(Invited) Performance and Stability of Mixed Conducting SOFC-Cathodes at High and Low Operating Temperatures
Authors: Weber André , Ivers-Tiffée Ellen 
Published: February 2020

Solid Oxide Fuel Cells (SOFCs) enable a highly efficient, environmentally-friendly power generation. Depending on the cell type, e.g. electrolyte-, anode- or metal supported, the nominal operating temperature of SOFC-stacks varies in-between 550 and 850 °C. Despite of this wide temperature range, today most SOFCs comprise a mixed ionic-electronic conducting (MIEC) cathode that is most commonly of the perovskite type composition (La,Sr)(Co,Fe)O3-
d (LSCF) (1-5). Thus different types of LSCF-cathodes, which have to show a suitable performance and stability at the targeted operating temperature, are required.

In this contribution performance and stability of LSCF cathodes, differing in composition (e.g. strontium and iron content (6,7)) and microstructure (e.g. porous, micro- and nanoscaled electrode layers (8-10)) will be presented for different operating temperature ranges. Area specific resistance values, evaluated by means of impedance spectroscopy and the distribution of relaxation times (11,12), will be compared with model predictions (13,14). Different degradation mechanisms, limiting the cell performance at high and low operating temperature respectively, will be discussed (15). The impact of air impurities as H2O, CO2, sulfur and chromium species will be considered (16). It will be shown that there are reversible and irreversible degradation mechanisms at low and high operating temperatures respectively and that a reduced operating temperature does not necessarily reduces degradation (17).

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