JPH0520872B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD This invention relates to a method for manufacturing a molten carbonate fuel cell having a pair of gas diffusive electrodes consisting of an anode and a cathode and an electrolyte tile plate sandwiched between the electrodes. [Prior art and its problems] Molten carbonate fuel cells (MCFC in the following text)
Since these batteries have high operating temperatures and use highly corrosive molten carbonate as an electrolyte, various performance requirements are imposed on the electrodes, which are one of the battery components. The characteristics required for the MCFC electrode, particularly the anode electrode related to the present invention, are as follows. (1) Stable in gas atmosphere. (2) High heat resistance, especially creep strength. (3) Ability to react with gas without sudden electrolyte inflow. (4) High electrical conductivity. (5) It must be inexpensive. Conventionally, porous Ni was used as an anode electrode for MCFC.
Electrode plates are widely used. This is because Ni has a good balance of corrosion resistance and conductivity, and high-quality powder is easily available, and porous electrodes are relatively easy to manufacture. The following methods are conventionally known as methods for manufacturing porous Ni electrode plates. (1) Tape casting method (2) Method of applying Ni powder slurry on Ni mesh and baking it (3) Method of applying Ni powder slurry on spongy Ni and sintering it (4) Graphite or alumina container A method is to fill Ni powder into the container and sinter it as is. The tape casting method (1) can produce electrochemically highly active Ni electrode plates with uniform thickness, but the process is complicated and is less economical.
Furthermore, it is difficult to select the type and composition of a plasticizer, dispersant, or solvent suitable for the raw material powder, and it is also difficult to control the manufacturing process. (2) or (3) Ni mesh or spongy Ni
The method of coating and baking a powder slurry is simpler and more economical than the tape casting method in (1).
Because it is difficult to uniformly apply Ni powder slurry, there are problems with the surface quality and uniformity of the thickness of the resulting Ni electrode plate.
Since the corpus cavernosum is used as a support, the disadvantage is that the specific surface area of the electrode plate is small and the electrochemical activity tends to decrease. Method (4) of filling a container with powder and sintering it in that state without applying pressure is the simplest and most economical method known to date. Not only is it extremely difficult to rationally control the thickness and porosity, but it also has the disadvantage of becoming more noticeable as the electrode plate becomes larger. On the other hand, the pore volume (porosity), average pore diameter, pore size distribution, etc. that are desirable for the anode electrode of MCFC are determined experimentally, but these mainly depend on the porosity of the electrolyte tile plate and the operating conditions of the battery. Dependent. In order to obtain good cell performance, the air space must be such that enough electrolyte flows through the electrolyte tiles to carry out the reaction, but not so much that it prevents the rapid diffusion of the reactant gases within the electrode. porosity,
Electrodes are required to have pore diameters, etc. Generally speaking, the porosity of a porous electrode plate to meet the above requirements is 60 to 80%, and the average pore diameter is 1 to 10 μm.
(preferably 4 to 7 μm), and the manufacturing method described above can produce a porous Ni electrode plate that substantially satisfies these requirements. However, porous Ni electrode plates made from Ni powder have low creep strength, so sintering progresses over time during battery operation, reducing porosity and surface area.
It has the disadvantage of reducing the battery performance of MCFC. [Objective of the Invention] The object of the present invention is to use a porous Ni electrode plate, which is highly sintering resistant and obtained by a manufacturing method that allows for easy enlargement of the electrode plate, as an anode electrode, thereby providing an anode with excellent life characteristics.
Our goal is to provide MCFC. [Summary of the Invention] According to the present invention, this purpose is to form an alloy containing an alloying element which is dissolved in Ni and whose metal oxide is easily reducible.
Ni alloy powder and wood pulp are mixed in water to form an aqueous slurry suitable for papermaking, and a flocculant is added to adsorb and agglomerate the powder onto the pulp to form a plate-shaped product. After heating the wood pulp to burn it out and scatter it, the wood pulp is heated in a reducing atmosphere to reduce the metal oxides produced in the heat treatment and sinter the powder. A porous electrode plate is used as an anode. This is achieved by using it as an electrode. Mechanisms of hardening and strengthening of solids such as metals include strain hardening, precipitation hardening, dispersion hardening, transformation hardening,
Methods such as solid solution hardening and diffusion hardening have been considered. In the present invention, we have decided to adopt the concept of solid solution strengthening as a method of improving the creep strength of a porous Ni electrode plate. This solid solution strengthening is hardening or strengthening by dissolving other elements in the main component and hindering the movement of dislocations within the solid. Furthermore, as described below, the method of the present invention includes a step of heating the molded product obtained by papermaking to around 500° C. in the air or an oxidizing atmosphere. In this process,
The powder forming the molding is necessarily oxidized. At this time, the metal oxide produced must be easily reduced by heat treatment in a reducing atmosphere at 650° to 1000°C. By the way, the stability of metal oxides produced by the reaction of metal and oxygen is usually investigated by free energy, and the greater the negative absolute value, the more stable the metal oxide is. Table 1 compares the free energies of various metals. The value is small for noble metals such as Ag and Au, and large for base metals such as Al and Cr.

