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’(x)A(1−x)B’(y)B(1−y)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’(x)Sr(1−x)B’(y)Fe(1−y)O(3−δ) driven by concentrated solar irradiation and (2) the oxidation of A’(x)Sr(1−x)B’(y)Fe(1−y)O(3−δ) in air to remove O(2), leaving N(2). The oxidized A’(x)Sr(1−x)B’(y)Fe(1−y)O(3−δ) is recycled back to the first step to complete the cycle, resulting in the separation of N(2) 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 O(2) pressure-swings between 573 and 1473 K and 20% O(2)/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 O(2) pressure-swing experiments.