Structure and Properties of Novel Cobalt-Free Oxides Nd_<i>x</i>Sr_1–<i>x</i>Fe_0.8Cu_0.2O_3−δ (0.3 ≤ <i>x</i> ≤ 0.7) as Cathodes of Intermediate Temperature Solid Oxide Fuel Cells

Abstract

Novel cobalt-free perovskite oxides NdxSr1–xFe0.8Cu0.2O3−δ (NSFCx, 0.3 ≤ x ≤ 0.7) have been prepared and evaluated as cathodes for intermediate temperature solid oxide fuel cells (IT-SOFC). Their structure, thermal expansion, electric, and electrochemical properties are investigated. The oxides exhibit all cubic structure and show excellent thermal and electrochemical performance stability. The Nd content (x) significantly affects the properties of NSCFx. NSFC0.5 has been found to be the optimum composition with a peak electrical conductivity of 124 S cm–1 at 700 °C, an average thermal expansion coefficient of 14.7 × 10–6 K–1 over 25–800 °C, a cathodic polarization resistance (Rp) of 0.071 Ω cm2 at 700 °C, and a peak power density of 900 mW cm–2 at 800 °C for samarium-doped ceria (SDC)-based single cells with NSFCx cathodes and Ni–SDC anodes. Moreover, no degradation has been observed for the Rp at 700 °C within 350 h. The concentration of surface oxygen vacancies and composition dependent crystallographic parameters have been found to be the dominating factors on performance of NdxSr1–xFe0.8Cu0.2O3−δ as IT-SOFC cathodes.