Hydrogen Production by Biomass Model Syngas Chemical Looping over Ce/Zr Doped NiFe₂O₄ Oxygen Carrier

Chemical looping hydrogen production (CLH) using biomass pyrolysis gas as fuel has garnered significant attention for its ability to efficiently convert biomass resources into high-concentration hydrogen, thus promoting resource reutilization and green, sustainable development. Oxygen carriers play a pivotal role in achieving the efficient operation of CLH. Doping of heterogeneous ions has proven to be an effective way to improve the performance of oxygen carriers based on mixed metal oxides. However, the interaction mechanisms and synergistic effects between the dopants and the parent crystal of oxygen carriers remain unclear, posing a key research challenge in this field. A series of oxygen carriers of NiFe2O4 modified by various Ce/Zr doping contents were prepared, and the results indicated that the oxygen carriers of Ce/Zr doping molar ratio of 0.3 exhibited the best performance: the hydrogen yield of 0.5 g of the reduced oxygen carriers (0.3CNF, 0.3ZNF) reached 11.83 and 12.22 mmol/g, respectively, with no significant performance degradation observed after 15 cycles. We investigated the interaction mechanisms between the doping elements and the NiFe2O4 spinel host through various characterization techniques and density functional theory (DFT) calculations. It was revealed that surface Ce elements enhance the reactivity and stability of the doped samples by reducing the oxygen vacancy formation energy and optimizing the electronic structure of active catalytic sites. Additionally, Zr elements significantly improved the material’s durability and resistance to sintering. These findings provide valuable theoretical insights and experimental evidence for the design and optimization of oxygen carriers in chemical looping hydrogen production.