| مستخلص: |
A detailed study aimed at understanding and confirming the reported highly promising performance of a La0.3Sr0.7Fe0.7Cr0.3O3−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 pO2atmospheres (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 CO2reduction at the cathode. Powdered LSFCr remains structurally stable in 20–100% CO2(balance N2, pO2= 10–11–10–12atm) without any decomposition. However, in 30% CO (balance N2, pO2∼ 10–26atm), 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= 10–17–10–18atm) mixtures at 800 °C, in 70 CO2/30 CO, minor impurities of SrCO3and 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 CO2electrolysis 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. |