JP2002184413A - Method of manufacturing electrode for phosphoric acid type fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method allowing the low-cost production of an electrode catalyst layer with catalyst particles and water repellent particles highly and uniformly dispersed. SOLUTION: After a catalyst is added to an alkaline solution, consisting of an ammonia water added to a pure water, and dispersed therein and then a fluorine contained resin is added thereto and highly and uniformly dispersed therein, phosphoric acid is added thereto into an acidic form and agglomerated. The obtained agglomerated slurry, arranged on a carbon paper, is sucked at its back, filtered and subjected to pure water cleaning and drying to obtain a fuel cell electrode having an electrode catalyst layer formed on a porous substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an electrode used in a phosphoric acid fuel cell in which a fuel gas and an oxidizing gas are introduced to obtain electric energy by an electrochemical reaction.

[0002]

2. Description of the Related Art FIG. 4 is a partial sectional view schematically showing the structure of an electrode and an electrolyte layer of a phosphoric acid fuel cell. Although the electrodes are arranged on both sides of the electrolyte layer, only one of the electrodes is shown in FIG. As shown in the figure, the electrode 1 is configured by attaching an electrode catalyst layer 4 on a porous carbon substrate 3. The electrode catalyst layer 4 is formed by binding catalyst particles 7 carrying noble metal fine particles 6 on the surface of a catalyst carrier 5 with water-repellent particles 8 such as fluororesin. The electrolyte layer 2 is obtained by impregnating a phosphoric acid electrolyte 9 into an electrolyte holding layer composed of silicon carbide fine particles 10. In this configuration, the reaction gas sent from the porous carbon substrate 3 and the phosphoric acid electrolyte 9 from the electrolyte layer 2 come into contact with each other inside the electrode catalyst layer 4 to form a three-phase interface, and the electrochemical reaction occurs. Progresses. In order to make the electrochemical reaction proceed efficiently, the catalyst particles 7 carrying the noble metal fine particles 6 and the water-repellent material particles 8 should be made as fine as possible. The catalyst particles 7 (solid phase) and the reaction gas (gas phase) are dispersed more uniformly with the water-repellent material particles 8 which are hardly wetted by 9.
It is necessary to increase the three-phase interface where the electrolyte and the electrolytic solution 9 (liquid phase) are in contact.

In the conventional method for forming the electrode catalyst layer 4, the catalyst fine particles 7 are dispersed in water containing a surfactant using ultrasonic waves or the like, and then the dispersion of the water-repellent material particles using the surfactant is performed. Is added to obtain a uniformly dispersed and mixed state of the catalyst fine particles 7 and the water-repellent material particles 8, and then an aggregating agent is added to produce an aggregate composed of the catalyst fine particles 7 and the water-repellent material particles 8. The electrode catalyst layer is formed by spraying and applying the aggregate on the porous carbon substrate 3, or by suction filtration, or by kneading the aggregate and stretching it with a calender roll to form a sheet. 4 are formed. The electrode catalyst layer 4 thus formed is heat-treated at a temperature near the melting point of the water-repellent material in order to stabilize the form as the electrode catalyst layer and to effectively exhibit the water-repellency of the water-repellent material. I have.

[0004]

As described above, in the conventional phosphoric acid type fuel cell, when forming the electrode catalyst layer,
In order to obtain a state in which the catalyst particles and the water-repellent material particles have a particle diameter of 1 μm or less and are well dispersed and mixed at a concentration which can be applied industrially, a surfactant is usually used.

[0005] However, when the catalyst particles and the water-repellent material particles are mixed and dispersed by using a very common nonionic surfactant and are agglomerated with an alcohol-based solvent, the zeta potential of the dispersed particles is reduced. Since there is no difference, the agglomerated particles have no selectivity and are often recondensed between the water-repellent material particles or between the electrically conductive particles. Therefore, even if the dispersion is uniform, the uniformity deteriorates due to the aggregation. In some cases.

In the case where a surfactant is used, if the surfactant remains in the fuel cell, the electrochemical reaction is hindered. To remove the surfactant. Therefore, when a surfactant is used, the number of steps in the manufacturing process increases, and there is a problem that the manufacturing cost increases.

Further, even if such a heat treatment step is provided to remove the surfactant, it is impossible to completely remove the surfactant, and a small amount of the surfactant or the surfactant is generated by decomposition. There is a high possibility that impurities will remain in the manufactured electrode, and when the surfactant is decomposed in the heat treatment step, the surface of the catalyst particles will be oxidized or will react with the surface of the catalyst to form a carbonyl group or hydroxyl group on the surface of the carrier. It is very likely to produce hydrophilic functional groups such as When such a situation occurs, the tendency of the entire electrode to be easily wetted by the electrolytic solution is increased, and the flow of the reaction gas into the three-phase interface is hindered by the electrolytic solution, so that the characteristics of the fuel cell are degraded. At the same time, the catalyst particles are eroded and corroded by the electrolytic solution, so that the power generation performance is reduced and the life characteristics of the battery are deteriorated.

