Decarbonized core-shell-like structure: Enhancing Fe-based oxygen carriers for superior hydrogen selectivity and stability

Fe-based oxygen carriers undergo deactivation due to repeated oxidation-reduction cycles in chemical looping gasification. The primary cause of deactivation lies in the agglomeration and phase separation behavior exhibited by Fe-based oxygen carriers. In this research, a core-shell-like structure was developed to strengthen the structural stability of the oxygen carrier. This was achieved by constraining the thermal motion dimensions of active sites and establishing two pathways for oxygen ion transport. Briefly, the core-shell-like structure was constructed with NiFe2O4 as the core and CaO as the shell. Through characterization analysis, it was found that the interaction between the core-shell-like structures resulted in lattice distortion, promoting the generation of oxygen vacancies and providing a prerequisite foundation for the rapid reaction of lattice oxygen. Furthermore, the protective mechanism of the core-shell-like structure on the active sites inhibited the agglomeration behavior of the oxygen carrier. Remarkably, a hydrogen yield of 70 % was achieved at a temperature of 600 °C, and the reaction characteristics remained stable over 20 cycles of experimentation. Density functional theory calculations revealed that C atoms present stronger electron transfer at the core-shell-like structure, which induces stronger adsorption energy.