Operando and in situ X-ray spectroscopies of degradation in La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ thin film cathodes in fuel cells

Information from ex situ characterization can fall short in describing complex materials systems simultaneously exposed to multiple external stimuli. Operando X-ray absorption spectroscopy (XAS) was used to probe the local atomistic and electronic structure of specific elements in a La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF) thin film cathode exposed to air contaminated with H₂O and CO₂ under operating conditions. While impedance spectroscopy showed that the polarization resistance of the LSCF cathode increased upon exposure to both contaminants at 7508C, XAS near-edge and extended fine structure showed that the degree of oxidation for Fe and Co decreases with increasing temperature. Synchrotron-based X-ray photoelectron spectroscopy tracked the formation and removal of a carbonate species, a Co phase, and different oxygen moieties as functions of temperature and gas. The combined information provides insight into the fundamental mechanism by which H₂O and CO₂ cause degradation in the cathode of solid oxide fuel cells.