A-site and B-site substitutions are effective methods towards improving well-studied oxygen carrier materials that are vital for emerging gasification technologies. Such materials include SrFeO3 , which greatly benefits from the inclusion of calcium and/or cobalt, and Sr0.8 Ca0.2 Fe0.4 Co0.6 O3 has been regarded as the best-performing composition. In this study, systems with higher calcium and lower cobalt contents are investigated with a view to lessening the societal and economic burdens of these dual-doped carriers. Density functional theory calculations are performed to illustrate the Fe-O bonding and relaxation contributions to the oxygen vacancy formation energy in Sr1-x Cax Fe1-y Coy O3 systems (x=0.1875, 0.25, 0.3125; y=0.125, 0.25, 0.375, 0.5) and determine that increased calcium A-site substitution requires the use of less cobalt B-site doping to reach the same oxygen vacancy formation. These findings are experimentally validated in situ and ex situ characterization of bulk Sr0.7 Ca0.3 Fe1-y Coy O3 materials. Sr0.7 Ca0.3 Fe0.7 Co0.3 O3 is found to have similar O2 adsorption/desorption rates and storage capacity to Sr0.8 Ca0.2 Fe0.4 Co0.6 O3 in air/N2 cycling experiments. Additionally, both materials are outperformed by Sr0.7 Ca0.3 Fe1-y Coy O3 systems with y=0-0.10 at 400-500 °C, which cycle 1.5 wt% O2 in under ten minutes.
Keywords: air separation; cobalt; density functional calculations; perovskites; sorbents.
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