JPH0520871B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field to Which the Invention Pertains] The present invention relates to a fuel cell that operates using molten carbonate as an electrolyte, and particularly to a method for manufacturing a fuel electrode (anode) incorporated in this fuel cell. [Prior art and its problems] Molten carbonate fuel cells (MCFC in the following section)
(hereinafter referred to as "anode") has a high operating temperature and uses highly corrosive molten carbonate, so the electrode materials used for the fuel electrode (hereinafter referred to as anode) and oxidation electrode (hereinafter referred to as cathode) also have various performance requirements. It is imposed. The characteristics required for the anode electrode are summarized as follows. (1) Stable in gas atmosphere. (2) High heat resistance, especially high cleave strength. (3) Ability to react with gas without sudden electrolyte inflow. (4) High electrical conductivity. (5) It must be inexpensive. Conventionally, porous Ni electrode plates have been widely used for MCFC anodes. This is because Ni has a good balance of corrosion resistance and conductivity, and good powder is easily available, and porous electrode plates are relatively easy to manufacture. Normally, porous Ni electrode plates use carbonyl nickel powder with a particle size of 3 to 7 μm, which is filled into a graphite mold with the desired size and shape, and heated at a temperature of about 650° to 1000°C in a reducing atmosphere. Manufactured by sintering in a range. The desired pore volume (porosity), average pore diameter, or pore size distribution for the anode electrode of MCFC are determined experimentally, but these mainly depend on the porosity of the electrolyte plate and the operating conditions of the battery. . In order to obtain good battery characteristics,
The porosity, pore size, etc. should be such that enough electrolyte flows from the electrolyte plate into the electrode to carry out the reaction, but not so much that it prevents rapid diffusion of the reaction gas within the electrode. The electrode is required to have the following properties. Generally speaking, to satisfy the above conditions, the porosity of the porous electrode plate is 60 to 80%, the average pore diameter is 1 to 10 μm (preferably 4 to 7 μm), and the porous Ni electrode plate is almost satisfies these requirements. However, the creep strength of porous Ni electrode plates is low, so sintering progresses over time during battery operation, resulting in a decrease in porosity and surface area, which deteriorates MCFC battery performance. ing. [Object of the Invention] An object of the present invention is to provide a method for manufacturing an anode electrode for MCFC that has excellent sintering resistance and allows easy enlargement of the electrode. [Summary of the Invention] According to the present invention, this purpose is to mix Ni powder and wood pulp in water to form an aqueous slurry suitable for papermaking, add a coagulant to this, and make the powder adsorbed and aggregated by the pulp, thereby producing papermaking. After the metal mesh is pressed onto the plate-shaped molded product obtained by this process, it is heated in an oxidizing atmosphere to burn off and scatter the wood pulp, and then the metal oxide produced by the heating is reduced. This is accomplished by heating the Ni powder in a high-temperature reducing atmosphere to sinter it. [Embodiments of the Invention] The Ni powder used in the present invention may be any commercially available electrolytic powder or carbonyl nickel powder, but in order to improve the electrochemical properties when used as an electrode, finer powder ( Particle size 1~10μ
m) is preferred. In addition, there are various types of pulp used to adsorb and agglomerate powder.
In the present invention, wood pulp was selected from the viewpoints that the fiber diameter is small, the fibers are often entwined with each other, and it is inexpensive. The amount of wood pulp added can be arbitrarily selected depending on the desired porosity of the anode, but in producing the anode contemplated by the present invention, the amount of wood pulp added is 30% based on the total weight of the molded product before sintering. ~15% was the preferred range. Suitable materials for the metal mesh, which is crimped onto the plate-shaped molding and serves as a reinforcing material for the electrode after sintering, are nickel, stainless steel, Kanthal, etc., which have strength, heat resistance, and corrosion resistance.
As for the mesh shape, a range of 10 to 80 meshes and a wire diameter of 0.1 to 0.3 mm met the purpose of the present invention. On the other hand, in order to pressure-bond a metal mesh to a plate-shaped molded product, a method is used in which the two are laminated and then the pressure is gradually increased using a press. The pressure is preferably in the range of 50 to 200 kg/cm ² . At this time, if necessary, the press machine is heated during press molding. For example, 60-150
Gradually increasing the temperature within a temperature range of ℃,
Good results can also be obtained by increasing the temperature in steps such as 30°, 60°, 90°, and 120°C. In addition, the press molding process not only presses the metal mesh onto the molded product, but also has the effect of drying the molded product, which has a large amount of moisture, by dehydrating it and keeping the surface texture flat and uniform. There is. After the above press molding process, the molded product with metal mesh is placed in an electric furnace and heated in an oxidizing atmosphere.
If necessary, heat from room temperature to 100℃/H with air flowing.
When heated at different speeds, the wood pulp and flocculant contained in the molded product begin to burn out and vaporize around 400°C, and are completely burned out at approximately 500°C.
Therefore, the heating temperature in an oxidizing atmosphere is 450°~
The holding time is preferably 1 to 3 hours at 600℃, but the most desirable is 1 to 2 hours at 500℃.
