Structure and electrochemical properties of cobalt-free perovskite cathode materials for intermediate-temperature solid oxide fuel cells

Abstract

Cobalt-free perovskite oxides, BaFeO3-δ and BaM0.05Fe0.95O3-δ (M = Ti, Zr and Ce), were prepared as the cathode of intermediate-temperature solid oxide fuel cells (IT-SOFCs). High temperature X-ray diffraction (HT-XRD) results show that BaFeO3-δ and BaTi0.05Fe0.95O3-δ (BTF) have a complex phase composition, and the phase composition changes with temperature. BaZr0.05Fe0.95O3-δ (BZF) has a cubic perovskite structure above 400 °C, while BaCe0.05Fe0.95O3-δ (BCF) has a cubic perovskite structure from room temperature (25 °C) to 1000 °C. Thermogravimetric analysis (TG) and oxygen temperature-programmed desorption (O2-TPD) analysis reveal that the phase transition affects the oxygen-release properties of these materials. In contrast to BaFeO3-δ and BTF showing phase-transition-dependent electrical conductivity, BZF and BCF show typical curves similar to other mixed ionic-electronic perovskite oxides. On an electrolyte of Sm0.2Ce0.8O1.9 (SDC), a single cell with a BCF cathode exhibits polarization resistances of 0.027, 0.046, 0.087 and 0.186 Ω cm2 at 750, 700, 650 and 600 °C, respectively. The peak power densities of the single cell are 482, 415 and 315 mW cm-2 at 750, 700 and 650 °C, respectively. This indicates that the Co-free BCF has a good electrocatalytic activity toward the oxygen reduction reaction and is a promising cathode for IT-SOFCs.