Hydroxylation and Cation Segregation in (La<sub>0.5</sub>Sr<sub>0.5</sub>)FeO<sub>3−δ</sub> Electrodes
Dawei Zhang, Michael L. Machala, Di Chen, Zixuan Guan, Hanshi Li, Slavomír Nemšák, Ethan J. Crumlin, Hendrik Bluhm, William C. Chueh
Abstract
Simultaneously achieving high activity and stability is the primary challenge when engineering (electro)catalysts. Transition metal perovskite oxides are employed as air electrodes for solid-oxide fuel cells and electrolyzers. However, degradation of oxygen exchange kinetics at the solid–gas interface, often linked to alkaline-earth cation segregation and precipitation, limits widespread commercialization. In this work, we systematically investigated the surface degradation mechanism induced by gas-phase impurities in (La0.5Sr0.5)FeO3−δ (LSF55) thin-film electrodes by varying the concentration of H2O, SO2, and CO2. Degradation of the area-specific resistance in ambient and humidified synthetic air is significantly greater than in dry ambient and dry synthetic air, pointing to the importance of water vapor. Time-resolved, in situ ambient pressure X-ray photoelectron spectroscopy performed in O2 showed that nonbulk Sr is present on the surface before the exposure to water vapor. Upon introduction of water vapor, neither additional Sr segregation nor precipitation driven by water vapor is a necessary condition for degradation. Rather, hydroxylation of the surface induces irreversible and significant degradation. At the same time, we show that Sr migration driven by water vapor is partially reversible. These fundamental insights can be used for the rational design of electrodes with improved catalytic stability.