[Embodiments of the invention]

Hereinafter, the present invention will be explained based on examples. Example 1 This example describes a method for manufacturing a porous electrode plate. (A) Sample preparation Ni-8Co (average particle size 6.5 μm, manufactured by co-reduction method)
45 parts wood pulp 5 parts water 1000 parts (B) Flocculant 0.1% aqueous solution of polyacrylamide-based anionic flocculant {manufactured by Sanyo Chemical Co., Ltd., product name "Sunfloc"
AH200P''} 30 parts polyacrylamide-based cationic flocculant 0.1% aqueous solution {manufactured by Sanyo Chemical Co., Ltd., product name: ``Sunfloc C-''
009P''} 20 parts Put 1,000 parts of water and 5 parts of wood pulp in a 2-sized container, stir for about 10 to 20 minutes to fully disperse it in the water, and add 45 parts of Ni-8Co alloy powder to it.
Stir for ~10 minutes to create an aqueous slurry. Add 30 parts of the polyacrylamide-based anion flocculant (0.1% aqueous solution) prepared in advance into the mixture, stir for about 1 minute, and then add 20 parts of the pre-prepared polyacrylamide-based cationic flocculant (0.1% aqueous solution). Add 100% of the mixture and stir for about 1 minute to form a cohesive 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 10 mm. This molded product was placed in an electric furnace, heated from room temperature to 500°C at a rate of 150°C/H in the air, and held at this temperature for 2 hours to burn off and scatter the wood pulp and flocculant contained in the molded product. After that, it was cooled to room temperature. Thereafter, the molded product subjected to the above treatment is placed in a hydrogen furnace, and the temperature is raised from room temperature to 600°C at a rate of 300°C/H while flowing hydrogen.
After this, the temperature was raised to 800°C at a rate of 150°C/H and held at 800°C for 1 hour to form a porous Ni-8Co.
An alloy electrode plate was obtained. The thickness of this electrode plate is 0.88
mm, porosity is 72.0%, average pore radius is 3.02μm
The specific surface area was 0.203 m ² /g. As described above, the method of the present invention satisfies the pore characteristics required for an anode electrode and can easily produce a large electrode plate. Note that it is clear that a porous electrode plate can be manufactured using other alloy powders as raw materials through the same process as described above. Example 2 In this example, a porous Ni electrode plate (using carbonyl nickel powder with an average particle size of 4.7 μm) obtained under the conditions of Example 1 and a Ni alloy electrode plate (using a carbonyl nickel powder with an average particle size of 4.7 μm produced by a co-reduction method) were used. (use powder with a diameter of 5 to 8 μm)
The creep strength of the steel was investigated. Creep strength was determined by performing a compression creep test at a temperature of 650° C., atmosphere: vacuum, and load: 2.5 Kg/cm ² and based on the magnitude of the compression creep strain at that time. Figure 1 shows the compressive creep strain of the porous electrode plate when tested under the above conditions for 200 hours. The creep strain of a porous Ni electrode plate is 47%, but that of a porous electrode plate containing alloying elements as a solid solution is less than 5%, indicating that the creep strength increases significantly with the solid solution of alloying elements. It could be confirmed. Example 3 In this example, a porous Ni alloy electrode plate according to the present invention and a comparative porous Ni electrode plate having a diameter of 35 mm and a thickness of about 0.9 mm were used as an anode electrode.
We constructed an MCFC and investigated its battery performance.
In MCFC, a 50 mm × 2 mm thick electrolyte tile plate containing 55% by weight of eutectic composition electrolyte components (47.5% by weight lithium carbonate - 52.5% by weight potassium) is placed between the anode and cathode using lithium aluminate as an electrolyte holding material. A unit cell was constructed in which an electrode plate and an electrolyte tile plate were pressed against each other from both sides of a housing that was equipped with a fuel chamber and an oxidizer chamber, and also served as a current collector. In a cell with this configuration, the fuel gas composition is H ₂ + 20% CO ₂ and the oxidant gas composition is Air + 30%.
A gas consisting of % CO ₂ was supplied at a flow rate of 0.5/min, and the relationship between current and voltage characteristics was measured at 650°C.
The results are shown in Table 2.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, a Ni alloy powder containing an alloying element that is dissolved in Ni and whose metal oxide is easily reducible is mixed in water with wood pulp to form an aqueous slurry. A flocculant is added to this to adsorb and agglomerate the powder, a plate-shaped molded product is obtained by papermaking, and this molded product is heat-treated in two steps: in an oxidizing atmosphere and in a reducing atmosphere. Focusing on the excellent sintering resistance of the manufactured porous Ni alloy electrode plate, they incorporated it into the MCFC anode, making it possible to maintain the long-term battery performance of the MCFC.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the results of compression creep tests on various porous electrode plates.

Claims (1)

[Claims] 1. A Ni alloy powder containing an element that is dissolved in Ni and whose metal oxide is easily reducible is mixed in water with wood pulp to form an aqueous slurry suitable for papermaking,
A plate-shaped molded product obtained by adding a coagulant and adsorbing and aggregating the powder to the pulp and forming it into paper is heated in an oxidizing atmosphere to burn off the wood pulp and scatter, and then heated in a reducing atmosphere to oxidize the metal. 1. A method for manufacturing a molten carbonate fuel cell, which comprises reducing a substance and sintering a powder to form an anode, and interposing an electrolyte tile between the anode and the cathode to constitute a unit cell. 2 The elements described in claim 1 include Cu, Co,
A method for producing a molten carbonate fuel cell, comprising at least one element selected from Ag, Pd, Fe, Mo, and W.