JPH0656556A - Production of porous electrode - Google Patents

Abstract

PURPOSE:To obtain a porous electrode whose orientational direction in the electrode is arrayed in the thickness direction of the electrode and also in which closed pores are hardly present. CONSTITUTION:An electrode raw material is formed of electronically conductive powder 2a prepared by mixing nylon short fiber 2c combined with ferroelectric powder and having an electrical polarity in the longitudinal direction, nickel oxide and zirconium oxide stabilized with yttrium, a binder and a solvent 2b etc. Electrostatic field is impressed on the electrode raw material to from an electrode green sheet 2B of the electrode raw material in the state that the orientational direction of the nylon short fiber 2c is arrayed in the thickness direction of the electrode. After the electrode green sheet 2B was pressed to stick to a solid electrolysis green sheet, the nylon short fiber 2c is eliminated by roasting, thus the porous electrode is produced.

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 a porous electrode used in gas sensors, humidity sensors, fuel cells and the like.

[0002]

2. Description of the Related Art A porous electrode having pores inside is required to have gas collection performance as well as gas permeation performance. In order to improve the gas permeability of this porous electrode, the gas permeation path length is shortened by aligning the orientation direction of the pores in the electrode with the thickness direction of the electrode, and the closed pores among the pores in the electrode are used. It is better to reduce the ratio of some.

However, according to the conventional method, an electrode raw material composed of a conductor powder, a binder, an organic solvent and an organic polymer for making it porous is applied to a ceramic substrate and baked, so that it is produced. It was not possible to reduce the orientation direction of pores of the electrode and the ratio of closed pores. Therefore,
An object of the present invention is to provide a porous electrode in which the orientation direction of the pores in the electrode is aligned with the thickness direction of the electrode and there are almost no closed pores.

[0004]

In order to solve the above-mentioned problems, the method for producing a porous electrode according to the present invention comprises: (a) an organic compound which is compounded with a ferroelectric powder and has an electric polarity in the longitudinal direction. A step of preparing an electrode raw material by mixing a polymer fiber, a conductor powder, a binder, and a solvent; and (b) applying an electrostatic field to the electrode raw material to change the orientation direction of the organic polymer fiber. A step of forming an electrode with the electrode raw material in a state of being aligned in the thickness direction of the electrode; and (c) a step of firing the formed electrode to scatter the organic polymer fibers to produce a porous electrode. And are provided.

[0005]

In the above method, the organic polymer fiber composited with the ferroelectric powder has an electric polarity in the length direction. When the organic polymer fibers are mixed with the electrode raw material, the orientation directions thereof are randomly oriented in all directions. When an electrostatic field is applied to this electrode raw material, the organic polymer fibers are oriented in the direction of the electrostatic field. Therefore, when an electrostatic field is applied so that the orientation direction of the organic polymer fibers is aligned with the thickness direction of the electrode, and the length of the organic polymer fibers is set to be approximately the same as or slightly longer than the thickness of the electrode, As shown in FIG. 2, both ends of the polymer fiber reach the front and back surfaces of the molded electrode. Then, by firing the formed electrode, the polymer fibers are scattered to form open pores in the traces of the polymer fibers which are substantially oriented in the thickness direction of the electrode.

[0006]

EXAMPLES An example of the method for producing a porous electrode according to the present invention will be described below. As an example, a case where the invention is applied to manufacture of an air side electrode and a fuel side electrode of a solid oxide fuel cell will be described. First, a method for manufacturing the green sheet for the fuel side electrode will be described.

FIG. 1 is a composition diagram showing a raw material 2A for the fuel side electrode. Nylon material and ferroelectric powder barium titanate are mixed, injection molded while applying an electric field in the injection direction, cut into 50 μm lengths, and nylon short fibers 2c having electrical polarity in the length direction are obtained. Create. Next, nickel oxide, which is a powdery ceramic material, and yttrium-stabilized zirconium oxide are mixed in equal weights to form a conductor powder 2a, and then a predetermined amount of the nylon short fibers 2c is added and mixed. Then, with respect to 100% by weight of the obtained mixture, 15% by weight of a binder (for example, polyvinyl butyral binder), a solvent (ethanol, toluene), a plasticizer, etc. (these are collectively indicated by 2b in the figure) Add an appropriate amount to make a slurry. In this state, the nylon short fibers 2c are randomly oriented in all directions.

Next, as shown in FIG. 2, while applying an electrostatic field in the X direction to the slurry-like raw material 2A, a 40 μm thick fuel-side electrode green sheet 2B was prepared by the doctor blade method. At this time, green sheet 2
B is manufactured in a state where its thickness direction is parallel to the electrostatic field. Therefore, each nylon short fiber 2c included in the green sheet 2B is substantially oriented in the thickness direction of the green sheet 2B. Moreover, since the length of the nylon short fiber 2c is slightly longer than the thickness of the green sheet 2B, both ends of the nylon short fiber 2c are green sheet 2B.
Has reached the front and back.

