Synergetic Polymetallic Activation: Boosting Performance of Calcium Ferrite Oxygen Carriers in Chemical Looping Combustion

Oxygen carriers (OCs) are the material basis for chemical looping combustion (CLC). Doping routine OCs with polymetallics is crucial for the design and construction of high-performance OCs. However, understanding the effects and mechanisms of polymetallic doping on calcium ferrite, which possesses a unique perovskite structure, has not yet been well achieved, and a comprehensive investigation by combined synthesis, structure, performance, and mechanism analysis is much desired. This study focuses on calcium ferrite OCs codoped with Ni, Cu, and Co, examining the effects on oxygen storage capacity, mobility, and surface oxygen vacancies. The doped OCs maintain the perovskite structure with lattice distortions due to atomic size differences, as confirmed by XRD. SEM and TEM show uniform particle dispersion with an average size of 200-400 nm, and XPS reveals surface oxygen defects. H2-TPR results indicate a decrease in activation energy for oxygen release with increased doping, with the lowest value of 26.7 kJ/mol achieved for the (CaFeCoNiCu)O OCs. DFT calculations elucidate the electronic structure, showing that doping increases the configurational entropy and enhances d-p orbital hybridization, crucial for OC activity. The presence of oxygen vacancies influences d orbital occupancy, affecting electron density and charge distribution, which promotes charge transfer and modulates OC-fuel interactions. This work provides insights into designing high-performance OCs for CLC applications.