Electrochemical Performance of SrFeO3−δ for Application as a Symmetric Electrode in Solid Oxide Fuel Cells

Abstract

SrFeO3−δ has been earlier reported to exhibit a large area-specific resistance even though it possesses high mixed ionic–electronic conductivity both in oxidizing and reducing conditions. The present study clarifies this aspect and investigates the defect chemistry and electrochemical performance correlations in SrFeO3−δ for the possible use as a symmetric electrode in solid oxide fuel cells. A conventional solid-state reaction method is adopted for powder synthesis. Structural characterization indicates an orthorhombic perovskite phase formation with a δ of 0.21. High dc electrical conductivities of ∼114.9 and 0.26 S·cm–1 are observed at 800 °C in air and reducing conditions, respectively. The area-specific resistance (ASR) for the SrFeO3−δ electrode is measured in a symmetrical half-cell configuration under various gas environments. At 800 °C, SrFeO3−δ offered low ASRs of 0.082, 0.055, and 0.122 Ω·cm2 in air, oxygen, and 3% H2O/H2, respectively. Although the ASR possesses excellent temporal stability in an oxidizing atmosphere, it increases to 0.42 Ω·cm2 after 100 h in reducing conditions owing to the brownmillerite phase formation. The redox cycling performance is also affected with the ASR rising from 0.13 to 0.24 Ω·cm2 at 800 °C in 3% H2O/H2 after 20 cycles. A maximum power density of 202 mW·cm−2 is achieved from the electrolyte-supported symmetric single cell based on the SrFeO3−δ electrodes at 800 °C. The results demonstrate the viability of using a SrFeO3−δ-based electrode for symmetrical solid oxide fuel cells.