 g/mm2.
This is 10 times higher than the previous value of ~120 g/mm2. The bar graph in FIG. 2 shows the comparison. (A), (B), (C), and (D) are the tensile strengths of the catalyst layer obtained by the method of the present invention, including variations, and (E) is the value obtained by the conventional manufacturing method. be. FIG. 3 is a diagram showing the output characteristics of a fuel cell equipped with an electrode obtained according to the present invention, in which the horizontal axis represents operating time and the vertical axis represents cell voltage. The curve (a) in FIG. 3 represents the electrode according to the present invention, and the curve (b) represents the electrode manufactured by the conventional manufacturing method. It can be seen from FIG. 3 that the fuel cell having the electrode obtained according to the present invention maintains stable characteristics even during long-term operation.

[0019]

[Effects of the Invention] Conventionally, one method for producing electrodes for fuel cells is to add an alcohol-based solvent to an ink in which catalyst particles and fluororesin particles are dispersed in water to cause the catalyst particles and fluororesin particles to coagulate. Previously, the solid material after solid-liquid separation was kneaded and rolled to obtain a sheet-like catalyst layer, which was then crimped onto a substrate, but this method required a mechanical process at the stage of forming the sheet-like catalyst layer by rolling. However, according to the method of the present invention, which was carried out to obtain a sheet-like catalyst layer with high mechanical strength, catalyst particles and fluororesin particles Solid materials kneaded with a small amount of high-boiling point organic solvent can be plastic-processed by applying large shear stress under heating. This method has the great effect that fibilization can be performed easily and extremely efficiently, and automation is also possible.

[Brief explanation of the drawing]

[Fig. 1] A schematic diagram showing the state of forming a sheet-like catalyst layer in the method of the present invention.

[Fig. 2] Bar graph showing the tensile strength of the sheet-like catalyst layer obtained by the method of the present invention in comparison with the conventional method.

[Figure 3] Schematic diagram showing the rolling situation of a sheet-like catalyst layer in the conventional method

[Fig. 4] A schematic vertical cross-sectional view showing the structure of a conventional electrode and electrolyte layer.

[Figure 5] Schematic diagram showing the rolling situation of a sheet-like catalyst layer

[Explanation of symbols]

1 Electrode 2 Electrolyte layer 3 Porous carbon base material 4 Electrode catalyst layer 5 Catalyst carrier 6 Precious metal particles 7 Catalyst particles 8 Fluororesin particles 9 Electrolyte 10 SiC fine particles 11 Calendar roll 12 Sheet catalyst layer 13 Extruder

Claims (18)

[Claims] 1. A method for producing a fuel cell electrode in which a sheet-like catalyst layer in which catalyst particles are bound with a fluororesin is pressed onto a carbon base material, the method comprising a PTFE (polytetrafluoroethylene) dispersion in the catalyst particles. Add and mix a high boiling point solvent to the dried powder to form a solid substance, then add 50 to 1
A method for producing an electrode for a fuel cell, comprising the step of forming a sheet by performing at least one of extrusion processing and rolling processing at 50° C. and then drying the sheet to form the sheet-like catalyst layer. 2. A method for producing an electrode for a fuel cell according to claim 1, characterized in that 20 to 70% of a petroleum solvent is added as the high boiling point solvent. 3. In the method according to claim 1, 70% or more of a petroleum solvent is added and mixed as a high boiling point solvent to form a solid, which is then compressed, excess solvent is removed, and the solvent content is reduced to 20 to 20%.
70%. A method for producing an electrode for a fuel cell. 4. The method according to claim 1 or 2, wherein the sheet is dried by heating in an inert gas atmosphere with two sides or the entire peripheral edge of the sheet fixed. Production method. 5. The method of claim 1 or 3, wherein the sheet is dried by fixing two sides or the entire peripheral edge of the sheet and heating and drying it in an inert gas atmosphere. Production method. 6. A method for producing an electrode for a fuel cell according to claim 1, characterized in that 20 to 70% of an alcoholic solvent is added as a high-boiling point solvent, and washing with water is carried out after molding. 7. In the method according to claim 1, an alcoholic solvent is used as the high boiling point solvent, and after adding and mixing 70% or more to form a solid, this is compressed, excess solvent is removed, and the solvent content is reduced to 20%. 70%. 8. A method for producing an electrode for a fuel cell according to claim 1, wherein the sheet is vacuum-dried or freeze-vacuum-dried. 9. A method for producing an electrode for a fuel cell according to claim 1 or 7, wherein the sheet is vacuum-dried or freeze-vacuum-dried. 10. A method for producing an electrode for a fuel cell in which a sheet-like catalyst layer in which catalyst particles are bound with a fluororesin is pressed onto a carbon base material, the catalyst particles being made of PTFE (polytetrafluoroethylene) fine powder. A high boiling point solvent is added to the mixed powder and mixed to form a solid, and then 50~
A method for producing an electrode for a fuel cell, comprising the steps of forming a sheet by performing at least one of extrusion and rolling at 150° C. and then drying the sheet to form the sheet-like catalyst layer. 11. A method for producing an electrode for a fuel cell according to claim 10, characterized in that 20 to 70% of a petroleum solvent is added as the high boiling point solvent. 12. In the method according to claim 10, 70% or more of a petroleum solvent is added and mixed as a high boiling point solvent to form a solid, which is then compressed, excess solvent is removed, and the solvent content is reduced to 2.
A method for producing an electrode for a fuel cell, characterized in that the ratio is 0 to 70%. 13. The method of claim 10 or 11, wherein the sheet is dried by fixing two sides or the entire peripheral edge of the sheet and heating and drying it in an inert gas atmosphere. Production method. 14. The method of claim 10 or 12, wherein the sheet is dried by fixing two sides or the entire peripheral edge of the sheet and heating and drying it in an inert gas atmosphere. Production method. 15. The method for producing an electrode for a fuel cell according to claim 10, wherein 20 to 70% of an alcoholic solvent is added as a high-boiling point solvent, and washing with water is carried out after molding. 16. In the method according to claim 10, an alcoholic solvent is used as the high boiling point solvent, and after adding and mixing 70% or more to form a solid, this is compressed, excess solvent is removed, and the solvent content is reduced to 20%. 70%. 17. A method for producing an electrode for a fuel cell according to claim 10 or 15, wherein the sheet is vacuum-dried or freeze-vacuum-dried. 18. A method for producing an electrode for a fuel cell according to claim 10 or 16, wherein the sheet is vacuum-dried or freeze-vacuum-dried.