A Metallic Interconnect for Intermediate Temperature, Planar, Solid Oxide Fuel Cell Technology

60716 Intermediate temperature (<800C), planar solid oxide fuel cells (SOFC) require the development of low-cost, oxidation-resistant, metallic interconnects. Commercially available alloys are limited for this application because they contain chromium, which oxidizes in both air and fuel, forming an electrically resistive layer that slowly evaporates, lowering SOFC efficiency. This project will develop suitable coatings that suppress oxidation kinetics, suppress the volatilization of chromium oxide, and lower the overall resistance, thus increasing efficiency. In Phase I, thin (~2000 Angstroms) coatings of certain metals and oxides were deposited on commercial nickel-based alloy and stainless steel foils. The foils were oxidized in air and fuel, and their resistance was measured both ex-situ (out of stack) and in-situ (in four cell stacks). The coatings suppressed the oxidation kinetics, and also lowered the net resistance. Stack power at 800¿C was more than doubled by using coated interconnects. Even more importantly, the interconnect resistance decreased with time, and correspondingly, stack power increased with time. In Phase II, the main focus will be on identifying coatings that will be able to suppress the oxidation kinetics of low cost materials, such as stainless steels, for several thousand hours while maintaining low resistance and achieving a stack power density of ~1W/?2 using natural gas as fuel. Low-cost, large volume methods for the deposition of coatings will be developed. Several four-cell stacks, and one 1 kW stack will be tested for long periods of time using coated interconnects exhibiting ultra-low resistance. Commercial Applications And Other Benefits as described by the awardee: The metallic interconnects should allow for numerous applications of highly efficient solid oxide fuel cells (SOFC) in distributed, residential, automotive, and portable power. The devices would operate on hydrocarbon fuels at high efficiency while creating negligible pollution.