Current-carrying component for a fused carbonate fuel cell with

Details Current-carrying component for a fused carbonate fuel cell with Current-carrying component for a fused carbonate fuel cell with

1999-08-04

2000-11-28

Nuzzolillo, Maria

Chemistry: electrical current producing apparatus, product, and

Having magnetic field feature

429 44, H01M 814

Patent

active

061533246

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND AND SUMMARY OF INVENTION

The invention relates to corrosion proofing of current-carrying components of molten carbonate fuel cells. In particular, the invention relates to a current-carrying component for a molten carbonate fuel cell, particularly an anode current collector or bipolar plate, with a substrate made of stainless steel and with a corrosion proofing coating provided on the substrate to protect the component from the anode gas atmosphere and the molten electrolyte of the fuel cell.
The conditions prevailing in the anode chamber of a molten carbonate fuel cell--carburizing atmosphere and low partial pressure of oxygen and presence of molten lithium and potassium carbonate--lead to rapid corrosion of the stainless steel components contained in the molten carbonate fuel cells. This corrosion is considerably accelerated by the high temperatures prevailing when molten carbonate fuel cells are operated. The reason for this is that the oxide layers formed in the carburizing, reducing atmosphere, by contrast to the oxide layers formed in an oxidizing atmosphere, are not dense or stable and are thus unable to protect the high alloy stainless steel used. The use of steels containing aluminum or the aluminizing of steels otherwise frequently chosen for corrosion proofing of stainless steels in a carburizing atmosphere suggests itself for current-carrying parts for use in fuel cells, namely in particular anode current collectors or bipolar plates, due to the very high electrical resistance of the resulting oxide layers.
A further problem is the tendency of the molten salts of the electrolyte to creep on such metal components. This creep is one of the electrolyte's loss mechanisms and hence places a limit on service life. Moreover, creep favors contamination of a cracked gas reaction catalyst provided for operation of the molten carbonate fuel cells and makes the use of direct internal reformation impossible although it would have been especially advantageous.
In principle, corrosion of the stainless steel components and creep of the molten salts on the metal components in the anode chambers of molten carbonate fuel cells can be prevented by coating the stainless steel sheets with nickel, as has been common in the past. Nickel is inert in the atmosphere contained in the anode chamber and is not wetted by the melt. When the components are flat, they are coated with nickel for example by plating and when the components have three-dimensional surfaces, they are coated galvanically. However previously unsolved problems arise at this point. With galvanically nickel-coated parts, the problem generally arises that the layers formed have pores. To make the porous layers impermeable, the nickel applied galvanically to the thinnest points must be at least 50 .mu.m thick. In components with a three-dimensional form, like a current collector used on the anode side, in the most favorable case a thickness ratio of 2:1 from the thickest to the thinnest points can be achieved, and this must be borne in mind when choosing the coating thickness. However, even with a thickness of 50 .mu.m, diffusion of components of the stainless steel such as Cr and Fe along the grain boundaries of the nickel layer to the surface of the component and diffusion of oxygen from the surface into the component are observed. This leads to oxide formation at the grain boundaries of the nickel layer and at the interface between the nickel layer and the stainless steel substrate.
DE 195 23 637 A1 already discloses a corrosion proofing coating for current-carrying components of molten carbonate fuel cells, in particular anode current collectors or bipolar plates, in which a thin layer of a nondiffusing material is applied to a substrate as a diffusion barrier layer and a thin layer of a corrosion-proof material is applied to the diffusion barrier layer. The substrate used is a stainless steel and the corrosion proofing layer may be made of nickel, gold, or copper.
The goal of the invention is to produce a current-carrying component for a mo

REFERENCES:
patent: 4555453 (1985-11-01), Appleby
"Carbonate Fuel Cell Endurance: Hardware Corrosion and Electrolyte Management Status", C.Y. Yuh et al., Extended Abstracts Spring Meeting 1993 May, 16-21 Honolulu Pennington, U.S., vol. 93/1, 1993, pp. 1518-1519.
Chemical Abstracts, vol. 111, No. 8, Aug. 21, 1989, JP 01 003 962 A, Atsushi Akimoto et al., Jan. 9, 1989.
Patent Abstracts of Japan, vol. 014, No. 252, JP 02 072562 A, Harufuji Yasuyuki, Mar. 12, 1990.
Patent Abstracts of Japan, vol. 009, No. 270, JP 60 115173 A, Iwaki Tsutomu, Jun. 21, 1985.

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