JP2002373664A - Method for producing electrode for phosphoric acid type fuel cell - Google Patents

Abstract

(57) [Problem] To provide a manufacturing method capable of manufacturing a high quality phosphoric acid fuel cell electrode in a short time and at low cost. A catalyst layer is formed by suction-filtering a slurry in which catalyst particles and water-repellent material (PTFE) particles are dispersed on a porous carbon material, and then suction-filtering a second slurry in which SiC particles are dispersed to form a catalyst. After the SiC layer is formed on the layer, the PTFE is melted by heating, drying and baking to give water repellency, and then the SiC layer is removed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing an electrode of a phosphoric acid type fuel cell which obtains electric energy by an electrochemical reaction using phosphoric acid as an electrolyte.

[0002]

2. Description of the Related Art In a fuel cell, since an electrochemical reaction occurs at a three-phase interface between a catalyst (solid), an electrolyte (liquid), and a reaction gas (gas), it is necessary to form many three-phase interfaces. For this reason, the electrodes arranged on both sides of the electrolyte layer are formed by forming a catalyst layer on a porous carbon material so as to also play a role of diffusing a reaction gas into the electrolyte layer, and particularly, pores serving as gas passages. In order to ensure a good water repellency, polytetrafluoroethylene (PTFE) is added to the catalyst.

FIG. 7 is a flowchart showing an example of a conventional method for manufacturing an electrode for a phosphoric acid fuel cell. FIG. 8 is a schematic diagram showing a basic configuration of a manufacturing apparatus used in the present manufacturing method. In this production method, first, 3 to 10 g of an anionic surfactant is added to 1000 g of pure water and stirred to obtain a dispersion medium containing about 0.3 to 1 wt% of the anionic surfactant. The anionic surfactant used at this time is preferably a sulfonic acid-based, polycarboxylic acid-based, phosphoric acid-based, or amino acid-based surfactant, and particularly, an amino acid-based or polycarboxylic acid-based surfactant is preferred. It is suitable. Next, 1 to 10 g of a catalyst in which platinum particles are supported on carbon particles in this dispersion medium (0.1 to 1 g)
(% by weight), and the mixture is stirred and homogenized by a method such as application of ultrasonic waves using an ultrasonic oscillator 2 in a stirring tank 1 as shown in FIG. 8A to obtain a dispersion (slurry). . At this time, the secondary particle diameter of carbon in the dispersion is adjusted to be 1 μm or less on average. Next, a PTFE dispersion (for example, Du Pont; 30-
J) is added. At this time, the addition amount of PTFE is desirably 60 to 100% of the weight of carbon in the catalyst. P
After the addition of TFE, measures such as application of ultrasonic waves using the ultrasonic oscillator 2 are taken and the mixture is stirred and homogenized to obtain a slurry 3 (FIG. 8A) in which the catalyst and PTFE are well dispersed. Thereafter, a strong acid is dropped into the slurry 3 and mixed to adjust the pH to 3 or less. In the low pH region, the anionic surfactant rapidly loses its ability as a surfactant and the charge of the catalyst and PTFE is reduced, so that the catalyst and PTFE aggregate and sediment without being separated from each other. As the strong acid, phosphoric acid, sulfuric acid, nitric acid, hydrochloric acid and the like are used, and phosphoric acid and nitric acid are particularly preferable.

[0004] Next, as shown in FIG. 8 (a), the valve 6 of the stirring tank 1 is opened, and the slurry 3 precipitated by adding an acid is placed on a porous carbon paper 4 serving as a base material of an electrode. Pour into the inside of the mounted frame 5 and use carbon paper 4
Is suctioned and filtered by a suction machine 7 arranged on the opposite side of the above. In addition, in order to smooth the surface of the filtration electrode, a method of performing filtration by dividing into several times is adopted. By this suction and filtration,
As shown in FIG. 8B, the catalyst layer 8 is formed on the carbon paper 4. Subsequently, the valve 6 is opened, the pure water 9 is poured into the inside of the frame, and the acid is removed by sucking and washing with the suction machine 7. Then, after removing water by natural drying, baking is performed at 320 to 350 ° C. in a nitrogen atmosphere to melt PTFE and impart water repellency, thereby completing the production of the electrode.

