JPS6124156A - Corrosion prevention coating for molten carbonate fuel cells - Google Patents

Abstract

PURPOSE:To obtain the corrosion resistance against high-temperature fused carbonate by forming a film of tungsten or molybdenum on the surface of a component material containing at least one of nickel and iron as the main component. CONSTITUTION:Surfaces of gas chamber frames 4, 5 arranged on both side of an anode electrode 2 and a cathode electrode 3 and made of either one of nickel, carbon steel, austenite-series stainless steel in contact with the electrolyte tile 1 holding fused carbonate are coated respectively with tungsten or molybdenum at a thickness of 10-150mum to form films 20, 20a. The film of tungsten or molybdenum can be formed by chemical deposition, physical deposition, or vapor plating.

Description

[Detailed description of the invention] [Technical field to which the invention pertains]

The present invention relates to corrosion prevention of components of molten carbonate fuel cells that are in contact with molten carbonate.

[Prior art and its problems]

In a molten carbonate fuel cell, a unit cell is constructed by disposing an anode electrode and a cathode electrode with an electrolyte tile holding molten carbonate as an electrolyte sandwiched between them, and a fuel gas as a reactant gas is placed on the outside of the anode electrode. A cell stack is formed by stacking a large number of plates, each of which has a plate that supplies oxidant gas to the cathode electrode, and reactant gas is supplied to each electrode in the cell stack through piping to cause an electrochemical reaction. to generate electricity. However, since this type of fuel cell operates at a high temperature, it is necessary to prevent corrosion of the constituent materials that come into contact with the molten carbonate. The prior art will be explained below based on the drawings. FIG. 2 is an explanatory cross-sectional view of a unit cell constituting a cell stack of a molten carbonate fuel cell. In Figure 2, number 1
is an electrolyte tile containing an alkali carbonate 1 such as lithium carbonate, sodium carbonate, potassium carbonate, calcium carbonate, etc., and an anode electrode 2 and a cathode electrode 3 are disposed with this electrolyte tile 1 sandwiched therebetween, and these are generally porous. Made of quality nickel or nickel alloy. Furthermore, a gas chamber frame 4.5 is arranged on the outside of the two electrodes, each forming a reaction gas channel. A chamber 15.16 is formed in the gas chamber frame 4.5 for supplying a reaction gas to each electrode, and a corrugated collector 10.11 is provided for transmitting the generated electricity to the gas chamber frame 4,5. A fuel gas supply pipe 6 and a discharge pipe 6a for supplying and discharging fuel gas to and from the gas chamber 15 are provided on opposite sides of the gas chamber frame 4.
At 6, an oxidizing gas supply pipe 7 and a discharge pipe 7a for supplying and discharging oxidizing gas are provided on opposite sides of the gas chamber frame 5. Electrical insulating plates 13 are interposed between the gas chamber frames 4 and 5 and the upper and lower pressing plates 17, respectively, and battery components such as the electrolyte tile 1 and the gas chamber frame 4.5 are fastened by studs 12. Further, a lead wire 14 for taking out electricity generated in the unit battery is attached to the gas chamber frame. This type of fuel cell is operated at an operating temperature of 500°C or higher, and fuel gas and oxidant gas are supplied through supply pipes 6 to 6.
．． 7 to the gas chamber 15.1-6, which supplies the anode electrode 2 and the cathode electrode 3 to the discharge pipes 6a, 7.
a, and an electrochemical reaction occurs with the molten carbonate in the electrolyte tile 1 to generate electricity, which is taken out from the lead wire 14. In a high-temperature (500-800°C) molten carbonate fuel cell using an alkali metal carbonate as an electrolyte, the electrochemical reaction proceeds as shown in equation (1) and +21 below.
Ion conduction is carried out by carbonate ions (Cod”). Anode: Hz + COs”-+HgO+COt+
2e (1) Cathode j 1/20. 10 COt
+28-* co, z-(21 This type of battery has a high operating temperature of 500°C or higher, so the reaction rate is high, and unlike room-temperature fuel cells, it does not require an expensive platinum metal catalyst.
Another advantage is that high current density can be obtained even with inexpensive fuel that does not easily react at room temperature. However, since it operates at high temperatures, the constituent materials that come into contact with the molten carbonate must be corrosion resistant. However, conventionally, metal materials such as nickel, carbon steel, and stainless steel are used for the constituent materials that come into contact with molten carbonate, such as the gas chamber frame that sandwiches electrodes and electrolyte tiles, but they have problems with corrosion due to molten carbonate. There is a demand for materials that can prevent corrosion.

