A- and B-site Codoped SrFeO₃ Oxygen Sorbents for Enhanced Chemical Looping Air Separation

Chemical-looping air separation has numerous potential benefits in terms of energy saving and emission reductions. The current study details a combination of density functional theory calculation and experimental efforts to design A- and B-site codoped SrFeO₃ perovskites as "low-temperature" oxygen sorbents for chemical-looping air separation. Substitution of the SrFeO₃ host structure with Ca and Co lowers oxygen vacancy formation energy by 0.24-0.46 eV and decreases the oxygen release temperature. As a result, Sr_1-x Ca_x Fe_1-y Co_y O₃ (SCFC; x=0.2, 0.0<y<1.0) spontaneously releases oxygen at 400-500 °C even under a relatively high oxygen partial pressure (e.g. P ${}_{O{}_2}$ =0.05 atm). Sr_0.8 Ca_0.2 Fe_0.4 Co_0.6 O₃ exhibits a significantly higher oxygen capacity of 1.2 wt % at 400 °C and under a P ${}_{O{}_2}$ swing between 0.05 and 0.2 atm, when compared to the <0.2 wt % capacity for undoped a SrFeO₃ (SF) and Ca-doped Sr_0.8 Ca_0.2 FeO₃ (SCF). Electrical conductivity relaxation (ECR) study demonstrates that codoping of Ca and Co lowers the activation energy of oxygen diffusion and surface oxygen exchange by 26.6 or 137.9 kJ mol^-1 , respectively, resulting in faster redox kinetics for SCFC than for SCF perovskite. The SCFC oxygen sorbent also exhibits excellent stability for 2000 redox cycles for air separation.