FIG. 9 is a flow chart showing another example of a conventional method for manufacturing an electrode for a phosphoric acid fuel cell. FIG. 10 is a schematic diagram showing a basic configuration of a manufacturing apparatus used in the present manufacturing method. The feature of the present manufacturing method is that, similarly to the above-described manufacturing method shown in FIG. 7, an acid is added to the slurry and the slurry is poured onto porous carbon paper, suctioned, filtered, and then washed with an alkaline solution. There is in the point. That is, in this manufacturing method, as shown in FIG. 10A, the valve 6 of the stirring tank 1 is opened, and the slurry 3 in which acid is added and settled is placed inside the frame 5 in which the slurry 3 is placed on the porous carbon paper 4. To form a catalyst layer 8 on the carbon paper 4 by suction and filtration with a suction machine 7, and then, as shown in FIG. 10B, a diluted alkaline solution 1 such as ammonia or ethanolamine.
2 was poured into the inside of the frame 5, and the surfactant remaining in the catalyst layer 8 was removed by suction and washing by the suction device 7, and then, as shown in FIG. The remaining alkali components are removed by suction and washing by the suction device 7. The drying and firing steps after washing are the same as those in the above-described manufacturing method shown in FIG.

[0006]

According to the production method using the suction filtration method as described above, a catalyst layer in which PTFE particles of a water-repellent material and catalyst particles are well dispersed can be obtained, and the number of production steps can be reduced. Therefore, it is extremely effective as a method for producing an electrode for a phosphoric acid type fuel cell. Nevertheless, the above-mentioned production method is not sufficient as a method for producing an electrode for a phosphoric acid fuel cell, and further reduction in the number of production steps is required to reduce the production cost. Later catalyst layer 8
A method of removing water by heating and drying, and a method of performing a hot press treatment to form a denser and smoother catalyst layer are being studied.

However, in the above-described manufacturing method, when heating and drying are employed to remove water from the catalyst layer 8, when moisture present between the aggregated catalyst particles is removed, the distance between the catalyst particles is reduced by the capillary force. Therefore, a so-called mud crack easily occurs. FIG. 11 is a cross-sectional view schematically illustrating generation of a mud crack. FIG.
After forming the catalyst layer 8 by suction filtration on the carbon paper 4 as shown in FIG. 1A, the catalyst layer 8 shrinks and breaks as shown in FIG. appear. When mud cracks occur in this manner, the possibility of cross leakage occurring due to surface irregularities increases.

In the above-mentioned production method, if a hot press treatment is added to form a denser and smoother catalyst layer, the molten PTFE adheres to a press plate or a metal foil inserted as a protective layer, The phenomenon of peeling from the porous material is likely to occur. FIG. 12 is a cross-sectional view schematically illustrating the occurrence of peeling. After forming the catalyst layer 8 by suction filtration on the carbon paper 4 as shown in FIG. 12A, a hot press treatment is performed, and a part 8a of the catalyst layer 8 is pressed as shown in FIG. It easily adheres to the plate 20 and peels off from the porous material. When such peeling occurs, the effective area is reduced and battery characteristics are impaired.

That is, in the method for producing an electrode for a phosphoric acid type fuel cell using a suction filtration method, the steps are shortened by incorporating a heating and drying step, and more dense and smooth by introducing a hot press treatment method. Although formation of a catalyst layer and the like are expected, in the conventional manufacturing method as described above, the risk of lowering battery characteristics is increased, and the yield of electrodes is reduced.

The present invention has been made in consideration of the problems of the conventional method for manufacturing an electrode for a phosphoric acid type fuel cell as described above, and an object of the present invention is to carry out heat drying and heat pressing. An object of the present invention is to provide a manufacturing method capable of manufacturing a high-quality phosphoric acid fuel cell electrode at a low cost in a short time by suppressing the occurrence of damage.

[0011]

In order to achieve the above object, in the present invention, an electrode for a phosphoric acid type fuel cell is provided by: (1) a first slurry in which catalyst particles and water repellent particles are dispersed; A catalyst layer forming step of forming a catalyst layer by suction filtration on a porous carbon material, a SiC layer forming step of forming a SiC layer on the catalyst layer by suction filtering a second slurry in which SiC particles are dispersed, and Manufactured using a method for manufacturing a phosphoric acid fuel cell electrode that includes a catalyst layer heating and firing step in which the catalyst layer on which the SiC layer is formed is heated and fired, and a SiC layer removing step in which the SiC layer is removed from the heated and fired catalyst layer I decided to.

(2) Further, the SiC particles dispersed in the second slurry of the above (1) are mixed with SiC particles having a particle size of 0.3 to 3 μm.
It is composed of a mixture of particles and SiC particles having a particle size of 7 to 15 μm. (3) Further, an alkali solution, for example, an ammonia solution or a triethanolamine solution is used as a dispersion solvent of the SiC particles forming the second slurry of the above (1) or (2).

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to embodiments. <Embodiment 1> FIG. 1 is a flow chart showing a method for manufacturing an electrode for a phosphoric acid fuel cell according to a first embodiment of the present invention. FIG. 2 is a schematic diagram showing a basic configuration of a manufacturing apparatus used in the present manufacturing method. The feature of the method for manufacturing the electrode for the phosphoric acid type fuel cell of this embodiment is that the catalyst layer 8 is formed on the carbon paper 4 by suction filtration and the pure water cleaning is performed in the conventional electrode manufacturing method shown in FIG. After that, a step of forming a SiC layer is incorporated, and further, a step of removing the SiC layer after heating and drying is incorporated.

That is, in this production method, 3 to 10 g of an anionic surfactant is first added to 1000 ml of pure water as in the conventional example.
g and stirring to add about 0.3 to 1 anionic surfactant.
A dispersion medium containing wt.% is prepared, and then 1 to 10 g of a catalyst in which platinum particles are supported on carbon particles is added to the dispersion medium, and an ultrasonic wave is generated by an ultrasonic oscillator 2 in a stirring tank 1 as shown in FIG. Is applied and the mixture is stirred and homogenized to obtain a dispersion. Next, a PTFE dispersion is added to this dispersion, and ultrasonic waves are applied and stirred to produce a slurry (first slurry) 3 in which the catalyst and PTFE are well dispersed. Thereafter, a strong acid is dropped and mixed into the slurry 3 to adjust the pH to 3 or less, the ability as a surfactant is removed, and the catalyst and PTFE are removed.
Are aggregated and settled without being separated from each other.
Next, the slurry 3 is poured into a frame 5 mounted on a porous carbon paper 4 serving as a base material of an electrode, and divided into several times by a suction device 7 arranged on the opposite surface of the carbon paper 4. To form a catalyst layer 8 having a smooth surface. Subsequently, as shown in FIG. 2B, pure water 9 is poured into the inside of the frame, suctioned by the suction device 7 and washed to remove the acid.

Next, as shown in FIG.
1010 wt% dispersed pure water 10 is poured onto the catalyst layer 8 inside the frame 5, suctioned and filtered by the suction device 7, and the SiC layer 1
Form one. Thereafter, after removing the water and the surfactant by heating / drying / baking at 240 to 280 ° C in a nitrogen atmosphere, a process of baking at 320 to 350 ° C to melt the PTFE to give water repellency is performed. Note that hot pressing may be performed during firing.

After that, the fabrication of the electrode is completed by removing the SiC layer 11. Since the SiC layer 11 does not contain a binder, it can be easily removed from the electrode after the heat treatment by brushing or pure water cleaning. In the electrode having the conventional configuration, when the catalyst layer 8 formed by suction and filtration was heated and dried / fired, the distance between the catalyst particles was reduced, and the possibility of generating a mud crack was high. In the electrode in which the SiC layer 11 is formed on the layer 8, since the SiC forms a dense layer, when the distance between the catalyst particles is reduced, the catalyst particles have a function of resisting the distance. The occurrence will be greatly reduced. Therefore, in the electrode of this configuration, it is possible to incorporate a heating / drying / sintering step into the manufacturing process, so that the manufacturing time is shortened as compared with the related art, and the electrode can be manufactured at low cost.

As the SiC particles dispersed in the pure water 10, SiC particles having a particle diameter of 0.3 to 3 μm are 50 to 70 μm.
%, And a mixture of SiC particles having a particle size of 7 to 15 μm at a ratio of 30 to 50%, suction filtration is rapidly performed, and the SiC layer formed by the filtration becomes dense. <Embodiment 2> FIG. 3 is a flowchart showing a method of manufacturing an electrode for a phosphoric acid fuel cell according to a second embodiment of the present invention. FIG. 4 is a schematic diagram showing a basic configuration of a manufacturing apparatus used in the present manufacturing method. A feature of the method for manufacturing an electrode for a phosphoric acid type fuel cell of this embodiment is that the catalyst layer 8 is formed on the carbon paper 4 by suction filtration in the conventional electrode manufacturing method shown in FIG. After that, a step of forming a SiC layer after washing with pure water and a step of removing the SiC layer after a heating drying step and a hot pressing step are incorporated.

