High-Performing Zr4+/Ti4+ Co-doped SrFeO3 as Electrodes for Symmetrical Solid Oxide Fuel Cells

Abstract

Bifunctional electrodes are critical for ensuring high performance and reliable operation in symmetrical solid oxide fuel cells (SSOFCs). This study introduces a novel Zr/Ti co-doping strategy in perovskite-structured SrFeO_3-δ, which significantly enhances performance stability, establishing it as a strong candidate for symmetrical electrode applications. A series of SrFe_1-xTi_x/2Zr_x/2O₃-_δ (x = 0-0.2) compositions are synthesised via the conventional solid-state reaction method. The co-doped samples retain a cubic phase, albeit with considerable oxygen deficiency in air. The optimized composition, SrFe_0.85Ti_0.075Zr_0.075O₃-_δ (SFTZ-0.15), demonstrates electrical conductivities of 68.5 S.cm^-1 in air and 3.6 S.cm^-1 in 3% H₂O/H₂ at 800°C. Under extreme reducing conditions, the brownmillerite phase and Fe particle exsolution occur. The area-specific resistance (ASR) offered by the SFTZ-0.15 electrode at 800°C is 0.046 Ω.cm² in air and 0.064 Ω.cm² in moist H₂. While stable in air, the ASR rises to 0.132 Ω.cm² after 100 h exposure in reducing conditions. Electrolyte-supported symmetrical single-cells with SFTZ-0.15 electrodes deliver a maximum power density of 732 mW.cm^-2 at 800°C, retaining 91.5% of their performance after 100 h of continuous operation at 1.2 A·cm^-2. These findings highlight the synergistic benefits of Zr⁴⁺/Ti⁴⁺ co-doping in SrFeO_3-δ, showcasing its potential as a bifunctional electrode for SSOFCs.