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

Abstract

A detailed study aimed at understanding and confirming the reported highly promising performance of a La 0.3 Sr 0.7 Fe 0.7 Cr 0.3 O 3−δ (LSFCr) perovskite catalyst in CO 2 /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 pO 2 atmospheres (pure CO 2 , CO alone (balance N 2 ), and a 90−70% CO 2 /10−30% CO containing mixture), related to the different conditions that could be encountered during CO 2 reduction at the cathode. Powdered LSFCr remains structurally stable in 20−100% CO 2 (balance N 2 , pO 2 = 10 −11 −10 −12 atm) without any decomposition. However, in 30% CO (balance N 2 , pO 2 ∼ 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% CO 2 /10−30% CO (pO 2 = 10 −17 −10 −18 atm) mixtures at 800 °C, in 70 CO 2 /30 CO, minor impurities of SrCO 3 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 CO 2 /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 CO 2 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.

Unlocking the Potential of A-Site Ca-Doped LaCo0.2Fe0.8O3−δ: A Redox-Stable Cathode Material Enabling High Current Density in Direct CO2 Electrolysis

“…Moreover, the chemical stability of cathode materials offers the potential for achieving stable cell performance. 22,37 Therefore, TGA was employed to estimate the redox stability of LCxCF materials by monitoring the weight changes at elevated temperatures in different atmospheres.…”

“…It is widely recognized that the presence of oxygen vacancies in cathode materials plays a pivotal role in enhancing CO 2 electrolysis by creating active sites for nonpolar CO 2 adsorption. Moreover, the chemical stability of cathode materials offers the potential for achieving stable cell performance. , Therefore, TGA was employed to estimate the redox stability of LC x CF materials by monitoring the weight changes at elevated temperatures in different atmospheres.…”

Copper-Enhanced CO2 Electroreduction in SOECs

“…Structural instability represents a serious issue for fuel electrodes in SOEC configuration too, especially when CO is mixed with the CO 2 feed or under large cathodic overpotential. B-site substitution with Cr or Ti was reported to stabilize the lanthanum ferrite lattice, retaining the perovskite structure in reducing conditions. − Alternatively, substitution with Mo or Mn resulted in a controlled phase transition to a Ruddlesden–Popper layered oxide after reduction. , This latter strategy might be less effective than the former, as the volume variation upon phase transition may lead to electrode delamination. Concerning stability, innovative electrodes for CO 2 -RR, tested on lab-scale systems, show durability in the range of tens to hundreds of hours. , …”

In situ construction of a double perovskite heterostructure with exsolved FeNi3 alloy nanoparticles for CO2 electrolysis in solid oxide electrolysis cells

“…As previously reported, perovskite-type oxides, such as mixed ionic and electronic conductors (MIECs), have been developed as promising alternative cathode materials for the CO 2 RR. MIECs, such as perovskites La x Sr 1−x -FeO 3−d (LSF), [8][9][10][11] La x Sr 1−x Co y Fe 1−y O 3−d (LSCF), 12 and La x Sr 1−x Cr y Fe 1−y O 3−d (LSCrF) 13 as well as double perovskite oxides PrBaCo 2 O 5+d (PBC) 14,15 and Sr 2 Fe 1.5 Mo 0.5 O 6−d (SFM), 16,17 exhibit superior redox stability and resistance to carbon deposition. Among them, Co-based perovskite oxides have been found to exhibit high catalytic activity in CO 2 electrolysis.…”

“…However, their application is limited by their thermal expansion coefficient (TEC) and high cost. Recently, Fe-based perovskite oxides, such as Sr 2 Fe 1.5 Mo 0.5 O 6−d (SFM), [18][19][20] La 0.5 Sr 0.5 FeO 3−d (LSF), 4,9,21 and BaFeO 3−d (BF), 22 have gained widespread attention because of their low thermal expansion coefficient, high stability and low cost. Unfortunately, the electrocatalytic performance of Fe-based perovskites is inferior to that of Cobased oxides owing to their lower conductivity and higher energy barriers for oxygen vacancy formation.…”