Cobalt-free double perovskite cathode GdBaFeNiO5+δ and electrochemical performance improvement by Ce0.8Sm0.2O1.9 impregnation for intermediate-temperature solid oxide fuel cells

To improve thermal expansion compatibility and structural stability of the cobalt-based double perovskite cathode such as GdBaCo2O5+delta, a cobalt-free double perovskite GdBaFeNiO5+delta (GBFN) is investigated as a potential cathode for intermediate-temperature solid oxide fuel cells based on Ce0.8Sm0.2O1.9 (SDC) electrolyte. The structure, properties and improved electrochemical performance of the GBFN material are reported in detail. The GBFN has a tetragonal structure at room temperature. Mixed valence states of Fe3+/Fe4+ and Ni2+/Ni3+ coexist in the GBFN material. The absence of spin state in Ni2+ contributes to a reduction in the thermal expansion coefficient (TEC). The average TEC of the GBFN sample is 14.7 x 10(-6) K-1 between 30 and 1000 degrees C in air. The GBFN undergoes a transition from semiconductor to metallically conductive behaviors at 400 degrees C. The substitution of Fe and Ni for Co significantly improves the structural stability of the GBFN. The GBFN material exhibits a good chemical compatibility with SDC electrolyte at temperatures below 1000 degrees C. The activity and performance of the GBFN cathode are further improved by the impregnation of nano-sized SDC particles: the polarization resistance is decreased by similar to 14.2 times and the maximum power density of cell is increased by similar to 1.9 times. The reason of electrochemical performance improvement is also discussed. (C) 2015 Elsevier Ltd. All rights reserved.