Characterization of SrCo0.7Fe0.2Nb0.1O3-δ cathode materials for intermediate-temperature solid oxide fuel cells

A new cubic perovskite oxide, SrCo0.7Fe0.2Nb0.1O3-delta(SCFN), is investigated as a cathode for intermediate-temperature solid oxide fuel cells (IT-SOFCs). XRD results show that there are no serious reactions between SCFN and Sm0.2Ce0.8O1.9(SDC) except a slight peak shift. XPS analysis shows that the transition-metal cations in the SCFN exist in two different valence states, i.e., [Sr2+][Co3+/Co4+](0.7)[Fe3+/Fe4+](0.2)[Nb4+/Nb5+](0.1)O3-delta. The electrical conductivity of the SCFN sample reaches a maximum 304 S cm(-1) at 350 degrees C in air. In order to optimize thermal expansion coefficients (TECs) and electrochemical performance of the SCFN cathode, we fabricate SCFN-xSDC (x = 0, 20, 30, 40, 50, 60, wt%) composite cathodes. The thermal expansion behavior shows that the TECs value of SCFN cathode decreases greatly with SDC addition. The SDC addition reduces the polarization resistance, and the lowest polarization resistance 0.0255 Omega cm(2) is achieved at 800 degrees C for SCFN-50SDC composite cathode. For SCFN-xSDC (x = 0, 40, 50, 60) composites, the maximum power densities of single-cells with SCFN-xSDC cathodes on 300 mum thick SDC electrolyte achieve 417, 557, 630 and 517 mW cm(-2) at 800 degrees C, respectively. These results indicate that SCFN-50SDC composite is a potential cathode material for application in IT-SOFCs. (C) 2014 Elsevier B.V. All rights reserved.