Cobalt-site cerium doped Sm xSr 1− xCoO 3− δ oxides as potential cathode materials for solid-oxide fuel cells

Abstract

A series of new oxides with the nominal composition of Sm x Sr 1− x Co 1− y Ce y O 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 x Sr 1− x Co 1− y Ce y− z O 3− δ (0 < z < y) and CeO 2 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 x Sr 1− x CoO 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 x Sr 1− x CoO 3− δ related oxides could be developed into promising cathode materials for SOFC.