SrCo0.50Fe0.40Ir0.10O3−δ Decorated with Pd and La0.8Sr0.2Ga0.83Mg0.17O3−δ: A Cleaner Electrode for Intermediate-Temperature Solid Oxide Fuel Cells with Reduced Cobalt Content

Abstract

Recent studies related to cathode materials for solid oxide fuel cells (SOFCs) have showcased the feasibility of stabilizing cubic or tetragonal perovskite phases in the SrCoO3−δ system at room temperature. This achievement has been facilitated by partially substituting Co atoms with small amounts of highly charged cations such as Ir4+ in SrCo0.90Ir0.10O3−δ. This specific material exhibits exceptional performance as a cathode for SOFCs operating at intermediate temperatures (800–850 °C). However, it contains a high amount of cobalt, which is both costly and toxic. In this study, our focus has been on further improving this material by reducing its cobalt content, resulting in a cleaner and more cost-effective cathode for SOFCs. The resulting SrCo0.50Fe0.40Ir0.10O3−δ perovskite, synthesized by the citrate method, introduces a 40% composition of Fe in the sites of Co and Ir, effectively decreasing the amount of Co in the material. The crystal structure of this perovskite oxide has been analyzed using X-ray diffraction (XRD) and neutron powder diffraction (NPD), allowing us to establish correlations with its mechanical and electrical properties. In the single-cell test, this material gave reasonable performances as a cathode at intermediate temperatures (800–850 °C), with La0.8Sr0.2Ga0.83Mg0.17O3−δ (LSGM) as the electrolyte. An analysis of the chemical compatibility between the cathode and the electrolyte, LSGM, demonstrated no interaction at elevated temperatures. Thermal expansion coefficient (TEC) measurements exhibited consistent linear expansion across the entire temperature range. Lastly, the perovskite displayed commendable electrical conductivity along with a promising power density measurement of 384 mW/cm2 at 850 °C. These findings collectively suggest the potential of this material as a viable cleaner cathode option for intermediate-temperature SOFCs. Moreover, the cathode was further optimized and the performance of the cell improved, by either infiltrating SrCo0.50Fe0.40Ir0.10O3−δ with a Pd(NO3)2 solution or mixing it with 30% of LSGM electrolyte, resulting in higher power densities (568 and 675 mW/cm2, respectively) in test cells fed with pure H2 as a fuel.