Investigation of Sr0.7Ca0.3FeO3 oxygen carriers with variable cobalt B-site substitution.

A-site and B-site substitution have shown to be effective methods towards improving well-studied oxygen carrier materials that are vital for emerging gasification technologies. This includes SrFeO 3 , which greatly benefits from the inclusion of calcium and/or cobalt, leading to reports regarding Sr 0.8 Ca 0.2 Fe 0.4 Co 0.6 O 3 as the best-performing composition. In this work, we investigate systems with higher calcium and lower cobalt contents to lessen the societal and economic burdens of these dual-doped carriers. We perform density functional theory calculations to illustrate the Fe-O bonding and relaxation contributions towards the oxygen vacancy formation energy in Sr 1-x Ca x Fe 1-y Co y O 3 systems ( x = 0.1875, 0.25, 0.3125; y = 0.125, 0.25, 0.375, 0.5) and determine that an increased calcium A-site substitution requires the use of less cobalt B-site doping to reach the same oxygen vacancy formation.. Experimentally, we validate these findings by focusing our characterization on bulk Sr 0.7 Ca 0.3 Fe 1-y Co y O 3 materials using in situ and ex situ XRD, O 2 -TPD, and TGA. We find that Sr 0.7 Ca 0.3 Fe 0.7 Co 0.3 O 3 has similar O 2 adsorption/desorption rate and storage capacity to Sr 0.8 Ca 0.2 Fe 0.4 Co 0.6 O 3 in our Air/N 2 cycling experiments. Additionally, both materials are outperformed by Sr 0.7 Ca 0.3 Fe 1-y Co y O 3 systems with y = 0-0.10 at 400-500 °C, which cycle 1.5 wt.% O 2 in under ten minutes.