Copper-Induced Lattice Engineering in CoFe2O4: Oxygen Vacancy Modulation for Enhanced Chemical Looping Hydrogen Production

Chemical looping hydrogen production is an attractive route for generating high-purity hydrogen because fuel oxidation and steam splitting are separated by the cyclic redox reactions of solid oxygen carriers. CoFe2O4 has been considered a potential oxygen carrier, but its reactivity and durability still need further improvement during repeated redox cycles. In this work, Cu was introduced into the CoFe2O4 lattice to tune the oxygen-defect environment and improve redox reversibility. Among the prepared samples, Cu0.2Co0.8Fe2O4 showed the most favorable performance, giving a hydrogen yield of 12.70 mmol g–1, compared with 9.95 mmol g–1 for pristine CoFe2O4. After 50 cycles, the hydrogen yield remained at 10.01 mmol g–1. XPS and H2-TPR results indicate that moderate Cu substitution increases defect-related oxygen species and facilitates lattice-oxygen removal. CO/CO2 pulse experiments further confirm improved oxygen exchange between the surface and bulk. Post-cycle XRD analysis shows that Cu0.2Co0.8Fe2O4 retains a reconstructed spinel fraction of 89.6%, suggesting enhanced phase reversibility. Cycled SEM images further indicate that moderate Cu substitution mitigates particle coarsening and sintering. These results indicate that suitable Cu incorporation improves the performance of CoFe2O4 by coupling oxygen-vacancy regulation, reversible spinel reconstruction, and improved resistance to sintering.