Enhanced Morphological Preservation and Redox Activity in Al-Incorporated NiFe₂O₄for Chemical Looping Hydrogen Production

Although chemical looping technology has enabled energy-efficient H2 production by combining separation and reaction through the lattice oxygen in oxygen storage materials (OSMs), metal oxides undergoing successive reduction-oxidation cycles generally suffer from a decline in long-term performance. This work investigates an Al-incorporated Ni-ferrite (NiFe2O4) particle to demonstrate a detailed deactivation mechanism induced by redox stress and suggests a strategy to prolong the lifespan of the particle. It is revealed that the grain coalescence and surface densification hamper the redox performance by decreased electrical conductivity and retarded gas transfer, eventually leading to deactivation over the cycles. The formation of a spinel solid solution with aluminum (Al) incorporation was found to be an effective strategy to prevent densification and maintain the long-term performance. Al incorporation at 3.3 wt % is determined as the best particle that can maintain the highest H2 yield (8.2 mmol H2·g-1) and average production rate (0.41 mmol H2·g-1·min-1) for 11 cycles.