Abstract
Fe partial substitution for Co on B-site may tradeoff stability-activity for BaCoO3-δ perovskite. However, large radius mismatch between Ba and Co/Fe favors the formation of a low symmetric hexagonal phase BaCo1-xFexO3-δ, which may experience phase structural transitions with varying temperatures and could induce structural reliability issue of associated devices. The B-site doping with high valence elements may facilitate to form cubic BaCo1-xFexO3-δ perovskite, it could also significantly deteriorate their catalytic property. The Yb3+ with ionic radius being larger than those of Co4+ and Fe4+ could be used as B-site dopant to tune Goldschmidt tolerance factor of BaCo1-xFexO3-δ to 1 and therefore stabilize its cubic structure. Additionally, the electronegativity of Yb is lower than that of Co and Fe. This would induce a slightly lower valance of Co and/or Fe when Yb is used as B-site dopant, facilitating oxygen vacancy generation and electrochemical kinetic process. In this research, Yb-doping effects on crystal structure and performance of BaCo0.7Fe0.3-xYbxO3-δ (x = 0.05, 0.10 and 0.15) are systematically evaluated. The results indicate that Yb partial substitution for Fe on B-site is able to effectively stabilize crystal structure with highly cubic symmetry and BaCo0.7Fe0.2Yb0.1O3-δ is among the best as cathode material for intermediate temperature SOFCs.
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