This is a condition for holding time. This is because when the temperature reaches around 600°C, more oxides are produced in the powder and mesh, which may have an adverse effect on the conductivity of the electrode. Heat treatment conditions in a reducing atmosphere for the purpose of reducing oxides generated when wood pulp and flocculant are burnt out and vaporized, sintering Ni powder, and diffusion bonding of Ni powder and metal mesh. is as follows. (1) Temperature: 650° ~ 1000°C (2) Holding time: 0.5 ~
3 hours (3) Atmosphere: hydrogen, nitrogen, argon, vacuum (10 ^-4 torr or less). Within this range of heat treatment conditions, it was possible to arbitrarily set the porosity, pore diameter, pore diameter distribution, specific surface area, etc. of the anode electrode desired in the present invention. Example 1 This example describes a method of manufacturing an electrode. (A) Sample preparation Carbonyl nickel powder (average particle size 4.7 μm) 45 parts Wood pulp 5 parts Water 1000 parts (B) Flocculant Polyacrylamide-based anionic flocculant 0.1% aqueous solution {manufactured by Sanyo Kasei Co., Ltd., product name: Sunfrotsuku AH200P''} 30 parts Polyacrylamide cationic flocculant 0.1% aqueous solution {manufactured by Sanyo Chemical Co., Ltd., trade name "Sunfrotsuku C-009P"} 20 parts Pour 1000 parts of water and 5 parts of wood pulp into a 2-sized container, Stir for about 10 to 20 minutes to fully disperse it in water, then add 45 parts of carbonyl nickel powder and stir for about 5 to 10 minutes to make an aqueous slurry. Add 30 parts of a pre-made polyacrylamide-based anionic flocculant (0.1% aqueous solution) into the mixture, stir for about 1 minute, and then add the pre-made polyacrylamide-based cationic flocculant (0.1%
% aqueous solution) and stirred for about 1 minute to form a coagulated floc. The sample agglomerated in the above step was made into a paper using a paper making machine to obtain a molded product having a square size of 300 mm and a thickness of 1.2 mm. Next, 20 meshes of Ni mesh with a wire diameter of 0.1 mm were laminated on the molded product, and a press machine was used to apply a pressure of 85 kg/cm ^2.
It was crimped onto a Ni mesh molded product. This is charged into an electric furnace and heated to 150°C/H from room temperature in the atmosphere.
The molded product was heated to 500° C. at a rate of 100° C., held at this temperature for 2 hours to burn off and scatter the wood pulp and flocculant contained in the molded product, and then cooled to room temperature. Then, while flowing hydrogen in a hydrogen furnace, raise the temperature from room temperature to 600°C at a rate of 300°C/H, then increase the temperature to 800°C at a rate of 150°C/H, and hold at 800°C for 1 hour. As a result, a porous Ni electrode plate with Ni mesh as a reinforcing material was obtained. The thickness of the porous Ni electrode plate obtained under these conditions was 0.83 mm, the porosity was 67%, and the average pore radius was
5.5 μm and specific surface area was 0.15 m ² /g. Example 2 In this example, the creep strength of the porous Ni electrode plate obtained in Example 1 was investigated. Creep strength: Temperature: 650℃, Atmosphere: Vacuum, Load: 2.5Kg/
A compression creep test was conducted under the condition of ^cm2 , and judgment was made based on the magnitude of the compression creep strain at that time. As a comparative product, carbonyl nickel powder with an average particle size of 4.7 μm was filled into a graphite mold with a depth of 1.0 mm.
A Ni electrode plate manufactured by sintering this in a hydrogen atmosphere at 780°C for 1 hour was used. This comparative product had a porosity of 73.3%, an average pore radius of 6.1 μm, and a specific surface area of 0.18 m ² /g. Figure 1 shows the relationship between creep strain and test time obtained in the compression creep test. The creep strain of the inventive product shown by solid line 1 is
The creep strain is around 5% even after 1000 hours, whereas the comparative product shown by solid line 2 exhibits a large creep strain even in a short period of time, reaching 55% after 1000 hours. Table 1 shows the changes in porosity, average pore radius, and specific surface area before the creep test and after 1000 hours of creep.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, Ni powder and wood pulp are mixed in water to form an aqueous slurry, a coagulant is added to this, the powder is adsorbed and agglomerated by the pulp, and the powder is formed into a plate shape by papermaking. A porous electrode plate is formed by obtaining a molded product, combining this molded product with a metal mesh by press molding, and then performing heat treatment in two steps, one in an oxidizing atmosphere and the other in a reducing atmosphere. Therefore, the metal mesh exhibits a reinforcing effect, resulting in an electrode with excellent sintering resistance. By incorporating this into the MCFC anode, it becomes possible to maintain the long-term battery performance of the MCFC.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between creep strain and test time in a compression creep test of an electrode plate, and Figure 2 is a graph showing the relationship between creep strain and test time in a compression creep test of an electrode plate.
2 is a graph showing the results of anode polarization values measured for the electrode plate after a time creep test.

Claims (1)

[Claims] 1. Mix Ni powder and wood pulp in water to make an aqueous slurry suitable for papermaking, add a coagulant, adsorb the powder to the pulp, coagulate it, and make paper. Press mold a metal mesh into a plate-shaped product. After the molded product is pressed in an oxidizing atmosphere to burn off and scatter the wood pulp, it is then heated in a high-temperature reducing atmosphere to reduce metal oxides produced by the oxidation and to remove Ni. A method for producing a fuel electrode for a molten carbonate fuel cell, the method comprising sintering a powder.