The present invention has been made in consideration of the problems of the prior art as described above, and an object of the present invention is to provide an electrode catalyst layer in which catalyst particles and water-repellent particles are highly uniformly dispersed, and that the number of steps is small. It is an object of the present invention to provide a method for producing an electrode for a phosphoric acid type fuel cell, which is manufactured at a low cost and has excellent cell characteristics at low cost.

[0009]

In order to achieve the above object, in the present invention, a dispersion slurry is prepared by dispersing catalyst particles and water-repellent particles in a dispersion medium, and the dispersion slurry is agglomerated. A phosphoric acid type fuel cell for producing an agglomerated slurry, attaching the obtained agglomerated slurry to a porous electrode substrate, washing and drying to produce an electrode catalyst layer composed of catalyst particles and water-repellent material particles In the method for manufacturing an electrode, (1) an alkaline dispersion medium is used as the dispersion medium, for example, a solution obtained by adding ammonia to pure water.

(2) In the above (1), the dispersion slurry is aggregated by adding an acid to the dispersion slurry to make it acidic. (3) Further, in the above (1) and (2), the aggregated slurry is disposed on the porous electrode substrate and suctioned from the back surface and filtered, or the aggregated slurry is placed on the porous electrode substrate. To apply the aggregated slurry to the porous electrode substrate.

When the dispersion medium is an alkaline solution such as ammonia as in the above (1), both the catalyst particles and the water-repellent material particles, for example, the fluororesin particles, have negative surface charges, thereby increasing the dispersibility. Therefore, a highly dispersed dispersion slurry is obtained. Further, as described in (2) above, if the dispersion slurry is made acidic by adding an acid such as phosphoric acid, the surface charge of the catalyst particles becomes positive and the surface charge of the water-repellent material particles becomes negative. be able to. When the surface charges of the two types of particles have different polarities, hetero-aggregation occurs in which the different types of particles selectively aggregate. Therefore, unlike the conventional case, the same type of particles are not aggregated, and an aggregated slurry in which the catalyst particles and the water repellent particles are highly dispersed can be obtained.

Therefore, if the aggregated slurry is adhered to the porous electrode substrate by the method (3), an electrode catalyst layer in which the catalyst particles and the water-repellent material particles are highly uniformly dispersed can be obtained. In the above (1) to (3), since the surfactant used in the conventional method is not used, a heat treatment step for removing the surfactant is not required, and the manufacturing cost can be reduced. In addition, deterioration of battery characteristics due to residual impurities and the like caused by use of the surfactant is also avoided. If an alkaline solution such as ammonia is used as a dispersion medium as in the above (1), ammonium phosphate or the like may be generated, but these salts are water-soluble and
Since the solubility is relatively high, it can be easily removed only by washing with water when forming the electrode catalyst layer.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the production method of the present invention will be described in more detail with reference to examples. FIG. 1 is a flow chart showing an embodiment of a method for producing an electrode for a phosphoric acid fuel cell according to the present invention. In this embodiment, first, a catalyst was added to an alkaline dispersion medium obtained by adding 10 ml of 25% ammonia water to 500 g of pure water.
50 g was added, and the catalyst was dispersed using an ultrasonic homogenizer. Next, a fluororesin 40
g, and dispersed using an ultrasonic homogenizer to obtain a dispersion slurry in which catalyst particles and fluororesin particles were uniformly and finely dispersed. Next, 5 ml of 105% phosphoric acid was added to the dispersed slurry to make it acidic, mixed and condensed to obtain an agglomerated slurry in which catalyst particles and fluororesin particles were heteroaggregated. Subsequently, the coagulated slurry was placed on carbon paper that would be a porous carbon substrate,
It was attached to one surface of the carbon paper by suction and filtration from the back. Furthermore, it is washed with pure water,
Thereafter, drying was performed to produce a fuel cell electrode.

