In situ preparation of a La_1.2Sr_0.8Mn_0.4Fe_0.6O₄ Ruddlesden-Popper phase with exsolved Fe nanoparticles as an anode for SOFCs

A highly stable electrode material of Ruddlesden-Popper structure, La_1.2Sr_0.8Mn_0.4Fe_0.6O₄ (RPLSMF), is prepared from La_0.6Sr_0.4Mn_0.2Fe_0.8O₃ (LSMF) perovskite by in situ annealing in flowing H₂ at the operation temperature of solid oxide fuel cells. The crystallinity, morphology, and oxidation states of each element and electrochemical properties of RPLSMF are characterized. Doping Mn into the B-site of RPLSMF improves the phase stability of the structure in H₂ to prevent formation of La₂O₃. The XPS results also suggest that improved phase stability promotes formation of Fe^2+/3+ pairs that facilitate fuel oxidation by redox coupling. Additionally, during phase transition to RPLSMF, metallic Fe nanoparticles form, which enlarge H₂ chemisorption and oxidation sites. Consequently, RPLSMF exhibits outstanding and stable electrochemical activity with a maximum power density of 0.72 W cm⁻² at 1073 K when used as an anode material in LSGM electrolyte-supported cells. As the phase transition between the RPLSMF and LSMF is reversible under a redox environment, RPLSMF/GDC is applied as an electrode in the symmetrical cell of RPLSMF-GDC/LSGM/LSMF-GDC. It exhibits a substantial power density of 0.64 W cm⁻² with a total polarization resistance of 0.51