An A- and B-Site Substitutional Study of SrFeO_3-δ Perovskites for Solar Thermochemical Air Separation

An A‑ and B‑site substitutional study of SrFeO_3-δ perovskites (A'A_1-B'B_1-O_3-δ, where A = Sr and B = Fe) was performed for a two‑step solar thermochemical air separation cycle. The cycle steps encompass (1) the thermal reduction of A'Sr_1-B'Fe_1-O_3-δ driven by concentrated solar irradiation and (2) the oxidation of A'Sr_1-B'Fe_1-O_3-δ in air to remove O₂, leaving N₂. The oxidized A'Sr_1-B'Fe_1-O_3-δ is recycled back to the first step to complete the cycle, resulting in the separation of N₂ from air and concentrated solar irradiation. A-site substitution fractions between 0 ≤ x ≤ 0.2 were examined for A' = Ba, Ca, and La. B-site substitution fractions between 0 ≤ y ≤ 0.2 were examined for B' = Cr, Cu, Co, and Mn. Samples were prepared with a modified Pechini method and characterized with X-ray diffractometry. The mass changes and deviations from stoichiometry were evaluated with thermogravimetry in three screenings with temperature- and O₂ pressure-swings between 573 and 1473 K and 20% O₂/Ar and 100% Ar at 1 bar, respectively. A' = Ba or La and B' = Co resulted in the most improved redox capacities amongst temperature- and O₂ pressure-swing experiments.