Abstract
Double perovskite-type Sr11Mo4O23 material exhibits unusual structural flexibility and oxygen ion mobility. However, the transition of Sr11Mo4O23 cubic phase to SrMoO4 tetragonal phase around 400 ℃ makes the conductivity drop by 45.8 %. Hence, it is necessary to stabilize the phase structure and improve the electrochemical performance of Sr11Mo4O23 in order to be used for implementing into intermediate temperature solid oxide fuel cells (IT-SOFCs). In this work, a novel Sr10.8A0.2Mo3.5Ta0.5O23-δ (A =Li, Na, K) electrolyte powders are synthesized by a citrate-nitrate combustion method. X-ray diffraction, scanning electron microscopy and electrochemical impedance spectroscopy are used to investigate the effects of acceptor-type Ta and alkali metals co-doping on phase structural, microstructure and electrical properties of Sr11Mo4O23. All Sr10.8A0.2Mo3.5Ta0.5O23-δ samples show the same single phases as Sr11Mo4O23 (Fdm space group, JCPDS 27-1441). Doping Ta element at the B-site of Sr11Mo4O23 can inhibit the phase transition of Sr11Mo4O23 to SrMoO4 so as to improve the structure stability of Sr11Mo4O23. On this basis, doping alkali metal at the A-site further enhances the electrical conductivity of Sr11Mo3.5Ta0.5O23-δ(SMTO). Among them, Sr10.8K0.2Mo3.5Ta0.5O23-δ (SKMTO) sample has the conductivity of 2.02 × 10−2 S/cm in the air at 800 ℃, which is ∼ 233 % higher than that measured for Sr11Mo4O23. Moreover, the reliable chemistry stability of the SKMTO samples was demonstrated under wet reducing 5 % H2 or dry 3 % CO2 atmospheres, respectively. Finally, the single cells with SKMTO and SMTO electrolytes supported were successfully prepared by screen-printing method, respectively. The power density of SKMTO-cell is improved by at least 254 % compared to SMTO-cell. It can be deduced that co-doped Sr10.8K0.2Mo3.5Ta0.5O23-δ can be considered as potential electrolyte for IT-SOFCs.
Published Version
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