Entropy-Engineered High-Entropy Spinel Oxides with Balanced Lattice Oxygen Reactivity for Efficient Chemical Looping...

Chemical looping reforming (CLR) is a promising route for converting biomass and its derivatives into syngas. However, its application is hindered by the trade-off between fuel conversion and syngas selectivity, largely governed by the lattice oxygen activity of the oxygen carrier (OC). Herein, we propose an entropy engineering strategy to regulate lattice oxygen activity using a high-entropy spinel oxide, Cr_0.2Mn_0.2Co_0.2Ni_0.2Mg_0.2Fe₂O₄ (HEO). The high-entropy configuration induces lattice distortion and multimetallic synergy, reconstructing the oxygen coordination environment and shifting the O 2p band center to an intermediate position, thereby achieving balanced lattice oxygen reactivity and regeneration performance. As a result, Cr_0.2Mn_0.2Co_0.2Ni_0.2Mg_0.2Fe₂O₄ with appropriate oxygen reactivity suppresses deep oxidation while maintaining sufficient oxygen availability for toluene partial oxidation. In CLR, it achieves a syngas yield of 4.75 Nm³ kg^-1 C₇H₈ with 95.68% purity, together with excellent sintering resistance and sustained cyclic stability over 100 h. Through experimental and DFT analyses, we identify the roles of each cation: Cr stabilizes the structure, Mn/Fe supply abundant lattice oxygen, Ni/Co modulate oxygen activity, and Mg promotes oxygen migration. These insights demonstrate that entropy engineering provides a general route to circumvent the reactivity-selectivity trade-off, establishing design guidelines for next-generation OCs in biomass conversion and syngas production.