Cobalt-site cerium doped Sm_xSr_1-xCoO_3-δ oxides as potential cathode materials for solid-oxide fuel cells

A series of new oxides with the nominal composition of Sm_xSr_1-xCo_1-yCe_yO_3-δ (x = 0.1, 0.3, 0.5; y = 0.05, 0.1) were synthesized. Their crystal structure, morphology, thermal expansion and electrochemical properties were systematically investigated. A phase-pure perovskite-type Sm_0.3Sr_0.7Co_0.95Ce_0.05O_3-δ oxide is obtained, while the other samples are actually composed of B-site cation deficient Sm_xSr_1-xCo_1-yCe_y-zO_3-δ (0 < z < y) and CeO₂ mixed phases. These two-phase samples exhibit larger oxygen nonstoichiometry (δ) and higher average thermal expansion coefficients (TEC), while the single-phase Sm_0.3Sr_0.7Co_0.95Ce_0.05O_3-δ oxide shows a smaller δ and a lower TEC as compared to Sm_0.3Sr_0.7CoO_3-δ. The introduction of cerium also effectively suppresses the chemical expansion and the growth of grain particles. The smaller grain size is beneficial in improving the electrode surface area. In addition, the electrical conductivities of Ce-doped Sm_xSr_1-xCoO_3-δ are all higher than 200 S cm^-1. EIS tests demonstrate that partially substituting Co with Ce and the B-site deficiency improve the cathode performance. Sm_0.3Sr_0.7Co_0.95Ce_0.05O_3-δ shows the lowest area specific resistance (ASR) among the others. Through proper cobalt-site cerium doping, the Sm_xSr_1-xCoO_3-δ related oxides could be developed into promising cathode materials for SOFC.