Phase Evolution in (La0.6Sr0.4)0.95Co0.2Fe0.8O3-Δ Oxygen Electrodes after SOEC Operation

Abstract

This work aims to evaluate the microstructural and compositional changes in (La0.6Sr0.4)0.95Co0.2Fe0.8O3-δ (LSCF) electrodes in solid oxide electrolysis cells (SOEC) before and after testing at 750°C for 2800 hours at 1.3V. Scanning electron microscopy (SEM) examination of the LSCF electrodes before and after SOEC operation was conducted. In untested LSCF electrodes, LSCF perovskite was a predominant phase with very minor presence of La(Fe,Co) oxide, and Fe,Co spinel phases. The post-tested electrodes exhibited a change where the La(Fe,Co) oxide phase exhibited a broader composition range, most notably with respect to the La/Fe ratio and potential loss of Co, and there was a noticeable increase in the volume fraction of Fe,Co spinel from 1.5% in the untested cell to over 3% after testing. To better understand the phases and their compositions, a transmission electron microscopy (TEM) study of tested and untested electrodes was undertaken using an aberration (Cs) corrected JEM-ARM200CF microscope operated at 200 kV. TEM confirmed the presence of cubic spinel particles with a composition of 26 at.% Fe and 13-15 at.% Co, with little to no Sr or La present. The composition of the La(Fe,Co) phase was more variable in agreement with the SEM analysis, with the Co/Fe ratio higher in the untested cell versus the cell tested at 2800 hours.