A cell of a phosphoric acid type fuel cell is manufactured by sandwiching the electrolyte layer between the two fuel cell electrodes manufactured as described above, and a fuel cell power generation experiment is performed under the conditions of atmospheric pressure and 190 ° C. Carried out. Air was used as the oxidizing gas supplied to the cathode, and a mixed gas of hydrogen and carbon dioxide was used as the fuel gas supplied to the anode. The characteristics obtained in this power generation experiment are as follows. FIG. 2 is a characteristic diagram showing an output voltage characteristic of a fuel cell manufactured by the manufacturing method of the example in comparison with a characteristic of a cell manufactured by a conventional method.
The characteristic A in the figure is the characteristic of the fuel cell manufactured by the manufacturing method of the embodiment, and the characteristic B is the characteristic of the cell manufactured by the conventional method under the same operating conditions. FIG. 3 is a characteristic diagram showing the life characteristics of the fuel cell manufactured by the manufacturing method of the embodiment in comparison with the characteristics of a battery manufactured by the conventional method. The characteristic of the battery, characteristic D, is the characteristic under the same operating conditions of the battery manufactured by the conventional method. As can be seen from FIG. 2, the fuel cell manufactured by the manufacturing method of the present embodiment has a higher output voltage over the entire current range as compared with the fuel cell manufactured by the conventional method. , An improvement of 2-3 mV is observed. Further, as shown in FIG. 3, the decrease in terminal voltage due to long-term continuous operation of the fuel cell manufactured by the manufacturing method of this embodiment is smaller than that of the fuel cell manufactured by the conventional method, and the output voltage is deteriorated. About a 9% improvement in speed is observed.

As described above, the fuel cell manufactured by the manufacturing method of the present embodiment has excellent cell characteristics as compared with the fuel cell manufactured by the conventional method.
An aggregate slurry in which catalyst particles and fluororesin particles are highly hetero-aggregated without using a surfactant is produced, and an electrode catalyst layer is produced with the aggregate slurry. Therefore, in the above embodiment, the electrode catalyst layer is produced by filtering the aggregated slurry, but the electrode catalyst layer is formed by a method of applying the aggregated slurry on carbon paper as a porous carbon substrate. Even in this case, a fuel cell having similarly excellent characteristics can be obtained.

Further, comparing the method for manufacturing an electrode of the present embodiment with a conventional manufacturing method using a surfactant, the method for manufacturing an electrode according to the present embodiment corresponds to the step of removing the surfactant. In this case, the number of steps is reduced, and the manufacturing cost is reduced.

[0017]

As described above, in the method for producing an electrode for a phosphoric acid type fuel cell according to the present invention, the catalyst particles and the water-repellent material particles are dispersed in an alkaline dispersion medium as described in the claims. A dispersion slurry is prepared, and an acid is added to the dispersion slurry to make the dispersion slurry acidic, thereby aggregating the dispersion slurry to prepare a flocculated slurry, and attaching the obtained flocculated slurry to a porous electrode substrate to form an electrode catalyst. Since the electrode layer is prepared, the electrode catalyst layer in which the catalyst particles and the water-repellent material particles are highly uniformly dispersed is manufactured with a small number of man-hours. Electrodes can be manufactured.

[Brief description of the drawings]

FIG. 1 is a flowchart showing an embodiment of a method for producing an electrode for a phosphoric acid fuel cell according to the present invention.

FIG. 2 is a characteristic diagram showing the output voltage characteristics of a fuel cell manufactured by the manufacturing method of the example in comparison with the characteristics of a cell manufactured by a conventional method.

FIG. 3 is a characteristic diagram showing the life characteristics of a fuel cell manufactured by the manufacturing method of the example in comparison with the characteristics of a cell manufactured by a conventional method.

FIG. 4 is a partial cross-sectional view schematically showing a configuration of an electrode and an electrolyte layer of a phosphoric acid fuel cell.

[Explanation of symbols]

 Reference Signs List 1 electrode 2 electrolyte layer 3 porous carbon substrate 4 electrode catalyst layer 5 catalyst carrier 6 noble metal fine particles 7 catalyst particles 8 water repellent material particles (fluororesin) 9 phosphoric acid electrolyte 10 silicon carbide fine particles

Claims (5)

[Claims] 1. A dispersion slurry is prepared by dispersing a catalyst particle and a water-repellent material particle in a dispersion medium, and the dispersion slurry is aggregated to form an aggregation slurry. A method for producing an electrode for a phosphoric acid type fuel cell, wherein the dispersion medium is an alkaline dispersion medium, wherein the dispersion medium is an alkaline dispersion medium. For producing an electrode for a phosphoric acid type fuel cell. 2. The method according to claim 1, wherein said alkaline dispersion medium comprises a solution obtained by adding ammonia to pure water. 3. The phosphoric acid type fuel cell according to claim 1, wherein the dispersion slurry is coagulated by adding an acid to the dispersion slurry to make the dispersion slurry acidic. Manufacturing method of electrode. 4. The method according to claim 1, wherein the adhesion of the aggregated slurry to the porous electrode substrate comprises disposing the aggregated slurry on the porous electrode substrate, A method for producing an electrode for a phosphoric acid fuel cell, wherein the method is performed by suction and filtration. 5. The method according to claim 1, wherein the adhesion of the aggregated slurry to the porous electrode substrate is performed by applying the aggregated slurry to the porous electrode substrate. A method for producing an electrode for a phosphoric acid type fuel cell, comprising: