JP4277463B2 - Method for manufacturing electrode for phosphoric acid fuel cell - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing an electrode of a phosphoric acid fuel cell that uses phosphoric acid as an electrolyte to obtain electric energy through an electrochemical reaction.
[0002]
[Prior art]
In a fuel cell, an electrochemical reaction occurs at a three-phase interface of a catalyst (solid), an electrolyte (liquid), and a reaction gas (gas), so it is necessary to form a large number of three-phase interfaces. Therefore, the electrodes arranged on both surfaces of the electrolyte layer are formed by forming a catalyst layer on the carbon porous material so as to also diffuse the reaction gas into the electrolyte layer. In order to ensure this, water repellent polytetrafluoroethylene (PTFE) is added to the catalyst.
[0003]
FIG. 7 is a flowchart showing an example of a conventional method for manufacturing a phosphoric acid fuel cell electrode. FIG. 8 is a schematic diagram showing a basic configuration of a manufacturing apparatus used in the 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 an 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. Next, 1 to 10 g (0.1 to 1 wt%) of a catalyst in which platinum particles are supported on carbon particles is added to the dispersion medium, and the ultrasonic oscillator 2 is used in the stirring tank 1 as shown in FIG. A dispersion (slurry) is obtained by stirring and homogenizer dispersion by a method such as applying ultrasonic waves. At this time, the secondary particle diameter of carbon in the dispersion is set to 1 μm or less on average. Next, a dispersion of PTFE (for example, Du Pont; 30-J) is added to the dispersion. At this time, the amount of PTFE added is desirably 60 to 100% of the weight of carbon in the catalyst. After the addition of PTFE, further measures such as applying ultrasonic waves using the ultrasonic oscillator 2 are taken and the mixture is stirred and homogenized to obtain slurry 3 (FIG. 8 (a)) in which the catalyst and PTFE are well dispersed. Thereafter, a strong acid is dropped into the slurry 3 and mixed to bring the pH to 3 or less. An anionic surfactant rapidly loses its ability as a surfactant in a low pH region, and the charges of the catalyst and PTFE become small. Therefore, the catalyst and PTFE aggregate and settle 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 agitation tank 1 is opened, and the slurry 3 that has been precipitated by adding an acid is mounted on the porous carbon paper 4 that serves as the electrode substrate. 5 is poured into the inside of the carbon paper 4 and sucked and filtered by a suction machine 7 disposed on the opposite surface of the carbon paper 4. In addition, in order to smooth the surface of the filtration electrode, a method of filtering by dividing into several times is adopted. By this suction and filtration, the catalyst layer 8 is formed on the carbon paper 4 as shown in FIG. Subsequently, the acid is removed by opening the valve 6 and pouring pure water 9 into the frame, and suctioning and washing with the suction device 7. Thereafter, moisture is removed by natural drying, followed by firing in a nitrogen atmosphere at 320 to 350 ° C., melting PTFE to impart water repellency, thereby completing the production of the electrode.
[0005]
FIG. 9 is a flow chart showing another example of a conventional method for manufacturing a phosphoric acid fuel cell electrode. FIG. 10 is a schematic diagram showing a basic configuration of a manufacturing apparatus used in this manufacturing method. The feature of this manufacturing method is that, as in the above-described manufacturing method shown in FIG. 7, a slurry prepared by adding an acid and poured is poured onto a porous carbon paper, suctioned and filtered, and then washed with an alkaline solution. There is in point. That is, in this manufacturing method, as shown in FIG. 10A, the valve 6 of the agitation tank 1 is opened, and the inside of the frame 5 in which the slurry 3 that has been precipitated by adding acid is disposed on the carbon paper 4 made of porous material. After forming the catalyst layer 8 on the carbon paper 4 by suction and filtration with a suction machine 7, as shown in FIG. 10 (b), a dilute alkaline solution 12 such as ammonia or ethanolamines is added. The inside of the frame 5 is poured and sucked and washed by the suction machine 7 to remove the surfactant remaining in the catalyst layer 8, and then pure water 9 is poured as shown in FIG. The remaining alkali component is removed by suction and washing by the No. 7. The drying and firing steps after washing are the same as the above-described manufacturing method shown in FIG.
[0006]
[Problems to be solved by the invention]
In the manufacturing method using the suction filtration method as described above, a catalyst layer in which the PTFE particles and the catalyst particles of the water repellent material are well dispersed can be obtained, and the number of manufacturing steps can be reduced. It is extremely effective as a manufacturing method.
Nonetheless, the above manufacturing method is also not sufficient as a manufacturing method of an electrode for a phosphoric acid fuel cell, and further reduction in manufacturing man-hours is required in order to reduce the manufacturing cost. A method for removing moisture from the catalyst layer 8 by heating and drying, and a method for performing a heat press treatment to form a denser and smoother catalyst layer have been studied.
[0007]
However, when heat drying is adopted for removing moisture from the catalyst layer 8 in the above production method, when the moisture present between the agglomerated catalyst particles is removed, the distance between the catalyst particles is reduced by the capillary force, so-called. Mud cracks are likely to occur. FIG. 11 is a cross-sectional view for schematically explaining the occurrence of mud cracks. When the catalyst layer 8 is formed by suction filtration on the carbon paper 4 as shown in FIG. 11 (a) and then dried by heating, the catalyst layer 8 shrinks and cracks and mud cracks as shown in FIG. 11 (b). Will occur. When mud cracks occur in this way, the possibility of cross leaks due to surface irregularities increases.
[0008]
In addition, in the above manufacturing method, when a hot press treatment is added to form a denser and smoother catalyst layer, the molten PTFE adheres to a metal foil or the like to be inserted as a press plate or a protective layer. Peeling phenomenon tends to occur. FIG. 12 is a cross-sectional view schematically illustrating the occurrence of peeling. When the catalyst layer 8 is formed on the carbon paper 4 by suction filtration as shown in FIG. 12 (a) and then hot pressing is performed, a part 8a of the catalyst layer 8 is pressed as shown in FIG. 12 (b). It becomes easy for the situation which it adheres to the board 20 and peels from a porous material. When peeling occurs in this manner, the effective area is reduced and the battery characteristics are impaired.
[0009]
That is, in the manufacturing method of the phosphoric acid fuel cell electrode using the suction filtration method, the process can be shortened by incorporating a heat drying process, and further, a denser and smoother catalyst layer can be formed by introducing a hot press treatment method. However, as described above, in the conventional manufacturing method, there is a high risk of lowering the battery characteristics, and the yield of the electrodes is reduced.
[0010]
The present invention has been made in consideration of the problems of the conventional method for manufacturing an electrode for a phosphoric acid fuel cell as described above, and an object of the present invention is to generate damage due to heat drying and further heat press treatment. It is an object of the present invention to provide a manufacturing method capable of manufacturing a high-quality phosphoric acid fuel cell electrode at a low cost in a short time.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, in the present invention,
Phosphate-type fuel cell electrode
(1) A catalyst layer forming step of forming a catalyst layer by suction filtration of the first slurry in which the catalyst particles and water repellent material particles are dispersed into a carbon porous material; and suction filtration of the second slurry in which the SiC particles are dispersed. Te and SiC layer forming step of forming a SiC layer on the catalyst layer, the phosphoric acid fuel cell electrode comprising a catalyst layer firing step of firing the catalyst layer in a state that the SiC layer is formed on the upper surface It shall be manufactured using a manufacturing method.
In the manufacturing method described above, a SiC layer removing step for removing the SiC layer from the catalyst layer after heating and firing is further provided.
[0012]
(2) Furthermore, the SiC particles dispersed in the second slurry of (1) are composed of a mixture of SiC particles having a particle size of 0.3 to 3 μm and SiC particles having a particle size of 7 to 15 μm. To do.
(3) In addition, an alkaline solution such as an ammonia solution or a triethanolamine solution is used as a dispersion solvent for the SiC particles forming the second slurry of (1) or (2).
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to examples.
<Example 1>
FIG. 1 is a flowchart 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 this manufacturing method. The feature of the method for manufacturing an electrode for a phosphoric acid fuel cell according to the present 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 process for forming the SiC layer is incorporated, and further, a process for removing the SiC layer after heating and drying is incorporated.
[0014]
That is, in this production method, as in the conventional example, 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 an anionic surfactant. Next, 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 applied by an ultrasonic oscillator 2 in the stirring tank 1 as shown in FIG. Dispersion is obtained by dispersing with a homogenizer. Next, a dispersion of PTFE is added to this dispersion, and an ultrasonic wave is applied and stirred to prepare slurry (first slurry) 3 in which the catalyst and PTFE are well dispersed. Thereafter, a strong acid is dropped and mixed in the slurry 3 to adjust the pH to 3 or less, the ability as a surfactant is removed, and the catalyst and PTFE are aggregated and settled without being separated from each other. Next, this slurry 3 is poured into the inside of a frame 5 mounted on a porous carbon paper 4 which is a base material of an electrode, and is divided into several times by a suction machine 7 arranged on the opposite surface of the carbon paper 4. Then, suction and filtration are performed to form a catalyst layer 8 having a smooth surface. Subsequently, as shown in FIG. 2B, pure water 9 is poured into the frame, and is sucked and washed with a suction machine 7 to remove the acid.
[0015]
Next, as shown in FIG. 2 (c), 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 sucked and filtered by the suction device 7 to form the SiC layer 11. Form.
Thereafter, after moisture and surfactant are removed by heat drying / baking at 240 to 280 ° C. in a nitrogen atmosphere, a treatment is further carried out at 320 to 350 ° C. to melt PTFE and impart water repellency. In addition, you may perform a hot press in the case of baking.
[0016]
Thereafter, the electrode layer is completed by removing the SiC layer 11. Since the SiC layer 11 does not contain a binder, it is easily removed from the electrode after heat treatment by brushing or pure water cleaning.
In the electrode having the conventional structure, when the catalyst layer 8 formed by suction and filtration is heated and dried / fired, the distance between the catalyst particles is reduced and mud cracks are likely to occur. In the electrode in which the SiC layer 11 is formed on the layer 8, since the SiC forms a dense layer, it acts to resist this when the distance between the catalyst particles is reduced. Occurrence is greatly reduced. Therefore, in the electrode of this configuration, it is possible to incorporate a heating / drying / firing process in the manufacturing process, and the manufacturing time is shortened compared to the conventional method, and the electrode can be manufactured at a low cost.
[0017]
The SiC particles dispersed in the pure water 10 are mixed by mixing 50 to 70% SiC particles having a particle size of 0.3 to 3 μm and 30 to 50% SiC particles having a particle size of 7 to 15 μm. If used, suction filtration is performed quickly, and the SiC layer formed by filtration becomes dense.
<Example 2>
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. The feature of the method for manufacturing an electrode for a phosphoric acid fuel cell of the present 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 cleaning with pure water, a process for forming a SiC layer is incorporated, and a process for removing the SiC layer is incorporated after a heat drying process and a heat press process.
[0018]
That is, in the present manufacturing method, as in the conventional electrode manufacturing method shown in FIG. 9, first, as shown in FIG. 4 (a), the valve 6 of the stirring tank 1 is opened and acid is added to cause precipitation. The slurry 3 is poured into the inside of a frame 5 disposed on a carbon paper 4 made of a porous material, and a catalyst layer 8 is formed on the carbon paper 4 by suction and filtration with a suction machine 7. As shown in FIG. 4 (b), the diluted alkaline solution 12 is poured into the frame 5, and is sucked and washed by the suction device 7 to remove the surfactant remaining in the catalyst layer 8, and then, FIG. As shown in FIG. 4 (c), pure water 9 is poured and sucked and washed by the suction device 7 to remove the remaining alkaline components.
[0019]
Next, as shown in FIG. 4 (d), 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, sucked and filtered by the suction machine 7, Layer 11 is formed.
Thereafter, in the same manner as in Example 1, heat drying / firing at 240 to 280 ° C. in a nitrogen atmosphere is performed to remove moisture and surfactant. Subsequently, in order to melt PTFE and impart water repellency, a heat baking treatment is performed at 320 to 350 ° C. by hot pressing. After these heat-firing treatments, the fabrication of the electrode is completed by removing the SiC layer by brushing or pure water cleaning.
[0020]
In the electrode manufactured as in this example, since the SiC layer 11 is formed on the catalyst layer 8 as in Example 1, the generation of cracks is small even if a heat drying / firing process is incorporated. Compared to this, the manufacturing time is shortened, and the electrode can be manufactured at low cost. Further, 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.
[0021]
The SiC particles dispersed in the pure water 10 are mixed by mixing 50 to 70% SiC particles having a particle size of 0.3 to 3 μm and 30 to 50% SiC particles having a particle size of 7 to 15 μm. If used, as in Example 1, suction filtration is performed quickly, and the SiC layer formed by filtration becomes dense.
<Example 3>
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. The feature of the method for manufacturing an electrode for a phosphoric acid fuel cell of this example is that, in the conventional electrode manufacturing method shown in FIG. 7, after forming the catalyst layer 8 on the carbon paper 4 by suction filtration, an alkaline solution Including the steps of cleaning and forming the SiC layer, and the step of removing the SiC layer after the heat-drying process and the hot press process.
[0022]
That is, in this production method, first, 3 to 10 g of an anionic surfactant is added to 1000 g of pure water and stirred to prepare a dispersion medium containing about 0.3 to 1 wt% of an anionic surfactant, To this dispersion medium, 1 to 10 g of a catalyst in which platinum particles are supported on carbon particles is added, and as shown in FIG. 6A, ultrasonic waves are applied by an ultrasonic oscillator 2 in a stirring tank 1 and dispersed by stirring and homogenizer. Obtain a liquid. Next, a dispersion of PTFE is added to the dispersion, and an ultrasonic wave is applied and stirred to prepare a slurry (first slurry) 3 in which the catalyst and PTFE are well dispersed, and then a strong acid is added to the slurry 3. The catalyst is dropped and mixed to adjust the pH to 3 or less, and the catalyst and PTFE are aggregated and settled without being separated. Next, this slurry 3 is poured into the inside of a frame 5 mounted on a porous carbon paper 4 which is a base material of an electrode, and is divided into several times by a suction machine 7 arranged on the opposite surface of the carbon paper 4. Then, suction and filtration are performed to form a catalyst layer 8 having a smooth surface.
[0023]
Next, as shown in FIG. 6 (b), a diluted alkaline solution 13 in which 2 to 10 wt% of SiC particles are dispersed is poured onto the catalyst layer 8 inside the frame 5, and sucked and filtered by the suction machine 7. The surfactant remaining in the catalyst layer 8 is removed by washing with the diluted alkaline solution 13 and the SiC layer 11 is formed on the catalyst layer 8.
Next, as shown in FIG. 6 (c), pure water 9 is poured into the frame 5, and suction and filtration are performed by the suction device 7 to remove the alkali component remaining in the electrode layer.
[0024]
Thereafter, in the same manner as in Example 2, heat drying / baking at 240 to 280 ° C. in a nitrogen atmosphere is performed to remove moisture and surfactant, and then heat is applied to melt PTFE to give water repellency. A baking process is performed at 320 to 350 ° C. by pressing. After these heat-firing treatments, removal of the SiC layer by brushing or pure water cleaning completes the production of the electrode.
[0025]
In the electrode manufactured as in this example, the SiC layer 11 is formed on the catalyst layer 8 in the same manner as in Example 1 or Example 2. Therefore, cracks are not generated even if the heating / drying / firing process is incorporated. Therefore, the manufacturing time is shortened compared to the conventional case, and the electrode can be manufactured at a low cost. Also, in this example, since heat press 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.
[0026]
As SiC particles dispersed in the diluted alkaline solution 13, 50 to 70% of SiC particles having a particle size of 0.3 to 3 μm and 30 to 50% of SiC particles having a particle size of 7 to 15 μm are mixed. If used, suction filtration is performed quickly, and the SiC layer formed by filtration becomes dense. As the alkaline solution for dispersing the SiC particles, an ammonia solution or a triethanolamine solution that is also used for the alkaline solution cleaning in Example 2 is suitable.
[0027]
【The invention's effect】
As mentioned above, according to the present invention,
A catalyst layer forming step of forming a catalyst layer by suction filtration of the first slurry in which the catalyst particles and the water repellent material particles are dispersed into the carbon porous material, and a catalyst layer by suction filtration of the second slurry in which the SiC particles are dispersed. The SiC layer formation process that forms the SiC layer on top, the catalyst layer heating and firing process that heats and fires the catalyst layer with the SiC layer formed on the top surface, and the SiC layer removal process that removes the SiC layer from the catalyst layer after heat and firing Since the phosphoric acid fuel cell electrode was manufactured using the manufacturing method including the above, it was possible to manufacture a high quality phosphoric acid fuel cell electrode with a high yield and at a low cost in a short time.
[Brief description of the drawings]
FIG. 1 is a flowchart showing a manufacturing method of a phosphoric acid fuel cell electrode 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 manufacturing method of the first embodiment. FIG. 3 is a flowchart showing a method for manufacturing a phosphoric acid fuel cell electrode according to a second embodiment of the present invention. FIG. 4 shows a basic configuration of a manufacturing apparatus used in the manufacturing method according to the second embodiment. Schematic diagram [FIG. 5] A flow chart showing a method of manufacturing a phosphoric acid fuel cell electrode according to a third embodiment of the present invention. [FIG. 6] A basic configuration of a manufacturing apparatus used in the manufacturing method of the third embodiment. Fig. 7 is a flow diagram 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 manufacturing method of Fig. 7. FIG. 10 is a flowchart showing another example of a conventional method for manufacturing a phosphoric acid fuel cell electrode. Fig. 11 is a schematic diagram showing the basic configuration of a manufacturing apparatus used in the manufacturing process. Fig. 11 is a cross-sectional view schematically explaining the generation of mud cracks accompanying heat drying in a conventional example. Cross-sectional view that schematically explains the occurrence of the phenomenon [Explanation 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 alkaline solution 13 Dilute alkaline solution (SiC particle dispersion)

Claims (5)

A catalyst layer forming step of forming a catalyst layer by suction filtration of the first slurry in which the catalyst particles and the water repellent material particles are dispersed into the carbon porous material, and a catalyst layer by suction filtration of the second slurry in which the SiC particles are dispersed. and SiC layer forming step of forming a SiC layer thereon, the manufacturing method of the phosphoric acid fuel cell electrode comprising a catalyst layer firing step of firing the catalyst layer in a state that the SiC layer is formed on the upper surface, a. From the catalyst layer after heating and firing,  SiC Remove layer  SiC The manufacturing method of the electrode for phosphoric acid fuel cells of Claim 1 including a layer removal process. The SiC particles dispersed in the second slurry used in the SiC layer forming step are composed of a mixture of SiC particles having a particle size of 0.3 to 3 μm and SiC particles having a particle size of 7 to 15 μm. The manufacturing method of the electrode for phosphoric acid fuel cells in any one of Claim 1 or 2. 4. The phosphoric acid fuel cell electrode according to claim 1, wherein a dispersion solvent of SiC particles forming the second slurry used in the SiC layer forming step is an alkaline solution. 5. Production method. The method for producing an electrode for a phosphoric acid fuel cell according to claim 4, wherein the alkaline solution is either an ammonia solution or a triethanolamine solution.