A Theoretical Study of the Reactive Mechanisms of Alkali Metal Doped Ni-Based Oxygen Carrier During Chemical Looping Combustion

Chemical looping combustion (CLC) is a promising technology for CO₂ capture, with the performance of the system largely dependent on the oxygen carrier. Although Ni-based carriers have been extensively investigated, their practical application is still constrained by inadequate reactivity. This study investigated the doping of alkali metals (Li, Na, K) into NiO to improve its performance in CLC. Through density functional theory calculations, the structural, electronic, and reactivity of doped NiO surfaces were systematically analyzed. Results reveal that doping induces lattice expansion and enhances CO adsorption, with adsorption energies strengthening to −0.53 eV for Li, −0.46 eV for Na, and −0.36 eV for K. Furthermore, alkali metal doping significantly reduces the energy barrier for CO₂ formation from 2.12 eV on pure NiO to 0.73 eV, 0.80 eV, and 0.99 eV on Li-, Na-, and K-doped surfaces, respectively. Oxygen vacancy formation energy also decreases from 3.60 eV to as low as 2.90 eV for K-doping, indicating markedly improved oxygen activity. Electronic structure analysis confirms that doping facilitates electron transfer and stabilizes key reaction intermediates. In conclusion, alkali metal doping substantially enhances the redox activity of NiO, providing an effective strategy for developing high-performance oxygen carriers in CLC.