Fabrication And Performance Improvement Of Novel Nb-doped Sr₂Fe_1.5Mo_0.5O_6-δ Electrode Material For SOFCs

Sr₂Fe_1.5Mo_0.5O_6-δ（SFM） with perovskite structure has excellent redox stability, high electrical conductivity and can be considered as both anode and cathode materials for intermediate-temperature solid oxide fuel cells（IT-SOFCs）, therefore it has attracted much attention. In order to further improve the electrochemical performance of SFM, in this paper, B-site doping and oxygen ion conductor composite were applied to improve the electrically catalytic activity at the intermediate temperature. At the same time, the possibility of B-site doped SFM material in symmetrical cel s were studied.A series of Sr₂Fe_1.5-xNb_xMo_0.5O_6-δ（SFNb_xM, x=0, 0.025, 0.05, 0.075, 0.1, 0.15, 0.2） materials were prepared by a facile one-step combustion method. The study of the effect of Nb-doping Fe-site on phase structure in air atmosphere, microstructure, element valence, conductivity of SFM material was carried out. Electrochemical impedance spectroscopy（EIS） was also tested. At the same time these powders were reduced in hydrogen atmosphere, and the reduced powders were analyzed by XRD, XPS and EIS test. XRD analysis indicates that SFM, SFNb0.05 M, SFNb0.1M materials are stable in both oxidation and reduction atmosphere, so these materials can be used as electrode materials of symmetrical cells. EIS test shows that no matter in the air or hydrogen atmosphere, when the doping amount of Nb elements is 0.05, the material shows the smallest resistance. The polarization resistance in air and hydrogen atmosphere at 800 oC are 0.080 Ω·cm2 and 1.52 Ω·cm2, respectively. Above results prove SFNb0.05 M material has the best electrochemical properties and it is a promising electrode material for symmetrical cel s.A series of composite electrodes Sr₂Fe_1.5Mo_0.4Nb_0.1O_6-δ-Sm_0.2Ce_0.8O_1.9（SFMNb-SDC） have been prepared by a facile one-step combustion method. XRD, SEM, TEM were tested, and the conductivity and thermal expansion coefficient（TEC） were also tested in the air. XRD confirms that pure phase structure of SFMNb-SDC can be prepared. EIS results exhibit that when the content of SDC in SFMNb-SDC cathode is 40 wt %, the cathode has the best electrochemical performance, and the polarization resistance is 0.047 Ω·cm2 at 800 oC, Furthermore the discharge performance was measured by preparing single cell with SS40 composite cathode. The peak power densities of single cells are 0.31, 0.47, 0.72 and 1.22 W·cm-2 at 650, 700, 750 and 800 oC, respectively. All these results suggest that SFMNb-SDC materials are promising cathodes for IT-SOFCs.