New Two-layer Ruddlesden-popper Cathode Materials for Protonic Ceramics Fuel Cells

Abstract New two-layer Ruddlesden-popper (RP) oxide La0.25Sr2.75FeNiO7-δ (LSFN) in the combination of Sr3Fe2O7-δ and La3Ni2O7-δ was successfully synthesized and studied as the potential active single-phase and composite cathode for protonic ceramics fuel cells (PCFCs). LSFN with the tetragonal symmetrical structure (I4/mmm) is confirmed, and the co-existence of Fe3+ /Fe4+ and Ni3+/Ni2+ couples is demonstrated by XPS analysis. The LSFN conductivity is apparently enhanced after Ni doping in Fe-site, and nearly three times those of Sr3Fe2O7-δ, which is directly related to the carrier concentration and conductor mechanism. Importantly, anode supported PCFCs using LSFN-BZCY composite cathode achieved high power density (426 mW·cm-2 at 650°C) and low electrode interface polarization resistance (0.26 Ω cm2). Besides, relaxation time distribution function (DRT) technology was further used to analysis the electrode polarization processes. The observed three peaks (P1, P2, P3) separated by DRT shifted to the high frequency region with the decreasing temperature, suggesting that the charge transfer at the electrode-electrolyte interfaces become more difficult at reduced temperature. Preliminary results demonstrate new two-layer PR phase LSFN can be a promising cathode candidate for PCFCs.