JPH0544780B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Application of the Invention] The present invention relates to a separator for a molten carbonate fuel cell. [Background of the Invention] In recent years, in response to the depletion of oil resources and soaring prices, the development and research of energy-saving equipment has become an important issue. In contrast, molten carbonate fuel cells that use LNG and coal gas aim to save energy and replace oil, and are a thermal power generation technology that is part of new energy development. FIG. 4 shows a basic structural diagram of a molten carbonate fuel cell. The battery consists of 1 electrolyte and 2 anode electrodes.
and a cathode 3, and a separator 4, which is the object of the present invention. A molten fuel cell is a fuel cell that uses an alkali metal carbonate such as lithium carbonate (Li ₂ , CO ₃ ) or potassium carbonate (K ₂ CO ₃ ) as an electrolyte and operates at a temperature range of 600 to 750°C, above its melting point. . In a battery, hydrogen or hydrogen-containing gas is supplied as a fuel to the anode, and air + carbon dioxide as an oxidizing agent is supplied to the cathode, whereby the electrochemical reaction shown in the following formula progresses and power is generated. It is something. Anode (hydrogen electrode): 2H ₂ +2CO ₃ ^2- →2CO ₂ +2H ₂ O+4e ^- …(1) Cathode (air electrode): O ₂ +2CO ₂ +4e ^- →2CO ₃ ^2-
...(2) Equation (1) + Equation (2): 2H ₂ +O ₂ +2H ₂ O ...(3) The separator 4 has the role of separating hydrogen combustion gas and oxidant gas and collecting current. Although FIG. 4 shows the configuration of a single separator battery, in an actual machine, a large number of batteries will be stacked to increase the voltage and increase the capacity. FIG. 5 shows the basic structure of a separator 4 that is applied as capacity increases. The separator 4 is a single plate with grooves 5 for gas circulation on the front and back surfaces. On the front and back sides are the above-mentioned (1),
As shown in equations (2) and (3), the electrical reactions and gas atmospheres are different. Therefore, the separator material is required to have excellent corrosion resistance in both the atmosphere (hydrogen-containing gas) on the anode side and the atmosphere (oxygen gas) on the cathode side at 600 to 750°C. Fuji Jiho (volume 55, 1982) is used as a separator material.
As stated in 2012), austenitic stainless steel SUS316 steel is used. However, in the corrosive environment of molten carbonate fuel cells, SUS316 suffers from a large amount of corrosion, which poses a problem for long-term use. [Object of the Invention] An object of the present invention is to provide a separator for a molten carbonate fuel cell that has excellent corrosion resistance even in the above-mentioned corrosive environment. [Summary of the Invention] The present invention provides a separator for molten carbonate fuel cells that provides excellent corrosion resistance in a hydrogen-containing atmosphere and an oxidizing atmosphere, and is
C0.03~0.1%, Si0.5~1.5%, Mn0.5~2.0%,
Cr21.5~30.5%, Mo0.08~2.80%, Al less than 0.7%,
Ti less than 0.7%, Al + Ti 0.4~0.7%, or above
It is characterized by containing 0.1 to 1.0% Y, with the remainder consisting of Fe and inevitable impurities. C is 0.03% to improve the stability and strength of the structure.
These are the necessary elements. However, adding 0.1% or more lowers toughness and corrosion resistance.
Therefore, C should be 0.03 to 0.1%. Cr is an element that improves corrosion resistance. However, if the content is less than 21.5%, the effect is small, and if it exceeds 30.5%, there is no significant effect, making the structure unstable and significantly reducing the toughness. Therefore, the amount of Cr added is 21.5 to 30.5%.
shall be. In addition to being added as a deoxidizing agent, Si is added to improve corrosion resistance, and is set at 0.5 to 1.5%. Al and Ti are added in small amounts to improve corrosion resistance. Each contains less than 0.7%,
If the total amount of both is less than 0.4%, there is no effect, and on the other hand, if it is more than 0.7%, there is no significant effect and workability is impaired. Therefore, it is set at 0.4 to 0.7%. Mn is added as a deoxidizing agent. The effect is 0.5-2.0%
is sufficient. Mo is effective in improving corrosion resistance and strength. There is no effect below 0.08%, and there is no significant effect even above 2.80%.
Therefore, it is set at 0.08 to 2.80%. Furthermore, even a small amount of Y is effective in improving corrosion resistance. The amount is
There is no effect when it is less than 0.1%, and there is no significant effect even when it exceeds 1.0%. Therefore, it is set at 0.1 to 1.0%. [Examples of the Invention] Table 1 shows the chemical compositions (% by weight) of samples used as separator materials. The remainder is Fe. Second
The table shows the corrosion test conditions conducted in the corrosion resistance corrosion experiment. The corrosion test conditions simulated the environment of the actual machine, and two types of corrosion conditions were used. The test temperature and time were both 650°C and 100 hours. Further, a carbonate of LiCO ₃ :K ₂ CO ₃ =62:38 (mole ratio) was coated on the test piece in advance. For comparison, commercially available SUS304 and 316 were tested. The shape of the corrosion test piece is 15 mm wide, 25 mm long, and 4 mm thick.
mm.

【table】

【table】

〔Effect of the invention〕

As described above, the present invention has excellent corrosion resistance,
It is clear that the separator has a long life as a separator for molten carbonate fuel cells.

[Brief explanation of the drawing]

Figures 1, 2, and 3 are diagrams showing the amount of corrosion of the separator material for a molten carbonate fuel cell according to the present invention, and Figure 4 is a diagram showing the amount of corrosion in a molten carbonate fuel cell to which the separator of the present invention is applied. FIG. 5 is a perspective view of the battery shown in FIG. 4, and a diagram of the laminated structure when the capacity is increased. 1... Electrolyte, 2... Anode, 3... Cathode, 4
...Separator.

Claims (1)

[Claims] 1. It is exposed to a mixed gas consisting of hydrogen, carbon dioxide, and water, and a mixed gas consisting of air and carbon dioxide, and molten carbonate adheres to the surface, and the temperature is 600℃.
In separators for molten carbonate fuel cells that reach ~750°C, 0.03-0.1% carbon and 0.5% silicon by weight.
~1.5%, manganese 0.5~2%, chromium 21.5~
30.5%, molybdenum 0.08-2.80%, aluminum
A separator for a molten carbonate fuel cell, characterized in that the total amount of aluminum and titanium is less than 0.7%, less than 0.7% titanium, the total amount of aluminum and titanium is 0.4 to 0.7%, and the balance is iron and inevitable impurities. 2. It is exposed to a mixed gas consisting of hydrogen, carbon dioxide, and water, and a mixed gas consisting of air and carbon dioxide, and molten carbonate adheres to the surface, and the temperature reaches 600℃.
In separators for molten carbonate fuel cells that reach ~750°C, 0.03-0.1% carbon and 0.5% silicon by weight.
~1.5%, manganese 0.5~2%, chromium 21.5~
30.5%, molybdenum 0.08-2.80%, aluminum
less than 0.7%, titanium less than 0.7%, total amount of aluminum and titanium 0.4-0.7%, yttrium 0.1-1.0
%, the balance being iron and unavoidable impurities.