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

Abstract

To improve thermal expansion compatibility and structural stability of the cobalt-based double perovskite cathode such as GdBaCo2O5+δ, a cobalt-free double perovskite GdBaFeNiO5+δ (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 14.7×10−6K−1 between 30 and 1000°C in air. The GBFN undergoes a transition from semiconductor to metallically conductive behaviors at 400°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°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 ∼14.2 times and the maximum power density of cell is increased by ∼1.9 times. The reason of electrochemical performance improvement is also discussed.