Sm3+ Doping-Induced Suppression of Ce3+ 4f1 Trap States in CeO2 for Efficient Photocatalytic Overall Water Splitting.

Defect engineering and electronic structure modification are central to the development of efficient metal oxide photocatalysts for overall water splitting. However, the role of specific electronic trap states that govern charge carrier dynamics remains incompletely understood. Herein, we report a lanthanide-assisted solid-state strategy to synthesize Sm3+-doped CeO2 that selectively suppresses detrimental Ce3+ 4f1 trap states while preserving surface active sites. Structural and spectroscopic characterizations indicate that Sm3+ preferentially segregates at the CeO2 surface, where its incorporation suppresses Ce3+ 4f1 trap states that act as dominant non-radiative recombination centers, thereby prolonging charge carrier lifetimes and enabling efficient migration to the catalytic surface. When integrated with dual cocatalysts (CoOx-Rh/Cr2O3), the optimized Sm3+-doped CeO2 achieves an apparent quantum yield of 12.6% ± 0.4% at 365 nm, representing the highest reported value for CeO2-based photocatalysts for overall water splitting. These findings establish surface lanthanide segregation as a versatile approach for regulating defect states and charge carrier dynamics, unlocking the intrinsic activity of CeO2 for solar-fuel production.