Investigations into the Kinetics of the Ni-YSZ-Cermet-Anode of a Solid Oxide Fuel Cell

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Abstract
SOFC anodes made from Ni-YSZ-cermet were investigated by impedance spectroscopy applied to symmetrical cells. The ambient temperature was varied between 800 and 1000°C, the feed gas composition was varied from 2% up to 90% water vapor in hydrogen and the cells could be artificially poisoned by hydrogen sulfide. Apart from the ohmic resistance of the electrolyte two well separated relaxations, one at some kHz, the other at 10 Hz, were found. From the dependence of the spectra on the operating conditions and by comparison with model calculations it was concluded that the high frequency relaxation is due to the combination of the charge transfer reaction and the ionic resistance within the cermet. The 10 Hz relaxation is attributed to gas diffusion along the gas supply channels caused by inefficient flushing.

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