[Purpose of the invention] In view of the above-mentioned points, an object of the present invention is to provide constituent materials of a molten carbonate fuel cell with sufficient corrosion resistance against molten carbonate. [Key points of the invention]

According to the present invention, the above object is to have a thickness of 10 to 150 μm made of either tungsten or molybdenum in the constituent material in contact with the molten carbonate containing at least one of nickel and iron as a main component. This is achieved by forming a film.

[Embodiments of the invention]

. The present invention will be explained in detail based on the drawings below. FIG. 1 is an explanatory cross-sectional view showing a structure material of a fuel cell according to an embodiment of the present invention provided with a corrosion-preventing coating. In Fig. 1, the same parts as in Fig. 2 are given the same reference numerals. The structure 9 of the fuel cell consisting of a chamber frame 4, 5, etc. is the same as that of the prior art, so the explanation will be omitted. A gas chamber frame 4.5 made of nickel, carbon steel, or austenitic stainless steel is coated with tungsten or molybdenum to a thickness of 10 to 150 μ- on each side in contact with the electrolyte tile 1 holding molten carbonate. A coating 20.20a is formed. Tungsten and molybdenum coatings are formed by chemical vapor deposition (CVD).
), physical vapor deposition (PVD), vapor phase plating, or the like. Corrosion tests were conducted by coating pure nickel, carbon steel, and austenitic stainless steel as base materials with tungsten and molybdenum as described above. The coating method was as follows: First, the three materials mentioned above were degreased and pickled, and then the materials other than pure nickel were plated with nickel to a thickness of 5 .mu.m by electroplating. This was followed by chemical vapor deposition (CVD) deposition of tungsten and molybdenum layers, each approximately 85 microns thick. An immersion corrosion test using molten carbonate on such a sample was conducted under the following conditions. Molten carbonate composition Potassium carbonate 38a+o1% Lithium carbonate 62mo1% Temperature 650°C Immersion time 100 hours Immersion method Static immersion of a sample suspended from a gold wire with a diameter of 0.5 m Atmosphere Spraying carbon dioxide gas above the liquid level This test The results are shown in Table 1. As shown in Table 1, it is understood that the weight loss is significant in the case without the tungsten or molybdenum coating, but the weight loss is very small in the case with the coating. At this weight loss rate, even with a film thickness of 10 μm, the fuel cell can withstand long-term operation. Further, from the viewpoint of the method of forming the film, the thickness of the film is set to be 150 μm or less. Severe erosion was observed in some areas on the surface of the material that was not coated with tungsten or molybdenum, but no such erosion was observed on the surface of the material that was coated with tungsten or molybdenum.

【Effect of the invention】

As is clear from the above description, according to the present invention, the surface of the constituent material containing at least one of nickel and iron as a main component is coated with either tungsten or molybdenum to a thickness of 10 to 150 μm. By forming the film, sufficient corrosion resistance against high-temperature molten carbonate can be provided, and a material that is less expensive in terms of corrosion resistance can be used as the constituent material of the fuel cell.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a molten carbonate fuel cell according to an embodiment of the present invention, and FIG. 2 is a sectional view of a conventional molten carbonate fuel cell. 1: Electrolyte tile, 4.5: Gas chamber frame, 20, 20a:
Coating. Figure 1

Claims (1)

[Scope of Claims] 1) The constituent material in contact with the molten carbonate containing at least one of nickel and iron as a main component is coated with 1.0 to 150 μm of either tungsten or molybdenum.
1. A corrosion-preventing coating for a molten carbonate fuel cell, characterized in that the coating has a thickness of m. 2) A corrosion-inhibiting coating for a molten carbonate fuel cell according to claim 1, wherein the constituent material is austenitic stainless steel.