That is, in this manufacturing method, as shown in FIG. 4A, first, as shown in FIG. 4A, the valve 6 of the stirring tank 1 is opened, and the acid is added. The precipitated slurry 3 is poured into a frame 5 arranged on a porous carbon paper 4, and is suctioned and filtered by a suction machine 7 to form a catalyst layer 8 on the carbon paper 4. Thereafter, as shown in FIG. 4 (b), the diluted alkaline solution 12 is poured into the inside of the frame 5, suctioned and washed by the suction device 7, and the surfactant remaining in the catalyst layer 8 is removed. Then, as shown in FIG. 4 (c), pure water 9 is poured, suctioned and washed by a suction device 7, and
Remove the remaining alkaline components.

Next, as shown in FIG. 4D, pure water 10 in which 2 to 10 wt% of SiC particles are dispersed is poured onto the catalyst layer 8 inside the frame 5, and is suctioned and filtered by the suction device 7. hand,
The SiC layer 11 is formed. Thereafter, as in the case of Example 1, heating and drying / baking at 240 to 280 ° C. in a nitrogen atmosphere is performed to remove water and the surfactant. Subsequently, 320-35 by hot pressing to melt the PTFE and make it water repellent.
Heat and bake at 0 ° C. After these heating and baking treatments, the electrode is completed by removing the SiC layer by brushing or pure water washing.

In the electrode manufactured as in the present embodiment, the SiC layer 11 is formed on the catalyst layer 8 as in the first embodiment. , The production time is shorter than before,
The electrode can be manufactured at low cost. Further, in the present embodiment, a hot press is used in the process of melting PTFE to impart water repellency, so that a dense and smooth catalyst layer can be obtained, and excellent battery characteristics can be obtained.

As the SiC particles dispersed in the pure water 10, SiC particles having a particle diameter of 0.3 to 3 μm are 50 to 70 μm.
%, And SiC particles having a particle size of 7 to 15 μm are mixed and used at a ratio of 30 to 50%, as in Example 1, suction filtration is rapidly performed, and a SiC layer formed by the filtration is formed. Become elaborate. <Embodiment 3> FIG. 5 is a flowchart showing a method of manufacturing an electrode for a phosphoric acid fuel cell according to a third embodiment of the present invention. FIG. 6 is a schematic diagram showing a basic configuration of a manufacturing apparatus used in the present manufacturing method. A feature of the method for manufacturing an electrode for a phosphoric acid type fuel cell of this embodiment is that, in the conventional method for manufacturing an electrode shown in FIG. 7, after forming a catalyst layer 8 on carbon paper 4 by suction filtration, an alkaline solution Cleaning and SiC
The point is that the process for forming the layer is incorporated, and the process for removing the SiC layer after the heating and drying process and the hot pressing process is also incorporated.

That is, in this manufacturing method, first,
Add 3 to 10 g of anionic surfactant to 1000 g of pure water,
By stirring, a dispersion medium containing about 0.3 to 1 wt% of an anionic surfactant is prepared. Then, 1 to 10 g of a catalyst in which platinum particles are supported on carbon particles is added to the dispersion medium, and the dispersion medium shown in FIG. As described above, an ultrasonic wave is applied from the ultrasonic oscillator 2 in the stirring tank 1 to stir and homogenize to obtain a dispersion. Next, a dispersion of PTFE is added to this dispersion, and the mixture is stirred by applying ultrasonic waves to prepare a slurry (first slurry) 3 in which the catalyst and PTFE are well dispersed. The catalyst and PTF were dropped and mixed to adjust the pH to 3 or less.
Aggregate and sediment without separating E. Next, the slurry 3 is poured into a frame 5 mounted on a porous carbon paper 4 serving as a base material of an electrode, and divided into several times by a suction device 7 arranged on the opposite surface of the carbon paper 4. To form a catalyst layer 8 having a smooth surface.

Next, as shown in FIG. 6B, a diluted alkaline solution 13 containing 2 to 10 wt% of SiC particles is
The surfactant remaining in the catalyst layer 8 is washed and removed with a dilute alkaline solution 13 by pouring onto the catalyst layer 8 inside the catalyst layer 8 and suctioning and filtering with a suction device 7. The SiC layer 11 is formed thereon. Next, as shown in FIG. 6 (c), pure water 9 is poured into the inside of the frame 5, and the alkali component remaining in the electrode layer is removed by suction and filtration by the suction device 7.

Then, as in Example 2, a nitrogen atmosphere,
Heat drying / baking at 240 to 280 ° C to remove moisture and surfactant, followed by heat baking to 320 to 350 ° C by hot pressing to melt PTFE and make it water repellent. . After these heating and baking treatments, the electrode is completed by removing the SiC layer by brushing or washing with pure water.

In the electrode manufactured as in the present embodiment, SiC is formed on the catalyst layer 8 in the same manner as in the first or second embodiment.
Since the layer 11 is formed, the generation of cracks is small even when the heating / drying / firing step is incorporated, the production time is reduced as compared with the conventional case, and the electrode can be manufactured at low cost. Also, in this example, since hot pressing is used in the process of melting PTFE to impart water repellency, a dense and smooth catalyst layer can be obtained, and excellent battery characteristics can be obtained.

As the SiC particles dispersed in the diluted alkaline solution 13, 50 to 70% of SiC particles having a particle diameter of 0.3 to 3 μm and 30 to 30% of SiC particles having a particle diameter of 7 to 15 μm are used.
When used by mixing at a ratio of 50%, suction filtration is performed quickly and the SiC layer formed by filtration becomes dense. Further, as the alkaline solution for dispersing the SiC particles, an ammonia solution or a triethanolamine solution which is also used for washing the alkaline solution in Example 2 is preferable.

[0027]

As described above, according to the present invention, a catalyst layer forming step of forming a catalyst layer by suction-filtering a first slurry in which catalyst particles and water-repellent material particles are dispersed into a carbon porous material; A step of forming a SiC layer on the catalyst layer by suction-filtering the second slurry in which the SiC particles are dispersed;
A catalyst layer heating and baking step for heating and baking the catalyst layer on which the SiC layer has been formed, and SiC for removing the SiC layer from the catalyst layer after baking.
Since the phosphoric acid fuel cell electrode is manufactured using the manufacturing method including the layer removing step, a high quality phosphoric acid fuel cell electrode can be manufactured at a high yield and at a low cost in a short time. It became.

[Brief description of the drawings]

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

FIG. 2 is a schematic diagram illustrating a basic configuration of a manufacturing apparatus used in the manufacturing method according to the first embodiment.

FIG. 3 is a flowchart showing a method for manufacturing an electrode for a phosphoric acid fuel cell according to a second embodiment of the present invention.

FIG. 4 is a schematic diagram showing a basic configuration of a manufacturing apparatus used in the manufacturing method according to the second embodiment.

FIG. 5 is a flowchart showing a method for manufacturing a phosphoric acid fuel cell electrode according to a third embodiment of the present invention.

FIG. 6 is a schematic diagram showing a basic configuration of a manufacturing apparatus used in the manufacturing method according to the third embodiment.

FIG. 7 is a flowchart showing an example of a conventional method for producing an electrode for a phosphoric acid fuel cell.

FIG. 8 is a schematic diagram showing a basic configuration of a manufacturing apparatus used in the manufacturing method of FIG. 7;

FIG. 9 is a flow chart showing another example of a conventional method for producing a phosphoric acid fuel cell electrode.

10 is a schematic diagram showing a basic configuration of a manufacturing apparatus used in the manufacturing method of FIG.

FIG. 11 is a cross-sectional view schematically illustrating generation of a mud crack accompanying heating and drying in a conventional example.

FIG. 12 is a cross-sectional view schematically illustrating occurrence of peeling due to hot press processing in a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Stirring tank 2 Ultrasonic oscillator 3 Slurry 4 Carbon paper 5 Frame 6 Valve 7 Suction machine 8 Catalyst layer 9 Pure water 10 Pure water (SiC particle dispersion) 11 SiC layer 12 Dilute alkali solution 13 Dilute alkali solution (SiC particle dispersion)

Claims (4)

[Claims] 1. A catalyst layer forming step of forming a catalyst layer by suction-filtering a first slurry in which catalyst particles and water-repellent material particles are dispersed on a porous carbon material, and suctioning a second slurry in which SiC particles are dispersed. A SiC layer forming step of filtering and forming an SiC layer on the catalyst layer, a catalyst layer heating and firing step of heating and firing the catalyst layer having the SiC layer formed on the upper surface, and a SiC layer obtained by heating and firing the catalyst layer.
A method for producing an electrode for a phosphoric acid type fuel cell, comprising a step of removing an SiC layer. 2. The method according to claim 1, wherein the SiC particles dispersed in the second slurry used in the SiC layer forming step have a particle size of 0.3 to 3 μm.
2. The method for producing an electrode for a phosphoric acid fuel cell according to claim 1, comprising a mixture of the above-mentioned SiC particles and SiC particles having a particle size of 7 to 15 μm. 3. 3. The phosphoric acid-type fuel according to claim 1, wherein the dispersion solvent of the SiC particles forming the second slurry used in the step of forming the SiC layer is an alkaline solution. A method for manufacturing a battery electrode. 4. The method according to claim 3, wherein said alkaline solution is one of an ammonia solution and a triethanolamine solution.