Investigation of Sr<sub>0.7</sub>Ca<sub>0.3</sub>FeO<sub>3</sub> Oxygen Carriers with Variable Cobalt B‐Site Substitution
Eric J. Popczun, Ting Jia, Sittichai Natesakhawat, Chris M. Marin, Thuy‐Duong Nguyen‐Phan, Yuhua Duan, Jonathan W. Lekse
Abstract
Abstract 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 SrFeO 3 , which greatly benefits from the inclusion of calcium and/or cobalt, and Sr 0.8 Ca 0.2 Fe 0.4 Co 0.6 O 3 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 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 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 Sr 0.7 Ca 0.3 Fe 1‐ y Co y O 3 materials. Sr 0.7 Ca 0.3 Fe 0.7 Co 0.3 O 3 is found to have similar O 2 adsorption/desorption rates and storage capacity to Sr 0.8 Ca 0.2 Fe 0.4 Co 0.6 O 3 in 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.