Characterization and evaluation of double perovskites LnBaCoFeO5+δ (Ln = Pr and Nd) as intermediate-temperature solid oxide fuel cell cathodes

Double perovskites LnBaCoFeO5+δ (Ln = Pr and Nd, PBCF and NBCF) are comparatively investigated as potential cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). LnBaCoFeO5+δ materials are chemically compatible with La0.9Sr0.1Ga0.8Mg0.2O3–δ (LSGM) electrolyte at temperatures below 1000 °C. Fe and Co ions in LnBaCoFeO5+δ exist in two oxidation states, 3+ and 4+. Pr ions are found in PBCF mostly as Pr3+. Thermal expansion coefficients (TECs) of PBCF and NBCF are 21.0 × 10−6 and 19.5 × 10−6 K−1, respectively, between 30 and 1000 °C; these are lower than the TECs of undoped LnBaCo2O5+δ. The best electrical conductivity for both materials is observed near 350 °C: 321 and 172 S cm−1 for PBCF and NBCF, respectively. Polarization resistances of PBCF and NBCF cathodes on LSGM electrolyte are 0.049 and 0.062 Ω cm2 at 800 °C, respectively. Maximum power densities of the single-cell with Ni/SDC as anode on a 0.3 mm-thick LSGM electrolyte reach 749 and 669 mW cm−2 for PBCF and NBCF cathodes at 800 °C, respectively. As cathodes for application in IT-SOFCs, the performance of PBCF and NBCF double perovskites is promising. [Display omitted] •Double perovskites LnBaCoFeO5+δ (Ln = Pr and Nd) with near metal stoichiometry were prepared by the modified sol–gel method.•We comparatively studied structures and properties of double perovskites LnBaCoFeO5+δ as IT-SOFC cathodes.•Mixed valence states of Pr3+/Pr4+, Co3+/Co4+ and Fe3+/Fe4+ coexisted in the PrBaCoFeO5+δ oxide.•Substitution of Fe for Co reduced the TECs of the LnBaCoFeO5+δ compared to undoped LnBaCo2O5+δ (Ln = Pr and Nd).•LnBaCoFeO5+δ as IT-SOFC cathodes on LSGM electrolyte exhibited good electrochemical performance.