Atomic-Scale Insights into Air Electrode Degradation after 10 Years of Fuel Cell Stack Operation

Abstract

Solid oxide cells (SOCs) represent a key technology for sustainable energy conversion due to their high efficiency and ability to integrate them into energy intensive industrial processes. Designing solid oxide stack systems that exhibit long-term durability is challenging, due to the harsh operation conditions for all applied materials, particularly at the air electrode side. In this study, we investigate the degradation mechanisms at the La₀.58Sr₀.₄Co₀.₂Fe₀.₈O₃₋δ (LSCF) air electrode of a solid oxide fuel cell (SOFC) short stack, which was operated for 93,000 hours in fuel cell mode at 700°C under constant current density of 0.5 A/cm², with 40% fuel utilization and hydrogen and oxygen as feed gases. We apply atomic-resolution scanning transmission electron microscopy and spectroscopy to analyze changes in structure and chemistry across the electrode and its interface with the Gd-doped ceria (GDC) diffusion barrier. While the bulk of the LSCF electrode mostly retained structural integrity with only minor local changes, significant degradation occurred at the LSCF–GDC interface. Heavy Sr leaching induced by chromium poisoning led to the formation of micron-sized SrCrO₄ crystallites. Simultaneously, Cr-containing decomposition products reacted with GDC to form substituted CeO₂-based nanoparticles, triggering gradual delamination of the electrode. These nanoscale interactions disrupted the contact between air electrode and barrier, significantly contributing to cell failure. Our findings provide critical insights into long-term degradation in SOCs and emphasize the need for improved material combinations to ensure stable operation over extended lifetimes.