Ruddlesden Popper oxides of LnSr₃Fe₃O_10-δ (Ln = La, Pr, Nd, Sm, Eu, and Gd) as active cathodes for low temperature solid oxide fuel cells

Ruddlesden Popper type oxides of LnSr₃Fe₃O_10-δ (Ln = La, Pr, Nd, Sm, Eu, and Gd) have been investigated as active cathodes for solid oxide fuel cells (SOFCs). Among the examined LnSr₃Fe₃O_10-δ, it was found that PrSr₃Fe₃O_10-δ shows the highest activity for the cathode reaction. The prepared LnSr₃Fe₃O_10-δ oxides have a tetragonal crystal structure with the space group I4/mmm. With decreasing the ionic size of Ln³⁺, the unit cell volume and crystallite size decrease. The temperature and P_O2 dependences of electrical conductivities indicate the metal-like behaviour and the predominant hole conduction. The thermal expansion coefficient (TEC) values derived from the non-linear expansion curves of LnSr₃Fe₃O_10-δ are reasonably compatible with those of La_0.9Sr_0.1Ga_0.8Mg_0.2O₃ (LSGM) electrolyte. The catalytic activity as cathodes for H₂-SOFCs depended on Ln ions. A high cathodic activity was achieved on PrSr₃Fe₃O_10-δ (PSFO10) and a maximum power density of 0.51 W cm^-2 was achieved at 1073 K when 0.3 mm thick LSGM electrolyte was used. The surface exchange coefficient, k, also confirms the high activity for the dissociation of oxygen on PSFO10. Therefore, PrSr₃Fe₃O_10-δ is highly promising as a cathode for low temperature SOFCs.