Electronic engineering and oxygen vacancy modification of La0.6Sr0.4FeO3−δ perovskite oxide by low-electronegativity sodium substitution for efficient CO2/CO fueled reversible solid oxide cells

Abstract

Reversible solid oxide cells (RSOCs) hold enormous potential for efficient direct CO₂ reduction or CO oxidation in terms of exceptional faradic efficiency and high reaction kinetics. The identification of an active fuel electrode is highly desirable for enhancing the performance of RSOCs. This study explores the use of a alkaline metal dopant (Na) to modify the perovskite oxide of Na_2x(La_0.6−xSr_0.4−x)FeO_3−δ (2x = 0, 0.10, 0.20) materials with powerful CO₂ chemical adsorption capacity, high oxygen ion conductivity, and low average valence of Fe sites for CO₂/CO redox reactions. The experimental results indicate that the cells with the NaLSF0.10 fuel electrode achieve a current density of 1.707 A cm⁻² at 1.5 V/800 °C and excellent stability over 120 hours at 750 °C for pure CO₂ electrolysis, approximately 33.4% improvement over the pristine sample. When operated under a mixed CO–CO₂ atmosphere under RSOC mode, the cell outputs the performance of 1.589 A cm⁻² at 1.5 V and 329 mW cm⁻² at 800 °C, and demonstrates relatively durable operation over 25 cycles. The addition of low valence sodium ions with high basicity and low electronegativity reduces the oxygen vacancy formation energy, increases the concentration of oxygen vacancies and modifies the electronic structure of LSF, thus enhancing CO₂ adsorption, dissociation processes and charge transfer steps as corroborated by the detailed experimental analysis. Combined with the acceptable anti-carbon deposition capability, we prove here a feasible strategy and provide new insights into designing novel electrodes for SOEC/RSOCs to effectively convert CO₂ with potential for renewable energy storage.