Cation synergy in Sr and Al substituted LaMnO3 during solar thermochemical CO2 splitting

Abstract

Perovskites (ABO₃) constitute an important category of oxygen carriers for applications in thermochemical redox processes. This study aims to derive the relationship of cation dependent parameters including the tolerance factor (τ), critical radius (R_c), free volume (V_F), electronegativity (χ), and metal–oxygen bond energy (λ) with O₂/CO evolution efficiencies during redox steps of La_xSr_1−xMn_yAl_1−yO₃ (x = 0.4, 0.5, and 0.6 and y = 0.4, 0.5, 0.6, and 0.75) perovskite series. Such parameters can reflect the lattice structural variations and bond polarity in these materials. The observed trends of O₂/CO evolution are nearly reversed, with regard to the variations in cation constitution. Inconclusive correlations were observed for τ, R_c, and V_F during reduction and re-oxidation, indicating that the role of these parameters in representing the observed redox behaviour is limited. In contrast, the cation electronegativities and metal–oxygen bond energies were found to induce a significant impact in depicting the redox chemistry of these materials. Rather than the individual effects, the entire cationic constituents are found to synergistically influence the reduction and re-oxidation reactions of the oxygen carriers used in this study. Direct relationships are observed for the calculated values of both χ and λ with the experimentally derived O₂/CO evolution. The outcomes of this study can possibly influence the design of oxygen carriers with an improved performance in thermochemical processes for converting CO₂ and utilizing solar energy.