Deciphering the Interaction of Single-Phase La_0.3Sr_0.7Fe_0.7Cr_0.3O_3-δ with CO₂/CO Environments for Application in...

A detailed study aimed at understanding and confirming the reported highly promising performance of a La_0.3Sr_0.7Fe_0.7Cr_0.3O_3-δ (LSFCr) perovskite catalyst in CO₂/CO mixtures, for use in reversible solid oxide fuel cells (RSOFCs), is reported in this work, with an emphasis on chemical and performance stability. This work includes an X-ray diffraction (XRD), thermogravimetric analysis (TGA), and electrochemical study in a range of pO₂ atmospheres (pure CO₂, CO alone (balance N₂), and a 90-70% CO₂/10-30% CO containing mixture), related to the different conditions that could be encountered during CO₂ reduction at the cathode. Powdered LSFCr remains structurally stable in 20-100% CO₂ (balance N₂, pO₂ = 10^-11-10^-12 atm) without any decomposition. However, in 30% CO (balance N₂, pO₂ ∼ 10^-26 atm), a Ruddlesden-Popper phase, Fe nanoparticles, and potentially some coke are observed to form at 800 °C. However, this can be reversed and the original perovskite can be recovered by heat treatment in air at 800 °C. While no evidence for coke formation is obtained in 90-70% CO₂/10-30% CO (pO₂ = 10^-17-10^-18 atm) mixtures at 800 °C, in 70 CO₂/30 CO, minor impurities of SrCO₃ and Fe nanoparticles were observed, with the latter potentially beneficial to the electrochemical activity of the perovskite. Consistent with prior work, symmetrical two-electrode full cells (LSFCr used at both electrodes), fed with the various CO₂/CO gas mixtures at one electrode and air at the other, showed excellent electrochemical performance at 800 °C, both in the SOFC and in SOEC modes. Also, LSFCr exhibits excellent stability during CO₂ electrolysis in medium-term potentiostatic tests in all gas mixtures, indicative of its excellent promise as an electrode material for use in symmetrical solid oxide cells.