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

Abstract

A new cubic perovskite oxide, SrCo0.7Fe0.2Nb0.1O3−δ (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+]0.1O3−δ. The electrical conductivity of the SCFN sample reaches a maximum 304 S cm−1 at 350 °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 Ω cm2 is achieved at 800 °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 μm thick SDC electrolyte achieve 417, 557, 630 and 517 mW cm−2 at 800 °C, respectively. These results indicate that SCFN–50SDC composite is a potential cathode material for application in IT-SOFCs.