Next, a method of manufacturing the green sheet for the air side electrode will be described. Similar to the method for producing the green sheet for the fuel side electrode, a predetermined amount of the above nylon short fibers is added to and mixed with powdered lanthanum manganite. Then, an appropriate amount of a binder (for example, polyvinyl butyral binder), a solvent (ethanol, toluene), a plasticizer, etc., of 15% by weight with respect to 100% by weight of the obtained mixture is added, and a raw material for an air-side electrode in a slurry state. And In this state, the orientation directions of the respective nylon short fibers are randomly oriented in all directions. While applying an electrostatic field to this slurry-like raw material,
A 40 μm thick air side electrode green sheet was prepared by the doctor blade method. At this time, the green sheet is produced with its thickness direction parallel to the electrostatic field. Therefore, each nylon short fiber contained in the green sheet is substantially oriented in the thickness direction of the green sheet.

Further, a green sheet of yttrium-stabilized zirconium oxide as a solid electrolyte was prepared. That is, 15 wt% of a binder (for example, polyvinyl butyral binder) and a solvent (ethanol, 15 wt% to 100 wt% of powdery yttrium-stabilized zirconium oxide).
Toluene), a plasticizer, etc. were added in appropriate amounts to form a slurry, and a solid electrolyte green sheet was produced from this slurry by the doctor blade method.

A green sheet for the fuel side electrode and a green sheet for the air side electrode are respectively stacked from above and below on a stack of an appropriate number of the produced solid electrolyte green sheets, and the sheets are cut into a predetermined size to form a molded body. Got The molded body was heated at a temperature of 400 ° C. for 3 hours to scatter the binder, then heated to 1300 ° C. at a rate of 1 ° C./min, and baked at this temperature for 2 hours. By this firing, the short nylon fibers are scattered, and open pores that are substantially oriented in the thickness direction of the molded body are formed in the traces of the short nylon fibers. Then, by cooling to room temperature, a solid electrolyte 1 having a fuel side electrode 2 and an air side electrode 3 which are porous electrodes provided on the front and back surfaces was obtained (see FIG. 3).

Two types of example products 1 and 2 thus obtained
Was evaluated for porosity and power generation capacity. The evaluation results are shown in Table 1. For comparison, the evaluation results of the conventional products 1 and 2 produced by the same method as the above-described production method are also shown except that the electrostatic field is not applied during the production of the green sheet.

[0013]

[Table 1]

The porosities of the electrodes 2 and 3 are determined by the SEM of the electrode cross section.
It was calculated by taking a picture and analyzing the picture. Further, as shown in FIG. 4, a fuel gas supply pipe 7a and an air supply pipe 7b were attached to the electrodes 2 and 3, respectively, to fabricate a fuel cell. Connect this fuel cell to the measuring circuit 19,
The power generation capacity was measured. That is, the fuel cell at 1000 ° C
Fuel gas and air are supplied to the electrodes 2 and 3, respectively, while maintaining the temperature of 3 A to cause an electrode reaction through the solid electrolyte 1, and 0.3 A per unit electrode area while observing with an ammeter 11. The voltage value generated in the fuel cell under the condition that a current of / cm ² flows was measured by the voltmeter 10. 8
Reference numerals a and 8b are platinum wires, and 9 is a variable resistor. The larger the value of this power generation capacity, the better the gas permeability of the electrode and the better the performance as a battery. Table 1 shows that the example products 1 and 2 have a larger power generation capacity than the conventional example products 1 and 2.

From the above, it can be seen that the products of Examples 1 and 2 are superior in gas permeability of the electrodes 2 and 3. The method for manufacturing the porous electrode according to the present invention is not limited to the above-mentioned embodiment, but can be variously modified within the scope of the gist. In particular, in the above-mentioned embodiment, the case where it is applied to the fuel side electrode and the air side electrode of the solid oxide fuel cell has been described, but other than this, it may be applied to, for example, a porous electrode of a gas sensor or a humidity sensor.

[0016]

As is apparent from the above description, according to the present invention, the organic polymer fibers aligned in the thickness direction of the electrode due to the application of the electrostatic field are scattered during firing to leave traces of the polymer fibers. It is possible to form open pores that are substantially oriented in the thickness direction of the electrode. Therefore, the gas permeability of the electrode can be improved as compared with the conventional one, and a porous electrode excellent in current collecting property can be obtained.

As a result, it becomes possible to improve the performance of the gas sensor, the humidity sensor, the fuel cell and the like.

[Brief description of drawings]

FIG. 1 is a composition diagram for explaining a manufacturing procedure showing an embodiment of a method for manufacturing a porous electrode according to the present invention.

FIG. 2 is a composition diagram for explaining a manufacturing procedure subsequent to FIG.

FIG. 3 is a structural diagram of a solid electrolyte in which the porous electrodes shown in FIG. 1 are provided on the front and back surfaces.

FIG. 4 is an electric circuit diagram showing a measuring circuit for measuring the power generation capacity of the fuel cell provided with the porous electrode shown in FIG.

[Explanation of symbols]

 2 ... Fuel side electrode 2A ... Fuel side electrode raw material 2B ... Fuel side electrode green sheet 2a ... Conductor powder 2b ... Binder, solvent, plasticizer, etc. 2c ... Nylon short fiber (organic polymer fiber)

Claims (1)

[Claims] 1. A step of preparing an electrode raw material by mixing an organic polymer fiber composited with a ferroelectric powder and having electric polarity in the length direction, a conductor powder, a binder, and a solvent. The step of forming an electrode with the electrode raw material in a state where the orientation direction of the organic polymer fibers is aligned with the thickness direction of the electrode by applying an electrostatic field to the electrode raw material, and the formed electrode is fired. And a step of scattering the organic polymer fibers to produce a porous electrode, the method for producing a porous electrode.