BaCo0.6Fe0.3Sn0.1O3-δ perovskite as a new superior oxygen reduction electrode for intermediate-to-low temperature solid oxide fuel cells

Abstract

BaCo0.6Fe0.3Sn0.1O3−δ (BCFSn631) is evaluated as an oxygen reduction electrode for intermediate-to-low temperature solid oxide fuel cells (SOFCs). XRD and HR-TEM analysis demonstrate that it is in a simple perovskite phase with cubic lattice symmetry. In situ HT-XRD and ex situ XRD confirm the favorable phase stability of the oxide under a wide range of temperatures and atmospheric oxygen partial pressures. The oxygen nonstoichiometry, electrical conductivity, oxygen reduction activity and electrochemical performance of BCFSn631 are systematically studied through thermogravimetric analysis, electrical conductivity relaxation tests and electrochemical impedance analysis. It has a low thermal expansion coefficient of [similar] ~15.8 x 10−6 K−1 in a temperature range of 25–800 °C and a high oxygen vacancy concentration. Electric conductivity relaxation measurement demonstrates the high oxygen surface exchange and bulk diffusion properties of BCFSn631, comparable to that of the state-of-the-art Ba0.5Sr0.5Co0.8Fe0.2O3−δ electrode. Low area specific resistances are obtained for the BCFSn631 electrode in the intermediate temperature range, determined by electrochemical impedance spectroscopy based on symmetrical cell configuration, suggesting its high activity for oxygen reduction reaction. Peak power densities of 1168, 896, 523 and 273 mW cm−2 are obtained from a fuel cell with BCFSn631 electrode at 600, 550, 500 and 450 °C, respectively. In addition, good long-term performance stability is demonstrated. All these results highly promise BCFSn631 as an excellent oxygen reduction electrode for next generation SOFCs.