In situ preparation of a La1.2Sr0.8Mn0.4Fe0.6O4 Ruddlesden-Popper phase with exsolved Fe nanoparticles as an anode for SOFCsElectronic supplementary information (ESI) available. See DOI: 10.1039/c6ta09692a

A highly stable electrode material of Ruddlesden-Popper structure, La 1.2 Sr 0.8 Mn 0.4 Fe 0.6 O 4 (RPLSMF), is prepared from La 0.6 Sr 0.4 Mn 0.2 Fe 0.8 O 3 (LSMF) perovskite by in situ annealing in flowing H 2 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 H 2 to prevent formation of La 2 O 3 . 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 H 2 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 Ω cm 2 . In situ reduction of LSMF perovskite promoted Ruddlesden-Popper RPLSMF formation with Fe nanoparticles, exhibiting outstanding electrochemical performance as a SOFC electrode.